Master of Science / Department of Kinesiology / Thomas J. Barstow / Background and Aim: Long-term microgravity exposure, via spaceflight or -6° head-down tilt bedrest, has been shown to produce significant cardiovascular deconditioning and decreases in exercise performance. However, there is little known about how acute microgravity exposure influences the cardiovascular system’s ability to adjust to increases in physical work. Therefore, the aim of this study was to compare cardiovascular and exercise performance during acute upright, supine and -6° head-down tilt positions. Methods: Seven healthy inactive men performed maximal cycle exercise (VO2peak) tests in the upright, supine, and -6° head-down tilt on separate days. Oxygen consumption and heart rate were measured continuously throughout the testing procedures. Cardiac output (acetylene exhalation technique) was measured periodically and interpolated to the 100-watt work rate. Stroke volume was calculated from cardiac output and heart rate data. Results: Peak oxygen uptake and heart rate were significantly decreased in the supine and -6° head-down tilt positions compared to the upright (VO2peak 2.01±0.46, 2.01±0.51 versus 2.32±0.61 L/min respectively; peak heart rate 161±13, 160±14 versus 172±11 bmp). However, cardiac output at 100-watts was similar in all three-exercise positions. Calculated stroke volume at 100-watts was significantly higher in the -6° head-down tilt position compared to the upright position (76.6±4.7 versus 71.2±4.5, ml). Conclusion: These results suggest that exercise capacity is immediately decreased upon exposure to a microgravity environment, prior to any cardiovascular deconditioning. Therefore, an astronaut’s exercise performance should be evaluated with exercise tests in the -6° head-down tilt position prior to space flight in order to establish a baseline response.

Doctor of Philosophy / Department of Anatomy and Physiology / Thomas J. Barstow / Peripheral arterial disease (PAD) is a manifestation of the systemic disease of atherosclerosis that results in arterial stenoses of the lower extremities. Patients with PAD demonstrate slowed dynamics of pulmonary oxygen uptake (VO2 kinetics) following the onset of exercise and a profound reduction in peak oxygen uptake and work capacity. However, whereas the primary pathophysiology of PAD results from the lower extremity hemodynamic limitation, there are abnormalities distal to the arterial stenoses in PAD-affected skeletal muscle that may also contribute to the impaired exercise responses. Thus, the potential contributions of abnormal muscle metabolism versus local circulatory defects in the PAD exercise impairment remains unclear. In this context, the purpose of the dissertation was to advance our understanding of the abnormal pulmonary VO2 kinetics in PAD and characterize the local muscle deoxygenation responses during the rest-exercise transition exercise in health and PAD. The present series of investigations were designed to: 1. localize the abnormal pulmonary VO2 kinetics in PAD to the affected lower extremities, 2. characterize the kinetics of calf muscle deoxygenation during walking in PAD and healthy subjects, 3. describe muscle deoxygenation kinetics in relation to exercise work rate and blood flow in PAD and health, and 4. evaluate the effect of arterial revascularization on pulmonary VO2 kinetics in PAD. These investigations revealed a persistent abnormality in muscle oxygen utilization in PAD-affected skeletal muscle that was not associated with the severity of hemodynamic compromise. In particular, we observed slowed pulmonary VO2 kinetics in PAD only during exercise of the PAD-affected skeletal muscles. Moreover, muscle deoxygenation kinetics following the onset of walking and lower intensity calf exercise were prolonged in PAD subjects while leg blood flow responses were normal. However, at higher work rates, PAD muscle deoxygenation kinetics accelerated, demonstrating a work rate and presumably blood flow dependence. Lastly, arterial revascularization tended to improve, but not consistently normalize, pulmonary VO2 kinetics in PAD subjects. Thus, these investigations demonstrate abnormal oxygen uptake kinetics in PAD and provide evidence that local abnormalities of the affected skeletal muscle may contribute to the abnormal VO2 kinetics and exercise intolerance of patients with PAD.

Master of Science / Department of Anatomy and Physiology / Mark L. Weiss / Wharton's jelly is a non-controversial source of mesenchymal stromal cells. Isolation of the cells is non-invasive and painless. The cells have been shown to have a wide array of therapeutic applications. They have improved symptoms when transplanted in a variety of animal disease models, can be used in tissue engineering applications to grow living tissue ex vivo for transplantation, and can be used as drug delivery vehicles in cancer therapy. The cells have also been shown to be non-immunogenic and immune suppressive. This thesis focuses on optimizing isolation protocols, culture protocols, cryopreservation, and characterization of cells in different growth conditions. Results from the experiments indicate that isolation of cells by enzyme digestion yields cells consistently, a freezing mixture containing 90% FBS and 10% DMSO confers maximum viability, and the expression of mesenchymal stromal cell consensus markers does not change with passage and cryopreservation. The results of the experiments also show that cells grow at a higher rate in 5% oxygen culture conditions compared to 21% oxygen culture conditions, serum does not have an effect on growth of the cells, serum and oxygen do not have effects on the expression of mesenchymal stromal cell consensus markers and the cells are stable without nuclear abnormalities when grown in 5% oxygen and serum free conditions for six passages after first establishing in serum conditions.