Myosin heavy chain composition of the human sternocleidomastoid muscle

Inspiratory effort and respiratory muscle activation during different breathing conditions in patients with weaning difficulties: An exploratory study

BACKGROUND

Recent studies suggest that fast and deep inspirations against either low or high external loads may provide patients with weaning difficulties with a training stimulus during inspiratory muscle training (IMT). However, the relationship between external IMT load, reflected by changes in airway pressure swings (ΔPaw), and total inspiratory effort, measured by oesophageal pressure swings (ΔPes), remains unexplored. Additionally, the association between ΔPes, ΔPaw, and inspiratory muscle activations remains unclear.

OBJECTIVES

The ai of this study was to compare ΔPes and ΔPaw and their relationship with inspiratory muscle activation in patients with weaning difficulties during different breathing conditions.

METHODS

ΔPes and scalene, sternocleidomastoid, and parasternal intercostal muscles activation were recorded during the following conditions: 1) (proportional) pressure support ventilation; 2) unsupported spontaneous breathing; 3) low-load IMT (load: <10% maximal inspiratory pressure, PImax = 3 cmH2O) executed with slow and deep inspirations (low-load slow) and 4) low-load IMT (load: <10% maximal inspiratory pressure, PImax = 3 cmH2O) executed with fast deep inspirations (low-load fast); and 5) high-load IMT (load ∼ 30% PImax) executed with fast and deep inspirations. ΔPaw, end-inspiratory lung volume, and peak inspiratory flow were recorded during conditions 2-5. Variables were compared across conditions using mixed-model analysis. Spearman's rank correlations were calculated between inspiratory muscle activations and both ΔPes and ΔPaw.

RESULTS

Five patients (age: 68 ± 1 y; 20% male; PImax: 37 ± 7 cmH2O [59 ± 23% predicted]; forced vital capacity: 0.66 ± 0.16 L [21 ± 6% predicted]) were included in the study. ΔPes values were 3-4 times larger than ΔPaw values during unsupported spontaneous breathing and IMT conditions. ΔPes, sternocleidomastoid activation, end-inspiratory lung volume, and peak inspiratory flow were larger during low-load fast IMT than during low-load slow IMT and unsupported spontaneous breathing but were similar between low-load fast and high-load IMTs. Inspiratory muscle activations correlated weakly to moderately with ΔPaw and moderately with ΔPes.

CONCLUSIONS

In five patients with weaning difficulties, low-load fast IMT provided a training stimulus similar to high-load IMT. Both yielded significantly higher training stimulus than low-load slow IMT and unsupported spontaneous breathing. These results should be considered in future trials comparing IMT with sham conditions.

CLINICAL TRIAL REGISTRATION NUMBERS

NCT03240263 and NCT04658498.

The mastoid triangle (Ma-Ast-Po) as a sexually dimorphic feature - a systematic review of 1604 human skulls and meta-analysis

The mastoid triangle is the area between the craniometric landmarks Mastoidale (Ma), Asterion (Ast) and Porion (Po), which has been studied in the field of physical anthropology as an alleged tool for sexual dimorphism. The evidence in the current scientific literature, however, is disputable. This systematic review aimed to find out how safe is the mastoid triangle for sexual dimorphism. A research protocol submitted to PROSPERO (CRD42023488216) was designed based on PRISMA-P. Pubmed, SciELO, LiLACS, LIVIVO, Open Gray and Open Access Theses and Dissertations were searched with structured strategies. The Joanna Briggs Institute manual was followed and the critical appraisal checklist for cross-sectional studies was used. The search found 14 eligible studies out of 2148 initially screened. The combined sample consisted of 1604 human skulls. Eight studies (57,14%) clearly encouraged the use of the mastoid triangle for sexual dimorphism, while three (21,42%) advised against it. All the studies had a low risk of bias (75-100%). The standardized mean difference between male and females was between 1.00 and 1.42 without statistically significant differences between geographic regions (p > 0.05). Expressive heterogeneity and large confidence intervals were detected, showing great variability across studies. A country-specific subgroup meta-analysis revealed lack of statistically significant differences based on geographic regions. This systematic review showed low level of evidence to support the use of the mastoid triangle as a tool for sexual dimorphism.

Excitation of the bottom-up pathways has no effect on remote muscle fatigue in healthy participants

The aim of this study is to investigate the effect of induced excitation of the bottom-up pathways at the lateral elbow muscles on local muscle fatigue in the neck region in healthy participants. Eligible participants (n:55) were randomly allocated to an intervention group (n:28) or a control group (n:27). The fatigue of bilateral neck flexor(sternocleidomastoid) and extensor (upper trapezius) muscles was evaluated using surface electromyography, at baseline and immediately post-intervention during a neck flexor and extensor endurance test respectively. Excitation of the bottom-up pathways was performed at multiple lateral elbow muscles in the intervention group by using a temporal summation protocol of mechanical pain, and the pressure pain threshold was determined once in each of the multiple lateral elbow muscles in the control group. Linear mixed model analyses were performed for each outcome measure to evaluate changes over time and within- and between-group differences. No significant "group X time" interaction effects were detected for any of the outcome measures. Significant main effects for time was found for "amplitude over time" of the left upper trapezius (p:0.003) and right sternocleidomastoid muscle (p: 0.013), and for "amplitude changes" of the left upper trapezius muscle (p:0.021). Significant within-group changes were identified in some outcomes in the control group: increased "amplitude over time" of the right sternocleidomastoid muscle (p:0.024) and decreased "amplitude changes" of the left upper trapezius muscle (p:0.024), decreased "normalized median frequency slope over time" of the left UT (p: 0.013). There were no significant within-group changes in the intervention group. No significant between-group differences for any of the outcome measures were found. This study shows no effect of the induction of excitation of the bottom-up pathways at the lateral elbow muscles on the neck muscles' fatigue characteristics compared to a control intervention. Clinical Trial Number: NCT05146960. Date of Registration: December 7, 2021.

Inter-rater reliability and test-retest reliability of the foot posture index (FPI-6) for assessing static foot posture in elderly female patients with knee osteoarthritis and its association with quadriceps muscle tone and stiffness

Objective

1. To assess the Inter-rater reliability and test-retest reliability of FPI-6 total score and individual scores in static foot posture evaluation among elderly female patients with knee osteoarthritis (KOA), aiming to establish the reliability of the FPI-6 scale. 2. To investigate the disparity between dominant and non-dominant quadriceps characteristics in elderly female KOA patients, as well as explore the correlation between quadriceps characteristics and abnormal foot posture, thereby offering novel insights for the prevention and treatment of KOA.

Methods

The study enrolled a total of 80 lower legs of 40 participants (all female) with unilateral or bilateral KOA, who were assessed by two raters at three different time points. The inter-rater and test-retest reliability of the FPI-6 was evaluated using the intra-class correlation coefficient (ICC), while the absolute reliability of FPI-6 was examined using the standard error of measurement (SEM), minimum detectable change (MDC), and Bland-Altman analysis. The internal consistency of FPI-6 was assessed using Spearman's correlation coefficient. Additionally, MyotonPRO was employed to assess quadriceps muscle tone and stiffness in all participants, and the association between quadriceps muscle tone/stiffness and the total score of FPI-6 was analyzed.

Result

Our study found excellent inter-rater and test-retest reliability (ICC values of 0.923 and 0.931, respectively) for the FPI-6 total score, as well as good to excellent reliability (ICC values ranging from 0.680 to 0.863 and 0.739-0.883) for individual items. The SEM and MDC values for the total score of FPI-6 among our study inter-rater were 0.78 and 2.15, respectively. and the SEM and MDC values for the test-retest total score of FPI-6 were found to be 0.76 and 2.11, respectively. Furthermore, the SEM and MDC values between inter-rater and test-retest across six individual items ranged from 0.30 to 0.56 and from 0.84 to 1.56. The Bland-Altman plots and respective 95% LOA showed no evidence of systematic bias. In terms of the mechanical properties of the quadriceps on both sides, the muscle tone and stiffness of rectus femoris (RF), vastus medialis (VM), and vastus lateralis (VL) were significantly higher in the non-dominant leg compared to the dominant leg. Additionally, in the non-dominant leg, there was a significant positive correlation between the muscle tone and stiffness of VM, VL, RF and the total score of FPI-6. However, in the dominant leg, only VM's muscle tone and stiffness showed a significant positive correlation with the total score of FPI-6.

Conclusion

The reliability of the FPI-6 total score and its six individual items was good to excellent. Our findings offer a straightforward and dependable approach for researchers to assess foot posture in elderly female patients with KOA. Furthermore, we observed significantly greater quadriceps tension and stiffness in the non-dominant leg compared to the dominant leg. The FPI-6 total score exhibited a significant correlation with changes in quadriceps muscle performance among KOA patients. These observations regarding the relationship between changes in quadriceps muscle performance and foot posture in elderly female KOA patients may provide novel insights for disease prevention, treatment, and rehabilitation.

Sternocleidomastoid Muscle Transfer for Treatment of Longstanding Facial Paralysis: Long-term Outcomes and Complications

BACKGROUND/AIM

The use of sternocleidomastoid muscle (SCM) flap for facial reanimation was established in the 1980s by the senior author of this paper. We aimed to analyze long-term outcome and complications of this procedure.

PATIENTS AND METHODS

We conducted a retrospective chart review of all patients undergoing SCM reanimation for longstanding facial palsy between January 2009 and December 2015. Patients with follow-up longer than 12 months (range=12-96) were included in the study. Facial muscle function was evaluated before and at each follow-up after the surgery with the House-Brackmann (HB) scale-facial nerve grading system and Facegram analysis. Donor site morbidity and overall complication rates were documented and analyzed.

RESULTS

Forty-two patients aged 18-66 years (mean age=37) with a mean duration of facial palsy of 5 years (range=2-48) met the inclusion criteria. The HB score 2 years after surgery improved significantly (p<0.05) in comparison to the pre-operative condition (3.6 vs. 4.7). Twelve months after surgery, oral commissure excursion improved by mean 8.95 mm. No flap necrosis occurred, nor compromise of neck and shoulder function despite an obvious contour defect in the SCM donor site. None of the patients presented head posture or movement issues.

CONCLUSION

The SCM flap transfer is a reliable and effective procedure to achieve moderate improvement of the oral commissure excursion using a local method with moderate donor site morbidity. It can be regarded as a valuable option for dynamic facial reanimation in case of longstanding facial palsy.

Effects of Age and Sex on Properties of Lumbar Erector Spinae in Healthy People: Preliminary Results From a Pilot Study

Background: The influences of age and sex on properties of lumbar erector spinae have not been previously studied. Changes in the performance of lumbar erector spinae properties associated with age represent a valuable indicator of risk for lower-back-related disease.

Objective: To investigate the lumbar erector spinae properties with regard to age and sex to provide a reference dataset.

Methods: We measured muscle tone and stiffness of the lumbar erector spinae (at the L3–4 level) in healthy men and women (50 young people, aged 20–30 years; 50 middle-aged people, aged 40–50 years; and 50 elderly people, aged 65–75 years) using a MyotonPRO device.

Results: In general, there are significant differences in muscle tone and stiffness among young, middle-aged, and elderly participants, and there were significant differences in muscle tone and stiffness between men and women, and there was no interaction between age and sex. The muscle tone and stiffness of the elderly participants were significantly higher than those of the middle-aged and young participants (P < 0.01), and the muscle tone and stiffness of the middle-aged participants were significantly higher than those of the young participants (P < 0.01). In addition, the muscle tone and stiffness of men participants were significantly higher than that of women participants (P < 0.01).

Conclusion: Our results indicate that muscle tone and stiffness of the lumbar erector spinae increase with age. The muscle tone and stiffness of the lumbar erector spinae in men are significantly higher than in women. The present study highlights the importance of considering age and sex differences when assessing muscle characteristics of healthy people or patients.

3D analysis of capillary network in skeletal muscle of obese insulin-resistant mice

In obesity, the skeletal muscle capillary network regresses and the insulin-mediated capillary recruitment is impaired. However, it has been shown that in the early stage of advanced obesity, an increased functional vascular response can partially compensate for other mechanisms of insulin resistance. The present study aimed to investigate the changes in the capillary network around individual muscle fibres during the early stage of obesity and insulin resistance in mice using 3D analysis. Capillaries and muscle fibres of the gluteus maximus muscles of seven high-fat-diet-induced obese and insulin-resistant mice and seven age-matched lean healthy mice were immunofluorescently labelled in thick transverse muscle sections. Stacks of images were acquired using confocal microscope. Capillary network characteristics were estimated by methods of quantitative image analysis. Muscle fibre typing was performed by histochemical analysis of myosin heavy chain isoforms on thin serial sections of skeletal muscle. Capillary length per muscle fibre length and capillary length per muscle fibre surface were increased by 27% and 23%, respectively, around small muscle fibres in obese mice, while there were no significant comparative differences around large fibres of obese and lean mice. Furthermore, the capillarization was larger around small compared to large fibres and there was a shift toward fast type myosin heavy chain isoforms, with no significant changes in muscle fibre diameters, tortuosity and anisotropy in obese mice. Overall, the results show that obese insulin-resistant mice have selective increase in capillarization around small predominantly intermediate muscle fibres, which is most likely related to the impaired glucose metabolism characteristic of type 2 diabetes.

Relationship between age, BMI, head posture and superficial neck muscle stiffness and elasticity in adult women

This study determined relationships between age, BMI and cranio-vertebral angle (CVA) (independent variables) and stiffness and elasticity of sternocleidomasteoid [SCM] and upper trapezius [UT] (dependent variables) muscles in sitting posture in 95 women across adult life. Moreover, a stepwise regression was performed to determine to what extent the dependent variables are explained by age, BMI and CVA. Age was moderately correlated with BMI (r = 0.41), and both age and BMI were moderately negatively correlated with CVA (r = −0.54 and −0.55, respectively). High (r = 0.73) and moderate (r = 0.53) linear relationships were present between age and logarithmic decrement (inversely related to elasticity) and stiffness of SCM muscle, respectively. Low (r = 0.36) and moderate (r = 0.47) relationships were present between age and logarithmic decrement and stiffness of UT muscle, respectively. Age accounted for 53% variance in elasticity and 28.5% variance in stiffness of SCM, and for 13% variance in elasticity and 22% variance in stiffness of UT muscle. Introduction of BMI but not CVA to the model explained the variance of these parameters by additional 0–8%. Among the studied factors age is the major correlate of stiffness and elasticity of neck muscles across the adult life.

Deoxygenation of inspiratory muscles during cycling, hyperpnoea and loaded breathing in health and disease: a systematic review

Assessing inspiratory muscle deoxygenation and blood flow can provide insight into anaerobic stress, recruitment strategies and mechanisms of inspiratory muscle limitation. Therefore, this review aimed to synthesize measurements of inspiratory muscle oxyhaemoglobin (O₂ Hb), deoxyhaemoglobin (HHb), blood volume and flow of the inspiratory muscles acquired via near-infrared spectroscopy (NIRS) during cycling, hyperpnoea and loaded breathing in healthy non-athletes, healthy athletes and patients with chronic obstructive pulmonary disease (COPD) or chronic heart failure (CHF). Searches were performed on Medline and Medline in-process, EMBASE, Central, Sportdiscus, PubMed and Compendex. Reviewers independently abstracted articles and assessed their quality using the modified Downs and Black checklist. Of the 644 articles identified, 21 met the inclusion criteria. Studies evaluated non-athletes (n = 9), athletes (n = 5), COPD (n = 2) and CHF (n = 5). The sample was 90% male and 73% were non-athletes and athletes. Interventions included cycle ergometry, hyperpnoea, loaded breathing, elbow flexor loading and combined loaded breathing and ergometry. Athletes and patients with CHF or COPD demonstrated deoxygenation of inspiratory accessory muscles that was often an opposite or exaggerated pattern compared to non-athletes. O₂ Hb decreased and HHb increased significantly in inspiratory muscles during cycle ergometry and loaded breathing with accentuated changes during combined ergometry and loaded breathing. During different regimens of hyperpnoea or loaded breathing, comparisons of inspiratory muscles demonstrated that the sternocleidomastoid deoxygenated more than the intercostals, parasternals or scalenes. Evaluating inspiratory muscle deoxygenation via NIRS can inform mechanisms of inspiratory muscle limitation in non-athletes, athletes and patients with CHF or COPD.

Neck inspiratory muscle activation patterns during well-controlled inspiration

PURPOSE

Surprisingly, the activation characteristics of the neck inspiratory muscles as a function of key inspiratory mechanical parameters have yet to be demonstrated experimentally under well-controlled conditions. This study aimed to elucidate the muscle activation patterns of the neck inspiratory muscles by strictly controlling flow rate and lung volume.

METHODS

Thirteen healthy subjects matched their inspiratory flow rate at approximately 20-100% of peak flow rate (PFR) as steady as possible during inspiration. Amplitude of surface electromyogram (EMG) of the sternocleidomastoid (SCM) and scalene were calculated for every increase in %PFR over a duration corresponding to an increase in lung volume by 10% of forced vital capacity (FVC), as well as for every 5% increment of FVC over a point corresponding to an increase in flow rate by 20%PFR to determine the %PFR-EMG and %FVC-EMG relations, respectively.

RESULTS

Regression analyses showed that EMGs of the neck inspiratory muscles exponentially increased with increase in %PFR and their associated variables which reflect recruitment onset when increasing flow rate increased with increasing %FVC. In %FVC-EMG relation, a linear regression analysis showed positive slope at all %PFR and positive y-intercept at 80% PFR.

CONCLUSIONS

The main new finding is that the neck inspiratory muscle activities increase with flow rate as well as lung volume. The positive y-intercept of the %FVC-EMG relation at higher %PFR indicates that the neck inspiratory muscles are always activated even when lung volume level is low, implying that SCM is not necessarily an "accessory" muscle as described in previous observations.

Assessment of mechanically ventilated patients intoxicated with organophosphates by a novel surface electromyographic index

PURPOSE

We present a new electromyographic index, named Engagement of Respiratory Muscle (ERM), for assessing the level of participation of respiratory muscles during spontaneous breathing test in patients poisoned with organophosphorus compound.

METHODS

Diaphragm and sternocleidomastoid muscles activity was recorded by surface electromyography during spontaneous breathing test. A population of 23 patients poisoned with organophosphates and mechanically ventilated, and a control group of 28 healthy subjects were analyzed.

RESULTS

All patients developed respiratory failure and 48% were diagnosed with intermediate syndrome by medical staff. The ERM index classified the patients in three clusters (p-value<0.005): Cluster I presented more engagement of the sternocleidomastoid compared to diaphragm, Cluster II had low muscle engagement of both muscles and also muscle weakness, Cluster III were characterized for the diaphragm recovery associated with higher engagement. The control group showed a similar muscle engagement to Cluster III. The capacity of ERM index for classifying patients with (sensitivity) and without (specificity) muscle weakness were 90.91% and 100% respectively.

CONCLUSIONS

The ERM is a promising index to assess the level of participation of respiratory muscle on spontaneous breathing test in patients poisoned with organophosphorus compounds, which could improve the extubation prognosis for these patients.

Composition of Muscle Fiber Types in Rat Rotator Cuff Muscles

The rat is a suitable model to study human rotator cuff pathology owing to the similarities in morphological anatomy structure. However, few studies have reported the composition muscle fiber types of rotator cuff muscles in the rat. In this study, the myosin heavy chain (MyHC) isoforms were stained by immunofluorescence to show the muscle fiber types composition and distribution in rotator cuff muscles of the rat. It was found that rotator cuff muscles in the rat were of mixed fiber type composition. The majority of rotator cuff fibers labeled positively for MyHCII. Moreover, the rat rotator cuff muscles contained hybrid fibers. So, compared with human rotator cuff muscles composed partly of slow-twitch fibers, the majority of fast-twitch fibers in rat rotator cuff muscles should be considered when the rat model study focus on the pathological process of rotator cuff muscles after injury. Gaining greater insight into muscle fiber types in rotator cuff muscles of the rat may contribute to elucidate the mechanism of pathological change in rotator cuff muscles-related diseases. Anat Rec, 299:1397-1401, 2016. © 2016 Wiley Periodicals, Inc.

Effect of acute hypoxia on inspiratory muscle oxygenation during incremental inspiratory loading in healthy adults

PURPOSE

To non-invasively examine the effect of acute hypoxia and inspiratory threshold loading (ITL) on inspiratory muscles [sternocleidomastoid (SCM), scalene (SA) and parasternal (PS)] oxygenation in healthy adults using near-infrared spectroscopy (NIRS).

METHODS

Twenty healthy adults (12 M/8 F) were randomly assigned to perform two ITL tests while breathing a normoxic or hypoxic (FIO2 = 15 %) gas mixture. NIRS devices were placed over the SCM, PS, SA, and a control muscle, tibialis anterior (TA), to monitor oxygenated (O2Hb), deoxygenated (HHb), total hemoglobin (tHb) and tissue saturation index (TSI). With the nose occluded, subjects breathed normally for 4 min through a mouthpiece that was connected to a weighted threshold loading device. ITL began by adding a 100-g weight to the ITL device. Then, every 2 min 50-g was added until task failure. Vital signs, ECG and ventilatory measures were monitored throughout the protocol.

RESULT

Participants were 31 ± 12 year and had normal spirometry. At task failure, the maximum load and ventilatory parameters did not differ between the hypoxic and normoxic ITL. At hypoxic ITL task failure, SpO2 was significantly lower, and ∆HHb increased more so in SA, SCM and PS than normoxic values. SCM ∆TSI decreased more so during hypoxic compared to normoxic ITL. ∆tHb in the inspiratory muscles (SCM, PS and SA) increased significantly compared to the decrease in TA during both hypoxic and normoxic ITL.

CONCLUSION

The SCM, an accessory inspiratory muscle was the most vulnerable to deoxygenation during incremental loading and this response was accentuated by acute hypoxia.

Unexpected dependence of RyR1 splice variant expression in human lower limb muscles on fiber-type composition

The skeletal muscle ryanodine receptor Ca(2+) release channel (RyR1), essential for excitation-contraction (EC) coupling, demonstrates a known developmentally regulated alternative splicing in the ASI region. We now find unexpectedly that the expression of the splice variants is closely related to fiber type in adult human lower limb muscles. We examined the distribution of myosin heavy chain isoforms and ASI splice variants in gluteus minimus, gluteus medius and vastus medialis from patients aged 45 to 85 years. There was a strong positive correlation between ASI(+)RyR1 and the percentage of type 2 fibers in the muscles (r = 0.725), and a correspondingly strong negative correlation between the percentages of ASI(+)RyR1 and percentage of type 1 fibers. When the type 2 fiber data were separated into type 2X and type 2A, the correlation with ASI(+)RyR1 was stronger in type 2X fibers (r = 0.781) than in type 2A fibers (r = 0.461). There was no significant correlation between age and either fiber-type composition or ASI(+)RyR1/ASI(-)RyR1 ratio. The results suggest that the reduced expression of ASI(-)RyR1 during development may reflect a reduction in type 1 fibers during development. Preferential expression of ASI(-) RyR1, having a higher gain of in Ca(2+) release during EC coupling than ASI(+)RyR1, may compensate for the reduced terminal cisternae volume, fewer junctional contacts and reduced charge movement in type 1 fibers.

Sternocleidomastoid muscle additionally innervated by the facial nerve: case report and review of the literature

An aberrant nerve branch from the facial nerve, additionally to the accessory nerve and cervical rami C2 and C3, was observed innervating the sternocleidomastoid (SCM) muscle in a 75-year-old male cadaver. We consider that the anomaly occurred as the result of a fusion of the muscular compartment from the digastric and SCM muscles during development. The aberrant innervation may be the source of the misinterpretation of electromyographic findings.