EFFECTS OF POSTURE, HYPOTENSION AND LOCALLY APPLIED VASOCONSTRICTION ON THE MIDDLE-EAR MICROCIRCULATION IN ANESTHETIZED HUMANS

Studies by laser-Doppler flowmetry of middle ear microcirculation chan ges induced by physical and chemical stimuli in the animal have only r ecently been made. This prospective study, performed in humans, was de signed to compare the effects of a postural manoeuvre (headup tilt 30 degrees), hypotension and locally applied vasoconstriction on middle e ar blood flow during anaesthesia. Circulatory changes provoked by a he adup tilt of 30 degrees, and successive intravenous boluses of potent vasodilators, were compared with circulatory changes provoked by local ly applied adrenaline, in ten healthy patients in good physical states undergoing middle ear surgical repair. Heart rate and direct arterial pressure were continuously recorded via a radial artery cannula. Midd le ear blood flow was continuously recorded via a laser-Doppler probe placed on the promontorium cavi tympani. Metabolic parameters (partial pressure of O-2 and CO2 in arterial blood, pH, arterial lactate conce ntrations) and arterial concentrations of propofol were measured just before and just after the experiment. Headup tilt did not modify heart rate, mean arterial pressure or middle ear blood flow. Vasodilators ( nicardipine, nitroprusside, nitroglycerin) provoked a fall in arterial pressure (P<0.0001, P<0.0001, P<0.019, respectively), but did not ind uce any significant variations in heart rate; variations occurred in m iddle ear blood flow (P>0.05, not significant) which were different ac cording to patients and agents. Locally applied adrenaline provoked a fall in the middle ear blood flow (P<0.0012), with no effect on heart rate and arterial pressure. There were no significant changes in metab olic values, or propofol serum concentrations. The behaviour of the mi ddle ear blood flow submitted to hypotension, posture, or to vasoconst riction could be related to counteracting regulatory responses and/or to direct vascular effects.