Final Accepted Version LOW ARTERIAL COMPLIANCE IN YOUNG AFRICAN AMERICAN MALES

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Final Accepted Version LOW ARTERIAL COMPLIANCE IN YOUNG AFRICAN AMERICAN MALES
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  Manuscript H-00497-2002.R3 1 Final Accepted VersionLOW ARTERIAL COMPLIANCE IN YOUNG AFRICAN AMERICAN MALES  Adrienne S. Zion 1, 5 , Vernon Bond 2 , Richard G. Adams 2 , Deborah Williams 2 , Robert E. Fullilove 3 , Richard P. Sloan 4 , Matthew N. Bartels 1 , John A. Downey 1  and Ronald E. De Meersman 1, 51 Departments of Rehabilitation Medicine, 2 Medicine and 4 Psychiatry, 3 Mailman School of Public Health, College of Physicians and Surgeons and 5 Teachers College, Columbia University, NYC 10032, and 2 Howard University, Department of Medicine, Washington, D.C., 20059. Address for correspondence Ronald E. De Meersman, Ph.D.630 West 168 th  St., box 38NYC, NY 10032Phone: (212) 305-3056Fax: (212) 305-1044Email: red13@columbia.edu  Acknowledgements: The  VIDDA   Foundation, HL61287 and GM08016 grant support Key Words: arterial hypertension, autonomic nervous system, compliance, baroreflex, Blacks Copyright (c) 2003 by the American Physiological Society. Articles in PresS. Am J Physiol Heart Circ Physiol (May 8, 2003). 10.1152/ajpheart.00497.2002  Manuscript H-00497-2002.R3 2Hypertension remains a common public health challenge because of its prevalence and increase in co-morbid cardiovascular diseases. Black males have disproportionate pathophysiological consequences of hypertension compared to any other group in the United States. Alterations in arterial wall compliance and autonomic function often precede the onset of disease. Accordingly, the purpose of this study was to investigate whether differences exist in arterial compliance and autonomic function between young, healthy African American males without evidence of hypertension and age and gender-matched non African-Americans. All procedures were carried out non-invasively following rest. Arterial compliance was calculated as the integrated area starting at the well-defined nadir of the incisura of the dicrotic notch to the end of diastole of the radial artery pulse wave  .  Power spectral analysis of heart rate and blood pressure variability provided distributions representative of parasympathetic and sympathetic modulations, and sympathovagal balance. Baroreflex sensitivity (BRS) was calculated using the sequence method. Thirty-two African American and 29 non African American males were comparable in anthropometrics and negative family history of hypertension. T-tests revealed lower arterial compliance, (5.8 ±  2.4 mmHg x sec vs. 8.6 ±  4.0 p = 0.0017; parasympathetic modulation 8.9 ±  1.1 (ln msec 2 ) vs 9.7 ±  1.1 p = 0.0063; BRS 13.7 ±  7.3 (msec/mmHg) vs. 21.1 ±  8.5 p = 0.0007; and higher sympathovagal balance 2.9 ±  3.2 vs. 1.5 ±  1.1 (p = 0.03) in the African American group. In summary, differences exist in arterial compliance and autonomic balance in African  American males. These alterations may be antecedent markers of disease and valuable in the detection of degenerative cardiovascular processes in individuals at risk. Hypertension (HT) in African American males continues to be a major health challenge because of the staggering financial costs related to medical and disability expenses. The increased  Manuscript H-00497-2002.R3 3 prevalence of morbidity and mortality due to HT in this group is among the highest in the world (63). Not only does HT occur more frequently, but also presents at an earlier age and causes increased complications of cardiovascular diseases compared to white Americans (57). Although the general prevalence of hypertension has decreased among all genders and ethnic groups in the United States, recent reports indicate that HT now ranks as the 13 th leading cause of death in the Unites States, having moved up from its former 15 th place. A variety of environmental, behavioral and biological factors have been proposed to account for the racial differences in the prevalence and severity of HT. Arterial hypertension is associated with structural and functional changes in the cardiovascular system. These changes involve the conductance in large arteries as well as the resistance in a small artery (31). In animal models, arterial compliance was attenuated in animals with hypertension compared to a normotensive group (12). Specifically, carotid arteries were stiffer due in part to increased smooth muscle mass (36). In humans, abnormalities in the diastolic waveform contour, as evidenced by a reduced area under the dicrotic notch and identified as reduced compliance, have been recognized in the Framingham and other studies as apossible markerfor cardiovascular morbidity and mortality and in the etiology of arterial disease, hypertension (42, 50), stroke (33, 52), (2), diabetes (41), and atherosclerosis (32). Increases in arterial wall stiffness lead to an augmentation in the stress-strain relationship, elevating blood pressures and accelerate hypertension, ultimately inducing atherosclerosis.Alterations in arterial compliance may precede the onset of clinically apparent disease and help to identify individuals atrisk before the onset of disease (25, 10). As with arterial wall compliance, there are conditions in which baroreflex sensitivity and autonomic function are impaired: in coronary artery disease, stroke (2), as demonstrated in the Framingham study (52), atherosclerosis, hypertension (26), diabetes (20, 4), in smokers (65), and in alcoholic neuropathy (28). Additionally, autonomic function becomes altered and baroreflex sensitivity declines as a natural part of the aging process  Manuscript H-00497-2002.R3 4(17, 9, 14,44). Underlying age-related changes that are thought to alter baroreflex mechanism include arterial stiffening and a reduced cardiovascular responsiveness to adrenergic stimulation (38). Strong evidence, accounting for racial differences in blood pressure, appears to point toward a decrease in vasodilation during mental and physical stress in normotensive African-American men which results in an attenuated buffering of blood pressure pulsatility (19, 21).Therefore, the rational of this study was to determine, whether differences in arterial compliance and autonomic function exist in young male normotensive African Americans with a negativefamily history of HT when compared to a similar group of non African Americans. Methods. Thirty-two African American volunteers were compared to a similar group of 29 non African American males recruited from the staff and student body of Columbia and Howard Universities. Prior to enrollment, potential subjects were screened for general medical history, physical fitness levels, and ancestral history. Subjects were excluded if they had any systemic medical illness, allergies that required medications, currently smoked, or had a positive family history of HT. In accordance with the Institutional Review Boards, subjects provided written informed consent prior to testing. Via self-report, individuals with two parents or two grandparents of African descent were assigned to the African American group (AA) and thosewho did not have any parent or grandparent of African descent were assigned to the non African American group (NAA). Subjects arrived at the laboratory between the hours of 7:00 am – 10:00 am Tuesday-Friday following an overnight fast. No testing took place on Mondays, as there may be an exaggerated increase in sympathetic modulation at the start of the workweek compared to other days (61). Prior to the testing protocol caffeinated products were not consumed. Following anthropometric measurements subjects were instrumented with electrocardiograms (Max 2000, Marquette  Manuscript H-00497-2002.R3 5Instruments, Marquette, WI), beat-by-beat radial blood pressures (BP) (Colin tonometer, Colin, San Antonio, TX), and respiratory recordings (YSI temperature probe Yellow Springs, OH) data were captured via an analog-to-digital conversion board (ATMIO-16, National Instruments, Austin, TX) and stored on a computer. Following a 15-minute seated equilibration period in which BPs, heart rates, and respiratory rates fluctuated less than 5%, 5 minutes of resting data were acquired in accordance with published recommendations (60) and sampled at 500 Hz. As previously mentioned, the area under the diastolic pressure waveform of the radial artery was utilized to estimate compliance (37). This method of pulse wave analysis has been shown to be a valid and reliable method for the early detection of vascular disease (10). For a more detailed description on the method as well as its shortcomings, the reader is referred to reference 39. Our laboratory has used a similar contour analysis method in the past to assess arterial compliance (13-15). Specifically, the analysis included two successive 10 beat radial BP waves that were extracted from the beat-to-beat BP recordings. A well-defined nadir of the incisura of the dicrotic notch and the end of diastole delineated the area of integration (37) .  The resultant values were averaged and yielded an estimate of arterial compliance. Power spectral density analysis of heart rate and blood pressure variability was used to derive measures of autonomic modulation (55). A priori power spectra of RR intervals within the 0.15 - 0.4 Hz range were defined as the high frequency (HF) component of heart rate variability (HRV) (HF HRV ), representing primarily parasympathetic modulation. The low frequency (LF) of HRV (0.04 to 0.15 Hz) is a mixture of both parasympathetic activity and sympathetic activity. Unlike parasympathetic activity, the sympathetic activity is not easily separated from the power spectrum of HRV (27). Sympathovagal balance was computed as the ratio between the LF and HF spectrum of heart rate variability (49). LF blood pressure modulation (LF BPV ) in the 0.04-0.15 Hz range represents sympathetic vasomotor
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