[Prolongation of circulation time during brain ischemia-induced hypertension in the rabbit]

Circulation time (CT) is markedly prolonged when arterial pressure is extremely elevated by global brain ischemia which elicits also bradycardia, decrease in cardiac output and apnea in anesthetized rabbits. To study the cause of the prolongation of CT, we measured separately CT in the large veins, cardiopulmonary circulation system (CPS) and large arteries by a dye-densitometer before and during the brain ischemia, and also examined effects of apnea and bradycardia on CT in the large veins and CPS. CT during the brain ischemia was prolonged in each portion as compared to that before the brain ischemia. The prolongation was shortest in the large veins and longest in the CPS. During the brain ischemia with apnea, there was a significant linear relationship between heart rate and the inverses of CT in the large veins, but not in the CPS. When artificial ventilation was performed during brain ischemia-induced apnea, the linear relationship became significant also in the CPS. We conclude as follows; During global brain ischemia the prolongation of CT occurs primarily in the large arteries due to constriction of the small arteries and it progresses towards the CPS and large veins. The bradycardia prolongs CT in the large veins and CPS, and the apnea may produce hypoxic pulmonary vasoconstriction which may also contribute to the prolongation of CT in the CPS.