CLINICAL SCIENCES: Clinical Investigations: GUEST EDITORIAL TO ACCOMPANY
Understanding and controlling hypertension continues to remain a major public health challenge as we enter the new millennium. Hypertension affects approximately 50 million adults in the United States (4) and is the leading cause of cardiovascular morbidity and mortality (1,3). Of particular concern is the fact that hypertension disproportionately affects the black population, in terms of both prevalence and subsequent mortality (1–3). The underlying factors for these phenomena have yet to be fully elucidated but likely involve multifaceted factors of both genetic and environmental origin. One potential factor in explaining the etiology of hypertension is cardiovascular reactivity (defined as a change in hemodynamic parameters from baseline in response to a specific stimulus) to stress. A recurring finding in the scientific literature concerning racial differences in cardiovascular reactivity is that blacks exhibit greater vascular tone and sympathetic nervous system activation in response to stressors than do whites (2). A greater understanding of racial influences on physiological and psychological coping strategies and their relationship to optimal cardiovascular health is required to facilitate the identification of those most at risk for cardiovascular disease and also to employ prudent and timely interventions. Toward this end, Jackson and Dishman examined cardiovascular reactivity during a series of active and passive stressors in young black female subjects and the relative influences of fitness and parental history of hypertension.
Whereas most previous studies have limited their stress reactivity physiological outcome measures solely to blood pressure, Jackson and Dishman employ a more comprehensive approach in examining the hemodynamic responses by also monitoring stroke volume, cardiac output, total peripheral resistance (TPR), calf blood flow (CBF), and calf vascular resistance (CVR).
Additionally, the authors extend prior findings by giving special attention to the confounding variables of both fitness and parental history of hypertension. Salient findings from their well-designed study include the report that V̇O2peak assessed from cycle ergometry was positively associated with enhanced blood pressure recovery after a forehead cold pressor test and a mental arithmetic test, despite its association with measures of increased vascular resistance during those tasks. This association, however, was weaker among the subjects who had hypertensive parents, suggesting that the level of fitness required to modify recovery after mental stress among black women may differ according to parental history of hypertension. Although it is apparent that fitness level has complex interactions with blood pressure and hemodynamic responses during and after passive and active stressors, Jackson and Dishman’s study does underscore the utility of including stroke volume and vascular resistance as important adjuncts in assessing cardiovascular reactivity during and after stress.
As stress reactivity may be related to increased risk for cardiovascular disease because of a slower recovery from stress (1,2), the implications of this study emphasize the importance of maintaining and improving overall aerobic fitness (1). One practical application based on Jackson and Dishman’s suggestion that the level of fitness required to modify recovery from mental stress among black women differs according to parental history of hypertension is in identifying those individuals most at risk who may derive the most benefit from exercise prescriptions designed for optimal cardiovascular health. As the authors suggest, additional research in this area could include measuring central sympathetic neural outflow. Assessing the vascular endothelium in relationship to cardiovascular reactivity would also seem warranted.
1. American College of Sports Medicine. Position stand. Physical activity, physical fitness, and hypertension. Med. Sci. Sports Exerc. 25: i–x, 1993.
2. Clark, R., and N. B. Anderson. Efficacy of racism-specific coping styles as predictors of cardiovascular functioning. Ethn. Dis. 11: 286–295, 2001.
3. Falkner, B. The role of cardiovascular reactivity as a mediator of hypertension in African Americans. Semin. Nephrol. 16: 117–125, 1996.
4. The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC V). Arch. Intern. Med. 157: 2413–2446, 1997.