Prevention of essential hypertension in minority populations

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

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 Autonomic Nervous System and Hypertension: Ethnic Differences and Psychosocial Factors

PURPOSE OF THE REVIEW

In the present paper, we overview emerging research examining the autonomic nervous system (ANS), especially the parasympathetic nervous system as indexed by heart rate variability (HRV), and the impact of psychosocial factors on hypertension-related disease in African Americans.

RECENT FINDINGS

A growing corpus of studies has shown that (1) usual patterns of compensatory sympathetic-parasympathetic regulation differ between African Americans and European Americans; (2) despite their enhanced cardiovascular disease risk profile, African Americans tend to exhibit higher HRV relative to European Americans; and (3) racial discrimination and other forms of psychosocial stress are associated with diminished HRV among African Americans. Significant disparities in hypertension-related disease exist such that African Americans have greater risk. The underlying factors associated with this increased risk are, to date, not fully understood. The present review provides evidence for a unique pattern of ANS regulation in African Americans and shows that psychosocial factors such as racial discrimination may contribute to this paradoxical situation.

Hemodynamics and Vascular Hypertrophy in African Americans and Caucasians With High Blood Pressure

BACKGROUND

Hypertension in African Americans is characterized by greater systemic vascular resistance (SVR) compared with Caucasian Americans, but the responsible mechanisms are not known. The present study sought to determine if peripheral vascular hypertrophy is a potential mechanism contributing to elevated SVR in African Americans with high blood pressure (BP).

METHODS

In a biracial sample of 80 men and women between the ages of 25 and 45 years, with clinic BP in the range 130/85-160/99mm Hg, we assessed cardiac output and SVR, in addition to BP. Minimum forearm vascular resistance (MFVR), a marker of vascular hypertrophy, also was assessed.

RESULTS

SVR was elevated in African Americans compared with Caucasians (P < 0.001). Regression models indicated that age, body mass index, 24-hour diastolic BP, and ethnicity were significant predictors of SVR. There was also a significant interaction between ethnicity and MFVR in explaining SVR in the study sample. In particular, there was a significant positive association between MFVR and SVR among African Americans (P = 0.002), whereas the association was inverse and not statistically significant among Caucasians (P = 0.601).

CONCLUSION

Hypertrophy of the systemic microvasculature may contribute to the elevated SVR that is characteristic of the early stages of hypertension in African American compared with Caucasians.