Human Performance in Hot Environments

1. Human Performance in Hot Environments LT Anthony Artino Aeromedical Safety Officer COMAEWWINGPAC

2. OVERVIEW • Heat injury statistics • Physiological response to heat • Heat stress • Preventing heat stress

3. Why E-2C’s Shouldn’t Fly Low!

4. HEAT INJURY STATISTICS • Each year many people die from heat-related injuries. • Average Death Count  60 people/year  • Heat Wave Death Counts... • Summer 1980 = 1700 people • Summer 1995 = 1021 people • Sept Climate Averages for Puerto Rico… • Temp Highs = 92oF • Relative Humidity = 75% National Weather Service

5. PHYSIOLOGICAL RESPONSE TO HEAT • Vasodilation • Blood vessels on the surface of the skin dilate • Blood flow to the surface of the skin increases • Heat is dissipated to the environment via conduction, convection, radiation and/or evaporation of sweat

6. PHYSIOLOGICAL RESPONSE TO HEAT • Sweating • Evaporation of sweat is our body’s primary means of losing heat • Our body’s ability to produce enough sweat is directly related to our hydration level • Sweat production during strenuous workouts in hot environments can equal 1 quart/hour

7. HEAT STRESS • Heat stress is a general term for all heat-related disorders • Heat stress occurs when the body builds up more heat than it can handle • Influencing factors are… • High temperatures • High humidity • Heavy workloads • Dehydration

8. HEAT STRESS • Heat Rash • An early sign of potential heat stress • Associated with humid environments where skin and clothing remain damp due to unevaporated sweat • Sweating production may be compromised • Treatment includes… • Keeping skin clean and dry for at least 12 hours • Applying a mild lotion

9. HEAT STRESS • Heat Cramps • Muscle cramps caused by fluid and salt imbalance during physical exercise in a hot environment • Treatment includes… • Firm pressure or gently massaging the affected muscle • Resting in a cooler environment (shade) • Re-hydrating with water and/or sports drinks

10. HEAT STRESS • Heat Exhaustion • Basically a water volume problem in the body caused by inadequate fluid replacement and profuse sweating • Body is having difficulty maintain BP and sending blood to the skin’s surface • Symptoms may include… • Fatigue, weakness, and/or fainting • Dizziness, nausea, and/or headache • Clammy skin (may be flushed or pale)

11. HEAT STRESS • Heat Exhaustion • Treatment includes… • Moving to a cooler environment (shade) • Lying down on a flat or slight declined surface • Applying cool, moist clothes and/or fanning • Re-hydrating with water and/or sports drinks • Call a doctor, especially if victim vomits or faints

12. HEAT STRESS • Heat Stroke • Life-threatening condition of increased core body temperature (hyperthermia >105 oF) • This is a medical emergency! (coma or death) • Body’s heat-regulating mechanism is overwhelmed • Symptoms may include… • Hot skin - the key to identification!! (dry or wet) • Increased pulse and respiratory rate • Headache, dizziness, abdominal distress, mental ’s

13. HEAT STRESS • Heat Stroke • Treatment includes… • Calling 911 • Immediate active cooling of body, including… • Move patient to a cooler environment • Pouring cool water on the extremities • Wrapping in wet, cool cloths • Whole body immersion in cool (not cold) water • Re-hydrating with water and/or sports drinks • CPR if necessary

14. PREVENTING HEAT STRESS • What NOT to do • Hydration • Acclimatization • Physical Fitness • Proper Clothing “Prevention is the best medicine.”

15. PREVENTING HEAT STRESS • What NOT to do • Don’t drink sugary fluids (>10% Carbo) or carbonated beverages • Don’t drink alcohol or caffeinated beverages • Don’t damage your skin with a sunburn • Don’t overdo it

16. PREVENTING HEAT STRESS • Hydration • Staying well hydrated is your best defense against all heat stress • Urine output and color is the best indicator of proper hydration • Urination should occur often • Urine should be light colored to clear • Thirst is a poor indicator of dehydration • The thirst mechanism is slow • Once you feel thirsty, you’re already dehydrated!

17. PREVENTING HEAT STRESS • Hydration • Average person requires about 3-4 quarts of fluid per day in a hot environment • In more extreme environments, 3-4 gallons may be required • Drinking frequently in small amounts is more effective than drinking large amounts at one time

18. PREVENTING HEAT STRESS • Hydration • Sugary fluids and carbonated beverages actually decrease water absorption • Sports drinks (6-8% Carbo) may increase absorption and can improve long-term performance (taste is also an issue) • When in doubt….DRINK WATER!

19. PREVENTING HEAT STRESS • Acclimatization (to heat) • Physiological adaptations that give the body an added ability to tolerate extreme heat • Accomplished through progressive degrees of heat exposure and physical exertion • Takes approximately 3 weeks to complete • Majority of the positive changes occur within the first week

20. PREVENTING HEAT STRESS • Acclimatization (to heat) • Physiological adaptations include… • Increase sweat production (>twofold increase) • Non-acclimatized - maximum 700mL of sweat • Acclimatized - maximum 2000mL of sweat • Decreased loss of salt in sweat and urine • i.e. sweat and urine are more dilute • Retained salt helps body hold more water overall

21. PREVENTING HEAT STRESS • Physical Fitness • Tolerance to heat is increased in individuals with high aerobic fitness • Rate of acclimatization is a function of fitness • Unfit individuals take up to 50% longer to acclimate

22. PREVENTING HEAT STRESS • Proper Clothing • Loose fitting, non-starched clothing • Starch blocks fabric pores and restricts air circulation • Light clothing also protects against sun burns

23. SUMMARY • Heat injury statistics • Physiological response to heat • Heat stress • Preventing heat stress

24. RESOURCES • Centers for Disease Control and Prevention(CDC). Extreme Heat: A Prevention Guide to Promote Your Personal Health and Safety, U.S. Department of Health and Human Services, 1996. • Curtis, Rick. Outdoor Action Guide to Heat-Related Illnesses & Fluid Balance, Princeton University, 1997. • Guyton, Authur. Textbook of Medical Physiology: Body Temperature, Temperature Regulation, and Fever, W.B. Saunders Company, 1991. • Reinhart, Richard. Basic Flight Physiology: Environmental Stresses, McGraw-Hill, 1996. • Tueller, John. Prevention of Heat Stress Injuries, Navy Message, DTG 280730Z APR 99. • Zhao, Wei & Kersting, Ann. Preventing Heat Stress in Agriculture, Rutgers Cooperative Extension.