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Effects of hypoxia and hypercapnia on thermoregulatory function

Final Report Summary - THERMOPHYSIO (Effects of hypoxia and hypercapnia on thermoregulatory function)

The regulation of internal (core) body temperature within a narrow range is vital for the well-being of humans. Appropriate changes in skin blood flow and sweat rate are critical responses for humans to regulate internal temperature, especially during situations such as exercise and/or heat stress. The control of skin blood flow and sweat rate occurs through distinct sympathetic neural pathways. In cool conditions that result in reductions in skin and/or internal temperature, sympathetic vasoconstrictor nerve activity increases leading to cutaneous vasoconstriction (a reduction in skin blood flow). Withdrawal of this cutaneous vasoconstrictor activity also results in slight increases in skin blood flow. During prolonged heating or intense heat stress exposure that causes elevations in skin and internal temperatures, the non-adrenergic sympathetic active vasodilator system is engaged and skin blood flow increases and sweating is initiated through sympathetic cholinergic (or sudomotor) nerves.

Other physiological factors can affect the control of skin blood flow and sweating; for example, aerobic fitness, disease and gender. Limited research has also suggested that alterations in oxygen and carbon dioxide levels, e.g. a reduction in oxygen (hypoxia) and an elevation in carbon dioxide (hypercapnia), could also affect the control of skin blood flow and sweating. Hypoxia and hypercapnia can occur in a variety of situations, such as altitude exposure, deep-sea diving, working in enclosed spaces, surgical procedures and respiratory disease. Furthermore, these situations can be frequently accompanied by environmental stressors (e.g. heat or cold stress), when appropriate sweat rate and/or skin blood flow responses are vital in order to maintain internal temperature and avoid a thermal related injury (e.g. heatstroke, hypothermia, frostbite). Therefore, it is important to understand the effects of hypoxia and hypercapnia on thermoregulatory function. Heretofore, however, the effects of hypoxia and hypercapnia on skin blood flow and sweat rate during thermoregulatory challenges have not been systematically examined and thus are largely unknown. Therefore specific aim #1 and #2 of this project are to examine the separate effects of hypoxia and hypercapnia on the skin blood flow and sweat rate responses to whole-body heating. Finally, specific aim #3 of this project is to examine the effect of hypoxia and hypercapnia on the skin blood flow response to whole-body cooling. The project's specific aims each involve the completion of several key tasks, which include, equipment acquisition and laboratory setup, methodology development, laboratory the submission of manuscript and conference papers, attendance at conferences, visits with an international collaborator and the development and submission of grant applications. These tasks are alongside other key objectives of the project relating to training / transfer of knowledge and integration.

Since the beginning of the project, good progress has been made towards preparing for the achievement of the specific aims in that key logistical tasks required for the data collection have been completed as well relating to collaboration and networking and researcher training / transfer of knowledge and integration. Methodologies for the studies have been finalised, key equipment has been acquired and the laboratory setup has been finalised. The researcher has also met the international collaborator twice and also attended several national and international conferences. Furthermore, the researcher has undergone a range of important training activities as part of his personal development at the Host Institute. These research and generic activities have included courses on preparing successful research funding applications, introduction to project management, introduction to PhD supervision, effective recruitment and ethical issues, as well as attendance at internal seminars and symposiums. The researcher has also been well integrated into the Unit where he is based, and is responsible for supervising PhD and undergraduate and postgraduate student research projects, training colleagues in a range of technical and research skills, pertinent to the project as well as other technical and generic research skills that the researcher has developed.

The findings from the proposed work will be significant as the results have the potential to substantially improve our understanding of the thermoregulatory control of skin blood flow and sweat rate and its interaction with respiratory physiology. Furthermore, the outcomes of these integrative research studies could have important implications for healthy and diseased individuals who exercise / work and/or are exposed to environmental extremes and air gas mixture variations and are potentially at risk of a thermal related injury.