Individual differences in thermoregulatory control, a review

2016-05-27T10:57:56Z (GMT) by George Havenith
Humans show a marked variation in their thermoregulatory behaviour. In this review, an attempt was made to determine in how far this variation is caused by differences in sex, age, anthropometric measures, hydration state and circadian rhythm and to which underlying parameters their effect can be ascribed. For the following factors (in approximate ranking order of significance), such parameters have been found: - State of acclimatization The state of acclimatization is defined by the sweat characteristics (high state of acclimatization implies high maximal sweat rate, high gain and/or low setpoint for sweat rate-Tcore relation. improved sweat distribution) and by the circulatory capacity (high state of acclimatization: more constant blood pressure and blood volume; lower heart frequency; high stroke volume). Physical fitness The effect of physical fitness on determined by circulatory capacity. As the state of acclimatization, it is acclimatization are strongly related. - Hydration state thermoregulation is mainly this is also a parameter for obvious that fitness and The influence of the state of hydration on thermoregulatory function is determined by two parameters: 1 Plasma osmolality: the plasma osmolality affects either the thermoregulatory centres in the brain or directly the function of the sweat gland. These effects may be ion specific ( Na+ • ca++). 2 Plasma volume: changes in plasma volume and consequently blood viscosity influence cardiac efficiency and through this the strain of the body during heat stress. - Anthropometric measures These will have a physical influence through: heat exchange surface area (body surface), insulation (fat) and weight load (inactive body mass). - Time of day The influence of the time of day on thermoregulation is determined by the related variations in sweat characteristics, skin blood flow and body temperature. In how far this also influences body heat strain and heat tolerance is yet unknown. The factors sex and age are supposed to be of little importance for the reactions to heat stress, as effects ascribed to these factors can be described by the above mentioned factors with their parameters. At the end of this report, the findings will be expressed in propositions for the determination of the selected factors and parameters.