EFFECT OF KETANSERIN ON GLOBAL CEREBRAL BLOOD-FLOW AND MIDDLE CEREBRAL-ARTERY FLOW VELOCITY

The aim of this study was to examine the influence of ketanserin, a 5- hydroxytryptamine antagonist antihypertensive agent, on the relationsh ip between cerebral blood flow (CBF) and middle cerebral artery flow v elocity (V-meanMCA) and to compare Doppler-sonographic indices of down stream resistance (pulsatility index, PI; resistance index, RI) with c alculations of cerebrovascular resistance (CVR) in 17 male patients un der fentanyl/midazolam anesthesia. CBF was measured with the Kety-Schm idt technique using argon as a tracer. Cerebral perfusion pressure (CP P) was calculated as the difference between mean arterial pressure (MA P) and jugular bulb pressure. Measurements of V-meanMCA and determinat ions of PI and RI were performed by use of a 2-MHz transcranial Dopple r ultrasound device. All variables were measured at normo- and moderat e hypocapnia before and after intravenous (IV) bolus administration of 0.3 mg/kg ketanserin followed by an infusion of 0.06 mg.kg(-1).h(-1). Ketanserin changed neither average CBF nor V-meanMCA. The CO2 reactiv ity of V-meanMCA was significantly lower than the CO2 reactivity of CB F (P < 0.01); however, ketanserin did not change the relationship betw een CBF and V-meanMCA. During hypocapnia, CVR as well as PI and RI sig nificantly increased (P less than or equal to 0.01), indicating consis tent directional changes in arteriolar resistance and flow velocity pu lsatility. In contrast, after TV administration of ketanserin, CVR dec reased (P < 0.05), whereas both Doppler-derived indices increased (P < 0.01). These results suggest that ketanserin in a clinically relevant dose does not alter the validity of serial V-meanMCA measurements as an index of global CBF and that ketanserin does not change the diamete r of middle cerebral arteries (MCAs). Doppler-derived indices of pulsa tility and resistance, which are supposed to estimate changes in downs tream resistance, reflect changes, after administration of ketanserin, in systemic hemodynamics rather than changes in CVR.