EFFECT ON PULMONARY GAS EXCHANGE OF VARIATIONS IN INSPIRATORY FLOW RATE DURING INTERMITTENT POSITIVE PRESSURE VENTILATION

Abstract

Eleven patients anaesthetized with sodium thiopentone, tubocurarine and halothane and ventilated with constant volume intermittent positive pressure were the subjects of a study of the effects of changes in inspiratory flow rate on alveolar-arterial oxygen difference, physiological shunt and physiological deadspace. The physiological deadspace increased significantly when inspiratory flow rate was raised above 25 l./min, but no change was demonstrable in venous admixture effect. The magnitude of the values derived and the possible mechanisms involved are discussed. The existence of a series of negative feed-back loops, with respect to the reduction of alveolar-arterial oxygen gradient, by intermittent positive pressure, is suggested.