By Dr Ananya Mandal, MD
Heat stroke and other heat related conditions occur when the body is exposed to high levels of heat and is unable to cool itself. (1-4)
Normally the human body can maintain a stable body temperature despite varying temperatures externally in the environment. This is called thermoregulation.
Normal skin temperature is 32-34°C (89.6-93.2°F). A body normally uses some techniques to cool itself when the core temperature rises. These include:
- Evaporation when the body produces sweat that evaporates and cools the body
- Radiation of heat from the body in waves
- Convection currents of cool air or water that runs over the skin to cool it
- Conduction when a cooler object is brought in contact with the body and its takes on the heat
When the environmental temperatures are higher than the body’s temperature, sweating is the first and most important way of cooling the body.
Sweating is regulated by a part of the brain called the hypothalamus. This part acts like a thermostat and stimulates sweating in response to excessive environmental heat. It also asks the body to stop sweating when the body is cool.
If the environmental air is not saturated with water, sweat will vaporize and cool the body surface.
The evaporation of 1.7 ml of sweat will consume 1 kcal of heat energy. At best sweating can dissipate about 600 kcal of heat per hour.
A severe lack of sweating may be caused by:
- dehydration and lack of body water
- wearing non breathable fabrics and tight fitting clothing
This may lead to increased core body temperature as the body fails to cool itself by its own.
Thus not only the environmental temperature but other factors like humid weather and physical exertion may also lead to heat strokes.
Types of heat stroke
Heatstroke is of two types the classic and exertional heatstroke.
Classic heat stroke commonly affects infants and babies under two years of age, elderly and those with long-term health conditions like diabetes, heart and kidney disease. This is seen commonly during heat waves and hot weathers.
Exertional heatstroke on the other hand may affect younger people, especially if they are doing strenuous, physical activity in hot conditions for very long time.
This is commonly seen among athletes, military personnel, firemen and construction workers and manual labours working in the sun.
Heat stroke in the elderly
In the elderly and those with long term health conditions the thermoregulation of the brain is not adequate. This puts these individuals at a higher risk of getting heat exhaustion and heatstroke.
Further elderly women have a slightly higher risk of heatstroke than older men. This may be because they have fewer sweat glands than men. Infants and children under two years are also susceptible since they sweat less and are more affected by dehydration.
People at high risk of heat stroke
High risk groups include:
- those with Alzheimer’s disease
- disabled and bed ridden patients
- babies and infants
- those who have taken too much alcohol - since alcohol causes dehydration.
- those with anorexia
- those with cystic fibrosis
- those with epilepsy
- those with diabetes insipidus
- those with gastroenteritis and diarrhea
- those with Parkinson’s disease
- those with thyroid overactivity and thyrotoxicosis
- those with low potassium levels in blood etc.
- people who are obese
- those who are unused to exertion when they undergo an unusual session of physical activity
- those wearing tight fitting, non-cotton and inappropriate clothing
- sleep deprived
- those with a sweat gland dysfunction
In addition, certain drugs also raise the risk of heat related health conditions. These include drugs of abuse like:
- amphetamines (speed and crystal meth)
- lysergic acid diethylamide (LSD)
- phencyclidine (PCP)
- ecstasy etc.
Medications that raise the risk of heat stroke include:
- antipsychotics used to treat mental disorders
- tranquillizers like benzodiazepines
- beta-blockers and calcium-channel blockers and diuretics or water pills used in heart disease and high blood pressure treatment
- alpha-adrenergics (used in high blood pressure)
- antihistamines (used in allergies)
- tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs) (both used in depressive disorders)
- lithium (mood stabilizing agent)
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)
Last Updated: Aug 6, 2012