Sympathetic Neurocirculatory Responses to Chemoreflex Activation in Young Women and Men

Abstract

Sex‐differences in the ventilatory responses to central and peripheral chemoreflex activation have been extensively examined. Along with the control of respiration, chemoreflexes play a key role in sympathetic regulation. Herein, we determined whether central, peripheral, and combined central and peripheral chemoreflex activation evoke differing sympathetic neurocirculatory responses in young women and men.In ten women (29±6 years, 23±2kg/m2: mean±SD) and ten men (30±7 years, 25±3kg/m2), we recorded muscle sympathetic nerve activity (MSNA), minute ventilation (V̇E) and mean arterial pressure (MAP) during 5‐min trials of breathing room‐air (eucapnia), isocapnic hypoxia (10% oxygen [O2]; peripheral chemoreflex activation), hypercapnic hyperoxia (7% carbon dioxide [CO2], 50% O2; central chemoreflex activation) and hypercapnic hypoxia (7% CO2, 10% O2). Trials were randomized. Women were studied in the early follicular phase of their menstrual cycle.During eucapnia and isocapnic hypoxia, no sex‐differences were observed in MSNA, V̇E and MAP (P>0.05). During hypercapnic hyperoxia (∆278±215 vs. ∆158±107%, P=0.05) and hypercapnic hypoxia (∆507±290 vs. ∆262±268%, P=0.05) MSNA responses were augmented in women compared to men, however V̇E responses were attenuated (hypercapnic hyperoxia ∆15.2±6.7 vs. ∆25.6±6.7L/min, P=0.007; hypercapnic hypoxia ∆28.8±9.3 vs. ∆39.9±12.5L/min, P=0.004). MAP responses were similar in women and men (hypercapnic hyperoxia ∆10±2 vs. ∆23±2mmHg, P=0.35; hypercapnic hypoxia ∆16±3 vs. ∆25±3mmHg, P=0.35).In summary, young women have greater MSNA response to central chemoreflex activation than young men, which explains their augmented sympathetic response to combined central and peripheral chemoreflex activation. Future studies should determine the effect of menopause on these sex‐differences in the sympathetic neurocirculatory responses to chemoreflex activation.