New Orleans, LA -- The threat of hypertension is real and deadly. According to the National Center for Health Statistics, 23 percent of Americans ages 20-74 suffer from hypertension (more commonly known as high blood pressure). Some 15,000 die each year from this disorder; more than 32 million visit the doctor's office each year for treatment, but the disease affects African Americans disproportionately.

African-American males are at higher risk for hypertension than other demographic groups. An estimated 35 percent of African American men have this disorder, leading to staggering financial costs related to medical and disability expenses.

For years, the scientific community has stated that a variety of environmental, behavioral and biological factors have been proposed to account for the racial differences in the prevalence and severity of hypertension. A new research study suggests that arterial compliance may be an indicator of potential hypertension in African American males.

One form of the disease, arterial hypertension (the elevation of systolic and/or diastolic blood pressure, either primary or secondary), is associated with structural and functional changes in the cardiovascular system. These changes modify the flow of blood through large arteries as well as in small resistance arteries. Arterial compliance is defined as how much the artery can be stretched expressed as a change in volume per unit change in pressure. In animal models as well as in human, HT causes stiffer vessels i.e., a loss in compliance. The loss of compliance is considered a predictor of cardiovascular illness and the cause of arterial disease, hypertension, stroke, diabetes, and atherosclerosis). Recognizing changes in arterial compliance may precede hypertension and help identify individuals at risk.

As with arterial wall compliance, there are conditions in which baroreflex sensitivity (sensory nerve mechanisms designed to regulate increases or decreases in blood pressure) and autonomic function (involuntary nervous system activity) are impaired: in coronary artery disease, stroke, atherosclerosis, hypertension, diabetes, in smokers, and in alcoholic nerve disease.

Autonomic function is composed of the sympathetic and parasympathetic branches. Simply, the stress or relaxation hormones are responsible for maintaining heart rate, blood pressure, and breathing rates to a given “fight or flight” challenge. Sympathetic nervous system activity may be representative of “stress”, while the parasympathetic branch may be defined as the ability to slow heart rate and blood pressure.

In the normal aging process, autonomic function becomes altered and baroreflex sensitivity declines; conversely, young, fit, and non-obese individuals have enhanced autonomic and baroreflex responses. Strong evidence, accounting for racial differences in blood pressure, appears to point toward a decrease in the widening of the blood vessel during mental and physical stress in normotensive African-American men which results in a weakened buffering of blood pressures.

A study was undertaken to determine whether differences in arterial compliance and autonomic function exist in young male African Americans with normal arterial blood pressure and without family history of hypertension compared to a similar group of non African Americans. The author of, "Race, Arterial Compliance and Autonomic Modulation," is Adrienne Stevens Zion, Ed.D. Dr. Zion will present her findings in detail during the American Physiological Society (APS) annual meeting, which is being held as part of the Experimental Biology (EB ’02) meeting. More than 12,000 scientific investigators are attending the conference, which begins April 20-24, 2002 at the Ernest N. Morial Convention Center, New Orleans, LA.

Thirty-two African American volunteers were compared to a similar group of 29 non African American males from staff and students at Columbia and Howard Universities. Potential subjects were screened for general medical history, physical fitness levels, and ancestral history. Systemic medical illness, significant allergies, smoking, and a history of hypertension were reasons for exclusion. Prior to the test, overnight fasting and no caffeine consumption was allowed. Electrocardiograms, beat-by-beat radial blood pressures (BP), and respiratory recordings were monitored. Arterial compliance was calculated as the area under the dicrotic notch of the blood pressure curve. Power spectral analysis of heart rate and blood pressure variability provided distributions representative of parasympathetic and sympathetic modulations, and the ratio of the two: sympathovagal balance. Baroreflex sensitivity (BRS) was calculated using the sequence method.

Despite similarities in anthropometrics, hemodynamics, and fitness, the African-American group displayed significantly lower arterial compliance, BRS, and parasympathetic modulation, and a higher sympathovagal balance than the non African-American group. Essentially, the African American group had less compliant vessels, a decreased ability to sense blood pressure changes, and were less able to lower their heart rates.

This investigation increases our understanding of possible predictors of hypertension - that the establishment of clinical disease may occur much earlier than believed. Based on public health statistics, it is conceivable that these subjects may develop hypertension at a future point in their lives. Accordingly, when markers of disease risk are verified in young asymptomatic African Americans, aggressive behavioral adaptations should be made early in life to minimize the onset and progression of cardiovascular disease.

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