Pressure ischemia is a medical condition characterised by the necrosis of the skin and underlying tissues in body areas exposed to prolonged pressure. This condition leads to the development of bedsores and affects 9% of hospitalised patients, costing the NHS between £1.4 and £2.1 billion per year. The severity of pressure ischemia has been linked to the concentration of sweat lactate, a product of sweat gland metabolism under anaerobic conditions, such as hypoxia. Normal levels of lactate in human sweat are 20±7 mM, but under ischemic conditions these can rise up to approximately 70 mM. This project presents the development of a novel flexible electrochemical enzyme-based biosensor for the continuous and non-invasive monitoring of sweat lactate with the potential for becoming a body-worn device for the early detection of pressure ischemia onset. The core of the recognition system is a flexible laminate, comprising two highly porous polycarbonate membranes, which provide support for the lactate oxidase enzyme, immobilised via covalent cross-linking. Oxidation of lactate produces H2O2, which is subsequently determined electrochemically. The transducer comprises a two-electrode system on a single flexible polycarbonate membrane, sputter-coated with gold (CE/RE) and platinum (WE) to render it conductive. The developed design has been improved through investigation into different factors regarding the immobilisation method of the enzyme in the laminate and the lowering of interferences from oxidising compounds present in sweat. The sensing system exhibits lactate selectivity at physiologically relevant concentrations in sweat for pressure ischemia (0–70 mM), with good reproducibility (7.2–12.2% RSD) for a hand-manufactured device. The reliability of the sensor’s performance and the capability to detect lactate fluctuations on human sweat samples has been demonstrated. The sensing system showed excellent operational and mechanical stability. The application of Nafion® on the WE lowered interferences from ascorbic acid and uric acid by 96.7 and 81.7% respectively. These results show promise towards the further development of a body-­‐worn monitoring device for determining lactate levels in undiluted human sweat samples in a reproducible, fast and accurate manner.

The purpose of this study was to determine whether ischemia would enhance muscle spindle responses to tendon tap and vibration during submaximal fatiguing contractions in the soleus muscle of able-bodied individuals. Nine healthy adults attended two experimental sessions approximately 48 hours apart. Both sessions were identical except that the fatigue task in one was performed with a pressure cuff placed above the knee and inflated to 180 mm Hg. Three 5s maximum voluntary contractions (MVCs) were performed prior to and after the fatigue task. Each participant held a target force of 20% MVC until endurance time (peak-to-peak tremor amplitude exceeded 5% MVC or target force dropped by 2% for 3s). Muscle spindle responses were evaluated using the peak-to-peak EMG amplitude of tendon taps (delivered by a custom-made tapper) and the Motor Unit Firing Rates (MUFR) during 15 s of vibration, recorded with fine-wire intramuscular electrodes. H reflex responses were measured before and after fatigue for each condition, to measure the net excitability of the spinal cord. There were no significant differences (p>0.05) in the P-P EMG of tendon taps or the MUFR across any conditions. The post-fatigue Maximal Voluntary Contraction forces were measured and were less than the pre-fatigue values under both conditions (and significantly different in the non-ischemic condition (p=0.01)). Absence of significant differences in the Hmax:Mmax ratios (p=0.94 in non-ischemic/fatigue and p=0.43 in ischemic condition) indicated that the spinal excitability was relatively unchanged across the conditions. Therefore, we could not conclude that ischemia enhanced the muscle spindle response. / text

abstract / Anaesthesiology / Doctoral / Doctor of Philosophy

Myocardial ischemia-reperfusion (I/R) injury is an important health concern in myocardial infarction and situations such as angioplasty and cardiac surgeries. Therefore, patients and physicians need therapeutic interventions that are applicable at the time of surgery. Flavonoids and ascorbate (vitamin C) are known for their antioxidant activity and may be involved in the currently known health benefits of plant based foods and drinks. The objectives of this study were to 1) determine the extent to which ascorbate or catechin alone at levels which could be in blood after dietary supplementation, can protect myocardial tissue in the reperfusion phase of I/R injury, and 2) evaluate the possible cooperative or synergistic protective effect of ascorbate and catechin when given together. Isolated rat hearts (n=48) were perfused in the retrograde mode with modified Krebs-Henseleit buffer, and following the induction of 30 min global ischemia, ascorbate (150 µM) and/or catechin (5 µM) were added directly into the perfusate during 90 min reperfusion. To determine the histopathological features, hematoxylin and eosin (H&E) stain was used in one heart per condition; while to assess the biochemical analysis, the heart tissues were assessed for apoptosis (caspase-3 activity), oxidative stress (thiobarbituric acid reactive substances (TBARS) and total malondialdehyde (MDA) levels), and redox status (reduced and oxidized glutathione tissue levels). A comparison of IR hearts with two controls, sham (perfused for a 15 min stabilization period) and continuous perfusion (perfused for 135 min), showed in most but not all measurements that this was a suitable model of IR injury. The treatment experiments showed that 150 µM ascorbate protected the heart against lipid peroxidation and cell apoptosis by 100%, while 5 µM catechin protected by 67% and 90% respectively. No cooperative protective effect could be observed when ascorbate and catechin were used together. None of the treatments significantly affected either reduced or oxidized glutathione levels. In conclusion, this study showed strong protection by ascorbate, which could be used in clinically relevant situations, and is the first to report the protection by catechin at this dose under conditions of myocardial ischemia-reperfusion injury.

Control of blood flow to skeletal muscle is essential to maintain the overall homeostasis of an organism. The primary route that skeletal muscle uses to accommodate an increased metabolic demand associated with physical activity is to increase its blood flow through functional hyperemia. The importance of functional hyperemia in ensuring proper skeletal muscle function spurred 130 years of investigation into the mechanism(s) regulating its occurrence.Despite not identifying the essential factor(s) for controlling skeletal muscle blood flow, the last century of investigation has uncovered much about the process; including the observation that skeletal muscle functional hyperemia is impaired with ischemic disease. In patients, this can result in immobility, chronic ulcerations, gangrene, and at worst, amputation. To develop efficacious therapies, we as scientists must develop a better understanding of the molecular mechanisms underlying impaired vascular function during ischemia.The goal of this work was to lay the foundation for investigations examining the role of specific gene products involved in modulating blood flow control during ischemic revascularization by assessing vascular function in the mouse following an ischemic event. Unique among research animals, the mouse is routinely accessible for targeted genetic disruption, which allows investigators to assess the requirement of specific gene-products in a physiological process. Unfortunately, to date, no publication that I am aware of describes blood flow measurement to contracting mouse skeletal muscle following an ischemic/revascularization event. Therefore, the primary objective of this work was to assess vascular function in genetically unaltered animals.I found that unlike other species thus far examined, vascular dysfunction is not an obligatory response to hindlimb ischemic revascularization in the mouse. Ex vivo vasodilation responses to acetylcholine were statistically significantly impaired in the muscular branch artery 14 days following an ischemic event. However, using a newly developed fluorescent microsphere-based approach for determining skeletal muscle blood flow, I found that functional hyperemia was similar for the gracilis posterior muscle between non-ischemic and day-14 ischemic animals. In light of the primary literature, these findings suggest that vascular growth, and not ischemia per se is the primary regulator of vascular function during health and disease.

No description available.

No description available.

Thesis (doctoral)--University of Copenhagen, 2007. / Thesis is based on seven published studies by the author. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2006. / Härtill 4 uppsatser.