Currently, the American College of Sports Medicine (ACSM) recommends that protocols for cardiopulmonary exercise testing (CPET) should last between eight and twelve minutes. However, the justification for these exercise durations rely on limited experimental data. These recommendations have a significant impact on the ability of frail patients to be assessed using CPET and should conform to evidence based practice. This thesis begins by assessing the validity of these recommendations in relation to maximal exercise responses before assessing the consequences of these recommendations on sub-maximal exercise measurements. These studies were conducted in a relatively large cohort (compared to the study that underpins the ACSM guidelines) of heterogeneous volunteers (they are both men and women, with a significant age range and varied functional capacity) to make the data more relevant to clinical exercise testing. The data presented in chapter three demonstrate that it is very difficult to obtain exercise duration conforming to the current ACSM guidelines by using a standardised ramp exercise protocol on both treadmill and cycle ergometer exercise. However, sub-group analyses for those subjects who achieved moderate (8-12 minutes) and short (less than 8 minutes) exercise durations. In addition, a separate analysis was carried out for a different sub-group of those who achieved moderate (8-12 minutes) and long (more than 12 minutes) of durations of exercise. Despite this, it was possible to demonstrate in sub-group analysis that there was no significant difference in peak oxygen uptake, peak carbon dioxide output, peak heart rate, peak ventilation and peak power output when exercise duration was less or more than that prescribed by the ACSM recommendations. In addition, the effects of long, moderate or short duration exercise per se were also analysed in this chapter and again exercise duration was shown to be without effect on the main maximal markers of exercise performance. In chapters four, five and six, the initial findings were extended to determine the effects of exercise duration on a range of clinically relevant sub-maximal markers of exercise performance. It was likely, since exercise duration did not affect maximal exercise that the physiological determinants of maximal performance were not significantly altered during short or long duration exercise and consequently it was likely that sub-maximal markers of functional capacity would not be affected. However, the quality of the data obtained during CPET can obviously influence the accurate measurement physiological responses during exercise and much of the analysis in these chapters focused on the validity of the data analysis. Chapter four investigated the limitations to measuring the break point in the relationship between oxygen uptake and carbon dioxide output during progressive exercise (the so called ventilatory threshold or ‘V-slope’). The accurate measurement of this break point was determined by standard gas exchange criteria and the effects of reducing the data available for analysis (by reducing the amount of breaths available for comparison at reduced exercise durations) were examined. The data showed that reducing the data available for analysis had an impact on the quality of the data (decreasing the goodness of fit) but no significant effect on the determination of the ventilatory threshold. Chapter five determined the effects of exercise duration on the oxygen uptake efficiency slope (OUES). As expected, the effects of exercise duration were not significant but additional investigation into the commonly employed data analysis procedures was performed. These data show that the log transformation of the relationship between ventilation and oxygen uptake allows reliable assessment of ventilatory efficiency in most cases, however, the impact of the lactate threshold on ventilation and the biological variability in where the threshold occurs as a proportion of functional capacity can impact on the sensitivity of this measurement to predict aerobic and/or anaerobic capacity. Chapter six determined the effects of exercise duration on the breathing reserve index and found no significant difference during short, moderate or long exercise duration exercise. Further analysis was performed to demonstrate limitations in the use of predicted maximum voluntary ventilation (rather than direct measurement). Taken together, these data demonstrate that the current ACSM recommendations for CPET are too restrictive and may limit the application of such testing in populations that cannot exercise for between eight and twelve minutes. The data further suggest that the testing and analysis procedures used during CPET are central to producing valid maximal and sub-maximal markers of functional capacity and the recommendations should focus include guidelines in relation to such aspects.

In Scotland, stroke is the third most common cause of death behind heart disease and cancer. However, most strokes are not fatal and can cause severe disability, with one third of survivors still functionally dependent after one year. The advent of recombinant tissue plasminogen activator (rT-PA) as a thrombolytic modality revolutionised the treatment for ischaemic stroke, providing a treatment aimed to promptly restore nutritional blood flow to the ischaemic penumbra, a transient tissue state which is amenable to salvage. Crucially, patient ineligibility from a multitude of factors (including the narrow time window for benefit and the risk of intracranial haemorrhage) means that fewer than 10% of all stroke patients are thrombolysed. Positive identification of penumbra is not employed in the current intravenous rT-PA administration strategy, which is instead based on two main prerequisites: stroke patients in whom intracerebral haemorrhage has been excluded with non-contrast computed tomography (CT) and who also present within 4.5 hours of symptom onset. The technical impracticalities and limited availability of the gold standard penumbral imaging modality, multitracer 15O positron emission tomography (PET), and the lack of standardised thresholds to identify penumbra using non-contrast CT have hindered the development and inclusion of routine brain imaging in the management of acute stroke patients. An alternative research tool which may potentially be used in clinical practice is magnetic resonance imaging (MRI) which defines penumbra on the basis of diffusion-perfusion (DWI/PWI) mismatch. However, this provides an imprecise measure of penumbra and fails to identify tissue viability. Current PET-derived definitions of penumbra use metabolic indices such as oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen (CMRO2), which are not fully incorporated into MR definitions. This thesis presents an alternative MRI method for identifying the metabolic penumbra in a rodent model of focal cerebral ischaemia. This utilises an MRI sequence similar to that used in functional MRI (fMRI) techniques, and uses 100% oxygen inhalation as a biotracer to detect penumbral tissue. Specifically, by using a blood oxygen level dependent (BOLD) T2*-weighted sequence in which changes in the deoxyhaemoglobin:oxyhaemoglobin ratio are detected - in conjunction with a transient hyperoxic challenge (Oxygen Challenge (OC) paradigm: 5 minutes breathing air followed by 5 minutes breathing 100% oxygen) - penumbral tissue can be distinguished from adjacent ischaemic core and benign oligaemia (Santosh et al, 2008). Changes in CBF, cerebral blood volume (CBV), tissue oxygenation, and oxidative metabolism can all influence the T2* signal (Ramsay et al, 1993; Corfield et al, 2001), so it was important to evaluate the possibility that factors other than tissue metabolism were influencing the signal change during OC. An initial study was performed which showed that baseline CBF did not influence T2* signal response to OC, whilst a greater increase in the percentage change in arterial oxygen saturation following OC caused an increased magnitude in T2* percentage signal change in contralateral tissue and penumbra, but not in ischaemic core. Arterial oxygen levels (PaO2) affect the magnitude of the T2* signal change to OC, with lower baseline PaO2 levels amplifying the T2* signal response in metabolically active regions, implying that careful control of physiological variables may optimise the T2*OC technique. The first validation study used [14C] 2-deoxyglucose autoradiography to determine the metabolic status of penumbra defined by T2*OC MRI. The results confirmed that glucose metabolism in the T2*OC-defined penumbra was comparable to contralateral values, whereas markedly different levels of glucose metabolism were evident in the ADC-derived ischaemic core and an adjacent region of increased 2DG phosphorylation. From this, it was concluded that metabolic information could be yielded from the ischaemic brain that may improve delineation of the penumbra using the OC technique. As penumbral tissue must fulfil the fundamental criteria of being potentially salvageable and responsive to therapy, the consequences of reperfusion on the T2*OC-defined penumbra was tested. This study confirmed that T2*OC-defined penumbra displayed a T2* signal change significantly higher than contralateral tissue during ischaemia which subsequently returned to contralateral levels following reperfusion and did not progress to infarction when assessed at day 7 following stroke. Finally, the spatiotemporal characteristics of the T2*OC-defined penumbra were investigated and compared with DWI/PWI mismatch-defined penumbra. Serial scanning demonstrated that T2*OC penumbra behaved in a similar manner to tissue defined by traditional mismatch criterion. The spatial location and tissue volumes of penumbra were similar with both methods, showing that, in animals where mismatch tissue volume reduced over time, T2*OC penumbra reduced similarly, and in animals where mismatch volume remained static over time, T2*OC-defined penumbra behaved similarly. Additionally, an interesting finding arose in the latter study which showed that ischaemic damage continues to progress beyond 4 hours following permanent MCAO, which may be relevant to the calculation of ADC and CBF thresholds used in defining DWI/PWI mismatch. Collectively, the preclinical data support the potential of T2*OC to discriminate tissue compartments in acute stroke based on metabolic status which thereby provides an alternative and improved means of defining the ischaemic penumbra.

Conduction abnormalities affect prognosis in chronic heart failure (CHF). Previous investigators have observed abnormal delay in atrioventricular (AV) conduction in a rabbit model of left ventricular dysfunction (LVD) due to apical myocardial infarction. In this model, AV conduction time increased with increasing pacing rates, suggesting the most likely site of delay is the AV node. The mechanisms by which this occurs are not fully understood. The purpose of this thesis was to confirm that the abnormal prolongation of AV conduction time originates at the AV node in a rabbit model of LVD due to apical myocardial infarction, and explore possible mechanisms underlying the observation. Using surface electrogram recording and standardised pacing techniques in an isolated AV node tissue preparation I confirmed that there is abnormal prolongation of AV nodal conduction in this rabbit model of LVD, as evidenced by prolongation of atrio-hisian (AH) interval and Wenckebach cycle length (WCL) in LVD compared to control. Furthermore, using optical mapping of electrical activation using voltage sensitive dye I observed that the prolongation of the AH interval is predominantly a consequence of conduction delay between the inputs of the AV node and the compact nodal region. Neuro-hormonal derangement in chronic heart failure has a central role in the pathogenesis of the disease, with evidence of downregulation of beta ()-adrenoceptors in the left ventricular myocardium. I therefore explored the possibility of β-adrenoceptor downregulation in the AV node as a mechanism underlying the abnormal AH interval prolongation in LVD. There was no evidence of β-adrenoceptor downregulation in the AV node in LVD compared to control to account for the observed abnormal conduction delay. Adenosine is known to have profound effects on AV nodal conduction and the possibility of tonic excess of adenosine in LVD was explored as a possible mechanism for the prolonged conduction delay. Using an exogenously applied adenosine A1 receptor antagonist there was no evidence of excess endogenous adenosine in LVD compared to control. There was, however, an increase in the sensitivity of the LVD samples compared to control to exogenous adenosine, with a significant increase in AH interval and WCL with increasing concentrations. This thesis also investigates the effect of acidosis on AV nodal conduction. There was significant prolongation of the spontaneous sinus cycle length, AH interval and WCL, as well as the AV nodal functional and effective refractory periods, proportional to the degree of acidosis. These effects were reversible with return to normal pH. Optical mapping studies showed that the spatiotemporal pattern of AV nodal delay during acidosis was similar to that observed in LVD, with the predominant delay in conduction between the AV nodal inputs and the compact AV node. In summary this thesis has confirmed that even in the absence of a direct ischaemic insult to the AV junction, conduction abnormalities in the AV node may still occur as a pathophysiological response to a myocardial infarction resulting in LVD. The mechanisms underlying this response are likely to be complex and multiple, and are not yet clear. Establishing the electrophysiological basis and the effects of neuro-hormonal modulators of atrioventricular nodal function may lead to development of targeted therapeutic strategies to improve overall survival and improve symptom control for patients with CHF.

Pulmonary Hypertension (PH) is a rare but devastating illness which results in progressive right ventricular (RV) failure and early death. RV function determines survival in all patients with PH but it is difficult to measure accurately using existing clinical techniques. The choice and design of the experiments in this thesis was driven by a desire to improve our understanding of the reasons for right, and left,ventricular dysfunction in this context. Cardiovascular magnetic resonance (CMR)imaging was utilized throughout as it allows the non-invasive, direct and accurate study of both ventricles; at rest and during stress. In Chapter 3, CMR imaging was used to identify an NT-proBNP threshold (1685 ng/l, sensitivity 100%, specificity 94%) for the non-invasive detection of RV systolic dysfunction in patients with PH. In Chapter 4, contrast-enhanced-CMR was utilized for the first time in PH patients and revealed previously unidentified areas of myocardial fibrosis within the RV insertion points and interventricular septum. The extent of these areas correlated inversely with RV ejection fraction (r = -0.762, p < 0.001). Septal contrast enhancement was particularly associated with bowing of the interventricular septum. Finally, in Chapter 5, dobutamine stress-CMR was used to determine the individual reasons for right and left ventricular stroke volume impairment during exercise in PH patients. ∆ RV stroke volume appeared limited by diminished contractile reserve as ∆ RVEF was lower in PH patients (27%) compared to controls (38%) and ∆ RVEF correlated with ∆ RV stroke volume (r = 0.94, p < 0.001). ∆ LV stroke volume appeared limited by impaired filling, probably due to reduced LV preload as RV stroke volume and LV end-diastolic volume remained closely related at rest (r = 0.821, p < 0.001) and stress (r = 0.693, p = 0.003).

The present thesis describes the impact of glycaemic index of high carbohydrate diets consumed for 5 days on exercise energy metabolism and capacity and fasting plasma lipids in healthy physically active individuals. The thesis consists of a literature review (Chapter 1), general methods (Chapter 2), four experimental chapters (Chapter 3-Chapter 6) and general discussion and conclusion (Chapter 7). Chapter 3 presents a pilot study aimed to investigate whether high carbohydrate meals with high and low glycaemic index of foods present within meals developed by using the glycaemic index values from the published glycaemic index tables, produce significant differences in postprandial glucose response. Eight healthy active women consumed prescribed high carbohydrate diets with either high or low glycaemic index in a randomised counterbalanced order. The experimental meals which consisted of breakfast, morning snack and lunch were consumed after an overnight fast. Plasma glucose responses were measured at baseline and every 30 minutes for 300 minutes after baseline. We concluded that high carbohydrate meals with high and low glycaemic index prescribed using the glycaemic index values from the existing glycaemic index tables in the literature produced a significant difference in postprandial plasma glucose responses. Thus, for further studies high carbohydrate diets with high and low glycaemic index were developed using glycaemic index values from available glycaemic index tables. The aim of Chapter 4 and Chapter 5 was to investigate the extent to which the glycaemic index of high carbohydrate diets consumed for 5 days reduces the rate of fat oxidation during endurance exercise and exercise capacity during running conducted in the fasted state in men and women. To determine this, 9 healthy physically active men (Chapter 4) and 9 healthy physically active women (Chapter 5) performed three treadmill runs to exhaustion at 65% max after their habitual diet, after 5 days on a high carbohydrate high glycaemic index diet, and after 5 days on high carbohydrate low glycaemic index diet, in a randomised counterbalanced order. Blood samples for the measurements of glucose, insulin, glycerol and non-esterified fatty acids, and expired air samples for the measurements of the rates of fat and carbohydrate oxidation were obtained at 15, 30, 45, 60, 75, 90 minutes and at the point of exhaustion. Running capacity was measured as time to exhaustion and distance covered. It was found that in both men and women, the extent to which high carbohydrate diets consumed for 5 days reduced the rate of fat oxidation during running in the fasted state was not influenced by the glycaemic index of the diet, and that glycaemic index of high carbohydrate diets consumed for 5 days had no impact on running capacity. Chapter 6 aimed to investigate the impact of the consumption of high carbohydrate diets with high and low glycaemic index for 5 days on fasting plasma concentration of lipids, insulin sensitivity and biomarkers for endothelial function (i.e. intercellular adhesion molecule-1 and vascular cell adhesion molecule-1) in physically active individuals. Fasting blood was collected from 17 healthy individuals on three occasions in a randomised counterbalanced order: after consuming habitual diet, after 5 days on high carbohydrate high glycaemic index diet and after 5 days on high carbohydrate low glycaemic index diet. It was found that the extent to which high carbohydrate diets consumed for 5 days increases fasting plasma concentration of triglyceride and reduces the concentration of high density lipoprotein cholesterol was not influenced by the glycaemic index of the diets. It was also found that glycaemic index of high carbohydrate diets consumed for 5 days had no impact on insulin sensitivity or on biomarkers of endothelial activation. In conclusion, consideration of the glycaemic index of high carbohydrate diets consumed by physically active healthy men and women for 5 days has no impact on insulin sensitivity and fasting concentration of plasma lipids, it does not influence the rate of fat oxidation induced by high carbohydrate diets during running conducted in the fasted state and has no influence on running capacity. Thus, when physically active individuals increase carbohydrate intake for the purposes of muscle glycogen accumulation, consideration of the glycaemic index is not important. Future studies are needed to determine whether the glycaemic index of high carbohydrate diets modify exercise energy metabolisms in top grade athletes.

This thesis examines the influence of selected environmental stimuli on spatial and temporal variation in acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD). Evidence indicates that the high level of humidity in the British climate, and the weather associated with the occurrence of mist and fog, may play an important part in the high incidence rates of asthma and COPD in the UK. Recent studies on this subject area are scarce. The influence of geographical features on pollutant concentrations and variation in meteorological conditions is often acknowledged when examining the effect of air quality and weather on respiratory health, but a thorough investigation is rarely conducted. Focussing on the localities of Worcester and Dudley, this research addresses these deficits by incorporating two main study elements. The first stage examined the variation in daily hospital admissions for asthma and COPD between 1998 and 2003. During the second phase of the study programme, a 12-month daily symptom study was undertaken in a cohort of 52 COPD subjects. The findings from the project demonstrate that relative humidity, temperature and dew point play a significant role in exacerbations of asthma and COPD. The direction of the correlation found for these meteorological variables indicates that their role is of a combined nature, rather than independent of each other, leading to significant changes in respiratory symptoms during weather associated with high levels of airborne water droplets or the formation of mist and fog. The deleterious influence of air pollution on respiratory wellbeing was also confirmed. Particulate matter showed the strongest effect on symptoms in COPD. Particles can serve as nuclei for the formation of airborne water droplets. Enhanced lung retention of droplet borne pollutants, in contrast to dry particles, is possible. Finally, the results from the research provide evidence of increased respiratory symptoms in lower altitude areas of river valleys. The findings show that airflow, humidity and temperature regimes produced in valley regions, by local topographic features, can lead to interaction between meteorological conditions and air pollution that have an adverse effect on respiratory health.

Acute pancreatitis is a serious and often lethal inflammatory disease. Its causes are diverse and incompletely understood; however, gallstones and alcohol abuse are the principal triggers. Oxidative stress has been proposed as a determinant of acute pancreatitis (AP) severity, and has been the subject of recent clinical trials. The major AP precipitants, alcohol, alcohol metabolites and bile salts, were investigated for their potential role in the production of reactive oxygen species (ROS), and their effects upon cell fate. Application of the bile salt taurolithocholic acid sulphate (TLC-S) to isolated human and murine pancreatic acinar cells generated significant Ca2+-dependent mitochondrial ROS which were inhibited with the antioxidant N-acetyl-L-cysteine (NAC), and promoted with dimethoxy-2-methylnaphthalene (DMN), an inhibitor of the antioxidant enzyme NAD(P)H quinone oxidoreductase (NQO1). Elevations of ROS mediated by bile salts were crucial in the determination of cell fate, producing apoptosis rather than necrosis. In contrast, ethanol and its metabolites, both oxidative (acetaldehyde) and non-oxidative (fatty acid ethyl esters: FAEEs), were shown to produce no significant ROS in similar circumstances. Assessment of ethanol and its metabolites revealed that ethanol and acetaldehyde showed little effect on cell fate. Low concentrations of ethanol with fatty acid, however, induced toxic elevations of [Ca2+]C, mitochondrial dysfunction and necrosis when oxidative metabolism was compromised. This effect was reversed by inhibition of FAEE synthase, suggesting important deleterious actions of non-oxidative alcohol metabolism in the pancreas.

Gamma oscillations, synchronous network activity between 30 and 100 Hz, have been linked to higher cognitive functions. Adenosine receptor modulation has been shown to alter cognitive function in animals and humans. In this thesis the effects of adenosine receptor modulation on in vitro and in vivo hippocampal gamma oscillations were investigated as well as the underlying mechanisms. \(A_1\)-receptor activation selectively decreased gamma oscillations while blocking \(A_1\)-receptors and activating \(A_{2A}\)-receptors increased gamma oscillations. Increasing endogenous adenosine levels suppressed gamma oscillations while decreasing endogenous adenosine levels facilitated gamma oscillations in vitro. Sharp electrode current clamp and whole-cell voltage clamp experiments showed that \(A_1\)-receptor activation hyperpolarised resting membrane potential, reduced firing rate and EPSP amplitude and shifted the IPSC reversal potential to more negative potentials. Blocking \(A_1\)-receptors increased pyramidal cell excitability and increased excitatory synaptic transmission. The results in vivo were more ambiguous but \(A_1\)-receptor activation decreased power in all frequency bands indicating that adenosine receptors can modulate hippocampal gamma oscillations in vivo. \(A_1\)-receptor blockage had no consistent effect on in vivo hippocampal gamma oscillations. Adenosine receptors modulate gamma oscillations in rodent hippocampal slices but are difficult targets for developing treatments that have cognitive benefits because of their ambiguous effects in vivo.

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease of the joints with predominant symptoms of pain, swelling and stiffness. Patients with RA are at increased risk of cardiovascular disease (CVD). The exact mechanism for this is unknown, but RA disease-related inflammation has been postulated to affect the vasculature and contribute to endothelial dysfunction. The studies presented in this thesis examine vascular function in patients with RA and explore associations with disease-related inflammation as well as CVD risk factors. A cross-sectional study was carried out with 99 RA patients and 32 healthy control participants who underwent assessments of microvascular endothelial function, macrovascular endothelial function and arterial stiffness (AIx). Microvascular and macrovascular endothelial function were similar in RA patients and healthy control participants, but AIx was higher in the RA patients, as was global CVD risk. RA disease-related inflammation was not associated with microvascular or macrovascular endothelial-dependent function, however, global CVD risk inversely correlated with microvascular endothelial-dependent function and macrovascular endothelial-independent function. A longitudinal study was conducted in 23 RA patients starting on anti-tumor necrosis factor-α (anti-TNF-α) treatment and all the above-mentioned assessments were repeated after 2 and 12 weeks of treatment. Treatment, which was successful in reducing disease activity at 2 and 12 weeks, resulted in an improvement in microvascular endothelial-dependent function at 2 weeks, but not at 12 weeks. There was no change in macrovascular endothelial-dependent function or arterial stiffness at any time point, nor in global CVD risk. Finally, a systematic review of the literature pertaining to endothelial function in RA was performed. This revealed that, on the whole, the evidence supporting a relationship between endothelial function and disease-related inflammation was not strong. The findings of these studies suggest that classical CVD risk may be a better predictor of endothelial function in RA than disease-related inflammation.

No description available.