CIRCULATORY EFFECTS OF RAISED AIRWAY PRESSURE DURING CYCLOPROPANE ANESTHESIA IN MAN 1

Abstract

It is generally agreed (3-7) that the most striking circulatory effect of positive pulmonary pressure, either intermittent or continuous, in normal conscious individuals, is a reduction of cardiac output. In some subjects cardiac output may be maintained during pressure breathing (7), but the stroke volume of the heart is low, and its output is maintained because of a marked rise in the pulse rate. The reduction of stroke volume is presumed to result (4) from a diminished filling of the right ventricle, caused by the rise in intrathoracic pressure occurring when the lungs are inflated under positive pressure. In response to these changes, a vasoconstriction occurs (2, 8-10) which tends to reduce peripheral pooling of blood and improves the return of blood to the heart. In animals studied under general anesthesia, the arterial pressure declined more in response to raised airway pressure when anesthesia was profound than when it was less deep ( 11 ). It has been assumed that the same would be true in man