Baroreflex stabilization of the double product.

We investigated whether the baroreflex control of heart rate (HR) stabilizes the product of arterial pressure (PA) and HR, called the double product (DP), an indirect indicator of left ventricular oxygen consumption. During pharmacological increases and decreases of PA in conscious rabbits, the mean (±SE) rate of change of the DP with respect to PA(dDP/dPA) was -88 ± 36 and -20 ± 36 DP units/mmHg, respectively. Regression analysis of all peak responses obtained in individual rats produced a dDP/dPA value of 15 ± 16 DP units/mmHg. These estimates were significantly less than the dDP/dPA value predicted if HR were constant (184 ± 7 DP units/mmHg) and were not significantly different from zero. We also compared values of baroreflex sensitivity (BRS) from the literature with those calculated to provide ideal stabilization of the DP. BRS values were significantly correlated with the calculated ideal values ( R = 0.95; n = 14). BRS averaged 128 ± 24% of the ideal value in all species and 148 ± 28% in mammals and birds. Our results suggest that stabilization of the DP is a common consequence of the baroreflex control of heart rate.