Ethnic differences in circadian hemodynamic profile.

Since the introduction of 24-h ambulatory blood pressure monitoring (ABPM), some studies, although not all, have suggested the presence of a blunted nocturnal blood pressure decline in black versus white subjects, a difference that may help explain the higher incidence of target organ damage in blacks. To better define ethnic differences in diurnal hemodynamic profiles, we studied ABPM recordings from 275 black (55.6% women) and 246 white (43.1% women) previously untreated subjects, with a similar age distribution (from 20 to 79 years) and a wide range of systolic (100-230 mm Hg) and diastolic (50-130 mm Hg) blood pressures. Average clinic systolic (diastolic) blood pressures were higher in black v white men by 10.2 (7.3) mm Hg; P = .04 (P = .004), with a similar trend in women (P = NS). On ABPM, blacks had higher average values, a difference that was greater during sleep (9.4 mm Hg for systolic blood pressure) than while awake (4.7 mm Hg; P = .003). Average diurnal change in systolic blood pressure (awake minus sleep values) was 13.1 +/- 0.7 v 18.0 +/- 0.6 mm Hg for blacks v whites (P < .001). There was a strong negative correlation between baseline (ie, sleep) blood pressure and the diurnal change (r = -0.58; P < .001), but at each given level, blacks had a lower daytime increment/nocturnal fall (P = .02). Results for diastolic blood pressure and heart rate were similar. The data suggest that the smaller diurnal change in blacks may be related in part to their higher blood pressure levels, but that there is an additional, independent effect of race. This results in a greater 24-h blood pressure load in blacks than whites for each given clinic (daytime) value, and may help explain differences in target organ damage. Future studies investigating the effects of blood pressure on target organs in different populations should consider diurnal profiles in addition to clinic blood pressure.

Diurnal blood pressure variation and cardiac mass in American blacks and whites and South African blacks.

American blacks exhibit higher nocturnal blood pressure than American whites with similar daytime pressure. To determine whether this represents a true racial difference, as opposed to a consequence of different environmental factors, we measured ambulatory blood pressure, cardiac left ventricular mass, and urinary electrolyte excretion in 22 South African blacks (15 women, aged 36 +/- 12 years) and age, sex, and daytime mean pressure-matched American blacks and whites. While all three groups exhibited similar daytime blood pressure, American blacks displayed significantly higher nighttime mean blood pressure. Both African blacks and American whites experienced the same fall in nighttime blood pressure. Left ventricular mass index was highest in American blacks and lowest in South African blacks. Urine sodium excretion was similar in all groups, but both black populations excreted significantly less potassium than American whites. The data suggest that the differences in diurnal blood pressure rhythm between American blacks and whites do not represent a true racial difference, but more likely are environmental in origin. Furthermore, since both black populations had similar cation excretion rates, yet differed in blood pressure pattern and cardiac mass, divergence in dietary sodium or potassium intake cannot explain the ethnic group differences in the United States.

Influence of diuretic therapy on the clonidine suppression test.

Moduretic has been reported to inhibit the suppression of plasma norepinephrine (NE) levels by the alpha 2 adrenoceptor agonist, clonidine. To determine whether plasma volume reduction by hydrochlorothiazide (HCTZ) or antagonism of Na+/H+ exchange by amiloride (the constituents of Moduretic) is responsible, the authors performed a modified clonidine suppression test (CST) in nine normal volunteers (aged 25 +/- 2 years), pretreated for 1 week with HCTZ 50 mg daily, amiloride 10 mg daily, or placebo, in a randomized, double-blind, crossover study. Baseline characteristics were identical on all study days, except serum [K+] and weight, which were lowest on HCTZ (3.6 +/- 0.2 mEq/L and 78.7 +/- 2.5 kg), compared with amiloride (4.2 +/- 0.1 mEq/L and 79.9 +/- 2.4 kg) and placebo (4.0 +/- 0.1 mEq/L and 80.2 +/- 2.7 kg, P less than .05). Oral clonidine (0.3 mg) produced a reduction in mean blood pressure by about 20%. Plasma norepinephrine levels were similar in patients receiving placebo, HCTZ, and amiloride (205 +/- 18, 272 +/- 40 and 277 +/- 44 pg/mL, P greater than .20), and decreased significantly during CST. The maximal reduction for each subject averaged 72.7 +/- 12.4%, 87.9 +/- 3.8%, and 82.9 +/- 5.7% for placebo, HCTZ, and amiloride. Clonidine also produced a four to seven-fold increase in plasma growth hormone levels, reduced salivary flow by about 75%, and increased the level of sedation. There were no differences among the three pretreatment regimens in the effects of clonidine, indicating that diuretic therapy does not need to be systematically discontinued in patients undergoing CST.

Diurnal blood pressure variation: differences among disparate ethnic groups.

We examined the possibility that excess cardiovascular morbidity in American blacks compared with whites might be partly the result of differences in diurnal blood pressure variation. Urban American blacks have higher night-time blood pressures and show a smaller increase in blood pressure during the waking day than whites. This difference is associated with a higher cardiac mass in the blacks and occurs despite similar duration and quality of sleep in blacks and whites. Both groups show similar levels of sympatho-adrenal activity at night, but the diurnal increase is smaller in blacks, paralleling the smaller increase in blood pressure. In Africa blacks show a diurnal pressure pattern similar to American whites. Disparities in cation consumption do not explain the differences in blood pressure variation between these groups.

Renal and hemodynamic effects of intravenous fenoldopam versus nitroprusside in severe hypertension.

The renal and hemodynamic effects of intravenously administered fenoldopam mesylate, a novel dopamine-1 receptor agonist, were compared with those of sodium nitroprusside in 28 patients (18 male; 26 black, two white; average age, 49 +/- 3 years) with an average blood pressure of 219/137 mm Hg, most of whom presented with acute target organ damage. Fenoldopam and nitroprusside lowered blood pressure safely to an average pressure of 176/105 mm Hg; highly significant dose-response relations were found for the 13 patients receiving fenoldopam and the 15 receiving nitroprusside. Volume and sodium, potassium, and creatinine concentrations were measured in freely voided urine specimens both before and during intravenous therapy. In the fenoldopam-treated patients, there were significant increases in urinary flow (92 +/- 21 to 168 +/- 37 ml/hr, p less than 0.003), sodium excretion (227 +/- 73 to 335 +/- 90 mu eq/min, p less than 0.001), and creatinine clearance (70 +/- 11 to 93 +/- 13 ml/hr, p less than 0.003). In the nitroprusside-treated group, however, all these parameters decreased, but not significantly. For direct comparison of the two agents, the increments in urinary flow rate (+76 +/- 20 vs. -16 +/- 15 ml/hr, fenoldopam vs. nitroprusside), sodium excretion (+109 +/- 28 vs. -39 +/- 28 mu eq/min), and creatinine clearance (+23 +/- 6 vs. -11 +/- 7 ml/min) were significantly greater (p less than 0.001 for each) in the fenoldopam-treated group. Significant differences were also obtained when these parameters were calculated as percentage increase over baseline. Fenoldopam and nitroprusside are effective therapies for severe, accelerated, or malignant hypertension, but fenoldopam had additional salutary renal effects in these patients.