EFFECT OF LABETALOL ON CEREBRAL BLOOD-FLOW, OXYGEN-METABOLISM AND AUTOREGULATION IN HEALTHY HUMANS

We have studied the effects of labetalol on cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO(2)) in eight healthy volunteers. CBF was measured by single photon emission computerized tomography before and during infusion of labetalol. CMRO(2) was calculated as CBF x cerebral arteriovenous oxygen content difference (Ca-O2-Cv(O2)). CBF autoregulation was tested during infusion of labetalol by changing arterial pressure and estimating relative changes in global CBF from changes in (Ca-O2-CVO2). CBF before and during infusion of labetalol was 67 and 65 ml/100 g min(-1) respectively (P > 0.05). CMRO, was 2.9 and 2.8 ml/100 g min(-1), respectively (P > 0.05). CBF autoregulation was preserved in all subjects. The lower limit of CBF autoregulation was 88 mm Hg (94% of baseline mean arterial pressure). We conclude that labetalol did not influence global or regional CBF, or CMRO(2), and CBF autoregulation was preserved.