Transmission of the Blood Flow Pulse through the Pulmonary Arterial Tree of the Dog

Abstract

We have made simultaneous measurements of the instantaneous flow in the main pulmonary artery using an electromagnetic flowmeter and the pulmonary capillaries using the nitrous oxide body plethysmograph method in six lightly anesthetized and spontaneously breathing dogs. We measured the transmission of the flow wave in the pulmonary arterial tree at a variety of heart rates and during alveolar hypoxia. Fourier analysis enabled us to study transmission in the intact animal in a way similar to that of imposed oscillations of flow in the isolated organ. The amplitude of the pulmonary capillary flow pulse was approximately half that in the main pulmonary artery. There was progressive decrease in amplitude from the first to the fourth harmonic in both the pulmonary arterial and pulmonary capillary flow pulses. Harmonics above the fourth were small and variable in amplitude. Transmission between pulmonary valve and capillaries was independent of heart rate. Hypoxia did not affect transmission. Assuming that the increase in resistance in this instance was due to precapillary vasoconstriction, this finding suggests that other factors may offset the effect of increase in resistance upon transmission.