Exercise Training Favourably Affects Autonomic and Blood Pressure Responses During Mental and Physical Stressors in African-American Men
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Journal of Human Hypertension (2009) 23, 267–273 & 2009 Macmillan Publishers Limited All rights reserved 0950-9240/09 $32.00 www.nature.com/jhh ORIGINAL ARTICLE Exercise training favourably affects autonomic and blood pressure responses during mental and physical stressors in African-American men V Bond1, MN Bartels2, RP Sloan3, RM Millis4, AS Zion5, N Andrews6 and RE De Meersman2,5 1Department of HHPLS, Howard University, Washington, DC, USA; 2Department of Rehabilitation Medicine, Columbia University, New York, NY, USA; 3Department of Psychiatry, Columbia University, New York, NY, USA; 4Department of Physiology and Biophysics, Howard University, Washington, DC, USA; 5Department of Biobehavioral Sciences, Teachers College, Columbia University, New York, NY, USA and 6Department of Cardiology, Howard University, Washington, DC, USA Aerobic exercise is a powerful mechanism by which compared with a matched sedentary control group, cardiovascular and autonomic parameters may be im- aerobic capacity of the trained group significantly proved. We sought to quantify the extent of benefit that increased by 16%. Autonomic modulations, arterial com- could be achieved by a short-term monitored exercise pliance and BP responses significantly improved during regimen on several autonomic parameters during recog- some of the stressors, whereas no such improvements nized mental and physical stressors in young normoten- were seen in the control group. Attenuated responses, sive African-American men matched for a family history of mediated through a favourable shift in sympathovagal hypertension, a group at high risk for the development of balance and enhanced arterial compliance, provide hypertension. Autonomic modulations were derived mechanistic evidence of how certain variables may be using spectral decomposition of the electrocardiogram improved due to aerobic conditioning in a population at and beat-to-beat blood pressures (BPs). Arterial compli- high risk for the development of hypertension. ance was obtained using contour analysis of the radial Journal of Human Hypertension (2009) 23, 267–273; artery pulse wave. The analysis of variance revealed that doi:10.1038/jhh.2008.125; published online 9 October 2008 Keywords: aerobic training; stress reactivity; autonomic responses; blood pressure; African-American men Introduction and BP have been documented following endurance training in animals and humans.8–12 Our prior study It has been hypothesized that repeated mental and/ has demonstrated an augmentation in parasympa- or physical excitation of the sympathetic nervous thetic or vagal modulation and enhanced baroreflex system, incongruent with metabolic needs, plays a sensitivity (BRS) and arterial compliance (AC) dominant role in the establishment and mainte- 13–21 1–4 following aerobic training. Not surprisingly, nance of high blood pressure (BP). To date, few of these studies assessed these effects in stress–response studies have demonstrated that African-American men, not in populations other African-American (AA) men and individuals with than whites. a positive family history of hypertension have a Accordingly, our aim was to determine the extent greater propensity towards augmented BP reactivity 4,5 of benefit that could be achieved in young normo- compared with non-AA men. These augmented tensive AA men, matched for a family history of BP responses appear to be mediated predominantly 5–7 hypertension. Specifically, our hypotheses were that through changes in autonomic modulation. following aerobic training, the trained group would Favourable modifications in autonomic modulation have an improved autonomic modulation profile, an enhanced arteriolar compliance and attenuated BP responses when compared with the non-trained Correspondence: Dr RE De Meersman, Rehabilitation Medicine, control group. These responses were compared Columbia University, 630 West 168th Street, Box 38, NYC, NY, during physical and mental stressors before and 10032, USA. E-mail: [email protected] following an aerobic training programme in Received 18 May 2008; revised 4 September 2008; accepted an experimental (exercise-trained) and control 6 September 2008; published online 9 October 2008 (sedentary) group. In addition to both groups being Exercise training and autonomic and blood pressure responses in African-American men V Bond et al 268 matched on body habitus, we also controlled for an aerobic exercise training programme or no family history of hypertension, a largely ignored exercise programme (sedentary lifestyle). confounder, yet potent mediator, of exaggerated stress responses.22 Study design Participants were scheduled to the laboratory four Methods times, at which time exercise and autonomic tests Participants were obtained. Visit 1: maximal-performance ex- Thirty-two healthy, normotensive AA men between ercise test using a cycling protocol was employed. 18 and 26 years of age met the inclusion criteria for Visit 2: autonomic tests: cold pressor, colour conflict participation and were enrolled in the study, which and deep breathing. Visits 3 and 4 were identical was approved by the University’s Human Partici- repeats of visits 1 and 2 following an 8-week aerobic pants Institutional Review Board of The Howard training or sedentary interval. Protocols for visits 1 University Institutional Review Board. The nature, and 2 as well as 3 and 4 were carried out within 1 purpose and risks of the study were explained to week, but at least 48 h apart. All post-testing was each participant before written informed consent carried out between 48 and 96 h following the last was obtained. An initial screening interview indi- training session. Descriptive data on participants are cated that all participants were non-smokers, ab- presented in Table 1. stained from use of alcohol (less than two standard alcohol drinks a day), took no prescription medica- tions, did not participate in regular exercise during Haemodynamic measures the previous year and were normotensive. Normo- Systolic BP and DBP were measured in the right arm tension was based upon two to three seated BP by a Colin STBP-680 automated BP monitor (Colin measurements during the initial screening inter- Medical Instruments, San Antonio, TX, USA), view. Participants were recruited through advertise- which meets established criteria for SBP and DBP ments placed throughout the university buildings. measures during rest and dynamic exercise.24 Mean All had resting systolic (SBP) and diastolic BP (DBP) arterial BP (MABP) was calculated using the con- within the recognized normotensive-to-pre-hyper- ventional formula: DBP þ 1/3 pulse pressure. Heart tensive BP range of o140/90 mm Hg. As familial rate was determined from a CM5 electrocardio- influence of hypertension is a strong risk modulator graphic tracing by the R-R interval measurement of the autonomic nervous system,22 equal numbers using the Colin STBP-680 monitor. In addition to of both positive and negative family history of these two monitors, participants were instrumented hypertension were included in the study. Partici- with an applanation tonometer (Colin NIBP ton- pants were assigned to either an experimental or a ometer; Colin Instruments) attached to the partici- control group with half of each group having a pant’s left radial artery and supported by an positive and/or negative family history of hyperten- adjustable table to the level of the atria. Following sion. Family history of hypertension was obtained the equilibration period, data were collected and all from the initial interview. When one family member signals, including electrocardiogram and beat-to- was taking antihypertensive medication, this re- beat radial BP waves, were collected at 500 Hz and sulted in the classification of positive family history, channelled into a computer (Dell computers, Aus- whereas no use resulted in a negative classification. tin, TX, USA) through an analog-to-digital conver- The Godin leisure time exercise questionnaire was sion board (ATMIO-16; National Instruments, used to characterize participants’ lifestyle/physical Austin, TX, USA). Following all data-acquisition activity level.23 Data obtained from the activity protocols, autonomic analyses were carried out questionnaire were converted to metabolic equiva- off-line in accordance with the recommendations 25 lents (METs) (1 MET ¼ 3.5 ml O2 per kg per min) and of the European and North American Task Force a weekly score of 20 was defined as ‘sedentary’. using LabView programs (LabView 7.0; National Each group was further randomly assigned to either Instruments). Table 1 Participant characteristics 2 . Group Age (years) Height (cm) Weight (kg) BMI (kg/m ) Peak VO2 (ml O2 per kg per min) Pre-treatment Post-treatment Controls (n ¼ 16) 22.4 (2.2) 179.2 (6.5) 80.5 (12) 25.0 32 (7.1) 33.6 (5.3) Trained (n ¼ 16) 20.4 (1.9) 179.8 (4.7) 78.4 (11) 24.2 31.8 (6) 40 (3.8)* Abbreviation: BMI, body mass index. Data are means and standard deviations (s.d.). *Significantly different from pre-training values at Po0.05. Journal of Human Hypertension Exercise training and autonomic and blood pressure responses in African-American men V Bond et al 269 Stress protocols participants performed a stroop CCT of 5 min in Rest: Following equilibration and attachment of duration. The CCT is designed to elicit responses at instruments to the subject, participants continued the cardiac autonomic level. to rest 15 min. Heart rates and beat-by-beat arteriolar Deep breathing: Participants were instructed to BPs were then extracted