Baroreflex Modulation by Isoflurane Anesthesia in Normotensive and Chronically Hypertensive Rabbits

Abstract

Hemodynamic instability has been well documented in both humans and animals in hypertensive and is presumed to be at least partly because of impaired baroreflex control of efferent sympathetic activity. Control of arterial pressure (AP) is further complicated during anesthesia, as anesthetics attenuate arterial baroreflexes. The study presented in this chapter has been designed to investigate the individual effects of isoflurane (ISO) anesthesia and chronic hypertensive (HT) on baroreflex control of heart rate (HR) and efferent sympathetic nerve activity. In addition, the integrative effects of HT and anesthesia are discussed. A couple of studies in the chapter have demonstrated that increases in the level of ISO in already anesthetized animals produce progressive depression of the sympathetic baroreflex. In addition, the upper plateau and range of the AP-renal efferent sympathetic nerve activity (RSNA) baroreflex has been significantly reduced at all levels of ISO. It is also demonstrated that the AP-RSNA baroreflex remains functional during ISO anesthesia, although the ability to respond to transient falls in AP is decreased with increasing levels of ISO. It is showed that the range and slope of the HR baroreflex do not differ between normotensive (NT) and HT rabbits. The results of the present study indicate that the range and slope of the AP-RSNA baroreflex is not altered by hypertension in conscious rabbits. In the present study the resting RSNA is not different between conscious NT and HT rabbits. But resting HR in the present study has been significantly lower in HT rabbits than in NT rabbits. The results of the present study indicate that ISO anesthesia depressed both baroreflex curves to the same degree in NT and HT rabbits. The only difference is that baroreflex curves in HT rabbits have been displaced to the right along the pressure axis.