Disorders Due To Heat Exposure
Stay Cool To Avoid Heat Exhaustion
A stable internal temperature requires a balance between heat production and heat loss, which the hypothalamus, a specialized center in the brain, regulates, by initiating changes in muscle tone, blood vessel tone, and sweat gland function. Sweat production and evaporation are major mechanisms of heat removal. Direct transfer of heat from the skin to the surrounding air also occurs, but with diminished efficiency, as the ambient temperature rises. The passive transfer of heat from a warmer to a cooler object by radiation accounts for 65% of body heat loss under normal conditions. Radiant heat loss decreases, as the temperature of the surrounding environment increases up to 37.2 degrees Celsius, the point at which heat transfer reverses direction. At normal temperatures, evaporation accounts for approximately 20% of the body's heat loss, but at high temperatures, it becomes the major mechanism for dissipation of heat.
Health conditions that inhibit sweat production or evaporation, and increase susceptibility to heat disorders include the following:
- Heat rash
- Reduced blood flow to the skin surface
- Low blood pressure
- Reduced cardiac output
Specific disorders due to heat exposure include the following:
1. Heat Syncope
In this condition, sudden unconsciousness can result from widening of blood vessels in the skin, with consequent lowering of cerebral and overall blood pressure. Systolic blood pressure is usually less than 100 mm Hg. The skin is cool and moist, and the pulse is weak. Vigorous physical exercise for two hours or more can precipitate an episode. If you come across an individual who has fainted due to heat syncope, then first and foremost move the person to a cooler place, if possible under tree shade. As a first aid measure, make him or her sit or lie down with legs raised, and slowly administer fluid containing necessary electrolytes. Shift the person to the nearest medical facility, as soon as possible.
2. Heat Cramps
Loss of fluid and salts from the body, due to excessive exposure to heat can result in slow, painful muscle contractions or cramps, and even more severe muscle spasms lasting 1-3 minutes, usually of the muscles most heavily used. The skin is moist and cool, and the muscles are tender (painful to touch). There may be muscle twitching. Involved muscle groups become hard and lumpy. The body temperature may be normal or slightly increased. This condition can also develop after vigorous activity. Cramping can occur hours later, at night or when relaxing. In order to prevent heat cramps, one may drink electrolyte solutions, when exposed to intense heat, and include fruits (such as apples and bananas) and veggies loaded with minerals, especially potassium, in the diet.
3. Heat Exhaustion
Heat exhaustion results from prolonged heavy activity with inadequate salt intake in a hot environment and is characterized by dehydration, sodium depletion, or fluid loss, accompanied by disturbances in the normal functioning of the heart. The skin is moist, and the pulse rate increased. The person may be quite thirsty and weak, with headache, fatigue, anxiety, sensation of pins and needles, impaired judgment, hysteria, and occasionally psychosis. It may progress to heat stroke if the sweating ceases.
First aid measures:
- Move away from heat, and rest preferably in an air-conditioned room.
- Drink plenty of fluids. Avoid caffeinated drinks.
- Remove any tight or unnecessary clothing.
- Take a cool shower or sponge bath.
- Use ice towels or bags..
If all the above measures fail to provide relief, then seek emergency medical help.
Basic First-Aid For A Heat Stroke Victim
Heat Stroke Victim Being Treated With Water Spray
4. Heat Stroke
It is a life-threatening medical emergency, resulting from the failure of thermoregulatory mechanism, in association with a warm environment. The term "heat stroke" is a misnomer, in that, it does not involve blockage of blood flow to the brain or hemorrhage of any feeding vessel. It may be categorized into the following types:
- Exertional heat stroke: It occurs in younger individuals exercising at ambient temperatures, and/or humidities. that are higher than normal. It may also occur as a complication of participation by unconditioned amateurs in strenuous athletic activities, such as marathon running and triathlon competition. Even in normal individuals, dehydration or the use of common medications (such as Over The Counter antihistaminics) may precipitate this disorder.
- Non-exertional or Classic heat stroke: This typically occurs in elderly individuals, particularly during heat wave conditions. The elderly, the bedridden, persons taking anticholinergic medicines, or diuretics, and individuals confined to poorly ventilated and unairconditioned environments are most susceptible. Failure of heat dissipation mechanism for any reason results in dizziness, weakness, emotional lability, nausea, and vomiting, diarrhea, confusion, delirium, blurred vision, convulsions, collapse and loss of consciousness. The skin is hot, and initially covered with perspiration. Later, it dries. The core temperature is usually over 41 degrees Celsius.
Exertional stroke may present with sudden collapse, and loss of consciousness, followed by irrational behavior.
Tips to prevent heat stroke:
- Drink plenty of electrolyte-rich fluids.
- Avoid excess heat and humidity.
- Wear light, loose-fitting clothes and wide-brimmed hats in light colors.
Emergency steps to be taken, when a person suffers heat stroke:
- Move the person to a cool area, and remove most of his clothes to promote heat loss.
- An affected individual should be bathed in cold water.
- Immerse in a tub filled with cold water. Do not use ice cold water, and avoid this step in an unconscious person.
- Apply cold compresses to the torso, head, neck and groin area.
- Place the person under a fan or a dehumidifying air-conditioning unit.
- Make him or her to drink electrolyte-rich liquids.
Factors That Increase The Risk Of Heat Disorders
- Increasing age
- Impaired cognition
- Concurrent illness
- Reduced physical fitness
- Insufficient acclimatization
5. Heat Oedema
This condition is characterized by swelling of hands and feet, that occurs from vasodilatory pooling of body fluids. Heat causes blood vessels to expand, so body fluids move into the arms and legs under the effect of gravity. If the loss of salt from the body is less than normal, then this excess salt also drags the fluid into hands and feet. Older adults, especially those suffering from peripheral vascular diseases, are at an increased risk. This dependent oedema can also occur in unacclimatized people from colder climates, who visit tropical countries during the summer season.
6. Tropical Anhidrotic Asthenia
It is a state of heat intolerance and exhaustion. The primary event is a total lack of sweating, that is largely the result of a blockage in the sweat duct pores, and consequent prickly heat rash. The disease, occasionally could also be a consequence of severe nerve damage. This disorder was prevalent among the military personnel during the Second World War when men were exposed to very hot and humid environment, for several weeks.
Hidromeiosis is a decrease in the rate of thermally induced sweating, that occurs after several hours of very active perspiration, in a humid environment. The decrease in sweating occurs as a consequence of occlusion of sweat pores from an overhydrated Stratum corneum of the skin. It is believed to play a key role in precipitating an attack of heat stroke.
It is a physiological adaptation of an individual to a hot environment. Acclimatization involves an earlier onset of sweating after exposure to heat, an increase in sweat rate, and a decrease in the salt loss, and also an increase in the size of sweat glands. There is no significant variation between men and women in their ability to acclimatize to the heat. It improves work efficiency while the unacclimatized are prone to heat stress.
Other heat-induced disorders include sudden failure of sweating due to thermoregulatory center fatigue, and sweat gland fatigue.