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.