Ethnic Differences in Resting Total Peripheral Resistance: A Systematic Review and Meta-Analysis

Abstract

Objective Decades of research suggest that there may be important ethnic differences in the hemodynamic mechanisms that co-determine arterial blood pressure, the primary diagnostic index of hypertension. In general, studies have observed that, compared with European Americans (EAs), African Americans (AAs) exhibit higher total peripheral resistance (TPR), an important summative index of peripheral vascular constriction. In contrast, EAs have been reliably shown to exhibit greater cardiac output (CO), which is directly linked to left ventricle and overall cardiac blood flow. We have previously proposed that elevated basal TPR, in particular, represents one component of the cardiovascular conundrum, characterized, paradoxically, by elevated resting heart rate variability among AAs relative to EAs. The present meta-analysis and systematic review of the literature sought to extend this previous work by establishing the magnitude of the empirically implied ethnic differences in resting TPR and CO. Methods A search of the literature yielded 140 abstracts on differences in TPR between AAs and EAs; 40 were included. Sample sizes, means, and standard deviations for baseline TPR with samples that included EAs and AAs were collected, and Hedges g was computed. Results Findings indicated that AAs had higher baseline TPR than did EAs (Hedges g = 0.307, SE = 0.043, confidence interval= 0.224 to 0.391, p < .001). In addition, EAs had higher resting CO than did AAs (Hedges g = −0.214, SE = 0.056, confidence interval = −0.324 to −0.104, p < .001). Conclusions We discuss the present findings in the context of the role of elevated TPR in the deleterious effects of high blood pressure specifically for AAs.

The Cardiovascular Conundrum in Ethnic and Sexual Minorities: A Potential Biomarker of Constant Coping With Discrimination

“…The aim of this study was to preliminarily investigate whether the dysfunctional physiological profile found in African Americans is seen also in other minority groups subjected to discrimination, such as LGB. First, study 1 replicated previous reports on the presence of a so-called Cardiovascular Conundrum in African Americans, that is a pattern of high resting HRV coupled with high TPR, that is likely due to a dysfunction at the baroreflex level ( Hill et al, 2015 for a meta-analysis of ethnic differences in HRV and Brownlow et al, 2020 for a meta-analysis on ethnic differences in TPR). Study 1 did not include a stressor because the Conundrum was originally found at rest, however, the fact that resting high HRV is also associated with a more prominent vascular hemodynamic reactivity to physical (i.e., orthostasis) and emotional (i.e., anger recall) stressors in African Americans has been previously reported ( Carnevali et al, 2019 ).…”

“…RMSSD was natural log-transformed to fit assumptions of linear analyses. Given extensive literature and meta-analyses (e.g., Hill et al, 2015 ; Brownlow et al, 2020 ) on baseline physiological differences between AAs and EAs, all tests were one-tailed and significance levels were evaluated using an alpha of 0.05. Effect sizes are reported as Cohen’s d.…”

“…This is surprising, given that low (not high) tonic HRV has been associated with a number of established and emerging modifiable and non-modifiable cardiovascular risk factors, including hypertension (e.g., Thayer et al, 2010 ). To make the picture even more complicated, this is also associated with higher total peripheral resistance (TPR; a measure of the amount of force affecting resistance to blood flow throughout the circulatory system) at rest ( Brownlow et al, 2020 for a meta-analysis) and a more vascular (compared to myocardial) hemodynamic profile in response to stressors (e.g., Carnevali et al, 2019 ) in African American. The term “hemodynamic profile” describes the relationship between cardiac output (CO; a measure of the amount of blood the heart pumps in a minute) and TPR in the homeostatic regulation of blood pressure ( Gregg et al, 2002 ).…”

Impaired vasodilation in pregnant African Americans: Preliminary evidence of potential antecedents and consequences

“…For example, to produce the same degree of vasodilation, greater doses of acetylcholine are needed in AAs compared to EAs (Jones et al., 1999). Further evidence for impaired vasodilation in AAs comes from the recently identified evidence of greater vagally mediated heart rate variability (HRV), a mechanism that should be associated with reduced TPR via the baroreflex, in the presence of elevated BP (Brownlow et al, 2020; Dorr et al, 2007; Hill et al, 2015). That is, in response to a BP increase baroreceptors enhance the vagal activity and inhibit the sympathetic activity via concomitant nucleus tractus solitarii (NTS) projections to the nucleus ambiguous (NA: to increase vagal activity) and to the caudal ventrolateral medulla (CVLM: to inhibit sympathetic activity) (Hesse et al., 2007).…”

α‐Adrenergic receptor blockade attenuates pressor response during mental stress in young black adults

“…In particular, young Black adults have been found to have an increased degree of vasoconstriction in response to a given increase in sympathetic activation. Black adults have greater vasoconstriction in response to infusion of the α 1 ‐adrenergic agonist, phenylephrine (Adefurin et al., 2013; Sherwood & Hinderliter, 1993; Stein et al., 2000), or in response to spontaneous bursts of muscle sympathetic activity, that is, neurovascular transduction (Vranish et al., 2018), that contributes to an increased pressor response to stress by inducing greater peripheral vascular constriction (Brownlow et al., 2020; Okada et al., 2016; Stein et al., 2000; Vranish et al., 2018). In addition, previous evidence has shown that Black individuals have exaggerated BP responses, during short acute sympathetic stimulation (<10 min) induced by the cold pressor test, intravenous administration of α‐adrenergic receptor agonists (Adefurin et al., 2013; Stein et al., 2000) or a video game (Murphy et al., 1986, 1994) although some reported no racial difference in BP response to different types of psychological stress (McAdoo et al., 1990).…”