how hot can the body get?

Monday, April 16, 2012

The Boston Marathon is known for Heartbreak Hill, a climb late in the race where dreams are won or lost. This year, the race was decided the night before by the weatherman. Unseasonably warm weather put runners in danger of heat exhaustion and race organizers gave them the opportunity to sit this marathon out and try again next year. It’s not an easy decision to make. Runners have to qualify to enter Boston, they have dedicated months to training and then there is the expense and travel for those who have come from around the world to enjoy the experience of running 26.2 miles. But race officials did not want to replay the 2007 Chicago Marathon where hundreds of people were sickened by the heat, water was in short supply and the race was shut down.

The body generates significant amounts of heat with exercise and without the ability to cool itself, bad things can happen. Heat related illness described a spectrum of symptoms that begin with heart cramps that can progress to heat exhaustion with weakness, nausea and vomiting and finally ending up with heat stroke, a lethal situation where temperatures can spike and the victim becomes confused, the victim lapses into coma and potentially dies.

The body cools itself by sweating. Evaporation dissipates heat and for that to happen, three conditions need to be present. The body has to have enough water to make sweat. The air surrounding the body needs to have room to accept the sweat and there needs to be some air movement to help that sweat evaporate. Heat becomes an issue when the body dehydrates and there is no sweat production. Humidity is an issue if it is so high that there is no place for the sweat to go. Still air makes evaporation more difficult and it’s why ceilings fans work to cool a room.

The body has the ability to acclimate to heat but it takes about 10 days for that to happen. Exceedingly warm days early in the spring present a problem to athletes and construction workers where if the same temperature happened in the middle of the summer, it would be less of an issue. As it turns out, it’s all about the math.

• The average body at rest produces 100 kcal of heat per hour but with strenuous activity that can increase 10 fold to 1,000 kcal per hour.
• A non-acclimated person can dissipate about 580 kcal of heat per hour, plenty to take care of routine activity but not exercise or work in the heat of the day.
• An acclimated person can dissipate 1740 kcal of heat per hour, three times more.

Hydration is another important consideration. When the body is hot, it tries to cool itself and can manufacture 2-3 liters of sweat per hour, or about 4- 6 pounds of water that can be lost trying to cool the body.

It makes sense that the mainstays of treatment for heat exhaustion begin with stopping activity, removing the victim from the hot environment and beginning rehydration. Most patients with heat cramps and heat exhaustion do well but may need intravenous fluids because nausea and vomiting get in the way of being able to drink enough fluids to get the body back to normal.

Heat stroke is a different matter completely, since there is a high mortality when the cooling system of the body breaks down completely. Instead of sweaty skin, there is no sweat left to be made and the skin is hot and dry. Temperature regulation is completely lost in the body with fever spikes greater than 106°F. The diagnosis maker is the change in mental status of the patient. They may be confused, lethargic or unarousable, in coma. Heat stroke is a disaster and is often deadly.

Boston got it right this year, warning runners of the dangers of participating and giving incentives for them to walk away. 4,700 people chose not to run, but more than 22,000 toed the starting line. The runners paid attention and ran slower and smarter. The organizers had enough water on the course and enough medical personnel to make certain that those who started were able to be monitored. And for everybody involved, the race was a success…nobody died.

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