Clothing directly affects the level of heat stress exposure. Useful measures to express the thermal characteristics are WBGT (wet bulb globe temperature) clothing adjustment factor (CAF) or apparent total evaporative resistance (Re,T,a). The CAF is assigned through laboratory wear trials following a heat stress protocol in which the air temperature and humidity are progressively increased until the participant clearly loses the ability to maintain thermal equilibrium. The critical condition is the point of thermal transition and from these conditions both the CAF and Re,T,a are computed. The first objective of this study is to compare the thermal characteristics of a coverall made from a prototype fabric to work clothes and a commercial limited-use coverall using CAF and Re,T,a. A second objective is to demonstrate that the Re,T,a of work clothes is the same for progressive or steady-state heat stress protocols. Five participants (4 men and 1 woman) walked on a treadmill at 1.25 m/s at an average metabolic rate of 175 W/m2. Each participant completed at least one progressive heat stress protocols in work clothes, Tyvek® 1422A coveralls [Tyvek® is a registered trademark of DuPont], and a developmental nonwoven polyolefin prototype ensemble provided by DuPont. In addition, four participants completed steady-state protocol in work clothes. Participants did not complete an acclimation period prior to the trials and each trail was separated by at least 40 hours. There are no within participant differences in metabolic rate among ensembles and protocols. There are no differences between the critical WBGT in the current participants and previously acclimatized participants from other studies suggesting that the participants responded as if they were acclimatized. Based on a mixed effects model, there are significant differences between work clothes and Tyvek® 1422A for Re,T,a (0.0103 and 0.0141 m2/W kPa, respectively) and critical WBGT. The CAF for Tyvek is 2.3 °C-WBGT. For the DuPont prototype ensemble, the apparent total evaporative resistance is 0.013 m2kPa/W and the CAF is 0.5 °C. The prototype ensemble shows no difference from work clothes or Tyvek® 1422A in critical WBGT and no difference from work clothes in Re,T,a. Overall, the prototype coveralls exhibited thermal characteristics that would have a lower level of heat stress than the Tyvek 1422A and not significantly different from work clothes. The values for Re,T,a for work clothes were not different between the steady state and progressive protocols. The steady-state protocol near the critical condition can be used for determination of Re,T,a. This opens up the possibility of estimating Re,T,a from studies that do not use the progressive protocol.

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Doctor of Philosophy / Department of Geography / John A. Harrington Jr / Extreme heat is a hazard that is capable of causing economic problems and potentially high mortality rates across several regions simultaneously. This dissertation was designed to provide a better understanding of how often and where heat waves occur within the United States. The research design assessed all places equally in order to evaluate geographic variations in the character of heat waves. In order to simplify the variety of extreme heat events that occur, this research developed two classifications; one for accumulated daily heat stress and a second for extended periods of extreme conditions (heat waves). Both new classification systems were designed to objectively categorize individual events using a scale from 1 (minor) to 5 (extreme). The heat wave classification system was applied to 70 locations for years 1980-2001 to determine the frequency, magnitude, and duration of daily heat stress events and heat waves. Hourly temperature and humidity data were used to determine heat index values, which were accumulated to provide the daily heat intensity measurement. Major findings from this research include: how heat stress distribution is influenced by topographical relief variations as well as latitude; daily heat stress classifications during an event were typically not in an intensify-then-weaken progression; Category 1 heat waves were the most frequent overall followed by Category 2 and Category 3 heat waves, however Category 5 events outnumbered Category 4 events over the temporal period of this study; and heat stress days/heat waves occurred most frequently in the Southeast, with the fewest occurring in the Northwest. The classification was also used to illustrate the extent and magnitude of the 1995 heat wave that caused high human mortality in the Midwest. Results from this research are presented in maps and tables to provide a detailed insight on the characteristics of heat stress throughout the United States as a function of the exposure component of hazard vulnerability.

Master of Science / Department of Animal Sciences and Industry / John F. Smith / A series of experiments was developed to investigate how Korral Kool® (KK) systems work in arid climates to prevent heat stress on dairy cows. These experiments were conducted during summer on a commercial dairy farm in eastern Saudi Arabia. In the first experiment, the core body temperatures (CBT) of 63 multiparous cows were evaluated when KK were operated for 18, 21 and 24h/d. Animals were housed in 9 different pens, which were randomly assigned to treatment sequence in a 3x3 Latin square design. In the second experiment, 21 multiparous and 21 primiparous cows were housed in 6 different pens, which were randomly assigned to sequence of treatments (KK operated for 21 or 24h/d) in a switchback design. In the third experiment, 7 primiparous and 6 multiparous lactating cows were assigned to one of two pens, which were randomly assigned to treatment sequence in a switchback design. Treatments in the third experiment were KK used with or without feedline soakers 24h/d. In the fourth experiment, 20 multiparous cows were randomly assigned to one of two pens, which were randomly assigned to treatment sequence in a switchback design. Treatments in this experiment were KK operated for 24h/d while feedline soakers were operated for 12h/d. In the fifth experiment, 2 different sizes of KK were compared (BIG and SMALL); 48 multiparous cows were randomly assigned to 8 pens and pens were randomly assigned to sequence of treatments (KK were operated for 21 or 24h/d) in a switchback design. Results demonstrated that for multiparous cows in desert climate conditions, it is advisable to operate KK systems continuously regardless of the size of KK system used, whereas KK operating time could potentially be reduced from 24 to 21h for primiparous cows. Reducing operation time should be done carefully, however, because CBT was elevated in all treatments. Feedline soakers complementing KK systems decreased the CBT of dairy cows housed in desert environments. However, the combined systems were not adequate to lower CBT to normal temperatures in this extreme environment.

Master of Science / Department of Anatomy and Physiology / Michael J. Kenney / Hyperthermia is an environmental stressor that produces marked increases in visceral sympathetic nerve discharge (SND) in young rats. The brainstem in rats contains the essential neural circuitry for mediating visceral sympathetic activation; however, specific brainstem sites involved remain virtually unknown. The rostral ventral lateral medulla (RVLM) is a key central nervous system region involved in the maintenance of basal SND and in mediating sympathetic nerve responses evoked from supraspinal sites. In the present study we tested the hypothesis that inhibition of RVLM synaptic activation at peak hyperthermia (internal body temperature, Tc, increased to 41.5°C) would affect heating-induced visceral sympathetic activation. Experiments were completed in chloralose-urethane anesthetized, baroreceptor-intact and sinoaortic-denervated, 3-6 month-old Sprague-Dawley rats. Bilateral inhibition of RVLM synaptic activation produced by muscimol microinjections (400 and 800 pmol) at 41.5°C resulted in immediate and significant reductions in peak heating-induced renal and splenic sympathoexcitation. Interruption of RVLM synaptic activation and axonal transmission by lidocaine microinjections (40 nmol) at 41.5°C produced significant reductions in hyperthermia-induced sympathetic activation to similar levels produced by RVLM muscimol microinjections. The total amount of SND inhibited by RVLM muscimol and lidocaine microinjections was significantly more during hyperthermia (41.5°C) than normothermia (38°C). These findings demonstrate that maintenance of sympathetic activation at peak hyperthermia is dependent on the integrity of RVLM neural circuits.

Limb haemodynamic responses during heat-stress and the importance of local vs. central temperature-sensitive mechanisms towards their regulation remain poorly understood, both at a whole-limb level and within individual tissues (i.e. skeletal muscle and skin). The aims of this thesis were to 1) investigate the haemodynamic responses at rest to direct thermal challenges both at a local level and during progressive elevations in systemic heat stress, 2) to ascertain the contribution of local vs. systemic mechanisms towards this regulation, and 3) to investigate the same responses during single-legged small-muscle mass exercise to near maximal levels. Results from Chapters 4 and 5 characterised the haemodynamic responses during isolated cooling and heating of the arm and leg, and provided evidence of alterations in both skin and skeletal muscle blood flow controlled solely through local temperature-sensitive mechanisms. While local cooling led to modest decreases in limb blood flow due to decreases in mean blood velocity alone, increases during heating occurred as a result of an increased antegrade flow, a diminished retrograde flow, and a reduction in the potentially pro-atherogenic oscillatory shear index. In Chapter 6, whole-body heating with isolated single leg cooling displayed the continued control of limb blood flow via local thermosensitive mechanisms alone, as cooled leg blood flow remained unchanged despite significant elevations in core temperature, cardiac output, and opposing heated leg blood flow. Furthermore, elevations in heated leg V̇O2 suggested a possible metabolic contribution to the observed skeletal muscle hyperaemic response. During incremental single-legged knee-extensor exercise to near maximal levels, blood flow was determined by a combination of metabolic workload and local tissue temperatures, regardless of whether systemic heat stress was present. Chapter 7 revealed that whilst skin and muscle blood flow in the leg continued to increase in line with local temperatures to levels of severe heat stress, rapid cooling of the leg when hyperthermic resulted in a similar reverse response in muscle tissues only, as skin blood flow remained elevated despite the abolition of high skin and subcutaneous temperatures. In addition, evidence was provided that moderate levels of whole-body heat stress provided little additional benefit to anti-atherogenic shear profiles than that experienced during isolated limb heating alone. Taken together, these findings suggest that local thermosensitive mechanisms dominate limb blood flow control during direct rapid heating in humans both at rest and during small muscle mass exercise, but that underlying central mechanisms may act to maintain flow when local temperatures are reduced in the face of high core temperatures.

The Arabidopsis HSP101 protein belongs to the Hsp100/ClpB family of AAA+ proteins (ATPases Associated with various cellular Activities). This family of proteins, in collaboration with the Hsp70 chaperone system, has the remarkable ability to solubilize protein aggregates and refold proteins back to their native forms. Thus, their chaperone activity is necessary for acquired thermotolerance in organisms as diverse as bacteria and plants. My dissertation project focused on understanding the mechanism of HSP101 action using Arabidopsis thaliana as a model system. The first approach used genetics to screen for suppressors of a specific missense mutant allele of HSP101, hot1-4, in order to find interacting cofactor proteins or key substrates of HSP101, or other processes involved in thermotolerance. Four extragenic suppressors that can overcome the heat-hypersensitive phenotype caused by the hot1-4 mutation were isolated and one of them (shot1) was identified as a mutation in a mitochondrion-targeted protein. Although shot1 mutations do not directly interfere with HSP101 function, they reveal independent mechanisms required for thermotolerance, which involve reduced oxidative stress. The second approach used to investigate HSP101 function was to affinity-purify HSP101 and identify associated proteins. For this purpose, transgenic Arabidopsis plants were generated expressing affinity-tagged wild-type and mutant variants of HSP101. As predicted, cytosolic Hsp70s were identified as an interacting partner of HSP101. Surprisingly, 26S proteasome regulatory subunits were also identified, suggesting a possible link between the protein degradation and reactivation pathways. Further experiments were also undertaken to define the importance of different domains of HSP101, as well as the localization of HSP101. Transgenic Arabidopsis plants expressing N- or C-terminally truncated HSP101 indicate that the N-terminal domain of HSP101 is required for full activity in protecting plants from heat stress. However, in contrast to the yeast ortholog, Hsp104, the C-terminal extension of HSP101 was found to be completely dispensable for thermotolerance of Arabidopsis. Additional transgenic plants expressing an HSP101-GFP were also characterized. Initial microscopic analysis confirms nuclear/cytoplasmic localization as has been reported previously for yeast Hsp104. However, the dynamics of subcellular redistribution upon heat stress need to be further investigated to fully understand the potential significance of the observed localization.

Climatic conditions inside the dairy barn do not concern dairy farmers until those conditions begin to affect productivity and, consequently, profits. As heat and humidity increase beyond the cow's comfort levels, milk production declines, as does fertility and the welfare of the cow in general. To reinforce the cooling mechanisms currently used, this work proposes an alternative system for reducing the risk of heat stress. This innovative conductive cooling system does not depend on current weather conditions, and it does not require significant modifications when it is installed or during its operation. Also, the system circulates water that can be reused. Given that a review of the literature found very few related studies, it is suggested that each freestall be equipped with a viable prototype in the form of a waterbed able to exchange heat. Such a prototype has been simulated using Computational Fluid Dynamics (CFD) and later verified by a set of experiments designed to confirm its cooling capacity. Furthermore, this investigation sets the foundation for modeling temperature in a water supply system linked to the waterbeds. EPANET, a software program developed by the Environmental Protection Agency, simulates the hydraulic model. Its Water Quality Solver has been modified according to an analogy in the governing equation that compares mass to heat transfer and serves to simulate water temperature as the water is transported from its source to the point of delivery and then as it returns to the same source.

Capacity to perform prolonged exercise is reduced in high ambient temperatures, but this premature fatigue is not adequately explained by peripheral mechanisms. The aim of this thesis was to examine some possible underlying mechanisms of central fatigue operating during prolonged exercise in a warm environment. The first series of experiments investigated the effect of nutritional manipulation of central serotonergic activity through alterations to the plasma concentration ratio of free-tryptophan to branched-chain amino acids (f-TRP:BCAA). In contrast to previous reports, acute BCAA supplementation failed to alter perceived exertion and delay the onset of fatigue (Chapter 3). This response was similar when exercise was preceded by an exercise and diet regimen designed to reduce glycogen availability (Chapter 4). The ingestion of meals containing added carbohydrate and fat did not alter f-TRP:BCAA at rest (Chapter 5). Acute dopaminergic / noradrenergic reuptake inhibition with bupropion increased exercise perfonnance by 9 % in warm conditions (30C), but this effect was not apparent at 18C (Chapter 6). This response was accompanied by attainment of a higher core temperature and heart rate towards the end of the bupropion trial in the heat despite no detectable difference in perceived exertion and thermal stress. These data suggested that maintenance of catecholaminergic activity may dampen inhibitory signals from the CNS due to the attainment of a high core temperature, allowing power output to be maintained. The blood-brain barrier (BBB) regulates the exchange of substances between the cerebral interstitial fluid and the blood to maintain a stable environment for the CNS. If the BBB is compromised this may adversely influence nonnal brain function. Serum S1OOb, a proposed peripheral marker of BBB penneability, was increased following exercise in a warm environment (Chapter 7). These data indicate that exposure to combined exercise and heat stress may result in a loss of BBB integrity.

Skeletal muscles in broilers are generally characterised by pathological muscle damage, indicated by greater plasma creatine kinase (CK) activity, higher incidence of haemorrhages, lighter and less coloured breast muscles, compared with layers and traditional breeds of chicken. Muscle damage is further exacerbated by exposure to stressful conditions such as high ambient temperatures which results in a further decrease in the quality of broiler meat and leads to the production of pale, soft and exudative (PSE) meat. This growing incidence of poor quality poultry meat is causing substantial losses to the meat industry. However, in contrast to pork the genetics of poor muscle and meat quality in chicken is unknown. The present project was conducted to identify the underlying genetics of this low quality meat by using heat-stress as a tool to amplify muscle damage and expression of the relevant genes. Whole-genome expression studies in broiler and layer breast muscles were conducted before and after heat-stress and some phenotypic data were also recorded. From the gene expression studies, 2213 differentially expressed genes (P<0.05) were found. About 700 of these genes had no gene ontology (GO) terms associated with them for biological process or function. The significant gene set was analysed in BioLayout Express and interesting clusters of the genes, based on their positive correlation with each other, were selected for further investigation. Genes were grouped together in 6 different categories or clusters, on the basis of their expression pattern. The genes in the selected clusters were analysed in Ingenuity Pathway Analysis (IPA) software, for each category separately, and relevant biological pathways and networks for those genes were studied. Similarly, the genes filtered out by BioLayout Express at a Pearson threshold of 0.80 were also analysed in IPA separately and interesting pathways and networks were selected. From the pathways and networks analyses of these genes, it was discovered that genes involved in inflammatory, cell death, oxidative stress and tissue damage related functions were up-regulated in control broilers compared with control and similar to heat-stressed layers. After exposure to heat-stress the expression levels of these genes were further increased in broilers. These results led us to develop the hypothesis that breast muscles in broilers are under stress-related damage even under the normal rearing conditions. This hypothesis was tested by rearing the broilers birds at normal/conventional and comparatively low ambient temperature and its effects on breast muscle quality and meat quality were studied. Significant improvement of breast muscle redness was observed. Additionally substantial numerical improvements for other meat and muscle quality traits like breast muscle lightness and histopathology were observed. From the key positions of interesting significant pathways and networks, candidate genes were selected for further investigation. In total, 25 candidate genes were selected for SNP genotyping: 19 genes were selected from the interesting pathways and networks and 6 genes were selected on the basis of their GO terms. For each gene 4-5 SNPs were selected, where possible, that were present in exons and promoter regions of the candidate genes. The selected SNPs were genotyped for muscle and meat quality traits in 34 breeds of chicken and significant causative SNPs for each trait including plasma CK activity, pHi and pHu for breast muscles, colour (L*, a*, and b*) traits for breast and thigh muscles were found. These SNPs were responsible for explaining a moderate to high (15-55%) percentage of phenotypic variance for these traits. To our knowledge this is the first study in which gene-expression in chicken breast muscle was conducted in response to heat-stress and additionally, for the first time, a set of novel SNPs for all of these traits were identified. Some of the significant causative SNPs were lying in the protein coding sequences and some were present in the promoter regions of the candidate genes.