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The effect of sustained Gz acceleration ("high G") upon endocrine function has been investigated in man using a human centrifuge. Five male volunteers were exposed to accelerations of up to 6Gz for one minute without G protection. No effect of acceleration was observed on the peripheral blood levels of growth hormone, prolactin, thyrotropin and the gonadotrophins. In contrast, cortisol levels increased in a "dose-related" manner following acceleration i.e. the higher the acceleration, the greater the response. The unusual specificity of these endocrine changes is discussed. In a second experiment on the same subjects exposed to 6Gz for one minute, the modification of this cortisol response by two methods of G protection, the anti-G suit and the reclined seat, was investigated. Noradrenaline, adrenaline and arginine vasopressin were also measured and shown to increase rapidly after acceleration. These endocrine changes were all reduced by the anti-G suit but reductions were not clearly observed with seat reclination until an angle of 80° from the vertical was reached. The mechanisms underlying the release of these hormones are discussed in terms of the circulatory disturbances produced by acceleration. Finally, the endocrine effects of positive pressure breathing (PPB), with and without counterpressure (CP) have been compared with the use of an anti-G suit alone in subjects exposed to +6Gz for one minute. Arterial oxygen saturation (SaO[2]) was monitored continuously by ear oximetry. SAO[2] fell during +Gz acceleration with only anti-G suit protection but this was ameliorated significantly by PPB. Further benefit was obtained with CP. No differences in endocrine responses were observed between these three conditions which suggested that hypoxia was not the stimulus for hormonal responses to high G. This assertion was confirmed by the failure of hypoxia, induced by breathing a gas mixture of low oxygen content, to induce hormonal changes in the subjects.

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Earth’s biosphere is sustained by its biological diversity, which forms an intricate network of biological, physical and chemical pathways. This network has many fail-safe redundant func-tions including buffer stocks of inert biomass, huge amounts of water and the large volume of gases in the atmosphere. By contrast, manmade habitats for human space exploration are closed ecosystems that represent only a trivial fraction of Earth’s biosphere. The employment of bio-regenerative processes complemented with physical-chemical tech-nologies is thought to have numerous advantages from the perspective of redundancy and reducing resupply mass for the sustained human presence in space or on other planetary surfaces. However, the combination of bio-regenerative processes, such as plant cultivation, with physical-chemical processes to form hybrid life support systems is challenging. Such systems are a concert of many interdependencies and interacting feedback loops, which are difficult to operate in a desired range of set points. Furthermore, the complexity of such sys-tems makes them vulnerable to perturbations. Applying system dynamics modelling to study hybrid life support systems is a promising ap-proach. System dynamics is a methodology used to study the dynamic behavior of complex systems and how such systems can be defended against, or made to benefit from, the per-turbations that fall upon them. This thesis describes the development of a system dynamics model to run exploratory simulations, which can lead to new insights into the complex behav-ior of hybrid life support systems. An improved understanding of the overall system behavior also helps to develop sustainable, reliable and resilient life support architectures for future human space exploration. A set of simulations with a hybrid life support system integrated into a Mars habitat has been executed and the results show a strong impact of space greenhouses on the life support sys-tem behavior and the different matter flows. It is also evident from the simulation results that a hybrid life support system can recover from a perturbation event in most cases without a fatal mission end. Recycling urine to produce a plant nutrient solution is a novel approach in further closing loops in space life support systems. Within this thesis, a number of experiments have been executed in order to determine the effectiveness of a urine-derived nutrient solution com-pared to a standard reference solution. The results show that in principle plants can be grown with a nutrient solution made of human urine, but that the yield is lower compared to the reference solution. However, the urine-derived solution might be tuned by adding small amounts of additional nutrients to remove the imbalance of certain elements. This way the nutrient salts supplied from Earth could be reduced.

Thesis (Ph. D.)--University of Oklahoma, 1994. / Includes bibliographical references (leaves 110-129).

Intro/Aims: Differences in end-of-life decision-making among minorities have been well described. However, among Native Hawaiian and Other Pacific Islanders (NHOPIs), this has not been well studied. Aim 1: Determine if differences in time to withdrawal of life support (WOLS) exist between NHOPIs and non-Hispanic whites (NHWs). Aim 2: If differences in time to WOLS between races are found, examine factors that may contribute to these differences. Methods: A retrospective study was conducted on patients admitted to a primary stroke center in Honolulu with diagnosis of spontaneous intracerebral hemorrhage (ICH). Medical records were reviewed for occurrence of WOLS and time of WOLS. Unadjusted and multivariable logistic regression models were performed to determine associations between race and WOLS. Kaplan Meier analysis and Cox regression were performed to estimate survival time to WOLS and to compare these results between racial groups. Results: 396 patients with diagnosis of spontaneous ICH were studied. Mean time to WOLS after ICH was found to be similar between NHWs and NHOPIs (p = .925). Prevalence of WOLS was significantly lower in NHOPIs in univariate analysis (odds ratio [OR] 0.35, 95% confidence interval [CI] 0.15, 0.80) and Kaplan Meier analysis predicted a significant difference in WOLS between NHOPI and NHWs within 30 days of ICH (p =<. 01). However, in multivariate analysis, race was no longer significant when adjusted for age (OR 0.59, 95% CI 0.25, 1.43) and when fully adjusted (OR 0.68, 95% CI 0.20, 2.39). NHOPIs were significantly younger at the time of ICH when compared to NHWs (p =<.001) although ICH severity and presentation such as initial Glasgow Coma Scale, presence of intraventricular hemorrhage and ICH volume were similar (p = .241; p = .604; p = .901, respectively). Conclusions: No difference in mean time to WOLS was noted between NHOPIs and NHW. However, secondary analysis showed WOLS was less prevalent after ICH in the NHOPI population compared to NHWs, although the significance of this finding was attenuated by age. NHOPIs in this population likely had a lower incidence of WOLS due to the fact that they presented with ICH at a significantly younger age, although small sample size also may have resulted in difficulty detecting variances between races.