Influence of hypoxia on mean circulatory pressure and cardiac output

Abstract

Many measurements have been made of the response of the arterial circuit to changes in the O2 content of inspired air. The response of the venous circuit is less well known. The present study is an attempt to delineate the contribution of the venous circuit, and in particular that of the venules and small veins, and the response of the total circulation to hypoxia, utilizing the mean circulatory pressure as an index of venous activity. Arterial pressure (AP), right atrial pressure (RAP), and mean circulatory pressure (MCP) were recorded fa 46 dogs both prior to and during inhalation of 8% O2 in N. The gradient for venous return (GVR) was taken as MCP-RAP. Cardiac output was recorded by an electromagnetic flow probe implanted several weeks prior to the experiment. After 5 min. of respiration with the hypoxic gas, AP increased 15% above control. Cardiac output was elevated 45%. RAP decreased 25%, whereas MCP increased 26.8%. The changes in RAP and MCP resulted in a net increase fa GVR of 27.6%. The rise fa AP was not of sufficient magnitude to have resulted fa so large a MCP increase. RAP declined, thus ruling out major influence of large veins.