Wall shear stresses are thought to have an influence on the formation of deposits of blood fats on the linings of the arteries, in atherosclerosis. Measuring velocities close to an artery wall to determine wall shears is difficult in view of the thinness of the boundary layer. Analytical solutions are limited to simple geometries and numerical analyses of three-dimensional, unsteady blood flows are expensive in terms of computational time. In the present study, finite element analyses of blood flow in models representative of the human aorta are based on two-dimensional sections in order to reduce the computational requirement.

xiv, 233 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / In general, postexercise hypotension is characterized by a sustained increase in systemic vascular conductance that is not completely offset by ongoing increases in cardiac output. These hemodynamic changes are present immediately after a single bout of moderate-intensity dynamic exercise in healthy (sedentary and endurance exercise-trained) and hypertensive humans. The mechanisms underlying this postexercise hypotension are currently under investigation; however, the overall hemodynamic response may be altered in response to different factors related to sex, training status, and fluid regulation. The purpose of this dissertation was to investigate the contribution of endogenous hormones associated with the normal menstrual cycle and training status and sex on postexercise hemodynamics and to better understand how fluid replacement and heat-stress affect postexercise hemodynamics in a group of highly trained men. In Chapter IV, the contribution of the menstrual cycle and sex to postexercise hemodynamics was investigated. The results showed that postexercise hemodynamics are largely unaffected by sex and factors associated with the menstrual cycle. In Chapter V, the role of heat-stress and fluid replacement on the postexercise cardiac hemodynamics in a group of endurance exercise-trained men was investigated. These data suggest that fluid replacement and heat-stress mitigate the previously observed fall in cardiac output during exercise recovery in trained men. In Chapter VI, the study investigated the hemodynamic profile in well-hydrated sedentary and trained men and women during recovery from exercise. In contrast to previous research, the results showed a lack of variation in the postexercise hemodynamic response across categories of subjects as there was no evidence of a sex and training interaction. Thus, it appears that factors such as heat-stress and fluid replacement can alter postexercise hemodynamics in trained men; however, factors such as menstrual cycle, sex, and training status do not seem to influence the hemodynamic recovery profile. Yet substantial variation in the postexercise response across individuals remains unexplained. This dissertation contains my previously published and my co-authored material. / Adviser: John R. Halliwill

Made available in DSpace on 2014-10-09T12:54:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:59Z (GMT). No. of bitstreams: 1 12801.pdf: 2431192 bytes, checksum: b7e93ba00685003bca6016af5031d88f (MD5) / Dissertação (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de São Paulo, São Paulo

Made available in DSpace on 2014-10-09T12:54:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:59Z (GMT). No. of bitstreams: 1 12801.pdf: 2431192 bytes, checksum: b7e93ba00685003bca6016af5031d88f (MD5) / Dissertação (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de São Paulo, São Paulo

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Exercise and/or heat-induced dehydration is associated with decreases in plasma volume (hypovolemia) and increases in plasma osmolality (hyperosmolality), which are thought to stimulate peripheral baroreceptors and central osmoreceptors respectively. Independently, plasma hyperosmolality and baroreceptor unloading have been shown to attenuate sweating and cutaneous vasodilation during heat stress, and therefore, negatively impact body temperature regulation. However, to date little is known regarding the combined influence of plasma hyperosmolality and baroreceptor unloading on thermoefferent activity. Therefore, we evaluated the separate and combined effects of baroreceptor unloading (via lower body negative pressure, LBNP) and plasma hyperosmolality (via infusion of 3% NaCl saline) on heat loss responses of sweating and cutaneous vascular conductance (CVC) during progressive whole-body heating. We show that the combined nonthermal influences of plasma hyperosmolality and baroreceptor unloading additively delay the onset threshold for CVC, relative to their independent effects. In contrast, baroreceptor unloading has no influence on the sweating response regardless of osmotic state. These divergent roles of plasma hyperosmolality and the baroreflex on heat loss responses might serve to enhance blood pressure and body core temperature regulation during dehydration and heat stress.

This study sought to determine the independent influence of hypoxia on thermoregulatory responses to exercise in compensable and uncompensable hot conditions. Eight participants completed three experimental trials of cycling in either normoxia (21% O2) or hypoxia (13% O2) in order to manipulate relative exercise intensity (%VO2peak), since VO2peak was reduced by ~30% in hypoxia. When trials were matched for %VO2peak, changes in core temperature and local sweat rates (LSR) were significantly lower in the hypoxic trial as a result of a lower rate of metabolic heat production (Hprod) in order to maintain a similar %VO2peak compared to normoxia. However, when Hprod was fixed between normoxic and hypoxic trials the systematic differences in core temperature and LSR were eliminated. Conversely, at a fixed Hprod skin blood flow (SkBF) was greater in hypoxia compared to normoxia by ~40%. Despite improvements in SkBF, the potential for maximum heat loss was unaffected during an incremental humidity ramp protocol, resulting in no difference between normoxia and hypoxia in the critical ambient vapour pressures at which core temperature inflected upwards. These data further demonstrate, using a within-subjects design, that metabolic heat production, irrespective of large differences in %VO2peak, determines thermoregulatory responses during exercise. Furthermore, this study suggests that the influence of large differences in skin blood flow on heat dissipation may be lesser than previously thought.

Studies that have investigated the effects of L-arginine supplementation on blood flow to the uterus have not determined the optimal time of supplementation. No research has been conducted on nitrite concentration in the placenta and blood of mares supplemented with L-arginine. L-arginine is a precursor of NO and therefore, should increase nitrite production both in blood as well as in expelled placenta. Presence of nitrites would also be indicative of increased angiogenesis. No studies have addressed placental efficiency in mares supplemented L-arginine. Placental efficiency is vital for production of a healthy foal. Therefore, to address these short-comings the objectives of this study were to supplement pregnant mares with L-arginine on effects of supplementation at differing time points on blood flow to the uterus, nitrite concentration in blood and placenta, and placental efficiency.

Melatonin is a strong antioxidant that has previously been observed to increase uteroplacental blood flow and increase postnatal calf growth when supplemented during gestation. The objective of the current study was to examine the effects of melatonin implants on uterine blood flow and subsequent offspring growth. Commercial beef heifers and cows were artificially inseminated and assigned to one of two treatment groups supplemented with (MEL) or without (CON) melatonin from days 180 to 240 of gestation. Total uterine artery blood flow was increased in MEL- versus CON-treated cattle. Fetal and birth weight were not different between treatments. However, at castration, body weight was increased in calves from MEL-treated dams compared with CON-treated dams. Further research on placental vascularization and the mechanism in which melatonin impacts angiogenic factors is necessary to understand the relationship between melatonin and compensatory growth that occurs in postnatal offspring.

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