Zoran Danov, MD, is Assistant Professor of Pediatrics, Division of Pediatric Pulmonology, University of Kentucky College of Medicine. Lexington, KY. Mary K. Schroth, MD, is Associate Professor of Pediatrics, Pediatric Pulmonology, University of Wisconsin School of Medicine and Public Health, Madison, WI.
Dr. Danov and Dr. Schroth have disclosed no relevant financial relationships.
Address correspondence to: Mary K. Schroth, MD, Associate Professor of Pediatrics, Pediatric Pulmonology, University of Wisconsin School of Medicine and Public Health, 600 Highland Ave., K4/938 CSC, Madison WI 53792-9988; fax: 608-263-0510; or e-mail: email@example.com
Respiratory failure is the most common cause of morbidity and mortality in individuals with neuromuscular disease (NMD). Multiple factors contribute to the progression to respiratory failure, including poor clearance of lower airway secretions, dysphagia with aspiration, recurrent pneumonias, scoliosis, and poor nutritional status. Therefore, interventions that may alter the natural history of some neuromuscular disorders include airway clearance techniques, early nocturnal respiratory support screening and application, nutritional intervention for dysphagia, and surgical intervention for scoliosis.1–3 Management of the respiratory complications of NMD is essential to survival of this population.
In this article, we review respiratory pump function in health, the pathophysiologic changes in children with different types of NMD, followed by review of current recommendations for the respiratory evaluation and management of NMD.
Respiratory Pump in Health
The primary purpose of the respiratory pump is to exchange oxygen (O2) for carbon dioxide (CO2), the waste product of cellular metabolism, through ventilation, distribution of air to the alveoli, and gas diffusion across the alveolar capillary membrane. Components of the respiratory pump include the thoracic cage, the respiratory muscles, the respiratory centers that control the muscles, and the neural pathways that transmit nerve impulses from the respiratory centers to the respiratory muscles.4
Respiratory muscles are divided into the inspiratory, expiratory, and accessory muscles of respiration. Furthermore, the muscles of the upper airways maintain upper airway patency during the respiratory cycle. The diaphragm is the primary muscle of inspiration and is innervated via the phrenic nerve that originates from C3-5 nerve roots. Diaphragm contraction pushes down the abdominal viscera, displaces the abdominal wall outward, and increases abdominal pressure while elevating the lower ribs causing outward displacement of the rib cage.
The intercostal muscles are located between the ribs and are divided into internal and external intercostal muscles. External intercostal muscle contraction elevates the ribs and sternum, facilitating inspiration. Inspiration is an active process, which involves contraction of the external intercostal muscles and the diaphragm to enlarge the thoracic cavity and decrease intra-thoracic pressure. This results in air flowing into the lungs (see Figure 1A). Expiration is passive and occurs by relaxation of the external intercostal muscles and diaphragm, returning the diaphragm, ribs, and sternum to the resting position (see Figure 1B).
Figure 1. Movement of Diaphragm, Chest, and Abdominal Wall During Normal Tidal Breathing. A (left). Inspiration. B (right). Expiration. Image Provided By: Zoran Danov, MD; and Mary K. Schroth, MD.
Active expiration occurs during exercise, cough, and during asthma exacerbations. The abdominal wall muscles, including the rectus abdominis, the external and internal oblique muscles, and the transversus abdominis, contract during active exhalation. Contraction of the abdominal muscles compresses the abdominal contents against the relaxed diaphragm, forcing it upward into the thoracic cavity while depressing the lower ribs and pulling down the anterior part of the lower chest. Contraction of the internal intercostal muscles depresses the rib cage downward opposite to the actions of the external intercostals. Elastic recoil and compliance of the lungs and chest wall influence the respiratory pump function and extent of chest wall movements.
The elastic recoil of the lungs and chest wall act in opposite directions and are in equilibrium at the end of quiet expiration, which determines functional residual capacity (FRC) of the lungs. If the chest wall is less compliant, additional energy is needed for the work of breathing. If the chest wall is too compliant, its motion will be inefficient, and the negative intrathoracic pressure will cause paradoxical inward movement of the chest wall during inspiration. Normal chest wall movement is synchronous with the movement of the abdomen: both move outward (expand) during expiration and move inward during exhalation (see Figure 1, page 770).
Cough requires intact respiratory muscles and serves the important function of clearing the airway of foreign material and secretions. Coughing consists of three phases: the inspiratory phase of rapid, large volume inspiration; the contraction phase of glottic closure and initial expiratory muscle contraction resulting in increased pressure in the abdominal, pleural, and alveolar spaces up to 300 cm H2O; and the expiratory phase of glottic opening followed by accelerating expiratory flow of approximately 12 L/sec generated by the abdominal muscles. High gas velocity in the compressed airways creates shearing force that dislodges mucus adhering to airway walls.5,6
Respiratory Complications in NMD
NMDs alter the normal respiratory pump by decreasing respiratory muscle strength. Inspiratory muscle weakness leads to suboptimal lung inflation and, therefore, low tidal volumes. Inhalation to low lung volumes chronically can result in derecruitment of alveoli and subsequent atelectasis, resulting in ventilation perfusion mismatch with hypoxemia and carbon dioxide retention. Expiratory muscle weakness decreases cough efficacy and leads to reduced airway secretion clearance, resulting in mucus plugging, atelectasis, and pneumonia. Bulbar muscle weakness (facial, oropharyngeal, and laryngeal muscles) impairs swallowing and speech, leading to increased risk of aspiration and, when coupled with weak expiratory muscles, can result in recurrent pneumonia. Bulbar weakness also contributes to decreased oral intake, resulting in weight loss and/or poor weight gain.7
Changes in Chest Wall Compliance, Motion, and Shape
Changes in chest wall compliance, motion, and shape occur over time. Infants and young children with neuromuscular weakness have highly compliant rib cages, resulting in paradoxical inward chest wall motion. This motion is inefficient and results in increased work of breathing, increased risk of atelectasis, and development of significant chest wall deformity, which may result in decreased lung growth as well as fatigue. In adults and adolescents, chest wall compliance is decreased, resulting in a stiffer chest that is also inefficient and requires increased work of breathing. To compensate, individuals with NMD breathe faster with shallow breaths (low tidal volumes). A consequence of low lung volumes is rib cage stiffening and contractures of costovertebral joints.7,8
Observation of chest wall motion provides valuable clues to the site and cause of respiratory muscle weakness. Intercostal muscle weakness, with sparing of the diaphragm, is characterized by inward rib cage and outward abdominal wall motion during inspiration as the rib cage is sucked inward by the negative intrapleural pressure developed by the contracting diaphragm (see Figure 2A, page 770). This is seen in children with spinal muscular atrophy type I or II.
Figure 2. Different Types of Paradoxical Chest and Abdominal Wall Movement During Inspiration. A (left). Intercostal Muscle Weakness. B (right). Diaphragm Weakness. Image Provided By: Zoran Danov, MD; and Mary K. Schroth, MD.
Diaphragm weakness results in outward chest wall and inward abdominal motion during inspiration (see Figure 2B, page 770). This paradoxical breathing pattern is caused by passive upward motion of the weak diaphragm as the dominant intercostal muscles develop negative intrathoracic pressure. This breathing pattern is seen in phrenic nerve injuries and in NMD that spare intercostal muscles relative to the diaphragm (Duchenne muscular dystrophy).
Scoliosis in children with NMD is due to weakness and imbalance of the paraspinal muscles to hold the spine upright against gravity. Severe scoliosis (greater than 40°) can further diminish vital capacity and total lung capacity, resulting in respiratory muscle realignment, increased work load, and reduced pressures generated by the muscles.
Sleep-disordered breathing is manifested most commonly by nocturnal hypoventilation in children with NMD and is due to respiratory muscle weakness exacerbating normal muscle relaxation during sleep. In addition, upper airway obstruction and obstructive sleep apnea or hypopnea are caused by weakness of upper airway muscles and their inability to resist the collapsing force of the negative intrapharyngeal pressure caused by the airflow through the upper airways (ie, Bernoulli effect).
Obstructive sleep apnea is exacerbated by obesity, which often occurs in children with NMD who transition from independent ambulation to wheelchair dependence.7 The progression from sleep-disordered breathing to chronic respiratory failure is gradual. Alveolar hypoventilation with hypoxemia and CO2 retention initially develops during REM sleep and over time progresses to non-REM and REM sleep, followed by progression to daytime hypoxemia and hypercarbia. Symptoms of morning headache, frequent waking, and lethargy may be present, but because of lack of ambulation, the progression to chronic respiratory failure may be insidious.7
Early in the course of the disease, normal ventilation is maintained when CO2 production is at baseline. However, when metabolic needs are increased due to illness, respiratory muscle weakness is exacerbated. Viral respiratory infections, lower respiratory infections, cardiac failure, pneumonia, atelectasis, and aspiration can speed the time course and cause acute respiratory failure.9 The imbalance between the respiratory load and the weakened work capacity of the respiratory muscles leads to muscle fatigue, which contributes to respiratory failure.
Common Neuromuscular Disorders
Muscular dystrophies are a group of genetic, degenerative diseases primarily affecting voluntary muscles. They may be inherited as X-linked or autosomal dominant or recessive (see Sidebar, page 771.)
Motor Neuron Diseases
- Duchenne muscular dystrophy
- Becker muscular dystrophy
- Emery-Dreifuss muscular dystrophy
- Limb girdle muscular dystrophy
- Facioscapulohumeral muscular dystrophy
- Myotonic dystrophy
- Distal muscular dystrophy
- Congenital muscular dystrophy
Diseases of Peripheral Nerve
- Spinal muscular atrophy type I (Werdnig-Hoffman disease)
- Spinal muscular atrophy type II (intermediate type)
- Spinal muscular atrophy type III (Kugelberg-Welander disease)
- Spinal muscular atrophy with respiratory distress (SMARD1)
Metabolic Diseases of Muscle
- Charcot-Marie-Tooth disease
- Friedrich’s ataxia
- Dejerine-Sottas disease
- Pompe disease
- Mitochondrial myopathy
- Nemaline myopathy
- Myotubular myopathy/centronuclear myopathy
- Congenital muscle fiber type disproportion
- Central core disease
- Minicore disease
Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the dystrophin gene resulting in progressive muscle degeneration, leading to loss of independent ambulation by early teen years, subsequent loss of respiratory muscle strength, and death. Most patients develop cardiomyopathy, but encephalopathy with behavioral disorders and cognitive defects, dysfunction of the smooth muscles of vessels and gastrointestinal tract may also occur. DMD symptoms onset is typically between 2 and 3 years with mild muscle weakness, waddling gait, and frequent falling. Diagnosis usually occurs by 5 years through gene mutation analysis or muscle biopsy, if necessary.
Disease progression is gradual, and by 9 to 12 years, children are wheelchair dependent. Children with DMD develop progressive kyphoscoliosis, joint contractures, and equinovarus deformity of their feet. Mean age of death is 20 years, usually from progressive cardiac and/or respiratory disease. Respiratory muscle weakness affects the diaphragm more than the intercostal muscles and results in paradoxical breathing (see Figure 2B, page 770), low tidal volumes, hypoventilation, and atelectasis of lower lung lobes.2,10,11
Spinal Muscular Atrophy
Spinal muscular atrophy (SMA) is an autosomal recessive inherited disease characterized by degeneration of the anterior horn cells of the spinal cord due to deletion in the survivor motor neuron (SMN1) gene. Approximately 95% of SMA can be diagnosed by gene mutation analysis. The associated progressive weakness is usually symmetrical, more proximal then distal, and is greater in the legs than in the arms. Sensation is preserved, tendon reflexes are absent, and tongue fasciculations are present. Severity of the weakness correlates with the age of onset and maximal milestone achieved (see Table 1, page 772).
Table 1. Spinal Muscular Atrophy Characteristics
The most severe form, SMA type I, is also called Werdnig-Hoffmann disease, and it is the most common form.3 Children with this type of NMD have impaired head control, weak cry, and cough. Swallowing, feeding and handling of oral secretions are impaired before 1 year of age. Because of intercostal muscle weakness and relative sparing of the diaphragm, the infants exhibit characteristic paradoxical breathing and bell-shaped chest, with chest wall collapse and abdominal protrusion (see Figure 2A, page 770). Early morbidity and mortality are associated with progressive respiratory failure and bulbar dysfunction. Children with SMA type 1 without respiratory support usually die within first 2 years of life.3,12,13
Congenital myopathies have characteristic microscopic changes (no dystrophy or inflammation) and reduced muscle function. There are multiple disorders, named by specific pathologic microscopic findings on muscle biopsy. Respiratory complications of congenital myopathies cannot be predicted by skeletal muscle strength. Insidious progression to respiratory failure and death has been reported in several disorders while the child continues to be ambulatory.14–16
Respiratory Evaluation of Children with NMD
Important historical information includes functional abilities, including ambulation and developmental milestones achieved; respiratory function, including daily respiratory symptoms when well and symptoms with illness and cough effectiveness; and symptoms of sleep disturbance, including frequency of waking, presence of morning headaches, enuresis, and daytime somnolence. Additionally, an assessment of the ability to eat safely, calories consumed, and presence of gastroesophageal reflux (GERD) affect respiratory function, if there is an identified risk of aspiration.
Objective data include weight, height (standing when possible and arm span when non-ambulatory), vital signs, and a complete physical exam. Children with loss of muscle mass will weigh less due to decreased density of fat and atrophied muscle compared with muscle bulk of normal children. Evaluation of the respiratory system is focused on careful observation of the chest wall and breathing to determine presence of chest wall deformity, paradoxical breathing and increased work of breathing, cough effectiveness, and breath sounds to auscultation. Frequency of evaluation by a pulmonologist is established for DMD and SMA based on whether an individual is ambulatory and severity of disease.2,3,10,11
Pulmonary Function Testing
Pulmonary function testing in young children is limited to pulse oximetry and CO2 measurement by end tidal CO2 (ETCO2) or transcutaneous CO2 (TCO2), serum HCO3, or blood gas. For cooperative children 4 years and older, spirometry, lung volumes, and respiratory muscle force testing are valuable to establish a baseline and monitor change over time. Pulmonary function tests in individuals with NMD helps to evaluate and monitor their respiratory status over time and provides an estimate for when further respiratory support may be necessary. Individuals with NMDs typically demonstrate a restrictive breathing pattern caused by respiratory muscle weakness, and the inability to fully expand the lungs (see Table 2, see page 773).
Table 2. Pulmonary Function Tests in NMD
Restrictive lung disease includes a decreased total lung capacity (TLC, how big the lungs are); vital capacity (VC, maximal exhalation volume after maximal inhalation); and expiratory reserve volume (ERV, air exhaled during active exhalation). Residual volume (RV, the volume of air that remains in the lungs after active exhalation) is elevated when the respiratory muscles are too weak to deflate the lungs completely and may be one of the earliest signs of expiratory muscle weakness resulting in an increased RV/TLC. The functional residual capacity (FRC) may be normal. Scoliosis will exaggerate the restrictive lung disease in children with NMD. Because of reduced VC, the forced expiratory volume in the first second (FEV1) to FVC is normal or high. Having FVC of less than 1 L, in patients with DMD, is the most accurate negative predictor of survival.11
Peak cough flow (PCF) measurements using a peak flow meter is a useful measure of expiratory muscle strength.17 PCF less than 160 L/minute in an adult suggests increased risk for recurrent pneumonia.11 Maximal inspiratory (MIP) and expiratory pressures (MEP) are indirect measures of respiratory muscle strength. This test measures the pressure at the mouth on a patient breathing through a mouthpiece against a closed shutter.
An initial chest radiograph is obtained to establish a baseline reference and to evaluate for infiltrates and chest wall deformity; subsequent studies are obtained as clinically indicated. Chest radiographs should be evaluated for signs of aspiration, atelectasis, pneumonia, lung field symmetry hemi diaphragm position, and cardiomegaly. The presence and degree of scoliosis should be determined with specific scoliosis studies.
Overnight polysomnography should be performed in most NMDs to assess for sleep-related hypoventilation and sleep-disordered breathing. Hypoventilation in patients with NMD has insidious onset; and the patient may be asymptomatic, especially in children with congenital myopathies. Polysomnography also can be used to initiate and titrate noninvasive respiratory support.
Management and Intervention
An important component to disease prevention is providing all immunizations, including 23-valent pneumococcal vaccine for children 2 years and older and an annual influenza vaccine for children 6 months and older.2,3,11 In addition, infants and young children with severe NMD may benefit from respiratory syncytial virus (RSV) antibody prophylaxis.3
Respiratory care management is based on monitoring for the most common complications of NMD and implementing a timely intervention. The most common complications are difficulty clearing coughing secretions and hypoventilation during sleep.
Individuals with NMD who are at risk for difficulty clearing secretions include those with significantly reduced pulmonary function testing and poor cough efficacy. Airway clearance techniques are taught to patients and their caregivers and include secretions mobilization techniques (eg, manual or mechanical chest physiotherapy, high frequency chest wall oscillation, and intrapulmonary percussive ventilation). This may be followed by postural drainage as tolerated by the patient; however, patients with diaphragm weakness may not tolerate Trendelenberg positioning.
In addition, techniques to promote cough, including manual cough assistance and mechanical insufflation/exsufflation with the CoughAssist (Philips Respironics, Murrysville, PA) machine18–20 are taught and provided to patients and their families. Pressures for CoughAssist machine should be high enough to mobilize secretions (eg, inhale and exhale pressures 30 to 40 cm H2O). In addition, techniques for lung volume recruitment using Ambu bag and breath stacking have been useful in improving chest wall compliance and decreasing respiratory complications of NMD.21
Pulse Oximetry Monitoring
Pulse oximetry can be used to spot check oxygen saturation during the day for hypoxemia and as a guide to airway clearance during illness. Patients with severe NMD (SMA type I) may be too weak to demonstrate clinical signs of respiratory distress before severe compromise.3
Respiratory Support Options
To optimally manage hypoventilation or chronic respiratory failure with or without obstructive apnea identified by polysomnography, implementation of a respiratory support device during sleep is indicated.2,3,7,11,12,22 In addition, because the natural history of SMA type I is relatively rapid respiratory failure before 2 years, initiation of a respiratory support device early in the disease course should be considered.3,12
Supplemental oxygen alone is not appropriate. Options for a respiratory support device include noninvasive ventilation (NIV) with bilevel positive airway pressure (BiPAP) devices or a mechanical ventilator, and invasive ventilation with a tracheotomy. A variety of respiratory support devices are available with several ventilation mode options to optimize ventilation, as well as user tolerance, and the technology continues to improve.
To optimally rest the compromised respiratory muscles and provide adequate ventilation, a backup respiratory rate set high enough to maintain normal pCO2 and oxygen saturation is indicated. Polysomnography is used to manage respiratory support device settings. Continuous positive airway pressure (CPAP) is not indicated in neuromuscular weakness, as it does not provide adequate ventilatory support and respiratory muscle rest.3,11
The options for NIV interfaces includes nasal mask or pillows or a full face mask; noninvasive daytime respiratory support can include mouthpiece or sip ventilation in children who are old enough to cooperate with this modality. Identifying a well-fitting interface can be challenging, but it is well worth evaluating multiple options and rotating masks for day-to-day use to limit skin breakdown and irritation. NIV has been shown to alter the chest wall deformity in young children with SMA and may improve lung development.23
NIV can be used as to bridge post-anesthesia recovery to prevent complications, including atelectasis and reintubation in individuals with NMD.24 During viral respiratory infections (VRI), NIV may be required for more hours during the day than at baseline due to increased neuromuscular weakness secondary to the VRI.25 Some children with NMD require full-time NIV, have frequent episodes of respiratory instability when off NIV, and may benefit from tracheostomy and mechanical ventilation. Tracheotomy is not an acute intervention.
Consideration of tracheotomy should be discussed with the patient and family as an option while discussing their care management goals. Supplemental oxygen should be used judiciously in individuals with NMD; overuse can contribute to blunting of the respiratory drive and contribute to respiratory failure.
During episodes of acute oxygen desaturation, the underlying etiology should be addressed. Most commonly, it is mucus plugging or atelectasis. The first intervention is mechanical airway-secretion mobilization and clearance with assisted coughing. The CoughAssist machine should be used as often as needed, and pulse oximetry should be used to guide intervention. If pulse oxygen saturation is less than 94%, assisted coughing should be used. If there is no improvement, an airway-clearance treatment should be initiated, and the individual should be placed on their respiratory support device. Assisted coughing techniques are preferred over deep suctioning and bronchoscopy.3,11
Increased NIV should be initiated early during acute illness. Bilevel positive airway pressure also decreases respiratory muscle work by increasing tidal volume and decreasing respiratory rate, and it improves gas exchange.22 The use of NIV with aggressive airway clearance may decrease the need for intubation. If airway clearance and respiratory support is maximized and hypoxemia continues, supplemental oxygen should be used.
NMD are heterogeneous disorders with the common thread of respiratory complications that often progress to respiratory failure. The respiratory complications include respiratory muscle weakness contributing to poor lung growth and chest wall development in infants; poor clearance of lower airway secretions (especially during a viral illness); and sleepdisordered breathing, most commonly, hypoventilation. Educating patients and their families and providing tools for the home setting, including airway clearance and cough techniques, respiratory support device, and pulse oximetry as clinically indicated, will facilitate survival.
- Oskoui M, Levy G, Garland CJ, et al. The changing natural history of spinal muscular atrophy type 1. Neurology. 2007;69(20):1931–1936. doi:10.1212/01.wnl.0000290830.40544.b9 [CrossRef]
- Bushby K, Finkel R, Birnkrant DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 2: implementation of multidisciplinary care. Lancet Neurol. 2010;9(2):177–189. doi:10.1016/S1474-4422(09)70272-8 [CrossRef]
- Wang CH, Finkel RS, Bertini ES, et al. Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol. 2007;22(8):1027–1049. doi:10.1177/0883073807305788 [CrossRef]
- Benditt JO. The neuromuscular respiratory system: physiology, pathophysiology, and a respiratory care approach to patients. Respir Care. 2006;51(8):829–837; discussion 837–839.
- Hadjikoutis S, Wiles CM, Eccles R. Cough in motor neuron disease: a review of mechanisms. QJM. 1999;92(9):487–494. doi:10.1093/qjmed/92.9.487 [CrossRef]
- Kravitz RM. Airway clearance in Duchenne muscular dystrophy. Pediatrics. 2009;123(Suppl 4):S231–235. doi:10.1542/peds.2008-2952G [CrossRef]
- Perrin C, Unterborn JN, Ambrosio CD, Hill NS. Pulmonary complications of chronic neuromuscular diseases and their management. Muscle Nerve. 2004;29(1):5–27. doi:10.1002/mus.10487 [CrossRef]
- Panitch HB. The pathophysiology of respiratory impairment in pediatric neuromuscular diseases. Pediatrics. 2009;123(Suppl 4): S215–218. doi:10.1542/peds.2008-2952C [CrossRef]
- Racca F, Del Sorbo L, Mongini T, Vianello A, Ranieri VM. Respiratory management of acute respiratory failure in neuromuscular diseases. Minerva Anestesiol. 2010;76(1):51–62.
- Bushby K, Finkel R, Birnkrant DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol. 2010;9(1):77–93. doi:10.1016/S1474-4422(09)70271-6 [CrossRef]
- Finder JD, Birnkrant D, Carl J, et al. Respiratory care of the patient with Duchenne muscular dystrophy: ATS consensus statement. Am J Respir Crit Care Med. 2004;170(4):456–465. doi:10.1164/rccm.200307-885ST [CrossRef]
- Schroth MK. Special considerations in the respiratory management of spinal muscular atrophy. Pediatrics. 2009;123(Suppl 4): S245–249. doi:10.1542/peds.2008-2952K [CrossRef]
- Bach JR, Baird JS, Plosky D, Navado J, Weaver B. Spinal muscular atrophy type 1: management and outcomes. Pediatr Pulmonol. 2002;34(1):16–22. doi:10.1002/ppul.10110 [CrossRef]
- Khan Y, Heckmatt JZ, Dubowitz V. Sleep studies and supportive ventilatory treatment in patients with congenital muscle disorders. Arch Dis Child. 1996;74(3):195–200. doi:10.1136/adc.74.3.195 [CrossRef]
- Rowe PW, Eagle M, Pollitt C, Bullock RE, Bushby KM. Multicore myopathy: respiratory failure and paraspinal muscle contractures are important complications. Dev Med Child Neurol. 2000;42(5):340–343. doi:10.1017/S0012162200000591 [CrossRef]
- Ryan MM, Schnell C, Strickland CD, et al. Nemaline myopathy: a clinical study of 143 cases. Ann Neurol. 2001;50(3):312–320. doi:10.1002/ana.1080 [CrossRef]
- Sharma GD. Pulmonary function testing in neuromuscular disorders. Pediatrics. 2009;123(Suppl 4):S219–221. doi:10.1542/peds.2008-2952D [CrossRef]
- Miske LJ, Hickey EM, Kolb SM, Weiner DJ, Panitch HB. Use of the mechanical inexsufflator in pediatric patients with neuromuscular disease and impaired cough. Chest. 2004;125(4):1406–1412. doi:10.1378/chest.125.4.1406 [CrossRef]
- Bach JR. Mechanical insufflation-exsufflation. Comparison of peak expiratory flows with manually assisted and unassisted coughing techniques. Chest. 1993;104(5):1553–1562. doi:10.1378/chest.104.5.1553 [CrossRef]
- Chatwin M, Ross E, Hart N, Nickol AH, Polkey MI, Simonds AK. Cough augmentation with mechanical insufflation/exsufflation in patients with neuromuscular weakness. Eur Respir J. 2003;21(3):502–508. doi:10.1183/09031936.03.00048102 [CrossRef]
- Armstrong A. Developing a breath-stacking system to achieve lung volume recruitment. Br J Nurs. 2009;18(19):1166–1169.
- Mehta S, Hill NS. Noninvasive ventilation. Am J Respir Crit Care Med. 2001;163(2):540–577.
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Spinal Muscular Atrophy Characteristics
|SMA Type||Age of Symptom Onset||Maximum Motor Milestone||Average Age of Death||Respiratory Muscle Weakness|
|I||< 6 months||Never sit||< 2 years||Severe intercostal muscle weakness|
|II||< 18 months||Sit independently, cannot stand||2nd to 3rd decade||Intercostal muscle weakness|
|III||> 18 months||Stand or walk independently||Normal life expectancy||In 2nd or 3rd decade, may develop respiratory muscle weakness|
Pulmonary Function Tests in NMD
|VC||Decreased ability to breathe|
|FEV1||Decreased ability to breathe|
|FEV1/VC||Normal ability to breathe|
|FEF25-75||Normal or decreased ability to breathe|
|TLC||Decreased ability to breathe|
|RV||Increased, normal, or decreased ability to breathe|
|RV/TLC||Increased ability to breathe|