Changes in distribution of cardiac output by surface-induced deep hypothermia in dogs

The effects of surface-induced deep hypothermia on organ blood flow and on the distribution of cardiac output were investigated in the anesthetized dog. Organ flows were determined by the radioactive microsphere technique. Phenoxybenzamine (POB) was administered prior to hypothermia to minimize vasoconstriction and hence facilitate cooling. Measurements were made before POB, on stabilization after POB, and during hypothermia. Cardiac output was reduced by POB as was blood flow to the pancreas, small intestine, and skeletal muscle. Hypothermia, following POB, produced a further fall in Q and during this maneuver blood flow fell in all organs and vascular beds studied. The relative distribution of Q during hypothermia was essentially the same as in the control except the brain, kidneys, and pancreas received a smaller fraction of the total output. The relatively normal distribution of a reduced cardiac output during hypothermia was in marked contrast to distribution of comparable low cardiac output induced by hemorrhage. In the latter condition, the fraction of the cardiac output perfusing the brain, kidneys, adrenals, and hepatic artery was increased.