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Heat exhaustion, and the more serious heat stroke (hyperpyrexia), is caused by a breakdown of the heat regulation system, for example from constant heat stress (day and night), insufficient physical fitness, being overweight, alcohol stress, too much physical stress, overly warm clothing, medications (e.g. "water pills"), infections and insufficient fluid intake. Sweat production diminishes and the body temperature rises to temperatures of around 39-41°C. The skin becomes dry and red; severe headaches occur.
The Body's Heat Regulation Mechanisms. Because the body must maintain a relatively constant body temperature of around 37°C, it needs to be able to eliminate excess heat. Most of the heat is conducted in the blood stream to the skin and then the heat is released in three ways: - Evaporation, in which excess heat is transferred to sweat which is then evaporated. Evaporation causes heat loss, but evaporation does not take place so easily in high humidity. So, on a hot, humid day, you can be dripping with sweat, but because the sweat is not evaporating it is not doing you any good.
- Radiation, in which excess heat is carried by means of electromagnetic radiation to cooler objects around the body. Blood vessels near to the skin dilate to provide a greater surface area. However, where the temperature of the surrounding air approaches body temperature (37°C), this will not have much effect.
- Convection, in which excess heat it transferred to air passing over the skin, particularly if it is windy.
Profuse sweating leads to a decrease in blood volume, i.e. dehydration. You should not rely on feeling thirsty: by the time you feel thirsty you are already low on fluids. The best indicator of proper fluid levels is urine output and color - your urine should be "copious and clear". Dark urine means the body has concentrated the urine because it is low on fluids. You also lose salts when sweating.
Heat illnesses include:- Heat Cramps - caused by insufficient salt. Replace salt and fluid and stretch the affected muscle(s).
- Heat Syncope (fainting) - In an effort to increase heat loss, skin blood vessels dilate to such an extent that blood flow to the brain is reduced resulting in faintness, dizziness, headache, increased pulse rate, nausea and vomiting. Dehydration contributes significantly to this.
- Heat Exhaustion - where fluid losses from sweating and respiration are greater than fluid reserves. The lack of fluid causes the body to constrict blood vessels especially in the arms and legs (making the skin pale and clammy), have decreased urine output and make the affected person feel weak, dizzy and thirsty with possible nausea and vomiting.
- Heat Stroke - A life-threatening condition where the core body temperature rises to above 41°C. There are two types of heat stroke:
- Fluid Depleted Heat Stroke - despite fluid loss due to sweating and inadequate fluid replacement, the person continues to function.
- Fluid Intact (fast onset) Heat Stroke - heat challenge overwhelms body's active heat loss even though fluid level is sufficient. The cause is generally overexertion despite already being overheated. Signs include hot, pale skin (may be dry or wet); severe change in mental status and motor/sensory function; possible dilation and unresponsiveness of pupils to light.
Sweat not only contains substantial amounts of sodium (1gm per liter), but also modest amounts of potassium and small amounts of minerals such as iron and calcium. Although it is possible to adapt to exercising in hot environments, one can not adapt to being dehydrated. One key adaptation is that your sweat becomes more dilute (there are fewer electrolytes, including sodium, dissolved in it). The 'weaker' sweat means that more sodium is being conserved inside the body; this preserved sodium 'pulls' more water into the blood, keeping blood volume high even in the face of fairly heavy sweating. A key benefit is that the higher blood volume helps to keep heart rate fairly low during hot-weather exertion, making exercise feel less demanding and troublesome.
The extra blood volume also lessens the intense conflict which is usually set up between the muscles and skin during hot weather. The muscles selfishly want more blood because of the oxygen it contains, while the skin demands blood for cooling. The increased blood volume allows both demands to be met fairly successfully.
While your sweat glands are being stingy with sodium, your kidneys also help you adapt to the heat by holding on to water more tightly (lowering your urine output), which also boosts blood volume. You become more resistant to both overheating and steep, hot-weather-related declines in performance.
Causes & Development
Heat exhaustion is mainly a problem in hot, humid environments. Hiking in hot weather often causes fingers and hands to become swollen and puffy, so much so that it may become hard to make a fist. If one is not taking in adequate electrolytes, the imbalance in salt levels between the blood stream, the cells, and the extracellular spaces essentially results in a trapping of the water in the tissues as the sodium is lost in sweat. The same thing can happen if too much salt is being taken.
Treatment & Prevention
The only method of treatment is by cooling the afflicted person. The entire body should be laid down in the shade and packed in moist compresses. The patient should be taken as soon as possible to a hospital.
Other treatment consists of sitting or laying the affected person in the shade, elevating the feet and administering fluids slowly. Putting half a teaspoon of salt and half a teaspoon of baking soda in each liter of water helps to replace lost electrolytes, as do 'oral rehydration salts'. Cool (but not cold), wet cloths should be used to reduce body temperature; using a fan will increase cooling by evaporation.
General advice includes staying hydrated and cool. Before exercising in hot weather (best avoided though, if possible), drink half a liter of water on waking up and add some salt to your breakfast to make sure you do not start the day dehydrated or low on sodium.
During exercise, wear light clothing to allow sweating; take on plenty of water and use cold, wet cloths to stay cool. Drink and rest regularly. Sweat consists sodium, chloride, potassium, proteins and fatty acids; in order to replace what you are losing, eat salty snacks and foods high in sodium and potassium.
After exercise, continue drinking regularly for the rest of the day to replace lost fluids.
Prognosis
Left untreated, this condition brings on a limitation of brain function, cramp attacks and finally coma. The fatality rate for severe hyperpyrexia is 20%.
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Signs, symptoms & indicators of Heat Exhaustion:
Recommendations and treatments for Heat Exhaustion: | | | | | Mineral |  Increased Salt Consumption | Most commerical sports drinks have modest sodium content in order to make them more palatable. A person exercising in heat needs as much as 2gm of sodium per liter for proper recovery - which would make sports drinks taste like seawater (there is about 0.5gm of sodium per liter of Gatorade). Drinking large amounts of plain water is not ideal in itself because it shuts off the sense of thirst and produces more urine which results in further fluid loss even though you are dehydrated.
You can increase your sodium intake by eating sodium-containing foods. Some people believe that table salt (sodium chloride, NaCl) is not a good way to get your sodium (note that there is 1gm of sodium in every 2.5gm of table salt), but others say that it is necessary. |
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Nutrient |
 Essential Fatty Acids |
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Preventive measures against Heat Exhaustion: | | | | | Environmental | Change In Clothing Habits| | Clothing should be made of a lightweight, breathable material so that sweat can evaporate. 100% cotton is a poor choice on hot days, since cotton holds large amounts of sweat, not allowing it to evaporate. The color of clothing is another consideration: white- or light-colored clothing is best because things that are white reflect all wavelengths of light (and associated heat) i.e. heat radiated from the sun. |
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KEY | | Weak or unproven link | | | Likely to help | | | Highly recommended |
GLOSSARY
Calcium
The body's most abundant mineral. Its primary function is to help build and maintain bones and teeth. The body also needs calcium to carry nerve signals, keep the heart functioning, contract muscles, clot blood and maintain healthy skin. Calcium helps control blood acid-alkaline balance, plays a role in cell division, muscle growth and iron utilization, activates certain enzymes, and helps transport nutrients through cell membranes. Calcium also forms a cellular cement called ground substance that helps hold cells and tissues together.
Cramp (Cramping, Cramps)
A sudden, involuntary, painful muscular contraction.
Electrolyte (Electrolytes)
An element or compound that, when melted or dissolved in water or other solvent, breaks up into ions and is able to carry an electric current.
Fatty Acids (Fatty Acid)
Chemical chains of carbon, hydrogen, and oxygen atoms that are part of a fat (lipid) and are the major component of triglycerides. Depending on the number and arrangement of these atoms, fatty acids are classified as either saturated, polyunsaturated, or monounsaturated. They are nutritional substances found in nature which include cholesterol, prostaglandins, and stearic, palmitic, linoleic, linolenic, eicosapentanoic (EPA), and decohexanoic acids. Important nutritional lipids include lecithin, choline, gamma-linoleic acid, and inositol.
Gland (Glands)
The glandular system is one of the most important and complicated systems of the body. Gland tissue can be either an organ or general tissue that secretes chemicals and there are two types of gland: exocrine and endocrine. Those glands which secrete chemicals through tubules or ducts are called exocrine and include sweat, tear and salivary glands. Ductless glands - part of the endocrine system - secrete special chemicals (hormones) directly into the blood.
Gram (gm, gms, Gramme, Grammes, Grams)
A metric unit of weight, there being approximately 28 grams in one ounce.
Iron
An essential mineral. Prevents anemia: as a constituent of hemoglobin, transports oxygen throughout the body. Virtually all of the oxygen used by cells in the life process are brought to the cells by the hemoglobin of red blood cells. Iron is a small but most vital, component of the hemoglobin in 20,000 billion red blood cells, of which 115 million are formed every minute. Heme iron (from meat) is absorbed 10 times more readily than the ferrous or ferric form.
Liter (Liters, Litre, Litres)
A metric measure of volume equivalent to 1.057 liquid quarts or 0.2642 gallons.
Mineral (Minerals)
Plays a vital role in regulating many body functions. They act as catalysts in nerve response, muscle contraction and the metabolism of nutrients in foods. They regulate electrolyte balance and hormonal production, and they strengthen skeletal structures.
Nausea
Symptoms resulting from an inclination to vomit.
Potassium
A mineral that serves as an electrolyte and is involved in the balance of fluid within the body. Our bodies contain more than twice as much potassium as sodium (typically 9oz versus 4oz). About 98% of total body potassium is inside our cells. Potassium is the principal cation (positive ion) of the fluid within cells and is important in controlling the activity of the heart, muscles, nervous system and just about every cell in the body. Potassium regulates the water balance and acid-base balance in the blood and tissues. Evidence is showing that potassium is also involved in bone calcification. Potassium is a cofactor in many reactions, especially those involving energy production and muscle building.
Protein (Proteins)
Compounds composed of hydrogen, oxygen, and nitrogen present in the body and in foods that form complex combinations of amino acids. Protein is essential for life and is used for growth and repair. Foods that supply the body with protein include animal products, grains, legumes, and vegetables. Proteins from animal sources contain the essential amino acids. Proteins are changed to amino acids in the body.
Sodium
An essential mineral that our bodies regulate and conserve. Excess sodium retention increases the fluid volume (edema) and low sodium leads to less fluid and relative dehydration. The adult body averages a total content of over 100 grams of sodium, of which a surprising one-third is in bone. A small amount of sodium does get into cell interiors, but this represents only about ten percent of the body content. The remaining 57 percent or so of the body sodium content is in the fluid immediately surrounding the cells, where it is the major cation (positive ion). The role of sodium in the extracellular fluid is maintaining osmotic equilibrium (the proper difference in ions dissolved in the fluids inside and outside the cell) and extracellular fluid volume. Sodium is also involved in nerve impulse transmission, muscle tone and nutrient transport. All of these functions are interrelated with potassium.
Stroke (Stroke-Type Event)
A sudden loss of brain function caused by a blockage or rupture of a blood vessel that supplies the brain, characterized by loss of muscular control, complete or partial loss of sensation or consciousness, dizziness, slurred speech, or other symptoms that vary with the extent and severity of the damage to the brain. The most common manifestation is some degree of paralysis, but small strokes may occur without symptoms. Usually caused by arteriosclerosis, it often results in brain damage.
Teaspoon (Teaspoons, tsp)
Equivalent to 5cc (5ml).
Last updated: Aug 25, 2008
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