Dynamics of Central Venous Resistance With Observations on Static Blood Pressure

Abstract

A special external venous circuit was used in 37 expts. on open-chest dogs for the study of progressive resistance to the return of blood to the heart. Studies were made on blood flow, arterial pressure, peripheral venous pressure, and right auricular pressure. As the flow of blood decreased progressively to zero, the arterial pressure fell slowly at 1st, then rapidly, and the venous pressure rose slightly to approach arterial pressure. The extrapolated point of approach of these 2 pressures compared favorably with static blood pressures measured by the following method. In 66 dogs the heart was fibrillated and arterial and venous pressures were allowed to come to equilibrium (sometimes aided by a pump between the arterial and venous systems). Various values for static blood pressure, and consequently the upper limit of venous pressure, under various conditions, were found to be: 1) within a few sec. after the hearts of normal dogs were fibrillated and before vasomotor reflexes could develop[long dash]5.96 mm. Hg; 2) after developing the most powerful vasomotor constriction that could be attained by a Cushing reflex[long dash]17.0 mm. Hg; 3) after giving infusions of fluid immediately before fibrillation of the heart[long dash]unlimited, depending on the amt. of fluid and how long before fibrillation it was admd. In the progressive central resistance expts. it was found that when the auricular pressure decreased 1 mm. Hg as the result of impeded venous return (other factors remaining constant as best they could be controlled), the cardiac input decreased an avg. of 37%.