Blood pressures, heart rate and finger volumes were recorded while supine subjects submitted to various degrees of continuous negative-pressure breathing. The lowest pressure was –30 cm H2O. Systolic and diastolic arterial pressures as well as heart rate remained essentially unchanged. The peripheral venous pressure estimated by an indirect method was slightly lowered. Finger plethysmography indicated a peripheral vasoconstriction to the same degree as observed during positive-pressure breathing. Various considerations suggest that during negative-pressure breathing the veins entering the thoracic cavity collapse and effectively divide the circulation into the thoracic one which operates at a considerably reduced pressure, and the nonthoracic circulation which is maintained at normal pressures. The pressure difference between these two circulations is maintained by the left ventricle.
Submitted on February 8, 1960