acutephysiologicalresponsestoheatstress(已修改)
2025-11-04 18:13 本頁面
【正文】 ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS Basic Mechanisms of Thermoregulation ? Core temperature maintained between 35 to 41o C despite environmental extremes which fluctuate between 88 to 58o C via: 1. Behavioral temperature regulation such as choice of clothing, shelter, ventilation, air conditioning, heating, humidifiers, and dehumidifiers. 2. Physiological temperature regulation controlled by rate of metabolic heat production, heat flow from core to skin, and sweating. Basic Mechanisms of Thermoregulation ? Physiological control systems operate on a graded or proportional response in which changes in controlled variables (., sweating and skin blood flow) are proportional to displacements of the regulated variable (., core temperature) from a threshold value. ? Note: each physiological response has a core temperature at which the responses start to increase and the actual response is dependent on mean skin temperature。 the lower the skin temperature, the higher the increase in core temperature before the response is initiated. Basic Mechanisms of Thermoregulation ? Thus, thermoregulatory responses are related to both core and mean skin temperature and hence, (1) at any given skin temperature each response is proportional to core temperature and (2) an increase in skin temperature will decrease the core temperature threshold and increase the response at any given core temperature. CORE TEMPERATURE ? Temperatures within body regions are dependent on: 1. The metabolic rate of surrounding tissues. 2. The source and magnitude of blood flow. 3. The temperature gradients between contiguous body regions. SKIN TEMPERATURE ? Determination of skin temperature is useful for: 1. Estimating the input of skin temperature receptors into the hypothalamus for thermoregulatory control. 2. Predicting core temperature. 3. Calculating mean body temperature for heat storage determination. 4. Calculating sensible (radiation and convection) heat exchange. Exercise Intensity and Core Temperature ? At rest, 70% of metabolic heat es from internal ans and viscera within the body core. During dynamic exercise, metabolic rate increases rapidly by 515 fold with 7090% of metabolic rate released as heat (humans are least efficient at slow and fast speeds of movement). Thermoregulatory effectors for heat dissipation respond more slowly. ? Core temperature increases rapidly, then gradually leveling off at a steadystate value when heat production equals heat loss. Exercise Intensity and Core Temperature ? Magnitude of core temperature at steadystate is largely independent of environmental conditions within a fairly wide prescription zone. Increases in core temperature are proportional to increases in metabolic rate. 1 watt = 6 kgm/min = .01433 kcal/min. ? The prescription zone is smaller at higher exercise intensities. Exercise Intensity and Core Temperature ? If exercise intensity is expressed in ab
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