New Study Shows Why Hypertension Affects Black Males
Disproportionately
Differences found in arterial compliance, autonomic balance
September 10, 2003 – Bethesda, MD – Hypertension
(HT) remains a public health challenge because it is so prevalent and leads
to increases in cardiovascular disease. It is a disease that
disproportionately affects African-American males. Not only does HT occur
more frequently among this group, it also presents itself earlier in their
life, and causes increased complications of cardiovascular diseases compared
with white Americans.
Because changes in the arterial wall compliance and
autonomic function often precede the onset of HT, a team of researchers has
sought to identify whether differences in these areas exist among young,
health African-American males who show no evidence of hypertension and
compared them with their non-African-American counterparts. A joint
research team from Columbia and Howard Universities has proven that indeed
such differences exist. Moreover, as changes in these regions may be
antecedent markers of HT, a safe, relatively inexpensive screening and
detection program should be considered to target individuals at risk. Such
early screening may help reduce the staggering human and financial impact
the disease has upon black men in America.
A New Study
The authors of a new study, “Low Arterial Compliance in
Young African-American Males,” are
Adrienne S. Zion, Richard P. Sloan,
Matthew N. Bartels, John A. Downey, Ronald E. De Meersman, and Robert E.
Fullilove, of Columbia University, New York, NY, and Vernon Bond, Richard G.
Adams and Deborah Williams, of Howard University, Washington, DC. Their
findings appear in the August 2003 edition of the American Journal of
Physiology -- Heart and Circulatory Physiology, one of 14 scientific
journals published monthly by the American Physiological Society (APS) (www.the-aps.org).
Methodology
Thirty-two African-American (AA) volunteers were
compared with a similar group of 29 non-African-American (NAA)
males recruited from the staff and student body of Columbia and
Howard Universities. All participants were American born, listed English as
their primary language, and had no familial history of HT. In
accordance with the Institutional Review Boards, subjects
provided written informed consent before being tested.
The AA group consisted of 32 males and the
NAA group consisted of 29 males. Via self-report, individuals with two
parents or two grandparents of African descent were assigned to
the AA group, and those who did not have any parent or
grandparent of African descent were assigned to the NAA group.
The racial distribution of the non-African-American group was 55%
Caucasian (16/29), 31% Asian (9/29), and 14% Hispanic of
non-African descent (4/29).
Subjects arrived at the laboratory between 7:00 and
10:00 AM Tuesday through Friday after an overnight fast.
Caffeinated products were not consumed before the testing
protocol. After anthropometric measurements were taken, subjects were
instrumented with electrocardiograms and beat-by-beat radial
blood pressure (BP). Respiratory recording data were captured and
stored on a computer. After a 15-min seated equilibration period in which
BP, heart rate, and respiratory rate fluctuated <5%, 5 min of
resting data were acquired in accordance with published
recommendations and sampled. The area under the diastolic
pressure waveform of the radial artery was utilized to estimate
compliance.
Resultant values were averaged and yielded an estimate
of arterial compliance. Power spectral density analysis of
heart rate variability (HRV) and blood pressure variability (BPV)
were used to derive measures of autonomic modulation. A priori
power spectra of R-R intervals within the 0.15- to 0.4-Hz range
were defined as the high-frequency (HF) component of HRV (denoted
as HFRR), representing primarily parasympathetic
modulation.
All spectral data were log transformed to
remove skewness and minimize the large standard deviations customarily
present in these data. Digitized R-R intervals and in-phase
systolic peaks determined spontaneous BRS by a modification of
the sequence technique shown to have a high correlation to
invasive methods. After these assessments were completed, maximum
oxygen consumption (
O2
max) capacity tests were performed and classic criteria
were used to determine whether a maximal effort had been achieved.
Independent t-tests were performed for
all variables pertaining to the hypotheses. As a secondary analysis,
a discriminant analysis was computed to determine the relative
strength of the arterial compliance, autonomic variables, and BRS
in distinguishing the members of one racial group from another
and in correctly predicting the racial group to which each sample
participant belonged.
Results
The investigators found that:
-
the AA group had lower arterial compliance, HFRR
(parasympathetic modulation), and BRS in addition to a higher LF/HF power
ratio (sympathovagal balance);
-
mean ages, heights, weights, and body mass
indexes were similar in both groups, and there were no
differences between groups for
O2
max values, resting heart rates, systolic BP (SBP), and
respiratory rates; and
-
the LFRR and LFSBP components
(sympathetic modulation) failed to reach levels of significance.
To further assess the accuracy of the
analysis, the researchers also computed discriminant scores for
each sample participant and compared each participant's predicted
racial group with his actual race. Approximately 77 percent of the cases
were correctly classified (P < 0.05) within the
discriminant analysis model; baroreflex sensitivity was the
single best predictor of race and was closely followed by arterial
compliance.
Conclusions
These results demonstrate that young, normotensive
African-American males have differences in arterial compliance and autonomic
modulation compared with a similar group of non-African-American males. The
loss of arterial compliance has been proposed as a possible mechanism in the
initiation, progression, and etiology of HT, and as a prognostic marker for
cardiovascular disease. The findings in this cross-sectional investigation
may be suggestive that the establishment of clinical disease may occur much
earlier than believed.
On the basis of public health statistics, it is
conceivable that these subjects may develop HT at a future point in their
lives. Accordingly, when preclinical markers of disease risk are verified in
young asymptomatic African-Americans, aggressive behavioral adaptations
should be made early to minimize the progression and onset of cardiovascular
disease.
The methods used to evaluate arterial compliance and
autonomic function in the study were safe, noninvasive and caused no
discomfort to the subjects. The results of this study and the methods used
for evaluation could thus lead to a screening and detection program
targeting individuals at risk.
-end-
Source: August 2003 edition of the
American Journal of Physiology -- Heart
and Circulatory Physiology.
The American Physiological Society (APS)
was founded in 1887 to foster basic and applied science, much of it relating
to human health. The Bethesda, MD-based Society has more than 10,000 members
and publishes 3,800 articles in its 14 peer-reviewed journals every year.
***
Editor’s
Note: Members of the press are invited to obtain a pdf version of the study
and to interview members of the research team. To do so, please contact
Donna Krupa at 703.527.7357 (direct dial), 703.967.2751 (cell) or djkrupa1@aol.com.
