Abstract
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) (P<0.05) and reservoir pressure (P<0.05), with no change in peripheral sAIx (P>0.05) or dAIx (P>0.05) when moving the arm from below to above heart level. Conversely, men showed an attenuated change in radial DPTI (P>0.05) concomitant with significant increases in reservoir pressure (P<0.05), sAIx (P<0.05), and dAIx (P<0.05). 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.
Highlights
There are well established sex differences in blood pressure (BP) regulation
Arm manipulation resulted in similar changes across sex in, mean blood pressure (MBP), brachial and radial systolic blood pressure (SBP), brachial and radial Pulse pressure (PP) and radial SPTI (Tables 1 and 2, P < 0.05 for time effects; P > 0.05 for sex-by-condition interactions)
For every centimeter of vertical displacement, it has been estimated that BP is altered by approximately 0.77 mmHg and this effect is deemed to be predominantly hydrostatic [42]
Summary
There are well established sex differences in blood pressure (BP) regulation. 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. 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]
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