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 zero end-expiratory pressure. Although no significant difference was seen between the patterns in animals with normal lung function (PaO2 greater than 85 Torr on the ascending pattern), the descending pattern resulted in a rise in PaO2 of about 10% (P less than 0.01) in animals with abnormal lung function (PaO2 less than 70 Torr on the ascending pattern). No significant difference in PaCO2 or cardiac output was detected when flow pattern was changed in any of the animals. We conclude that inspiratory flow pattern is not a significant factor when ventilating normal lungs, but may improve gas exchange significantly when severe ventilation-perfusion maldistributions exist.