Effects of anesthesia on sympathetic nerve rhythm: power spectral analysis

It has been shown that central transduction of the input from arterial baroreceptors shows bandpass characteristics. Previous studies have demonstrated that anesthesia may affect the gain of arterial baroreflex control of sympathetic nerve activity, but whether anesthesia affects the frequency response of central transduction of the arterial baroreflex system is not known. We examined cardiac cycle-related oscillation of renal sympathetic nerve activity (RNA) in conscious (n = 5) and alpha-chloralose-anesthetized (n = 10) rabbits. Power spectra of arterial pressure and RNA were obtained at rest, after i.v. propranolol and after i.v. isoproterenol. At rest with a cardiac cycle at about 5 Hz, cardiac cycle-related oscillation of RNA was observed in conscious rabbits, but it was not present or markedly attenuated in anesthetized rabbits. As the cardiac cycle was slowed by propranolol in anesthetized rabbits, cardiac cycle-related oscillation of RNA gradually appeared. These results suggest that alpha-chloralose anesthesia in rabbits narrowed the bandpass region of the central baroreflex system so that the baroreceptor input at a high frequency (above 5 Hz) was no longer transduced into RNA.