A Physiologic Reference Point for Measuring Circulatory Pressures in the Dog—Particularly Venous Pressure

¹ From the Department of Physiology and Biophysics, School of Medicine, University of Mississippi, Jackson, Mississippi

A physiologic reference point for measuring pressures in the circulatory system has been located by rotating dogs into all positions in space and locating the axes of rotation at which least variation in right atrial pressure occurs. This point remains extremely precise from one animal to another and also extremely precise regardless of the state of the circulation of the animal. The apparent reason for such precise localization is that the heart operates as a feedback control system for controlling the end-diastolic pressure in the right ventricle; that is, increasing the end-diastolic pressure increases cardiac output, and this automatically returns the end-diastolic pressure back toward normal. The physiologic reference point was found to be located approximately in the lower portion of the right ventricle described by the following dimensions: a) midway between the two lateral margins of the chest; b) anterior to the back 0.614 times the thickness of the chest; c) caudal to the sternal notch 0.767 times the distance from the sternal notch to the tip of the xiphoid process.