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 compu terized calculation of the baroreceptor reflex sensitivity (BRS) of th e heart rate in rats, Design The BRS was calculated from spontaneous c hanges in blood pressure and pulse interval using spectral analysis as well as time-series techniques, The BRS values obtained with these te chniques were compared with those obtained by standard pharmacological methods, Methods The blood pressure and pulse interval in adult Wista r-Kyoto (WKY) rats were recorded on a beat-to-beat basis for two conse cutive 30 min periods. During one of these periods the BRS was determi ned pharmacologically by injections of nitroprusside and phenylephrine . Measurements were performed after administration of saline as vehicl e or during manipulation of the autonomic nervous system by infusion o f metoprolol, methyl-atropine and hexamethonium. Sequential time-serie s 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 s ine-aortic denervation or to electrical lesioning of the nucleus tract us solitarius. Results The correlation coefficient between BRS values in intact WKY rats derived from the pharmacological method and those f rom spectral analysis techniques was tow (R-2 = 0.16), The correlation coefficient between BRS values from the pharmacological method and th ose 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 elimina tion of the baroreflex, the algorithm returned BRS values close to zer o throughout the 24 h period, The BRS estimate was found to be a measu re of the parasympathetic rather than of the sympathetic component of the baroreceptor reflex, Conclusion The developed time-series method c alculates an index of the gain of the cardiac baroreflex in rats faith fully, This method can be implemented in data acquisition software, al lowing continuous on-tine monitoring of the cardiac baroreflex gain.