Sex Differences in Autonomic Function

This chapter focuses on sex differences in autonomic function and orthostatic intolerance and hypotension. In humans, both normal and pathophysiological mechanisms of autonomic control of blood pressure are modified by sex. Tonic sympathetic nerve activity can be measured using microneurography to measure muscle sympathetic nerve activity (MSNA) or norepinephrine spill-over techniques. Central estrogen administration also increases resting vagal tone in female mice, suggesting the sex hormones might also influence parasympathetic outflow to the heart. It is well accepted that even healthy young women who do not have symptoms of POTS are predisposed to orthostatic intolerance or hypotension at a greater rate compared to men. The exact mechanisms underlying this predisposition are unclear. The sympathetic nerve system is involved in the pathogenesis of hypertension, with many studies demonstrating that sympathetic nerve activity is elevated among individuals with hypertension. Aging is associated with an increased risk of developing hypertension. In this context, aging is associated with a gradual augmentation in sympathetic nerve activity and arterial pressure.