Motivation Hypertension is a pertinent health problem for urban black African men (hereafter referred to as African). Sympathetic hyperactivity and a dominant α-adrenergic response pattern have both been implicated as contributing factors to their poor cardiovascular health. In addition to the deleterious effect of neurogenic hypertension on target organs, sympathetic hyperactivity may promote the accelerated progression of left ventricular hypertrophy and structural vascular disease. Aim The overarching aim of this study is to scrutinize autonomic control of the cardiovascular system in a cohort of urban African and Caucasian men during a mental challenge. Associations were investigated between potential sympatho-vagal imbalance, blood pressure and target organ damage markers to determine cardiovascular risk in ethnic male groups. Methodology The SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study involved the participation of 200 male teachers (99 African and 101 Caucasian) in the Kenneth Kaunda Education District of the North-West Province, South Africa. Of the participant group, HIV-infected (13 African) and clinically confirmed diabetics (1 Caucasian and 6 African men) were excluded from further analyses. Stratification was based on ethnicity and further as indicated through statistical interaction effects. Cardiovascular and autonomic responses were assessed during rest and on stressor exposure (cold pressor test and Stroop colour-word conflict test). Autonomic measures included baroreceptor sensitivity (BRS), 3-methoxy-4-hydroxy-phenylglycol (MHPG) and nitric oxide metabolite (NOx) levels. Cardiovascular variables consisted of blood pressure, cardiac output, stroke volume, total peripheral resistance, heart rate, arterial compliance and ST-segment from the 12-lead electrocardiogram. Markers of target organ damage included the Cornell product (indication of left ventricular hypertrophy) and carotid intima-media thickness as indication of structural vascular disease. Means and proportions were compared by means of standard t-test and Chi-square test, respectively. Significant differences of mean cardiovascular and autonomic measures between ethnic male groups were also determined through analysis of covariance. Uni- and multivariate regression analyses were employed to demonstrate associations between target organ damage, cardiovascular and autonomic markers. Results and conclusion of each manuscript To assess autonomic nervous system and cardiovascular function as well as target organ damage, we clearly focussed on responses where our participants were challenged. Markers of autonomic responses assessed were baroreceptor sensitivity, 3-methoxy-4-hydroxyphenylglycol and nitric oxide metabolites.  The first manuscript (Chapter 2) focused on left ventricular hypertrophy as marker of target organ damage, blood pressure and baroreceptor sensitivity as marker of autonomic function. The objective was to determine whether BRS was significantly lower in African men than in the Caucasian men. Furthermore, the possible association between attenuation of BRS and increased levels of ambulatory blood pressure as well as left ventricular hypertrophy was investigated in these population groups. Results revealed that the African men had significantly lower BRS stress responses. This attenuated BRS profile was coupled with dominant α-adrenergic response patterns, which was associated with an elevation of ambulatory blood pressure. BRS attenuation (rest and stress response) was not associated with left ventricular hypertrophy. It was concluded that lower BRS, especially during stress, may pose a significant health threat for urban African men regarding the development or promotion of α-adrenergic-driven hypertension and higher cardiovascular disease risk.  The aim of the second sub-study (Chapter 3) was to investigate possible associations between structural vascular disease (carotid intima-media thickness as marker), autonomic function (MHPG as marker) and nocturnal blood pressure in the African and Caucasian men. Results showed a higher prevalence of nocturnal hypertension in the African men, with night-time blood pressure significantly higher compared to the Caucasian men. In the African and Caucasian men, carotid intima-media thickness was linearly predicted by nocturnal systolic and diastolic blood pressure respectively. In conclusion, no associations were demonstrated between MHPG and carotid intimamedia thickness or between MHPG and nocturnal blood pressure. Elevated nocturnal blood pressure evidently seems to promote structural vascular disease in this cohort of urban African and Caucasian men.  The aim of the third manuscript presented in Chapter 4, was to investigate bioavailability of NO during mental challenge (autonomic function marker) and the possible association with structural vascular disease (carotid intima-media thickness as marker). In the African men, an attenuated NOx response was demonstrated to the Stroop colour-word conflict test. After stratification into high and low NOx response groups, in the African men with a low NOx response enhanced α-adrenergic with significant STsegment depression responses was demonstrated indicating reduced myocardial oxygen supply during mental stressor exposure. Only in the African men, a ST-segment depression was significantly associated with structural vascular disease. It was concluded that the African men demonstrated a vulnerable cardiovascular profile. In this cohort of African men, the significant association between structural vascular disease and myocardial ischemia may particularly indicate a possible higher risk for future cardiovascular events. General conclusion Through the assessment of autonomic and cardiovascular responses a possible higher cardiovascular risk was demonstrated in the African men. In this cohort sympathetic hyperactivity was evident, coupled with dominant vascular response patterns and reduced myocardial oxygen supply during mental stress exposure. Based on these findings, this population group’s risk for accelerated target organ damage, as well as for future cardiovascular events, appear significantly higher than those of the Caucasian male cohort. / Thesis (PhD (Physiology))--North-West University, Potchefstroom Campus, 2013.

Motivation Hypertension is a pertinent health problem for urban black African men (hereafter referred to as African). Sympathetic hyperactivity and a dominant α-adrenergic response pattern have both been implicated as contributing factors to their poor cardiovascular health. In addition to the deleterious effect of neurogenic hypertension on target organs, sympathetic hyperactivity may promote the accelerated progression of left ventricular hypertrophy and structural vascular disease. Aim The overarching aim of this study is to scrutinize autonomic control of the cardiovascular system in a cohort of urban African and Caucasian men during a mental challenge. Associations were investigated between potential sympatho-vagal imbalance, blood pressure and target organ damage markers to determine cardiovascular risk in ethnic male groups. Methodology The SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study involved the participation of 200 male teachers (99 African and 101 Caucasian) in the Kenneth Kaunda Education District of the North-West Province, South Africa. Of the participant group, HIV-infected (13 African) and clinically confirmed diabetics (1 Caucasian and 6 African men) were excluded from further analyses. Stratification was based on ethnicity and further as indicated through statistical interaction effects. Cardiovascular and autonomic responses were assessed during rest and on stressor exposure (cold pressor test and Stroop colour-word conflict test). Autonomic measures included baroreceptor sensitivity (BRS), 3-methoxy-4-hydroxy-phenylglycol (MHPG) and nitric oxide metabolite (NOx) levels. Cardiovascular variables consisted of blood pressure, cardiac output, stroke volume, total peripheral resistance, heart rate, arterial compliance and ST-segment from the 12-lead electrocardiogram. Markers of target organ damage included the Cornell product (indication of left ventricular hypertrophy) and carotid intima-media thickness as indication of structural vascular disease. Means and proportions were compared by means of standard t-test and Chi-square test, respectively. Significant differences of mean cardiovascular and autonomic measures between ethnic male groups were also determined through analysis of covariance. Uni- and multivariate regression analyses were employed to demonstrate associations between target organ damage, cardiovascular and autonomic markers. Results and conclusion of each manuscript To assess autonomic nervous system and cardiovascular function as well as target organ damage, we clearly focussed on responses where our participants were challenged. Markers of autonomic responses assessed were baroreceptor sensitivity, 3-methoxy-4-hydroxyphenylglycol and nitric oxide metabolites.  The first manuscript (Chapter 2) focused on left ventricular hypertrophy as marker of target organ damage, blood pressure and baroreceptor sensitivity as marker of autonomic function. The objective was to determine whether BRS was significantly lower in African men than in the Caucasian men. Furthermore, the possible association between attenuation of BRS and increased levels of ambulatory blood pressure as well as left ventricular hypertrophy was investigated in these population groups. Results revealed that the African men had significantly lower BRS stress responses. This attenuated BRS profile was coupled with dominant α-adrenergic response patterns, which was associated with an elevation of ambulatory blood pressure. BRS attenuation (rest and stress response) was not associated with left ventricular hypertrophy. It was concluded that lower BRS, especially during stress, may pose a significant health threat for urban African men regarding the development or promotion of α-adrenergic-driven hypertension and higher cardiovascular disease risk.  The aim of the second sub-study (Chapter 3) was to investigate possible associations between structural vascular disease (carotid intima-media thickness as marker), autonomic function (MHPG as marker) and nocturnal blood pressure in the African and Caucasian men. Results showed a higher prevalence of nocturnal hypertension in the African men, with night-time blood pressure significantly higher compared to the Caucasian men. In the African and Caucasian men, carotid intima-media thickness was linearly predicted by nocturnal systolic and diastolic blood pressure respectively. In conclusion, no associations were demonstrated between MHPG and carotid intimamedia thickness or between MHPG and nocturnal blood pressure. Elevated nocturnal blood pressure evidently seems to promote structural vascular disease in this cohort of urban African and Caucasian men.  The aim of the third manuscript presented in Chapter 4, was to investigate bioavailability of NO during mental challenge (autonomic function marker) and the possible association with structural vascular disease (carotid intima-media thickness as marker). In the African men, an attenuated NOx response was demonstrated to the Stroop colour-word conflict test. After stratification into high and low NOx response groups, in the African men with a low NOx response enhanced α-adrenergic with significant STsegment depression responses was demonstrated indicating reduced myocardial oxygen supply during mental stressor exposure. Only in the African men, a ST-segment depression was significantly associated with structural vascular disease. It was concluded that the African men demonstrated a vulnerable cardiovascular profile. In this cohort of African men, the significant association between structural vascular disease and myocardial ischemia may particularly indicate a possible higher risk for future cardiovascular events. General conclusion Through the assessment of autonomic and cardiovascular responses a possible higher cardiovascular risk was demonstrated in the African men. In this cohort sympathetic hyperactivity was evident, coupled with dominant vascular response patterns and reduced myocardial oxygen supply during mental stress exposure. Based on these findings, this population group’s risk for accelerated target organ damage, as well as for future cardiovascular events, appear significantly higher than those of the Caucasian male cohort. / Thesis (PhD (Physiology))--North-West University, Potchefstroom Campus, 2013.

MOTIVATION: The increasing prevalence of metabolic syndrome (MetS) is creating immense concern worldwide. In 2009, the International Diabetes Federation (IDF) announced the new MetS definition. MetS is diagnosed by any 3 of the following 5 indicators being present: increased waist circumference (WC), blood pressure (BP), triglycerides, and fasting glucose values, and decreased high–density lipoprotein cholesterol (HDL–C) concentrations. Psychosocial stress relating to an urban environment or acculturation greatly influences the prevalence of both MetS and target organ damage (TOD). Furthermore, in urban Africans, active coping (AC) responses have been associated more with MetS and the related cardiovascular pathology than avoidance. A further synergistic effect of MetS and AC responses was also revealed in African men, in strong association with both subclinical atherosclerosis and renal impairment. Microalbuminuria was four times higher in Africans with MetS, than in those without any MetS indicators. Furthermore, Africans, especially those utilising AC responses, present with greater carotid intima–media thickness (CIMT) than their Caucasian counterparts, although they exhibit a lipid profile that is anti–atherogenic. OBJECTIVES: The objectives were firstly to indicate and compare differences regarding AC responses in the African and Caucasian men, in accord with the prevalence of MetS indicators. Secondly, the extent to which AC responses and MetS indicators predict endothelial dysfunction was investigated. METHODOLOGY: This comparative target population study is nested in the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study, which was conducted from February until the end of May in both 2008 (Africans) and 2009 (Caucasians), avoiding seasonal changes. The Ethics Committee of the North–West University approved the study, and all volunteers gave written informed consent prior to participation. Procedures were conducted according to the institutional guidelines of the Declaration of Helsinki. The participants included 202 male teachers of which 101 were African and 101 Caucasian. Ambulatory blood pressure (BP) measurements were recorded with the Cardiotens CE120 at 30 minute intervals during the day and 60 minutes at night. Actical accelerometers determined physical activity (PA). Registered clinical psychologists supervised completion of the psychosocial questionnaires, including the Coping Strategy Indicator. Participants fasted overnight; after the last BP recording, disconnection of the Cardiotens CE120 and Actical followed. A fasting 8 hour overnight collected urine sample was obtained from each participant. Anthropometric measurements followed, after which a registered nurse commenced blood sampling. The SonoSite Micromaxx was used for the scanning of CIMT. MetS indicators (glucose, triglyceride, and HDL–C), together with gamma glutamyl transferase, cotinine, and ultrahigh–sensitivity C–reactive protein (hs–CRP), were analyzed with Konelab 20i. The albumin–to–creatinine ratio and CIMT determined TOD. Participants were stratified according to ethnicity and median splits of AC response scores (high AC and low AC). Diabetic medication users (n= 8), and participants with renal impairment (n= 2) or HIV positive (n= 13), were excluded from analyses. 2×2 ANCOVA’s determined significant interactions for ethnicity and AC. Partial correlations between MetS indicators and TOD were performed within each ethnic and AC group, independent of age, alcohol consumption and PA. Regression analyses were performed for four models, firstly with microalbuminuria and secondly with CIMT as dependent variables. Significant values were noted as p 0.05, r 0.35, and adjusted R2 0.25. RESULTS: Caucasian men were physically more active than African men, whilst BP, alcohol consumption and hs–CRP levels were significantly higher in African men. Psychological variables revealed higher avoidance scores in Caucasian men and higher social support scores in African men. More MetS indicators exceeded the IDF cut–off points in high AC African men (14.71%) than in their Caucasian counterparts (3.33%). Furthermore, more MetS indicators predicted endothelial dysfunction in African men, especially the high AC responders. CONCLUSION: The following hypotheses were accepted: high AC responses in urban African men were associated with a higher prevalence of MetS indicators than in their Caucasian counterparts, while MetS indicators were associated with a marker of TOD in urban high AC African men, but not in their Caucasian counterparts. / Thesis (M.Sc. (Physiology))--North-West University, Potchefstroom Campus, 2011.

MOTIVATION: The increasing prevalence of metabolic syndrome (MetS) is creating immense concern worldwide. In 2009, the International Diabetes Federation (IDF) announced the new MetS definition. MetS is diagnosed by any 3 of the following 5 indicators being present: increased waist circumference (WC), blood pressure (BP), triglycerides, and fasting glucose values, and decreased high–density lipoprotein cholesterol (HDL–C) concentrations. Psychosocial stress relating to an urban environment or acculturation greatly influences the prevalence of both MetS and target organ damage (TOD). Furthermore, in urban Africans, active coping (AC) responses have been associated more with MetS and the related cardiovascular pathology than avoidance. A further synergistic effect of MetS and AC responses was also revealed in African men, in strong association with both subclinical atherosclerosis and renal impairment. Microalbuminuria was four times higher in Africans with MetS, than in those without any MetS indicators. Furthermore, Africans, especially those utilising AC responses, present with greater carotid intima–media thickness (CIMT) than their Caucasian counterparts, although they exhibit a lipid profile that is anti–atherogenic. OBJECTIVES: The objectives were firstly to indicate and compare differences regarding AC responses in the African and Caucasian men, in accord with the prevalence of MetS indicators. Secondly, the extent to which AC responses and MetS indicators predict endothelial dysfunction was investigated. METHODOLOGY: This comparative target population study is nested in the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study, which was conducted from February until the end of May in both 2008 (Africans) and 2009 (Caucasians), avoiding seasonal changes. The Ethics Committee of the North–West University approved the study, and all volunteers gave written informed consent prior to participation. Procedures were conducted according to the institutional guidelines of the Declaration of Helsinki. The participants included 202 male teachers of which 101 were African and 101 Caucasian. Ambulatory blood pressure (BP) measurements were recorded with the Cardiotens CE120 at 30 minute intervals during the day and 60 minutes at night. Actical accelerometers determined physical activity (PA). Registered clinical psychologists supervised completion of the psychosocial questionnaires, including the Coping Strategy Indicator. Participants fasted overnight; after the last BP recording, disconnection of the Cardiotens CE120 and Actical followed. A fasting 8 hour overnight collected urine sample was obtained from each participant. Anthropometric measurements followed, after which a registered nurse commenced blood sampling. The SonoSite Micromaxx was used for the scanning of CIMT. MetS indicators (glucose, triglyceride, and HDL–C), together with gamma glutamyl transferase, cotinine, and ultrahigh–sensitivity C–reactive protein (hs–CRP), were analyzed with Konelab 20i. The albumin–to–creatinine ratio and CIMT determined TOD. Participants were stratified according to ethnicity and median splits of AC response scores (high AC and low AC). Diabetic medication users (n= 8), and participants with renal impairment (n= 2) or HIV positive (n= 13), were excluded from analyses. 2×2 ANCOVA’s determined significant interactions for ethnicity and AC. Partial correlations between MetS indicators and TOD were performed within each ethnic and AC group, independent of age, alcohol consumption and PA. Regression analyses were performed for four models, firstly with microalbuminuria and secondly with CIMT as dependent variables. Significant values were noted as p 0.05, r 0.35, and adjusted R2 0.25. RESULTS: Caucasian men were physically more active than African men, whilst BP, alcohol consumption and hs–CRP levels were significantly higher in African men. Psychological variables revealed higher avoidance scores in Caucasian men and higher social support scores in African men. More MetS indicators exceeded the IDF cut–off points in high AC African men (14.71%) than in their Caucasian counterparts (3.33%). Furthermore, more MetS indicators predicted endothelial dysfunction in African men, especially the high AC responders. CONCLUSION: The following hypotheses were accepted: high AC responses in urban African men were associated with a higher prevalence of MetS indicators than in their Caucasian counterparts, while MetS indicators were associated with a marker of TOD in urban high AC African men, but not in their Caucasian counterparts. / Thesis (M.Sc. (Physiology))--North-West University, Potchefstroom Campus, 2011.