The value of respiratory muscle testing in children with neuromuscular disease

A comparison of peak cough flow and peak expiratory flow in children with neuromuscular disorders

Spirometry and peak cough flow testing (PCF) are commonly used in the respiratory assessment of children with a neuromuscular disorder (NMD). Testing uses two different machines, increases laboratory time, costs and resource utilisation. No studies have assessed the correlation between peak expiratory flow (PEF) obtained from spirometry and PCF in children with NMD using one device. An audit of children with a NMD managed at the Children's Hospital at Westmead in 2022-2024 aged < 20 years who performed spirometry and PCF testing on the same device (Vyaire Body BoxTM, Ultrasonic flow meter-based, or Vyaire PneumotachographTM, Pneumotach flow meter-based; Germany) was conducted to assess the correlation between PCF and PEF. Fifty-one sets of testing were identified, and 40 subjects (9F) had reproducible testing and were included. Median (range) age was 14.95 (7.20-19.00) years. Median PEF (L/min) was 4.05 (1.22-10.26) and median PCF (L/min) was 4.29 (1.69-10.82). PEF and PCF had a strong Pearson's correlation coefficient, (R = 0.97, p = 0.03). The coefficient of determination was 0.93. If laboratory resources permit, spirometry should be the test of choice for children with NMD. On average, spirometry required multiple practices to achieve reproducibility to meet ATS/ERS standards. PCF testing can be utilised for children where performing technically acceptable spirometry is not possible.

Can postural changes in spirometry in children with Duchenne muscular dystrophy predict sleep hypoventilation?

AIM

To explore the relationship between postural changes in lung function and polysomnography (PSG) in children with Duchenne muscular dystrophy (DMD).

METHODS

In this prospective cross-sectional study, children with DMD performed spirometry in sitting and supine positions. A control group of age and gender matched healthy children also underwent postural lung function testing. PSG was performed within six months of spirometry.

RESULTS

Seventeen children with DMD, aged 12.3 ± 3 years performed sitting spirometry. 14 (84%) performed acceptable spirometry in the supine position. Mean FEV1sit and FVCsit were 77% (SD ± 22) and 74% (SD ± 20.4) respectively, with mean% ΔFVC(sit-sup) 9% (SD ± 11) (range 2% to 20%), and was significantly greater than healthy controls 4% (n = 30, SD ± 3, P < 0.001). PSG data on the 14 DMD children with acceptable supine spirometry showed total AHI 6.9 ± 5.9/hour (0.3 to 29), obstructive AHI 5.2 ± 4.0/hour (0.2 to 10), and REM AHI 14.1 ± -5.3/hour (0.1 to 34.7). ΔFVC(sit-sup) had poor correlation with hypoventilation on polysomnography.

CONCLUSION

Children with DMD and mild restrictive lung disease showed greater postural changes in spirometry than healthy controls but lower supine spirometry was not predictive of sleep hypoventilation.

Non-Invasive Respiratory Assessment in Duchenne Muscular Dystrophy: From Clinical Research to Outcome Measures

Ventilatory failure, due to the progressive wasting of respiratory muscles, is the main cause of death in patients with Duchenne muscular dystrophy (DMD). Reliable measures of lung function and respiratory muscle action are important to monitor disease progression, to identify early signs of ventilatory insufficiency and to plan individual respiratory management. Moreover, the current development of novel gene-modifying and pharmacological therapies highlighted the urgent need of respiratory outcomes to quantify the effects of these therapies. Pulmonary function tests represent the standard of care for lung function evaluation in DMD, but provide a global evaluation of respiratory involvement, which results from the interaction between different respiratory muscles. Currently, research studies have focused on finding novel outcome measures able to describe the behavior of individual respiratory muscles. This review overviews the measures currently identified in clinical research to follow the progressive respiratory decline in patients with DMD, from a global assessment to an individual structure–function muscle characterization. We aim to discuss their strengths and limitations, in relation to their current development and suitability as outcome measures for use in a clinical setting and as in upcoming drug trials in DMD.

Sleep disordered breathing: Assessment and therapy in the age of emerging neuromuscular therapies

The term neuromuscular disease (NMD) encompasses a large variety of disorders that result in abnormal muscle function. Although it may be conventional to relate the use of this term to the most common muscular diseases (Duchenne muscular dystrophy [DMD], spinal muscular atrophy [SMA], and amyotrophic lateral sclerosis, etc), it is important to extend the term to pathologies manifested by severe neurologic (brain and spinal cord) malformations and injuries. In many of these scenarios, there are common mechanisms that contribute to sleep disordered breathing (SDB) and respiratory insufficiency although comorbidities may be somewhat different. Advances in the understanding of these diseases and their natural history, and increasing availability of mechanical ventilation to these patients have improved survival. The development of novel genetic and molecular therapies (as in the cases of DMD, SMA, and X-linked myotubular myopathy) provides an opportunity to use SDB as a reasonable outcome measure while also allowing the use of polysomnography as a validation tool in the assessments of effectiveness of therapies. We seek to provide an understanding of SDB in NMDs, and in the same light, would like to begin the conversation of thinking about weaning respiratory support when possible.

Respiratory management of children with spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) causes a predominantly bilateral proximal muscle weakness and atrophy. The respiratory muscles are also involved with a weakness of the intercostal muscles and a relatively spared diaphragm. This respiratory muscle weakness translates into a cough impairment, resulting in poor clearance of airway secretions and recurrent pulmonary infections, restrictive lung disease due to a poor or insufficient chest wall and lung growth, nocturnal hypoventilation and, finally, respiratory failure. Systematic and regular monitoring of respiratory muscle performance is necessary in children with SMA in order to anticipate respiratory complications, such as acute and chronic respiratory failure, and guide clinical care. This monitoring is based in clinical practice on volitional and noninvasive tests, such as vital capacity, sniff nasal inspiratory pressure, maximal static pressures, peak expiratory flow and peak cough flow because of their simplicity, availability and ease. In young children, those with poor cooperation or severe respiratory muscle weakness, other, mostly invasive, tests may be required to evaluate respiratory muscle performance. A sleep study, or at least overnight monitoring of nocturnal gas exchange is mandatory for detecting nocturnal alveolar hypoventilation. Training for patients and caregivers in cough-assisted techniques is recommended when respiratory muscle strength falls below 50% of predicted or in case of recurrent or severe respiratory infections. Noninvasive ventilation (NIV) should be initiated in case of isolated nocturnal hypoventilation and followed by a pediatric respiratory team with expertise in NIV. Multidisciplinary (neurology and respiratory) pediatric management is crucial for optimal care of children with SMA. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

Impact of Aquatic Exercise on Respiratory Outcomes and Functional Activities in Children with Neuromuscular Disorders: Findings from an Open-Label and Prospective Preliminary Pilot Study

Neuromuscular disorders (NMD) lead to the progressive loss of motor and respiratory functions and a decline in daily activities and participation. We aimed to evaluate respiratory changes and functional outcomes in children attending an aquatic therapy program. Eleven patients diagnosed with NMD (4-18 years, Vignos scale 1-9) were involved in a 10-week aquatic exercise program. The ventilation variables were: peak cough flow, volumes (forced expiratory volume in one second-FEV₁ and inspiratory volume) and respiratory pressures to evaluate strength and oxygen saturation (O₂ sat). Functional skills were measured in the aquatic environment (Water Orientation Test Alyn 1) and on dry land, (Pediatric Evaluation of Disability Inventory), together with quality of life (Pediatric Quality of Life Inventory). Our evaluation included several 2 × 6 mixed-model repeated measures analysis of covariance (ANCOVA) with time (baseline, post 1 session, pre-post at five weeks and pre-post at 10 weeks). Important improvements in functional skills were observed in and out of the water and children under the age of 11 displayed a significant difference for inspirational volume (p = 0.002) and O₂ sat (p = 0.029). Clinical, statistically insignificant changes were found for peak cough flow and expiratory pressures values after aquatic exercise. These results may support a relationship between aquatic exercise in NMD, respiratory outcomes and functional activities in water and on land.

Investigating the clinical use of structured light plethysmography to assess lung function in children with neuromuscular disorders

BACKGROUND

Children and young people with neuromuscular disorders (NMD), such as Duchenne Muscular Dystrophy (DMD), develop progressive respiratory muscles weakness and pulmonary restriction. Pulmonary function monitoring of the decline in lung function allows for timely intervention with cough assist techniques and nocturnal non-invasive ventilation (NIV). NMD may find the measurement of lung function difficult using current techniques. Structured Light Plethysmography (SLP) has been proposed as a novel, non-contact, self-calibrating, non-invasive method of assessing lung function. The overarching aim of this study was to investigate the use of SLP as a novel method for monitoring respiratory function in children with neuromuscular disease.

METHODS

SLP thoraco-abdominal (TA) displacement was correlated with forced vital capacity measurements recorded by spirometry and the repeatability of the measurements with both methods examined. SLP tidal breathing parameters were investigated to assess the range and repeatability of regional right and left side TA displacement and rib cage and abdominal wall displacement.

RESULTS

The comparison of the FVC measured with SLP and with spirometry, while having good correlation (R = 0.78) had poor measurement agreement (95% limits of agreement: -1.2 to 1.2L) The mean relative contribution of right and left TA displacement in healthy controls was 50:50 with a narrow range. Repeatability of this measure with SLP was found to be good in healthy controls and moderate in NMD children with/without scoliosis but with a wider range. The majority of the control group displayed a predominant rib cage displacement during tidal breathing and those who displayed predominant abdominal wall displacement showed displacement of both regions close to 50:50 with similar results for the rib cage and abdomen. In comparison, children with NMD have a more variable contribution for all of these parameters. In addition, SLP was able to detect a reduction in abdominal contribution to TA displacement with age in the DMD group and detect paradoxical breathing in children with NMD. Using SLP tracings during tidal breathing we were able to identify three specific patterns of breathing amongst healthy individuals and in children with NMD.

CONCLUSIONS

SLP is a novel method for measuring lung function that requires limited patient cooperation and may be especially useful in children with neuromuscular disorders. Measuring the relative contributions of the right and left chest wall and chest versus abdominal movements allows a more detailed assessment.

Cough and airway clearance in Duchenne muscular dystrophy

People with Duchenne muscular dystrophy (DMD), develop a respiratory muscle weakness that results in weakened cough, airway clearance impairment and over time respiratory failure and death. Assessment of cough effectiveness through vital capacity, peak cough flow and maximal inspiratory and expiratory pressures has been used to identify the optimal timing of cough augmentation techniques initiation. The choice of therapies depends on physician knowledge, and patient/care giver abilities. The purpose of this review is to clarify mechanisms of action, benefits and disadvantages of available techniques, such as manual cough-assisting manoeuvres, glossopharyngeal breathing, air stacking by resuscitator bag or by volume-cycle ventilator, and mechanical insufflator-exsufflator. Mechanisms of mucus mobilization, like intrapulmonary percussive ventilation, may have a therapeutic role in the case of persistent atelectasis. It is also crucial to recognize the initial phase of an acute respiratory exacerbation, increase the use of these techniques which may reduce morbidity and mortality.

A New Method for Measuring Bell-Shaped Chest Induced by Impaired Ribcage Muscles in Spinal Muscular Atrophy Children

The involvement of the respiratory muscular pump makes SMA children prone to frequent hospitalization and morbidity, particularly in type 1. Progressive weakness affects ribcage muscles resulting in bell-shaped chest that was never quantified. The aims of the present work were: (1) to quantify the presence of bell-shaped chest in SMA infants and children and to correlate it with the action of ribcage muscles, assessed by the contribution of pulmonary ribcage to tidal volume (ΔV_{RC, p}); (2) to verify if and how the structure of the ribcage and ΔV_{RC, p} change after 1-year in SMA type 2. 91 SMA children were studied in supine position during awake spontaneous breathing: 32 with type 1 (SMA1, median age: 0.8 years), 51 with type 2 (SMA2, 3.7 years), 8 with type 3 (SMA3, 5.4 years) and 20 healthy children (HC, 5.2 years). 14 SMA2 showed negative ΔV_{RC, p} (SMA2px), index of paradoxical inspiratory inward motion. The bell-shaped chest index was defined as the ratio between the distance of the two anterior axillary lines at sternal angle and the distance between the right and left 10th costal cartilage. If this index was < < 1, it indicated bell shape, if ~1 it indicated rectangular shape, while if >> 1 an inverted triangle shape was identified. While the bell-shaped index was similar between HC (0.92) and SMA3 (0.91), it was significantly (p < 0.05) reduced in SMA2 (0.81), SMA2px (0.74) and SMA1 (0.73), being similar between the last two. There was a good correlation (Spearman's rank correlation coefficient, ρ = 0.635, p < 0.001) between ribcage geometry and ΔV_{RC, p}. After 1 year, ΔV_{RC, p} reduced while bell-shaped chest index did not change being significantly lower than HC. The shape of the ribcage was quantified and correlated with the action of ribcage muscles in SMA children. The impaired ribcage muscles function alters the ribcage structure. HC and SMA3 show an almost rectangular ribcage shape, whereas SMA2, SMA2px and SMA1 are characterized by bell-shaped chest. In SMA, therefore, a vicious cycle starts since infancy: the disease progressively affects ribcage muscles resulting in reduced expansion of lung and ribcage that ultimately alters ribcage shape. This puts the respiratory muscles at mechanical disadvantage.

Respiratory Diagnostic Tools in Neuromuscular Disease

Children with neuromuscular disease (NMD) are at risk of acquiring respiratory complications. Both clinical assessments and respiratory diagnostic tests are important to optimize the respiratory health and care of such children. The following respiratory diagnostic tools and their utility for evaluating children with NMD are discussed in this article: lung function testing (spirometry and lung volumes), peak cough flow (PCF), respiratory muscle strength testing, oximetry, capnography, and polysomnography.

Sleep in infants with congenital myasthenic syndromes

BACKGROUND AND OBJECTIVES

Infants with congenital myasthenic syndrome (CMS) are at risk of brief resolved unexplained event (BRUE) and sleep-disordered breathing. The aim of the study was to explore sleep in infants with CMS with a particular focus on heart rate (HR) variability.

METHODS

Overnight polygraphy was performed and HR variations associated with respiratory events were analysed. Bradycardia and tachycardia were defined as a variation of HR of ±10 bpm from baseline and analysed as events/hour.

RESULTS

The data of 5 infants with CMS were analysed. Two patients had known mutations (COLQ and RAPSN). One patient had a tracheostomy. The apnoea-hypopnoea index (AHI) was abnormal in all the patients (range 2.8-47.7 events/h), with the highest AHI being observed in the 3 youngest infants. Nocturnal transcutaneous gas exchange was normal in all patients except the tracheostomised patient. Mean HR was 114 ± 23 bpm with a mean HR index of 4.5 ± 4.3 events/h. The amplitudes of HR variations (bradycardia or tachycardia) were around 15-20 bpm, regardless of the type of respiratory event, and comparable between patients. No correlations were found between HR indexes or variations and the type and mean duration of respiratory events. Ventilatory support was initiated in 3 infants immediately after the sleep study because of a high AHI and/or nocturnal hypoventilation.

CONCLUSIONS

All 5 infants had an abnormal AHI with younger infants having the highest AHI. Three infants required ventilatory support after the polygraphy, underlining its clinical usefulness. No significant abnormalities of HR were observed during the sleep studies.

Respiratory magnetic resonance imaging biomarkers in Duchenne muscular dystrophy

OBJECTIVE

To examine the diaphragm and chest wall dynamics with cine breathing magnetic resonance imaging (MRI) in ambulatory boys with Duchenne muscular dystrophy (DMD) without respiratory symptoms and controls.

METHODS

In 11 DMD boys and 15 controls, cine MRI of maximal breathing was recorded for 10 sec. The lung segmentations were done by an automated pipeline based on a Holistically-Nested Network model (HNN method). Lung areas, diaphragm, and chest wall motion were measured throughout the breathing cycle.

RESULTS

The HNN method reliably identified the contours of the lung and the diaphragm in every frame of each dataset (~180 frames) within seconds. The lung areas at maximal inspiration and expiration were reduced in DMD patients relative to controls (P = 0.02 and <0.01, respectively). The change in the lung area between inspiration and expiration correlated with percent predicted forced vital capacity (FVC) in patients (r_s  = 0.75, P = 0.03) and was not significantly different between groups. The diaphragm position, length, contractility, and motion were not significantly different between groups. Chest wall motion was reduced in patients compared to controls (P < 0.01).

INTERPRETATION

Cine breathing MRI allows independent and reliable assessment of the diaphragm and chest wall dynamics during the breathing cycle in DMD patients and controls. The MRI data indicate that ambulatory DMD patients breathe at lower lung volumes than controls when their FVC is in the normal range. The diaphragm moves normally, whereas chest wall motion is reduced in these boys with DMD.

Spontaneous Breathing Pattern as Respiratory Functional Outcome in Children with Spinal Muscular Atrophy (SMA)

Introduction

SMA is characterised by progressive motor and respiratory muscle weakness. We aimed to verify if in SMA children 1)each form is characterized by specific ventilatory and thoraco-abdominal pattern(VTAp) during quiet breathing(QB); 2)VTAp is affected by salbutamol therapy, currently suggested as standard treatment, or by the natural history(NH) of SMA; 3)the severity of global motor impairment linearly correlates with VTAp.

Materials and methods

VTAp was analysed on 32 SMA type I (SMA1,the most severe form), 51 type II (SMA2,the moderate), 8 type III (SMA3,the mildest) and 20 healthy (HC) using opto-electronic plethysmography. Spirometry, cough and motor function were measured in a subgroup of patients.

Results

In SMA1, a normal ventilation is obtained in supine position by rapid and shallow breathing with paradoxical ribcage motion. In SMA2, ventilation is within a normal range in seated position due to an increased respiratory rate(p<0.05) with reduced tidal volume(p<0.05) secondary to a poor contribution of pulmonary ribcage(%ΔV_RC,P, p<0.001). Salbutamol therapy had no effect on VTAp during QB(p>0.05) while tachypnea occurred in type I NH. A linear correlation(p<0.001) was found between motor function scales and VTAp.

Conclusion

A negative or reduced %ΔV_RC,P, indicative of ribcage muscle weakness, is a distinctive feature of SMA1 and SMA2 since infancy. Its quantitative assessment represents a non-invasive, non-volitional index that can be obtained in all children, even uncollaborative, and provides useful information on the action of ribcage muscles that are known to be affected by the disease.Low values of motor function scales indicate impairment of motor but also of respiratory function.

Sleep study as a diagnostic tool for unexplained respiratory failure in infants hospitalized in the PICU

PURPOSE

The aim of the study was to analyze the diagnostic and therapeutic value of a polygraphy (PG) in infants hospitalized for unexplained respiratory failure or life-threatening events in the PICU.

MATERIAL AND METHODS

The PG of 13 infants (4 girls), mean age 6.8±7.7months, were analyzed.

RESULTS

Eight infants were admitted for unexplained respiratory failure and 5 for life-threatening events. PG showed features suggestive of respiratory muscle weakness in 5 infants whose final diagnoses were nemaline rod myopathy (n=2), congenital myasthenia (n=2), and diaphragmatic dysfunction (n=1). Four of these patients were successfully treated with noninvasive ventilation (NIV). PG was suggestive of brainstem dysfunction in 4 infants; 2 were treated successfully with NIV and another with caffeine. PG showed obstructive sleep apnea in 3 infants; 2 were treated successfully with NIV and one patient was lost during follow up. A typical pattern of congenital central hypoventilation syndrome was observed in the last patient who was treated successfully with invasive ventilation. One patient with diaphragmatic dysfunction and one with brain stem dysfunction died.

CONCLUSIONS

PG may assist the diagnosis and guide the management of unexplained respiratory failure or life-threatening events in infants hospitalized in the PICU.

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.