F Maltais, H Reissmann and SB Gottfried
Division of Respiratory, Montreal General Hospital, Quebec, Canada.

Exercise training has been of limited success in patients with severe chronic airflow obstruction (CAO), in part because of the reduced ventilatory capacity and excessive dyspnea experienced. Pressure support (PS) is a new form of mechanical ventilation which can effectively assist ventilation when applied noninvasively to patients in acute respiratory failure. It was hypothesized that PS might also be used to improve exercise performance, and ultimately physical conditioning, in ambulatory patients with CAO undergoing exercise training. To begin to address this concept, the objectives of the present study were (1) to examine the feasibility of providing PS to exercising patients with CAO and (2) to determine its effects on breathing pattern, inspiratory effort, and dyspnea. Flow and volume, mouth, esophageal, and gastric pressure were measured in seven patients with severe CAO (mean FEV1 = 0.75 +/- SEM 0.09 L) performing constant workload bicycle exercise (33 +/- 6 watts) during control conditions and with the application of PS (approximately 10 cm H2O). PS increased minute ventilation as a result of changes in both tidal volume and respiratory rate. This occurred despite marked reductions in inspiratory effort, as indicated by the pressure-time integrals of esophageal (68 +/- 5% control, p < 0.0005) and transdiaphragmatic pressure (52 +/- 8% control, p < 0.0005). Using a 5-point bidirectional scale to assess changes in dyspnea, breathlessness improved significantly with the addition of PS (2.3 +/- 0.6, p < 0.05) and worsened to a similar degree when it was removed (2.1 +/- 0.5, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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