Effects of oscillating and intermittent ventilatory flow on efficacy of pulmonary O 2 transfer in the duck

Abstract

Parabronchial gas exchange was studied in ducks with unidirectional ventilation at constant or periodically changing flow rate. Two types of periodic flow pattern were used, sinusoidal oscillation with minimum flow close to zero (Series I) and intermittent flow directed for equal periods of time to either lung (Series II). Lung diffusing capacity for O 2 (D) was assessed from measurements of O 2 partial pressures in lung gas and blood at constant ventilatory flow, and an apparent O 2 diffusing capacity (D app) was calculated similarly using measurements obtained during periodic flow. Deviations of Dapp D from unity were ascribed to effects of periodic flow on gas exchange. With frequencies of sinusoidal changes (Series I) close to resting respiratory rates of ducks (8 to 13 min −1), D app was on the average only slightly smaller than D. Using the intermittent flow pattern (Series II) at longer periods (20 sec) a decreased efficacy of O 2 transfer could be demonstrated, Dapp D under these conditions averaging 0.74. It is concluded that under physiological conditions the periodic ventilatory flow pattern constitutes no significant impairment of parabronchial gas exchange and that analysis of gas exchange using simplifying models is not invalidated by the assumption of continuous rather than periodic flow.