RELATIVE DISTRIBUTION OF CARDIAC OUTPUT IN ACUTE HYPOXEMIA

Abstract

The return of blood flow to the heart through the superior or the inferior vena cava was measured in 13 dogs subjected to acute hypoxia produced by N2 breathing. With the onset of acute hypoxemia the blood flow and pressure increased. After about 75 sec. the flow through the inferior vena cava fell rapidly to nearly zero levels although the superior vena cava flow remained above normal. As the hypoxemia progressed, the superior vena cava flow also diminished. At this time the blood pressure was low and the heart was seen to be dilated and beating slowly. Reoxygenation resulted in an immediate recovery of cardiac function, of blood flow in both circuits and of the blood pressure, which, with a temporary overswing, returned to the previous control levels within a few minutes. The mechanisms of some of the hemodynamic changes occurring during the induction of and recovery from acute hypoxemia are discussed.