Chapter 1 7 Environmental Physiology

1. Chapter 17 Environmental Physiology

2. Section I: Exercise When Exposed to Altered Pressure Exercise at Increased Altitude As altitude increases, there is a decrease in pressure. This reduced pressure causes air molecules to be more dispersed. Thus, for a given air volume, even though the relative presence (gas fraction) of a gas remains the same, there is less of a given gas. For example, Sea level PO2 in air = 760 mmHg x 0.2093 = 159 mmHg At Pikes Peak, CO (4,000 m or 14,300 ft) PO2 in air = 430 mmHg x 0.2093 = 90 mmHg

3. Altitude (ft) Altitude (m)

4. meters feetPressure (Torr)PIO2 (Torr) PAO2 (Torr)SaO2 (%) 1 Torr = 1 mmHg ; 1 m = 3.28 ft ; PB = 760 [e-(m/7924)] ; PIO2 = (PB - 47) x 0.2093 ; PAO2 ~ (PB - 47) x 0.146 ; SaO2 approximated from %O2-Hb dissociation curve

5. At rest During steady state exercise At VO2max ACUTE CHRONIC Blood lactate Ventilation Plasma volume Blood volume a-vO2 Stroke volume Heart rate Cardiac output VO2 Percent change (%) Percent change (%)

6. Decreases in VO2max During Acute Hypoxic Exposure -9.2%/1,000 m > 1,500 m 1,500 m ~ 5,000 ft

7. sea level 3,000 m 4,000 m Is this difference a beneficial or detrimental adaptation? Unacclimatized Acclimatized

8. Does living at altitude improve exercise tolerance at altitude? • Yes, • VO2max decrement is not as large • Ventilation is higher • Maximal blood lactate is lower • AMS symptoms are less severe Does training at altitude improve exercise tolerance at sea level? ??? This question has not adequately been answered. However, there are recent findings that may indicate a benefit of sleeping at altitude (> 7,000 ft) and training at low-moderate altitude (< 7,000 ft).

9. Exercise During Hyperbaria Hyperbaria refers to exposure to increased pressure above 1 atmosphere (atm = 760 mmHg). For example; When submerged in sea water, pressure increases by 1 atm every 10 m. In fresh water, the pressure change is not as great and approximates 10.4 m. • Physiological changes associated with hyperbaria include, • cutaneous blood flow • central blood volume and venous return •  heart rate • diuresis • VO2

10. O2 CO2 O2 CO2

11. Section II: Exercise And Thermal Stress Dehydration - decrease in total body water. Occurs at a faster rate during exercise in hot and/or humid environments for example, sweat rates can to 2-3 L/Hr Deleterious effects of dehydration on exercise occur with as little as fluid loss equal to 2% body weight. For a 70 kg male; 70 x 0.02 = 1.4 kg ~ 1.4 L This could occur with as little as 30 min of exercise!!!! Hyperthermia - increased body temperature resulting from body heat storage

14. Physiological changes during dehydration • Core temperature • Plasma volume • Venous return • Stroke volume • Heart rate • Cardiac output • a-vO2 • Skin blood flow • Catecholamines •  Blood lactate •  VO2 • CNS dysfunction • Exercise tolerance • Sweat rate • Evaporative cooling

15. Improving Exercise Tolerance During Heat Exposure • Fluid intake (pre-during and post-exercise) • Do not rely on thirst mechanism • Complete heat acclimation or acclimatization Acclimation - chronic adaptations induced by exposure to artificial environmental conditions (eg. environmental chambers, sauna, exercise) Acclimatization - chronic adaptations induced by exposure to foreign a foreign climat (eg. geographical relocation)

16. Chronic adaptations to exercise and exercise in a hot environment that improve acclimation to exercise in the heat

17. Heat Illness, Heat Exhaustion and Heat Stroke These conditions are more severe clinical manifestations of heat exposure. Heat Exhaustion - the decreased cardiovascular function that accompanies dehydration and mild hyperthermia Heat Stroke - when heat stress continues, or is worsened beyond that of heat exhaustion (core temp > 39.5 C), physiological symptoms progress to CNS dysfunction - disorientation, confusion, psychoses Heat exhaustion and heat stroke are both heat illnesses. However, heat stroke can be potentially lethal due potential organ damage and failure.

18. Evaluating Environmental Conditions For Risk of Heat Injury An index has been developed that incorporates all contributors to thermal heat stress - Wet Bulb Globe Index (WBGI) Dry bulb temperature - measure of air temperature Black bulb temperature - measure of the potential for radiative heat gain Wet bulb temperature - measure of the potential for evaporative cooling WBGI = (0.7 x Tw) + (0.2 x Tb) + (0.1 x Td)

19. The relative risks for heat injury at different ranges of the WBGI

20. Cold Exposure

21. Section III: Human Function and Performance During Gravitational Challenge Microgravity The early space programs of the USA and Russia revealed that prolonged exposure to microgravity was detrimental to human physiology. The earth has a reference gravitational force = 1 g The moon’s gravitational force = 0.17g Outside a planetary orbit (eg. Space Shuttle), gravitatonal force = 0g Research models that have been used to mimic physiological responses to microgravity are, head-down bed rest lower body negative pressure tilt testing

22. Physiological Effects of Exposure to Microgravity • Muscle atrophy • Bone mineral • Muscle enzymes • Blood volume •  Diuresis •  Heart rate • Stroke volume • Compromised regulation of peripheral blood vessels and vascular resistance

23. Section IV: Exercise And Air Pollution