Effect of water immersion on renal sympathetic nerve activity and arterial baroreflex in conscious rabbits with heart failure.

Several studies have indicated an interaction between cardiopulmonary mechanoreflex and arterial baroreflex. However, the contribution of cardiopulmonary mechanoreflex to an abnormal arterial baroreflex in chronic heart failure (CHF) has not been fully investigated. We examined the effect of the activation of cardiopulmonary mechanoreceptors induced by head-out water immersion (WI) on the arterial baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in conscious rabbits with CHF induced by myocardial infarction. The arterial baroreflex sensitivity (BRS) of both HR and RSNA were decreased in CHF. WI induced a small decrease in RSNA in CHF compared to a sham-operated group (Sham), despite a similar increase in central venous pressure. WI did not affect BRS of HR or RSNA in either Sham or CHF. By averaging rectified RSNA recordings, we found that miniature RSNA in the control in CHF was higher than that in Sham. WI decreased the synchronized RSNA without changing miniature RSNA in either group. These results suggest that cardiopulmonary mechanoreflex control of RSNA is reduced in CHF, and that cardiopulmonary mechanoreflex has little effect on arterial baroreflex. An increase in miniature RSNA may reflect sympatho-excitation in CHF.