Physiologic response of ventilator-dependent patients with chronic obstructive pulmonary disease to proportional assist ventilation and continuous positive airway pressure

To investigate the physiologic effects of proportional assist ventilation ( PAV) in difficult-to-wean, mechanically ventilated patients with advanced C OPD, we measured in eight ICU patients the breathing pattern, neuromuscular drive (P-0.1), lung mechanics, and inspiratory muscle effort (PTPdi and PT Ppl) during both spontaneous breathing (SB) and ventilatory support with PA V, CPAP, and CPAP + PAV (in random sequence). PAV (volume assist [VA] and f low assist [FA]) was set as follows: dynamic lung elastance and inspiratory pulmonary resistance were measured during SE; then VA and FA were set to c ounterbalance the elastic and resistive loads exceeding the normal values, respectively, the inspiratory muscles bearing a normal elastic and resistiv e workload. CPAP was set close to dynamic intrinsic PEEP (8.3 +/- 3.4 cm H2 O). We found significant reductions in P-0.1 and PTPdi during both CPAP (-4 5 and -37%, respectively) and PAV (-50 and -48%, respectively). However, on ly 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 br eathing pattern compared with SE (tidal volume: 0.69 +/- 0.33 versus 0.33 /- 0.14 L; breathing frequency, 14.6 +/- 4.6 versus 21.0 +/- 6.5 breaths/mi n, respectively), without generating ineffective inspiratory efforts. We co nclude that in difficult-to-wean COPD patients, (1) PAV improves ventilatio n 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 thos e found in normal subjects.