Augmented resting beat-to-beat blood pressure variability in young, healthy, non-Hispanic black men

Abstract

New findings: What is the central question of this study? The prevalence of hypertension in black individuals exceeds that in other racial groups. Despite this well-known heightened risk, the underlying contributory factors remain incompletely understood. We hypothesized that young black men would exhibit augmented beat-to-beat blood pressure variability compared with white men and that black men would exhibit augmented total peripheral resistance variability. What is the main finding and its importance? We demonstrate that young, healthy black men exhibit greater resting beat-to-beat blood pressure variability compared with their white counterparts, which is accompanied by greater variability in total peripheral resistance. These swings in blood pressure over time might contribute to the enhanced cardiovascular risk profile in black individuals.

Abstract: The prevalence of hypertension in black (BL) individuals exceeds that in other racial groups. Recently, resting beat-to-beat blood pressure (BP) variability has been shown to predict cardiovascular risk and detect target organ damage better than ambulatory BP monitoring. Given the heightened risk in BL individuals, we hypothesized young BL men would exhibit augmented beat-to-beat BP variability compared with white (WH) men. Furthermore, given studies reporting reduced vasodilatation and augmented vasoconstriction in BL individuals, we hypothesized that BL men would exhibit augmented variability in total peripheral resistance (TPR). In 45 normotensive men (24 BL), beat-to-beat BP (Finometer) was measured during 10-20 min of quiet rest. Cardiac output and TPR were estimated (Modelflow method). Despite similar resting BP, BL men exhibited greater BP standard deviation (e.g. systolic BP SD; BL, 7.1 ± 2.2 mmHg; WH, 5.4 ± 1.5 mmHg; P = 0.006) compared with WH men, which was accompanied by a greater TPR SD (P = 0.003), but not cardiac output SD (P = 0.390). Other traditional measures of variability provided similar results. Histogram analysis indicated that BL men exhibited a greater percentage of cardiac cycles with BPs higher (> +10 mmHg higher) and lower (< -8 mmHg lower) than mean systolic BP compared with WH men (interaction, P < 0.001), which was accompanied by a greater percentage of cardiac cycles with high/low TPR (P < 0.001). In a subset of subjects (n = 30), reduced sympathetic baroreflex sensitivity was associated with augmented BP variability (r = -0.638, P < 0.001), whereas cardiac baroreflex sensitivity had no relationship (P = 0.447). Herein, we document an augmented beat-to-beat BP variability in young BL men, which coincided with fluctuations in vascular resistance and reduced sympathetic BRS.

Keywords: african american; arterial baroreflex; cardiac output; caucasian american; racial differences; total peripheral resistance.

© 2020 The Authors. Experimental Physiology © 2020 The Physiological Society.

Figures

Figure 1.

Histogram analysis of systolic blood pressure (SBP; Fig. 1A) and mean arterial blood pressure (MAP; Fig. 1B) in Non-Hispanic Black (BL; n=24, red bars) and Non-Hispanic White (WH; n=21, blue bars) men. Areas of the histogram wherein both WH and BL men exhibit cardiac cycles (i.e., overlap) are denoted in purple. Data represent blood pressure values binned in 1 mmHg increments away from each respective mean value. For statistical analysis and because of the markedly different range in values between WH and BL men, a sliding bin scale was used to normalize all histograms to 17 bins (see Methods). Dotted lines represent the bounds of each statistical bin. Brackets denote areas of the histogram where there is a significant difference (P

Figure 2.

Histogram analysis of cardiac output (CO; Fig. 2A) and total peripheral resistance (TPR; Fig. 2B) in Non-Hispanic Black (BL; n=24, red bars) and Non-Hispanic White (WH; n=21, blue bars) men. Areas of the histogram wherein both WH and BL men exhibit cardiac cycles (i.e., overlap) are denoted in purple. Data represent CO values binned in increments of 100mL/min, and TPR binned in 0.2 mmHg/L/min increments away from the mean respective values. For statistical analysis and because of the markedly different range in values between WH and BL men, a sliding bin scale was used to normalize all histograms to 17 bins (see Methods). Dotted lines represent the bounds of each statistical bin. Brackets denote areas of the histogram where there is a significant difference (P

Figure 3.

Mean summary data for spontaneous cardiac baroreflex sensitivity (BRS; Fig. 3A, left panel) and spontaneous sympathetic BRS (Fig. 3B; left panel) in Non-Hispanic Black (BL; black bars and circles) and Non-Hispanic White (WH; open bars and circles) men. The right panels depict the correlations between cardiac (Fig. 3A, right panel) and sympathetic (Fig. 3B, right panel) BRS, and mean arterial pressure (MAP) standard deviation (SD), as an index of blood pressure (BP) variability. Bar graph data are presented as mean ± SD, with N=24 BL men and N=21 WH men for cardiac BRS, and N=15 BL men and N=15 WH men for sympathetic BRS. Correlations use the same number of individuals. *P