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Anger and hostility have been attributed as early risk factors of coronary heart disease (CHD). However, many inconsistencies exist in the literature linking both of these constructs to CHD, as well as to cardiovascular reactivity (CVR) to stressors likely to give rise to CHD. A potential moderating influence discussed in the CVR literature concerns the issue of anger provocation, whereas assessment of the ability to evaluate the source of provocation may moderate the recovery process. The current study adopts a multivariate approach to assess the interactive effects of dispositional anger in predicting the CVR and recovery to mental arithmetic (MA) stress with and without harassment in 47 male undergraduate psychology students. Results revealed anger out (AO) to be associated with high vagal and low frequency power suppression in response to the MA task with harassment. Exposure to experimenter evaluation was associated with attenuated diastolic blood pressure recovery and facilitated vagal recovery in high AO subjects, whereas the opposite pattern was apparent for low AO subjects. The general findings suggest that trait anger interacts with situational influences to predict CVR and recovery to stressors. / Ph. D.

Motivation The prevalence of cardiovascular disease is on the increase in sub-Saharan Africa largely owing to lifestyle changes associated with urbanisation. Traditional diets are being replaced with diets high in saturated fat and sugar. In addition to the nutritional transition, urbanisation in developing African countries also contributes to a more sedentary lifestyle. Together these trends contribute to a higher prevalence of obesity and hypertension that are major risk factors for the development of cardiovascular disease. Adipose tissue is now widely recognised as an endocrine organ that secretes numerous inflammatory mediators as well as adipocytokines such as leptin. The primary role of leptin is to induce satiety after a meal and to suppress appetite. However, in recent years the role of leptin in the development of obesity-related cardiovascular disease has gained increasing attention and interest. Furthermore, leptin levels not only differ with regard to gender but also ethnicity. Africans have higher leptin levels than Caucasians due to higher subcutaneous fat in Africans. Furthermore, the prevalence of hypertension and stroke are also greater in the African population. Taken together, it is important to investigate mechanisms by which elevated leptin may contribute to the development of cardiovascular disease, especially in cardiovascular disease-prone Africans. Aim The general aim of this study is to increase our understanding of the role of leptin in cardiovascular disease development by investigating associations of leptin with markers of sympathetic activity, endothelial dysfunction, and cardiovascular reactivity and recovery in Africans and Caucasians. Methodology Data from the SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study was used and presented in the original research articles described in Chapter 2, 3 and 4. This study included 409 African and Caucasian schoolteachers working in the Potchefstroom district in the North West Province of South Africa. Groups were stratified by ethnicity, gender and ethnicity or obesity in order to demonstrate potential differences. We performed cardiovascular measurements and determined levels of leptin, renin, cortisol, plasminogen activator inhibitor-1 (PAI-1), von Willebrand factor (vWF) and urinary albumin-to-creatinine ratio (ACR). Independent t-tests were done to compare means between groups and Chi-square tests to compare proportions. Pearson’s correlations were determined to investigate associations as well as partial correlations after minimal adjustment for potential confounders. Multiple regression analyses were performed to investigate independent associations of leptin with cardiovascular and biochemical markers according to the specific focus of each research manuscript. Results and conclusions of the individual manuscripts  Leptin may contribute to obesity-related hypertension through its sympatho-activating effects. In the first research article (Chapter 2), we compared mean leptin levels and markers of autonomic activity between Africans and Caucasians. We also investigated associations between markers of autonomic activity and leptin. Africans had higher leptin, body mass index, blood pressure and heart rate compared to Caucasians. Furthermore, Africans also demonstrated reduced heart rate variability that is indicative of autonomic imbalance. Markers of autonomic activity that collectively reflected sympathetic overactivity associated with leptin in both Africans and Caucasians, independent of significant covariates and confounders including body mass index. These findings suggest that leptin may contribute to the development of hypertension by inducing autonomic dysfunction.  Leptin exerts direct vascular effects and may thereby contribute to increased cardiovascular disease risk in the obese. We therefore investigated associations between circulating markers of endothelial dysfunction (PAI-1, vWF and ACR) and leptin in lean and obese groups, irrespective of ethnicity (Chapter 3). As expected, leptin and plasminogen activator inhibitor-1 antigen levels were higher in the obese group. We found no differences for von Willebrand factor antigen and urinary albumin-to-creatinine ratio. In the obese group, all markers of endothelial dysfunction were positively associated with leptin in univariate analysis. However, after full adjustment in multiple regression analyses, only the association with plasminogen activator inhibitor-1 remained significant. Higher leptin levels in the obese may possibly induce endothelial dysfunction through mechanisms related to thrombotic vascular disease.  Greater cardiovascular reactivity to stress and prolonged recovery thereafter associates with increased cardiovascular disease risk. In the final research article (Chapter 4), we therefore investigated the relationship between cardiovascular reactivity and recovery to acute stress, induced by the cold pressor test, and leptin in Africans and Caucasians. Africans demonstrated greater cardiovascular reactivity compared to Caucasians. Associations of blood pressure, stroke volume, cardiac output, total peripheral resistance and arterial compliance reactivity with leptin were investigated during the stressor application and 1, 3 and 5 minutes post-stressor. There were no independent associations between cardiovascular reactivity and leptin during the stressor, and a few correlations at 1 and 3 minutes post-stressor. Associations were mostly evident at 5 minutes post-stressor and in Africans. We argue that higher leptin levels relate to impaired post-stress recovery and thereby could contribute to hypertension development in Africans. General conclusion Elevated leptin relates to sympathetic overactivity, vascular damage and delayed post-stress recovery, and thereby could contribute to increased cardiovascular disease risk. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015

Motivation The prevalence of cardiovascular disease is on the increase in sub-Saharan Africa largely owing to lifestyle changes associated with urbanisation. Traditional diets are being replaced with diets high in saturated fat and sugar. In addition to the nutritional transition, urbanisation in developing African countries also contributes to a more sedentary lifestyle. Together these trends contribute to a higher prevalence of obesity and hypertension that are major risk factors for the development of cardiovascular disease. Adipose tissue is now widely recognised as an endocrine organ that secretes numerous inflammatory mediators as well as adipocytokines such as leptin. The primary role of leptin is to induce satiety after a meal and to suppress appetite. However, in recent years the role of leptin in the development of obesity-related cardiovascular disease has gained increasing attention and interest. Furthermore, leptin levels not only differ with regard to gender but also ethnicity. Africans have higher leptin levels than Caucasians due to higher subcutaneous fat in Africans. Furthermore, the prevalence of hypertension and stroke are also greater in the African population. Taken together, it is important to investigate mechanisms by which elevated leptin may contribute to the development of cardiovascular disease, especially in cardiovascular disease-prone Africans. Aim The general aim of this study is to increase our understanding of the role of leptin in cardiovascular disease development by investigating associations of leptin with markers of sympathetic activity, endothelial dysfunction, and cardiovascular reactivity and recovery in Africans and Caucasians. Methodology Data from the SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study was used and presented in the original research articles described in Chapter 2, 3 and 4. This study included 409 African and Caucasian schoolteachers working in the Potchefstroom district in the North West Province of South Africa. Groups were stratified by ethnicity, gender and ethnicity or obesity in order to demonstrate potential differences. We performed cardiovascular measurements and determined levels of leptin, renin, cortisol, plasminogen activator inhibitor-1 (PAI-1), von Willebrand factor (vWF) and urinary albumin-to-creatinine ratio (ACR). Independent t-tests were done to compare means between groups and Chi-square tests to compare proportions. Pearson’s correlations were determined to investigate associations as well as partial correlations after minimal adjustment for potential confounders. Multiple regression analyses were performed to investigate independent associations of leptin with cardiovascular and biochemical markers according to the specific focus of each research manuscript. Results and conclusions of the individual manuscripts  Leptin may contribute to obesity-related hypertension through its sympatho-activating effects. In the first research article (Chapter 2), we compared mean leptin levels and markers of autonomic activity between Africans and Caucasians. We also investigated associations between markers of autonomic activity and leptin. Africans had higher leptin, body mass index, blood pressure and heart rate compared to Caucasians. Furthermore, Africans also demonstrated reduced heart rate variability that is indicative of autonomic imbalance. Markers of autonomic activity that collectively reflected sympathetic overactivity associated with leptin in both Africans and Caucasians, independent of significant covariates and confounders including body mass index. These findings suggest that leptin may contribute to the development of hypertension by inducing autonomic dysfunction.  Leptin exerts direct vascular effects and may thereby contribute to increased cardiovascular disease risk in the obese. We therefore investigated associations between circulating markers of endothelial dysfunction (PAI-1, vWF and ACR) and leptin in lean and obese groups, irrespective of ethnicity (Chapter 3). As expected, leptin and plasminogen activator inhibitor-1 antigen levels were higher in the obese group. We found no differences for von Willebrand factor antigen and urinary albumin-to-creatinine ratio. In the obese group, all markers of endothelial dysfunction were positively associated with leptin in univariate analysis. However, after full adjustment in multiple regression analyses, only the association with plasminogen activator inhibitor-1 remained significant. Higher leptin levels in the obese may possibly induce endothelial dysfunction through mechanisms related to thrombotic vascular disease.  Greater cardiovascular reactivity to stress and prolonged recovery thereafter associates with increased cardiovascular disease risk. In the final research article (Chapter 4), we therefore investigated the relationship between cardiovascular reactivity and recovery to acute stress, induced by the cold pressor test, and leptin in Africans and Caucasians. Africans demonstrated greater cardiovascular reactivity compared to Caucasians. Associations of blood pressure, stroke volume, cardiac output, total peripheral resistance and arterial compliance reactivity with leptin were investigated during the stressor application and 1, 3 and 5 minutes post-stressor. There were no independent associations between cardiovascular reactivity and leptin during the stressor, and a few correlations at 1 and 3 minutes post-stressor. Associations were mostly evident at 5 minutes post-stressor and in Africans. We argue that higher leptin levels relate to impaired post-stress recovery and thereby could contribute to hypertension development in Africans. General conclusion Elevated leptin relates to sympathetic overactivity, vascular damage and delayed post-stress recovery, and thereby could contribute to increased cardiovascular disease risk. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015

Persistent pain conditions are a major health problem throughout the world and are one of the primary reasons that people seek medical treatment (Gureje, Von Korff, Simon, & Gater, 1998; Verhaak, Kerssens, Dekker, Sorbi, & Bensing, 1998). These conditions are characterized by complex interactions between cognitive, emotional, and physiological disturbances and are often associated with comorbid psychological disorders (Gatchel, 2004). Though previous studies have examined the effect of interventions targeting persistent pain, such as physical self-regulation interventions, few studies have examined the complex interaction between such interventions and other variables such as psychological and physiological functioning and presence of social support. The current study was designed to evaluate the effect of a physical self-regulation intervention (i.e. diaphragmatic breathing entrainment) on response to a brief physical stressor (i.e., mild thermal stimulation) as well as to evaluate whether presence or absence of a supportive partner influenced this relationship. Participant response was measured via self-report of pain intensity and unpleasantness and via physiological measures of respiration rate, blood pressure, heart rate, and heart rate variability. The study consisted of 154 female participants who participated in pairs (i.e., 77 pairs). Each participant was randomly assigned to training in diaphragmatic breathing or a control condition as well as being randomly assigned to complete the study with or without their supportive partner present. Analyses revealed that breathing entrainment resulted in significantly slower breathing rate during the thermal stressor task (p < .01). Presence of a supportive partner interacted with breathing entrainment to influence heart rate during the thermal stressor task (p < .05) such that participants who completed the study with a support person present had a lower heart rate when trained in diaphragmatic breathing than when trained in a control protocol and participants who did not have a support person present showed the opposite effect. Presence of a supportive partner also interacted with breathing entrainment to influence ratings of task unpleasantness (p < .05) such that participants who were trained in diaphragmatic breathing rated the task similarly regardless of presence or absence of a supportive partner, whereas participants who were trained in a control protocol rated the task as more unpleasant when accompanied by a supportive partner. In conclusion, the present study demonstrates the impact of training in diaphragmatic breathing and presence of social support on response to thermal stimuli as measured by both self-report (i.e., ratings of task unpleasantness) and physiological (i.e., respiration rate and heart rate) measures. This study highlights the usefulness of implementing a self-regulatory training strategy for treatment of pain and in considering the efficacy of incorporating a supportive partner into such training.

Divorce is a stressor associated with long-term health risk, though the mechanisms of this effect are poorly understood. Cardiovascular reactivity is one biological pathway implicated as a predictor of poor long-term health after divorce. A sample of recently separated and divorced adults (N = 138) was assessed over an average of 7.5 months to explore whether individual differences in heart rate variability—assessed by respiratory sinus arrhythmia—operate in combination with subjective reports of separation-related distress to predict prospective changes in cardiovascular reactivity, as indexed by blood pressure reactivity. Participants with low resting respiratory sinus arrhythmia at baseline showed no association between divorce-related distress and later blood pressure reactivity, whereas participants with high respiratory sinus arrhythmia showed a positive association. In addition, within-person variation in respiratory sinus arrhythmia and between-persons variation in separation-related distress interacted to predict blood pressure reactivity at each laboratory visit. Individual differences in heart rate variability and subjective distress operate together to predict cardiovascular reactivity and may explain some of the long-term health risk associated with divorce.

Because of the impact of stress on health, it is important to understand the variables that underlie cardiovascular reactivity to stress because it may lead to more focused targets of intervention for helping people to reduce or otherwise better manage their stress. The purpose of the present study was to answer the following questions: does lack of eudaimonic well-being (a combination of psychological and social well-being) predict increased cardiovascular reactivity to stress in a clinically distressed population? And does increased eudaimonic well-being protect against increased cardiovascular reactivity to stress when hedonic well-being (a combination of positive affect and life satisfaction) is low and depression and stress are high? If so, then it may be possible to reduce the effects of stress on health even if depression and stress are present. One hundred twenty-nine college students (ages 18-29) who were clinically distressed were administered a questionnaire that included questions about demographic variables and measures of hedonic and eudaimonic well-being, depression, and general perceived stress. After answering the questionnaire, a baseline reading of cardiovascular activity was taken. After the baseline reading, participants were subjected to the Trier Social Stress Test (TSST), an interpersonal stressor that consists of an anticipation period, a speech, and a math task. Measurements of cardiovascular activity were taken throughout the TSST. I predicted that lower levels of eudaimonic and hedonic well-being, mental health, and higher amounts of general perceived stress would predict increased cardiovascular reactivity to the TSST as measured by systolic blood pressure, diastolic blood pressure, and heart rate. Then, should the prior hypothesis be true, I predicted that higher eudaimonic well-being will suppress the effect of lower hedonic will-being, lower mental health, and higher general perceived stress on cardiovascular activity to acute stress. Results of the study found no effect of eudaimonic well-being, hedonic well-being, depression, and general perceived stress on cardiovascular reactivity during the TSST. The results suggest that there is no relationship between well-being, depression, and general perceived stress and cardiovascular reactivity to stress in a young college student population.

This experiment investigated sex differences in dynamic functional cerebral laterality effects on cardiovascular reactivity and dichotic listening in response to a stressor (a cold pressor). 120 right-handed undergraduate men (N = 60) and women (N = 60) underwent physiological measurements of systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) before and after exposure to the cold pressor and a phonemic dichotic listening task. Functional cerebral laterality was assessed through the administration of the phonemic dichotic listening task. Group differences in dynamic functional cerebral laterality were predicted. Findings indicated a sex by focus interaction effect where men's, but not women's, systolic blood pressure increased significantly when focusing on sounds presented at the left ear during the dichotic listening task. Also, a compartmentalized, dynamic response in dichotic listening test performance was evidenced in both men and women (as both experienced increased accuracy at the right, but not left, ear), brought about as a function of the cold pressor. Men and women both evidenced increased cardiovascular reactivity, with men experiencing significantly more cardiovascular reactivity (SBP) than women in response to cold pressor pain. Women were also able to identify significantly more speech sounds presented to the left ear than men, and they were able to dynamically increase accuracy at the targeted ear identified within each focus group (left or right). Speech sounds processing (dichotic listening task) significantly decreased men's, but not women's, systolic blood pressure. These results contribute to the literature on sex differences in functional cerebral laterality. / Master of Science