High-frequency positive-pressure ventilation with the MA-1 ventilator.

A conventional, low-frequency ventilator was modified to ventilate dogs at high frequencies of 85 to 185 cycle/min while cardiovascular and pulmonary variables were monitored. Although gas transport was adequate, cardiac output was diminished when compared to low-frequency ventilation. The addition of an in-line pneumotachograph markedly increased PaCO2 during high-frequency ventilation. Carbon dioxide transport was primarily dependent upon the magnitude of the tidal volume at all high frequencies tested.