CALL FOR PAPERS Sex and Gender Differences in Cardiovascular Physiology— Back to the Basics Sex differences in forearm vasoconstrictor response to voluntary apnea

Patel HM, Heffernan MJ, Ross AJ, Muller MD. Sex differences in forearm vasoconstrictor response to voluntary apnea. Am J Physiol Heart Circ Physiol 306: H309–H316, 2014. First published December 6, 2013; doi:10.1152/ajpheart.00746.2013.—Clinical evidence indicates that obstructive sleep apnea is more common and more severe in men compared with women. Sex differences in the vasoconstrictor response to hypoxemia-induced sympathetic activation might contribute to this clinical observation. In the current laboratory study, we determined sex differences in the acute physiological responses to maximal voluntary end-expiratory apnea (MVEEA) during wakefulness in healthy young men and women (26 1 yr) as well as healthy older men and women (64 2 yr). Mean arterial pressure (MAP), heart rate (HR), brachial artery blood flow velocity (BBFV, Doppler ultrasound), and cutaneous vascular conductance (CVC, laser Doppler flowmetry) were measured, and changes in physiological parameters from baseline were compared between groups. The breath-hold duration and oxygen-saturation nadir were similar between groups. In response to MVEEA, young women had significantly less forearm vasoconstriction compared with young men ( BBFV: 2 7 vs. 25 6% and CVC: 5 4 vs. 31 4%), whereas MAP (12 2 vs. 16 3 mmHg) and HR (4 2 vs. 6 3 bpm) were comparable between groups. The attenuated forearm vasoconstriction in young women was not observed in postmenopausal women ( BBFV 21 5%). We concluded that young women have blunted forearm vasoconstriction in response to MVEEA compared with young men, and this effect is not evident in older postmenopausal women. These data suggest that female sex hormones dampen neurogenic vasoconstriction in response to apnea-induced hypoxemia.