Amyotrophic Lateral Sclerosis: Predictors for Prolongation of Life by Noninvasive Respiratory Aids

Transcription

1 828 Amyotrophic Lateral Sclerosis: Predictors for Prolongation of Life by Noninvasive Respiratory Aids John Robert Bach, AID ABSTRACT. Bach JR. Amyotrophic lateral sclerosis: predictors for prolongation of life by noninvasive respiratory aids. Arch Phys Med Rehabil 1995;76: The purpose of this study was to determine which pulmonary function variables best predicted the potential for prolonging survival of individuals with amyotrophic lateral sclerosis (ALS) by the use of physical medicine respiratory muscle aid alternatives to tracheostomy for ventilatory support and airway suctioning. The records of 27 such ALS ventilator users with less than 15 minutes of ventilator-free breathing time for a mean _+ standard deviation of 23.7 _ months (range, 1 to 65) were reviewed. All patients underwent measurements of vital capacity (VC), maximum insufflation capacity (MIC), MIC VC difference, forced expiratory volumes, and peak cough expiratory flows (PCEF) every 1 to 6 months, depending on rate of disease progression, until requiring 24-hour ventilatory support. The ability to generate assisted PCEF in excess of 3L/sec and the ability to hold an insufflation deeper than the VC were associated with the capacity to prolong survival by methods other than tracheostomy, whereas the extent of decrease in VC and autonomous breathing ability were not. Because the PCEF and MIC VC difference correlate with bulbar muscle function, it can be concluded that the ability to use 24-hour ventilatory support by noninvasive means is a function of residual bulbar muscle strength and is independent of VC or the extent of need for ventilatory support. Properly equipped and trained, some ALS patients can use noninvasive respiratory muscle aids to delay or eliminate the need for tracheostomy by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Survival can be prolonged for most individuals with amyotrophic lateral sclerosis (ALS) by providing intermittent positive pressure ventilation (IPPV) via an indwelling tracheostomy tube and performing transtracheal suctioning of airway secretions. However, many clinicians have ethical reservations about offering ventilator use to these individuals, especially via tracheostomy, and in some states, fewer than 10% of ALS patients are offered or agree to undergo tracheostomy. J Nevertheless, like ventilator users with other severe neuromuscular disorders, 2'3 the great majority of ALS ventilator users indicate that they are contented with the decision to use a ventilator and would do it again.l'4 Many individuals who require 24-hour-a-day ventilatory support are maintained without resort to an indwelling tracheostomy tube by continuous use of noninvasive respiratory muscle aids. 5-9 The most important noninvasive inspiratory aids are IPPV delivered to the airway via appropriate interfaces 5-7 and the intermittent abdominal pressure ventilator (IAPV). 8'9 IPPV is delivered from a portable volume-triggered ventilator, via a simple mouthpiece for daytime ventilatory support, a mouthpiece retained in the mouth with a lipseal retention system a for nocturnal support, or via a nasal interface (commercially available continuous positive airway pressure [CPAP] mask or custom-molded mask F ) for daytime or nocturnal support. Occasionally an interface covering both mouth and nose is used for nocturnal support, m The From the Department of Physical Medicine and Rehabilitation, UMD-New Jersey Medical School, Newark, NJ. Submitted for publication December 19, Accepted in revised form April 23, No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to John R. Bach, MD, 17 Woodbine Terrace, Sparta, NJ by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation /95/ /0 IAPV acts on the abdomen to move the diaphragm to assist alveolar ventilation. Because it is convenient, optimizes appearance, and is effective with the individual erect, it is most useful for daytime support, especially for ventilator-assisted individuals with little or no vital capacity (VC) or ventilatorfree breathing time. 8 The expiratory muscle aids include the use of deep breaths or insufflations followed by manually assisted coughing, mechanically assisted coughing with the use of mechanical insufflation-exsufflation, or simultaneous use of both. The assisted coughing methods can eliminate airway secretions and obviate the need for transtracheal suctioning when the peak cough expiratory flows (PCEF) generated by them exceed 3L/sec. 1 As early as 1970 the use of tracheostomy IPPV was delayed 4 years and 3 months for one ALS ventilator user by 24-hour-a-day noninvasive IPPV and use of an Exsufflation Belt.b ~2 There have been no similar subsequent reports for ALS patients. We now report 27 ALS ventilator users who succeeded in using ventilatory support by noninvasive methods for a mean standard deviation of months. The purpose of this study was to determine which factors predicted the successful use of these noninvasive alternatives to IPPV via an indwelling tracheostomy. PATIENTS AND METHODS All of the referrals to the author from 1981 to the present were studied. The presence of ALS was documented in all cases by clinical and electrodiagnostic evaluation. All patients underwent regular measurements of VC (maximum observed value in 4 to 7 attempts), maximum insufflation capacity (MIC; the deepest insufflation provided by air stacking delivered air volumes from a manual resuscitator or portable volume ventilator and held with a closed glottis), ~3c forced expiratory volume in 1 second divided by forced

2 ALS SURVIVAL WITH RESPIRATORY AIDS, Bach 829 Abbreviations ALS: amyotrophic lateral sclerosis CPAP: continuous positive airway pressure FEV1/FVC: forced expiratory volume in 1 second divided by forced expiratory volume IPPV: intermittent positive pressure ventilation MIC: maximum insufflation capacity PCEF: peak cough expiratory flows SaQ: oxyhemoglobin saturation VC: vital capacity expiratory volume (FEV1/FVC) as a percentage of predicted normal, and PCEF a every 1 to 6 months depending on rate of disease progression. Oxyhemoglobin saturation (Sa02) ~ and end-tidal Pc02 (ETCO2) f monitoring were performed with the patient in both sitting and supine positions during each clinic visit once the VC was determined to be decreasing. Nocturnal Sa02 monitoring was performed every 6 months when the VC was below 60% of predicted normal, or when symptoms characteristic of hypoventilation were noted, until the onset of ventilator use, then less frequently thereafter. 5 These indications for nocturnal monitoring were used because hypercapnia has been described to develop when the VC decreases below 40% 14 to 55% 15 of predicted normal. It has been found that most patients who have VCs (measured in the supine position) less than 30% of predicted normal require nocturnal ventilatory support. 5 Therefore, when the VC was first noted below 40% of predicted normal or when Sao2 or ETCO2 was found to be abnormal, the patients were familiarized with the use of volume ventilators and instructed to periodically deliver maximum tolerated insufflations to themselves via a mouthpiece, or occasionally, via a nosepiece. Early on, manual resuscitators were used for this purpose to temporarily increase dynamic pulmonary compliance 16 and, most importantly, to assure the clinician that the patient would be able to use mouthpiece IPPV, nasal IPPV, or both for ventilatory support in the event of acute respiratory deterioration. When unassisted PCEF were found to be less than 5L/sec, the patients were also instructed in the use of manually and mechanically assisted coughing j3 and were instructed to increase maximal assisted PCEF with practice. They were provided with an oximeter and instructed to always maintain Sao2 greater than 94% (oximetry biofeedback) by using noninvasive IPPV, up to 24 hours a day if necessary, and by using assisted coughing methods when needed. The choice of noninvasive inspiratory aids, to a degree, was left to the patient. These methods became critical at the first signs of respiratory tract infection, airway congestion, or respiratory distress for any reason. Twenty-seven patients succeeded in using these noninvasive aids to maintain normal Sao2 and avert or reverse acute respiratory failure without supplemental oxygen administration or intubation. They all developed 24-hour dependence on noninvasive aids as their VCs diminished ("noninvasive users"). Approximately 50 patients either did not learn how to use noninvasive aid.s, often because of irregular clinic visits, or experienced acute respiratory failure before having access to them. These patients either died suddenly or underwent tracheostomy in local hospitals without attempting to use noninvasive aids to manage their respiratory failure. Some patients had not been provided with an oximeter early enough to capture the acute event, and in failing to maintain normal Sao2 by using noninvasive aids, presented with pneumonia and severe oxygenation impairment that necessitated oxygen therapy. Oxygen therapy generally precludes effective nocturnal use of noninvasive IPPV. ~7 Data collection was inadequate for these patients to be included in this study. Another 23 patients learned how to use noninvasive aids, but because their use did not reverse their first episode of respiratory failure, they underwent tracheostomy ("unsuccessful group"). All of these patients developed respiratory failure suddenly, in many cases without hypercapnia observed during waking hours (by capnography) in the 1 to 3 preceding months, and often during an otherwise benign upper respiratory tract infection during which they could not successfully clear airway secretions. During these episodes most patients could maintain normal or low Paco2 levels when using noninvasive IPPV. However, because most had been found to be aspirating food and saliva during barium swallow evaluations, and were unable to fully abduct their vocal cords or firmly close their glotti, their PCEF were low and none were able to sufficiently clear their airways of aspirated food, saliva, and airway secretions. As a result, oxyhemoglobin desaturation and dyspnea could not be reversed by assisted coughing, and tracheostomy became necessary. Successful noninvasive aid users eventually required tracheostomy, or died, or they continue to use 24-hour noninvasire support. Those who underwent tracheostomy did so when, because of inadequate generation of expiratory flows to eliminate airway secretions by assisted coughing, or inability to prevent excessive ventilator insufflation air leakage out of the nose or mouth because of severe soft palate, lip, and buccal muscle paralysis, Sao2 could not be maintained within the normal range and the patients became dyspneic despite noninvasive ventilatory support. At this point, patients appeared to continuously aspirate their saliva and had decreased upper airway patency because of vocal cord paralysis. Pulmonary function parameters were longitudinally compared between the noninvasive aid users and the unsuccessful group. The duration of 24-hour dependence on noninvasive aids was calculated from the point at which the ventilator user could tolerate ventilator-free breathing for 15 minutes or less. The t test was used to compare the means of the ages of the chronological milestones and other respiratory parameters of the two groups. A p -<.05 was considered significant. RESULTS The rate of clinical disease progression was similar for both ALS groups (table 1). The 27 successful noninvasive aid users used noninvasive aids up to 16 hours a day for months and 24 hours a day with less than 15 minutes of free breathing time for 19.7 _ months (range, 1 to 65). This was 20.2 _ months (range, 1 to 65) before tracheostomy for 14 patients, 24.1 _ 15.6 months (range, 4

3 830 ALS SURVIVAL WITH RESPIRATORY AIDS, Bach Table 1: Phenotypic Comparison of ALS Patient Groups Successful Group Unsuccessful Group Number of patients Age at onset of ALS (22-66) ( ) Age at diagnosis 51.3 ± ± 15.1 ( ) ( ) Time from onset 1.8 ± ± 1.3 ( ) (0-6.1) Loss of ambulation 52.1 _ _ ( ) ( ) Time from diagnosis 1.9 _ ± 2.0 (0-10) (0-8.4) Time from onset 2.6 _ ± 2.7 ( ) ( ) Age at onset of ventilatory aid ± 13.7 ( ) ( ) Time from onset 4.9 ± ± 4.8 ( ) ( ) Time from diagnosis 3.0 ± ± 4.6 (0.3-13) (0-25) Noninvasive aid use* ( ) 0 Part of day 0.3 ± 1.1 ( ) 24 hours a day ( ) Total ventilatory support ± 3.2 ( ) ( ) Deceased All figures are in years + standard deviation except where indicated. * Noninvasive aids used part of day, ie, up to 16 hours per day; and 24 hours a day with little or no ventilator-free breathing time. to 50) for 7 patients who died without being intubated, and (range, 1 to 51) months for 6 patients still using noninvasive aids. These patients received ventilatory support by all means for a total of 3.9 +_ 5.2 years (range, 1 month to 26.5 years). This was years (range, 3 months to 10 years) for the 16 who died and 5.5 _ 8.0 years (range, 1 month to 26.5 years) for the 11 ventilator users still using support. Only 7 of these ventilator users underwent tracheostomy before gastrostomy. Despite relatively high VCs just before undergoing tracheostomy, all ventilator-free breathing time was lost within days to weeks and VC decreased precipitously once patients in the tracheostomy-only group had undergone tracheostomy for IPPV. The results of the nocturnal oximetry studies performed once the successful group required 24-hour aid without significant free breathing time were as follows: the 22 nasal IPPV users had mean Sao2 of 94%, with 5 having desaturation below 90% between 5% and 10% of the time and no prolonged desaturation below 85%; the 3 mouthpiece with lipseal a IPPV users had mean Sao2 of 95%; and the 2 exsufflation belt users had mean nocturnal Sao2 of 95% early on, diminishing ultimately to below 90% after months of nocturnal use. For daytime aid, 4 patients used Exsufflation Belts, b 10 used mouthpiece IPPV, and 13 whose lip and oral muscle function was inadequate to hold a mouthpiece used nasal IPPV. Two of the patients used exsufflation belts 24 hours a day. Custom molded nasal interfaces were constructed for 5 nasal IPPV users, and most nasal IPPV users had two or more nasal interfaces, mostly commercially available CPAP masks. They alternated mask use to avoid excessive pressure on skin surfaces in contact with any particular interface. Four of the nasal IPPV users were also eventually switched to lipseal IPPV because of the gradual deterioration in mean nocturnal Sao2 as the soft palate became incompetent to seal off the nose, thereby permitting excessive ventilator air delivery (insufflation) leakage out of the nose. Pulmonary parameter comparisons between the 27 successful noninvasive aid users and the 23 unsuccessful or tracheostomy-only ventilator users are listed in table 2. Because it is most likely that the majority of patients who did not use noninvasive aids when experiencing acute respiratory failure would have failed to use them successfully anyway because as a group they were less cooperative, had predominantly bulbar-onset ALS, severe bulbar muscle Table 2: Comparison of ALS Patient Groups' Pulmonary Parameters Successful Unsuccessful Group Group p (27 Patients) (23 Patients) value Within 3 months of initial ventilator use VC sitting (ml)* 732 _ _ (300-1,440) (540-1,670) VC supine (ml)t 672 _ ± ( ) (360-1,480) MIC (ml) 1, ,052 _ (990-1,945) (560-1,700) PCEF (L/sec) 4.6 _ 1.1 2,5 1.3 <.0005 ( ) (0-5.1) At the time of initial use noninvasive ventilatory support methods VC sitting (ml) 720 _ 231 (300-1,440) VC supine (ml) 668 _+ 228 ( ) MIC (ml) 1,404 ± 372 (990-1,945) PCEF (L/sec) 4.6 _ 1.1 ( ) At the point of requiring 24-hour noninvasive ventilatory support VC sitting (ml) 580 _+ 195 ( ) VC supine (ml) ( ) MIC (ml) 1,010 ± 205 (630-1,450) PCEF (L/sec) 4.1 ± 1.0 ( ) At tracheostomy$ VC sitting (ml) ± 427 <.0005 (0-470) ( ) VC supine (ml) 143 _ ± 411 <.0005 (0-440) ( ) MIC (ml) _+ 187 <.0005 (0-655) ( ) PCEF (L/sec) < 1 (0-2.6) < 1 (0-2.5) -- * Vital capacity measured with the subject in the sitting position. t Vital capacity measured with the subject supine. At tracheostomy for 14 patients in successful group.

4 ALS SURVIVAL WITH RESPIRATORY AIDS, Bach 831 involvement, and in some cases dementia, these 50 patients are considered unsuccessful users. There were significant differences between those who succeeded in using noninvasive aids for prolonged survival and the 23 who were unsuccessful, in VC (both absolute VC and VC as a percentage of predicted normal), MIC, and PCEF. The FEV1/FVC as a percentage of predicted normal was within normal limits before ventilator use for all patients and was not measured subsequently. The "successful group" had significantly lower VC but greater MIC and PCEF within 3 months of becoming ventilator-dependent and significantly lower VC at the time of switching from noninvasive aids to tracheostomy IPPV. The unsuccessful group had greater MIC at the time of tracheostomy, but the MIC was only slightly greater than the VC, indicating inability to use the oropharyngeal muscles to hold an adequate breath to permit an effective cough. Twenty of the 27 noninvasive aid users remained in the community setting. The remaining 7 were institutionalized after undergoing tracheostomy. Twelve of 13 ventilator users who used noninvasive aids and who never underwent tracheostomy were also never institutionalized. DISCUSSION This study demonstrated that individuals with ALS who could generate PCEF exceeding 3L/sec and who had a high MIC or high M][C VC difference could use noninvasive physical medicine aids as alternatives to tracheostomy for long-term, 24-hour-a-day ventilatory support and airway secretion management. Thus, the ability to hold a deep insufflation and to generate adequate PCEF can decrease the risk of pulmonary complications and eliminate the need for tracheostomy despite the patient retaining little or no measurable VC and no ventilator-free breathing time] 8'19 This is not surprising because noninvasive methods of ventilatory support can prov;tde normal alveolar ventilation for anyone with global alveolar hypoventilation irrespective of the extent of inspiratory muscle dysfunction; however, irreversible airway obstruction because of failure to effectively mobilize airway secretions invariably leads to oxyhemoglobin desaturation and, eventually, pulmonary infiltration. Airway secretions are normally eliminated by coughing. A normal cough involves taking a deep breath to about 2.3L, 2 closing the glottis, and using expiratory muscles to create sufficient thoracoabdominal pressures to generate 6 to 16L/sec of PCEF, depending on sex, height, and age, 2 '2~ on glottic opening. The effectiveness of airway mucus clearance is largely &~pendent on the magnitude of the PCEF. 22 Bulbar muscle function is vital both for closing the glottis to permit adequate generation of precough pressures and for optimizing airway patency by vocal cord abduction during the explosive decompression that actually generates the flows. No specific tests, however, have been developed to quantitate bulbar muscle function and, in particular, the relationship between bulbar function and risk of pulmonar-y complications. Although they required 24-hour ventilator use, the noninvasive aid users retained MICs that were several hundred milliliters greater than their VCs. Their greater bulbar muscle function and glottic control enabled them to have assisted PCEFs greater than 3L/sec while avoiding excessive aspiration of saliva and food. Thus, tracheal intubation was unnecessary either for ventilatory support or for airway secretion clearance in this group despite, in many cases, total absence of respiratory muscle function. The low incidence of need for gastrostomy tube placement also signified better bulbar muscle function in this group. In the unsuccessful group, tracheostomy was performed during episodes of acute respiratory distress triggered by aspiration of food, upper airway secretions, or both, which resulted in oxyhemoglobin desaturation that could not be reversed by the use of noninvasive respiratory muscle aids. During episodes of bronchial congestion, mucus plugging causes sudden severe oxyhemoglobin desaturations and respiratory distress, and VC and assisted PCEF decrease precipitously. When assisted PCEF decreases below about 3L/ sec, indicating poor inspiratory volumes and glottic control, airway debris cannot be cleared noninvasively, Sao2 cannot be normalized, and tracheal intubation is necessary for survival. Poor glottic control prevents both the retention of adequate insufflation volumes for an effective cough and the upper airway patency needed to permit explosive decompression. For those patients who underwent tracheostomy, there was an additional post-tracheostomy loss in VC and a rapid loss of ventilator-free breathing time that may be explained by exacerbation of weakness due to acute illness, 23 inspiratory muscle deconditioning from the tendency to use tracheostomy IPPV for unnecessarily long periods of time, and the fact that tracheostomy IPPV users tend to complain of air hunger unless they are hyperventilated. 24 This decreases tolerance for free breathing time, which may, in turn, lead to respiratory muscle deconditioning. By normalizing alveolar ventilation and eliminating airway secretions, the use of noninvasive respiratory muscle aids eases the patient's and family's feelings of helplessness when shortness of breath or airway congestion occurs in the home. Use of noninvasive aids can also test the family's resolve and the patient's home support before resort to tracheostomy needs to be considered for some, and it can help maintain the patient in the communityy We have recently had considerable success in some patients with less than 3L/sec of unassisted or manually assisted PCEF by using mechanical insufflation-exsufflation to clear airway secretions to renormalize Sat2. ~8 This technique bypasses the need for glottic control to retain a deep insufflation because the deep insufflation is delivered via an oralnasal mask just before an instantaneous decrease in pressure of approximately 80cmHzO to generate expiratory flow. It remains to be seen whether this method will enable many ALS patients with PCEF below 3L/sec to maintain adequate vocal cord abduction and upper airway patency, thus permitting the use of this technique to effectively eliminate airway secretions on a long-term basis. Because the majority of patients who were in the group that failed to use noninvasive aids in the prescribed manner would have most likely been unsuccessful with them, we conclude that noninvasive respiratory muscle aids can prolong survival and delay need for tracheostomy for at least a significant minority of ALS patients. In particular, patients

5 832 ALS SURVIVAL WITH RESPIRATORY AIDS, Bach who have adequate bulbar muscle function to permit assisted PCEF to exceed 3L/sec can use noninvasive ventilatory support and airway secretion management alternatives to tracheostomy IPPV and suctioning. These patients can generally clear aspirated food, saliva, or airway secretions sufficiently to maintain virtually normal Saoz with the use of noninvasive inspiratory and expiratory aids. Thus, aspiration of food or saliva appears to be significant only when airway clearance mechanisms, including assisted coughing, are inadequate to maintain normal Sa02 despite effective ventilatory support. Extent of ventilatory failure, even absence of measurable VC, is not in itself an indication for tracheostomy. It is instructive that there are no previous comparable studies of this nature. These noninvasive physical medicine applications deserve more widespread application to spare patients the hazards, cost, discomfort, and impairments of swallowing, taste, communication, and appearance associated with tracheostomy. 26 Further information is available regarding the use of noninvasive respiratory muscle aids.5'6'] 'J3'lS'19 References 1. Moss AH, Casey P, Stocking CB, Roos RP, Brooks BR, Siegler M. Home ventilation for amyotrophic lateral sclerosis patients: outcomes, costs, and patient, family, and physician attitudes. Neurology 1993; 43: Bach JR, Campagnolo DI, Hoeman S. Life satisfaction of individuals with Duchenne muscular dystrophy using long-term mechanical ventilatory support. Am J Phys Med Rehabil 1991 ;70: Bach JR, Campagnolo D. Psychosocial adjustment of post-poliomyelitis ventilator assisted individuals. Arch Phys Med Rehabil 1992;73: Oppenheimer EA, Baldwin-Myers A, Tanquary P. Ventilator use by patients with amyotrophic lateral sclerosis. In: Make B, editor. Proceedings of the International Conference on Pulmonary Rehabilitation and Home Ventilation. Denver: National Jewish Center, 1991: Bach JR, Alba AS. Management of chronic alveolar hypoventilation by nasal ventilation. Chest 1990;97: Bach JR, Alba AS, Saporito LR. Intermittent positive pressure ventilation via the mouth as an alternative to tracheostomy for 257 ventilator users. Chest 1993; 103: Bach JR, Saporito LS. Indications and criteria for decannulation and transition from invasive to noninvasive long-term ventilatory support. Respir Care 1994;39: Bach JR, Alba AS. Total ventilatory support by the intermittent abdominal pressure ventilator. Chest 1991;99: Bach JR, Beltrame F. Alternative methods of ventilatory support. In: Rothkopf MM, Askanazi J, editors. Intensive homecare. Baltimore: Williams & Wilkins, 1992: McDermott I, Bach JR, Parker C, Sortor S. Custom-fabricated interfaces for intermittent positive pressure ventilation. Int J Prosthodontics 1989;2: Bach JR. Update and perspectives on noninvasive respiratory muscle aids: part 2--the expiratory muscle aids. Chest 1994; 105: Alba A, Pilkington LA, Kaplan E, Baum J, Schultheiss M, Ruggieri A, et al. Long-term pulmonary care in amyotrophic lateral sclerosis. Respir Ther 1976;6:49-56, Bach JR. Pulmonary rehabilitation considerations for Duchenne muscular dystrophy: the prolongation of life by respiratory muscle aids. Crit Rev Phys Rehabil Meal 1992;3: Canny GJ, Szeinberg A, Koreska J, Levison H. Hypercapnia in relation to pulmonary function in Duchenne muscular dystrophy. Pediatr Pulmonology 1989;6: Braun NMT, Arora NS, Rochester DF. Respiratory muscle and pulmonary function in polymyositis and other proximal myopathies. Thorax 1983;38: Miller WF. Rehabilitation of patients with chronic obstructive lung disease. Med Clin North Am 1967;51: Bach JR, Robert D, Leger P, Langevin B. Sleep fragmentation in kyphoscoliotic individuals with alveolar hypoventilation treated by nasal IPPV. Chest 1995; 107: Bach JR. Mechanical insufflation-exsufflation: comparison of peak expiratory flows with manually assisted and unassisted coughing techniques. Chest 1993; 104: Bach JR, Smith WH, Michaels J, Saporito LS, Alba AS, Dayal R, et al. Airway secretion clearance by mechanical exsufflation for postpoliomyelitis ventilator assisted individuals. Arch Phys Med Rehabil 1993; 74: Leith DE. Cough. In: Brain JD, Proctor D, Reid L, editors. Lung biology in health and disease: respiratory defense mechanisms, part 2. New York: Marcel Dekker, 1977: Leiner GC, Abramowitz S, Small MJ, Stenby VB, Lewis WA. Expiratory peak flow rate. Standard values for normal subjects. Am Rev Respir Dis 1963;88: King M, Brock G, Lundell C. Clearance of mucus by simulated cough. J Appl Physiol 1985;58: Mier-Jedrzejowicz A, Brophy C, Green M. Respiratory muscle weakness during upper respiratory tract infections. Am Rev Respir Dis 1988; 138: Haber II, Bach JR. Normalization of blood carbon dioxide levels by transition from conventional ventilatory support to noninvasive inspiratory aids. Arch Phys Med Rehabil 1994;75: Bach JR, Intintola P, Alba AS, Holland I. The ventilator-assisted individual: cost analysis of institutionalization versus rehabilitation and inhome management. Chest 1992; 101: Bach JR. A comparison of long-term ventilatory support alternatives from the perspective of the patient and care giver. Chest 1993; 104: Suppliers a. Puritan Bennett Inc., 1915 Clements Road, Unit 7, Picketing, Ontario LIW 3V1. b. Lifecare International Inc., 1401 West 122nd Ave., Westminster, CO c. Wright Spirometer Mark 14; Ferraris Development and Engineering Co., Ltd., 26 Lea Valley Trading Estate, Angel Road, Edmonton, London N18 3JD. d. Peak Flow Meter Model 710; Health Scan Products, Inc., 908 Pompton Avenue, Cedar Grove, NJ e. Ohmeda model 3760; Ohmeda Inc., 1315 West Century Drive, Louisville, CO f. Microspan 8090 Capnograph; Biochem International Inc., W238 N1650 Rockwood Drive, Waukesha, WI