Intrinsic myocardial function in hemorrhagic shock

Hemorrhage is a stress on the cardiovascular system that results in decreas ed loading of the heart but also decreased blood pressure and thus decrease d perfusion pressure for tissue blood flow. The heart's response to hemorrh age is governed by both an increase in sympathetic nervous system activatio n of the heart and decreased preload and afterload for the heart. Whether t he heart can maintain normal contractile function and reserves under condit ions of prolonged hemorrhagic shock is not clear. To assess the effects of hemorrhagic shock of different lengths on intrinsic cardiac contractile fun ction, guinea pigs were surgically prepared for the measurement of blood pr essure, heart rate, and cardiac output and blood samples were taken for the measurement of metabolic indices of cardiovascular stress. Fifty percent o f the animals' blood volume was removed and then animals were followed for 1, 2, or 3 h of hemorrhagic shock. Hearts were then removed for measurement of intrinsic contractile function. Hearts from animals exposed to 1 or 2 h of shock exhibited normal ventricular function although hearts removed aft er 3 h exhibited changes in ventricular function. Maintenance of normal car diac function through at least 2 h of shock must represent adequate physiol ogic modulation of coronary blood flow to deliver adequate oxygen to match the myocardial oxygen demands under conditions of severe blood loss. This b alance may be disrupted by 3 h of shock thus resulting in loss of contracti le reserve.