Thesis (Ph. D.)--University of Chicago, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "1 April 2009." Includes bibliographical references (leaves [263]-274). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 119-125).

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvii, 147 p.: ill. Includes abstract and vita. Advisor: David H. Bromwich, Dept. of Geography. Includes bibliographical references (p. 140-147).

In man, tolerance to an orthostatic stress varies widely. Compensatory cardiovascular responses to orthostatic stressors such as head-up tilt, +Gz acceleration, and lower body negative pressure (LBNP) have been identified. However, physiologic reactions associated with the capacity to withstand a presyncopal- limited orthostatic exposure requires additional clarification. The relationship between maximal oxygen uptake (‘VO₂ max) and presyncopal-limited LBNP tolerance was examined in adult male subjects categorized into high (HAC) and low (LAC) aerobic capacity groups. In addition to similar (N.S.) cardiovascular responses, the (mean) and cumulative LBNP stress indices (CS)) observed in the HAC (722 torr•min) and LAC (784 torr•min) groups were also similar (N.S.). These data fail to support a relationship between LBNP tolerance and ‘VO₂ max. Cardiovascular responses associated with LBNP tolerance were measured during the control period (pre-LBNP) and final minute (peak LBNP) of decompression. The CSI criterion distinguished high (HT, n = 10) and low (LT, n = 8) LBNP tolerant groups was 640 torr•min. A greater (p < 0.05) end-diastolic volume and cardiac output was observed in the HT subjects during pre-LBNP may have provided a larger reserve to utilize throughout exposure to LBNP. At peak LBNP, both groups demonstrated similar (N.S.) cardiac outputs despite a higher (p < 0.05) HT heart rate. These data suggest that a major mechanism in prolonging LBNP tolerance may have been a greater LBNP-induced tachycardia. Blood samples were drawn to determine group differences in vasoactive neuroendocrine response. During peak LBNP, concentrations of norepinephrine increased (p < 0.05) in both groups. The HT group displayed greater (p < 0.05) LBNP-induced increases in vasopressin and plasma renin activity. These data suggest that HT subjects may have supplemented the catecholamine pressor response by involving the vasopressin and renin-angiotensin systems. The affect of cholenergic and beta-adrenergic blockades on cardiovascular responses to LBNP were examined in six HT and five LT subjects. CSI in both groups were unchanged (N.S.) by administration of atropine as compared to a placebo LBNP exposure. Propranolol however, reduced (p < 0.05) LBNP tolerance in both groups. This CSI reduction was greater (p < 0.05) in the HT subjects. The reduction in LBNP tolerance appeared closely associated with the negative chronotropic effect.

published_or_final_version / Medicine / Master / Doctor of Medicine

published_or_final_version / abstract / toc / Physiology / Master / Master of Philosophy

No description available.

The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) are the most pronounced modes of extratropical atmospheric wintertime variability in the Northern Hemisphere. This thesis investigates different aspects of the AO and NAO on the in traseasonal and seasonal time scales. First, the question of how the differences between the AO and NAO are influenced by the choice of the definitions of the NAO and to what extent the AO and NAO differ from each other is investigated using the daily NCEP/NCAR reanalysis data spanning 51 boreal winters. One AO index and four different NAO indices are used in this study. It is found that the AO and NAO are quite similar to each other when both are defined using pattern-based indices, while some notable differences are observed between them when the NAO is defined using a station/gridpoint-based index. Then the predictability of the AO and NAO is examined using a simple general circulation model (SGCM). Numerical experiments are performed to determine the sensitivity of the setup processes of the AO and NAO to the details of the initial conditions. The predictive skills for the AO and NAO are compared to each other. Finally, the potential role of tropical Pacific forcing in driving the seasonal variability of the AO is explored using both observations and the SGCM. The results indicate that a negative thermal forcing over the western tropical Pacific and a positive forcing north of the equatorial mid-Pacific play important roles in producing an AO-like atmospheric response.

The mean dynamic topography (MDT) of the ocean is closely related to the mean surface circulation. The objective of this thesis is to produce estimates of the MDT for the North Atlantic using newly available data from ocean and gravity observing systems, to evaluate these new estimates and so improve our understanding of the circulation. Oceanographic estimates of the MDT are based on the mean temperature and salinity (TS) fields of the ocean. These are typically averages from sparse observations collected over many decades. The ocean is a non-stationary system so it is more appropriate to define the mean for shorter, specific periods. Whilst the Argo observing system has increased the frequency and resolution of in situ oceanographic measurements, high frequency (eddy) variability remains. A new technique is described for removing this variability using satellite altimeter measurements of the sea surface height. A new TS mean is produced, relating to the period from 2000 to 2007, and this is used to map a new oceanographic estimate of the MDT using an ocean circulation model. New geodetic estimates of the MDT are produced using geoid models that incorporate gravity measurements from the ongoing GRACE and GOCE satellite missions. These are compared with the new oceanographic estimate and validated against independent observations such as drifter speeds. The geodetic method produces realistic estimates of the mean surface circulation, thereby realizing the long time dream of oceanographers to observe the ocean circulation from space. The new oceanographic estimates are not as accurate, but the new TS mean contributes to improvements in the performance of ocean models, a necessary step in understanding and predicting the oceans. Coastal tide gauges can provide an accurate estimate of the alongshore tilt of the coastal MDT and this has been used to evaluate the above estimates. Temporal variability of the tilt along the coast of the South Atlantic Bight is used, with statistical methods and an ocean circulation model, to identify the processes contributing to the tilt. A new opportunity to use tide gauges as part of an observing system for the ocean circulation is discussed.