Hypertensive cardiovascular disease in African Americans

Vitamin D Levels in Black Americans and the Association With Left Ventricular Remodeling and Incident Heart Failure With Preserved Ejectin Fraction: The Jackson Heart Study

BACKGROUND

In observational studies, a lower serum vitamin D₃ concentration has been associated with an increased risk of cardiovascular disease. However, the associations between serum vitamin D₃ levels and left ventricular (LV) structure and heart failure with preserved ejection fraction (HFpEF) have not been well-characterized among Black Americans. The prevalence of vitamin D₃ deficiency is higher among Black Americans than in other race/ethnicity groups. We hypothesized that serum vitamin D₃ levels are associated with LV concentric remodeling and incident HFpEF in Black Americans.

METHODS AND RESULTS

Among 5306 Black Americans in the Jackson Heart Study cohort, we investigated the relationships between serum vitamin D₃ levels and LV structure and function, evaluated with echocardiography, and incident HF hospitalization, categorized as either HF with reduced EF (HFrEF; an EF of <50%) or HFpEF (an EF of ≥50%). After adjustment for possible confounding factors, lower vitamin D₃ levels were associated with greater relative wall thickness (β for 1 standard deviation [SD] increase -0.003, 95% confidence interval -0.005 to -0.000). Over a median follow-up period of 11 years (range 10.2-11.0 years), 340 participants developed incident HF (7.88 cases per 1000 person-years), including 146 (43%) HFrEF and 194 (57%) HFpEF cases. After adjustment, higher serum vitamin D₃ levels were associated with decreased hazard for HF overall (hazard ratio for 1 SD increase 0.88, 95% confidence interval 0.78-0.99) driven by a significant association with HFpEF (hazard ratio for 1 SD increase 0.84, 95% confidence interval 0.71-0.99).

CONCLUSIONS

In this community-based Black American cohort, lower serum vitamin D₃ levels were associated with LV concentric remodeling and an increased hazard for HF, mainly HFpEF. Further investigation is required to examine whether supplementation with vitamin D₃ can prevent LV concentric remodeling and incident HFpEF in Black Americans.

Heart Rate Variability Reflects Similar Cardiac Autonomic Function in Explosive and Aerobically Trained Athletes

Autonomic cardiac function can be indirectly detected non-invasively by measuring the variation in microtiming of heart beats by a method known as heart rate variability (HRV). Aerobic training for sport is associated with reduced risk for some factors associated with cardiovascular diseases (CVD), but effects on autonomic function in different athlete types are less known. To compare cardiac autonomic modulation using a standard protocol and established CVD risk factors in highly trained intercollegiate athletes competing in aerobic, explosive, and cross-trained sports. A total of 176 college athletes were categorized in distinct sports as explosive (EA), aerobic (AA), or cross-trained (mixed) athletes. Eight different HRV measures obtained at rest were compared across training type and five health factors: systolic (SBP), diastolic blood pressure (DBP), body weight (BW), sex, and race. All athletic types shared favorable HRV measures that correlated with low CVD risk factors and indicated normal sympathovagal balance. A significant correlation was reported between DBP and pNN50 (% RR intervals > 50 ms) (β = -0.214, p = 0.011) and between BW and low-frequency (LF) power (β = 0.205, p = 0.006). Caucasian and African American athletes differed significantly (p < 0.05) with respect to four HRV variables: pNN50, HF power, LF power, and LF/HF ratios. Explosive, aerobic and mixed athletes had similar cardiovascular and autonomic HRV results in all eight HRV parameters measured. All athletes reported LF and pNN50 values that were significantly correlated with two CVD risk factors: DBP and BW. Compared with Caucasian teammates, African American athletes demonstrated lower LF/HF and higher pNN50, indicating an even more favorable resting sympathovagal activity and healthy CV function.

Physical Activity, Inflammation, Coronary Artery Calcification, and Incident Coronary Heart Disease in African Americans: Insights From the Jackson Heart Study

OBJECTIVE

To examine associations between physical activity (PA), inflammation, coronary artery calcification (CAC), and incident coronary heart disease (CHD) in African Americans.

METHODS

Among Jackson Heart Study participants without prevalent CHD at baseline (n=4295), we examined the relationships between PA and high-sensitivity C-reactive protein, the presence of CAC (Agatston score ≥100), and incident CHD. Based on the American Heart Association's Life's Simple 7 metrics, participants were classified as having poor, intermediate, or ideal PA.

RESULTS

After adjustment for possible confounding factors, ideal PA was associated with lower high-sensitivity C-reactive protein levels (β, -0.15; 95% CI, -0.15 to -0.002) and a lower prevalence of CAC (odds ratio, 0.70; 95% CI, 0.51-0.96) compared with poor PA. During a median of 12.8 years of follow-up, there were 164 incident CHD events (3.3/1000 person-years). Ideal PA was associated with a lower rate of incident CHD compared with poor PA (hazard ratio, 0.55; 95% CI, 0.31-0.98).

CONCLUSION

In a large community-based African American cohort, ideal PA was associated with lower inflammation levels, a lower prevalence of CAC, and a lower rate of incident CHD. These findings suggest that promotion of ideal PA may be an important way to reduce the risk of subclinical and future clinical CHD in African Americans.

Relation of Low Normal Left Ventricular Ejection Fraction to Heart Failure Hospitalization in Blacks (From the Jackson Heart Study)

There is no clear consensus on a lower cutoff value for normal left ventricular ejection fraction (EF) and the prognostic implications of low normal EF (LNEF) are poorly understood, particularly in Blacks. Therefore, we investigated the association of LNEF and incident heart failure (HF) in a community-based cohort of Blacks. We studied 3,669 participants (mean age 54 years, 63% women) of the Jackson Heart Study without prevalent HF or coronary heart disease (CHD). Participants were divided into three groups: (1) Reduced EF (<50%), (2) LNEF (≥50%, <55%), and (3) Normal EF (≥55%). There were 197 cases of incident HF hospitalizations over a median follow-up of 10 years (interquartile range 9.4 to 10). After adjustment for conventional risk factors and incident CHD, the LNEF group had a higher rate of incident HF hospitalization than the Normal EF group (HR 1.58, 95% CI 1.04 to 2.38, p<0.05). Furthermore, this relation remained statistically significant after additionally adjusting for LV mass index but was not significant after adjusting for LV diastolic dysfunction grade. In participants with LNEF with incident HF, 63% developed HF with reduced EF and 37% developed HF with preserved EF. In conclusion, LNEF is associated with higher risk of incident HF hospitalization in comparison with normal EF in a community-based cohort of Blacks. In those with LNEF who went on to develop HF, most cases were HF with reduced EF. These findings suggest that strategies are needed for risk stratification and management to improve outcomes in patients with LNEF.

Higher plasma leptin levels are associated with reduced left ventricular mass and left ventricular diastolic stiffness in black women: insights from the Genetic Epidemiology Network of Arteriopathy (GENOA) study

Our previous experimental animal data suggest a beneficial effect of leptin on LV structure and function. We hypothesized that leptin levels are associated with lower LV mass and myocardial stiffness which are important risk factors for the development of heart failure with preserved ejection fraction (HFpEF). We evaluated 1172 blacks, in which the prevalence of HFpEF is quite high, with preserved LV ejection fraction (EF > 50%) from the Genetic Epidemiology Network of Arteriopathy Study (mean age 62.9 years, 72% women), a community-based study to identify genes influencing blood pressure and target organ damage due to hypertension. Associations between leptin levels and indices of LV structure and function were evaluated using generalized estimating equations accounting for clustering in siblings. LV myocardial stiffness was evaluated using diastolic wall strain (DWS) measured by echocardiography. Analyses were stratified by sex because leptin levels were three times higher in women than men (p < 0.001). After adjustment for confounders, higher leptin levels were associated with lower LV mass (coefficient for 1 s.d. increase of leptin level: -5.825 g, 95% CI: -9.755 to -1.895 g, P = 0.004) and higher DWS (lower LV stiffness) (coefficient for 1 s.d. increase of leptin level: 0.009, 95% CI: 0.002-0.015, P = 0.007) in women. There were no statistically significant associations in men. In women, there were interactions between leptin levels and body mass index quartiles on LV mass and stiffness (p < 0.05 for both). Higher leptin levels were associated with lower LV mass and stiffness in obese but not lean black women.

Diastolic wall strain is associated with incident heart failure in African Americans: Insights from the atherosclerosis risk in communities study

BACKGROUND

Increased left ventricular (LV) myocardial stiffness may be associated with impaired LV hemodynamics and incident heart failure (HF). However, an indicator that estimates LV myocardial stiffness easily and non-invasively is lacking. The purpose of this study was to determine whether diastolic wall strain (DWS), an echocardiographic estimator of LV myocardial stiffness, is associated with incident HF in a middle-aged community-based cohort of African Americans.

METHODS AND RESULTS

We investigated associations between DWS and incident HF among 1528 African Americans (mean age 58.5 years, 66% women) with preserved LV ejection fraction (EF ≥50%) and without a history of cardiovascular disease in the Atherosclerosis Risk in Communities Study. Participants with the smallest DWS quintile (more LV myocardial stiffness) had a higher LV mass index, higher relative wall thickness, and lower arterial compliance than those in the larger four DWS quintiles (p<0.01 for all). Over a mean follow-up of 15.6 years, there were 251 incident HF events (incidence rate: 10.9 per 1000 person-years). After adjustment for traditional risk factors and incident coronary artery disease, both continuous and categorical DWS were independently associated with incident HF (HR 1.21, 95%CI 1.04-1.41 for 0.1 decrease in continuous DWS, p=0.014, HR 1.40, 95%CI 1.05-1.87 for the smallest DWS quintile vs other combined quintiles, p=0.022).

CONCLUSIONS

DWS was independently associated with an increased risk of incident HF in a community-based cohort of African Americans. DWS could be used as a qualitative estimator of LV myocardial stiffness.

Increased Proximal Aortic Diameter is Associated With Risk of Cardiovascular Events and All-Cause Mortality in Blacks The Jackson Heart Study

BACKGROUND

Enlargement of the proximal aorta is associated with aortic wall tissue remodeling, including fragmentation of the elastin fibers, increased synthesis of collagen, and calcification, all of which are associated with aortic wall stiffening. We hypothesized that the proximal aortic diameter (AoD) is associated with cardiovascular events in a community-based cohort of blacks.

METHODS AND RESULTS

We investigated the associations between AoD and cardiovascular events among 3018 black participants (mean age, 55.9 years; 69% women) without past history of cardiovascular disease in the Jackson Heart Study. AoD was measured using echocardiography at the level of the sinuses of Valsalva at end diastole. Cardiovascular event was defined as incident myocardial infarction, fatal coronary artery disease, stroke, or heart failure hospitalization. Cox proportional hazards regression models were used to evaluate the association between baseline AoD and cardiovascular events. Over a median follow-up of 8.3 years, there were 258 cardiovascular events (incident rate, 10.5 per 1000 person-years). After adjustment for traditional risk factors, increased AoD was significantly associated with cardiovascular events (hazard ratio per 1-cm increase, 1.72; 95% CI, 1.10-2.69; P<0.05). Participants in the top AoD quintile had a higher incidence of cardiovascular events compared to those not in the top quintile (hazard ratio, 1.47; 95% CI, 1.11-1.94; P<0.005) after adjustment for risk factors.

CONCLUSIONS

Greater AoD was associated with an increased risk of cardiovascular events in a community-based cohort of blacks. AoD may be useful as a predictor of incident cardiovascular events and further investigation is warranted.

Physical Activity Is Associated With Reduced Left Ventricular Mass in Obese and Hypertensive African Americans

BACKGROUND

Physical activity (PA) has been associated with decreased left ventricular (LV) hypertrophy in previous studies. However, little is known about the relationship between PA and LV structure and factors which influence this relationship among African Americans.

METHODS

We evaluated 1,300 African Americans with preserved LV ejection fraction (EF > 50%) from the Genetic Epidemiology Network of Arteriopathy (GENOA) Study (mean age 62.4 years, 73% women). PA index was calculated as 3 * heavy activity hours + 2 * moderate activity hours + slight activity hours/day. The relationship between PA index and LV structure was evaluated using generalized estimating equation. The association between PA index and LV mass index by age group, sex, body mass index (BMI), history of hypertension, diabetes or coronary heart disease, estimated glomerular filtration rate, and current smoking status were plotted.

RESULTS

After adjustment for these factors, higher PA index was independently associated with lower LV mass index (P < 0.05). There were significant interactions between PA index and obesity (BMI ≥ 30) and history of hypertension on LV mass index (P for interaction <0.05, for both). Higher PA index was associated with lower LV mass index more in obese or hypertensive participants compared with nonobese or nonhypertensive participants.

CONCLUSIONS

Higher PA index was associated with reduced LV hypertrophy in obese and hypertensive African Americans. Prospective studies aimed at assessing whether increasing PA prevents LV hypertrophy and potentially reduces the risk of heart failure in these at risk groups are warranted.

Heart rate variability on antihypertensive drugs in black patients living in sub-Saharan Africa

Background

Compared with Caucasians, African Americans have lower heart rate variability (HRV) in the high-frequency domain, but there are no studies in blacks born and living in Africa.

Methods

In the Newer versus Older Antihypertensive agents in African Hypertensive patients trial (NCT01030458), patients (30–69 years) with uncomplicated hypertension (140–179/90–109 mmHg) were randomized to single-pill combinations of bisoprolol/hydrochlorothiazide (R) or amlodipine/valsartan (E). 72 R and 84 E patients underwent 5-min ECG recordings at randomization and 8, 16 and 24 weeks. HRV was determined by fast Fourier transform and autoregressive modelling.

Results

Heart rate decreased by 9.5 beats/min in R patients with no change in E patients (− 2.2 beats/min). R patients had reduced total (− 0.13 ms²; p = 0.0038) and low-frequency power (− 3.6 nu; p = 0.057), higher high-frequency (+ 3.3 nu; p = 0.050) and a reduced low- to high-frequency ratio (− 0.08; p = 0.040). With adjustment for heart rate, these differences disappeared, except for the reduced low-frequency power in the R group (− 4.67 nu; p = 0.02). Analyses confined to 39 R and 47 E patients with HRV measurements at all visits or based on autoregressive modelling were confirmatory.

Conclusion

In native black African patients, antihypertensive drugs modulate HRV, an index of autonomous nervous tone. However, these effects were mediated by changes in heart rate except for low-frequency variability, which was reduced on beta blockade independent of heart rate.

Aldosterone and alterations of hypertension-related vascular function in African Americans

BACKGROUND

African Americans have a high prevalence of hypertension and hypertension-related vascular disease. We previously reported that plasma aldosterone concentrations are relatively high in hypertensive African Americans. This study evaluates the hypothesis that hypertension and hypertension-related alterations of peripheral vascular and renal vascular function are associated with aldosterone.

METHODS

Twenty four-hour blood pressures, cardiac output, renal blood flow (RBF), plasma renin activity (PRA), and plasma aldosterone were measured in hypertensive and normotensive African Americans. Hemodynamic measurements were repeated in response to graded infusions of norepinephrine (NE).

RESULTS

Ambulatory blood pressures in hypertensives and normotensives were 142 +/- 1/86 +/- 1 and 117 +/- 1/70 +/- 1 mm Hg, respectively. Cardiac index (CI) was lower (P < 0.01), peripheral vascular resistance was higher (P < 0.0001), arterial compliance was lower (P < 0.0001), RBF was lower (P = 0.04), and renal vascular resistance (RVR) was higher (P < 0.0001) in the hypertensives. Overall, blood pressures were positively correlated with peripheral vascular resistance (P < 0.0001) and inversely correlated with vascular compliance (P < 0.0001). In response to NE, hypertensives had greater increases of systolic blood pressure (P < 0.004) and pulse pressure (P < 0.005). PRA was lower (P < 0.0001) and plasma aldosterone was higher (P < 0.0001) in the hypertensives. Overall, blood pressures and pulse pressure were correlated with aldosterone (P < or = 0.01). Vascular compliance, RVR, and the increment of RVR in response to NE were also correlated with aldosterone (P < or = 0.03).

CONCLUSIONS

Aldosterone may contribute to hypertension and to hypertension-related alterations of peripheral vascular and renal vascular function in African Americans.

Angiotensin‐Converting Enzyme Inhibitors and Angiotensin Receptor Blockers in African‐American Patients With Hypertension

African-American patients with hypertension are less responsive to blockers of the renin-angiotensin system than white patients. The relative efficacy of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers and the extent of cross-resistance to these agents has not been studied. Fifty-one African-American patients with stage 1-2 hypertension were randomly assigned to enalapril or candesartan cilexetil for 8 weeks and then crossed over to the other treatment. Nonresponders to enalapril and candesartan used a combination of the two. Of the 51 patients randomized (average age 61.2+/-9 years, blood pressure 148/100 mm Hg, heart rate 74 bpm, and body weight 92.8 kg), 44 completed the study. At Week 8, systolic blood pressure (SBP) was reduced by 4.8 mm Hg with enalapril and by 4.7 mm Hg with candesartan (p=NS), and diastolic blood pressure (DBP) was reduced by 4.4 mm Hg and 5.6 mm Hg, respectively (p<0.04). Of these 44 patients, 11 (25%) responded to enalapril by SBP criteria and 19 (43%) by DBP criteria. Seven patients (16%) responded by both SBP and DBP criteria, and 21 patients (48%) were nonresponders. With candesartan, 13 patients (29%) responded by SBP criteria, 20 (45%) by DBP criteria and 12 (27%) by both SBP and DBP criteria (p<0.04, compared with enalapril). Only six patients (14%) responded to both enalapril and candesartan by both SBP and DBP criteria. Of the 18 nonresponders to either enalapril or candesartan, the combination of the two had minimal additional effect. Significant changes in plasma-renin activity and angiotensin II levels were noted only with the high dose of each drug. In this small group of patients, treatment with candesartan resulted in slightly higher response and control rates than enalapril, more than 40% of patients who responded to enalapril did not respond to candesartan and vice versa, and in nonresponders, a combination of candesartan and enalapril offered little additional antihypertensive effect.

Association of Adrenal Steroids With Hypertension and the Metabolic Syndrome in Blacks

Blacks have a high prevalence of hypertension and adrenal cortical adenomas/hyperplasia. We evaluated the hypothesis that adrenal steroids are associated with hypertension and the metabolic syndrome in blacks. Ambulatory blood pressures, anthropometric measurements, and measurements of plasma renin activity (PRA), aldosterone, fasting lipids, glucose, and insulin were obtained in 397 subjects (46% hypertensive and 50% female) after discontinuing antihypertensive and lipid-lowering medications. Hypertension was defined as average ambulatory blood pressure >130/85 mm Hg. Late-night and early morning salivary cortisol, 24-hour urine-free cortisol, and cortisone excretion were measured in a consecutive subsample of 97 subjects (40% hypertensive and 52% female). Compared with normotensive subjects, hypertensive subjects had greater waist circumference and unfavorable lipid profiles, were more insulin resistant, and had lower PRA and higher plasma aldosterone and both late-night and early morning salivary cortisol concentrations. Twenty-four-hour urine-free cortisol and cortisone did not differ. Overall, ambulatory blood pressure was positively correlated with plasma aldosterone (r=0.22; P<0.0001) and late-night salivary cortisol (r=0.23; P=0.03) and inversely correlated with PRA (r=-0.21; P<0.001). Plasma aldosterone correlated significantly with waist circumference, total cholesterol, triglycerides, insulin, and the insulin-resistance index. Based on Adult Treatment Panel III criteria, 17% of all of the subjects were classified as having the metabolic syndrome. Plasma aldosterone levels, but not PRA, were elevated in subjects with the metabolic syndrome (P=0.0002). The association of aldosterone with blood pressure, waist circumference, and insulin resistance suggests that aldosterone may contribute to obesity-related hypertension in blacks. In addition, we speculate that relatively high aldosterone and low PRA in these hypertensive individuals may reflect a mild variant of primary aldosteronism.

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.

Extracellular water: greater expansion with age in African Americans

Aging is associated with the onset of chronic diseases that lead to pathological expansion of the extracellular water (ECW) compartment. Healthy aging, in the absence of disease, is also reportedly accompanied by a relative expansion of the ECW compartment, although the studies on which this observation is based are few in number, applied different ECW measurement methods, included small ethnically homogeneous subject samples, and failed to adjust ECW for non-age-related influencing factors. The aim of the current study was to examine, in a large (n = 1,538) ethnically diverse [African American (AA), Asian, Caucasian, Hispanic] subject group the cross-sectional relationships between ECW and age after controlling first for other potential factors that may influence fluid distribution. ECW and intracellular water (ICW) were derived from measured total body water (isotope dilution) and potassium (40K whole body counting). The cross-sectional relationships between ECW, ICW, and ECW/ICW (E/I), and age were developed using multiple regression modelling methods. Body weight, weight squared, height, age, sex, race, and interactions were all significant ECW predictors. The slope of the observed race x age interaction was significantly greater in AA (beta = 0.0005, P = 0.005) than in the three other race groups. Race, sex, and age differences in fluid distribution persisted after adjusting for body composition in a subgroup (n = 994) with dual-energy X-ray absorptiometry lean soft tissue and fat measurements. A relative ECW expansion (i.e., E/I) was present with greater age in most sex-race groups, although the effect was not significantly larger in AA males (P > 0.05) compared with the other race groups, except Asians (P < 0.05). For females, a larger E/I-age effect was found in AA compared with the other race groups, but only the comparison against Hispanics was significant (P < 0.05). The ECW compartment and E/I are thus variably larger, according to race, in healthy older subjects independent of sex, lean soft tissue, and fat mass.

Genetic linkage of albuminuria and renal injury in Dahl salt-sensitive rats on a high-salt diet: comparison with spontaneously hypertensive rats

Our aim was to study the effects of high-salt diet on the genetics of albuminuria and renal injury in the Dahl salt-sensitive (SS) rat. We compared SS with salt-resistant spontaneously hypertensive rats (SHR) and with genetically related salt-sensitive stroke-prone SHR (SHRSP). Moreover, we performed genome-wide linkage analysis to identify quantitative trait loci (QTL) contributing to salt-induced renal injury in an F2population derived from SS and SHR ( n = 230). In response to high-salt diet SS and SHRSP developed a striking increase in systolic blood pressure, urinary albumin excretion (UAE), and renal damage indices compared with SHR. Both SHRSP and SS developed severe glomerulosclerosis, whereas microangiopathy, tubulointerstitial fibrosis, and inflammation were more pronounced in SHRSP. We detected two QTL with significant linkage to UAE on rat chromosomes (RNO) 6 and 19. Comparison with the recently identified salt-independent UAE QTL in young animals revealed that the UAE QTL on RNO6 is unique to high-salt conditions, whereas RNO19 plays a significant role during both low- and high-salt conditions. Some F2animals demonstrated severe microangiopathy and tubulointerstitial injury, which exceeded the degree observed in the parental SS strain. Three loci demonstrated suggestive linkage to these phenotypes on RNO3, RNO5, and RNO20, whereas no linkage to glomerular damage was found. Further analyses at these loci indicated that the severity of renal injury was attributable to the SHR allele. Our data suggest that the SHR genetic background confers greater susceptibility for the development of microangiopathy and tubulointerstitial injury in salt-sensitive hypertension than the SS background.

Low arterial compliance in young African-American males

Hypertension remains a common public health challenge because of its prevalence and increase in co-morbid cardiovascular diseases. Black males have disproportionate pathophysiological consequences of hypertension compared with any other group in the United States. Alterations in arterial wall compliance and autonomic function often precede the onset of disease. Accordingly, our purpose was to investigate whether differences exist in arterial compliance and autonomic function between young, healthy African-American males without evidence of hypertension and age- and gender-matched non-African-American males. All procedures were carried out noninvasively following rest. Arterial compliance was calculated as the integrated area starting at the well-defined nadir of the incisura of the dicrotic notch to the end of diastole of the radial artery pulse wave. Power spectral analysis of heart rate and blood pressure variability provided distributions representative of parasympathetic and sympathetic modulations and sympathovagal balance. Baroreflex sensitivity (BRS) was calculated using the sequence method. Thirty-two African-American and twenty-nine non-African-American males were comparable in anthropometrics and negative family history of hypertension. t-Tests revealed lower arterial compliance (5.8 +/- 2.4 vs. 8.6 +/- 4.0 mmHg. s; P = 0.0017), parasympathetic modulation (8.9 +/- 1.1 vs. 9.7 +/- 1.1 ln ms2; P = 0.0063), and BRS (13.7 +/- 7.3 vs. 21.1 +/- 8.5 ms/mmHg; P = 0.0007) and higher sympathovagal balance (2.9 +/- 3.2 vs. 1.5 +/- 1.1; P = 0.03) in the African-American group. In summary, differences exist in arterial compliance and autonomic balance in African-American males. These alterations may be antecedent markers of disease and valuable in the detection of degenerative cardiovascular processes in individuals at risk.

Genetic loci contribute to the progression of vascular and cardiac hypertrophy in salt-sensitive spontaneous hypertension

OBJECTIVE

The salt-sensitive Dahl rat and the spontaneously hypertensive rat develop comparable spontaneous hypertension on a low-salt diet, whereas only the salt-sensitive Dahl rat strain develops a striking increase in blood pressure and cardiovascular hypertrophy on a high-salt diet. We set out to identify quantitative trait loci (QTLs) contributing to the progression of salt-induced organ damage in hypertension by studying an F2 population derived from both strains.

METHODS AND RESULTS

We determined systolic blood pressure (SBP), vascular aortic hypertrophy (AH), cardiac left ventricular (LV) hypertrophy (LVH), and LV fibrosis in 230 male F2-animals on a high-salt diet. A strong correlation between AH and LVH was found (r=0.58, P<0.0001), and genome-wide QTL mapping detected suggestive or significant QTLs in overlapping chromosomal fragments for AH and LVH on chromosomes 1, 3, and 19, respectively. A significant influence of SBP on the extent of LVH and AH was evident at all QTLs, although significant linkage to SBP (together with LVH) was only found on chromosome 9. No QTLs for LV fibrosis were detected.

CONCLUSIONS

This study demonstrates a strong correlation between AH and LVH in salt-sensitive hypertension and identifies QTLs contributing to the progression of cardiovascular hypertrophy in this condition.

Therapeutic lifestyle changes for hypertension and cardiovascular risk reduction

Elevated blood pressure is the most common chronic illness in the United States, affecting more than 50 million people. Hypertension is an even greater problem in the African American community. Traditionally, management of hypertension and cardiovascular risk reduction has focused on drug therapy; however, several studies have shown the benefits of therapeutic lifestyle changes for blood pressure lowering and cardiovascular risk reduction. Therapeutic lifestyle changes to reduce blood pressure have enormous potential as a means for preventing and controlling hypertension and thereby reducing the risk of coronary heart disease. Although the reductions in blood pressure are relatively modest with these approaches, they could potentially have a beneficial impact on overall cardiovascular morbidity and mortality when applied to the whole population. Because of their high prevalence of certain cardiovascular risk factors (e.g., obesity, diabetes mellitus) and greater salt sensitivity, therapeutic lifestyle changes have particular relevance for African Americans.

Identification of hypertension-related QTLs in African American sib pairs

To link hypertension-related phenotypes with chromosomal loci, genome scans were performed in 150 African American sib pairs concordant for essential hypertension. Phenotypes included blood pressure, anthropomorphic measurements, and estimates of body fluid compartments as determined by impedance plethysmography. These phenotypes were also measured in 335 normotensive African Americans. Phenotypes with LOD scores >3.3 were further evaluated for significance by use of permutation procedures. Significant linkage was detected for body mass index (BMI) on chromosomes 1 and 8 and for the ratio of extracellular water to total body water (ECF/TBW) on chromosomes 3, 5, 6, and 7. Both BMI and ECF/TBW were greater in hypertensive sibs than in normotensive subjects (P<0.001). In a subset of hypertensive sibs and normotensive subjects, average 24-hour blood pressures were correlated with ECF/TBW (P<0.01). A region linked to BMI in the hypertensive sibs corresponds to a region of conserved synteny containing blood pressure-related QTLs in an F2 cross of Brown NorwayxDahl salt-sensitive rats. Focusing on hypertension-related phenotypes is a promising approach for identifying the genetic determinants of hypertension.

The association between hypertension and other cardiovascular risk factors in young adult African Americans

Hypertension is a major cause of cardiovascular disease in African Americans. The excess morbidity and mortality due to cardiovascular disease in African Americans compared to Caucasians is not well explained. The purpose of this study was to examine the association between hypertension and other cardiovascular risk factors in young adult African Americans. A risk factor scoring system was developed, based on national guidelines for obesity, smoking, cholesterol levels, glucose tolerance, and blood pressure. Data from a previously studied cohort of 206 women and 117 men were analyzed for the association of hypertension with other risk factors. Among women, risk factor intensification is due to impaired glucose tolerance and obesity. Among men, intensification appears to be related to all major risk factor categories. These findings indicate that among hypertensive African Americans there is an amplification of other risk factors. The data also support the clinical management of multiple risk factors as well as the achievement of blood pressure control.