Increased Cardiac Workload in the Upright Posture in Men: Noninvasive Hemodynamics in Men Versus Women

Abstract

Background: Men and women differ in the risk of cardiovascular disease, but the underlying mechanisms are not completely understood. We examined possible sex-related differences in supine and upright cardiovascular regulation.

Methods and results: Hemodynamics were recorded from 167 men and 167 women of matching age (≈45 years) and body mass index (≈26.5) during passive head-up tilt. None had diabetes mellitus or cardiovascular disease other than hypertension or used antihypertensive medication. Whole-body impedance cardiography, tonometric radial blood pressure, and heart rate variability were analyzed. Results were adjusted for height, smoking, alcohol intake, mean arterial pressure, plasma lipids, and glucose. Supine hemodynamic differences were minor: Men had lower heart rate (-4%) and higher stroke index (+7.5%) than women (P<0.05 for both). Upright systemic vascular resistance was lower (-10%), but stroke index (+15%), cardiac index (+16%), and left cardiac work were clearly higher (+20%) in men than in women (P<0.001 for all). Corresponding results were observed in a subgroup of men and postmenopausal women (n=76, aged >55 years). Heart rate variability analyses showed higher low:high frequency ratios in supine (P<0.001) and upright (P=0.003) positions in men.

Conclusions: The foremost difference in cardiovascular regulation between sexes was higher upright hemodynamic workload for the heart in men, a finding not explained by known cardiovascular risk factors or hormonal differences before menopause. Heart rate variability analyses indicated higher sympathovagal balance in men regardless of body position. The deviations in upright hemodynamics could play a role in the differences in cardiovascular risk between men and women.

Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01742702.

Keywords: cardiac output; hemodynamics; sex‐specific.

© 2016 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.

Figures

Figure 1

Line graphs show mean arterial pressure (A), heart rate (B), stroke index (C), cardiac index (D), left cardiac work index (E), and systemic vascular resistance index (F) in 167 men and 167 women during supine position and passive head‐up tilt (means and 95% CIs of the mean). P values denote differences between sexes in unadjusted analysis and in analyses adjusted for low‐ and high‐density lipoprotein cholesterol, triglycerides, glucose, mean arterial pressure, smoking habits, alcohol intake, and height.

Figure 2

Box plots of heart rate variability in men and women during 5 minutes in supine and upright positions: total power (A), LF power (B), HF power (C), and LF/HF ratio (D) (median [line inside box], 25th to 75th percentile [box], and range [whiskers); outliers were excluded from the figure but were included in the statistics). P values denote differences between sexes in unadjusted analysis and in analyses adjusted for low‐ and high‐density lipoprotein cholesterol, triglycerides, glucose, heart rate,42 mean arterial pressure, smoking habits, alcohol intake, and height. HR indicates high frequency; LF, low frequency.

Figure 3

Participants using statins or hormone replacement therapy were excluded. Line graphs show mean arterial pressure (A), cardiac index (B), left cardiac work index (C), and systemic vascular resistance index (D) in 160 men and 125 women during supine position and passive head‐up tilt (means and 95% CIs of the mean). P values denote differences between sexes in unadjusted analysis and in analyses adjusted for low‐ and high‐density lipoprotein cholesterol, triglycerides, glucose, mean arterial pressure, smoking habits, alcohol intake, age, and body mass index.

Figure 4

All included participants aged ≥55 years. Line graphs show mean arterial pressure (A), cardiac index (B), left cardiac work index (C), and systemic vascular resistance index (D) in 43 men and 33 women (no hormone replacement therapy in use) during supine position and passive head‐up tilt (means and 95% CIs of the mean). P values denote differences between sexes in unadjusted analysis and in analyses adjusted for low‐ and high‐density lipoprotein cholesterol, triglycerides, glucose, mean arterial pressure, smoking habits, alcohol intake, age, and body mass index.

Figure 5

Overall, 878 participants were examined. Line graphs show mean arterial pressure (A), cardiac index (B), left cardiac work index (C), and systemic vascular resistance index (D) in 480 men and 398 women during supine position and passive head‐up tilt (312 men and 303 women were without medications with direct cardiovascular actions; means and 95% CIs of the mean). P values denote differences between sexes in unadjusted analysis and in analyses adjusted for low‐ and high‐density lipoprotein cholesterol, triglycerides, glucose, mean arterial pressure, smoking habits, alcohol intake, age, and body mass index. In adjusted analyses, the numbers of participants ranged from 402 to 411 for men and from 332 to 342 for women.