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 +/- 20.3 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.