Heat related illness

Excessive heat and humidity are the norm for summers in Central Virginia.  Already we have experienced several days with heat indices over 100 degrees.  While most of us will fare just fine, taking shelter in air-conditioned homes and work places, the temperature and humidity affect susceptible others to a host of heat-related illness.
The body’s temperature regulation system is complex and finely-tuned.  It keeps the normal core body temperature within just tenths of degrees around 98o F.  The hypothalamus and spinal cord are the brain’s main temperature regulators.  Peripheral structures in the skin, blood vessels, and other key organs contribute input and output as well.

When the temperature around us starts to heat up, our bodies begin to gain heat.  This happens through the processes of convection (gaining heat from contact with hot air) and radiation (gaining heat without direct contact, for example – the sun’s rays).  In response to the heat, the body naturally tries to get rid of excess heat mainly through the skin.  Blood vessels in the skin will dilate to move more blood closer to the skin, allowing heat loss through it.   

This heat loss process is facilitated by wearing lighter or less clothing and through perspiration.  Perspiration, or sweating, can greatly increase the amount of heat the body loses through evaporation on hot temperatured days.  However, when the air is very humid, the perspiration doesn’t evaporate as readily and it is more difficult to lose the heat.

So, on summer days when the heat index suddenly goes above 95o F, it is difficult for our bodies to stay cool through these natural processes.  On the flip side, a healthy body can adapt to the high heat stress if given adequate time and gradual exposure.    

Children are more prone to heat related stress because they have a greater surface area to body mass ratio.  This allows the environment to transfer more heat to their bodies more rapidly.  In addition, they have slower sweat rates, are slower to acclimate to heat, and have less of a thirst response when hot.

Elderly individuals are also more prone to heat due to chronic medical conditions (heart and kidney disease), diminished body fluid volume, lower overall fitness, and they are generally on more medications that can affect temperature control.  Young, healthy athletes, military personnel and individuals who work out in the heat are also prone to heat related illness if they are not allowed to slowly adapt to the condition changes.

Heat-related illness can range from milder heat cramps, to more severe exhaustion, and finally heat stroke.  Heat cramps develop due to dehydration and the loss of electrolytes such as sodium.  Treatment consists of hydration, rest and stretching the affected muscle groups.  

Symptoms of heat exhaustion include headache, weakness, dizziness, nausea, vomiting, loss of coordination and irritability, but normal mental abilities.  Excess clothing should be removed and the person should be moved to a cool, shaded environment.  Lying down with the legs elevated is beneficial and fluids are given to rehydrate.  
Heat stroke is a true emergency when the individual’s core body temperature reaches 104o F or greater.  At these temperatures, the brain and other vital organs can be damaged.  The person should be transported to a medical facility for rapid cooling and hydration.  

The content in this column is for informational purposes only.  Consult your physician for appropriate individual treatment.  Dr. Reynolds practices Family Medicine in Chesterfield.     

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