Functional assessment of the diaphragm by speckle tracking ultrasound during inspiratory loading

A Study on the Diagnostic Accuracy of Tidal Volume-Diaphragmatic Contraction Velocity: A Novel Index for Weaning Outcome Prediction

OBJECTIVES

Weaning failure from mechanical ventilation (MV) is primarily caused by increased respiratory load and decreased respiratory neuromuscular competency, leading to a rapid shallow breathing pattern. We hypothesized that the product of diaphragmatic contraction velocity (a sonographic estimate of respiratory load) and tidal volume (an estimate of breathing pattern), termed the volume-velocity index (VVI), may predict weaning outcomes.

DESIGN

The diagnostic accuracy of VVI (mL*cm/s) in predicting weaning outcomes was prospectively assessed, along with its relationship to indices of breathing effort, including esophageal pressure swings (ΔPes), the pressure-time product of esophageal pressure (PTPes), and maximal inspiratory pressure (MIP). A power analysis, informed by the results of an inception cohort, determined the required sample size for the validation cohort. Patients were enrolled through consecutive sampling. Weaning failure was defined as failure of the spontaneous breathing trial (SBT) or the need for MV within 48 hours.

SETTING

The study was conducted in a tertiary academic ICU.

PATIENTS

VVI was evaluated in critical care patients undergoing a SBT for the first time.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In the inception cohort (n = 30), VVI was significantly higher in successful weaning compared to failures (764.76 [±432.61] vs. 278 [±183.66], p < 0.001). It correlated with ΔPes (r = 0.74, R2 = 0.55), PTPes (r = 0.76, R2 = 0.58), and MIP (r = 0.75, R2 = 0.55) all p values less than 0.001. In the validation cohort (n = 40), VVI was higher in successful weaning (840 [550, 1220] vs. 250 [225, 302.5], p < 0.001) and predicted weaning success with an area under the receiver operating characteristic of 0.92 (95% CI, 0.83-1).

CONCLUSIONS

VVI effectively differentiates between weaning success and failure, shows a strong correlation with respiratory effort indices, and may enhance weaning protocols.

Diaphragmatic ultrasonographic evaluation as an assessment guide for predicting noninvasive ventilation failure in acute exacerbation of chronic obstructive pulmonary disease

BACKGROUND

Dynamic hyperinflation in severe acute exacerbation of chronic obstructive pulmonary disease (AECOPD) leads to diaphragmatic fatigue and causes acute respiratory failure. Ultrasound is reliable for evaluating diaphragmatic function. In this study, we aimed to assess the ability of diaphragmatic ultrasound to predict noninvasive ventilation (NIV) failure.

METHODS

This prospective single-center observational cohort study was performed on patients with AECOPD who required NIV in the emergency department between October 1, 2020, and September 30, 2022, at a tertiary healthcare center. The diaphragmatic ultrasound was measured using diaphragmatic excursion (DE) before applying NIV and diaphragmatic thickening fraction (DTF) during NIV use for 2 h. The area under the receiver-operating characteristic (AUROC) curves analysis and multivariable logistic regression was performed to assess the ability of diaphragmatic ultrasound to predict NIV failure in 48 h.

RESULTS

111 patients were included in this study. DTF was an independent variable associated with NIV failure, with an adjusted odds ratio of 0.91 (95 % confidence interval [CI] 0.85-0.98), with a p-value of 0.009. DE and DTF had AUROC of 0.905 (95 % CI 0.835-0.975) and 0.940 (95 % CI 0.894-0.986), respectively, to predict NIV failure within 48 h. The lower DE and DTF increased the probability of NIV failure. The cutoff value of the DTF was 20 %, with a sensitivity of 92.0 % (95 % CI 74.0 % - 99.0 %) and a specificity of 93.0 % (95 % CI 85.4 % - 97.4 %) and the cutoff of the DE was 1.2 cm, with a sensitivity of 88.0 % (95 % CI 68.8 % - 97.5 %) and a specificity of 84.9 % (95 % CI 75.5 % - 91.7 %).

CONCLUSION

Diaphragmatic ultrasound, especially DTF at 2 h during NIV use, is a validated tool for predicting NIV failure in patients with AECOPD. Early detection of diaphragmatic dysfunction with diaphragmatic ultrasound in AECOPD with NIV could help identify high-risk patients and guide clinical decisions. However, further benefits from its implementation in management are required.

Advancements in imaging techniques for monitoring the respiratory muscles

This review highlights the latest advancements in imaging techniques for monitoring respiratory muscles in critically ill patients. At the bedside, conventional ultrasound has been widely adopted to measure diaphragm thickness, thickening and excursion. It has also been used to assess extradiaphragmatic respiratory muscles, including parasternal intercostal and abdominal muscles. Advanced ultrasound-derived techniques have expanded its applications, enabling the evaluation of tissue velocity (tissue Doppler imaging), stiffness (shear wave elastography), and local tissue displacement (speckle tracking). Facility-based imaging modalities such as magnetic resonance imaging and chest tomography provide complementary insights into respiratory muscles structure and function, offering valuable information for evaluating the effects of therapeutic interventions. Finally, imaging techniques have emerged as valuable tools for evaluating the metabolic demands of respiratory muscles, with advanced methods such as positron emission tomography and contrast-enhanced ultrasound showing significant potential.

Speckle tracking ultrasound as a new tool to predict the weaning outcome of mechanical ventilation patients: a prospective observational study

Introduction

Speckle tracking ultrasound is a novel technique for evaluating diaphragm movement, yet its guidance in weaning mechanically ventilated patients remains unclear. In this study, we assessed diaphragmatic function using speckle tracking ultrasound and guided the weaning process.

Methods

A total of 86 mechanically ventilated patients were included and divided into successful or failed weaning groups. Diaphragmatic function was assessed using speckle tracking ultrasound, M-ultrasound diaphragm excursion (DE), and diaphragmatic twitch force (DTF) after 30 min spontaneous breathing trial (SBT). The diagnostic performance of these indicator in predicting weaning outcomes was also evaluated.

Results

In this study, a total of 86 patients completed the follow-up for weaning outcomes, with 35 cases of weaning failure and 51 cases of successful weaning. Logistic regression analysis identified whole strain (p = 0.037) and DE (p = 0.004) as independent predictors of weaning outcome. Receiver operating characteristic (ROC) curve showed that the strain threshold for Costal Diaphragm (Dlcos) was -9.836, Area Under the Curve (AUC) value was 0.760, the predictive specificity for weaning failure was 72.5%, and the sensitivity was 80%. DE value exceeding 1.015 cm had an AUC value of 0.785, noting that DE value had a high specificity (90.2%) for predicting successful weaning, but a lower sensitivity (60%). After merging, the AUC of whole strain and DE was 0.856, and the sensitivity (80%) and specificity (80.4%) were more balanced compared to using DE alone.

Conclusion

The findings of this study demonstrate the feasibility of using speckle tracking ultrasound to assess diaphragmatic function in mechanically ventilated patients. The combined utilization of whole strain and DE provides a more precise evaluation of diaphragmatic function in ICU patient, which may improve patient outcome.

Diaphragm ultrasound and diaphragmatic 2D speckle tracking imaging in acute heart failure: a case series

Background

Respiratory muscle function can be affected in patients with heart failure. Ultrasound can be used to assess diaphragm, the main inspiratory muscle. Speckle tracking imaging is an imaging technology providing the evaluation of tissue deformation during contraction. We aimed to evaluate the contribution of traditional echography and 2D speckle tracking imaging in the evaluation and monitoring of patients with acute heart failure (AHF).

Case summary

We report a series of four cases of AHF. Diaphragm ultrasound coupled with diaphragm 2D speckle tracking imaging was performed at admission and after decongestive therapy, in cardiac intensive care unit. Patients, at admission, disclosed higher diaphragm 2D strain value and higher diaphragm inspiratory motion value in the context of higher cardiac loading that significantly decrease after decongestive therapy, except for one patient. Diaphragm motion remained less than 10 mm (weakness), despite medical therapy in Cases 2, 3, and 4. Among them, 3 months later, one patient (Case 3) experienced an episode of AHF.

Discussion

Diaphragm ultrasound coupled with diaphragm 2D speckle tracking imaging is feasible and may be used to monitor respiratory status patients with AHF.

The Application of Diaphragm Ultrasound in Chronic Obstructive Pulmonary Disease: A Narrative Review

Chronic Obstructive Pulmonary Disease (COPD) is a prevalent condition that poses a significant burden on individuals and society due to its high morbidity and mortality rates. The diaphragm is the main respiratory muscle, its function has a direct impact on the quality of life and prognosis of COPD patients. This article aims to review the structural measurement and functional evaluation methods through the use of diaphragmatic ultrasound and relevant research on its application in clinical practice for COPD patients. Thus, it serves to provide valuable insights for clinical monitoring of diaphragm function in COPD patients, facilitating early clinical intervention and aiding in the recovery of diaphragm function.

Decreased diaphragm moving distance measured by ultrasound speckle tracking reflects poor prognosis in amyotrophic lateral sclerosis

Objective

Decreased cephalocaudal diaphragm movement may indicate respiratory dysfunction in amyotrophic lateral sclerosis (ALS). We aimed to evaluate diaphragm function in ALS using ultrasound speckle tracking, an image-analysis technology that follows similar pixel patterns.

Methods

We developed an offline application that tracks pixel patterns of recorded ultrasound video images using speckle-tracking methods. Ultrasonography of the diaphragm movement during spontaneous quiet respiration was performed on 19 ALS patients and 21 controls to measure the diaphragm moving distance (DMD) in the cephalocaudal direction during a single respiration. We compared respiratory function measures and analyzed the relationship between the clinical profiles and DMD.

Results

DMD was significantly lower in ALS patients than in the control group (0.6 ± 1.4 mm vs 2.2 ± 2.2 mm, p < 0.01) and positively correlated with phrenic nerve compound motor action potential amplitude (R = 0.63, p = 0.01). DMD was negatively correlated with the change in the ALS Functional Rating Scale-Revised scores per month after the exam (R = -0.61, p = 0.02), and those with a larger rate of decline had a significantly lower DMD (p = 0.03).

Conclusions

Diaphragm ultrasound speckle tracking enabled the detection of diaphragm dysfunction in ALS.

Significance

Diaphragm ultrasound speckle tracking may be useful for predicting prognosis.

Ultrasonographic Assessment of the Diaphragm

Mechanical ventilation injures not only the lungs but also the diaphragm, resulting in dysfunction associated with poor outcomes. Diaphragm ultrasonography is a noninvasive, cost-effective, and reproducible diagnostic method used to monitor the condition and function of the diaphragm. With advances in ultrasound technology and the expansion of its clinical applications, diaphragm ultrasonography has become increasingly important as a tool to visualize and quantify diaphragmatic morphology and function across multiple medical specialties, including pulmonology, critical care, and rehabilitation medicine. This comprehensive review aims to provide an in-depth analysis of the role and limitations of ultrasonography in assessing the diaphragm, especially among critically ill patients. Furthermore, we discuss a recently published expert consensus and provide a perspective for the future.

Ultrasound assessment of diaphragmatic dysfunction in non-critically ill patients: relevant indicators and update

Diaphragm dysfunction (DD) can be classified as mild, resulting in diaphragmatic weakness, or severe, resulting in diaphragmatic paralysis. Various factors such as prolonged mechanical ventilation, surgical trauma, and inflammation can cause diaphragmatic injury, leading to negative outcomes for patients, including extended bed rest and increased risk of pulmonary complications. Therefore, it is crucial to protect and monitor diaphragmatic function. Impaired diaphragmatic function directly impacts ventilation, as the diaphragm is the primary muscle involved in inhalation. Even unilateral DD can cause ventilation abnormalities, which in turn lead to impaired gas exchange, this makes weaning from mechanical ventilation challenging and contributes to a higher incidence of ventilator-induced diaphragm dysfunction and prolonged ICU stays. However, there is insufficient research on DD in non-ICU patients, and DD can occur in all phases of the perioperative period. Furthermore, the current literature lacks standardized ultrasound indicators and diagnostic criteria for assessing diaphragmatic dysfunction. As a result, the full potential of diaphragmatic ultrasound parameters in quickly and accurately assessing diaphragmatic function and guiding diagnostic and therapeutic decisions has not been realized.

Advanced Respiratory Monitoring during Extracorporeal Membrane Oxygenation

Advanced respiratory monitoring encompasses a diverse range of mini- or noninvasive tools used to evaluate various aspects of respiratory function in patients experiencing acute respiratory failure, including those requiring extracorporeal membrane oxygenation (ECMO) support. Among these techniques, key modalities include esophageal pressure measurement (including derived pressures), lung and respiratory muscle ultrasounds, electrical impedance tomography, the monitoring of diaphragm electrical activity, and assessment of flow index. These tools play a critical role in assessing essential parameters such as lung recruitment and overdistention, lung aeration and morphology, ventilation/perfusion distribution, inspiratory effort, respiratory drive, respiratory muscle contraction, and patient-ventilator synchrony. In contrast to conventional methods, advanced respiratory monitoring offers a deeper understanding of pathological changes in lung aeration caused by underlying diseases. Moreover, it allows for meticulous tracking of responses to therapeutic interventions, aiding in the development of personalized respiratory support strategies aimed at preserving lung function and respiratory muscle integrity. The integration of advanced respiratory monitoring represents a significant advancement in the clinical management of acute respiratory failure. It serves as a cornerstone in scenarios where treatment strategies rely on tailored approaches, empowering clinicians to make informed decisions about intervention selection and adjustment. By enabling real-time assessment and modification of respiratory support, advanced monitoring not only optimizes care for patients with acute respiratory distress syndrome but also contributes to improved outcomes and enhanced patient safety.

The Role of Ultrasonography in the Process of Weaning from Mechanical Ventilation in Critically Ill Patients

Weaning patients from mechanical ventilation (MV) is a complex process that may result in either success or failure. The use of ultrasound at the bedside to assess organs may help to identify the underlying mechanisms that could lead to weaning failure and enable proactive measures to minimize extubation failure. Moreover, ultrasound could be used to accurately identify pulmonary diseases, which may be responsive to respiratory physiotherapy, as well as monitor the effectiveness of physiotherapists' interventions. This article provides a comprehensive review of the role of ultrasonography during the weaning process in critically ill patients.

Ultrasound assessment of diaphragm thickness, contractility, and strain in healthy pediatric patients

BACKGROUND

Ultrasound-based diaphragmatic assessments are becoming more common in pediatric acute care, but baseline pediatric diaphragm thickness and contractility values remain unknown.

METHODS

We conducted a prospective, observational study of healthy children aged <18 years undergoing elective surgery. Diaphragm thickness at end-expiration (Tdi-exp), thickening fraction (DTF) and excursion were measured by ultrasound during spontaneous breathing and during mechanical ventilation. Diaphragm strain and peak strain rate were ascertained post hoc. Measurements were compared across a priori specified age groups (<1 year, 1 to <3, 3 to <6, 6 to <12, and 12 to <18 years) and with versus without mechanical ventilation.

RESULTS

Fifty subjects were evaluated (n = 10 per age group). Baseline mean Tdi-exp was 0.19 ± 0.04 cm, DTF 0.19 ± 0.09, excursion 1.69 ± 0.97 cm, strain -10.3 ± 4.9, peak strain rate -0.48 ± 0.21 s-1 . No significant difference in Tdi-exp or DTF was observed across age groups (p > .05). Diaphragm excursion increased with age (p < .0001). Diaphragm strain was significantly greater in the 12-17-year age group (-14.3 ± 6.4), p = .048, but there were no age-related differences in peak strain rate (p = .08). During mechanical ventilation, there were significant decreases in DTF 0.12 ± 0.04 (p < .0001), excursion 1.08 ± 0.31 cm (p < .0001), strain -4.60 ± 1.93 (p < .0001), and peak strain rate -0.20 ± 0.10 s-1 (p < .0001) while there was no change in Tdi-exp 0.18 ± 0.03 cm (p = .25) when compared to baseline values.

CONCLUSION

Pediatric Tdi-exp, DTF, and diaphragm peak strain rate were similar across age groups. Diaphragm excursion and strain varied across age groups. All measures of diaphragm contractility were diminished during mechanical ventilation.

Diaphragm Dysfunction Predicts Weaning Outcome after Bilateral Lung Transplant

BACKGROUND

Diaphragm dysfunction and its effects on outcomes of ventilator weaning have been evaluated in mixed critical care populations using diaphragm thickening fraction (the ratio of the difference between ultrasound diaphragm thickness at end-inspiration and end-expiration to diaphragm thickness at end-expiration) or neuroventilatory efficiency (the ratio of tidal volume and peak electrical activity of the diaphragm). Such data are not available in bilateral-lung transplant recipients. The authors hypothesized that (1) diaphragm dysfunction, as defined by a diaphragm thickening fraction less than 29%, is more likely to occur in difficult weaning; (2) diaphragm thickening fraction and neuroventilatory efficiency predict weaning outcome; and (3) duration of mechanical ventilation before the first spontaneous breathing trial is associated with diaphragm dysfunction.

METHODS

Adult bilateral-lung transplant patients admitted to the intensive care unit were screened at the time of the first spontaneous breathing trial (pressure-support of 5 cm H2O and 0 positive end-expiratory pressure). At the fifth minute, diaphragm thickening fraction and neuroventilatory efficiency were measured during three respiratory cycles. Weaning was classified as simple, difficult, or prolonged (successful extubation at the first spontaneous breathing trial, within three or after three spontaneous breathing trials, respectively).

RESULTS

Forty-four subjects were enrolled. Diaphragm dysfunction occurred in 14 subjects (32%), all of whom had difficult weaning (78% of the subgroup of 18 patients experiencing difficult weaning). Both diaphragm thickening fraction (24 [20 to 29] vs. 39 [35 to 45]%) and neuroventilatory efficiency (34 [26 to 45] vs. 55 [43 to 62] ml/µV) were lower in difficult weaning (both P < 0.001). The areas under the receiver operator curve predicting difficult weaning were 0.88 (95% CI, 0.73 to 0.99) for diaphragm thickening fraction and 0.85 (95% CI, 0.71 to 0.95) for neuroventilatory efficiency. The duration of ventilation demonstrated a linear inverse correlation with both diaphragm thickening fraction and neuroventilatory efficiency.

CONCLUSIONS

Diaphragm dysfunction is common after bilateral-lung transplantation and associated with difficult weaning. In such patients, average values for diaphragm thickening fraction and neuroventilatory efficiency were reduced compared to patients with simple weaning. Both parameters showed similar accuracy for predicting success of ventilator weaning, demonstrating an inverse relationship with duration of ventilation.

EDITOR’S PERSPECTIVE

Reliability and validity of ultrasonography in evaluating the thickness, excursion, stiffness, and strain rate of respiratory muscles in non-hospitalized individuals: a systematic review

OBJECTIVE

To summarize the reliability and validity of ultrasonography in evaluating the stiffness, excursion, stiffness, or strain rate of diaphragm, intercostals and abdominal muscles in healthy or non-hospitalized individuals.

LITERATURE SEARCH

PubMed, Embase, SPORTDiscus, CINAHL and Cochrane Library were searched from inception to May 30, 2022.

STUDY SELECTION CRITERIA

Case-control, cross-sectional, and longitudinal studies were included if they investigated the reliability or validity of various ultrasonography technologies (e.g., brightness-mode, motion-mode, shear wave elastography) in measuring the thickness, excursion, stiffness, or strain rate of any respiratory muscles.

DATA SYNTHESIS

Relevant data were summarized based on healthy and different patient populations. The methodological quality by different checklist depending on study design. The quality of evidence of each psychometric property was graded by the Grading of Recommendations, Assessment, Development and Evaluations, respectively.

RESULTS

This review included 24 studies with 787 healthy or non-hospitalized individuals (e.g., lower back pain (LBP), adolescent idiopathic scoliosis (AIS), and chronic obstructive pulmonary disease (COPD)). Both inspiratory (diaphragm and intercostal muscles) and expiratory muscles (abdominal muscles) were investigated. Moderate-quality evidence supported sufficient (intra-class correlation coefficient > 0.7) within-day intra-rater reliability of B-mode ultrasonography in measuring right diaphragmatic thickness among people with LBP, sufficient between-day intra-rater reliability of M-mode ultrasonography in measuring right diaphragmatic excursion in non-hospitalized individuals. The quality of evidence for all other measurement properties in various populations was low or very low. High-quality evidence supported sufficient positive correlations between diaphragm excursion and forced expiratory volume in the first second or forced vital capacity (r >  = 0.3) in healthy individuals.

CONCLUSIONS

Despite the reported sufficient reliability and validity of using ultrasonography to assess the thickness, excursion, stiffness, and strain rate of respiratory muscles in non-hospitalized individuals, further large-scale studies are warranted to improve the quality of evidence regarding using ultrasonography for these measurements in clinical practice. Researchers should establish their own reliability before using various types of ultrasonography to evaluate respiratory muscle functions.

TRIAL REGISTRATION

PROSPERO NO. CRD42022322945.

Diaphragm excursions as proxy for tidal volume during spontaneous breathing in invasively ventilated ICU patients

There is a need to monitor tidal volume in critically ill patients with acute respiratory failure, given its relation with adverse clinical outcome. However, quantification of tidal volume in non-intubated patients is challenging. In this proof-of-concept study, we evaluated whether ultrasound measurements of diaphragm excursion could be a valid surrogate for tidal volume in patients with respiratory failure. Diaphragm excursions and tidal volumes were simultaneously measured in invasively ventilated patients (N = 21) and healthy volunteers (N = 20). Linear mixed models were used to estimate the ratio between tidal volume and diaphragm excursion. The tidal volume-diaphragm excursion ratio was 201 mL/cm in ICU patients [95% confidence interval (CI) 161-240 mL/cm], and 361 (294-428) mL/cm in healthy volunteers. An excellent association was shown within participants (R2 = 0.96 in ICU patients, R2 = 0.90 in healthy volunteers). However, the differences between observed tidal volume and tidal volume as predicted by the linear mixed models were considerable: the 95% limits of agreement in Bland-Altman plots were ± 91 mL in ICU patients and ± 396 mL in healthy volunteers. Likewise, the variability in tidal volume estimation between participants was large. This study shows that diaphragm excursions measured with ultrasound correlate with tidal volume, yet quantification of absolute tidal volume from diaphragm excursion is unreliable.

In vivo shear wave elasticity imaging for assessment of diaphragm function in muscular dystrophy

Duchenne muscular dystrophy (DMD) causes patients to suffer from ambulatory disability and cardiorespiratory failure, the latter of which leads to premature death. Due to its role in respiration, the diaphragm is an important muscle for study. A common method for evaluating diaphragm function is ex vivo force testing, which only allows for an end point measurement. In contrast, ultrasound shear wave elastography imaging (US-SWEI) can assess diaphragm function over time; however, US-SWEI studies in dystrophic patients to date have focused on the limbs without preclinical studies. In this work, we used US-SWEI to estimate the shear wave speed (SWS) in diaphragm muscles of healthy (WT) mice, mdx mice, and mdx mice haploinsufficient for utrophin (mdx-utr) at 6 and 12 months of age. Diaphragms were then subjected to ex vivo force testing and histological analysis at 12 months of age. Between 6 and 12 months, a 23.8% increase in SWS was observed in WT mice and a 27.8% increase in mdx mice, although no significant difference was found in mdx-utr mice. Specific force generated by mdx-utr diaphragms was lower than that of WT diaphragms following twitch stimulus. A strong correlation between SWS and collagen deposition was observed, as well as between SWS and muscle fiber size. Together, these data demonstrate the ability of US-SWEI to evaluate dystrophic diaphragm functionality over time and predict the biochemical and morphological make-up of the diaphragm. Additionally, our results highlight the advantage of US-SWEI over ex vivo testing by obtaining longitudinal measurements in the same subject. STATEMENT OF SIGNIFICANCE: In DMD patients, muscles experience cycles of regeneration and degeneration that contribute to chronic inflammation and muscle weakness. This pathology only worsens with time and leads to muscle wasting, including in respiratory and cardiac muscles. Because respiratory failure is a major contributor to premature death in DMD patients, the diaphragm muscle is an important muscle to evaluate and treat over time. Currently, diaphragm function is assessed using ex vivo force testing, a technique that only allows measurement at sacrifice. In contrast, ultrasonography, particularly shear wave elasticity imaging (USSWEI), is a promising tool for longitudinal assessment; however, most US-SWEI in DMD patients aimed for limb muscles only with the absence of preclinical studies. This work broadens the applications of US-SWE imaging by demonstrating its ability to track properties and function of dystrophic diaphragm muscles longitudinally in multiple dystrophic mouse models.

An optimized optical-flow-based method for quantitative tracking of ultrasound-guided right diaphragm deformation

OBJECTIVES

To develop a quantitative analysis method for right diaphragm deformation. This method is based on optical flow and applied to diaphragm ultrasound imaging.

METHODS

This study enrolls six healthy subjects and eight patients under mechanical ventilation. Dynamic images with 3-5 breathing cycles were acquired from three directions of right diaphragm by a portable ultrasound system. Filtering and density clustering algorithms are used for denoising Digital Imaging and Communications in Medicine (DICOM) data. An optical flow based method is applied to track movements of the right diaphragm. An improved drift correction algorithm is used to optimize the results. The method can automatically analyze the respiratory cycle, inter-frame/cumulative vertical and horizontal displacements, and strain of the input right diaphragm ultrasound image.

RESULTS

The optical-flow-based diaphragm ultrasound image motion tracking algorithm can accurately track the right diaphragm during respiratory motion. There are significant differences in horizontal and vertical displacements in each section (p-values < 0.05 for all). Significant differences are found between healthy subjects and mechanical ventilation patients for both horizontal and vertical displacements in Section III (p-values < 0.05 for both). There is no significant difference in global strain in each section between healthy subjects and mechanical ventilation patients (p-values > 0.05 for all).

CONCLUSIONS

The developed method can quantitatively evaluate the inter-frame/cumulative displacement of the diaphragm in both horizontal and vertical directions, as well as the global strain in three different imaging planes. The above indicators can be used to evaluate diaphragmatic dynamics.

The oesophageal balloon for respiratory monitoring in ventilated patients: updated clinical review and practical aspects

There is a well-recognised importance for personalising mechanical ventilation settings to protect the lungs and the diaphragm for each individual patient. Measurement of oesophageal pressure (P oes) as an estimate of pleural pressure allows assessment of partitioned respiratory mechanics and quantification of lung stress, which helps our understanding of the patient's respiratory physiology and could guide individualisation of ventilator settings. Oesophageal manometry also allows breathing effort quantification, which could contribute to improving settings during assisted ventilation and mechanical ventilation weaning. In parallel with technological improvements, P oes monitoring is now available for daily clinical practice. This review provides a fundamental understanding of the relevant physiological concepts that can be assessed using P oes measurements, both during spontaneous breathing and mechanical ventilation. We also present a practical approach for implementing oesophageal manometry at the bedside. While more clinical data are awaited to confirm the benefits of P oes-guided mechanical ventilation and to determine optimal targets under different conditions, we discuss potential practical approaches, including positive end-expiratory pressure setting in controlled ventilation and assessment of inspiratory effort during assisted modes.

Managing respiratory muscle weakness during weaning from invasive ventilation

Weaning is a critical stage of an intensive care unit (ICU) stay, in which the respiratory muscles play a major role. Weakness of the respiratory muscles, which is associated with significant morbidity in the ICU, is not limited to atrophy and subsequent dysfunction of the diaphragm; the extradiaphragmatic inspiratory and expiratory muscles also play important parts. In addition to the well-established deleterious effect of mechanical ventilation on the respiratory muscles, other risk factors such as sepsis may be involved. Weakness of the respiratory muscles can be suspected visually in a patient with paradoxical movement of the abdominal compartment. Measurement of maximal inspiratory pressure is the simplest way to assess respiratory muscle function, but it does not specifically take the diaphragm into account. A cut-off value of -30 cmH2O could identify patients at risk for prolonged ventilatory weaning; however, ultrasound may be better for assessing respiratory muscle function in the ICU. Although diaphragm dysfunction has been associated with weaning failure, this diagnosis should not discourage clinicians from performing spontaneous breathing trials and considering extubation. Recent therapeutic developments aimed at preserving or restoring respiratory muscle function are promising.

Pearls and pitfalls of respiratory testing in a patient with amyotrophic lateral sclerosis and COPD

Interpretation of pulmonary function testing in patients with amyotrophic lateral sclerosis must account for coexisting lung diseases, when making patient care decisions. https://bit.ly/3Co2yR0.

Skeletal Muscle Assessment Using Quantitative Ultrasound: A Narrative Review

Ultrasound (US) is an important imaging tool for skeletal muscle analysis. The advantages of US include point-of-care access, real-time imaging, cost-effectiveness, and absence of ionizing radiation. However, US can be highly dependent on the operator and/or US system, and a portion of the potentially useful information carried by raw sonographic data is discarded in image formation for routine qualitative US. Quantitative ultrasound (QUS) methods provide analysis of the raw or post-processed data, revealing additional information about normal tissue structure and disease status. There are four QUS categories that can be used on muscle and are important to review. First, quantitative data derived from B-mode images can help determine the macrostructural anatomy and microstructural morphology of muscle tissues. Second, US elastography can provide information about muscle elasticity or stiffness through strain elastography or shear wave elastography (SWE). Strain elastography measures the induced tissue strain caused either by internal or external compression by tracking tissue displacement with detectable speckle in B-mode images of the examined tissue. SWE measures the speed of induced shear waves traveling through the tissue to estimate the tissue elasticity. These shear waves may be produced using external mechanical vibrations or internal "push pulse" ultrasound stimuli. Third, raw radiofrequency signal analyses provide estimates of fundamental tissue parameters, such as the speed of sound, attenuation coefficient, and backscatter coefficient, which correspond to information about muscle tissue microstructure and composition. Lastly, envelope statistical analyses apply various probability distributions to estimate the number density of scatterers and quantify coherent to incoherent signals, thus providing information about microstructural properties of muscle tissue. This review will examine these QUS techniques, published results on QUS evaluation of skeletal muscles, and the strengths and limitations of QUS in skeletal muscle analysis.

The Effects of Positive End Expiratory Pressure and Lung Volume on Diaphragm Thickness and Thickening

Introduction: Diaphragm dysfunction is common in patients undergoing mechanical ventilation. The application of positive end-expiratory pressure (PEEP) and the varying end-expiratory lung volume cause changes in diaphragm geometry. We aimed to assess the impact of the level of PEEP and lung inflation on diaphragm thickness, thickening fraction and displacement. Methods: An observational study in a mixed medical and surgical ICU was conducted. The patients underwent a PEEP-titration trial with the application of three random levels of PEEP: 0 cmH₂O (PEEP0), 8 cmH₂O (PEEP8) and 15 cmH₂O (PEEP15). At each step, the indices of respiratory effort were assessed, together with arterial blood and diaphragm ultrasound; end-expiratory lung volume was measured. Results: 14 patients were enrolled. The tidal volume, diaphragm displacement and thickening fraction were significantly lower with higher levels of PEEP, while both the expiratory and inspiratory thickness increased with higher PEEP levels. The inspiratory effort, as evaluated by the esophageal pressure swing, was unchanged. Both the diaphragm thickening fraction and displacement were significantly correlated with inspiratory effort in the whole dataset. For both measurements, the correlation was stronger at lower levels of PEEP. The difference in the diaphragm thickening fraction during tidal breathing between PEEP 15 and PEEP 0 was negatively related to the change in the functional residual capacity and the change in alveolar dead space. Conclusions: Different levels of PEEP significantly modified the diaphragmatic thickness and thickening fraction, showing a PEEP-induced decrease in the diaphragm contractile efficiency. When using ultrasound to assess diaphragm size and function, the potential effect of lung inflation should be taken into account.

Diaphragm Ultrasound in Critically Ill Patients on Mechanical Ventilation—Evolving Concepts

Mechanical ventilation (MV) is a life-saving respiratory support therapy, but MV can lead to diaphragm muscle injury (myotrauma) and induce diaphragmatic dysfunction (DD). DD is relevant because it is highly prevalent and associated with significant adverse outcomes, including prolonged ventilation, weaning failures, and mortality. The main mechanisms involved in the occurrence of myotrauma are associated with inadequate MV support in adapting to the patient’s respiratory effort (over- and under-assistance) and as a result of patient-ventilator asynchrony (PVA). The recognition of these mechanisms associated with myotrauma forced the development of myotrauma prevention strategies (MV with diaphragm protection), mainly based on titration of appropriate levels of inspiratory effort (to avoid over- and under-assistance) and to avoid PVA. Protecting the diaphragm during MV therefore requires the use of tools to monitor diaphragmatic effort and detect PVA. Diaphragm ultrasound is a non-invasive technique that can be used to monitor diaphragm function, to assess PVA, and potentially help to define diaphragmatic effort with protective ventilation. This review aims to provide clinicians with an overview of the relevance of DD and the main mechanisms underlying myotrauma, as well as the most current strategies aimed at minimizing the occurrence of myotrauma with special emphasis on the role of ultrasound in monitoring diaphragm function.

[Weaning from invasive ventilation : Challenges in the clinical routine]

Modern intensive care medicine is caught between the conflicting demands of an efficient but also increasingly more technical intensive care treatment with numerous therapeutic options and, at the same time, an ageing society with increasing morbidity. This is reflected, among other things, in an increasing number of ventilated patients in intensive care units and an increasing proportion of patients for whom ventilation cannot easily be discontinued. Weaning from a ventilator, which can account for more than 50% of the total ventilation time, therefore plays a central role in this process. This main topic article presents the need for strategically wise and holistic actions to minimize the consequences of invasive mechanical ventilation for patients. An attempt is made to shed more light on individual aspects of the ventilation weaning process with high relevance for clinical practice. Especially for prolonged weaning from ventilation, many more concepts are needed than simply ending ventilation.

Comparison of assessment of diaphragm function using speckle tracking between patients with successful and failed weaning: a multicentre, observational, pilot study

Background

Diaphragmatic ultrasound has been increasingly used to evaluate diaphragm function. However, current diaphragmatic ultrasound parameters provide indirect estimates of diaphragmatic contractile function, and the predictive value is controversial. Two-dimensional (2D) speckle tracking is an effective technology for measuring tissue deformation and can be used to measure diaphragm longitudinal strain (DLS) to assess diaphragm function. The purpose of this study was to determine the feasibility and reproducibility of DLS quantification by 2D speckle tracking and to determine whether maximal DLS could be used to predict weaning outcomes.

Methods

This study was performed in the intensive care unit of two teaching hospitals, and was divided into two studies. Study A was a prospective study to evaluate the feasibility, reliability, and repeatability of speckle tracking in assessing DLS in healthy subjects and mechanically ventilated patients. Study B was a multicentre retrospective study to assess the use of maximal DLS measured by speckle tracking in predicting weaning outcomes.

Results

Twenty-five healthy subjects and twenty mechanically ventilated patients were enrolled in Study A. Diaphragmatic speckle tracking was easily accessible. The intra- and interoperator reliability were good to excellent under conditions of eupnoea, deep breathing, and mechanical ventilation. The intraclass correlation coefficient (ICC) ranged from 0.78 to 0.95. Ninety-six patients (fifty-nine patients were successfully weaned) were included in Study B. DLS exhibited a fair linear relationship with both the diaphragmatic thickening fraction (DTF) (R2 = 0.73, p < 0.0001) and diaphragmatic excursion (DE) (R2 = 0.61, p < 0.0001). For the prediction of successful weaning, the areas under the ROC curves of DLS, diaphragmatic thickening fraction DTF, RSBI, and DE were 0.794, 0.794, 0.723, and 0.728, respectively. The best cut-off value for predicting the weaning success of DLS was less than -21%, which had the highest sensitivity of 89.19% and specificity of 64.41%.

Conclusions

Diaphragmatic strain quantification using speckle tracking is easy to obtain in healthy subjects and mechanically ventilated patients and has a high predictive value for mechanical weaning. However, this method offers no advantage over RSBI. Future research should assess its value as a predictor of weaning.

Trial registration

This study was registered in the Chinese Clinical Trial Register (ChiCTR), ChiCTR2100049816. Registered 10 August 2021. http://www.chictr.org.cn/showproj.aspx?proj=131790

Ultrasound-assessed diaphragm dysfunction predicts clinical outcomes in hemodialysis patients

Skeletal muscle atrophy is prevalent and remarkably increases the risk of cardiovascular (CV) events and mortality in hemodialysis (HD) patients. However, whether diaphragm dysfunction predicts clinical outcomes in HD patients is unknown. This was a prospective cohort study of 103 HD patients. After assessment of diaphragm function by ultrasonography and collection of other baseline data, a 36-month follow-up was then initiated. Participants were divided into diaphragm dysfunction (DD+) group and normal diaphragm function (DD−) group, according to cutoff value of thickening ratio (i.e. the change ratio of diaphragm thickness) at force respiration. The primary endpoint was the first nonfatal CV event or all-cause mortality. A secondary endpoint was less serious CV events (LSCEs, a composite of heart failure readmission, cardiac arrhythmia or myocardial ischemia needed pharmacological intervention in hospital). 98 patients were eligible to analysis and 57 (58.16%) were men. 28 of 44 patients(63.64%) in DD+ group and 23 of 54 patients (42.59%) in DD− group had at least one nonfatal CV event or death (p = 0.038). Compared to DD− group, DD+ group had significantly higher incidence of LSCEs (21 vs.14, p = 0.025) and shorter survival time (22.02 ± 12.98 months vs. 26.74 ± 12.59 months, p = 0.046). Kaplan–Meier analysis revealed significantly higher risks of primary endpoint (p = 0.039), and LSCEs (p = 0.040) in DD+ group. Multivariate hazard analysis showed that DD+ group had significantly higher risk of primary endpoint [hazard ratio (HR) 1.59; 95% confident interval (CI) 1.54–1.63], and LSCEs (HR 1.47; 95%CI 1.40–1.55). Ultrasound-assessed diaphragm dysfunction predicts clinical outcomes in HD patients.

Trial registration: This study was registered with Chinese Clinical Trials Registry (www.chictr.org.cn) as ChiCTR1800016500 on Jun 05, 2018.

Association of diaphragm thickness and echogenicity with age, sex, and body mass index in healthy subjects

Introduction/Aims

Diaphragm ultrasound is increasingly used in the diagnosis of diaphragm dysfunction and to guide respiratory management in patients with neuromuscular disorders and those who are critically ill. However, the association between diaphragm ultrasound variables and demographic factors like age, sex, and body mass index (BMI) are understudied. Such relationships are important for correct interpretation of normative values and comparison with selected patients groups. The aim of this study was to determine the associations between diaphragm ultrasound variables and subject characteristics.

Methods

B‐mode ultrasound was used to image the diaphragm at the zone of apposition in 83 healthy subjects. Diaphragm thickness at resting end‐expiration (T_end‐exp), diaphragm thickness at maximal end‐inspiration (T_max‐insp), diaphragm thickening ratio (T_max‐insp/T_end‐exp), and diaphragm echogenicity were measured. Multivariate linear regression was used to explore the associations between diaphragm ultrasound variables and subject characteristics.

Results

T_end‐exp, T_max‐insp, and thickening ratio do not change with age whereas diaphragm echogenicity increases with age. The thickening ratio had a weak negative association with BMI, while T_end‐exp was positively associated with BMI. Men had a larger T_end‐exp and T_max‐insp than women (T_end‐exp 1.6 ± 0.5 and 1.4 ± 0.3 mm; p = .011, T_max‐insp 3.8 ± 1.0 and 3.2 ± 0.9 mm; p = .004), but similar thickening ratios.

Discussion

Diaphragm thickness, thickening, and echogenicity measured with ultrasound are associated with factors such as age, BMI, and sex. Therefore, subject characteristics should be considered when interpreting diaphragm ultrasound measurements. In the absence of normative values, matched control groups are a prerequisite for research and in clinical practice.

Poor Correlation between Diaphragm Thickening Fraction and Transdiaphragmatic Pressure in Mechanically Ventilated Patients and Healthy Subjects

BACKGROUND

The relationship between the diaphragm thickening fraction and the transdiaphragmatic pressure, the reference method to evaluate the diaphragm function, has not been clearly established. This study investigated the global and intraindividual relationship between the thickening fraction of the diaphragm and the transdiaphragmatic pressure. The authors hypothesized that the diaphragm thickening fraction would be positively and significantly correlated to the transdiaphragmatic pressure, in both healthy participants and ventilated patients.

METHODS

Fourteen healthy individuals and 25 mechanically ventilated patients (enrolled in two previous physiologic investigations) participated in the current study. The zone of apposition of the right hemidiaphragm was imaged simultaneously to transdiaphragmatic pressure recording within different breathing conditions, i.e., external inspiratory threshold loading in healthy individuals and various pressure support settings in patients. A blinded offline breath-by-breath analysis synchronously computed the changes in transdiaphragmatic pressure, the diaphragm pressure-time product, and diaphragm thickening fraction. Global and intraindividual relationships between variables were assessed.

RESULTS

In healthy subjects, both changes in transdiaphragmatic pressure and diaphragm pressure-time product were moderately correlated to diaphragm thickening fraction (repeated measures correlation = 0.40, P < 0.0001; and repeated measures correlation = 0.38, P < 0.0001, respectively). In mechanically ventilated patients, changes in transdiaphragmatic pressure and thickening fraction were weakly correlated (repeated measures correlation = 0.11, P = 0.008), while diaphragm pressure-time product and thickening fraction were not (repeated measures correlation = 0.04, P = 0.396). Individually, changes in transdiaphragmatic pressure and thickening fraction were significantly correlated in 8 of 14 healthy subjects (ρ = 0.30 to 0.85, all P < 0.05) and in 2 of 25 mechanically ventilated patients (ρ = 0.47 to 0.64, all P < 0.05). Diaphragm pressure-time product and thickening fraction correlated in 8 of 14 healthy subjects (ρ = 0.41 to 0.82, all P < 0.02) and in 2 of 25 mechanically ventilated patients (ρ = 0.63 to 0.66, all P < 0.01).

CONCLUSIONS

Overall, diaphragm function as assessed with transdiaphragmatic pressure was weakly related to diaphragm thickening fraction. The diaphragm thickening fraction should not be used in healthy subjects or ventilated patients when changes in diaphragm function are evaluated.

EDITOR’S PERSPECTIVE

Changes in Diaphragmatic Function Induced by an Increased Inspiratory Load Experienced by Military Divers: An Ultrasound Study

Background: Inspiratory loading is experienced by military divers when they use rebreather device. Our objective was to assess the changes in diaphragm function induced by an increase in inspiratory load at values similar to those experienced by divers in real life.

Methods: We recorded the excursion and the thickness of the right hemidiaphragm in 22 healthy male volunteers under inspiratory load conditions, using ultrasound in B- and M-mode. The measurements were performed at tidal volume and during breathing at 50% of inspiratory capacity. The breathing rate was regulated and similar in the various sessions with and without load.

Results: The rebreather device used by French military divers leads to an increase in inspiratory load of close to 30 cmH₂O. Consequently, the session under load was performed using a device set to this threshold. Significant increases in the excursion and the thickening fraction of the diaphragm were observed between the sessions at tidal volume and at high volume. With addition of the inspiratory load, the excursion of the right hemidiaphragm increased significantly from 2.3 to 3.4cm at tidal volume and from 3.9 to 4.7cm at high volume. The thickening fraction increased significantly from 30.4 to 76.6% at tidal volume and from 70 to 123% at high volume. The statistical analysis demonstrated that assessment of the changes of the thickening fraction during breathing at tidal volume was the most relevant marker to assess the impact of the inspiratory load on the diaphragm.

Conclusion: Diaphragm ultrasound can be used to assess the changes in the diaphragm contraction pattern secondary to an increase in the respiratory load that can be generated by use a diving apparatus. The recording of the changes of the motion, and more importantly of the thickness of the diaphragm, during the breathing cycle is able to provide relevant information regarding the inspiratory load.

Evaluation of diaphragm thickening by diaphragm ultrasonography: a reproducibility and a repeatability study

PURPOSE

We have focused on the two-dimensional (B-mode) and the time-motion (M-mode) analysis of the zone of apposition to determine the reliability of diaphragm ultrasonography in the clinical environment.

METHODS

Ten healthy volunteers were enrolled and studied by three operators with different skills in ultrasonography. For every volunteer, each operator acquired three images of the diaphragm for each side, both in B-mode and in M-mode. Then a fourth operator calculated the thickening fraction (TF), by means of the formula TF = (TEI - TEE)/TEE (TEI is the thickness at end inspiration and TEE the thickness at end expiration). Afterwards, intraclass correlation coefficients (ICCs) were computed on TF to establish reproducibility and repeatability both in the B- and M-modes. A Coefficient of Repeatability or repeatability (CR) ≤ 0.3 was considered acceptable.

RESULTS

Both B-mode (CRs 0.16-0.26) and M-mode (CRs 0.10-0.15) were sufficiently repeatable to assess TF, except for the less experienced operator (CRs B-Mode 0.20-0.32). Reproducibility was moderate to good between operators with CRs much narrower for the M-Mode (0.13-0.14).

CONCLUSIONS

The results of our study have shown that diaphragm ultrasound is repeatable and reproducible when carried out by a radiologist or an intensivist with a basic curriculum in ultrasonography. The method is more accurate when using the M-mode for less experienced operators, and in this case, repeatability and reproducibility are not sufficient to make clinical decisions. No TF value lower than 36% was obtained using both techniques. This suggests the existence of a cut-off value that could be used as an initial tool to discriminate healthy subjects from those affected by diaphragmatic dysfunction.

CLINICAL TRIAL REGISTRATION

EUDRACT 2015-004635-12.

Is sarcopenia a risk factor for reduced diaphragm function following hepatic resection? A study protocol for a prospective observational study

INTRODUCTION

Sarcopenia is associated with reduced pulmonary function in healthy adults, as well as with increased risk of pneumonia following abdominal surgery. Consequentially, postoperative pneumonia prolongs hospital admission, and increases in-hospital mortality following a range of surgical interventions. Little is known about the function of the diaphragm in the context of sarcopenia and wasting disorders or how its function is influenced by abdominal surgery. Liver surgery induces reactive pleural effusion in most patients, compromising postoperative pulmonary function. We hypothesise that both major hepatic resection and sarcopenia have a measurable impact on diaphragm function. Furthermore, we hypothesise that sarcopenia is associated with reduced preoperative diaphragm function, and that patients with reduced preoperative diaphragm function show a greater decline and reduced recovery of diaphragm function following major hepatic resection. The primary goal of this study is to evaluate whether sarcopenic patients have a reduced diaphragm function prior to major liver resection compared with non-sarcopenic patients, and to evaluate whether sarcopenic patients show a greater reduction in respiratory muscle function following major liver resection when compared with non-sarcopenic patients.

METHODS AND ANALYSIS

Transcostal B-mode, M-mode ultrasound and speckle tracking imaging will be used to assess diaphragm function perioperatively in 33 sarcopenic and 33 non-sarcopenic patients undergoing right-sided hemihepatectomy starting 1 day prior to surgery and up to 30 days after surgery. In addition, rectus abdominis and quadriceps femoris muscles thickness will be measured using ultrasound to measure sarcopenia, and pulmonary function will be measured using a hand-held bedside spirometer. Muscle mass will be determined preoperatively using CT-muscle volumetry of abdominal muscle and adipose tissue at the third lumbar vertebra level (L3). Muscle function will be assessed using handgrip strength and physical condition will be measured with a short physical performance battery . A rectus abdominis muscle biopsy will be taken intraoperatively to measure proteolytic and mitochondrial activity as well as inflammation and redox status. Systemic inflammation and sarcopenia biomarkers will be assessed in serum acquired perioperatively.

ETHICS AND DISSEMINATION

This trial is open for recruitment. The protocol was approved by the official Independent Medical Ethical Committee at Uniklinik (Rheinish Westphälische Technische Hochschule (RWTH) Aachen (reference EK309-18) in July 2019. Results will be published via international peer-reviewed journals and the findings of the study will be communicated using a comprehensive dissemination strategy aimed at healthcare professionals and patients.

TRIAL REGISTRATION NUMBER

ClinicalTrials. gov (EK309-18); Pre-results.

Positive end-expiratory pressure affects geometry and function of the human diaphragm

Positive end-expiratory pressure (PEEP) is routinely applied in mechanically ventilated patients to improve gas exchange and respiratory mechanics by increasing end-expiratory lung volume (EELV). In a recent experimental study in rats, we demonstrated that prolonged application of PEEP causes diaphragm remodeling, especially longitudinal muscle fiber atrophy. This is of potential clinical importance, as the acute withdrawal of PEEP during ventilator weaning decreases EELV and thereby stretches the adapted, longitudinally atrophied diaphragm fibers to excessive sarcomere lengths, having a detrimental effect on force generation. Whether this series of events occurs in the human diaphragm is unknown. In the current study, we investigated if short-term application of PEEP affects diaphragm geometry and function, which are prerequisites for the development of longitudinal atrophy with prolonged PEEP application. Nineteen healthy volunteers were noninvasively ventilated with PEEP levels of 2, 5, 10, and 15 cmH₂O. Magnetic resonance imaging was performed to investigate PEEP-induced changes in diaphragm geometry. Subjects were instrumented with nasogastric catheters to measure diaphragm neuromechanical efficiency (i.e., diaphragm pressure normalized to its electrical activity) during tidal breathing with different PEEP levels. We found that increasing PEEP from 2 to 15 cmH₂O resulted in a caudal diaphragm displacement (19 [14-26] mm, P < 0.001), muscle shortening in the zones of apposition (20.6% anterior and 32.7% posterior, P < 0.001), increase in diaphragm thickness (36.4% [0.9%-44.1%], P < 0.001) and reduction in neuromechanical efficiency (48% [37.6%-56.6%], P < 0.001). These findings demonstrate that conditions required to develop longitudinal atrophy in the human diaphragm are present with the application of PEEP.NEW & NOTEWORTHY We demonstrate that PEEP causes changes in diaphragm geometry, especially muscle shortening, and decreases in vivo diaphragm contractile function. Thus, prerequisites for the development of diaphragm longitudinal muscle atrophy are present with the acute application of PEEP. Once confirmed in ventilated critically ill patients, this could provide a new mechanism for ventilator-induced diaphragm dysfunction and ventilator weaning failure in the intensive care unit (ICU).

Speckle tracking ultrasonography as a new tool to assess diaphragmatic function: a feasibility study

A reliable method of measuring diaphragmatic function at the bedside is still lacking. Widely used two-dimensional (2D) ultrasonographic measurements, such as diaphragm excursion, diaphragm thickness, and fractional thickening (FT) have failed to show clear correlations with diaphragmatic function. A reason for this is that 2D ultrasonographic measurements, like FT, are merely able to measure the deformation of muscular diaphragmatic tissue in the transverse direction, while longitudinal measurements in the direction of contracting muscle fibres are not possible. Speckle tracking ultrasonography, which is widely used in cardiac imaging, overcomes this disadvantage and allows observations of movement in the direction of the contracting muscle fibres, approximating muscle deformation and the deformation velocity. Several studies have evaluated speckle tracking as a promising method to assess diaphragm contractility in healthy subjects. This technical note demonstrates the feasibility of speckle tracking ultrasonography of the diaphragm in a group of 20 patients after an aortocoronary bypass graft procedure. The results presented herein suggest that speckle tracking ultrasonography is able to depict alterations in diaphragmatic function after surgery better than 2D ultrasonographic measurements.

Diaphragm dysfunction: A comprehensive review from diagnosis to management

Although the diaphragm represents a critical component of the respiratory pump, the clinical presentations of diaphragm dysfunction are often non-specific and can be mistaken for other more common causes of dyspnoea. While acute bilateral diaphragm dysfunction typically presents dramatically, progressive diaphragm dysfunction associated with neuromuscular disorders and unilateral hemidiaphragm dysfunction may be identified incidentally or by recognising subtle associated symptoms. Diaphragm dysfunction should be considered in individuals with unexplained dyspnoea, restrictive respiratory function tests or abnormal diaphragm position on plain chest imaging. A higher index of suspicion should occur for individuals with profound orthopnoea, those who have undergone procedures in proximity to the phrenic nerve(s) or those with co-morbid conditions that are associated with diaphragm dysfunction, particularly neuromuscular disorders. A systematic approach to the evaluation of diaphragm function using non-invasive diagnostic techniques such as respiratory function testing and diaphragm imaging can often confirm a diagnosis. Neurophysiological assessment may confirm diaphragm dysfunction and assist in identifying an underlying cause. Identifying those with or at risk of respiratory failure can allow institution of respiratory support, while specific cases may also benefit from surgical plication or phrenic nerve pacing techniques. This article is protected by copyright. All rights reserved.

A narrative review of diaphragmatic ultrasound in pediatric critical care

The use of point of care ultrasound (POCUS) at the bedside has increased dramatically within emergency medicine and in critical care. Applications of POCUS have spread to include diaphragmatic assessments in both adults and children. Diaphragm POCUS can be used to assess for diaphragm dysfunction (DD) and atrophy or to guide ventilator titration and weaning. Quantitative, semi-quantitative and qualitative measurements of diaphragm thickness, diaphragm excursion, and diaphragm thickening fraction provide objective data related to DD and atrophy. The potential for quick, noninvasive, and repeatable bedside diaphragm assessments has led to a growing amount of literature on diaphragm POCUS. To date, there are no reviews of the current state of diaphragm POCUS in pediatric critical care. The aims of this narrative review are to summarize the current literature regarding techniques, reference values, applications, and future innovations of diaphragm POCUS in critically ill children. A summary of current practice and future directions will be discussed.

Does diaphragm ultrasound improve the rapid shallow breathing index accuracy for predicting the success of weaning from mechanical ventilation?

BACKGROUND

This prospective study investigated whether taking into account diaphragmatic excursion (DE) measured by ultrasonography would improve the performance of the rapid shallow breathing index (RSBI) to predict extubation success or failure.

OBJECTIVES

The aim of the study was to compare the new composite index named the rapid shallow diaphragmatic index (RSDI), and the RSBI measured during a spontaneous breathing trial regarding their ability to predict the need for re-intubation at 72 h.

METHODS

One hundred mechanically ventilated patients underwent daily 30-min spontaneous breathing trials (SBTs) under pressure support ventilation of 6 cm H₂O and end-expiratory pressure of 0 cm H₂O until the SBT was considered successful and followed by extubation. The performances of RSBI (respiratory rate/tidal volume) and of the ratio RSBI/DE measured at 5 and 25 min of the successful SBT were compared in terms of area under the receiver operating characteristics curve (AUC), for predicting extubation success at 72 h. As secondary analysis, extubation and weaning success at 7 d were also considered. As exploratory analyses, predictive indices incorporating both clinical characteristics, the DE, and ultrasound diaphragm thickening fraction (DTF) were investigated.

RESULTS

RSBI and RSBI/DE showed AUCs with 95% confidence intervals consistently extending below 0.50, either at the 5th (0.55 [0.36-0.74] and 0.55 [0.34-0.75], respectively) or at the 25th minute of SBT (0.49 [0.27-0.71] and 0.50 [0.29-0.68], respectively) for predicting weaning success at 72 h or at 7 d (5th min: 0.53 [0.37-0.70] and 0.54 [0.37-0.70], respectively; 25th min: 0.54 [0.37-0.71] and 0.55 [0.39-0.71], respectively). An exploratory index incorporating the accessory respiratory muscle activity, DE, DTF, and respiratory rate at 5th min of SBT showed AUCs for predicting extubation success at 7 d in the 78 patients with DTF measurement (0.77 [0.64-0.90]) that were significantly higher than that of the RSBI (P = 0.017) and RSBI/DE (P < 0.001) in the same respective populations.

CONCLUSIONS

The RSBI and the ratio RSBI/DE failed to predict weaning success when measured during an SBT performed under minimal pressure support. Predictive indices incorporating ultrasound DE and DTF may merit further investigation.

Diaphragmatic speckle tracking imaging for 2D-strain assessment in mechanical ventilation weaning test

Ultrasound (US) is recognized as a useful tool for detecting lung physiology and pathology. Lung US is compared with standard techniques for evaluating lung structure and function such as computed tomography and pulmonary function tests. At present, markers of normal physiology and pathology are detected using expected image patterns. Detecting the latter depends on the experience of the operator. Diaphragmatic dysfunction is a particularly frequent problem in intensive care. Diaphragmatic dysfunction is easily assessed using lung US. Speckle tracking analysis, a known method for assessing tissue displacement and deformation in cardiology, is proposed to be utilized in lung US for detecting and quantifying lung sliding. Using speckle tracking analysis to diaphragmatic deformation quantification could be an informative and new tool for weaning from mechanical ventilation.

Respiratory muscle imaging by ultrasound and MRI in neuromuscular disorders

Respiratory muscle weakness is common in neuromuscular disorders and leads to significant respiratory difficulties. Therefore, reliable and easy assessment of respiratory muscle structure and function in neuromuscular disorders is crucial. In the last decade, ultrasound and MRI emerged as promising imaging techniques to assess respiratory muscle structure and function. Respiratory muscle imaging directly measures the respiratory muscles and, in contrast to pulmonary function testing, is independent of patient effort. This makes respiratory muscle imaging suitable to use as tool in clinical respiratory management and as outcome parameter in upcoming drug trials for neuromuscular disorders, particularly in children. In this narrative review, we discuss the latest studies and technological developments in imaging of the respiratory muscles by US and MR, and its clinical application and limitations. We aim to increase understanding of respiratory muscle imaging and facilitate its use as outcome measure in daily practice and clinical trials.

Muscle ultrasound: Present state and future opportunities

Muscle ultrasound is a valuable addition to the neuromuscular toolkit in both the clinic and research settings, with proven value and reliability. However, it is currently not fulfilling its full potential in the diagnostic care of patients with neuromuscular disease. This review highlights the possibilities and pitfalls of muscle ultrasound as a diagnostic tool and biomarker, and discusses challenges to its widespread implementation. We expect that limitations in visual image interpretation, posed by user inexperience, could be overcome with simpler scoring systems and the help of deep-learning algorithms. In addition, more information should be collected on the relation between specific neuromuscular disorders, disease stages, and expected ultrasound abnormalities, as this will enhance specificity of the technique and enable the use of muscle ultrasound as a biomarker. Quantified muscle ultrasound gives the most sensitive results but is hampered by the need for device-specific reference values. Efforts in creating dedicated muscle ultrasound systems and artificial intelligence to help with image interpretation are expected to improve usability. Finally, the standard inclusion of muscle and nerve ultrasound in neuromuscular teaching curricula and guidelines will facilitate further implementation in practice. Our hope is that this review will help in unleashing muscle ultrasound's full potential.

Ultrasound and non-ultrasound imaging techniques in the assessment of diaphragmatic dysfunction

Diaphragm muscle dysfunction is increasingly recognized as an important element of several diseases including neuromuscular disease, chronic obstructive pulmonary disease and diaphragm dysfunction in critically ill patients. Functional evaluation of the diaphragm is challenging. Use of volitional maneuvers to test the diaphragm can be limited by patient effort. Non-volitional tests such as those using neuromuscular stimulation are technically complex, since the muscle itself is relatively inaccessible. As such, there is a growing interest in using imaging techniques to characterize diaphragm muscle dysfunction. Selecting the appropriate imaging technique for a given clinical scenario is a critical step in the evaluation of patients suspected of having diaphragm dysfunction. In this review, we aim to present a detailed analysis of evidence for the use of ultrasound and non-ultrasound imaging techniques in the assessment of diaphragm dysfunction. We highlight the utility of the qualitative information gathered by ultrasound imaging as a means to assess integrity, excursion, thickness, and thickening of the diaphragm. In contrast, quantitative ultrasound analysis of the diaphragm is marred by inherent limitations of this technique, and we provide a detailed examination of these limitations. We evaluate non-ultrasound imaging modalities that apply static techniques (chest radiograph, computerized tomography and magnetic resonance imaging), used to assess muscle position, shape and dimension. We also evaluate non-ultrasound imaging modalities that apply dynamic imaging (fluoroscopy and dynamic magnetic resonance imaging) to assess diaphragm motion. Finally, we critically review the application of each of these techniques in the clinical setting when diaphragm dysfunction is suspected.

Monitoring diaphragm function in the ICU

PURPOSE OF REVIEW

To review the clinical problem of diaphragm function in critically ill patients and describes recent advances in bedside monitoring of diaphragm function.

RECENT FINDINGS

Diaphragm weakness, a consequence of diaphragm dysfunction and atrophy, is common in the ICU and associated with serious clinical consequences. The use of ultrasound to assess diaphragm structure (thickness, thickening) and mobility (caudal displacement) appears to be feasible and reproducible, but no large-scale 'real-life' study is available. Diaphragm ultrasound can also be used to evaluate diaphragm muscle stiffness by means of shear-wave elastography and strain by means of speckle tracking, both of which are correlated with diaphragm function in healthy. Electrical activity of the diaphragm is correlated with diaphragm function during brief airway occlusion, but the repeatability of these measurements exhibits high within-subject variability.

SUMMARY

Mechanical ventilation is involved in the pathogenesis of diaphragm dysfunction, which is associated with severe adverse events. Although ultrasound and diaphragm electrical activity could facilitate monitoring of diaphragm function to deliver diaphragm-protective ventilation, no guidelines concerning the use of these modalities have yet been published. The weaning process, assessment of patient-ventilator synchrony and evaluation of diaphragm function may be the most clinically relevant indications for these techniques.

Ultrasound shear wave elastography for assessing diaphragm function in mechanically ventilated patients: a breath-by-breath analysis

Background

Diaphragm dysfunction is highly prevalent in mechanically ventilated patients. Recent work showed that changes in diaphragm shear modulus (ΔSMdi) assessed using ultrasound shear wave elastography (SWE) are strongly related to changes in Pdi (ΔPdi) in healthy subjects. The aims of this study were to investigate the relationship between ΔSMdi and ΔPdi in mechanically ventilated patients, and whether ΔSMdi is responsive to change in respiratory load when varying the ventilator settings.

Methods

A prospective, monocentric study was conducted in a 15-bed ICU. Patients were included if they met the readiness-to-wean criteria. Pdi was continuously monitored using a double-balloon feeding catheter orally introduced. The zone of apposition of the right hemidiaphragm was imaged using a linear transducer (SL10-2, Aixplorer, Supersonic Imagine, France). Ultrasound recordings were performed under various pressure support settings and during a spontaneous breathing trial (SBT). A breath-by-breath analysis was performed, allowing the direct comparison between ΔPdi and ΔSMdi. Pearson’s correlation coefficients (r) were used to investigate within-individual relationships between variables, and repeated measure correlations (R) were used for determining overall relationships between variables. Linear mixed models were used to compare breathing indices across the conditions of ventilation.

Results

Thirty patients were included and 930 respiratory cycles were analyzed. Twenty-five were considered for the analysis. A significant correlation was found between ΔPdi and ΔSMdi (R = 0.45, 95% CIs [0.35 0.54], p < 0.001). Individual correlation displays a significant correlation in 8 patients out of 25 (r = 0.55–0.86, all p < 0.05, versus r = − 0.43–0.52, all p > 0.06). Changing the condition of ventilation similarly affected ΔPdi and ΔSMdi. Patients in which ΔPdi–ΔSMdi correlation was non-significant had a faster respiratory rate as compared to that of patient with a significant ΔPdi–ΔSMdi relationship (median (Q1–Q3), 25 (18–33) vs. 21 (15–26) breaths.min⁻¹, respectively).

Conclusions

We demonstrate that ultrasound SWE may be a promising surrogate to Pdi in mechanically ventilated patients. Respiratory rate appears to negatively impact SMdi measurement. Technological developments are needed to generalize this method in tachypneic patients.

Trial registration

NCT03832231.

Ultrafast ultrasound coupled with cervical magnetic stimulation for non-invasive and non-volitional assessment of diaphragm contractility

KEY POINTS

Twitch transdiaphragmatic pressure elicited by cervical magnetic stimulation of the phrenic nerves is a fully non-volitional method for assessing diaphragm contractility in humans, yet it requires invasive procedures such as oesophageal and gastric catheter balloons.  Ultrafast ultrasound enables a very high frame rate allowing the capture of transient events, such as muscle contraction elicited by nerve stimulation (twitch). Whether indices derived from ultrafast ultrasound can be used as an alternative to the invasive measurement of twitch transdiaphragmatic pressure is unknown.  Our findings demonstrate that maximal diaphragm tissue velocity assessed using ultrafast ultrasound following cervical magnetic stimulation is reliable, sensitive to change in cervical magnetic stimulation intensity, and correlates to twitch transdiaphragmatic pressure.  This approach provides a novel fully non-invasive and non-volitional tool for the assessment of diaphragm contractility in humans.

ABSTRACT

Measuring twitch transdiaphragmatic pressure (P_di,tw ) elicited by cervical magnetic stimulation (CMS) is considered as a reference method for the standardized evaluation of diaphragm function. Yet, the measurement of P_di requires invasive oesophageal and gastric catheter-balloons. Ultrafast ultrasound is a non-invasive imaging technique enabling frame rates high enough to capture transient events such as evoked muscle contractions. This study investigated relationships between indices derived from ultrafast ultrasound and P_di,tw , and how these indices might be used to estimate P_di,tw . CMS was performed in 13 healthy volunteers from 30% to 100% of maximal stimulator intensity in units of 10% in a randomized order. P_di,tw was measured and the right hemidiaphragm was imaged using a custom ultrafast ultrasound sequence with 1 kHz framerate. Maximal diaphragm axial velocity (V_di ,_max ) and diaphragm thickening fraction (TF_di,tw ) were computed. Intra-session reliability was assessed. Repeated-measures correlation (R) and Spearman correlation coefficients (ρ) were used to assess relationships between variables. Intra-session reliability was strong for P_di,tw and V_di,max and moderate for TF_di,tw . V_di,max correlated with P_di,tw in all subjects (0.64 < ρ < 1.00, R = 0.75; all P < 0.05). TF_di,tw correlated with P_di,tw in eight subjects only (0.85 < ρ < 0.93, R = 0.69; all P < 0.05). Coupling ultrafast ultrasound and CMS shows promise for the non-invasive and fully non-volitional assessment of diaphragm contractility. This approach opens up the prospect of both diagnosis and follow-up of diaphragm contractility in clinical populations.

Assessment of diaphragmatic function by ultrasonography: Current approach and perspectives

This article reports the various methods used to assess diaphragmatic function by ultrasonography. The excursions of the two hemidiaphragms can be measured using two-dimensional or M-mode ultrasonography, during respiratory maneuvers such as quiet breathing, voluntary sniffing and deep inspiration. On the zone of apposition to the rib cage for both hemidiaphragms, it is possible to measure the thickness on expiration and during deep breathing to assess the percentage of thickening during inspiration. These two approaches make it possible to assess the quality of the diaphragmatic function and the diagnosis of diaphragmatic paralysis or dysfunction. These methods are particularly useful in circumstances where there is a high risk of phrenic nerve injury or in diseases affecting the contractility or the motion of the diaphragm such as neuro-muscular diseases. Recent methods such as speckle tracking imaging and ultrasound shear wave elastography should provide more detailed information for better assessment of diaphragmatic function.

Respiratory muscle ultrasonography: methodology, basic and advanced principles and clinical applications in ICU and ED patients-a narrative review

Respiratory muscle ultrasound is used to evaluate the anatomy and function of the respiratory muscle pump. It is a safe, repeatable, accurate, and non-invasive bedside technique that can be successfully applied in different settings, including general intensive care and the emergency department. Mastery of this technique allows the intensivist to rapidly diagnose and assess respiratory muscle dysfunction in critically ill patients and in patients with unexplained dyspnea. Furthermore, it can be used to assess patient-ventilator interaction and weaning failure in critically ill patients. This paper provides an overview of the basic and advanced principles underlying respiratory muscle ultrasound with an emphasis on the diaphragm. We review different ultrasound techniques useful for monitoring of the respiratory muscle pump and possible therapeutic consequences. Ideally, respiratory muscle ultrasound is used in conjunction with other components of critical care ultrasound to obtain a comprehensive evaluation of the critically ill patient. We propose the ABCDE-ultrasound approach, a systematic ultrasound evaluation of the heart, lungs and respiratory muscle pump, in patients with weaning failure.

Speckle tracking quantification of lung sliding for the diagnosis of pneumothorax: a multicentric observational study

PURPOSE

Lung ultrasound is used for the diagnosis of pneumothorax, based on lung sliding abolition which is a qualitative and operator-dependent assessment. Speckle tracking allows the quantification of structure deformation over time by analysing acoustic markers. We aimed to test the ability of speckle tracking technology to quantify lung sliding in a selected cohort of patients and to observe how the technology may help the process of pneumothorax diagnosis.

METHODS

We performed retrospectively a pleural speckle tracking analysis on ultrasound loops from patients with pneumothorax. We compared the values measured by two observers from pneumothorax side with contralateral normal lung side. The receiver operating characteristic (ROC) curve was constructed to evaluate the performance of maximal pleural strain to detect the lung sliding abolition. Diagnosis performance and time to diagnosis between B-Mode and speckle tracking technology were compared from a third blinded observer.

RESULTS

We analysed 104 ultrasound loops from 52 patients. The area under the ROC curve of the maximal pleural strain value to identify lung sliding abolition was 1.00 [95%CI 1.00; 1.00]. Specificity was 100% [95%CI 93%; 100%] and sensitivity was 100% [95%CI 93%; 100%] with the best cut-off of 4%. Over 104 ultrasound loops, the blinded observer made two errors with B-Mode and none with speckle tracking. The median diagnosis time was 3 [2-5] seconds for B-Mode versus 2 [1-2] seconds for speckle tracking (p = 0.001).

CONCLUSION

Speckle tracking technology allows lung sliding quantification and detection of lung sliding abolition in case of pneumothorax on selected ultrasound loops.

Musculoskeletal application and validation of speckle-tracking ultrasonography

Background

Diseased, injured, or dysfunctional skeletal muscles may demonstrate abnormal function and contractility. Currently, only few in vivo imaging techniques are able to characterize the contractile properties of muscle tissue. This study aimed to test the hypothesis that muscle strain can be tracked in two upper extremity skeletal muscles by speckle-tracking ultrasonography (STU) and correlates with isometric muscle contractions.

Methods

A convenience sample of 10 healthy, adult volunteers with normal shoulder function were tested. The 5 women and 5 men had a mean age of 45 years (range: 39–59 years) and BMI < 30. STU was applied to the supraspinatus (SS) and biceps brachii (BB) muscles using a M11 L-MHz linear transducer (frequency 8–15 MHz) hooked to a Vivid E 9TM ultrasound machine. Strain validation was performed by correlating peak strain against standardized sub-maximal, isometric load conditions of the two muscles (20–80% of maximal voluntary contraction) using a custom-built muscle dynamometer based on strain-gauge technique. Data were analyzed offline using the EchoPac speckle-tracking software and were blinded to the examiner.

Results

Intramuscular strain measured by STU in the SS and BB muscles showed moderate to strong correlations with external muscle load (SS: r = − 0.76, p < 0.0001 and BB: r = − 0.60, p < 0.0001). We found strain to vary from approximately 10–20% during increasing submaximal, isometric conditions.

Conclusions

We demonstrate that STU can be applied on healthy skeletal musculature (SS and BB muscles). The observed correlations between strain and isometric contractions suggest a valid technique. However, the concept of measuring muscle strain non-invasively needs further investigation for validity, accuracy, responsiveness, and reliability before its therapeutic and research potential can be realized.

Diaphragm contractile weakness due to reduced mechanical loading: role of titin

The diaphragm, the main muscle of inspiration, is constantly subjected to mechanical loading. Only during controlled mechanical ventilation, as occurs during thoracic surgery and in the intensive care unit, is mechanical loading of the diaphragm arrested. Animal studies indicate that the diaphragm is highly sensitive to unloading, causing rapid muscle fiber atrophy and contractile weakness; unloading-induced diaphragm atrophy and contractile weakness have been suggested to contribute to the difficulties in weaning patients from ventilator support. The molecular triggers that initiate the rapid unloading atrophy of the diaphragm are not well understood, although proteolytic pathways and oxidative signaling have been shown to be involved. Mechanical stress is known to play an important role in the maintenance of muscle mass. Within the muscle's sarcomere, titin is considered to play an important role in the stress-response machinery. Titin is a giant protein that acts as a mechanosensor regulating muscle protein expression in a sarcomere strain-dependent fashion. Thus titin is an attractive candidate for sensing the sudden mechanical arrest of the diaphragm when patients are mechanically ventilated, leading to changes in muscle protein expression. Here, we provide a novel perspective on how titin and its biomechanical sensing and signaling might be involved in the development of mechanical unloading-induced diaphragm weakness.

Diaphragm shear modulus reflects transdiaphragmatic pressure during isovolumetric inspiratory efforts and ventilation against inspiratory loading

The reference method for the assessment of diaphragm function relies on the measurement of transdiaphragmatic pressure (Pdi). Local muscle stiffness measured using ultrafast shear wave elastography (SWE) provides reliable estimates of muscle force in locomotor muscles. This study aimed at investigating whether SWE could be used as a surrogate of Pdi to evaluate diaphragm function. Fifteen healthy volunteers underwent a randomized stepwise inspiratory loading protocol of 0–60% of maximal isovolumetric inspiratory pressure during closed-airways maneuvers and 0–50% during ventilation against an external inspiratory threshold load. During all tasks, Pdi was measured and SWE was used to assess shear modulus of the right hemidiaphragm (SMdi) at the zone of apposition. Pearson correlation coefficients ( r) and repeated-measures correlation coefficients ( R) were computed to determine within-individual and overall relationships between Pdi and SMdi, respectively. During closed-airways maneuvers, mean Pdi correlated to mean SMdi in all participants [ r ranged from 0.77 to 0.96, all P < 0.01; R = 0.82, 95% confidence intervals (0.76, 0.86), P < 0.01]. During ventilation against inspiratory threshold loading, Pdi swing correlated to maximal SMdi in all participants [ r ranged from 0.40 to 0.90, all P < 0.01; R = 0.70, 95% confidence intervals (0.66, 0.73), P < 0.001]. Changes in diaphragm stiffness as assessed by SWE reflect changes in transdiaphragmatic pressure. SWE provides a new opportunity for direct and noninvasive assessment of diaphragm function.

NEW & NOTEWORTHY Accurate and specific estimation of diaphragm effort is critical for evaluating and monitoring diaphragm dysfunction. The measurement of transdiaphragmatic pressure requires the use of invasive gastric and esophageal probes. In the present work, we demonstrate that changes in diaphragm stiffness assessed with ultrasound shear wave elastography reflect changes in transdiaphragmatic pressure, therefore offering a new noninvasive method for gauging diaphragm effort.

Human diaphragm atrophy in amyotrophic lateral sclerosis is not predicted by routine respiratory measures

Amyotrophic lateral sclerosis (ALS) patients show progressive respiratory muscle weakness leading to death from respiratory failure. However, there are no data on diaphragm histological changes in ALS patients and how they correlate with routine respiratory measurements.

We collected 39 diaphragm biopsies concomitantly with laparoscopic insertion of intradiaphragmatic electrodes during a randomised controlled trial evaluating early diaphragm pacing in ALS (https://clinicaltrials.gov; NCT01583088). Myofibre type, size and distribution were evaluated by immunofluorescence microscopy and correlated with spirometry, respiratory muscle strength and phrenic nerve conduction parameters. The relationship between these variables and diaphragm atrophy was assessed using multivariate regression models.

All patients exhibited significant slow- and fast-twitch diaphragmatic atrophy. Vital capacity (VC), maximal inspiratory pressure, sniff nasal inspiratory pressure (SNIP) and twitch transdiaphragmatic pressure did not correlate with the severity of diaphragm atrophy. Inspiratory capacity (IC) correlated modestly with slow-twitch myofibre atrophy. Supine fall in VC correlated weakly with fast-twitch myofibre atrophy. Multivariate analysis showed that IC, SNIP and functional residual capacity were independent predictors of slow-twitch diaphragmatic atrophy, but not fast-twitch atrophy.

Routine respiratory tests are poor predictors of diaphragm structural changes. Improved detection of diaphragm atrophy is essential for clinical practice and for management of trials specifically targeting diaphragm muscle function.