Effect of negative pressure ventilation on ventilatory muscle endurance in patients with severe chronic obstructive pulmonary disease.

Abstract

We studied five men with chronic obstructive pulmonary disease (COPD) (mean age, 65 +/- SEM 2 yr; FEV1, 0.68 +/- 0.08 L; and FEV1/FVC, 38 +/- 2%) to determine the relationship between ventilatory muscle endurance (VME) and ventilatory muscle rest (VMR) elicited by negative-pressure ventilation (NPV). VME was measured as the maximal sustainable ventilation (MSVC) that the subjects could maintain for 12 min. Prior to therapy, MSVC for the subjects was 25.0 +/- 3.6 L/min. During the therapy phase, subjects received 4 wk of daily "in-hospital-supervised" NPV therapy (4 h/day). While subjects received therapy, we quantified VMR by (1) the percentage of breaths that were "in synchrony" and by (2) the percentage of breaths showing "turn-off" of the diaphragmatic EMG signal (EMGdl). During the therapy sessions, 93 +/- 2% of breaths were in synchrony, whereas 66 +/- 11% showed EMGdl turn-off. During post-therapy testing, an increase in MSVC was noted in each of the subjects; the mean increase was 4.0 +/- 1.3 L/min (p less than 0.05), which represented an increase of 16 +/- 4% over pretherapy values. Increases in MSVC were highly correlated with both the percentage of in-synchrony breaths (r = 0.96, p less than 0.01) and the percentage of breaths showing EMGdl turn-off (r = 0.92, p less than 0.02). However, NPV therapy elicited no other improvements in either clinical or laboratory measurements. Moreover, patients exhibited marked dyspnea with initiation and termination of daily NPV therapy.(ABSTRACT TRUNCATED AT 250 WORDS)