Sex differences in carotid baroreflex control of arterial blood pressure in humans: relative contribution of cardiac output and total vascular conductance

Kim A, Deo SH, Vianna LC, Balanos GM, Hartwich D, Fisher JP, Fadel PJ. Sex differences in carotid baroreflex control of arterial blood pressure in humans: relative contribution of cardiac output and total vascular conductance. Am J Physiol Heart Circ Physiol 301: H2454-H2465, 2011. First published September 30, 2011; doi:10.1152/ajpheart.00772.2011.-It is presently unknown whether there are sex differences in the magnitude of blood pressure (BP) responses to baroreceptor perturbation or if the relative contribution of cardiac output (CO) and total vascular conductance (TVC) to baroreflex-mediated changes in BP differs in young women and men. Since sympathetic vasoconstrictor tone is attenuated in women, we hypothesized that carotid baroreflex-mediated BP responses would be attenuated in women by virtue of a blunted vascular response (i.e., an attenuated TVC response). BP, heart rate (HR), and stroke volume were continuously recorded during the application of 5-s pulses of neck pressure (NP; carotid hypotension) and neck suction (NS; carotid hypertension) ranging from +40 to -80 Torr in women (n = 20, 21 +/- 0.5 yr) and men (n = 20, 21 +/- 0.4 yr). CO and TVC were calculated on a beat-to-beat basis. Women demonstrated greater depressor responses to NS (e.g., -60 Torr, -17 +/- 1% baseline in women vs. -11 +/- 1% baseline in men, P < 0.05), which were driven by augmented decreases in HR that, in turn, contributed to larger reductions in CO (-60 Torr, -15 +/- 2% baseline in women vs. -6 +/- 2% baseline in men, P < 0.05). In contrast, pressor responses to NP were similar in women and men (e. g., +40 Torr, +14 +/- 2% baseline in women vs. +10 +/- 1% baseline in men, P > 0.05), with TVC being the primary mediating factor in both groups. Our findings indicate that sex differences in the baroreflex control of BP are evident during carotid hypertension but not carotid hypotension. Furthermore, in contrast to our hypothesis, young women exhibited greater BP responses to carotid hypertension by virtue of a greater cardiac responsiveness.