Dehydration from Heat

Strenuous physical activity combined with extreme summer weather may lead to serious heat injuries. The body dissipates about 60% of heat by radiation (heat transfer to the air), 20-25% by evaporation, and about 15% by convection.

During intense physical activity, core body temperature might increase by one degree of Centigrade every 5 minutes–this could result in heat stroke within 15-20 minutes of the start of exercise if precautions are not taken.

Heat illness ranges from mild heat cramps to fatal heat stroke. With repeated exposure to heat, the body acclimatizes. However, it is important to remember that children do not have the same ability to tolerate heat stress as adults, so prevention is very important.

Heat cramps are the most common heat injury. They most often affect the calf and hamstring muscles. The best treatment for heat cramps is an electrolyte solution, such as Gatorade.

Heat-Related Fainting and Passing out after exercising on a hot day is caused by dehydration and poor vasomotor tone. This condition improves after lying down to cool off and hydrating with an electrolyte solution.

Before the body has a chance to get used to hot weather, the initial exposure to heat may result in a slight swelling of hands and feet. This condition resolves as the body gets used to the temperature.

When the respiratory rate increases in response to overheating, a person might experience tingling in the hands and feet. Moving to a cooler environment and decreasing the respiratory rate resolves these symptoms.

Moderate heat injury is characterized by body temperature of 99-104.

Heat Exhaustion is manifested as a headache, nausea and vomiting, weakness, goose bumps and passing out. Heat injury and/or heart disease should be considered in any athlete who faints during exercise.

Treatment of heat exhaustion includes moving to a cool environment, cooling the body with fans, removing excess clothing, placing ice over the neck, groin, and underneath the armpits. Fluids, like Gatorade should be offered. If an individual cannot tolerate oral fluids, IV fluids are indicated. The person should be closely monitored for signs of heat stroke.

Heat stroke occurs when body temperature exceeds 104F and there is alteration of one’s mental status. It is a medical emergency! The mortality rate from a heat stroke is 50%.

Heat stroke with dry, hot skin is common in elderly and chronically ill persons exposed to hot weather over time. On the other hand, sports-related heat stroke is caused by excessive sweating and extreme exertion, and has a quick onset.

Exertion during hot weather puts athletes at an increased risk for dehydration. When the blood volume decreases because of dehydration, blood vessels constrict in an attempt to maintain a normal blood pressure.

This vasoconstriction impedes body’s ability to dissipate heat. The “trapped” heat leads to low blood pressure, as well as swelling of the lungs and brain. These symptoms constitute a medical emergency. If they are not promptly reversed, death results.

The most important step in preventing heat illness is to hydrate before, during, and after physical activity. Dehydration is common in all heat illnesses. Mild dehydration (2%) can decrease athletic performance as well as decrease the body’s ability to regulate temperature. Thirst in not a good indicator of dehydration, because it is activated when the body is already 2-3% dehydrated. You should drink 8-12 ounces of fluid before exercise, and every 20 minutes during exercise.

Water is adequate for hydration only if exercising lasts less than 1 hour. Fluids with electrolytes should be given to everybody who exercises for longer than 1 hour.

Dehydration from Heat

Cytoprotective immune responses to exercise, heat, and dehydration stresses in men.
by: Elaine Choung-Hee Lee
publisher: ProQuest, UMI Dissertation Publishing, published: 2011-09-04
ASIN: 1243634421
EAN: 9781243634429
price: $69.00 (new), $77.70 (used)

In response to stress, hsp70 (heat shock protein 70) has been observed to increase acutely, and remain elevated with peak expression typically around 24 hours post-stress. Additionally, cells expressing inducible hsp72 are more resilient in the face of in vitro heat shock (42°C, 1+ hr), as measured by early apoptosis marker annexin V. NFAT5 (Nuclear Factor of Activated T cells) has been shown to have a similar protective effect in response to osmolal stimuli. CD40L is, like NFAT5 a less studied protective factor, that has been investigated as a response to exercise stress in the context of cardiovascular risk. This study completed three sets of experiments examining each of these three protective proteins in up to six health, college-aged males ((mean +/- SD) age 23 +/- 4 years; body mass 82.96 +/- kg; height 175.33 +/- 9.69; running VO2max 82.96 +/- 2.88 mL·min-1·kg-1) who completed five experimental days each. Prior to experimental day, subjects began passive dehydration after noon until the next morning. On experimental day subjects submaximally exercised for two hours in the environmental chamber (35°C, 32% r.h.) to additionally dehydrate to a final value of -4–5% body mass. Subjects rested and rehydrated for 60 minutes and then completed an exercise challenge (25 minutes run at 70% VO2max, 800 m maximal sprint, 5 minutes maximal self-paced box-lifting) in the heat. This study found, according to predefined hypotheses, that intracellular hsp72, extracellular hsp70, and NFAT5 were elevated acutely with stress with acute decrease during rehydration. Values stayed elevated through 24 hours following experimental day. In response to one hour heat shock, PBMCs exhibited less annexin V expression with timepoints where hsp72 levels were concurrently higher when compared among PBMC samples collected at various timepoints. CD40L decreased acutely with stress and increased during recovery, as seen with sCD40L in other studies. Conclusive inferences from this studies are that hsp72 protects cells in response to acute stress and recovery periods, NFAT5 does so in response to hydration status, and surface CD40L appears to decrease with acute stress and increase during recovery to baseline levels.

Dehydration, Heat Injuries, and Sports Drinks [VHS]
publisher: Coaches Choice
ASIN: B0002V7PDC
EAN: 9781585180325
sales rank: 643598

Examines the temperature-related complications of exercise and the role of adequate hydration in preventing heat injuries. Covers before, during, and after exercise fluid replacement. Length 51 minutes.

Emergency Management of Heat Illness
publisher: Emergency Management of Heat Illness
ASIN: B0026XPUCM
price: $75.00 (used)

Dr. Travis Stork: How Dehydration Can Lead to Heat Stroke
Dr. Travis Stork, host of the Emmy-nominated The Doctors TV show, says one of the most common summer ailments is also the easiest to prevent. Dr. Stork, an emergency room physician at the Vanderbilt Medical Center in Nashville, is sharing simple hydration tips that can have a big impact on hot-weather health and fitness. Refresh Yourself using a Reusable Water Bottle: Keep a BPA-free, reusable water bottle at your side at all times. Some are better than others at keeping people hydrated. A water bottle study conducted at Pepperdine University and released July 8, 2009, found that people drank up to 24 percent more water with the CamelBak® Better Bottle™ than with other water bottles. The CamelBak bottle costs less than disposables over time, keeps plastic bottles out of landfills and helps you easily monitor how much water youre drinking.
Dehydration & Heat Exhaustion: Prevention, Signs & Symptoms
Dr. Curt Nyhus shares tips for avoiding dehydration and heat exhaustion.

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