HEALTHWATCH
Beat the summer heat
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Keep cool during the hot days. Dr. V. R. RANJITH
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Photo: M.A. Sriram
Maintaining the temperature: The body has its own mechanisms to deal with the scorching heat.
WITH a well developed thermostatic mechanism, humans are homoeothermic in that they can maintain their body temperature despite wide fluctuations in the external temperature. Heat is produced within the body due to metabolic processes, the prime area
s being the muscles and the liver.
The body acquires heat when exposed to an ambient temperature greater than its own, as in summer. The body dissipates heat primarily through the skin and secondarily through water vapour in the exhaled air from the lungs. The hypothalamus, the body’s thermostat in the lower part of the brain, initiates processes that transfer heat from the core to the periphery by increasing blood flow to the skin and the sweat glands, and also stimulates sweat formation.
What is sweating?
As much as 30 per cent of the cardiac output can be shunted to the skin for this purpose. Thence heat is lost from the skin partly through radiation but mainly through sweating, the evaporation of which causes cooling.
Sweating is a physiological process that consumes metabolic energy. There are more than 2,500,000 sweat glands in the skin and they are richly supplied with blood vessels and nerves stimulated through a neurotransmitter chemical called acetylcholine.
Sweat is a weak solution of sodium chloride in water along with small amounts of potassium, urea and lactic acid. Though the loss of sodium chloride through sweat is less in the acclimatised, replacing only water without electrolytes after excessive sweating can lead to muscle cramps.
The rate of sweating varies from 1.5 litres/hour in the unacclimatised to four litres/hour in the maximally acclimatised. Sweating by itself only provides the water required for cooling which happens only through evaporation, a process dependent on climatic conditions. Under ideal climatic conditions, one litre of sweat can take away about 600 calories of heat from the body.
Factors
Evaporation of sweat depends on four factors: air temperature, humidity, velocity of air movement and sources of radiant heat nearby. Excessive sweating during hot weather produces no cooling if it is humid since this inhibits evaporation; there is only further sweating. So for cooling, the body has to sweat several folds causing considerable exhaustion, as sweating consumes energy.
McArdle’s sweat factor, an index of thermal comfort, classifies a sweat rate of beyond three litres an hour as ‘intolerable’. Further shunting of blood to the periphery slows down digestive and intellectual processes by reducing flow to internal organs.
Humidity in a region is proportional to its proximity to the sea. So people in the coastal regions sweat more than those inland where dry weather causes instant evaporation.
But proximity to the sea is also a blessing since the atmosphere cools down after mid-day thanks to sea breeze. Thus climate is influenced by geography, which determines the kind of measures adopted to offset heat.
In milder forms, heat stress is due to loss of water and electrolytes through sweat and shunting of blood to the skin together causing dehydration, muscle cramps and fall in blood pressure. There is loss of appetite, dryness of mouth, reduced work capacity and drop in intellectual performance.
In humid regions, excessive sweating can increase fungal infections in covered areas and also prickly heat, which is over stimulated engorged sweat glands. Generally obese individuals experience greater heat stress than the non-obese.
Serious conditions
Heat stroke and heat hyperpyrexia are serious conditions where the body’s heat dissipation mechanisms are overwhelmed causing a dangerous rise in body temperature from 106° F to 110° F. Associated with high mortality these need to be treated in an ICU.
The very young and old, bed-ridden people, those living in homes with badly designed insulation and cooling systems and those working in very hot and humid conditions without adequate precautions are particularly vulnerable. Those on drugs such as those used to treat Parkinson’s disease and certain antihistamines, which inhibit the action of acetylcholine, and diuretics that cause dehydration need to be particularly cautious.
The roof of any enclosure is maximally exposed and heated by sunlight. A wall is heated if the afternoon sun shines directly on it. Also hot air entering through ope n windows during the day heats up the room. All this makes the air, floor, furniture and mattresses sources of radiant heat for several hours after sunset.
Reducing the heat
Air-conditioning would be the easiest solution, but it is the most expensive and may not suit those with allergic respiratory illnesses.
The deleterious effects of air conditioning can be reduced if the gradient between air conditioned and the outside air is kept between 8-10° C. This reduces the stress on the mucous membranes of the respiratory tract.
In dry inlands the next best alternative is an air cooler, which provides nebulised water for cooling. In the humid coastal areas, the best way is to stop the ceiling and walls from heating and prevent entry of hot air.
Insulation of the ceiling from direct sunlight is possible by either erecting a temporary structure using steel pipes and sintex sheets. This is long lasting but expensive. A cheaper option is to cover the ceiling with dried coconut leaves spread over a thin frame placed on bricks.
Use an exhaust fan in the bed room in the evening after the sea breeze sets in and after 3-4 hours the inside air will be equal to the outside. But this is not possible where the external air is impure.
Try to wear light coloured clothes. Pure cotton is the best fabric as synthetics do not absorb sweat or allow evaporation. Prickly heat is worse with synthetics.
Those travelling on two wheelers can place wet cloth on the forehead, face and nape of neck and wear moist socks on the feet to reduce heat stress.
Fluid intake
Butter milk and curds have a high specific heat and hence cool down core temperature when consumed. This effect is enhanced when curd is taken mixed with ragi porridge containing raw onions, a traditional South Indian food in summer.
A high fluid intake of about three litres a day is mandatory to maintain fluid balance and prevent urinary infections. Salt intake has to be slightly more than in winter.
In individuals with mild blood pressure, anti-hypertensive medication requirements tend to reduce during summer because of a fall in peripheral resistance as a consequence of increased blood flow to the skin.
Wash the body 3-4 times a day and just mop the excess water without drying the body to reduce excessive sweating.
Apply powders containing talc and zinc oxide, especially over areas such as the armpits and the groin to avoid prickly heat and infections.
The writer is a family physician.
Quick tips
Reduce the heat within the house with the use of air conditioners or insulation of ceilings.
Wear light coloured clothes made of pure cotton.
Place wet cloth on face and neck while driving a two-wheeler during the day.
Maintain a high fluid intake. Use buttermilk and curds to combat heat.
Wash the body regularly and do not rub dry. Just mop off the excess water.
Use powder in areas like armpits and groin to avoid prickly heat and fungal infections.
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