Gender differences in muscle sympathetic nerve activity and arterial pressure oscillations during progressive central hypovolemia (680.2)

: Increased tolerance to central hypovolemia is generally associated with greater oscillatory patterns of mean arterial pressur (MAP) and greater physiological reserve capacity. We tested the hypothesis that women with high tolerance (HT) to hypovolemia would display similar physiological reserve capacity for tachycardia, sympathoexcitation, oscillations in MAP at pre‐syncope compared to men. METHODS : 9 men and 4 women were exposed to progressive lower body negative pressure (LBNP) until presyncope. All subjects were classified as HT because they completed at least ‐60 mmHg level of lower body negative pressure (LBNP). Muscle sympathetic serve activity (MSNA) was measured via microneurography and arterial pressure was measured by photoplethysmography. RESULTS : LBNP time to presyncope was lower ( P <0.01) in women (1727±154 sec) than in men (2035±308 sec). At presyncope, MSNA (bursts/min) in men and women was similar (p=0.87). Coincident with smaller stroke volume (SV), women had lower MAP but similar heart rates compared with men. MAP/MSNA coherence was higher (p =0.04) in men (0.77±0.10) than women (0.67±0.04). Women had lower (p =0.06) oscillations in MAP compared to men. CONCLUSIONS : Our data corroborate the hypothesis that lower tolerance in women is not related to differences in sympathoexcitation or tachycardia, but reduced coherence (MSNA/MAP) and lower oscillatory patterns in MAP.Grant Funding Source : Department of Defense