Am. J. Respir. Crit. Care Med., Volume 159, Number 5, May 1999, 1510-1517

Physiologic Response of Ventilator-dependent Patients with Chronic Obstructive Pulmonary Disease to Proportional Assist Ventilation and Continuous Positive Airway Pressure

LORENZO APPENDINI, ANDREA PURRO, MARTA GUDJONSDOTTIR, PAOLO BADERNA, ANTONIO PATESSIO, SILVIO ZANABONI, CLAUDIO F. DONNER, and ANDREA ROSSI

Salvatore Maugeri Foundation, IRCCS, Rehabilitation Institute of Veruno, Division of Pulmonary Disease, Veruno (No), Italy; and Respiratory Division, Ospedale Maggiore di Borgo Trento, Azienda Ospedaliera di Verona, Verona, Italy

To investigate the physiologic effects of proportional assist ventilation (PAV) in difficult-to-wean, mechanically ventilated patients with advanced COPD, we measured in eight ICU patients the breathing pattern, neuromuscular drive (P_0.1), lung mechanics, and inspiratory muscle effort (PTPdi and PTPpl) during both spontaneous breathing (SB) and ventilatory support with PAV, CPAP, and CPAP + PAV (in random sequence). PAV (volume assist [VA] and flow assist [FA]) was set as follows: dynamic lung elastance and inspiratory pulmonary resistance were measured during SB; then VA and FA were set to counterbalance the elastic and resistive loads exceeding the normal values, respectively, the inspiratory muscles bearing a normal elastic and resistive workload. CPAP was set close to dynamic intrinsic PEEP (8.3 ± 3.4 cm H₂O). We found significant reductions in P_0.1 and PTPdi during both CPAP (45 and 37%, respectively) and PAV (50 and 48%, respectively). However, only the combination of PAV and CPAP brought P_0.1 (1.69 ± 0.97 cm H₂O) and PTPdi (100 ± 68 cm H₂O · s) within normal values, and ameliorated the breathing pattern compared with SB (tidal volume: 0.69 ± 0.33 versus 0.33 ± 0.14 L; breathing frequency, 14.6 ± 4.6 versus 21.0 ± 6.5 breaths/min, respectively), without generating ineffective inspiratory efforts. We conclude that in difficult-to-wean COPD patients, (1) PAV improves ventilation and reduces both P_0.1 and inspiratory muscle effort; (2) the combination of PAV and CPAP can unload the inspiratory muscles to values close to those found in normal subjects.

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