Abstract
The body's ability to rapidly and appropriately regulate blood pressure in response to changing physiological demand is a key feature of a healthy cardiovascular system. Passively tilting the body, thereby changing central blood volume, is a well-recognized and controlled method of evaluating this ability. However, such studies usually involve single tilt angles, or intermittent tilting separated by supine, resting periods; valuable information concerning the adaptive capacity of the regulatory systems involved is therefore currently lacking. Furthermore, despite increasing recognition that men and women differ in the magnitude of their haemodynamic response to such stimuli, little is known about the degree to which gender differences in body composition and anthropometry influence these regulatory pathways, or indeed if these differences are apparent in response to graded, incremental tilting. In the present study we measured, in 23 young, healthy adults (13 men, 10 women), the continuous beat-to-beat haemodynamic response to graded, incremental tilting (0°, 20°, 40°, 60°, and back to 40°) with each tilt angle lasting 16 min. On average, we observed increases in heart rate (+41%), blood pressure (+10%), and total peripheral resistance (+16%) in response to tilting. However, whilst men showed an immediate decrease in cardiac output upon tilting (−8.9%) cardiac output in women did not change significantly from supine values. Interestingly, the decrease in stroke volume observed in women was significantly less than that observed in men (−22 vs. −36%, p < 0.05); although the present study could not determine if this difference was due to gender per se or due to differences in body size (in particular height) between the two gender groups. Such disparities in the magnitude of autonomic response may indicate (in the case of our gradual incremental tilt procedure) a better buffering capacity to progressive changes in central blood volume in women; which warrants further investigation, particularly in light of the well-recognized differences in cardiovascular disease risk between men and women.
Highlights
The appropriate and effective regulation of blood pressure, in order to maintain homeostasis despite changing physiological requirements, is a fundamental aspect of cardiovascular health
It has only recently been recognized that men and women regulate blood pressure through different physiological mechanisms—with young women generally showing enhanced parasympathetic input to cardiac regulation, compared to the predominance of sympathetic vascular regulation observed in men (Evans et al, 2001; Hart et al, 2009, 2012; Kim et al, 2011; Joyner et al, 2015; Reulecke et al, 2016)
Whilst a number of studies have explored gender differences using a single tilt angle compared to supine (Fu et al, 2005; Ndayisaba et al, 2015; Kangas et al, 2016; Patel et al, 2016; Reulecke et al, 2016), fewer studies have investigated these differences in response to graded, incremental tilting (i.e., no return to supine between each tilt angle (Shoemaker et al, 2001)
Summary
The appropriate and effective regulation of blood pressure, in order to maintain homeostasis despite changing physiological requirements, is a fundamental aspect of cardiovascular health. It has only recently been recognized that men and women regulate blood pressure through different physiological mechanisms—with young women generally showing enhanced parasympathetic (vagal) input to cardiac regulation, compared to the predominance of sympathetic vascular regulation observed in men (Evans et al, 2001; Hart et al, 2009, 2012; Kim et al, 2011; Joyner et al, 2015; Reulecke et al, 2016). Such studies are warranted as they may provide important information regarding response thresholds and possible gender differences in such thresholds
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