Validation of a continuous baroreceptor reflex sensitivity index calculated from spontaneous fluctuations of blood pressure and pulse interval in rats

Objective To develop and validate a technique for the continuous computerized calculation of the baroreceptor reflex sensitivity (BRS) of the heart rate in rats, Design The BRS was calculated from spontaneous changes in blood pressure and pulse interval using spectral analysis as well as time-series techniques, The BRS values obtained with these techniques were compared with those obtained by standard pharmacological methods, Methods The blood pressure and pulse interval in adult Wistar-Kyoto (WKY) rats were recorded on a beat-to-beat basis for two consecutive 30 min periods. During one of these periods the BRS was determined pharmacologically by injections of nitroprusside and phenylephrine. Measurements were performed after administration of saline as vehicle or during manipulation of the autonomic nervous system by infusion of metoprolol, methyl-atropine and hexamethonium. Sequential time-series methods for continuous BRS calculation were tested for 24 h periods in intact WKY rats as well as in WKY rats that had been subjected to sine-aortic denervation or to electrical lesioning of the nucleus tractus solitarius. Results The correlation coefficient between BRS values in intact WKY rats derived from the pharmacological method and those from spectral analysis techniques was tow (R-2 = 0.16), The correlation coefficient between BRS values from the pharmacological method and those from the developed time-series method was higher (R-2 = 0.64), The BRS measured using the latter method was found to vary over 24 h with the highest values during the sleeping period, After surgical elimination of the baroreflex, the algorithm returned BRS values close to zero throughout the 24 h period, The BRS estimate was found to be a measure of the parasympathetic rather than of the sympathetic component of the baroreceptor reflex, Conclusion The developed time-series method calculates an index of the gain of the cardiac baroreflex in rats faithfully, This method can be implemented in data acquisition software, allowing continuous on-tine monitoring of the cardiac baroreflex gain.