Overheating

Thermal effects disrupt many physiological functions and can lead to dehydration. Most people in this situation experience mild, but unpleasant symptoms, although in some cases they can vary from swelling and seizures to fainting and heat stroke. In some cases of heat illness, body temperature rises. With dehydration, tachycardia, tachypnea and orthostatic hypotension are possible. CNS dysfunction indicates the most serious pathology - heat stroke, in which disorientation and drowsiness further reduce the ability to leave the zone that became the source of overheating and begin rehydration.

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Reason for overheating

Thermal disorders develop as a result of increased intake of heat into the body and a decrease in heat transfer. Clinical manifestations are intensified by the inability to tolerate increased cardiovascular load, dehydration, electrolyte disorders, and the use of certain drugs. High-risk groups include children and the elderly, as well as patients with cardiovascular pathology or an electrolyte metabolism disorder (for example, with diuretics).

Excess heat enters the body at high loads and / or when the ambient temperature rises. The reason for the increase in body temperature may also be some painful conditions (for example, hyperthyroidism, malignant neuroleptic syndrome) or the use of stimulant drugs such as amphetamines, cocaine, ecstasy (an amphetamine derivative).

Cooling is complicated by tight clothing (especially protective in workers and athletes), high humidity, obesity and everything that interferes with the production and evaporation of sweat. Sweat production can be disrupted by skin lesions (eg, sweating, extensive psoriasis or eczema, scleroderma) or with the use of anticholinergic drugs (phenothiazines, H ₂ -receptor blockers and anti-Parkinsonics).

The pathophysiology of overheating

The human body receives heat from the external environment and heat, formed as a result of metabolism. Heat transfer occurs through the skin by radiation, evaporation (for example, during sweating) and convection; the contribution of each of these mechanisms depends on the temperature and humidity of the environment. At room temperature, radiation predominates, but as the ambient temperature approaches the body temperature, the value of convection increases, at> 35 ° C it provides cooling by almost 100%. However, high humidity significantly limits the possibility of convection cooling.

Heat transfer depends on changes in skin blood flow and sweating. The rate of cutaneous blood flow, at a normal ambient temperature of 200-250 ml / min, under stress thermal exposure increases to 7-8 l / min, which requires a significant increase in cardiac output. In addition, as the ambient temperature rises, sweating increases from a mild to 2 l / h or more, which can quickly lead to dehydration. Since sweat contains electrolytes, hyperthermia can lead to significant losses. However, with prolonged exposure to high temperatures, adaptive physiological changes (acclimatization) occur in the body, for example, sweat contains Na ⁺ at a concentration of 40 to 100 mEq / L in unadapted people, and after acclimatization, its content drops to 10-70 mEq / L.

The body can maintain normothermia with significant heat loads, but a pronounced or prolonged exposure to high temperatures leads to an increase in body temperature. Moderate non-prolonged hyperthermia is tolerable, but a marked increase in body temperature (usually> 41 ° C), especially when working hard in the heat, leads to protein denaturation and the release of inflammatory cytokines (such as tumor necrosis factor a, IL-1R). As a result, cellular dysfunction develops, activating a chain of inflammatory reactions leading to functional disorders of most organs and triggering the coagulation cascade. These pathophysiological processes are similar to those in the syndrome of multiple organ failure, which follows a prolonged shock.

Compensatory mechanisms include an acute phase response involving other cytokines that inhibit the inflammatory response (for example, by stimulating the production of proteins that reduce the production of free radicals and inhibit the release of proteolytic enzymes). In addition, elevated body temperature triggers the expression of heat shock proteins. These substances regulate cardiovascular reactions and temporarily increase the body's temperature stability, but the mechanism of this process has so far been little studied (possibly the role of the denaturation of the protein plays a role). With a prolonged or sharp increase in body temperature, the compensatory mechanisms are broken or not functioning at all, which leads to inflammation and the development of multiple organ failure.

Prevention of overheating

The best prevention is common sense. In the heat of children and the elderly, one should not stay in unventilated and non-conditioned rooms. Do not leave children in the car in the sun. If possible, extreme physical exertion should be avoided in high-temperature and unventilated environments, and heavy, insulated clothing should not be worn.

To monitor dehydration after exercise or hard work use the indicator of weight loss. With a decrease in body weight by 2-3%, it is necessary to drink an increased amount of liquid so that before the beginning of the load on the next day the difference in body weight is within 1 kg of the initial value. If you lose more than 4% of body weight, you should limit physical activity to 1 day.

If physical stress in the heat is unavoidable, the liquid (whose losses are usually invisible in very hot and very dry air) must be repaired with frequent drinking, evaporation should be facilitated by wearing open clothing and using fans. Thirst is a bad indicator of dehydration at high physical exertion, therefore, regardless of its appearance, one should drink every few hours. However, hyperhydration should be avoided: athletes who consume too much fluid during exercise have significant hyponatraemia. To compensate for the loss of fluid during the maximum physical activity, it is enough ordinary water, the cool water is better absorbed. In special rehydration solutions (for example, sports drinks), there is no need, but their taste contributes to increasing the amount of fluid consumed, and a moderate salt content is useful when the body's need for liquid is increased. It is recommended the use of water in combination with the reception of abundant salted food. Laborers and other sweating people with sweat may lose more than 20 grams of salt per day, which increases the likelihood of thermal seizures. In this case, the loss of sodium must be compensated for by liquid and food. A pleasant drink, containing about 20 mmol salt per liter, can be prepared by adding a spoonful of table salt to the slab to 20 liters of water or any soft drink. People on a diet with a low salt content should increase its intake.

With a gradual increase in the duration and severity of heat loads, acclimatization eventually occurs, which allows people to work in conditions that were previously unbearable or life threatening. The increase in work during the hot season with 15 minutes of daily moderate physical activity (sufficient to stimulate sweating) to 1.5 hours of intense exercise during 10-14 days is usually well tolerated. During adaptation, the amount of sweating (and, consequently, cooling) during a certain period of work is significantly increased, the electrolyte content in pot is markedly reduced. Acclimatization significantly reduces the risk of developing a heat illness.