ISOFLURANE-MEDIATED INHIBITION OF THE CONSTRICTION OF MESENTERIC CAPACITANCE VEINS AND RELATED CIRCULATORY RESPONSES TO ACUTE GRADED HYPOXIC HYPOXIA

We measured the effects of inhaled isoflurane on hypoxemia-induced cha nges in the diameter of small mesenteric (capacitance-regulating) vein s, sympathetic efferent neural activity, heart rate, and arterial bloo d pressure. Simultaneous changes in these dependent variables were mea sured in situ in response to 40-s periods of sequentially administered 10%, 5%, 2.5%, and 0% inspired oxygen before, during, and after eithe r 0.75% or 1.5% vol/vol inhaled isoflurane in alpha-chloralose-anesthe tized rabbits. Isoflurane inhibited hypoxia-mediated venoconstriction, increases in sympathetic efferent nerve activity, arterial hypertensi on, and bradycardia. Furthermore, inhibition of diameter, blood pressu re, and heart rate responses persisted after washout of isoflurane. Di fferences in the attenuation of these respective hypoxia-mediated resp onses were minimal between the two concentrations of inhaled isofluran e. These results further demonstrate that isoflurane alters the abilit y to produce cardiovascular adjustments to circulatory stress, includi ng changes in vascular capacitance, which is a major regulatory mechan ism.