Sex‐specific sympathetic responses to chemoreflex stress in healthy young men and women

While muscle sympathetic nerve activity (MSNA) responses to baroreceptor unloading are typically greater in men than women, it is unclear whether chemoreflex responses differ between the sexes. We tested the null hypothesis that MSNA responses to concurrent hypoxia and hypercapnia would not be different between sexes. Microneurographic recordings of fibular nerve MSNA, heart rate (HR) and mean arterial pressure (MAP; Finometer) were acquired from healthy young men and women (n=6 each, 25±3y). Females were tested in the early follicular phase of the menstrual cycle. Following baseline recordings, an oxygen partial pressure of 70 torr and an end tidal carbon dioxide partial pressure of 50 torr were achieved through a rebreathing protocol. Immediately succeeding the rebreathing protocol, an end‐inspiratory apnea commenced following inhalation of these gas concentrations. Baseline values for HR, MAP, and MSNA levels did not differ between the sexes. The HR and MAP responses to chemoreflex stress were also similar between men and women ( P >0.05). However, during the apnea increases in MSNA burst frequency (+39±16 versus +23±9 bursts/min, P =0.03) and burst incidence (+54±21 versus +38±15 bursts/100 heart beats, P =0.04) were larger in women than men, respectively. These data suggest that sympathetic responses to an apneic hypoxic‐hypercapnic stimulus are greater in women than in men. Supported by NSERC and CIHR.