Effects of Heat and Cold

Hypothermia and hyperthermia are frequent causes of death by law and high temperatures, the ones out body cannot protect from and fight with. The limits of our body start and finish at certain levels.

Hot Air

Normal body temperature is generally considered to be 98.6°F (37°C) orally and approximately 1 °F (0.6°C) higher rectally. Body temperature can vary from individual to individual, by age, time of day or physical exertion. Thus, newborns and the elderly have temperatures averaging 1°C higher. Cyclic changes in body temperature occur with decreases of 0.5 °C early in the morning (approximately 1:00 to 2:00 a.m.) and slight elevations later in the morning and afternoon. Hard exercise can raise the rectal temperature up to 104°F.  Rectal temperatures of 39–40 °C are common in marathoners after a race.

Maintenance of normal body temperature is a delicate balance between heat load and heat loss. Heat load is the sum of heat generated by oxidation of metabolic products and heat acquired from the environment. Heat is lost by three mechanisms:

• conduction,
• radiation,
• evaporation.

Loss of heat by conduction is either by direct conduction from the surface of the body to another object or by conduction to air. Loss of heat by direct conduction to objects is relatively minor. For example, if an individual sits in a chair, heat conducted from the body will raise the temperature of the chair to that of the body. When this has occurred, heat loss will stop. The molecules composing the skin transfer heat to contiguous air molecules, producing a thin zone of heated air adjacent to the skin. If this layer of heated air is continually removed and new air introduced (by a fan or wind), the loss of heat by conduction will continue. This movement of air around the body, with resultant continued loss of heat, is known as convection. Winds will blow away the layer of air immediately adjacent to the skin, thus accounting for the feeling of cold and increased heat loss when the wind blows. There is, however, a limitation on this process. Once the wind has cooled the skin to a certain temperature, the rate at which heat flows from the core of the body to the skin is the limiting factor in heat loss, rather than the rate of conduction and convection. The second method of heat loss is by radiation. It is loss of heat in the form of infrared rays. These radiate from the body in all directions. Heat rays radiate from all masses... walls, floors, the ground, etc. all radiate infrared heat rays. If the environment becomes hotter than the body, radiant heat given up by the surroundings will exceed the loss of heat from the body by radiation. The third method of heat loss is by evaporation. This is the primary method of cooling the overheated body. As water evaporates from the body, 0.58 calories of heat are lost for each gram of water that evaporates. The two mechanisms of heat loss by evaporation are insensible heat loss and sweating. Insensible heat loss is loss of moisture from the non-sweating individual. This is water that evaporates from the skin and lungs. It occurs at a rate of about 600 mL per day, that is, a continual heat loss of 12-16 cal/h. Insensible heat loss is caused by continued diffusion of water molecules through the skin and respiratory surfaces regardless of the body temperature. To prevent this, individuals exposed to high temperatures are urged to increase their fluid intake. This is especially necessary in those engaging in strenuous activities such as manual labor or jogging. Some people ingest too much fluid and develop hyponatremia. The symptoms of this are nonspecific — nausea, vomiting, headache, muscle weakness, confusion, and seizures. Symptoms occur when serum sodium levels decrease to <130 mmol/L, becoming severe at levels <125 mmol/L. When serum sodium drops below 120 mmol/L, more than 50% of individuals have seizures.

The skin, subcutaneous tissues, and fat act as heat insulators in the body. Fat is especially important because it conducts heat only one third as readily as other tissues. When no blood is flowing from internal organs to the skin, the insulating properties of the male body are approximately equal to three fourths the insulating properties of the usual suit of clothes. In women, because of greater body fat, this insulation is still better.

When individuals’ ability to cool the body can no longer compensate for the heat load, they develop heat stroke. This is a life-threatening condition classically manifested by hyperthermia (a rectal temperature of 105–106°F or higher), hot, dry skin, altered sensorium, tachycardia, hypotension, and hyperventilation. The very old and very young are more susceptible to heatstroke.

Obese individuals show a greater susceptibility to heat stroke. This is due to a number of factors: (1) Increased adipose tissue creates an greater demand on the heart; (2) the fat provides extra insulation for the body, preventing loss of heat; (3) since metabolic heat is produced in proportion to the bulk of the tissue and is lost in proportion to the surface area, the larger bulk-toarea ratio in the obese reduces efficient heat loss. Heat stroke is generally seen in two settings. First is that involving relatively young individuals exposed to high temperatures while undergoing extreme exertion — military recruits and football players in training are examples. The other setting is a prolonged heat wave. In this flatter circumstance, affected individuals are generally over the age of 60. Deaths from heat stroke also occur in children left unattended in automobiles for long periods of time in the summer. Diagnosis of heat stroke antemortem is relatively easy because of the characteristic symptoms and signs, as well as the elevated body temperature. The autopsy findings of heat stroke, however, are not specific. Individuals surviving more than 24h may show lobular pneumonia, acute tubular necrosis of the kidneys, adrenal hemorrhage, or necrosis of the liver. Hyperthermia can be due to various other causes. Though body temperature may be normal or only slightly elevated in thyrotoxicosis, in thyrotoxic crisis, rectal temperatures of 40°C can occur. Cocaine, methamphetamine and aspirin intoxication can all cause hyperthermia through excess heat production. In severe salicylate intoxication, there is excess heat production as salictylates uncouple the bonds formed by oxidative phosphorylation in skeletal-muscle mitochondria.

Freezing Air

The term hypothermia is used when an individual’s body temperature is below 95°F (35°C). This will occur when the loss of body heat exceeds heat production. The most common cause of hypothermia is exposure to low temperatures. Accidental hypothermia occurs in alcoholics going to sleep or passing out in a cold environment, individuals lost while hiking or skiing, and those who have been immersed in ice-cold water. This last condition, immersion hypothermia, is extremely dangerous because of the more rapid loss of heat in water than in air. Body heat is lost three times faster in water than in dry, cold air of the same temperature, as water conducts heat 20 to 25 times faster than dry air.

The body’s defense against cold is vasoconstriction of blood vessels in the skin and muscles so as to conserve heat, combined with an increase in generation of heat. Heat production is increased in two ways: First, there is shivering. During maximum shivering, heat production can rise as high as five times normal. Second, there is chemical thermogenesis, i.e., an immediate increase in the rate of cellular metabolism. The degree of thermogenesis that occurs is directly proportional to the amount of brown fat. In adults, who have almost no brown fat, it is rare that chemical thermogenesis increases the rate of heat production more than 10–15%. In infants, who have a large amount of brown fat, the increased heat production is as much as 100%.

Heat production by the body, such as that caused by shivering, can maintain body temperature to about 90°F (32°C), where impairment of cerebral functioning, manifested by analgesia, clouding of consciousness, hallucinations, and slowing of reflexes, begins. Shivering ceases between 90 and 85°F. Respiration becomes less frequent and more shallow and there is a decrease in the pulse rate. Below 85°F, the ability of the hypothalamus to regulate temperature is completely lost. Cold narcosis appears at 85°F and reflexes are abolished at 81°F  (27.2°C). As hypothermia develops, electrocardiographs show prolongation of the PQRS waves with inverted T waves. At about 86°F (30°C), atrial fibrillation often appears. Between 82 and 77 °F (27.7°C and 25°C), death may occur from ventricular fibrillation.

Many cases of hypothermia seen by the police and the forensic pathologist involve individuals who die of exposure while under the influence of alcohol. Alcohol is said to contribute to the fatal outcome by causing cutaneous dilatation of peripheral vessels and thus loss of heat. This is the warm flush that an individual experiences when drinking alcohol. However, a number of individuals have been reported as surviving deep hypothermia because of alcohol intake. This survival is attributed to protection against cardiac fibrillation by the alcohol.

Cold Water. Almost Frozen.

Clothing retards body cooling in water, though not as effectively as in air. In very cold water, exercise accelerates the rate at which the body temperature falls, because increased flow of blood to exercising muscles carries away more heat than is produced by the exercise. Deaths have been reported within a half hour following immersion in water at 32°F (0°C). The individuals who die under these circumstances probably do not die primarily of hypothermia. Death is probably caused by cardiovascular etiology due to the effects on the heart of the sudden cooling of the skin, i.e., constriction of blood vessels, and reflex stimulation of the heart, with increased blood pressure and cardiac output, with resultant sudden increase in the work of the left ventricle. Both ventricular and atrial ectopic beats are common during the first few minutes of cold immersion. Reflex disturbances of breathing could also account for some of the rapid deaths following immersion in cold water. Sudden cooling of the skin following immersion in water with a temperature approaching 0°C causes marked reflex stimulation of breathing for a few minutes such that breathing can often not be controlled voluntarily. Post-immersion deaths can occur following the rescue from cold water of individuals who appear to be in no danger of dying. The individual may be conscious when taken out of the water, only to lose consciousness when taken into the warmth of the facility. This appears to be related to the “afterdrop phenomenon.” It happens because an individual’s body temperature continues to fall for a period of time before it starts to rise. The critical temperature to maintain thermo-equilibrium in water was determined to be 35°C (95°F)

Cold weather is often associated with sudden death in individuals with coronary artery disease. The lower the temperature, the greater the risk of a coronary attack. Individuals with angina pectoris almost invariably experience pain on exposure to air temperature of less than 15°F (-10°C). This pain is caused by coronary spasm or increased stroke volume induced by breathing cold air.

Acknowledgements:

The Police Department; 

https://www.politie.nl/mijnbuurt/politiebureaus/05/burgwallen.html and a Chief Inspector – Mr. Erik Akerboom                                 ©

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