Pulmonary Capillary Flow Pulse and the Site of Pulmonary Vasoconstriciton in the Dog.

• The amplitude of the capillary pulse is markedly dependent on resistance to blood flow through precapillary vessels. Recent studies by Lee and DuBois indicate that blood flow through the pulmonary capillaries * is normally pulsatile. This result points to the possibility that reactions of pulmonary arterial vessels may be studied by their effects on the amplitude of the pulmonary capillary pulse. We have adapted, therefore, the plethysmographic-nitrous oxide technique of Lee and DuBois to a detailed experimental analysis of factors affecting the amplitude of the pulmonary capillary pulse in dogs. The results indicate that the purely mechanical effects on pulse amplitude of changes in heart rate or pulmonary arterial pressure can be distinguished from the effects of active changes in caliber of the pulmonary vessels. Evidence will also be presented that the principal site of pulmonary vasoconstriction induced by hypoxia involves the precapillary vessels.