Blunted blood pressure response to central sympathoinhibition in normotensive blacks: increased importance of nonsympathetic factors in blood pressure maintenance in blacks

Sympathetic transduction at rest and during cold pressor test in young healthy non-Hispanic Black and White women

Non-Hispanic Black (BL) individuals have the highest prevalence of hypertension and cardiovascular disease (CVD) compared with all other racial/ethnic groups. Previous work focused on racial disparities in sympathetic control and blood pressure (BP) regulation between young BL and White (WH) adults, have mainly included men. Herein, we hypothesized that BL women would exhibit augmented resting sympathetic vascular transduction and greater sympathetic and BP reactivity to cold pressor test (CPT) compared with WH women. Twenty-eight young healthy women (BL: n = 14, 22 [Formula: see text] 4 yr; WH: n = 14, 22 [Formula: see text] 4 yr) participated. Beat-to-beat BP (Finometer), common femoral artery blood flow (duplex Doppler ultrasound), and muscle sympathetic nerve activity (MSNA; microneurography) were continuously recorded. In a subset (BL n = 10, WH n = 11), MSNA and BP were recorded at rest and during a 2-min CPT. Resting sympathetic vascular transduction was quantified as changes in leg vascular conductance (LVC) and mean arterial pressure (MAP) following spontaneous bursts of MSNA using signal averaging. Sympathetic and BP reactivity were quantified as changes in MSNA and MAP during the last minute of CPT. There were no differences in nadir LVC following resting MSNA bursts between BL (-8.70 ± 3.43%) and WH women (-7.30 ± 3.74%; P = 0.394). Likewise, peak increases in MAP following MSNA bursts were not different between groups (BL: +2.80 ± 1.42 mmHg; vs. WH: +2.99 ± 1.15 mmHg; P = 0.683). During CPT, increases in MSNA and MAP were also not different between BL and WH women, with similar transduction estimates between groups (ΔMAP/ΔMSNA; P = 0.182). These findings indicate that young, healthy BL women do not exhibit exaggerated sympathetic transduction or augmented sympathetic and BP reactivity during CPT.NEW & NOTEWORTHY This study was the first to comprehensively investigate sympathetic vascular transduction and sympathetic and BP reactivity during a cold pressor test in young, healthy BL women. We demonstrated that young BL women do not exhibit exaggerated resting sympathetic vascular transduction and do not have augmented sympathetic or BP reactivity during cold stress compared with their WH counterparts. Collectively, these findings suggest that alterations in sympathetic transduction and reactivity are not apparent in young, healthy BL women.

Hypertension in Obese Black Women is Not Caused by Increased Sympathetic Vascular Tone

Background

Black women have one of the highest prevalence rates of hypertension and obesity in the United States. We previously reported that sympathetic activation induced by obesity is a significant contributor to hypertension in white patients. It is unknown whether sympathetic activity similarly contributes to hypertension in obese black women.

Methods and Results

We studied 42 obese women (16 white, body mass index 36±4 kg/m², 44% with hypertension; 26 black, body mass index 35±4 kg/m², 46% with hypertension). Antihypertensive medications were discontinued for 2 weeks before the day of the study. All patients underwent complete autonomic blockade with trimethaphan at a dosage of 4 mg/min. Resting sympathetic activity determined from muscle sympathetic nerve recordings was similar between obese black women with hypertension and those with normotension. In whites, sympathetic activity was elevated in obese patients with hypertension compared with normotension; the decrease in mean arterial blood pressure produced by trimethaphan was greater in obese white patients with hypertension compared with those with normotension (−26.8±9.7 mm Hg versus −14.8±7.9 mm Hg, P=0.02). In contrast, there was no difference in the depressor responses induced by trimethaphan between obese black women with hypertension and those with normotension (−15.5±10.5 mm Hg versus −12.3±10.2 mm Hg, P=0.45). Mean arterial blood pressure remained elevated in obese blacks with hypertension compared with those with normotension during trimethaphan infusion (83.7±15.0 mm Hg versus 71.7±9.8 mm Hg, P=0.02). Heart rate increased similarly with trimethaphan between white (P=0.11) and black (P=0.76) women with hypertension and normotension.

Conclusions

These findings suggest that sympathetic activity does not contribute to hypertension in obese black women and provide further evidence for racial differences in hypertension mechanisms.

The role of vasodilating β-blockers in patients with complicated hypertension: focus on nebivolol

Despite their proven mortality and morbidity outcomes benefits, β-blockers remain substantially underused in patients with cardiac conditions. Reluctance to prescribe β-blockers may be owing to concerns about tolerability with the traditional drugs in this class. β-blockers with vasodilatory properties, such as carvedilol and nebivolol, may overcome the tolerability and metabolic issues associated with traditional β-blockers. Because endothelial dysfunction, the pathophysiologic hallmark of hypertension, may be heightened in populations with difficult-totreat hypertension (e.g., elderly patients, African American patients), a vasodilating β-blocker may be a particularly appropriate choice for these patient groups.

Autonomic responses to stress in Black versus Caucasian Africans: the SABPA study

Underlying mechanisms of increased pressor responses to stress in Blacks are poorly understood. Cardiovascular regulation of normotensive Black (n=43) and Caucasian (n=90) Africans was studied during a cold pressor and color-word conflict test. Autonomic evaluation was performed by spectral analysis. Higher diastolic pressor and heart rate responses to the cold pressor test were observed in Black compared to Caucasian Africans. Autonomic efferent outflow to stress was comparable between groups. Transient downregulation of baroreflex during stress was evident in Blacks but not in Caucasians. Greater diastolic pressor responses were related to a higher cardiac reactivity, a baroreflex desensitization, and higher stress perception in Black Africans. Thus, increased stress perception may facilitate cardiac and diastolic hyperreactivity, indirectly affecting baroreflex function in Black Africans.

The role of vasodilating beta-blockers in patients with complicated hypertension: focus on nebivolol

Despite their proven mortality and morbidity outcomes benefits, beta-blockers remain substantially underused in patients with cardiac conditions. Reluctance to prescribe beta-blockers may be owing to concerns about tolerability with the traditional drugs in this class. Beta-blockers with vasodilatory properties, such as carvedilol and nebivolol, may overcome the tolerability and metabolic issues associated with traditional beta-blockers. Because endothelial dysfunction, the pathophysiologic hallmark of hypertension, may be heightened in populations with difficult-to-treat hypertension (e.g., elderly patients, African American patients), a vasodilating beta-blocker may be a particularly appropriate choice for these patient groups.

A longitudinal study in youth of heart rate variability at rest and in response to stress

BACKGROUND

Few longitudinal studies have examined ethnic and sex differences, predictors and tracking stabilities of heart rate variability (HRV) at rest and in response to stress in youths and young adults.

METHODS

Two evaluations were performed approximately 1.5 years apart on 399 youths and young adults (189 European Americans [EAs] and 210 African Americans [AAs]; 190 males and 209 females). HRV was measured at rest and during a video game challenge.

RESULTS

AAs showed significantly higher resting root mean square of successive differences (RMSSD) of normal R-R intervals and high-frequency (HF) power than EAs (ps<0.01). Females displayed larger decrease of RMSSD and HF during video game challenge than males (ps<0.05). These ethnic and sex differences were consistent across 1.5 years. No significant sex difference of resting HRV or ethnic difference of HRV response to stress was observed. In addition to age, ethnicity or sex, baseline resting HRV or HRV response to stress are predictors of the corresponding variables 1.5 years later (ps<0.01). Furthermore, weight gain indexed by either body mass index or waist circumference predicts declined resting HRV levels during follow up (ps<0.05). Tracking stabilities were high (>0.5) for resting HRV, but relatively low (<0.3) for HRV in response to stress.

CONCLUSION

AAs show higher resting HRV than EAs, and females display greater HRV response to stress than males; and these ethnic and sex differences are consistent across 1.5 years. Resting HRV declines with weight gain.

The efficacy and tolerability of nebivolol in hypertensive African American patients

Hypertensive African Americans often respond poorly to beta-blocker monotherapy, compared with whites. There is evidence, however, that suggests that this response may be different if beta-blockers with vasodilating effects are used. This 12-week, multi-center, double-blind, randomized placebo-controlled study assessed the antihypertensive efficacy and safety of nebivolol, a cardioselective, vasodilating beta1-blocker, at doses of 2.5, 5, 10, 20, or 40 mg once daily in 300 African American patients with stage I or II hypertension (mean sitting diastolic blood pressure [SiDBP] > or =95 mm Hg and < or =109 mm Hg). The primary efficacy end point was the baseline-adjusted change in trough mean SiDBP. After 12 weeks, nebivolol significantly reduced least squares mean SiDBP (P< or =.004) at all doses of 5 mg and higher and sitting systolic blood pressure (P< or =.044) at all doses 10 mg and higher, compared with placebo. The drug was safe and well-tolerated, with no significant difference in the incidence of adverse events compared with placebo. Nebivolol monotherapy provides antihypertensive efficacy, with few significant adverse effects, in hypertensive African Americans.

Heart Failure Management in African Americans: Meeting the Challenge

Heart failure affects 3% of African Americans. The etiology of disease and prognosis for these patients differs substantially from those for non-African Americans. A history of hypertension is associated with development of heart failure more often in African Americans than in non-African Americans and it also appears that target organ involvement is more severe in African Americans with hypertension than in other patient subgroups. Reviewing the results from large-scale clinical end point studies suggests that optimal treatment for heart failure in African Americans may differ from that of their non-African American counterparts. More importantly, concomitant use of beta blockers and angiotensin-converting enzyme inhibitors may be as effective in African Americans as in non-African Americans. Utilizing angiotensin-converting enzyme inhibitors alone may not represent ideal therapy. Of the drugs studied, especially among the beta blockers, carvedilol may be the most effective to use for this population.

Age and ethnicity differences in short-term heart-rate variability

OBJECTIVE

Hypertension is more frequent and more severe in older individuals and in African Americans. Differences in autonomic nervous system activity might contribute to these differences. Autonomic effects on the heart can be studied noninvasively through analysis of heart rate variability (HRV). We examined the effects of age and ethnicity on HRV.

METHODS

We studied 135 subjects (57 African Americans and 78 Caucasian Americans), aged 23 to 54 years. Using their surface electrocardiogram (ECG) data, we calculated the HRV indices with spectral analyses. High frequency (HF) power was used to index parasympathetic activity, whereas the ratio of low to high frequency power (LF/HF) was used to index sympathovagal balance.

RESULTS

Three HRV indices (HF, LF power, and LF/HF) were significantly related to age in Caucasian Americans but not in African Americans. The effect of age, ethnicity, and the age-by-ethnicity interaction on HF and LF power was significant, even after controlling for gender, body mass index, and blood pressure.

CONCLUSIONS

Young African Americans manifested a pattern of HRV response similarly to older Caucasian Americans. These results suggest that young African American individuals might show signs of premature aging in their autonomic nervous system.

Ethnic differences and heritability of heart rate variability in African- and European American youth

This study investigated whether heart rate variability (HRV) in young African-Americans differed from that in young European Americans. It further examined the genetic and/or environmental sources of HRV variance and to what extent they depend on ethnicity or gender in young twins. Subjects were available from 1 data set including 166 subjects (mean age 16 +/- 2 years; 63 African-Americans) and another including 219 twins (11 singletons [4 African-Americans] and 104 pairs [42 African-Americans]; mean age 15 +/- 2 years). HRV was measured over 256 RR intervals in a supine position. Two time-domain variables, the SD of normal RR intervals (SDNN) and the root-mean-square of successive differences (RMSSD) of normal RR intervals, and 3 frequency-domain variables, high-frequency (HF) power, low-frequency (LF) power, and the LF power/HF power ratio, were used. African-Americans had higher RMSSDs (p <0.01) and HF power (p = 0.047) and lower LF power/HF power ratios (p <0.01) than European Americans. These differences remained significant after adjusting for covariates. All HRV parameters were heritable; estimated heritability ranged from 32% to 71%. Model fitting showed no ethnic or gender differences for any measure. SDNN, RMSSD, and HF power were strongly correlated (r values >0.8). One factor explaining >90% of the variance for all 3 measures was identified. The heritability of this combined HRV score was 70%. In conclusion, this study suggests that ethnic differences in HRV already exist in youth, with African-Americans having greater HRV than European Americans. High heritability estimates for HRV measures were observed, and no differences in HRV heritability estimates were noted for ethnicity or gender.

Differences in resting cardiovascular parameters in 10- to 15-year-old children of different ethnicity: the contribution of physiological and psychological factors

BACKGROUND

The health status of children in the North West Province of South Africa was examined using the Transition and Health during Urbanization in South Africa in Children study. This is an epidemiological, cross-sectional study for which 1,244 children between 10 and 15 years of age were recruited from 44 schools.

PURPOSE

Our objective was to investigate whether differences exist between resting cardiovascular parameters of Black, White, colored, and Indian children and evaluate the contribution of physiological and psychological factors.

METHODS

Blood pressure was monitored with the Finapres apparatus. By means of the Fast Modelflo software program, the systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure, heart rate, cardiac output (CO), total peripheral resistance (TPR), and "Windkessel" compliance (Cw) of the arterial system were obtained. The psychological data were obtained by validated questionnaires.

RESULTS

After correction for body mass index, the SBP of the White children was significantly higher (p < .05) than the SBP of the other ethnic groups. The DBP showed no significant differences. The TPR measurements of the Black and colored children were significantly higher (p < .05) than the TPR of the White children, and the Cw measurements of the Black and colored children were significantly lower than the Cw of the White children. Significant correlations (p < .05) were found between the SV, CO, TPR, Cw, and the total score on violence in the Black and colored children.

CONCLUSIONS

There are differences in the resting cardiovascular parameters in the different ethnic groups studied. The higher levels of violence to which the Black and colored children are exposed could alter vascular sensitivity to sympathetic stimulation. This may contribute via the higher -adrenergic sensitivity to the pathogenesis of hypertension in their later lives.

Selective alpha2-adrenergic properties of dexmedetomidine over clonidine in the human forearm

We tested the hypothesis that dexmedetomidine (Dex) has greater alpha(2)- vs. alpha(1) selectivity than clonidine and causes more alpha(2)-selective vasoconstriction in the human forearm. After local beta-adrenergic blockade with propranolol, forearm blood flow (plethysmography) responses to brachial artery administration of Dex, clonidine, and phenylephrine (alpha(1)-agonist) were determined in healthy young adults before and after alpha(2)-blockade with yohimbine (n = 10) or alpha(1)-blockade with prazosin (n = 9). Yohimbine had no effect on phenylephrine-mediated vasoconstriction but blunted Dex-mediated vasoconstriction (mean +/- SE: -41 +/- 5 vs. -11 +/- 2%; before vs. after yohimbine) more than clonidine-mediated vasoconstriction (-39 +/- 5 vs. -28 +/- 4%; before vs. after yohimbine) (P < 0.02). Prazosin blunted phenylephrine-mediated vasoconstriction (-39 +/- 4 vs. -8 +/- 2%; before vs. after prazosin) but had similar effects on both Dex- (-30 +/- 4 vs. -39 +/- 6%; before vs. after prazosin) and clonidine-mediated vasoconstriction (-29 +/- 3 vs. -41 +/- 7%; before vs. after prazosin) (P > 0.7). Both Dex and clonidine reduced deep forearm venous norepinephrine concentrations to a similar extent (-59 +/- 12 vs. -55 +/- 10 pg/ml; Dex vs. clonidine, P > 0.6); this effect was abolished by yohimbine and blunted by prazosin. These results suggest that Dex causes more alpha(2)-selective vasoconstriction in the forearm than clonidine. The similar vasoconstrictor responses to both drugs after prazosin might be explained by the presynaptic effects on norepinephrine release.

Will tomorrow's medicines work for everyone?

Throughout much of the world, 'race' and 'ethnicity' are key determinants of health. For example, African Americans have, by some estimates, a twofold higher incidence of fatal heart attacks and a 10% higher incidence of cancer than European Americans, and South Asian- or Caribbean-born British are approximately 3.5 times as likely to die as a direct result of diabetes than are British of European ancestry. The health care that people receive also depends on 'race' and 'ethnicity'. African Americans are less likely to receive cancer-screening services and more likely to have late-stage cancer when diagnosed than European Americans. Health disparities such as these are one of the greatest social injustices in the developed world and one of the most important scientific and political challenges.

Heart failure-the importance of ethnicity

Heart failure is a major public health problem in the Western world. Aetiological factors involved in its development include hypertension, diabetes, and ischaemic heart disease--all of which differ in prevalence, and possibly mechanism, between patients of differing ethnicity. Unfortunately, epidemiological and therapeutic trials have involved almost exclusively white populations, and evidence from these trials cannot necessarily be assumed to be generalisable to populations that include high proportions of patients from other ethnic origins. This review will discuss the mechanistic and therapeutic differences that exist in heart failure between those of European origin, and patients from the major ethnic minority groups of the UK.

Postexercise hypotension differs between white and black women

BACKGROUND

Because data are lacking, we examined the acute effect of exercise on ambulatory blood pressure (BP) in premenopausal white women (n = 18) and black women (n = 15) with normal (n = 21) and high (n = 12) BP.

METHODS

Women performed 40 minutes of control and moderate-intensity exercise. BP and hormones were measured before, during, and after the control and exercise periods. By means of RMANCOVA (repeated measures analysis of covarience), we tested whether BP and hormones differed with time and between ethnic, BP, and experimental groups. Multiple regression analysis was used to examine hormonal mediators of the postexercise BP response.

RESULTS

Among white women with hypertension, average daytime systolic (S) and diastolic (D) BP decreased 11.0 +/- 3.3 mm Hg (-2.9, -19.1; P =.017) and 8.2 +/- 2.8 mm Hg (-1.2, -13.9; P =.000), from 142.6 +/- 5.8 mm Hg and 96.1 +/- 2.8 mm Hg, respectively, after exercise. Among black women with high BP, mean daytime SBP rose 12.5 +/- 5.2 mm Hg (-2.0, 27.1; P =.000) after exercise, from 121.8 +/- 6.1 mm Hg, whereas DBP was similar before and after exercise (81.4 +/- 4.3 mm Hg and 82.8 +/- 4.7 mm Hg, respectively). In white women without hypertension, daytime SBP and DBP were similar before and after exercise. In black women without hypertension, mean daytime SBP increased 6.3 +/- 2.6 mm Hg (0.4, 12.1; P =.000) after exercise from 103.6 +/- 1.4 mm Hg, and DBP did not change. In black women, hypertension (P = 0.000) and exercise-mediated insulin decreases (P =.005) explained 85.6% of the postexercise SBP response (P =.000). In white women, hypertension (P =.003) and baseline plasma renin (P =.049) accounted for 53.3% of the postexercise SBP response (P =.001). Exercise acutely reduced daytime BP in white women, but not in black women with high BP.

CONCLUSION

Endurance exercise may adversely affect the BP of black women.

The role of race in heart failure therapy

Heart failure in blacks is a unique malady characterized by a different natural history, more worrisome prognosis, and potential variances in the response to current medical therapy for heart failure. The overwhelming burden of hypertension as a putative cause of left ventricular dysfunction identifies this illness. Although differences in the response to medical therapy have been described, angiotensin-converting enzyme inhibitors and beta-blockers remain the most appropriate therapy. Certain genetic polymorphisms may exist that explain the observed differences.

Race and the response to adrenergic blockade with carvedilol in patients with chronic heart failure

BACKGROUND

The benefits of angiotensin-converting-enzyme inhibitors and beta-blockers may be smaller in black patients than in patients of other races, but it is unknown whether race influences the response to carvedilol in patients with chronic heart failure.

METHODS

In the U.S. Carvedilol Heart Failure Trials Program, 217 black and 877 nonblack patients (in New York Heart Association class II, III, or IV and with a left ventricular ejection fraction of no more than 0.35) were randomly assigned to receive placebo or carvedilol (at doses of 6.25 to 50 mg twice daily) for up to 15 months. The effects of carvedilol on ejection fraction, clinical status, and major clinical events were retrospectively compared between black and nonblack patients.

RESULTS

As compared with placebo, carvedilol lowered the risk of death from any cause or hospitalization for any reason by 48 percent in black patients and by 30 percent in nonblack patients. Carvedilol reduced the risk of worsening heart failure (heart failure leading to death, hospitalization, or a sustained increase in medication) by 54 percent in black patients and by 51 percent in nonblack patients. The ratios of the relative risks associated with carvedilol for these two outcome variables in black as compared with nonblack patients were 0.74 (95 percent confidence interval, 0.42 to 1.34) and 0.94 (95 percent confidence interval, 0.43 to 2.05), respectively. Carvedilol also improved functional class, ejection fraction, and the patients' and physicians' global assessments in both the black patients and the nonblack patients. For all these measures of outcome and clinical status, carvedilol was superior to placebo within each racial cohort (P<0.05 in all analyses), and there was no significant interaction between race and treatment (P> 0.05 in all analyses).

CONCLUSIONS

The benefit of carvedilol was apparent and of similar magnitude in both black and nonblack patients with heart failure.

Hypertension in black people: study of specific genotypes and phenotypes will provide a greater understanding of interindividual and interethnic variability in blood pressure regulation than studies based on race

Hypertension is more frequent and more severe in some Black populations. Although many studies have focused on hypertension in black people in an attempt to understand the genetic and environmental factors that regulate blood pressure, this approach has not been productive. Study of the relationship between specific phenotypes and genotypes, both within and across ethnic groups, is more likely to advance our understanding of the regulation of blood pressure than studies focused on race and blood pressure.

Predictors of cardiovascular response to smoked cocaine in humans

The purpose of this study was to examine the predictors of heart rate and blood pressure changes following cocaine administration. Sixty-two smoked cocaine users received a single 0.4 mg/kg dose of smoked cocaine. Male sex, African American race, higher body weight and current marijuana use predicted a greater cardiovascular response to cocaine. In contrast, higher baseline blood pressure, heart rate, amount and frequency of current cocaine use and presence of current cocaine snorting predicted a diminished cardiovascular response to cocaine. Whether these predictors of the cardiovascular response to smoked cocaine in the laboratory also predict cardiovascular complications from long-term cocaine use needs to be studied further.

Cardiac and systemic sympathetic activity in response to clonidine in human heart failure

OBJECTIVES

We studied the effects of clonidine on cardiac sympathetic activity and left ventricular function in patients with congestive heart failure (CHF).

BACKGROUND

Sympathetic activation has major prognostic implications in patients with heart failure. Clonidine, an imidazoline and alpha2-receptor agonist, has been shown to cause a reduction in generalized sympathetic activity.

METHODS

Nine patients with CHF (left ventricular ejection fraction 22+/-4% [mean+/-SEM]) received a 50 microg and 100 microg bolus of clonidine intravenously. Study measurements included right and left heart hemodynamics, cardiac output, rate of rise in left ventricular peak positive pressure (LV + dP/dt) and tau, along with cardiac and total body norepinephrine spillover. The radiotracer method was used for calculation of norepinephrine spillover.

RESULTS

Right and left heart filling pressures did not change in response to either dose of clonidine. Mean arterial pressure fell after the second dose of clonidine, from 94+/-8 to 82+/-6 mm Hg (p < 0.05). The LV + dP/dt was reduced from 737+/-53 to 629+/-43 mm Hg/s (p < 0.05). Clonidine also caused a significant increase in tau, as measured by the method of Weiss (65+/-3 vs. 74+/-4 ms, p < 0.01) and the direct pressure half-time technique (48+/-2 vs. 54+/-3 ms, p < 0.01). Cardiac norepinephrine spillover fell from 121+/-29 to 52+/-20 pmol/min in response to 100 microg of clonidine (p < 0.01 vs. control).

CONCLUSIONS

Despite a significant fall in arterial pressure, clonidine caused a marked reduction in sympathetic activity directed at the heart. The negative inotropic and lusitropic effects appear to be secondary to this reduction in sympathetic drive. Because increased cardiac and generalized sympathetic activity are strong predictors of an adverse outcome in patients with CHF, the role of centrally active sympathoinhibitory agents in the therapy of CHF deserves further exploration.