Martha E. Wilson

A longitudinal study of ethnic differences in ambulatory blood pressure patterns in youth

BACKGROUND Many studies demonstrated an ethnic difference in ambulatory blood pressure (BP) patterns. We examined: 1) the stability of this difference; 2) demographic and anthropometric characteristics that predict the difference over 2 years; and 3) the clinical significance of the difference. METHODS Recordings were performed 2 years apart on 94 African American and 92 European American youths with a positive family history of hypertension, aged 14 +/- 2 years at initial testing. RESULTS African Americans had higher nighttime systolic BP (SBP) on the initial (109 +/- 9 v 105 +/- 8 mm Hg; P < .001) and follow-up (110 +/- 10 v 105 +/- 8 mm Hg; P < .0001) visits despite similar daytime SBP. This was associated with greater left ventricular mass/height2.7 (LVM/height2.7) during the initial (31 +/- 8 v 28 +/- 6 g/height2.7; P < .01) and follow-up (32 +/- 8 v 28 +/- 8 g/height2.7; P < .02) visits. Sex accounted for 17% (P < .0001) of the variance of follow-up daytime SBP in African Americans, and age for an additional 10% (P < .001). In comparison, initial height accounted for 11% (P < .001) of the variance in European Americans. Sex accounted for 18% (P < .0001) of the variance of follow-up nighttime SBP in African Americans, age for an additional 12% (P < .0001), and initial LVM/height2.7 an additional 6% (P < .02). In contrast, sex accounted for 13% of the variance of follow-up nighttime SBP in European Americans, and initial height accounted for an additional 8% (P < .004). CONCLUSIONS The pattern of higher nighttime BP despite similar daytime BP in African Americans is stable over time, with sex as the most important predictor of nighttime BP in both groups. This study provides confirmatory data on the clinical significance of the differences.

Impaired stress-induced pressure natriuresis increases cardiovascular load in African American youths

BACKGROUND We hypothesized that impaired stress-induced pressure natriuresis increases blood pressure (BP) load. METHODS The 118 African American youths were brought into similar levels of sodium balance. The protocol consisted of a 2-h baseline period, a 1-h stress period (competitive video games), and a 2-h recovery period. RESULTS Normal pressure natriuresis (n = 80) resulted from a resistance-mediated (r = 0.23; P <.03) increase in BP (P <.001). In contrast, impaired pressure natriuresis (n = 38), leading to an extended period of elevated BP (P <.05), resulted from a volume-mediated (r = 0.55; P <.002) increase in BP (P <.001). CONCLUSIONS Impaired stress-induced pressure natriuresis may contribute to the development of essential hypertension, particularly in African Americans.

Adiposity Is Related to Gender Differences in Impaired Stress-Induced Pressure Natriuresis

Abstract—The purpose of this study was to determine if there are gender differences in stress-induced pressure natriuresis and to examine the effects of adiposity on these differences. The subjects were 151 boys and 141 girls 15 to 18 years of age who underwent a 5-hour stress protocol (2-hour prestress, 1-hour stress, 2-hour poststress) after being brought into similar levels of sodium balance. The gender-by-condition interaction was significant for systolic and diastolic blood pressure (P =0.001 for both), and the effect of condition was significant for sodium excretion (P =0.001). Systolic blood pressure was higher for boys throughout the protocol (P =0.001 for each) and correlated with body mass index at each condition (range in r =0.28 to 0.35; P <0.001 for each). Hemodynamically, in boys body mass index was correlated with cardiac output during stress (r =0.23; P =0.006), which was correlated with systolic blood pressure (r =0.21; P =0.01). With respect to natriuresis, body mass index was inversely correlated with sodium excretion during stress (r =−0.22; P =0.008) and positively correlated with angiotensin II in a subsample of boys (n=89:r =0.31; P =0.003). The inverse correlation between angiotensin II and sodium excretion during stress approached significance (r =−0.17; P <0.06). Similar results were not observed for girls. In conclusion, gender differences in stress-induced pressure natriuresis appear to be related to the influence of adiposity on both blood pressure and natriuresis.

A comparison of ambulatory blood pressure patterns across populations

BackgroundBlack individuals are characterized by a blunted nocturnal decline (i.e. dipping) in blood pressure compared with whites. The resulting increase in cardiovascular load has been hypothesized to contribute to ethnic differences in hypertension and its sequelae. ObjectiveTo examine data from two different locations and determine factors related to ethnic differences in ambulatory blood pressure pattern. MethodsAmbulatory blood pressure recordings were performed on 300 youths from Memphis, Tennessee and 195 youths from Augusta, Georgia, USA. Stepwise regressions were performed to determine the factors associated with daytime and night-time blood pressure and the nocturnal decline in blood pressure. The factors examined were recording location, ethnicity, gender, age, height, weight and genetic predisposition. ResultsSignificant factors in the model for the nocturnal decline in systolic blood pressure included location (R2 = 0.031, P < 0.001), followed by ethnicity (R2 change = 0.015, P < 0.006) and height (R2 change = 0.009, P < 0.03). Significant factors in the model for the nocturnal decline in diastolic blood pressure included location (R2 = 0.176, P < 0.001), followed by ethnicity (R2 change = 0.016, P < 0.002) and height (R2 change = 0.02, P < 0.001). The nocturnal decline was greater in the Augusta subjects because of higher daytime systolic (P < 0.002) and diastolic (P < 0.001) blood pressure. Weight contributed significantly to the models for resting blood pressure and daytime blood pressure. Gender was the only variable that contributed to the model for resting systolic blood pressure. ConclusionsBoth genetic and environmental factors contribute to individual differences in ambulatory blood pressure patterns. Much of the variance of ambulatory blood pressure levels and patterns remains, however, unexplained.

P-131: Sex differences in stress induced pressure natriuresis in African-American youths

African-Americans are characterized by an increased prevalence of essential hypertension, with a greater prevalence for males than females. We have hypothesized that stress induced impaired sodium regulation contributes to disparity. Therefore, the purpose of this study was to examine the factors related to changes in urinary sodium excretion (UNaV) during an extended stress period in African-American youths. Methods: The 40 subjects were 21 males and 19 females aged 15 to 18 years. The subjects were placed on a controlled sodium intake (4,0006200 mg/day) for 3 days prior to testing to bring them into similar levels of sodium balance. The test was performed on the fourth day. It consisted of a two hour baseline period, a one hour stress period (competitive video game), and a two hour recovery period. The subjects were provided with water throughout the study. Urine samples were collected hourly and blood pressure (BP) each 15 minutes. Overall, U NaV increased from the baseline to the stress period (10 65 v 1368 mEq/hr; p,0.002) and decreased from stress to recovery (7 64 mEq/hr; p,0.0001). Systolic BP (SBP) increased from the baseline period to the stress period (115 610 v 119612 mm Hg; p,0.009) and decreased during the recovery period (112 610 mmHg; p,0.07). However, different patterns were observed for males and females. Females had significant increases in U NaV form baseline to stress (9 65 v 1469 mEq/hr; p,0.002), and a significant decrease during recovery (7 64 mEq/hr; p,0.0001). SBP did not increase during stress. In contrast, males did not show a significant change in U NaV during stress; however, they did show a significant increase in SBP (116 610 v 124611 mmHg; p,0.002) which was still elevated into the second hour of recovery (118 6 10 mmHg; P,0.01). In conclusion, these results are consistent with our hypothesis that stress induced impaired pressure natriuresis resulting in an increased BP load contributes to the increased prevalence of hypertension in African-American males.