Effects of inspiratory pressure oscillation on pulmonary gas exchange and circulatory functions in anesthetized, mechanically ventilated dogs.

Anesthetized, mechanically ventilated dogs were used to study the effects of inspiratory pressure oscillation on gas exchange. Respiratory failure was induced in dogs artificially, changing either tidal volume or ventilatory rate. Pressure oscillation of approximately 2 Hz with amplitudes of 2 to 7 cmH2O was applied on the inspiratory phase of mechanical ventilation. PaO2 and PaCO2 were improved consistently by pressure oscillation while minute ventilation was kept fixed. No significant change was observed in AaDO2, cardiac output, heart rate, ECG and both systemic and pulmonary arterial pressures under oscillated ventilation. The oscillated ventilation could be continued for more than 60 minutes without causing any significant change in circulatory function. The ratio of alveolar ventilation to minute ventilation (VA/VE) increased and that of dead space to tidal volume (VD/VT) decreased significantly. The oscillated ventilation while breathing He-O2 and SF6-O2 showed no consistent difference in the effects on gas exchange. It can be concluded that simple pressure oscillation improves gas mixing in the lungs and may be applied to respiratory care. However the mechanism remains to be elucidated.