Noninvasive measurement of the tension-time index in children with neuromuscular disease

Normal values for maximal respiratory pressures in children and adolescents: A systematic review with meta-analysis

BACKGROUND

The non-invasive assessment of maximal respiratory pressures (MRP) reflects the strength of the respiratory muscles.

OBJECTIVE

To evaluate the studies which have established normative values for MRP in healthy children and adolescents and to synthesize these values through a meta-analysis.

METHODS

The searches were conducted until October 2023 in the following databases: ScienceDirect, MEDLINE, CINAHL, SciELO, and Web of Science. Articles that determined normative values and/or reference equations for maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) in children and adolescents published in English, Portuguese, or Spanish regardless of the year of publication were included. Two reviewers selected titles and abstracts, in case of conflict, a third reviewer was consulted. Articles that presented sufficient data were included to conduct the meta-analysis.

RESULTS

Initially, 252 studies were identified, 28 studies were included in the systematic review and 19 in the meta-analysis. The sample consisted of 5798 individuals, and the MIP and MEP values were stratified by sex and age groups of 4-11 and 12-19 years. Values from females 4-11 years were: 65.8 cmH2O for MIP and 72.8 cmH2O for MEP, and for males, 75.4 cmH2O for MIP and 84.0 cmH2O for MEP. In the 12-19 age group, values for females were 82.1 cmH2O for MIP and 90.0 cmH2O for MEP, and for males, they were 95.0 cmH2O for MIP and 105.7 cmH2O for MEP.

CONCLUSIONS

This meta-analysis suggests normative values for MIP and MEP in children and adolescents based on 19 studies.

Clinical Challenges in Pediatric Ventilation Liberation: A Meta-Narrative Review

OBJECTIVES

To map the evidence for ventilation liberation practices in pediatric respiratory failure using the Realist And MEta-narrative Evidence Syntheses: Evolving Standards publication standards.

DATA SOURCES

CINAHL, MEDLINE, COCHRANE, and EMBASE. Trial registers included the following: ClinicalTrials.gov, European Union clinical trials register, International Standardized Randomized Controlled Trial Number register.

STUDY SELECTION

Abstracts were screened followed by review of full text. Articles published in English language incorporating a heterogeneous population of both infants and older children were assessed.

DATA EXTRACTION

None.

DATA SYNTHESIS

Weaning can be considered as the process by which positive pressure is decreased and the patient becomes increasingly responsible for generating the energy necessary for effective gas exchange. With the growing use of noninvasive respiratory support, extubation can lie in the middle of the weaning process if some additional positive pressure is used after extubation, while for some extubation may constitute the end of weaning. Testing for extubation readiness is a key component of the weaning process as it allows the critical care practitioner to assess the capability and endurance of the patient's respiratory system to resume unassisted ventilation. Spontaneous breathing trials (SBTs) are often seen as extubation readiness testing (ERT), but the SBT is used to determine if the patient can maintain adequate spontaneous ventilation with minimal ventilatory support, whereas ERT implies the patient is ready for extubation.

CONCLUSIONS

Current literature suggests using a structured approach that includes a daily assessment of patient's readiness to extubate may reduce total ventilation time. Increasing evidence indicates that such daily assessments needs to include SBTs without added pressure support. Measures of elevated load as well as measures of impaired respiratory muscle capacity are independently associated with extubation failure in children, indicating that these should also be assessed as part of ERT.

Pulmonary function testing in patients with neuromuscular disease

Progressive neuromuscular disease leads to muscle weakness or failure that produces loss of pulmonary function and clinical respiratory morbidity. Tracking pulmonary function in a practical and effective way is very important because it can help identify a stage of disease when a morbidity, such as inadequate airway clearance or respiratory failure, may be present. There are four general categories of pulmonary function outcome measures such as volume, flow, pressure, and gas exchange. These outcome measures have variable precision and accuracy in predicting clinical change, and practicality in performing them relative to age and condition. It is widely recommended to follow multiple measurements longitudinally and create an accurate and timely clinical picture. This manuscript will review the most commonly used and most practical measures for use in clinical practice and how they can help to assess morbidity, disease state, and help optimize patient management.

The effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in spinal muscular atrophy

In patients with spinal muscular atrophy (SMA), obstructive sleep apnea syndrome (OSAS) constitutes an important cause of cardiovascular morbidity and mortality. We investigated heart rate variability (HRV) to evaluate the effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in patients with SMA and OSAS. Six patients with SMA (type 1 and 2) and six age- and sex-matched healthy children were consecutively enrolled. A whole-night diagnostic polysomnography was performed, and SMA patients with OSAS were given non-invasive mechanical ventilation therapy. HRV analysis was performed on the basis of whole-night electrocardiography recordings via a computer-base program. Apnea-hypopnea index (AHI) was 9.2 ± 6.2/hr in SMA patients, while it was 0.4 ± 0.5/hr in controls (p = 0.036). All SMA patients had OSAS, while none of the controls had OSAS (p = 0.012). Mean percentage of successive R wave of QRS complex (R-R) intervals>50 ms was significantly lower in SMA patients than those in controls (p = 0.031). Significant correlations were found between AHI and high-frequency power, low/high-frequency ratio in wakefulness and in sleep (p<0.05). Repeated HRV analysis in SMA patients following OSAS therapy showed significant reductions in average R-R duration (p = 0.028) and percentage of successive R-R intervals>50 ms (p = 0.043). Our study demonstrates the beneficial effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in SMA patients with OSAS.

Respiratory Involvement in Patients with Neuromuscular Diseases: A Narrative Review

Respiratory muscle weakness is a major cause of morbidity and mortality in patients with neuromuscular diseases (NMDs). Respiratory involvement in NMDs can manifest broadly, ranging from milder insufficiency that may affect only sleep initially to severe insufficiency that can be life threatening. Patients with neuromuscular diseases exhibit very often sleep-disordered breathing, which is frequently overlooked until symptoms become more severe leading to irreversible respiratory failure necessitating noninvasive ventilation (NIV) or even tracheostomy. Close monitoring of respiratory function and sleep evaluation is currently the standard of care. Early recognition of sleep disturbances and initiation of NIV can improve the quality of life and prolong survival. This review discusses the respiratory impairment during sleep in patients with NMDs, the diagnostic tools available for early recognition of sleep-disordered breathing and the therapeutic options available for overall respiratory management of patients with NMDs.

Inspiratory muscle training in severe spinal muscular atrophy: a case report

Background/Aims

Inspiratory muscle training aims to preserve or improve respiratory muscle strength in children with neuromuscular diseases in order to prevent or minimise pulmonary morbidity. The aim of this study was to determine the effect of inspiratory muscle training on clinical outcomes and health-related quality of life in a child with advanced neuromuscular disease and severe pulmonary restriction.

Methods

A one patient pre-test post-test study design was implemented. General function, spirometry, peak expiratory cough flow and health-related quality of life were measured at baseline and after a 6-week inspiratory muscle training programme. Inspiratory muscle strength (maximal inspiratory mouth pressure and sniff nasal inspiratory pressure) was measured every 2 weeks. The patient used a tapered flow threshold inspiratory training device (POWERbreathe K3) at an intensity of ± 30% of maximal inspiratory mouth pressure twice a day, 5 days per week.

Findings

The non-ambulatory 10-year-old girl with type 2 spinal muscular atrophy initially had a forced vital capacity of 18% predicted and peak expiratory cough flow of 60 litres/minute. A substantial improvement was seen in inspiratory muscle strength between baseline and 4 weeks. Patient health-related quality of life improved and patient satisfaction was high, with a score of 9/10. The patient developed a lower respiratory tract infection towards the end of the inspiratory muscle training period. No other adverse events occurred.

Conclusions

Improved inspiratory muscle strength and health-related quality of life was associated with inspiratory muscle training in a child with advanced spinal muscular atrophy. Controlled clinical trials are recommended to determine the safety and efficacy of inspiratory muscle training in children with advanced spinal muscular atrophy and severe respiratory muscle weakness to inform clinical practice.

Determinants of inspiratory muscle function in healthy children

BACKGROUND

Children are affected by disorders that have an impact on the respiratory muscles. Inspiratory muscle function can be assessed by means of the noninvasive tension-time index of the inspiratory muscles (TTI_mus). Our objectives were to identify the determinants of TTI_mus in healthy children and to report normal values of TTI_mus in this population.

METHODS

We measured weight, height, upper arm muscle area (UAMA), and TTI_mus in 96 children aged 6-18 years. The level and frequency of aerobic activity was assessed by questionnaire.

RESULTS

TTI_mus was significantly lower in male subjects (0.095 ± 0.038, mean ± SD) compared with female subjects (0.126 ± 0.056) (p = 0.002). TTI_mus was significantly lower in regularly exercising (0.093 ± 0.040) compared with nonexercising subjects (0.130 ± 0.053) (p < 0.001). TTI_mus was significantly negatively related to age (r = -0.239, p = 0.019), weight (r = -0.214, p = 0.037), height (r = -0.355, p < 0.001), and UAMA (r = -0.222, p = 0.030). Multivariate logistic regression analysis revealed that height and aerobic exercise were significantly related to TTI_mus independently of age, weight, and UAMA. The predictive regression equation for TTI_mus in male subjects was TTI_mus = 0.228 - 0.001 × height (cm), and in female subjects it was TTI_mus = 0.320 - 0.001 × height (cm) .

CONCLUSION

Gender, age, anthropometry, skeletal muscularity, and aerobic exercise are significantly associated with indices of inspiratory muscle function in children. Normal values of TTI_mus in healthy children are reported.

The role of sleep diagnostics and non-invasive ventilation in children with spinal muscular atrophy

Spinal muscular atrophy (SMA) is a degenerative motor neurone disorder causing progressive muscular weakness. Without assisted ventilation or novel therapies, most children with SMA type 1 die before the second year of life due to respiratory failure as the respiratory muscles and bulbar function are severely affected. Active respiratory treatment (mechanically assisted cough, invasive or non-invasive ventilation) has improved survival significantly in recent decades, but often at the cost of becoming ventilator dependent. The advent of a new oligonucleotide based therapy (Nusinersen) has created new optimism for improving motor function. However, the long-term effect on respiratory function is unclear and non-invasive respiratory support will remain an important part of medical management in patients with SMA. This review summarises the existing knowledge about sleep-disordered breathing and respiratory failure in patients with SMA, especially type 1, as well as the evidence of improved outcome and survival in patients treated with non-invasive or invasive ventilation. Practical considerations and ethical concerns are delineated with discussion on how these may be affected by the advent of new therapies such as Nusinersen.

Validating Lung Models Using the ASL 5000 Breathing Simulator

OBJECTIVE

This study sought to validate pediatric models with normal and altered pulmonary mechanics.

METHODS

PubMed and CINAHL databases were searched for studies directly measuring pulmonary mechanics of healthy infants and children, infants with severe bronchopulmonary dysplasia and neuromuscular disease. The ASL 5000 was used to construct models using tidal volume (VT), inspiratory time (TI), respiratory rate, resistance, compliance, and esophageal pressure gleaned from literature. Data were collected for a 1-minute period and repeated three times for each model. t tests compared modeled data with data abstracted from the literature. Repeated measures analyses evaluated model performance over multiple iterations. Statistical significance was established at a P value of less than 0.05.

RESULTS

Maximum differences of means (experimental iteration mean - clinical standard mean) for TI and VT are the following: term infant without lung disease (TI = 0.09 s, VT = 0.29 mL), severe bronchopulmonary dysplasia (TI = 0.08 s, VT = 0.17 mL), child without lung disease (TI = 0.10 s, VT = 0.17 mL), and child with neuromuscular disease (TI = 0.09 s, VT = 0.57 mL). One-sample testing demonstrated statistically significant differences between clinical controls and VT and TI values produced by the ASL 5000 for each iteration and model (P < 0.01). The greatest magnitude of differences was negligible (VT < 1.6%, TI = 18%) and not clinically relevant.

CONCLUSIONS

Inconsistencies occurred with the models constructed on the ASL 5000. It was deemed accurate for the study purposes. It is therefore essential to test models and evaluate magnitude of differences before use.

Reference Values for Respiratory Muscle Strength in Children and Adolescents

BACKGROUND

Measurement of respiratory muscle function is important in the diagnosis of respiratory muscle disease, respiratory failure, to assess the impact of chronic diseases, and/or to evaluate respiratory muscle function after treatment.

OBJECTIVES

To establish reference values for maximal inspiratory and expiratory pressure, and the tension-time index at rest in healthy children and adolescents aged 8-19 years, as well as to present sex- and age-related reference centiles normalized for demographic and anthropometric determinants.

METHODS

In this cross-sectional observational study, demographic, anthropometric, and spirometric data were assessed, as well as data on respiratory muscle strength (PImax and PEmax) and work of breathing at rest (TT0.1), in a total of 251 children (117 boys and 134 girls; mean age 13.4 ± 2.9 years). Reference values are presented as reference centiles developed by use of the lambda, mu, sigma method.

RESULTS

Boys had significantly higher PImax and PEmax values. Next to sex and age, fat-free mass appeared to be an important predictor of respiratory muscle strength. Reference centiles demonstrated a slight, almost linear increase in PImax with age in boys, and a less steep increase with age in girls. TT0.1 values did not differ between boys and girls and decreased linearly with age.

CONCLUSION

This study provides reference values for respiratory muscle strength and work of breathing at rest. In addition to sex and age, fat-free mass was found to be an important predictor of respiratory muscle strength in boys and girls.

Upper extremity resistance exercise with elastic bands for respiratory function in children with cerebral palsy

[Purpose] We investigated the effects of upper extremity resistance exercise with elastic bands on respiratory function in children with cerebral palsy. [Subjects and Methods] Fifteen children were divided into two groups: the experimental (n=8) and control (n=7) groups. Both groups performed general exercises for 30 minutes per session, two times a week during the intervention period. The experimental group performed an additional upper extremity resistance exercise with elastic bands for 20–30 minutes per session, twice weekly for 8 weeks. Pulmonary function, and respiratory muscle and grip strength were measured before and after the exercise. [Results] There was no significant difference in forced vital capacity, forced expiratory volume in one second, the ratio of forced expiratory volume in one second to forced vital capacity, and peak expiratory flow before and after the intervention in either group. The increment of maximal expiratory pressure was significantly greater in the experimental group, compared with the control group. In addition, grip strength was significantly increased in the experimental group after the intervention than before. [Conclusion] We found that upper extremity resistance exercise with elastic bands has a positive effect on expiration and improves grip strength in children with cerebral palsy.

Physiology of respiratory disturbances in muscular dystrophies

Muscular dystrophy is a group of inherited myopathies characterised by progressive skeletal muscle wasting, including of the respiratory muscles. Respiratory failure, i.e. when the respiratory system fails in its gas exchange functions, is a common feature in muscular dystrophy, being the main cause of death, and it is a consequence of lung failure, pump failure or a combination of the two. The former is due to recurrent aspiration, the latter to progressive weakness of respiratory muscles and an increase in the load against which they must contract. In fact, both the resistive and elastic components of the work of breathing increase due to airway obstruction and chest wall and lung stiffening, respectively. The respiratory disturbances in muscular dystrophy are restrictive pulmonary function, hypoventilation, altered thoracoabdominal pattern, hypercapnia, dyspnoea, impaired regulation of breathing, inefficient cough and sleep disordered breathing. They can be present at different rates according to the type of muscular dystrophy and its progression, leading to different onset of each symptom, prognosis and degree of respiratory involvement.

KEY POINTS

A common feature of muscular dystrophy is respiratory failure, i.e. the inability of the respiratory system to provide proper oxygenation and carbon dioxide elimination.In the lung, respiratory failure is caused by recurrent aspiration, and leads to hypoxaemia and hypercarbia.Ventilatory failure in muscular dystrophy is caused by increased respiratory load and respiratory muscles weakness.Respiratory load increases in muscular dystrophy because scoliosis makes chest wall compliance decrease, atelectasis and fibrosis make lung compliance decrease, and airway obstruction makes airway resistance increase.The consequences of respiratory pump failure are restrictive pulmonary function, hypoventilation, altered thoracoabdominal pattern, hypercapnia, dyspnoea, impaired regulation of breathing, inefficient cough and sleep disordered breathing.

EDUCATIONAL AIMS

To understand the mechanisms leading to respiratory disturbances in patients with muscular dystrophy.To understand the impact of respiratory disturbances in patients with muscular dystrophy.To provide a brief description of the main forms of muscular dystrophy with their respiratory implications.

Inspiratory muscle conditioning exercise and diaphragm gene therapy in Pompe disease: Clinical evidence of respiratory plasticity

Pompe disease is an inherited disorder due to a mutation in the gene that encodes acid α-glucosidase (GAA). Children with infantile-onset Pompe disease develop progressive hypotonic weakness and cardiopulmonary insufficiency that may eventually require mechanical ventilation (MV). Our team conducted a first in human trial of diaphragmatic gene therapy (AAV1-CMV-GAA) to treat respiratory neural dysfunction in infantile-onset Pompe. Subjects (aged 2-15years, full-time MV: n=5, partial/no MV: n=4) underwent a period of preoperative inspiratory muscle conditioning exercise. The change in respiratory function after exercise alone was compared to the change in function after intramuscular delivery of AAV1-CMV-GAA to the diaphragm with continued exercise. Since AAV-mediated gene therapy can reach phrenic motoneurons via retrograde transduction, we hypothesized that AAV1-CMV-GAA would improve dynamic respiratory motor function to a greater degree than exercise alone. Dependent measures were maximal inspiratory pressure (MIP), respiratory responses to inspiratory threshold loads (load compensation: LC), and physical evidence of diaphragm activity (descent on MRI, EMG activity). Exercise alone did not change function. After AAV1-CMV-GAA, MIP was unchanged. Flow and volume LC responses increased after dosing (p<0.05 to p<0.005), but only in the subjects with partial/no MV use. Changes in LC tended to occur on or after 180days. At Day 180, the four subjects with MRI evidence of diaphragm descent had greater maximal voluntary ventilation (p<0.05) and tended to be younger, stronger, and use fewer hours of daily MV. In conclusion, combined AAV1-CMV-GAA and exercise training conferred benefits to dynamic motor function of the diaphragm. Children with a higher baseline neuromuscular function may have greater potential for functional gains.

Novel methods of inspiratory muscle training via the Test of Incremental Respiratory Endurance (TIRE)

The favorable effects of inspiratory muscle training (IMT) in health and disease are becoming much more apparent. A variety of IMT methods exist, but few studies have compared IMT methods. The purpose of this article is to review the methods and outcomes of the Test of Incremental Respiratory Endurance (TIRE).

Assessment and management of respiratory function in patients with Duchenne muscular dystrophy: current and emerging options

Duchenne muscular dystrophy (DMD) is an X-linked myopathy resulting in progressive weakness and wasting of all the striated muscles including the respiratory muscles. The consequences are loss of ambulation before teen ages, cardiac involvement and breathing difficulties, the main cause of death. A cure for DMD is not currently available. In the last decades the survival of patients with DMD has improved because the natural history of the disease can be changed thanks to a more comprehensive therapeutic approach. This comprises interventions targeted to the manifestations and complications of the disease, particularly in the respiratory care. These include: 1) pharmacological intervention, namely corticosteroids and idebenone that significantly reduce the decline of spirometric parameters; 2) rehabilitative intervention, namely lung volume recruitment techniques that help prevent atelectasis and slows the rate of decline of pulmonary function; 3) scoliosis treatment, namely steroid therapy that is used to reduce muscle inflammation/degeneration and prolong ambulation in order to delay the onset of scoliosis, being an additional contribution to the restrictive lung pattern; 4) cough assisted devices that improve airway clearance thus reducing the risk of pulmonary infections; and 5) non-invasive mechanical ventilation that is essential to treat nocturnal hypoventilation, sleep disordered breathing, and ultimately respiratory failure. Without any intervention death occurs within the first 2 decades, however, thanks to this multidisciplinary therapeutic approach life expectancy of a newborn with DMD nowadays can be significantly prolonged up to his fourth decade. This review is aimed at providing state-of-the-art methods and techniques for the assessment and management of respiratory function in DMD patients.

The value of respiratory muscle testing in children with neuromuscular disease

Routine lung function and respiratory muscle testing are recommended in children with neuromuscular disease (NMD), but these tests are based on noninvasive volitional maneuvers, such as the measurement of lung volumes and maximal static pressures, that young children may not always be able to perform. The realization of simple natural maneuvers such as a sniff or a cough, and the measurement of esophageal and gastric pressures during spontaneous breathing can add valuable information about the strength and endurance of the respiratory muscles in young children. Monitoring respiratory muscles in children with NMD may improve understanding of the natural history of NMD and the evaluation of disease severity. It may assist and guide clinical management and it may help the identification and selection of optimal end points, as well as the most informative parameters and patients for clinical trials.

Respiratory muscle function in infants with spinal muscular atrophy type I

OBJECTIVE

To determine the feasibility and safety of respiratory muscle function testing in weak infants with a progressive neuromuscular disorder.

RATIONALE

Respiratory insufficiency is the major cause of morbidity and mortality in infants with spinal muscular atrophy type I (SMA-I).

HYPOTHESIS

Tests of respiratory muscle strength, endurance, and breathing patterns can be performed safely in SMA-I infants. Useful data can be collected which parallels the clinical course of pulmonary function in SMA-I.

STUDY DESIGN AND SUBJECT SELECTION

An exploratory study of respiratory muscle function testing and breathing patterns in seven infants with SMA-I seen in our neuromuscular clinic. Measurements were made at initial study visit and, where possible, longitudinally over time.

METHODOLOGY

We measured maximal inspiratory (MIP) and transdiaphragmatic pressures, mean transdiaphragmatic pressure, airway occlusion pressure at 100 msec of inspiration, inspiratory and total respiratory cycle time, and aspects of relative thoracoabdominal motion using respiratory inductive plethysmography (RIP). The tension time index of the diaphragm and of the respiratory muscles, phase angle (Φ), phase relation during the total breath, and labored breathing index were calculated.

RESULTS

Age at baseline study was 54-237 (median 131) days. Reliable data were obtained safely for MIP, phase angle, labored breathing index, and the invasive and non-invasive tension time indices, even in very weak infants. Data obtained corresponded to the clinical estimate of severity and predicted the need for respiratory support.

CONCLUSIONS

The testing employed was both safe and feasible. Measurements of MIP and RIP are easily performed tests that are well tolerated and provide clinically useful information for infants with SMA-I.

Normal values for inspiratory muscle function in children

Assessment of inspiratory muscle function (IMF) is limited in children with neuromuscular disorders, because respiratory muscle tests are poorly standardized and valid normative data are unavailable. We investigated maximum inspiratory pressure after exhalation to residual volume (MIP), mouth occlusion pressure (P0.1) and time of inspiration during quiet breathing and derived inspiratory muscle load (P0.1/MIP), and tension time index (TTI) in 301 healthy schoolchildren 6-16 years old. Gender-specific and age-dependent percentile curves for MIP were drawn with the median, 5%, 10%, 25%, 75% and 95% percentile. P0.1 was equal in boys and girls (0.23  ±  0.11 kPa), while MIP was significantly higher in boys (6.8  ±  2.2 versus 5.8  ±  2.4 kPa). Consequently, P0.1/MIP (4.8% ± 3.2% versus 4.0% ± 3.1%) and TTI (0.2  ±  0.14 versus 0.16  ±  0.14) were significantly higher in girls. MIP was 2.90 + 0.36 × age (kPa) and 3.19 + 0.24 × age (kPa) in boys and girls, respectively. The 95% confidence intervals for boys and girls, respectively, were MIP, 6.3-7.3 kPA and 5.4-6.2 kPa; P0.1/MIP, 3.5%-4.5% and 4.3%-5.3%; TTI, 0.14-0.18 and 0.18-0.22; and P0.1, 0.20-0.24 kPa for both. IMF in children has a wide interindividual variability; however percentile curves facilitate a longitudinal assessment of individual patients. Furthermore, narrow confidence intervals allow for comparisons of study populations, making IMF an appropriate endpoint for clinical trials.

Respiratory muscle decline in Duchenne muscular dystrophy

OBJECTIVES

Duchenne muscular dystrophy (DMD) causes progressive respiratory muscle weakness. The aim of the study was to analyze the trend of a large number of respiratory parameters to gain further information on the course of the disease.

STUDY DESIGN

Retrospective study.

SUBJECT SELECTION

48 boys with DMD, age range between 6 and 19 year old, who were followed in our multidisciplinary neuromuscular clinic between 2001 and 2011.

METHODOLOGY

Lung function, blood gases, respiratory mechanics, and muscle strength were measured during routine follow-up over a 10-year period. Only data from patients with at least two measurements were retained.

RESULTS

The data of 28 patients were considered for analysis. Four parameters showed an important decline with age. Gastric pressure during cough (Pgas cough) was below normal in all patients with a mean decline of 5.7 ± 3.8 cmH2 O/year. Sniff nasal inspiratory pressure (SNIP) tended to increase first followed by a rapid decline (mean decrease 4.8 ± 4.9 cmH2 O; 5.2 ± 4.4% predicted/year). Absolute forced vital capacity (FVC) values peaked around the age of 13-14 years and remained mainly over 1 L but predicted values showed a mean 4.1 ± 4.4% decline/year. Diaphragmatic tension-time index (TTdi) increased above normal values after the age of 14 years with a mean increase of 0.04 ± 0.04 point/year.

CONCLUSIONS

This study confirms the previous findings that FVC and SNIP are among the most important parameters to monitor the evolution of DMD. Expiratory muscle strength, assessed by Pgas cough, and the endurance index, TTdi, which are reported for the first time in a large cohort, appeared to be informative too, even though measured through an invasive method.

Respiratory muscle function in patients with cystic fibrosis

Respiratory muscle function in patients with cystic fibrosis (CF) can be assessed by measurement of maximal inspiratory pressure (Pimax ), maximal expiratory pressure (Pemax ), and pressure-time index of the respiratory muscles (PTImus ). We investigated the differences in maximal respiratory pressures and PTImus between CF patients with no gross hyperinflation and healthy controls and described the effects of pulmonary function and nutrition impairment on respiratory muscle function in this group of CF patients. Forced expiratory volume in 1 sec (FEV1 ), forced vital capacity (FVC) and maximal expiratory flow between 25% and 75% of VC (MEF25-75 ), body mass index (BMI), upper arm muscle area (UAMA), Pimax , Pemax , and PTImus were assessed in 140 CF patients and in a control group of 140 healthy subjects matched for age and gender. Median Pimax and Pemax were significantly lower in CF patients compared to the controls [Pimax  = 74 (57-94) in CF vs. 84 (66-102) in controls, P = 0.009], [Pemax  = 71 (50-95) in CF vs. 84 (66-102) in controls, P < 0.001]. Median PTImus in CF patients compared to controls was significantly increased [PTImus  = 0.110 (0.076-0.160) in CF vs. 0.094 (0.070-0.137) in controls, P = 0.049] and it was significantly higher in CF patients with impaired pulmonary function. In CF patients, PTImus was significantly negatively related to upper arm muscle area (r = 0.184, P = 0.031). These findings suggest that CF patients with no severe lung disease compared to healthy subjects exhibit impaired respiratory muscle function, while CF patients with impaired pulmonary function and nutrition indices exhibit higher PTImus values.

Pulmonary complications of neuromuscular disease: a respiratory mechanics perspective

Paediatric neuromuscular disease compromises both the gas exchange and pump functions of the respiratory system. This can have profound implications for both growth and development of the respiratory system, as well as morbidity and mortality. Aspiration lung disease is common, and leads to increasingly restrictive pulmonary physiology over time. Abnormal lung and chest wall mechanics, and weak respiratory muscles, can combine to cause respiratory failure. Improving the balance between the work of breathing (by decreasing the respiratory load) and the respiratory pump (by improving respiratory muscle strength and decreasing respiratory muscle fatigue) can help prevent the onset of respiratory failure. Airway clearance techniques and non-invasive ventilation are two important tools in this effort. Better ways of assessing the respiratory pump, mechanical function, control and fatigue are needed especially in children.

Sleep, sleep disordered breathing, and nocturnal hypoventilation in children with neuromuscular diseases

Sleep disordered breathing (SDB) is now well recognized in children with neuromuscular diseases (NMD) and may lead to significant morbidity and increased mortality. Predisposing factors to SDB in children with NMD include reduced ventilatory responses, reduced activity of respiratory muscles during sleep and poor lung mechanics due to the underlying neuro-muscular disorder. SDB may present long before signs of respiratory failure emerge. When untreated, SDB may contribute to significant cardiovascular morbidities, neuro-cognitive deficits and premature death. One of the problems in detecting SDB in patients with NMD is the lack of correlation between lung function testing and daytime gas exchange. Polysomnography is the preferred method to evaluate for SDB in children with NMD. When the diagnosis of SDB is confirmed, treatment by non-invasive ventilation (NIV) is usually recommended. However, other modalities of mechanical ventilation do exist and may be indicated in combination with or without other supportive measures.

Tension-time index as a predictor of extubation outcome in ventilated children

RATIONALE

Indices that assess the load on the respiratory muscles, such as the tension-time index (TTI), may predict extubation outcome.

OBJECTIVES

To evaluate the performance of a noninvasive assessment of TTI, the respiratory muscle tension time index (TTmus), by comparison to that of the diaphragm tension time index (TTdi) and other predictors of extubation outcome in ventilated children.

METHODS

Eighty children (median [range] age 2.1 yr [0.15-16]) admitted to pediatric intensive care units at King's College and St Mary's Hospitals who required mechanical ventilation for more than 24 hours were studied.

MEASUREMENTS AND MAIN RESULTS

TTmus, maximal inspiratory pressure, respiratory drive, respiratory system mechanics, and functional residual capacity using a helium dilution technique, the rapid shallow breathing and CROP indices (compliance, rate, oxygenation, and pressure) indexed for body weight were measured and standard clinical data recorded in all patients. TTdi was measured in 28 of the 80 children using balloon catheters. Eight children (three in the TTdi group) failed extubation. TTmus (0.199 vs. 0.09) and TTdi (0.157 vs. 0.07) were significantly higher in children who failed extubation. TTmus greater than 0.18 (n = 80) and TTdi greater than 0.15 (n = 28) had sensitivities and specificities of 100% in predicting extubation failure. The other predictors performed less well.

CONCLUSIONS

Invasive and noninvasive measurements of TTI may provide accurate prediction of extubation outcome in mechanically ventilated children.

The pathophysiology of respiratory impairment in pediatric neuromuscular diseases

This is a summary of the presentation on the pathophysiology of respiratory impairment in pediatric neuromuscular disorders presented as part of the program on pulmonary management of pediatric patients with neuromuscular disease at the 30th annual Carrell-Krusen Neuromuscular Symposium on February 20, 2008.

Noninvasive determination of the tension-time index in Duchenne muscular dystrophy

OBJECTIVE

Noninvasive determination of the tension-time index of the inspiratory muscles (TT MUS) can identify predisposition to respiratory muscle fatigue in neuromuscular disease. We correlated TT MUS with age and extent of need of ventilator use for patients with Duchenne muscular dystrophy.

DESIGN

Maximal inspiratory pressure, inspiratory pressure 0.1 sec after the onset of inspiration (P 0.1), and the breathing pattern during spontaneous breathing were measured in 46 subjects with Duchenne muscular dystrophy and in 46 healthy males of the same age. TT MUS (TT MUS = T I/T TOT x P I/MIP) was determined by calculating P I from P 0.1 (P I = 5 x P 0.1 x T I). The data were compared with normal values and related to age and ventilator use.

RESULTS

TT MUS was significantly higher in the entire Duchenne muscular dystrophy group than in controls (0.21 +/- 0.11 vs. 0.06 +/- 0.02, P < 0.001) and increased with age in the patients (P < 0.001). TT MUS was significantly higher in subjects ventilated 8-20 hrs per day than in nocturnal-only users and in patients ventilated >20 hrs per day than in those ventilated 8-20 hrs per day (P < 0.001). TT MUS surpassed 0.23 in 95% of subjects ventilated 8-20 hrs. TT MUS exceeded 0.37 in 95% of individuals ventilated >20 hrs per day, whereas it was less than this value in 95% of patients ventilated 8-20 hrs.

CONCLUSIONS

TT MUS increases significantly with disease progression and is a sensitive indicator of risk of inspiratory muscle fatigue and ventilator use. Longitudinal determination of TT MUS in patients with Duchenne muscular dystrophy may help to justify the extent of need for mechanical ventilation.

Non-invasive tension time index in relation to severity of disease in children with cystic fibrosis

The non-invasive tension-time index of the inspiratory muscles at rest (TTMUS) can be used for assessing respiratory muscle function in children with cystic fibrosis (CF). This study aimed to investigate how TTMUS becomes altered with increasing pulmonary impairment, and which factors determine TTMUS changes in CF. We assessed TTMUS in 47 patients with stable CF ranging in age from 9 to 26 years and in 47 controls of same age and gender. Pulmonary impairment was assessed by the pulmonary function score (PFS) according to Cropp (PFS 0-2 = no, 3-7 = mild, 8-12 = moderate, and 13-18 = severe dysfunction). Median TTMUS was significantly higher in the entire CF-group than in controls ((0.112 (0.079-0.174) vs. 0.07 (0.052-0.094), P < 0.001)). It was nearly identical in CF-patients without (0.079 (0.056-0.114)) and mild (0.080 (0.059-0.128)) pulmonary dysfunction. It was non-significantly higher in subjects with moderate (0.118 (0.103-0.173)) and grossly elevated in individuals with severe (0.232 (0.211-0.31), P < 0.001)) respiratory impairment when compared to the other PFS-groups. TTMUS was significantly related to percent predicted airway resistance (Raw%pred) (r = 0.60, P < 0.001), percent predicted Forced Expiratory Volume in 1 sec (r = -0.49, P < 0.001), percent predicted Vital Capacity (-0.57, P < 0.001), Functional Residual Capacity in percent Total Lung Capacity (r = 0.42, P = 0.003), and transcutaneous oxygen saturation (r = -0.49, P < 0.001). By contrast, Raw%pred was the only variable that had a significant effect on TTMUS (P = 0.01), when a multivariate logistic regression was applied, using the median of the entire CF-cohort to dichotomise TTMUS. These findings suggest that subjects with stable CF and severe pulmonary dysfunction are prone to respiratory muscle fatigue, and that airway obstruction is an important factor contributing to the increase of TTMUS in CF. Regular determination of TTMUS may be clinically useful during course of disease, and may aid the decision to institute therapies like respiratory muscle training or non-invasive intermittent ventilation.