Joseph K. Murphy

Race and gender influence ambulatory blood pressure patterns of adolescents.

&NA; The purpose of this study was to examine ambulatory blood pressure and heart rate patterns in healthy, normotensive adolescents and to determine the influence of race and gender on these patterns. Ambulatory blood pressure recordings were performed on 199 adolescents; 42 were black males, 55 were white males, 65 were black females, and 37 were white females. The mean age (±SD) was 13±2 years. Blood pressure readings were obtained with an automatic, noninvasive recorder. Black adolescents and white adolescents had similar blood pressures while awake (116/69 vs. 116/69 mm Hg), with boys having higher levels of systolic blood pressure (118 vs. 114 mm Hg) and comparable levels of diastolic blood pressure (69 vs. 69 mm Hg) relative to girls. The patterns while the adolescents were asleep, however, were different. White boys (106 mm Hg), white girls (105 mm Hg), and black girls (105 mm Hg) had similar systolic blood pressures during sleep. Black boys (112 mm Hg), however, had significantly higher systolic blood pressures while asleep. Black adolescents, as a group, had significantly higher diastolic blood pressures than white adolescents while asleep (64 vs. 61 mm Hg). Changes in blood pressure from awake to asleep were not related to changes in heart rate. Results of this study indicate that both race and gender are important determinants of the diurnal pattern of blood pressure and heart rate in adolescents. (Hypertension 1989;14:598‐603)

Race and cardiovascular reactivity. A neglected relationship.

The magnitude of the cardiovascular response to stress has been implicated in the pathogenesis of cardiovascular disease. Psychological stress procedures have received increased usage as an alternative to expensive physical (exercise) stress procedures. In the present investigation, 213 healthy, black or white, male or female children between the ages of 6 and 18 years were exposed to the psychological stress of a video game. The video game challenge was administered by a black or a white experimenter and was played under three levels of increasing stress, 1) personal challenge, 2) experimenters challenge, and 3) experimenters challenge accompanied by a financial incentive, while blood pressure and heart rate were monitored. Results indicated that the video games provoked significant and incremental cardiovascular reactivity across the games. Black children demonstrated significantly greater reactivity than white children; the racial difference was more reliably observed for systolic and diastolic blood pressure than for heart rate. Furthermore, the race of the experimenter exerted a significant effect and often interacted with the race of the child, such that greater reactivity occurred in same-race pairings than in mixed-race pairings. These results suggest that reactivity is affected by an individuals race and social milieu and that reactivity may be one mechanism responsible for the greater prevalence of hypertension among blacks.

Aerobic fitness and the diurnal rhythm of blood pressure in adolescents.

We examined the effects of aerobic fitness and race on the diurnal rhythm of blood pressure of 175 healthy adolescents who performed a cycle ergometer maximal exercise test while oxygen consumption was measured. A median split of maximum oxygen consumption for boys and girls separately classified them as either “more-fit” or “less-fit” subjects. Ambulatory blood pressure recordings were also performed, and the data were analyzed for means while subjects were awake and asleep. Less-fit black boys had higher systolic pressures than more-fit black boys while awake (124 vs. 115 mm Hg;p < 0.009) and asleep (117 vs. 108;p < 0.001). Less-fit black boys also had higher systolic pressures than less-fit white boys while awake (114;/?< 0.002) and asleep (105; /?< 0.001), and they had higher systolic pressures than more-fit white boys while asleep (105;p < 0.01). Less-fit black girls had higher systolic pressures than more-fit black girls while awake (116 vs. 109;p < 0.004) and asleep (109 vs. 100;p < 0.001). Less-fit black girls also had higher diastolic pressures than more-fit black girls while awake (71 vs. 66; p < 0.002) and asleep (66 vs. 61;p < 0.001). In addition, less-fit black girls had higher systolic pressures than more-fit white girls while asleep (104; p < 0.05), higher diastolic pressures than more-fit white girls while awake (68;p < 0.05) and asleep (60; p < 0.006), and higher diastolic pressures than less-fit white girls while asleep (61;p < 0.001). These findings indicate that fitness influences ambulatory blood pressure profiles, particularly in black adolescents.

Race and cardiovascular reactivity. A replication.

In a previous study, we reported that black children demonstrated greater cardiovascular reactivity than did white children to the psychological stress of a television video game. Reliance on urban volunteers and the wide age range of the children may have limited conclusions concerning the generalizability of those results. In the present study, 481 of 484 children enrolled in the third grade of the public schools of an entire rural county in Tennessee were examined with the same video game procedure used previously. Results indicated greater heart rate and blood pressure reactivity among black children than among white children. Thus, the previous results were replicated. The greater prevalence of hypertension among black adults may relate to the greater reactivity among black children; reactivity may be either a marker or a mechanism in the development of hypertension.

A comparison of two automated monitors in the measurement of blood pressure reactivity

Cardiovascular reactivity is the change in blood pressure, pulse, and other parameters of cardiovascular function in response to a challenging task. During the conduct of cardiovascular reactivity protocols, researchers frequently use automated blood pressure devices to measure blood pressure reactivity. However, the accuracy of automated devices in measuring blood pressure reactivity is unknown. To investigate the accuracy and precision of the Dinamap 1846 SXP and the VitaStat 2600B in the measurement of blood pressure reactivity, we compared blood pressure reactivity recorded by the VitaStat and Dinamap with that obtained by observers using a conventional mercury sphygmomanometer. At three sites, 159 normotensive subjects performed the same task twice, once with blood pressure reactivity measured by the manual observers and once by the VitaStat (n = 79) or Dinamap (n = 80), with the order determined at random. Ratios (VitaStat/Dinamap) of aggregate within-person variance for baseline and task, systolic and diastolic blood pressures ranged from 1.53 to 4.93 (all P < 0.01), suggesting that the Dinamap has better precision than the VitaStat. For both diastolic and systolic blood pressure reactivity and for both types of automated devices, the mean differences in blood pressure reactivity between manual and automated measurements were small (range, -1.8 to 0.8 mm Hg). However, the VitaStat versus manual scatter plot of diastolic blood pressure reactivity showed greater dispersion (correlation coefficient r = 0.16, P = 0.15) than the Dinamap versus manual scatter plot (r = 0.36, P = 0.001). For systolic blood pressure reactivity, the VitaStat versus manual and Dinamap versus manual scatter plots were similar. Our data indicate that the Dinamap is superior to the VitaStat in the measurement of blood pressure reactivity. The substantial performance differences between the VitaStat and Dinamap suggest that other automated blood pressure monitors must be evaluated prior to use in cardiovascular reactivity studies.

CARDIOVASCULAR RISK FACTORS IN CHILDREN: SOCIOECONOMIC VARIABLED AFFECTING THE COLLECTION OF VALID DATA

Though physical fitness and activity level (AL) have been associated with disease and mortality reductions, few studies have examined methods applicable to epidemiologic studies of children. In this study, parents classified their childs AL as (1) sedentary, (2) slightly active, or (3) active. Children (25 black females [BM], 32 white females [WM], 47 black males [BM], and 52 white males [WM] aged 6-18) completed a maximal exercise test. AL reports correlated significantly with maximal oxygen consumption (VO2 max) largely due to the association among WM. Analysis of household (HH) demographic variables indicated that in mother-headed HH, AL reports were uncorrelated with VO2 max (Table of means and correlations; *p≤.05; **p≤.01). Indirectly, race affected AL reports, i.e., 59% of black children were from mother-headed HH versus 13% of white children. Thus, a single question provided an approximation of childrens fitness; the accuracy was affected by family structure, e.q., mothers who head HHs may have less time to observe their children.

DECREASED ERYTHROCYTE Na+ PUMP ACTIVITY IN NORMOTENSIVE CHILDREN OF HYPERTENSIVE PARENTS

Increased erythrocyte (RBC) intracellular Na+ and depressed RBC Na+-pump activity (NaPA) occur in adults with essential hypertension (EH). Lithium-Na countertransport (Na influx) has been found to be increased in RBC of normotensive (N) children of hypertensive parents, and may serve as a marker for later EH. To examine whether RBC NaPA (Na efflux) was also associated with parental EH, and perhaps with an increased likelihood of subsequent EH, we assayed ouabain-sensitive 86Rb-uptake in the RBC of 61 N children, 41 with N parents (Group I), and 20 with at least 1 parent with EH (Group II). RBC NaPA was assessed both in plasma from the same subject and in a Krebs buffer. when NaPA was assayed in plasma, values were significantly lower in Group II, 3.07 ± 0.39 (mean ± sem) nmol/mg prot/30 min, compared to Group I, 4.35 ± 0.36 (p<0.03). RBC NaPA assayed in Krebs buffer was not statistically different (2.45 ± 0.48 vs 3.25 ± 0.40 p<0.2) for Groups II and I, respectively). Racial comparisons showed consistent trends (B>W), but no statistical significance. Thus, in a small biracial sample, NaPA was inhibited in N children whose parent(s) had EH. This may prove to be a sensitive marker for adult-onset EH, allowing prospective detection, intervention, and possible prevention of EH.

INDIVIDUAL AND SOCIOECONOMIC VARIABLES AFFECTING BLOOD PRESSURE RESPONSES TO PSYCHOLOGICAL STRESS

Exaggerated blood pressure (BP) responses to stress may be a mechanism or marker for the development of hypertension. In a sample of 211 healthy children between the ages of 6-18 years, we administered a psychological stressor (3 video games) while monitoring BP. If a childs BP (systolic and diastolic) values for each video game were above the median, the child was classified as hyperreactive. We found that 34, or 16%, were classified as hyperreactive. Variables investigated for possible association with hyperreactivity included gender, race, income (as a measure of socio-economic status [SES]), physical activity level, Quetelet index, age, and family history of cardiovascular disease. Only two variables were significantly associated classification as hyperreactive: race and SES. Black children were 3.5 times more likely to demonstrate hyperreactivity than white children. Likewise, children of low SES were 3.2 times more likely to demonstrate hyperreactivity than high SES children. Thus, in normotensive healthy children, low SES black children were at the highest risk of being classified as hyperreactive to a psychologic stressor, i.e., 4.7 times more likely than high SES white children. These data may have critical impact upon research investigating the pathogenesis of hypertension in black Americans. Intervention studies in high risk populations, such as low SES blacks, which attempt to reduce physiologic response to environmental stress, seem to be justified.