The Effect Of An Acute Increase In Central Blood Volume On Dynamic Cerebral Autoregulation

Abstract

Previous investigations demonstrated that cerebral blood flow was influenced by changes in central blood volume and arterial blood pressure even within the range of cerebral autoregulation (60-150 mmHg). Recently, we found that during acute microgravity (parabolic flight condition), the acute increase in central blood volume decreased gradually arterial blood pressure via the arterial and cardiopulmonary baroreflexes. Despite the acute hypotension and central hypervolemia, steady-state cerebral blood flow was well maintained during this condition. However, the dynamic relationship between central blood volume and cerebrovascular control remains unclear. PURPOSE: The purpose of the present study was to examine dynamic cerebral autoregulation during an acute hypotension with central hypervolemia. METHODS: Nine young healthy subjects voluntarily participated in this study. In order to measure dynamic cerebral autoregulation, change in middle cerebral artery mean blood flow velocity (MCA Vmean) was analyzed during acute hypotension caused by two methods: 1) thigh-cuff occlusion release (without change in central blood volume) and 2) lower body negative pressure (-50 mmHg, LBNP) release (with acute increase in central blood volume). RESULTS: As expected, the thigh-cuff occlusion release caused acute hypotension and decrease in MCA Vmean accordingly, but MCA Vmean returned to the baseline value quickly. LBNP release increased and then decreased arterial blood pressure acutely. During the phase of decreased arterial blood pressure, however, the rate of regulation, as an index of dynamic cerebral autoregulation during LBNP release, was significantly lower than that during cuff release (0.112 ± 0.116 and 0.236 ± 0.053 sec-1, respectively, P=0.030). CONCLUSIONS: These findings suggest that an acute change in central blood volume modifies dynamic cerebral autoregulation.