Isoflurane-mediated inhibition of the constriction of mesenteric capacitance veins and related circulatory responses to acute graded hypoxic hypoxia.

Abstract

We measured the effects of inhaled isoflurane on hypoxemia-induced changes in the diameter of small mesenteric (capacitance-regulating) veins, sympathetic efferent neural activity, heart rate, and arterial blood pressure. Simultaneous changes in these dependent variables were measured in situ in response to 40-s periods of sequentially administered 10%, 5%, 2.5%, and 0% inspired oxygen before, during, and after either 0.75% or 1.5% vol/vol inhaled isoflurane in alpha-chloralose-anesthetized rabbits. Isoflurane inhibited hypoxia-mediated venoconstriction, increases in sympathetic efferent nerve activity, arterial hypertension, and bradycardia. Furthermore, inhibition of diameter, blood pressure, and heart rate responses persisted after washout of isoflurane. Differences in the attenuation of these respective hypoxia-mediated responses were minimal between the two concentrations of inhaled isoflurane. These results further demonstrate that isoflurane alters the ability to produce cardiovascular adjustments to circulatory stress, including changes in vascular capacitance, which is a major regulatory mechanism.