We examined the peripheral hemodynamic response to passive arm postural changes in young men and women. Radial artery pulse waveforms were captured using applanation tonometry in 20 men (age 27 ± 2？yrs, BMI 25 ± 1？kg/m2) and 20 women (age 27 ± 2？yrs, BMI 23±1？kg/m2). Arm position was maintained at either heart level or supported 14？cm above/below heart level in a randomized fashion. Systolic augmentation index (sAIx) and diastolic augmentation index (dAIx) were used as estimates of pressure from wave reflections arriving in systole and diastole, respectively. A novel reservoir-wave separation technique was used to obtain arterial reservoir pressure (pressure generated by arterial capacitance). Women showed a significant reduction in radial diastolic pressure-time integral (DPTI) ( ) and reservoir pressure ( ), with no change in peripheral sAIx ( ) or dAIx ( ) when moving the arm from below to above heart level. Conversely, men showed an attenuated change in radial DPTI ( ) concomitant with significant increases in reservoir pressure ( ), sAIx ( ), and dAIx ( ). Gravity-mediated changes in regional hemodynamics produced by passive arm postural shifts are sex specific. Men demonstrate less change in regional diastolic pressure concomitant with increased augmentation index and arterial reservoir pressure. 1. Introduction There are well established sex differences in blood pressure (BP) regulation. While hypertension affect more young men, hypotension and subsequent orthostatic intolerance affects more young women [1]. Although numerous mechanisms have been put forth (autonomic, hormonal, etc.), none fully explain sex differences in BP and its regulation [2]. Sex differences in the hemodynamic response to changes in hydrostatic pressure gradients [3, 4] have been implicated as an important factor contributing to sex differences in orthostatic tolerance [1]. Gravity is an often neglected factor that contributes to the genesis of pressure in the systemic circulation. According to the hydrostatic theory, liquid in a tube exerts pressure on the vessel wall and this is influenced by the density of the fluid, the height of the column/vertical displacement between two points in the tube, and the acceleration of the fluid medium due to gravitation effects [5]. Recently it has been suggested that hydrostatic effects cannot be the sole arbitrator of pressure changes in the systemic circulation with postural shifts in vivo and additional consideration should be given to dynamic vascular mechanical properties [6]. Pulse waveform analysis may provide novel insight into
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