Heat and the Body – Heat-Related Disorders
Low Blood Pressure
Your blood vessels widen with rising temperature to let more blood flow to the skin. The heart needs then to apply less pressure to pump the same amount of blood through the vessels – so the blood pressure falls. A comparison between outside air temperatures and the blood pressure of blood donors reveals an average 10-15% lower blood pressure during the warmer months of the year and an increase by the same amount during the colder winter months.
This sounds good for people with high blood pressure. Keep in mind, however, that when the body needs to shed excess heat, the pulse rate increases dramatically and puts the heart under considerable strain. Physical exertion in combination with an underlying heart disease is a major contributor to high death rates during heat waves.
Sweating excessively without replacing the lost fluid results in dehydration and an imbalance of body salt levels (electrolytes). As a consequence, painful cramps in the major muscles develop rapidly, but sometimes not until several hours after the event. Especially vulnerable are the hamstrings of your legs and the muscles of your arms and stomach. They become hard and painfully tense and often disable the affected person.
Electrolytes are chemicals that make fluids electrically conductive. You probably heard the term in relation to your car battery. The mechanic replenishes the electrolyte, in this case battery acid, when it is too low. Without electrolyte you wouldn’t have an electric current – your engine wouldn’t start. The body, too, requires electrolytes. Besides their conductive properties, body salts regulate the fluid levels in the body cells and control the function of the kidneys. The two major chemicals acting as electrolytes in the body fluids are sodium (table salt) and potassium.
After heavy sweating, replenish yourself with water and electrolytes. Half a teaspoon of salt dissolved in each litre of water is generally sufficient to top up the electrolyte levels. Sports drinks, or salty food together with water, are similarly effective. Rest in a cool place, out of the sun, to avoid a deterioration of the condition. See a doctor if you also have symptoms (see below) of heat exhaustion or heatstroke.
The purpose of sweat is to evaporate and cool your body. Wearing non-porous covers, such as plastic baby diapers, oily make-up or tight-fitting garments, however, will hold the sweat within the glands. This may lead to an irritation of the glands and the formation of small red pimples or even blisters – symptoms of heat rash. It isn’t generally serious, but can develop into a secondary skin infection. Hot and humid weather is almost always the cause, but obesity, genetic factors and sensitive skin also add to your chances of heat rash.
Heat rash – also known as prickly heat and baby rash – is more common amongst the very young, because their underdeveloped sweat glands clog easily.
Even in winter an overdressed infant in a wet diaper can develop the pimples between the legs and on the buttocks.
Prevent heat rash by removing the cause of the sweat gland blockage. Don’t wear tight-fitting and non-porous garments in the summer heat. Avoid oily ointments and creams where possible and wash off any sweat or dirt. Change baby diapers regularly and apply moisture-absorbing powder. If prevention comes too late, your pharmacy has antiseptic cleansers or soothing remedies.
Although heat rash is a non-serious and common medical condition in babies, it is also a sign that the infant is too hot, and may progress to a more dangerous heat-related disorder.
The cause of heat exhaustion is similar to that of heat cramp – dehydration and/or an imbalance of body salts. In this case, however, the body’s temperature regulation system fails to adequately respond to an increase in body temperature as well. The disorder often follows overexertion in hot weather during sport or outdoor work. Elderly patients on diuretic medicines are also at great risk.
The signs and symptoms are similar to shock and include:
- Weakness, exhaustion, fatigue
- Nausea and vomiting
- Heat cramps
- Lack of coordination, giddiness, faintness
- Rapid pulse and breathing
- Cold and clammy skin
- Profuse sweating.
Someone showing these symptoms should be moved to a cool place, have their unnecessary garments removed and their body cooled. Lost fluids and electrolytes should be replaced. Consult a doctor if the person can’t keep the fluid down or doesn’t recover promptly. The condition is very similar to heatstroke, but the body temperature is usually less than 39°C.
Heatstroke is the most dangerous of all heat-related illnesses and requires immediate medical attention. I have previously explained the limitations of the body’s ability to regulate its temperature. When the self-cooling process is stressed beyond its capabilities, it may collapse completely. The condition becomes life threatening and, despite medical attention, approximately 10% of heatstroke patients die. The rate is much higher during heat wave conditions or in regions where medical help is limited.
A healthy person is not likely to succumb to heat and high humidity unless that person increases their body temperature during work or exercise in hot conditions. The elderly and the very young with a deficient or underdeveloped heat regulation mechanism, however, are always at risk to suffer from heatstroke, with or without physical activity. Chronic illnesses, genetic makeup and some types of medication can also increase the risk.
The signs and symptoms of heatstroke are:
- Body temperature climbs to 40.5°C or higher
- Nausea, vomiting
- Visual disturbances
- Altered mental state whereby dizziness, irritability, confusion, progression to seizures and unconsciousness is possible
- Rapid pulse
- Flushed and usually dry skin. Sweat can be present in exertional heatstroke.
Recognition of heatstroke symptoms is vital to allow prompt medical attention. If the patient isn’t cooled immediately, the high body temperature will damage the tissue of almost every organ. Muscle meltdown (rhabdomyolisis) and blood clotting (thrombosis) often accompany heatstroke.
A survey of several heatstroke patients showed that all suffered from multiorgan dysfunction. About half had kidney problems and showed symptoms of blood clotting. More than half had breathing difficulties and required intubation, where a tube was inserted to help them breathe. Most survivors recovered to almost normal conditions, but a third were left with permanent organ or brain damage.