HEMODYNAMIC ALTERATIONS IN NORMOTENSIVE AND HYPERTENSIVE SUBJECTS DURING THE PYROGENIC REACTION

Abstract

A study of the hemodynamic changes induced by the afebrile pyrogenic reaction (in pre-medicated subjects) has been made in 2 normal and 6 hypertensive persons. In every instance, cardiac output increased as a result of an increase in both pulse rate and stroke volume, while total peripheral resistance decreased. In normal subjects and in some hypertensive individuals, reciprocal changes in peripheral resistance and cardiac output resulted in adequate maintenance of arterial pressures. In 2 hypertensive subjects, however, arterial pressure fell to normotensive levels and in a third marked hypotension developed. In the latter, a change to head-down position was necessary to maintain the blood pressure at physiologically adequate levels. Normotensive subjects are capable of adequate vascular adjustment to postural change during the pyrogenic reaction. Among hypertensives, however, even though adjustment may be adequate in the recumbent position, orthostasis may result in a shock-like state. The observations reported here indicate that a fall in cardiac output is responsible for circulatory inadequacy under these conditions. Renal hyper-emia occurred in each instance studied and in the 5 subjects in whom cardiac output and renal blood flow were measured simultaneously, the renal fraction increased, implying relatively greater vasodilation in the renal vascular bed than in the rest of the circulatory system.