HEMODYNAMIC SEQUELAE OF VENTRICULAR TACHYARRHYTHMIAS ON CEREBRAL BLOOD-FLOW

The present experiments were designed to compare the behavior of cereb ral blood flow (CBF) during acute moderate and severe hypotensive epis odes induced by either ventricular tachycardias (VT) or by hemorrhage. Using the microsphere method CBF was determined in 20 Sprague-Dawley rats during sinus rhythm (Group A), in 28 animals during high-rate VT (Group B) and in 10 animals after hemorrhage (Group C). According to t he decrease in blood pressure and with respect to the lower threshold oi cerebral autoregulation Group B was divided into 2 subgroups (B-1: 80-130 mmHg; B-2: 50-80 mmHg) retrospectively. While CBF remained cons tant in Group B-1 (0.98+/-0.3 ml g(-1) min(-1) vs. 1.01+/-0.32 in cont rols, NS), CBF decreased markedly during severely hypotensive VT in Gr oup B-2 (0.52+/-0.2 ml g(-1) min(-1), p < 0.001 vs. A; p < 0.05 vs. C) and during hypovolemic hypotension in Group C (0.77+/-0.22 ml g(-1) m in(-1) vs. A; NS). Cerebrovascular resistance and autoregulation indic es indicated a maintenance of CBF regulation during hypovolemic hypote nsion and a failure during normovolemic hypotension. These findings in dicate that the autoregulatory ability of the brain is substantially m ore stable during hypovolemic hypotension than during normovolemic hyp otension. Therefore, the hemodynamic sequelae of acute hypotensive epi sodes on CBF depend on the underlying cause of hypotension.