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Disorders of Ventilation

2000; Elsevier BV; Volume: 117; Issue: 2 Linguagem: Inglês

10.1378/chest.117.2.301

1931-3543

John R. Bach, Seong‐Woong Kang,

Neurogenetic and Muscular Disorders Research

The article by Misuri et al, "Mechanism of CO2 Retention in Patients With Neuromuscular Disease," in this issue of CHEST (see page 447) points out something concerning the lungs of patients with neuromuscular disorders that has long been recognized concerning their limbs: the loss of function results from a combination of weakness and increases in soft tissue elastance. The latter is caused by the failure to fully mobilize the soft tissues and joints because of muscle weakness.1Halar EM Bell KR Rehabilitation's relationship to inactivity.in: Kottke FJ Lehmann JF Krusen's handbook of physical medicine and rehabilitation. 3rd ed. WB Saunders, Philadelphia PA1990: 1113-1133Google Scholar Muscle strength also diminishes as soft tissues adaptively shorten over time. As muscle loses its normal flexibility and weaker muscles are stretched by their stronger antagonists, changes in their length-tension relationships result in decreased peak tensions, strength, and endurance.2Kisner C Colby LA Therapeutic exercise: foundations and technique. 3rd ed. FA Davis Company, Philadelphia PA1996: 143-182Google Scholar, 3Grossman M Sahrmann S Rose S Review of length-associated changes in muscle.Phys Ther. 1982; 62: 1799-1808PubMed Google Scholar When a foreshortened position of a muscle is maintained for > 5 to 7 days, the loose connective tissue in the muscle belly shortens and then gradually changes into dense connective tissue.1Halar EM Bell KR Rehabilitation's relationship to inactivity.in: Kottke FJ Lehmann JF Krusen's handbook of physical medicine and rehabilitation. 3rd ed. WB Saunders, Philadelphia PA1990: 1113-1133Google Scholar These tissues lose their normal elasticity and plasticity, resulting in the loss of range of motion (ROM) and joint contractures.2Kisner C Colby LA Therapeutic exercise: foundations and technique. 3rd ed. FA Davis Company, Philadelphia PA1996: 143-182Google Scholar A joint is contracted when it lacks full passive ROM. The muscle and other soft tissue limitations that result in joint contractures can also cause bony deformities, particularly in young, growing patients.1Halar EM Bell KR Rehabilitation's relationship to inactivity.in: Kottke FJ Lehmann JF Krusen's handbook of physical medicine and rehabilitation. 3rd ed. WB Saunders, Philadelphia PA1990: 1113-1133Google Scholar Upper limb contractures cause discomfort and diminish the ability to perform activities of daily living.4Willig TN Bach JR Rouffet MJ et al.Correlation of flexion-contractures with upper extremity function for spinal muscular atrophy and congenital myopathy patients.Am J Phys Med Rehabil. 1995; 74: 33-38Crossref PubMed Scopus (24) Google Scholar Lower limb contractures cause the premature loss of the ability to walk.5Bach JR McKeon J Orthopedic surgery and rehabilitation for the prolongation of brace-free ambulation of patients with Duchenne muscular dystrophy.Am J Phys Med Rehabil. 1991; 70: 323-331PubMed Google Scholar For example, contractures of hip flexors reduce hip extension, thereby shortening stride and requiring the patient to walk on the balls of the feet with increased lumbar lordosis and a consequent increase in energy consumption.1Halar EM Bell KR Rehabilitation's relationship to inactivity.in: Kottke FJ Lehmann JF Krusen's handbook of physical medicine and rehabilitation. 3rd ed. WB Saunders, Philadelphia PA1990: 1113-1133Google Scholar Knee flexion contractures of 30° increase the work of the calf muscles and the knee extensors by 50%. It has been demonstrated that while the combination of moderate leg weakness and contractures can result in frequent falls and wheelchair dependence, when leg contractures are prevented by ROM mobilization or surgery, the same patients can walk longer without assistance and without falls despite worsening weakness.5Bach JR McKeon J Orthopedic surgery and rehabilitation for the prolongation of brace-free ambulation of patients with Duchenne muscular dystrophy.Am J Phys Med Rehabil. 1991; 70: 323-331PubMed Google Scholar Flexibility exercises performed three times a week for 10 to 15 min in healthy but inactive subjects are sufficient to maintain the optimal resting lengths of the long muscles that would otherwise not be put through full ROM during normal daily activities. However, the independent performance of flexibility exercises requires that the subjects have normal strength. When strength is diminished, passive ROM with a sustained terminal stretch can be effective in preventing contractures if applied for 20 to 30 min bid.1Halar EM Bell KR Rehabilitation's relationship to inactivity.in: Kottke FJ Lehmann JF Krusen's handbook of physical medicine and rehabilitation. 3rd ed. WB Saunders, Philadelphia PA1990: 1113-1133Google Scholar Normally, people take deep breaths or sigh regularly. These actions stretch the respiratory structures. Patients with chronic respiratory muscle weakness have reductions in lung volumes and vital capacity (VC) and can develop hypercapnia that greatly exceeds what might be anticipated from the loss of muscle force; and they may have decreases in lung distensibility that contribute to the disproportionate hypercapnia from lung volume restriction.6Gibson GJ Pride NB Newsom Davis J et al.Pulmonary mechanics in patients with respiratory muscle weakness.Am Rev Respir Dis. 1977; 115: 389-395PubMed Google Scholar, 7De Troyer A Borenstein S Cordier R Ankylosis of lung volume restriction in patients with respiratory muscle weakness.Thorax. 1980; 35: 603-610Crossref PubMed Scopus (196) Google Scholar As shown by Mizuri et al, failure to fully expand the lungs causes increases in lung tissue and chest wall elastance and decreases in compliance. The total mechanical work of breathing (WOB) is the sum of the work of overcoming both the elastic and frictional forces opposing inflation. In healthy adults, about two thirds of the WOB can be attributed to elastic forces opposing ventilation. The remaining third is due to frictional resistance to gas and tissue movement. In diseased states, the WOB can dramatically increase. In patients with restrictive lung disease, work is the integration of the volume-pressure breathing curve. The increase in the WOB is a function of tissue elastance and an inverse function of pulmonary compliance.8Scanlan CL Ruppel GL Ventilation Scalan CL Spearman CB Sheldon RL Egan's fundamentals of respiratory care. 6th ed. Mosby Year-Book, St. Louis MO1995: 252-253Google Scholar, 9Slonim NB Hamilton LH Respiratory physiology St.5th ed. Mosby, Louis MO1987: 26-38Google Scholar Failure to take periodic deep breaths can change alveolar surface forces and increase the tendency for alveolar collapse.10Scanlan CL Ruppel GL El-Gendy A Synopsis of cardiopulmonary disease.in: Scalan CL Spearman CB Sheldon RL Egan's fundamentals of respiratory care. 6th ed. Mosby Year-Book, St Louis MO1995: 483Google Scholar Gross muscle weakness alters the passive recoil of the thoracic cage, modifying the neutral position at which lung and cage recoil pressures are balanced.11Estenne M Heilporn A Delhez L et al.Chest wall stiffness in patients with chronic respiratory muscle weakness.Am Rev Respir Dis. 1977; 115: 389-395Google Scholar This results in altered inspiratory muscle length-tension relationships, just as the stretching of weak lower limb muscles causes a decrease in their peak tensions by altering their optimal length-tension relationships. The lungs and chest walls are also, therefore, susceptible to the effects of incomplete regular mobilization. The tendons and ligaments of the rib cage and the costovertebral and costosternal articulations stiffen, and the latter ankylose,11Estenne M Heilporn A Delhez L et al.Chest wall stiffness in patients with chronic respiratory muscle weakness.Am Rev Respir Dis. 1977; 115: 389-395Google Scholar as the intercostal and other respiratory muscles become fibrotic and contracted.11Estenne M Heilporn A Delhez L et al.Chest wall stiffness in patients with chronic respiratory muscle weakness.Am Rev Respir Dis. 1977; 115: 389-395Google Scholar, 12Estenne M Gevenois PA Kinnear W et al.Lung volume restriction in patient with chronic respiratory muscle weakness.Thorax. 1993; 48: 698-701Crossref PubMed Scopus (97) Google Scholar While it is common for patients with neuromuscular disease to undergo an intensive home program of limb joint mobilization, lung and chest wall mobilization is invariably ignored. Yet, without deep insufflations these patients first develop microatelectasis. Microatelectasis can develop in 1 h when normal tidal volumes cannot be increased.13Miller WF Rehabilitation of patients with chronic obstructive lung disease.Med Clin North Am. 1967; 51: 349-361Crossref PubMed Scopus (22) Google Scholar The long-term inability to take deep breaths, or chronic hypoinflation, results in permanent pulmonary restriction. For children, this causes the underdevelopment of lung tissues and decreased chest wall elasticity14De Troyer A Deisser P The effects of intermittent positive pressure breathing on patients with respiratory muscle weakness.Am Rev Respir Dis. 1981; 124: 132-137PubMed Google Scholar, 15Estenne M De Troyer A The effects of tetraplegia on chest wall statics.Am Rev Respir Dis. 1986; 134: 121-124PubMed Google Scholar and static pulmonary compliance.6Gibson GJ Pride NB Newsom Davis J et al.Pulmonary mechanics in patients with respiratory muscle weakness.Am Rev Respir Dis. 1977; 115: 389-395PubMed Google Scholar, 16Smith PEM Edwards RHT Calverley PMA Oxygen treatment of sleep hypoxaemia in Duchenne muscular dystrophy.Thorax. 1989; 44: 997-1001Crossref PubMed Scopus (45) Google Scholar, 17De Troyer A Borenstein S Cordier R Analysis of lung volume restriction in patients with respiratory muscle weakness.Thorax. 1980; 35: 603-610Crossref PubMed Scopus (128) Google Scholar Thus, decreased pulmonary compliance results initially from microatelectasis and ultimately from increased stiffness of the chest wall and lung tissues themselves.15Estenne M De Troyer A The effects of tetraplegia on chest wall statics.Am Rev Respir Dis. 1986; 134: 121-124PubMed Google Scholar The presence of scoliosis can exacerbate the loss of compliance which, in turn, further increases the WOB. The airways normally divide 27 times by 8 years of age. The alveoli and respiratory exchange membrane continue to grow, reaching 80 m2,18De Troyer A Estenne M Functional anatomy of the respiratory muscles.Clin Chest Med. 1988; 9: 175-193Abstract Full Text PDF PubMed Google Scholar the equivalent surface area of the football fields, by late adolescence.9Slonim NB Hamilton LH Respiratory physiology St.5th ed. Mosby, Louis MO1987: 26-38Google Scholar Lung growth peaks with the plateauing of the VC at 19 years of age. With severe or advanced neuromuscular disease, upper thoracic volumes can decrease during inspiration.19Lissoni A Aliverti A Molteni F et al.Spinal muscular atrophy: kinematic breathing analysis.Am J Phys Med Rehabil. 1996; 75: 332-339Crossref PubMed Scopus (23) Google Scholar For infants with spinal muscular atrophy, for example, this can result in the underdevelopment of the lungs and chest wall and in the boney deformity, pectus excavatum. It is ironic that although few patients die from stiff ankles and wrists, the inability to attain a volume of air > 1,500 mL invariably results in diminished spontaneous and assisted cough flows,20Bach JR Mechanical insufflation-exsufflation: comparison of peak expiratory flows with manually assisted and unassisted coughing techniques.Chest. 1993; 104: 1553-1562Abstract Full Text Full Text PDF PubMed Scopus (369) Google Scholar and this greatly increases the risk of pulmonary morbidity and mortality.21Bach JR Ishikawa Y Kim H Prevention of pulmonary morbidity for patients with Duchenne muscular dystrophy.Chest. 1997; 112: 1024-1028Abstract Full Text Full Text PDF PubMed Scopus (420) Google Scholar Patients with VCs of 300 mL who have predicted VCs of perhaps 3,000 mL can expand < 10% of their lungs on their own. Incentive spirometry is, therefore, useless for them. However, these patients can receive insufflations delivered to them via oral, nasal, or oronasal interfaces from a manual resuscitator, volume-cycled ventilator, or cough machine (In-exsufflator; J. H. Emerson Co; Cambridge, MA).20Bach JR Mechanical insufflation-exsufflation: comparison of peak expiratory flows with manually assisted and unassisted coughing techniques.Chest. 1993; 104: 1553-1562Abstract Full Text Full Text PDF PubMed Scopus (369) Google Scholar Lung hyperinflation has been shown to reverse acute lung compliance reductions in dogs as well as in humans.22Mead J Collier C Relation of volume history of lungs to respiratory mechanics in anesthetized dogs.J Appl Physiol. 1959; 14: 669-678Crossref Google Scholar, 23Egberg LD Laver MB Bendixen HH Intermittent deep breaths and compliance during anesthesia in man.Anesthesiology. 1963; 24: 57-59Crossref Google Scholar However, the only studies of the effects of long-term regimens of deep insufflations on static pulmonary compliance in humans were instituted only after patients already had severe pulmonary restriction (VCs < 50% of predicted normal), involved the use of insufflation pressures < 30 cm H2O (grossly inadequate to fully expand the lungs), and called for the use of insufflations for only minutes each day.24McCool FD Mayewski RF Shayne DS et al.Intermittent positive pressure breathing in patients with respiratory muscle weakness: alterations in total respiratory system compliance.Chest. 1986; 90: 546-552Crossref PubMed Scopus (48) Google Scholar Although short periods of mechanical hyperinflation20Bach JR Mechanical insufflation-exsufflation: comparison of peak expiratory flows with manually assisted and unassisted coughing techniques.Chest. 1993; 104: 1553-1562Abstract Full Text Full Text PDF PubMed Scopus (369) Google Scholar, 25Bach JR Update and perspectives on noninvasive respiratory muscle aids. Part 1: the inspiratory muscle aids.Chest. 1994; 105: 1230-1240Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar can briefly increase the dynamic pulmonary compliance associated with airway changes and reverse acute atelectasis,23Egberg LD Laver MB Bendixen HH Intermittent deep breaths and compliance during anesthesia in man.Anesthesiology. 1963; 24: 57-59Crossref Google Scholar, 26Mead J Collier C Relation of volume history of lungs to respiratory mechanics in anesthetized dogs.J Appl Physiol. 1959; 14: 669-678Crossref Google Scholar, 27O'Donohue W Maximum volume IPPB for the management of pulmonary atelectasis.Chest. 1976; 76: 683-687Crossref Scopus (10) Google Scholar multiple daily periods of mechanical hyperinflations of < 30 cm H2O pressure do not improve static compliance in adults.24McCool FD Mayewski RF Shayne DS et al.Intermittent positive pressure breathing in patients with respiratory muscle weakness: alterations in total respiratory system compliance.Chest. 1986; 90: 546-552Crossref PubMed Scopus (48) Google Scholar Studies on paralyzed animals with lungs comparable to those of human babies suggest that insufflation pressures of 40 cm H2O may be needed to reverse atelectasis.28Day R Goodfellow AM Apgar V et al.Pressure-time relations in the safe correction of atelectasis in animal lungs.Pediatrics. 1952; 10: 593-602Crossref PubMed Google Scholar The maximum insufflation capacity (MIC) is a measure of the maximum volume of air that can be held with a closed glottis and then expelled.29Kang SW, Bach JR: Maximum insufflation capacity: the relationships with vital capacity and cough flows for patients with neuromuscular disease. Am J Phys Med Rehabil (in press).Google Scholar The MIC is obtained by some combination of the airstacking of mechanically delivered insufflations or glossopharyngeal breathing. The MIC is a function of pulmonary compliance and strength of oropharyngeal and laryngeal muscles. A MIC of at least 500 to 1,000 mL is necessary to achieve adequate manually assisted peak cough flows to prevent airway mucus accumulation, atelectasis, and pneumonia during chest infections.29Kang SW, Bach JR: Maximum insufflation capacity: the relationships with vital capacity and cough flows for patients with neuromuscular disease. Am J Phys Med Rehabil (in press).Google Scholar While the MIC can be limited to the VC or little more than the VC in patients with severely dysfunctional bulbar musculature or those not regularly receiving deep insufflation therapy, it can become much greater than the VC and even improve with practice as VCs decrease with progressive disease (S. W. Kang and J. R. Bach; unpublished data; March 1999). This can help maintain patients free of respiratory complications and tracheostomy despite having little or no remaining VC and requiring continuous noninvasive ventilation. In summary, the lungs and chest walls of patients with muscle weakness require regular ROM mobilization, as do weak limbs. This can by provided by the delivery of maximal insufflations or stacking air volumes to the MIC. If patients have sufficient bulbar muscle control to stack volumes of air so that their MICs exceed their VCs, they can use noninvasive ventilation long term as an alternative to tracheostomy, even in the absence of measurable VC (S. W. Kang and J. R. Bach; unpublished data; March 1999). For children, positive pressure insufflations that are provided as necessary can reverse pectus excavatum and, by preventing this boney deformity, promote more normal lung growth (V. Niranjan and J. R. Bach; unpublished data; July 1999).