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3. ACUMEN
4.3 TEMPERATURE
4.3.3 Effects of Heat on Health
4.3.3.1 Hot Environment
Exposure to high levels of heat can affect a person’s health in two ways.
First, increased temperature on the skin can lead to tissue damage from
burning (e.g., over 45°C or 113°F). This situation is usually manageable because it is observable and the people react to it by distancing themselves from the heat. The second way heat can affect health is more serious and dangerous. It deals with increased core body temperature to about 42°C (108°F), where heat stroke (hyperthermia) occurs. This rise in core body temperature results in an increase in metabolism, which in turn produce heat that needs to be dissipated. If the cycle is allowed to continue, death can ensue. This cycle is referred to as Q10 effect (for every 1°C increase in deep body temperature, metabolism rises 10%). There are two pos- sible reasons why the heat generated does not leave the body: The body is exposed to heat and humidity that reduces the sweat evaporation; and some protective clothing acts as insulation.
The continuous exposure to hot environmental conditions and the heat stress it generates can lead to several forms of heat illnesses, with heat stroke being the most serious:
• Heat rash, also known as prickly heat—where the skin erupts with red pimples with intense itching and tingling caused by inflammation around the sweat gland ducts.
• Heat cramps—spasms of the muscles result from loss of salt.
• Heat exhaustion—results from dehydration, with a general feeling of headache, loss of performance through muscular weakness, dizziness, possible vomiting.
• Heat stroke—a significant and alarming increase in core body tem- perature and the failure of the body to loose the heat. The general symptoms are headache, dizziness, vomiting, shortness of breath, strange behavior, and eventually loss of consciousness and death.
Heat stroke is caused mainly by strenuous physical work or exercise in hot conditions, duration of exposure to extreme heat sources, and highly motivated and competitive individuals (i.e., sports).
In addition, the exposure and tolerance to heat stress is a function of individual differences (Burse, 1979; Strydom, 1971; Sanders and McCormick, 1993):
• Gender. Generally, women are less tolerant to hot environmental con- ditions and, therefore, more vulnerable to heat illnesses than men.
• Age. Older people are more vulnerable to heat illnesses than younger people.
• Physical fitness. The more the person is physically fit, the longer is the tolerance to hot environmental conditions, up to a point.
• Body fat. Body fat acts as an insulating layer blocking the release of heat. It also acts as an extra weight to move around, increasing the level of physical activity leading to higher body heat and energy expenditure.
• Alcohol. Alcohol affects peripheral nervous functioning and produces dehydration.
4.3.3.2 Cold Environment
Exposure to cold can lead to a drop in core or deep body temperature, likely to produce a risk to health. When the core body temperature falls below 35°C (95°F), the state is referred to as hypothermia or cold stress.
With core body temperature below 35°C (95°F), the risk of disorientation, hallucination, and unconsciousness increases, leading to cardiac arrhyth- mia as the core temperature drops even further and subsequent death from cardiac arrest.
As the body is exposed to cold and the core body temperature starts to drop, the body automatically and rapidly uses its regulation system and produces two physiological reactions to cold stress:
• Shivering—Shivering is characterized by increased muscular activi- ties and contractions to produce heat rapidly; the colder it is and the faster the core body temperature drops, the faster and more intense shivering becomes, leading to exhaustion, until core body tempera- ture reaches 30–33°C (86–91°F), where shivering gradually is replaced by muscular rigidity.
• Constriction of blood vessels, also known as vasoconstriction—
Vasoconstriction is characterized by an increase in the constriction of the peripheral (skin and extremities) blood vessels and an eventual shut off of blood flow to these regions as the core body temperature drops further, leading to an increase in blood pressure. This process
serves two main purposes: First, the warm blood is diverted from the cold skin, such as hands, fingers, and face, and distributed to the inter- nal organs, so less body heat is lost. Second, the insulating capacity of the skin is increased up to six times by cutting off the flow of blood (Sanders and McCormick, 1993). As the constriction of blood vessels increases and blood flow is shut off, the temperature of all exposed areas (hands, fingers, toes, face, nose) rapidly approaches the air tem- perature, causing freezing of body tissues (cold injury) or frostbite.
In addition, the exposure and tolerance to cold exposure is a function of individual differences (Timbal, Loncle, and Boutelier, 1976):
• Body composition—amount of subcutaneous (under the skin) fat around the body, which acts as good insulating material. This is espe- cially important when blood vessels constrict in response to the cold and blood is diverted away from the body surface toward the inter- nal organs for survival.
• Individual size and weight—since the degree of heat loss is propor- tional to the body’s surface area, the bigger an individual is in terms of height and weight, the greater is the amount of heat that can be generated by shivering. Note that the heat generated through shiver- ing depends on the mass of active muscular tissues in the body.
• Physical fitness—the better the physical fitness, the more efficient the production of heat through the shivering process and the longer it is maintained with delayed physical exhaustion.