EFFECTS OF INSPIRATORY FLOW PATTERN ON GAS-EXCHANGE IN NORMAL AND ABNORMAL LUNGS

To study the influence of inspiratory flow pattern on gas exchange in normal and abnormal lungs, 15 dogs were mechanically ventilated with the ascending or descending half of a rectified sine-wave flow pattern during pentobarbital anesthesia. Blood gas status and cardiac output were monitored during each pattern. Pulmonary injury was induced in 9 animals by prior injection of oleic acid into the right atrium. Ventilation was with room air and end-expiratory pressure. Although no significant difference was seen between the patterns in animals with normal lung function (PaO2 [arterial O2 pressure] > 85 Torr on the ascending pattern), the descending pattern resulted in a rise in PaO2 of about 10% (P < 0.01) in animals with abnormal lung function (PaO2 < 70 Torr on the ascending pattern). No significant difference in PaCO2 [arterial O2 pressure] or cardiac output was detected when flow pattern was changed in any of the animals. Inspiratory flow pattern was not a significant factor when ventilating normal lungs, but it may improve gas exchange significantly when severe ventilation-perfusion maldistributions exist.