Thermal state and water-salt metabolism at high ambient temperatures

In humans and other mammals advanced body temperature is kept constant through the mechanisms of thermoregulation, which ensure normal functioning of the organism. Increased body temperature leads to significant shifts metabolism and function of organs and systems. When the temperature of 2 ° is there are significant abnormalities in the cardiovascular system and a noticeable decrease in performance. Raising it to a 4 – 5 ° and more incompatible with the life of the organism.

Interest is the relationship of body temperature to changes in ambient temperature. The experiments were performed in 1967 – 1982 years. relatively cool in the morning hours (air temperature 18 – 23 °), the body temperature in subjects kept within the 36,0 – 36,2 °. In the daytime it was an increase of 1.5 – 2 ° with a maximum coinciding with the air temperature in the 14 – 15 hours. Then it gradually started to decline, returning to the initial morning. The most significant of its figures were reported in the days when the air temperature in the shade reached 44 – 48 °. Some of the subjects body temperature under the tongue rose to 39,0 – 39,3 °. Simultaneously, increased heart rate exceeded 100 beats per minute. Observed on the ECG changes, characterized by the appearance of metabolic disorders in the myocardium. Objective changes in indicators of physiological functions accompanied by a sharp deterioration in health subjects: marked confusion, weakness, shortness of breath, dizziness, discomfort in the heart area. Together, these symptoms were characterized by us as harbingers of heat stroke and is a signal to stop the experiments. The results showed that the violation of heat exchange in autonomous existence in the desert under the impact of high ambient temperature (45 – 49 ° in the shade) can lead to heat stroke events even in patients that are resistant to the effects of heat on the general background of a slight dehydration (when weight loss of no more than 4 – 5% of the initial value).

Heat stress tolerance criterion is usually the body temperature. The maximum permissible temperature of the body (under the tongue) for subjects in the experiments carried out by us in the wilderness, was 38,9 °. It should be noted that in the context of significant overheating of the stabilization of body temperature at a high level (38,5-39,0 °) rapid deterioration of health and a further increase in body temperature may occur suddenly, and they are rapidly progressing. Probably, for a more complete assessment of the thermal state in addition to a fixed value of the temperature of the body should consider the temporal parameters of hyperthermia.

According to domestic and foreign authors, the critical temperature for the human body exposed to temperature extremes, we can assume 38,4 – 38,9 ° and even 39,2-39,4 °.

Characterize the level of hyperthermia may value the excess heat content in the body, referred to the surface of the body. The maximum permissible value teplonakopleniya in the body of the subjects during the experiments in the desert was 70 – 75 kcal / sq. m further increase the heat content, we observed the appearance of precursors of heat stroke. According to some foreign researchers, the maximum tolerable level of accumulation of excess heat in the range 65 – 85 kcal / sq. m and even 89 – 100 kcal / sq. m

A similar conclusion was Krichagina (1966), A.N.Azhaev (1979), Dorodnitsyn, EY Shepelev (1961) who conducted research in a heat chamber at an ambient temperature of 45-75 °. SM Gorodinskiy colleagues found that the maximum allowable accumulation of heat alone is 89 + 9 kcal / sq. m, with moderate physical work – 84 + 9 kcal / sq. m, and in severe – 113 + 6 kcal / sq. m

This significant difference in the determination of the critical numbers teplonakopleniya various authors is apparently due to the fact that the thermal load tolerance, not only is an individual, but can range from one and the same person, depending on the health status, violations of work and leisure, physical load, etc. So, for example, taking a small dose of alcohol before the experiment almost 2-fold reduced the stability of the test to heat.

It is obvious that all the excess heat that threatens to break temperature homeostasis requires immediate removal. Normally, this process takes a number of ways: 28% of heat – convection, 37% by radiation, 11% evaporation of water through the lungs, 2% thermal conductivity of 4% when heated food intake and inhaled air, 4% – in the expired air and 14% water evaporation through the skin (perspiration). However, with the increase in air temperature of sweating in the role of thermoregulation increases significantly. If the air temperature 15,5 ° of the total number of lost fluid (1.40 l / day) evaporation of the body to lose 0.94 liters, then at 32,2 ° of 2.994 liters per share of 2.444 liters of sweat accounts. When the air temperature 33 ° to maintain the heat balance is in fact only the evaporation of sweat, because other ways are closed. Thus, in the desert just him, saving pot, can rid the body of heat, taking every gram evaporate 585 calories of heat.

Water loss through sweat at temperatures of 37,8 ° reach 300 g / h and a further increase in temperature every half-degree increase by 20 g / h. In severe exercise general loss of fluid per day may exceed 10-12 liters.

True, with a decrease in reserves of liquid in the body sweating slightly more than usual, that is, there is a definite relationship between the level of perspiration and the degree of dehydration. Thus, according to S.Robinzona, sweating is reduced by 15 – 20% is the dehydration of 3-4%. Observing the dynamics of sweating in the subjects – the research participants in the desert, we also noted a certain decrease from the first to the third day of the experiment, which seems to be evidence of the braking function of sweat glands, caused by developing dehydration.

Studying the structure of water losses showed that the loss of body weight and 4.0 – 4.5% is due to dehydration vnesosu-carbon extracellular fluid, with a deficit of 4.5 to 6.0% of circulating plasma volume (CGO) is reduced by 15 – 20%. Later in the weight loss up to 8 – 10% reduction in CGO and extracellular fluid while generally not progressed, but there was a decrease in intracellular water.

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