No description available.

Persons with chronic fatigue syndrome (CFS) often complain of an inability to maintain activity levels and experience a variety of orthostatic symptoms such as dizziness, trembling, nausea, postural hypotension with bradycardia or tachycardia, sweating, palpitations, paleness, and syncope. Orthostatic intolerance (OI) may be defined as an inability to maintain systolic blood pressure (SBP) within 20 mmHg of resting level upon moving from a supine to upright posture. The primary objective of this study is to determine whether men and women with CFS are more susceptible to OI during a 3-stage head-up tilt (HUT) than non CFS, sedentary subjects matched by age, sex, and ethnicity. The secondary objective is to examine whether possible underlying mechanisms may be predictively associated with OI susceptibility in CFS. Possible causes of OI include autonomic nervous system (ANS) dysfunction and altered hematological profile. Thus, specific aims included within this objective are: 1) to determine whether there are differences in resting cardiovascular function {i.e., blood pressure [BP], heart rate [HR], stroke volume [SV], cardiac output [CO], total peripheral resistance [TPR], and contractility [i.e., ejection fraction (EF), fractional shortening (FS), and the velocity of circumferential shortening corrected by HR (VCFc)]}, ANS function {i.e., beta1-, beta2-, and alpha-receptor sensitivities, baroreceptor sensitivity [BRS], and vagal function [i.e., respiratory sinus arrhythmia (RSA), RSA envelope (RSAE), high frequency (HF) spectral component, and HR range]}, and hematological profile [i.e., red blood cell volume (RBCV), plasma volume (PBV), and total blood volume (TBV)] between CFS and non-CFS groups; and 2) to determine whether cardiovascular, ANS, and hematological measures differentially predicted OI during HUT. The results indicate that OI susceptibility does not occur with greater prevalence in persons with CFS than non-CFS sedentary persons. However, power analyses revealed that with a much larger sample size group differences in OI susceptibility would be found. The CFS group was distinguished from the control group only by differences in blood volume measures. There appears to be no substantive group differences in a range of cardiovascular and ANS measures; moreover, none of these measures, including the blood volume measures, accounted for differences in OI susceptibility. Compensatory mechanisms may be present in CFS for the diminished blood volume that could explain the lack of group differences in OI susceptibility. In addition, future research may find some clues relevant to CFS pathophysiology in the assessment of hemodynamic responses during orthostatic challenge in the present subjects.

Motivation: The prevalence of obesity is the highest among African women in South Africa. Since obesity is a major cardiovascular risk factor, African women in South Africa could be regarded as a high risk group. However, investigations on obesity-related hypertension are limited in this population group. The associations of body fat distribution and hormones such as leptin and endothelin-1 with cardiovascular function have not yet been determined in these women. It has been determined that endothelin-1 is a role player in the development and/or maintenance of hypertension in various population groups, especially African Americans. Endothelin-1 has also been found to be involved in obesity-related hypertension in non-African population groups. It has been indicated that the obesity-related hormone, leptin, also plays a role in obesity-related hypertension, especially in African Americans. Leptin levels have been found to be higher in obese hypertensive African American women compared to an obese normotensive control group. Since the above-mentioned two hormones playa prominent role in obesity and hypertension in African American and non-African population groups, the lack of data on African women in South Africa serves as motivation to conduct this investigation. Aim: To investigate obesity-related hypertension in African women through the determination of associations between various anthropometric and endocrinological variables with cardiovascular, especially vascular function. Methodology: Manuscripts presented in Chapters 2, 3 and 4 made use of data from the POWIRS (Profiles of Obese Women suffering from the Insulin Resistance Syndrome) I project where African women were selected from a government institution in the North West Province. A group of 98 women were divided into lean normotensive, overweight/obese normotensive and overweight/obese hypertensive groups. Anthropometric and cardiovascular measurements were taken and the lipid profile, leptin and endothelin-1 levels determined. The analysis of covariance (ANCOVA) was used to show significant differences between groups while adjusting for age. Partial correlation coefficients were used to show associations between various variables while adjusting for age. Stepwise linear regression analysis was also used to show associations between variables. The study presented in Chapter 5 made use of both POWIRS I and II, which are studies including Africans and Caucasians, respectively. The methodology of the two studies was the same. All subjects gave informed consent in writing and the Ethics Committee of the North-West University approved the study. The reader is referred to the "Materials and Methods" section of Chapters 2-5 for a more elaborate description of the subjects, study design and analytical methods used in each article. vii Results and conclusions of the individual manuscripts > Results from Chapter 2 showed that the volume loading effect associated with obesity was present in both overweight/obese normotensive and overweight/obese hypertensive groups, however, the accommodating effect observed in the overweight/obese normotensive group was absent in the overweight/obese hypertensive group due to decreased vascular function. This was confirmed by a high pulse pressure. Decreased vascular functioning was associated with the abdominal skin fold. This suggests that abdominal subcutaneous fat may either be a marker of visceral fat, or may in itself contribute to increased cardiovascular risk in Africans. > Results from Chapter 3 showed a negative result. Plasma endothelin-1 levels were similar for the lean normotensive, overweight/obese normotensive and overweight/obese hypertensive groups. After re-dividing the groups into normotensive and hypertensive, and then into lean and overweight/obese, still no differences could be obtained. Additionally, no correlations could be obtained between endothelin-1 and cardiovascular function in any of the groups. These findings suggest that endothelin-1 is not implicated in obesity-related hypertension in African women. > In Chapter 4, leptin levels were elevated in both overweight/obese normotensive and hypertensive groups compared to the lean normotensive group. However, leptin levels did not differ between the two overweight/obese groups. Even though leptin levels were the same, leptin was directly and positively associated with systolic blood pressure and pulse pressure and negatively with arterial compliance only in the overweight/obese hypertensive group, independent of obesity, insulin resistance, hyperinsulinemia and age. > In Chapter 5 the volume loading, as well as the accommodating effect, that is, decreased total peripheral resistance and increased arterial compliance, was present in both African and Caucasian obese groups compared to their lean controls. Even though leptin levels, body mass index and age were similar for both African and Caucasian obese groups, the accommodating effect seemed to be more prominent in the obese Caucasian group, explaining a lower diastolic blood pressure compared to the obese African group. Leptin showed a favourable negative association with diastolic blood pressure and total peripheral resistance in the obese Caucasian group, but not in the obese African group. This may indicate that leptin predominantly exerts pathological influences on obese African women, as determined previously in Chapter 4. / Thesis (Ph.D. (Physiology))--North-West University, Potchefstroom Campus, 2005.

Motivation: The prevalence of obesity is the highest among African women in South Africa. Since obesity is a major cardiovascular risk factor, African women in South Africa could be regarded as a high risk group. However, investigations on obesity-related hypertension are limited in this population group. The associations of body fat distribution and hormones such as leptin and endothelin-1 with cardiovascular function have not yet been determined in these women. It has been determined that endothelin-1 is a role player in the development and/or maintenance of hypertension in various population groups, especially African Americans. Endothelin-1 has also been found to be involved in obesity-related hypertension in non-African population groups. It has been indicated that the obesity-related hormone, leptin, also plays a role in obesity-related hypertension, especially in African Americans. Leptin levels have been found to be higher in obese hypertensive African American women compared to an obese normotensive control group. Since the above-mentioned two hormones playa prominent role in obesity and hypertension in African American and non-African population groups, the lack of data on African women in South Africa serves as motivation to conduct this investigation. Aim: To investigate obesity-related hypertension in African women through the determination of associations between various anthropometric and endocrinological variables with cardiovascular, especially vascular function. Methodology: Manuscripts presented in Chapters 2, 3 and 4 made use of data from the POWIRS (Profiles of Obese Women suffering from the Insulin Resistance Syndrome) I project where African women were selected from a government institution in the North West Province. A group of 98 women were divided into lean normotensive, overweight/obese normotensive and overweight/obese hypertensive groups. Anthropometric and cardiovascular measurements were taken and the lipid profile, leptin and endothelin-1 levels determined. The analysis of covariance (ANCOVA) was used to show significant differences between groups while adjusting for age. Partial correlation coefficients were used to show associations between various variables while adjusting for age. Stepwise linear regression analysis was also used to show associations between variables. The study presented in Chapter 5 made use of both POWIRS I and II, which are studies including Africans and Caucasians, respectively. The methodology of the two studies was the same. All subjects gave informed consent in writing and the Ethics Committee of the North-West University approved the study. The reader is referred to the "Materials and Methods" section of Chapters 2-5 for a more elaborate description of the subjects, study design and analytical methods used in each article. vii Results and conclusions of the individual manuscripts > Results from Chapter 2 showed that the volume loading effect associated with obesity was present in both overweight/obese normotensive and overweight/obese hypertensive groups, however, the accommodating effect observed in the overweight/obese normotensive group was absent in the overweight/obese hypertensive group due to decreased vascular function. This was confirmed by a high pulse pressure. Decreased vascular functioning was associated with the abdominal skin fold. This suggests that abdominal subcutaneous fat may either be a marker of visceral fat, or may in itself contribute to increased cardiovascular risk in Africans. > Results from Chapter 3 showed a negative result. Plasma endothelin-1 levels were similar for the lean normotensive, overweight/obese normotensive and overweight/obese hypertensive groups. After re-dividing the groups into normotensive and hypertensive, and then into lean and overweight/obese, still no differences could be obtained. Additionally, no correlations could be obtained between endothelin-1 and cardiovascular function in any of the groups. These findings suggest that endothelin-1 is not implicated in obesity-related hypertension in African women. > In Chapter 4, leptin levels were elevated in both overweight/obese normotensive and hypertensive groups compared to the lean normotensive group. However, leptin levels did not differ between the two overweight/obese groups. Even though leptin levels were the same, leptin was directly and positively associated with systolic blood pressure and pulse pressure and negatively with arterial compliance only in the overweight/obese hypertensive group, independent of obesity, insulin resistance, hyperinsulinemia and age. > In Chapter 5 the volume loading, as well as the accommodating effect, that is, decreased total peripheral resistance and increased arterial compliance, was present in both African and Caucasian obese groups compared to their lean controls. Even though leptin levels, body mass index and age were similar for both African and Caucasian obese groups, the accommodating effect seemed to be more prominent in the obese Caucasian group, explaining a lower diastolic blood pressure compared to the obese African group. Leptin showed a favourable negative association with diastolic blood pressure and total peripheral resistance in the obese Caucasian group, but not in the obese African group. This may indicate that leptin predominantly exerts pathological influences on obese African women, as determined previously in Chapter 4. / Thesis (Ph.D. (Physiology))--North-West University, Potchefstroom Campus, 2005.

Motivation: Cardiovascular disease (CVD) is one of the leading causes of death worldwide, with the greatest mortality rates occurring in low and middle income countries. The increase in the prevalence of risk factors such as hypertension, obesity and diabetes in Sub-Saharan Africa has led in an increase of the prevalence of CVD. It remains largely unclear whether psychological distress and more specifically the perception of own health and / depression may contribute to this observed increase in the prevalence of CVD in this population group. To our knowledge investigations exploring these aspects have not been done in the African context, thus the association between depression as an outcome of psychological distress and cardiovascular dysfunction in Africans is a new frontier that requires further exploration in the population group. Objective: The aim of this study was to investigate the association between psychological distress and cardiovascular function in urbanized black South Africans which included a target population of 200 Africans, men (n=101) and women (n=99). The participants were stratified into a hypertensive (HT) and normotensive (NT) group. Methodology: The manuscript presented in chapter 2 made use of the data obtained from the SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) project. A group of 200 black Africans from governmental institutions of the North West Province of South Africa were recruited. All procedures conducted were approved by the North-West University Ethics Committee and written informed consent was given by all the participants prior to the study. Anthropometric measurements were taken with the assistance of registered biokinetisists. Resting cardiovascular variables such as heart rate (HR), arterial compliance (Cw), total peripheral resistance (TPR) and the mean arterial pressure (MAP) were obtained with the use of a Finometer device. The 24 hours ambulatory blood pressure (BP) (AMBP) measurements were obtained with a Cardiotens apparatus. The resting ECG NORAV PL-1200 data determined left ventricular hypertrophy (L VH) by making use of the Cornell product (RaVL+ SV3) *QRS. Psychological distress questionnaire assessed the perception of health (General Health Questionnaire; GHQ-28) and depression severity (Patient Health Questionnaire; PHQ-9). Participants were stratified into hypertensive and normotensive groups based on the European Society of Hypertension (ESH) 2007 guidelines using the 24hr AMBP as a norm. Results were adjusted for confounders (age, body mass index, smoking, alcohol consumption and physical activity). One way Analysis of Covariance (ANCOVA) was done to determine significant differences between age, body mass index, lifestyle factors cardiovascular variables and psychological parameters. For more detailed description of the subjects, study design and analytical procedures used in this study the reader is referred to the Methods section in Chapter 2. Results and Conclusion: The hypertensive (HT) men and women were more obese (p<0.01) with a larger waist circumference (WC) (p=0.05) and a lower compliance (p</=0.05) compared to their normotensive (NT) counterparts. Only the HT men revealed a higher Cornell product value (p=0.06) compared to NT counterparts. In HT men, somatisation was positively associated with blood pressure (SBP & DBP), while in HT women it was associated with heart rate (HR). Major depression was associated with a left ventricular hypertrophy in HT men and MAP in HT women. Logistic regression analysis followed to predict the strongest contributor to HT in Africans. It was indicated that depressed women are 1.13 times more likely to develop hypertension than men. In conclusion, these results suggest a possible association between depression as an outcome of psychological distress and cardiovascular dysfunction in urbanised Africans. Depression has also been identified as a contributor to HT in African women. / Thesis (M.Sc. (Physiology))--North-West University, Potchefstroom Campus, 2009.

Motivation: Cardiovascular disease (CVD) is one of the leading causes of death worldwide, with the greatest mortality rates occurring in low and middle income countries. The increase in the prevalence of risk factors such as hypertension, obesity and diabetes in Sub-Saharan Africa has led in an increase of the prevalence of CVD. It remains largely unclear whether psychological distress and more specifically the perception of own health and / depression may contribute to this observed increase in the prevalence of CVD in this population group. To our knowledge investigations exploring these aspects have not been done in the African context, thus the association between depression as an outcome of psychological distress and cardiovascular dysfunction in Africans is a new frontier that requires further exploration in the population group. Objective: The aim of this study was to investigate the association between psychological distress and cardiovascular function in urbanized black South Africans which included a target population of 200 Africans, men (n=101) and women (n=99). The participants were stratified into a hypertensive (HT) and normotensive (NT) group. Methodology: The manuscript presented in chapter 2 made use of the data obtained from the SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) project. A group of 200 black Africans from governmental institutions of the North West Province of South Africa were recruited. All procedures conducted were approved by the North-West University Ethics Committee and written informed consent was given by all the participants prior to the study. Anthropometric measurements were taken with the assistance of registered biokinetisists. Resting cardiovascular variables such as heart rate (HR), arterial compliance (Cw), total peripheral resistance (TPR) and the mean arterial pressure (MAP) were obtained with the use of a Finometer device. The 24 hours ambulatory blood pressure (BP) (AMBP) measurements were obtained with a Cardiotens apparatus. The resting ECG NORAV PL-1200 data determined left ventricular hypertrophy (L VH) by making use of the Cornell product (RaVL+ SV3) *QRS. Psychological distress questionnaire assessed the perception of health (General Health Questionnaire; GHQ-28) and depression severity (Patient Health Questionnaire; PHQ-9). Participants were stratified into hypertensive and normotensive groups based on the European Society of Hypertension (ESH) 2007 guidelines using the 24hr AMBP as a norm. Results were adjusted for confounders (age, body mass index, smoking, alcohol consumption and physical activity). One way Analysis of Covariance (ANCOVA) was done to determine significant differences between age, body mass index, lifestyle factors cardiovascular variables and psychological parameters. For more detailed description of the subjects, study design and analytical procedures used in this study the reader is referred to the Methods section in Chapter 2. Results and Conclusion: The hypertensive (HT) men and women were more obese (p<0.01) with a larger waist circumference (WC) (p=0.05) and a lower compliance (p</=0.05) compared to their normotensive (NT) counterparts. Only the HT men revealed a higher Cornell product value (p=0.06) compared to NT counterparts. In HT men, somatisation was positively associated with blood pressure (SBP & DBP), while in HT women it was associated with heart rate (HR). Major depression was associated with a left ventricular hypertrophy in HT men and MAP in HT women. Logistic regression analysis followed to predict the strongest contributor to HT in Africans. It was indicated that depressed women are 1.13 times more likely to develop hypertension than men. In conclusion, these results suggest a possible association between depression as an outcome of psychological distress and cardiovascular dysfunction in urbanised Africans. Depression has also been identified as a contributor to HT in African women. / Thesis (M.Sc. (Physiology))--North-West University, Potchefstroom Campus, 2009.

Perinatal asphyxia is a significant contributor to neonatal brain injury. In the clinical environment there is variability in the severity of neural injury in neonates with similar clinical histories. Whilst the duration and intensity of hypoxia is well known to influence the severity of neurological outcome, the global physiological responses to hypoxia may also affect the subsequent variability in neurological outcome. The first step in this project was to identify which physiological response/s during a constant global hypoxic-ischemic insult influence the severity of neurological outcome in the newborn piglet and to assess the relative importance of these responses. Hypoxia/hypercapnia was induced in anaesthetized piglets by reducing the fraction of inspired oxygen to 0.1 (10%) and the ventilation rate from 30-10 breaths per minute for 45 minutes. Neurological outcome was determined by using functional markers including aEEG amplitude and cerebral impedance, and the structural marker microtubule associated protein-2 immunohistochemistry at 6 hours post hypoxia. The results from the initial study indicated that there was significant variability in neurological outcome following a constant hypoxia/hypercapnia insult. Serum cortisol concentrations were highly variable at the end of hypoxia (mean ± SD; 240.7 ± 90.9 nmol/L) and associated with cardiovascular function (time heart rate below baseline; r = 0.69) and neurological outcome (r = 0.70). Cardiovascular function (time heart rate was below baseline) and neurological outcome were strongly associated (r = 0.77). In this study we observed an oscillating pattern in cardiovascular function during hypoxia in some animals. In the regression analysis variability in cortisol concentrations and cardiovascular function explained 68% of the variability in the severity of neurological outcome. Additional physiological factors did not improve the strength of the association with neurological outcome. The variability in the physiological responses, particularly cardiovascular and endocrine responses to hypoxia may be more important determinants of neurological outcome then previously recognised. Results from the initial study opened up several questions about the relationship between cortisol and cardiovascular function during hypoxia and the relationship to the subsequent neurological outcome. Since variability in cortisol concentrations was associated with both cardiovascular function and neurological outcome the second step of this thesis was to investigate what factors contributed to the variability in serum cortisol concentrations during hypoxia. It is important to understand why some individuals produce more cortisol than others, and as a result are protected against brain injury. The aim was to determine if the variability in serum cortisol concentrations was the result of variability in ACTH concentrations during acute global hypoxia. The results from this study showed that early changes in serum cortisol concentration (15 minutes) were not correlated with ACTH (R2 = 0.26, P = 0.1), however, later changes (30 – 45 minutes) were (R2 0.45 - 0.68). This suggests that the primary factor controlling serum cortisol concentrations before hypoxia and during later hypoxia is ACTH concentrations. These data suggest that other factors may control cortisol secretion during early hypoxia; a key mechanism responsible for these changes may be the activity of the sympathetic nervous system and the maturity of the adrenal medullae. Since, higher cortisol concentrations were associated with better cardiovascular function and neurological outcome. As a result of this observation the aim of this study was to determine if cortisol concentrations during hypoxia are the causative factor responsible for improved cardiovascular function and better neurological outcome. The results from this study showed that manipulating serum cortisol concentrations into high (<500nmol/l) and low (>50nmol/l) levels during hypoxia did not affect cardiovascular function (P = 0.68) or neurological outcome (P = 46). Within each group (low, high and control hypoxia group) there was significant variability in cardiovascular function during hypoxia, which was associated with neurological outcome. (r = -0.63, p = 0.01). This study showed that serum cortisol concentrations during hypoxia are not the causative factor impacting on improved cardiovascular function and neurological outcome. It is possible that factors affecting both cardiovascular function and cortisol production such as activity of the sympathetic nervous system, may be a possible mechanism behind the variability in neurological outcome and cardiovascular function. Additionally, this study showed that cortisol concentrations at 3 hours post hypoxia were associated with neurological outcome (r = -0.67, p = 0.01). The animals with poorer outcome may also be those with greater multi-organ damage and thus reduced ability to clear cortisol from the systemic circulation. In light of this finding it may be interesting to assess cortisol concentration in the human neonate at 3 hours post hypoxia and determine the relationship to neurological outcome. In the final study of this thesis the function of the cardiovascular system during hypoxia was investigated in more detail because of its strong association with neurological outcome (results observed in Chapter 2 and 4. Few researchers have reported on oscillations in cardiovascular function, particularly type-3 waves, during hypoxia in the neonate. The aim of this study was to determine the characteristics and occurrence of type-3 waves in the neonatal piglet and their relationship to neurological outcome following acute global hypoxia. The result showed that the development of type-3 waves in cardiovascular function occurred in 56% of animals. An oscillating pattern was significantly associated with better neurological outcome (p = 0.01) and a lower duration of hypotension during hypoxia (p = 0.02), and occurred more frequently in females (p = 0.024). The development of type-3 waves during acute global hypoxia is a key mechanism in promoting natural tolerance; and may be the result of greater activity, maturity or sensitivity of the sympathetic nervous system in females compared to males. This may explain the improved neurological outcome following hypoxia in the female neonate seen in the clinical setting.

Perinatal asphyxia is a significant contributor to neonatal brain injury. In the clinical environment there is variability in the severity of neural injury in neonates with similar clinical histories. Whilst the duration and intensity of hypoxia is well known to influence the severity of neurological outcome, the global physiological responses to hypoxia may also affect the subsequent variability in neurological outcome. The first step in this project was to identify which physiological response/s during a constant global hypoxic-ischemic insult influence the severity of neurological outcome in the newborn piglet and to assess the relative importance of these responses. Hypoxia/hypercapnia was induced in anaesthetized piglets by reducing the fraction of inspired oxygen to 0.1 (10%) and the ventilation rate from 30-10 breaths per minute for 45 minutes. Neurological outcome was determined by using functional markers including aEEG amplitude and cerebral impedance, and the structural marker microtubule associated protein-2 immunohistochemistry at 6 hours post hypoxia. The results from the initial study indicated that there was significant variability in neurological outcome following a constant hypoxia/hypercapnia insult. Serum cortisol concentrations were highly variable at the end of hypoxia (mean ± SD; 240.7 ± 90.9 nmol/L) and associated with cardiovascular function (time heart rate below baseline; r = 0.69) and neurological outcome (r = 0.70). Cardiovascular function (time heart rate was below baseline) and neurological outcome were strongly associated (r = 0.77). In this study we observed an oscillating pattern in cardiovascular function during hypoxia in some animals. In the regression analysis variability in cortisol concentrations and cardiovascular function explained 68% of the variability in the severity of neurological outcome. Additional physiological factors did not improve the strength of the association with neurological outcome. The variability in the physiological responses, particularly cardiovascular and endocrine responses to hypoxia may be more important determinants of neurological outcome then previously recognised. Results from the initial study opened up several questions about the relationship between cortisol and cardiovascular function during hypoxia and the relationship to the subsequent neurological outcome. Since variability in cortisol concentrations was associated with both cardiovascular function and neurological outcome the second step of this thesis was to investigate what factors contributed to the variability in serum cortisol concentrations during hypoxia. It is important to understand why some individuals produce more cortisol than others, and as a result are protected against brain injury. The aim was to determine if the variability in serum cortisol concentrations was the result of variability in ACTH concentrations during acute global hypoxia. The results from this study showed that early changes in serum cortisol concentration (15 minutes) were not correlated with ACTH (R2 = 0.26, P = 0.1), however, later changes (30 – 45 minutes) were (R2 0.45 - 0.68). This suggests that the primary factor controlling serum cortisol concentrations before hypoxia and during later hypoxia is ACTH concentrations. These data suggest that other factors may control cortisol secretion during early hypoxia; a key mechanism responsible for these changes may be the activity of the sympathetic nervous system and the maturity of the adrenal medullae. Since, higher cortisol concentrations were associated with better cardiovascular function and neurological outcome. As a result of this observation the aim of this study was to determine if cortisol concentrations during hypoxia are the causative factor responsible for improved cardiovascular function and better neurological outcome. The results from this study showed that manipulating serum cortisol concentrations into high (<500nmol/l) and low (>50nmol/l) levels during hypoxia did not affect cardiovascular function (P = 0.68) or neurological outcome (P = 46). Within each group (low, high and control hypoxia group) there was significant variability in cardiovascular function during hypoxia, which was associated with neurological outcome. (r = -0.63, p = 0.01). This study showed that serum cortisol concentrations during hypoxia are not the causative factor impacting on improved cardiovascular function and neurological outcome. It is possible that factors affecting both cardiovascular function and cortisol production such as activity of the sympathetic nervous system, may be a possible mechanism behind the variability in neurological outcome and cardiovascular function. Additionally, this study showed that cortisol concentrations at 3 hours post hypoxia were associated with neurological outcome (r = -0.67, p = 0.01). The animals with poorer outcome may also be those with greater multi-organ damage and thus reduced ability to clear cortisol from the systemic circulation. In light of this finding it may be interesting to assess cortisol concentration in the human neonate at 3 hours post hypoxia and determine the relationship to neurological outcome. In the final study of this thesis the function of the cardiovascular system during hypoxia was investigated in more detail because of its strong association with neurological outcome (results observed in Chapter 2 and 4. Few researchers have reported on oscillations in cardiovascular function, particularly type-3 waves, during hypoxia in the neonate. The aim of this study was to determine the characteristics and occurrence of type-3 waves in the neonatal piglet and their relationship to neurological outcome following acute global hypoxia. The result showed that the development of type-3 waves in cardiovascular function occurred in 56% of animals. An oscillating pattern was significantly associated with better neurological outcome (p = 0.01) and a lower duration of hypotension during hypoxia (p = 0.02), and occurred more frequently in females (p = 0.024). The development of type-3 waves during acute global hypoxia is a key mechanism in promoting natural tolerance; and may be the result of greater activity, maturity or sensitivity of the sympathetic nervous system in females compared to males. This may explain the improved neurological outcome following hypoxia in the female neonate seen in the clinical setting.

No description available.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Background: Myocardial oxidative fuel supply is increased in obese conditions. How this metabolic environment and altered cardiometabolic phenotype associated with prediabetic obesity impacts on cardiac function and tolerance to ischaemia/reperfusion injury remains uncertain. While obese individuals are likely to be treated with PPARα agonists, controversy exists as to how activation of the PPARα receptor influences cardiovascular function and post-ischaemic recovery. Aims: To determine in a model of hyperphagia-induced obesity 1) whether protracted obesity is associated with left ventricular (LV) mechanical dysfunction; 2) the responsiveness of these hearts to insulin stimulation; 3) whether insulin can afford cardioprotection against ischaemia/reperfusion damage; and 4) how obesity and chronic PPARα agonist (K-111) treatment influences myocardial function, substrate metabolism, mitochondrial function and post-ischaemic outcomes. Methods: Male Wistar rats were fed standard rat chow or a high caloric diet. 1) In vivo LV mechanical function was assessed echocardiographically in 32 week fed animals. Ex vivo LV function was measured in the presence of glucose, insulin and/or fatty acid (FA); 2) Ex vivo myocardial insulin sensitivity was assessed by measuring insulin stimulated glycolytic flux in 16 week fed rats. Insulin was also administered prior to and during regional ischaemia to determine its effect on post-ischaemic function and infarct size; 3) K-111 was added to the drinking water during the last 10 weeks of feeding (feeding period of 18 weeks); a) Ventricular mitochondrial function was determined polarographically in the presence of either glutamate or palmitoyl-L-carnitine as substrates; b) Myocardial carbohydrate and lipid metabolism, and in a separate series of perfusions, myocardial infarct size were determined in the presence of physiological or high insulin (30 or 50μIU/ml) and FA (0.7 or 1.5mM) concentrations. Results: 1) Obese animals maintained normal in vivo LV mechanical function. Glucose perfused hearts from obese animals had depressed aortic outputs compared to the control group (32.58±1.2 vs. 46.17±0.91 ml/min; p<0.001) which was abolished by the presence of FA; 2) Hearts from obese animals had reduced insulin stimulated glycolytic flux rates (1.54±0.42 vs. 2.16±0.57 μmol/g ww/min, p<0.01). Although insulin reduced infarct size in the obese group (20.94±1.60 vs. 41.67±2.09 %, p<0.001), its cardioprotective effect was attenuated in the presence of FA; 3) By simulating the in vivo metabolic environment of control and obese animals in ex vivo perfusions, elevated insulin and FA levels associated with obesity increased infarct sizes in the obese group compared to the control group (47.44±3.13 vs. 37.17±2.63 %, p<0.05); 4) While chronic K-111 treatment reversed systemic metabolic abnormalities associated with obesity, neither obesity nor the drug influenced myocardial and mitochondrial function or postischaemic outcomes. K-111 was able to reduce palmitate oxidation in the obese group. Conclusion: Elevated levels of circulating FFA may be important in maintaining normal LV mechanical function in the obese condition. While obesity had no impact on myocardial mitochondrial function and post-ischaemic outcomes during comparable perfusion conditions, the specific metabolic environment associated with obesity may augment post-ischaemic injury. K-111 is effective in reducing obesity related metabolic abnormalities, but has no effects on myocardial function, mitochondrial function or ischaemic tolerance. / AFRIKAANSE OPSOMMING: Agtergrond: Miokardiale oksidatiewe substraat voorsiening is verhoog in vetsug. Hoe hierdie metaboliese omgewing en veranderde miokardiale metaboliese fenotipe in prediabetiese vetsug miokardiale funksie en iskemie/herperfusie skade beïnvloed, is onseker. Alhoewel vetsugtige individue met PPARα agoniste behandel kan word, is die resultate verkry van hierdie reseptor aktivering op miokardiale funksie en iskemiese skade teenstrydig. Doelwitte: Om te bepaal of 1) verlengde vetsug linker ventrikulêre (LV) funksie beïnvloed; 2) hierdie harte sensitief vir insulien stimulasie is; 3) insulien die hart teen iskemie/herperfusie beskadiging beskerm; en of 4) vetsug en chroniese K-111 behandeling miokardiale funksie, substraat metabolisme, mitochondriale funksie en post-iskemiese herstel in vetsugtige, insulienweerstandige rotte beïnvloed. Metodes: Manlike Wistar rotte is met gewone rotkos, of ʼn hoé kalorie dieet gevoer. 1) In vivo LV funksie in 32 week gevoerde rotte is met behulp van eggokardiografie bepaal. Ex vivo LV funksie is met of sonder insulien en/of vetsure in die perfusaat bepaal; 2) Die ex vivo insuliensensitiwiteit is in 16 weke gevoerde rotte bepaal deur miokardiale glikolise te meet. Insulien is ook voor en tydens streeksiskemie toegedien, ten einde sy effek op miokardiale beskerming te bepaal; 3) K-111 is in die drink water van rotte toegedien vir die laaste 10 weke van hul dieet (voedingsperiode van 18 weke); a) Ventrikulêre mitochondriale funksie is polarografies bepaal in die aanwesigheid van glutamaat of palmitiel-L-karnitien; b) Miokardiale koolhidraat- en lipied metabolisme, en in ʼn aparte groep rotte, infarktgrootte, is bepaal in die teenwoordigheid van fisiologiese of hoë insulien- (30 of 50μIU/ml) en vetsuurvlakke (0.7 of 1.5mM). Resultate: 1) Vetsugtige rotte het normale in vivo LV funksie gehandhaaf. Glukose geperfuseerde harte van vet rotte se LV funksie was laer as die van kontroles (Aorta omset: 32.58±1.2 vs. 46.17±0.91 ml/min; p<0.001), maar dit het verbeter in teenwoordigheid van vetsure; 2) Harte van vetsugtige rotte het verlaagde insuliengestimuleerde glikolise getoon (1.54±0.42 vs. 2.16±0.57 μmol/g ww/min, p<0.01). Alhoewel insulien infarktgrootte in die vetsugtige groep verlaag het (20.94±1.60 vs. 41.67±2.09 %, p<0.001), is sy beskermende effekte in die teenwoordigheid van vetsure verlaag; 3) deur die in vivo metaboliese omgewing van kontrole en vetsugtige rotte in die perfusaat van die harte ex vivo te simuleer, is dit aangetoon dat die verhoogde vlakke van insulien en vetsure, geassosieer met vetsugtigheid, infarktgroottes in die vetsugtige groep teenoor die kontrole groep verhoog het (47.44±3.13 vs 37.17±2.63 %, p<0.05); 4) Hoewel chroniese gebruik van K-111 die metaboliese abnormaliteite gepaardgaande met vetsug normaliseer het, het beide vetsug en die middel geen invloed op miokardiale of mitochondriale funksie of vatbaarheid vir iskemiese beskadiging gehad nie. K-111 het miokardiale palmitaatoksidasie in die vetsugtige behandelde groep verlaag. Gevolgtrekking: Verhoogde bloed vetsuurvlakke in vetsug mag n belangrike rol in die handhawing van sistoliese funksie speel. Dit blyk dat die spesifieke in vivo omgewing geassosieer met vetsug wel tot verhoogte vatbaarheid vir iskemie/herperfusie skade mag lei. K-111 is effektief om die sistemiese metaboliese abnormaliteite gepaard met vetsugtigheid te verbeter, maar het geen effek op miokardiale funksie, mitochondriale funksie of vatbaarheid vir iskemie gehad nie.