William B. Strong

Social support for exercise: Relationship to physical activity in young adults

BACKGROUNDnPhysical inactivity is an independent risk factor for cardiovascular disease, yet little is known concerning factors which influence participation in physical activity or exercise. Two studies assessed the relationships between self-reported physical activity and social support for exercise.nnnMETHODnOne study involved a biracial sample of middle-class male and female teachers (mean age = 38.5 +/- 8.9 years) and one involved a biracial sample of lower- to middle-class males and females (mean age = 35.8 +/- 5.1 years).nnnRESULTSnIn both studies the social support scales had high internal consistencies and a two-component solution identical to the original validation study. In both studies, social support for exercise positively correlated with physical activity, but the relationships were mediated by race, gender, specific types of support (i.e., family, friend), and dimensions of physical activity (i.e., global, work, sports, and leisure). In both studies, regardless of work status and race, womens overall activity, particularly during leisure time, was positively related to family support for exercise. In both studies white womens overall activity levels, especially sports and leisure activities, were positively related to friend support. In both studies, black womens sports activity was positively associated with family support. Among white men in both studies, sports activities and total energy expenditure were positively related to family and friend support. Black mens sports-related activity was positively related to family support among the teachers and to friend support among subjects in the second study.nnnCONCLUSIONnFindings are discussed in terms of future research directed toward identification of other familial and sociocultural variables which might influence individuals involvement in physical activity.

Racial differences in hemodynamic responses to the cold face stimulus in children and adults.

&NA; The prevalence of essential hypertension is higher among blacks than whites. One reason for this difference may be that blacks are more reactive to stressors that produce vasoconstrictive responses. Two studies were conducted to test this hypothesis, one with 10‐ to 14‐year‐old males (20 whites, 20 blacks) and one with young adult males (10 whites, 10 blacks). Subjects had blood pressure, heart rate, cardiac output, and total peripheral resistance measured before, during, and after exposure to forehead cold stimulation. In both studies, blacks exhibited greater increases in diastolic blood pressure and total peripheral resistance to the stressor than whites. The findings are discussed in relation to blacks greater pressor reactivity to stress, which appears to be mediated by changes in total peripheral resistance.

Blood pressure response to dynamic exercise in healthy children--black vs white.

In order to determine normal values for systolic blood pressure response to cycle ergometer stress testing in children, we performed 405 studies in subjects from 6 to 15 years of age, of whom 184 were black and 221 were white. We analyzed the data in relation to sex, color, age, and body surface area. Resting systolic blood pressure showed no differences between groups of black and white children, analyzed either by age or surface area. Peak exercise blood pressures were higher in the black females, in comparison to their white counterparts, only when separated into groups by body surface area. The black males had higher exercise blood pressure values than the whites, both by age and surface area evaluation. Our data suggest a difference in the blood pressure response to dynamic exercise within the black population. Further studies are needed to define the mechanism of this difference and whether this difference may provide a clue to the identification of children at increased risk for developing hypertension later in life.

Acute effects of transcendental meditation on hemodynamic functioning in middle-aged adults.

OBJECTIVEnIncreased peripheral vasoconstriction (ie, total peripheral resistance, or TPR) has been implicated as playing an important role in the early development of essential hypertension. Some studies have demonstrated that Transcendental Meditation (TM) reduces high blood pressure, but the hemodynamic adjustments behind these blood pressure reductions have not been elucidated. The aim of this study was to provide a preliminary investigation of the acute effects of TM on TPR.nnnMETHODSnSubjects were 32 healthy adults (16 women and 16 men; 30 white and two African American; mean age, 46.4 +/- 3.9 years). Subjects were divided into a TM group of long-term TM practitioners (eight white women, nine white men, and one African American man; mean years of twice-daily TM practice, 22.4 +/- 6.7) and a control group (eight white women, five white men, and one African American man). Hemodynamic functioning was assessed immediately before and during three conditions: 20 minutes of rest with eyes open (all subjects), 20 minutes of TM (TM group), and 20 minutes of eyes-closed relaxation (control group).nnnRESULTSnDuring eyes-open rest, the TM group had decreases in systolic blood pressure (SBP) and TPR, compared with increases in the control group (SBP: -2.5 vs. +2.4 mm Hg, p < .01; TPR: -0.7 vs. +0.5 mm Hg/liter per minute, p < .004). During TM, there was a greater decrease in SBP due to a concomitantly greater decrease in TPR compared with the control group during eyes-closed relaxation (SBP: -3.0 vs. +2.1 mm Hg, p < .04; TPR: -1.0 vs. +0.3 mm Hg/liter per minute, p < .03).nnnCONCLUSIONSnTPR decreased significantly during TM. Decreases in vasoconstrictive tone during TM may be the hemodynamic mechanism responsible for reduction of high blood pressure over time. The results of this study provide a preliminary contribution to the understanding of the underlying hemodynamic mechanisms responsible for the beneficial influence of TM on cardiovascular risk factors.

Responses to ergometer exercise in a healthy biracial population of children.

To determine normal values for the exercise variables heart rate, blood pressure, maximal workload, physical working capacity index, J point displacement, and ST segment slope, we stress tested 405 healthy children. We analyzed the data for four body surface area-determined groups, to discover whether there were any racial differences between healthy white children and black children. There were numerous racial differences in blood pressure, maximal workload, and physical working capacity index; there were no differences in the heart rate values. The incidence of false-positive J point displacement was less than or equal to 3% when the PR isoelectric line method was used. The ST segment slope in healthy children was always greater than zero at maximal exercise. Thus, norms for exercise variables must be expressed in relation to both sex and race. The nomograms presented in this report provide an easy-to-use set of normative data for cycle ergometer stress testing in children.

Noninvasive assessment of cardiac output in children using impedance cardiography

This study evaluated the effect of intracardiac shunting on the accuracy of thoracic bioimpedance-derived cardiac output determinations. Twenty-six patients, ranging in age from 3 months to 17 years, underwent cardiac catheterization during which simultaneous Fick and impedance measurements of cardiac output were obtained. The subjects were divided into three groups: 10 children with no intracardiac shunts, nine children with predominant left-to-right intracardiac shunts, and seven children with predominant right-to-left intracardiac shunts. Positive correlations between impedance and Fick-derived cardiac output determinations were obtained in the non-shunt group (r = 0.84), with lower correlations in the left-to-right shunt group (r = 0.70). In the right-to-left shunt group, the impedance derived cardiac output correlated with Fick pulmonary flow (r = 0.82), but the variability was unacceptably large. Although further study is needed, impedance cardiography appears to have validity as a methodology in pediatric critical care and cardiovascular health research.

Cardiac size and function in children with sickle cell anemia

Cardiac size and function were studied echocardiographically in 124 children with sickle cell anemia. A group of 78 healthy black children served as control subjects. Sickle cell patients exhibited progressive chamber enlargement and progressively increasing left ventricular mass. Although contractility indices were normal, when the opposing influences of volume overload due to anemia and ventricular dysfunction were separated, abnormalities of systolic time intervals were identified. Left ventricular systolic time interval ratio and left ventricular preejection period were higher in the sickle cell group and became increasingly abnormal with growth, suggesting that left ventricular function deteriorated with time.

Ethnicity, gender, family history of myocardial infarction, and hemodynamic responses to laboratory stressors in children.

Relationship among ethnicity, gender, grandparents histories of early myocardial infarction, and hemodynamic responses to forehead cold and treadmill exercise were examined in 87 6-to-8-year-olds (57 White, 30 Black). Boys had greater increases in systemic vascular resistance and decreases in cardiac index to forehead cold. Girls had greater increases and quicker recovery in heart rate to dynamic exercise. Blacks had greater increases and slower recovery in diastolic pressure to exercise and forehead cold. Blacks showed greater increases and slower recovery in systemic vascular resistance to forehead cold. Positive-family-history children had greater increases in diastolic pressure and systemic vascular resistance to forehead cold and greater diastolic pressure increases to exercise. Positive-family-history Blacks had greater increases in systolic pressure to exercise and slower recovery than all other groups.

Prediction of left ventricular mass in youth with family histories of essential hypertension

To determine predictors of left ventricular mass (LVM) and hypertrophy (LVH), 56 black and 30 white normotensive healthy youths (mean age 12.6 +/- 2.3 years at initial visit) were studied twice, 2.5 years apart. During the initial visit, anthropometric variables and hemodynamics were measured at rest and before, during, and after 4 physical and behavioral stressors. 2-D directed M-mode echocardiography was performed to derive LVM. Hierarchical multiple regression analyses indicated that follow-up LVM was predicted by initial LVM, weight, height (ht), and gender (males > females; total model R2 = 0.77, P < 0.0001). Predictors of LVM/ht2.7 were initial LVM/ht2.7, weight, ethnicity (blacks > whites), and the aggregate index of blood pressure reactivity (total model R2 = 0.66, P < 0.0001). Youth with LVH at follow-up were taller, heavier, and exhibited greater blood pressure reactivity at initial evaluation. These findings are important since interventional strategies can be developed that target obesity and exaggerated reactivity to stress.

Effects of race, sex, and socioeconomic status upon cardiovascular stress responsivity and recovery in youth

Cardiovascular (CV) responsivity to and recovery from acute laboratory stressors, as derived from aggregate scores of CV functioning during and after postural change, video game challenge, social competence interview, and parent-child conflict discussion, were evaluated in 272 youths [mean age 13.5 +/- 2.6 years; 162 Blacks (77 males, 85 females), 110 Whites (60 males, 50 females)], all with a positive family history of essential hypertension. Blacks demonstrated greater systolic and diastolic blood pressure (SBP, DBP) and lower heart rate responsivity compared to Whites (all P values < 0.05). A race by neighborhood socioeconomic status (SES) interaction for SBP responsivity was also observed where low SES Whites and high SES Blacks had the greatest responsivity compared to their same race cohorts. Additionally, upper SES Whites had the lowest total peripheral resistance responsivity. For recovery, Blacks and males exhibited higher SBP during recovery compared to Whites and females, respectively. These findings extend previous studies and provide further support for the hypothesis that recovery from stress is a potentially informative component of the contribution of stress responsivity to cardiovascular disease.