Objective: To compare the short-term physiologic effects of mask pressure support ventilation (PSV) and proportional assist ventilation (PAV) in patients in clinically stable condition with chronic ventilatory failure (CVF).
Design: Randomized, controlled physiologic study.
Setting: Lung function units of two pulmonary rehabilitation centers.
Patients: Eighteen patients with CVF caused by COPD (11 patients) and restrictive chest wall diseases (RCWDs) [7 patients].
Methods: Assessment of breathing pattern and minute ventilation (E), respiratory muscles and lung mechanics, and patient/ventilator interaction during both unassisted and assisted ventilation. After baseline assessment during spontaneous breathing (SB), mask PSV and PAV were randomly applied at the patient's comfort, with the addition of the same level of continuous positive airway pressure (2 cm H2O or 4 cm H2O in all patients), for 30 min each, with a 20-min interval of SB between periods of assisted ventilation.
Results: A longer time was spent to set PAV than PSV (663 +/- 179 s and 246 +/- 58 s, respectively; p < 0.001). Mean airway opening pressure (Pao) computed over a period of 1 min, but not peak Pao, was significantly lower with PAV than with PSV (151 +/- 45 cm H2O/s/min and 207 +/- 73 cm H2O/s/min, respectively; p < 0.002). Tidal volume (VT) exhibited a greater variability with PAV than with PSV (variation coefficient, 16.3% +/- 10.5% vs 11.6% +/- 7.7%, respectively; p < 0.05). Compared with SB, both modalities resulted in a significant increase in VT (by 40% and 36% with PAV and PSV, respectively, on average) and E (by 37% and 35%) with unchanged breathing frequency and duty cycle. Both modalities significantly reduced esophageal (by 39% and 51%) and diaphragmatic (by 42% and 63%) pressure-time products, respectively. Ineffective efforts were observed with neither modes of assistance in any patient.
Conclusions: In resting, awake patients in clinically stable condition with CVF caused by either COPD or RCWD, noninvasive application of PAV, set at the patient's comfort, was not superior to PSV either in increasing VT and E or in unloading the inspiratory muscles. We failed to find any difference in patient/ventilator interaction between ventilatory modes.