C H A P T E R 11

1. C H A P T E R 11 EXERCISE IN HYPOBARIC, HYPERBARIC, AND MICROGRAVITY ENVIRONMENTS

2. w Discover what conditions and health risks are unique to hypobaric environments (underwater). (continued) Learning Objectives w Find out how hypobaric environments (at altitude) limit or contribute to perfor- mance. w Learn the physiological adjustments that accompany acclimatization to altitude. w Discern whether an endurance athlete who trains at altitude can perform better at sea- level.

3. Learning Objectives w Learn what physiological and pathological problems face scuba divers who descend 30 m or more. w Examine what happens to muscles, bones, and blood in a microgravity environment (in space). w Find out how tissues and physiological systems change with prolonged exposure to microgravity and what countermeasures can assist an astronaut on his or her return to Earth.

4. Conditions at Altitude w Defined as at least 1,500 m (4,921 ft) above sea level w Reduced barometric pressure (hypobaric) w Reduced partial pressure of oxygen (PO2) w Reduced air temperature w Low humidity w Increase in solar radiation intensity

5. CONDITIONS AT VARIOUS ALTITUDES oC oF

6. Effects of Altitude on PO2 Gradient The reduction in PO2 at altitude decreases the partial pressure gradient between the blood and the tissues and thus lowers oxygen transport. This primarily explains the decrease in endurance sports performance at altitude. PO2 at sea level = 760 mmHg  0.2093 = 159 mmHg PO2 at 8,000 ft = 564 mmHg  0.2093 = 118 mmHg Sea Level8,000 ft Arterial PO2 100 mmHg 60 mmHg Muscle PO240 mmHg40 mmHg ΔPO2 60 mmHg 20 mmHg (diffusion gradient)

7. . w As PO2 decreases above 1600 m, VO2max decreases linearly. Acute Respiratory Responses to Altitude w Pulmonary ventilation increases because of chemoreceptor response to hypoxia (low arterial PO2) – body fluids become more alkaline from blowing off CO2. This is followed by increased excretion of bicarbonate by the kidneys. w Pulmonary oxygen diffusion decreases because of ↓ ΔPO2. w Oxygen transport is slightly impaired; reduced Hb saturation from 98% at sea level to 90-92% at 8,000 ft. w Thus, VO2max is impaired once you are above 1,600 m.

8. . CHANGES IN VO2MAX WITH ALTITUDE Denver – 5280 feet

9. . VO2MAX RELATIVE TO PO2

10. . Altitude does not affect VO2max until approximately 1,600 m (5,294 ft). Above this level, the decrease in VO2max is approximately 8-11% for every 1,000 m (3,281 ft). . Effect of Altitude on Aerobic Capacity

11. . w Initial increase in HR and Q during submaximal work to compensate for less O2; SV is decreased with plasma volume decline . w Decrease in HR, SV, and Q during maximal work, which contributes to the decrease in VO2max. Acute Cardiovascular Responses to Altitude w Initial decrease in plasma volume (more red blood cells per unit of blood, thus more oxygen per unit of blood)

12. Thought Question How would you explain the immediate drop in plasma volume that occurs when one goes to altitude?

13. Acute and Chronic Cardiovascular Responses to Altitude during Submaximal Exercise Brooks et al., Exercise Physiology, 2000

14. Metabolic Responses to Altitude w Increase in anaerobic metabolism w Increase in lactic acid production w Less lactic acid production at maximal work rates at altitude than at sea level because it isn’t possible to exercise at as high an intensity

15. Acute and Chronic Metabolic Responses to Altitude during Submaximal Exercise Brooks et al., Exercise Physiology, 2000

16. Acute and Chronic Catecholamine Responses to Altitude during Submaximal Exercise Brooks et al., Exercise Physiology, 2000

17. w Endurance athletes can prepare for competitions at altitude by performing high-intensity endurance training at any elevation to increase their VO2max. . Key Points Performance at Altitude w At altitude, endurance activity is affected the most due to the reduced oxygen transport because of low PO2. w Anaerobic sprint activities that last 2 min or less are the least affected by altitude. w The thinner air at altitude provides less aerodynamic resistance and less gravitational pull, thus potentially improving sprinting, jumping, and throwing events.

18. . w Decrease in VO2max with initial exposure does not improve much Acclimatization to Altitude w Increase in number of red blood cells (RBC) w Short term decrease in plasma volume, later reversed wIncrease in RBC, hemoglobin, and blood viscosity w Decrease in muscle fiber areas and total muscle area, therefore shorter O2 diffusion distances from capillaries to muscle fiber mitochondria w Increase in capillary density w Increase in pulmonary ventilation

19. Hb CONCENTRATIONS AT ALTITUDE College Station – 362 feet Denver – 5280 feet

20. Altitude Training for Sea-Level Performance w Increased red blood cell mass w Not proven that altitude training improves sea-level performance w Difficult to study since intensity and volume are reduced at altitude – thus, what you gain in elevated RBC, you lose because of reductions in training intensity w Live at high altitude and train at lower altitudes—living high/training low

21. LIVING HIGH, TRAINING LOW 3,000 km time was tested at sea level before and after 27 days of training at 4,100 ft. and living at 8,200 ft. The mean increase in 3,000 km time was 1.1%, and the mean increase in VO2max was 3.2%.

22. . w Increase VO2max at sea level to be able to compete at a lower relative intensity while at altitude Training for Optimal Altitude Performance w Compete within 24 hours of arrival to altitude w Train at 1,500 to 3,000 m above sea level for at least 2 weeks before competing

23. Acute Altitude Sickness w Nausea, vomiting, dyspnea, insomnia w Appears 6 to 96 h after arrival at altitude w May result from carbon dioxide accumulation w Avoid by ascending no more than 300 m (984 ft) per day above 3,000 m (9,843 ft)

24. High-Altitude Pulmonary Edema (HAPE) w Shortness of breath, excessive fatigue, blue lips and fingernails, mental confusion w Occurs after rapid ascent above 2,700 m (8,858 ft) w Accumulation of fluid in the lungs which interferes with air movement w Cause unknown w Administer supplemental oxygen and move to lower altitude

25. High-Altitude Cerebral Edema (HACE) w Mental confusion, progressing to coma and death w Most cases occur above 4,300 m (14,108 ft) w Accumulation of fluid in cranial cavity w Cause unknown w Administer supplemental oxygen and move to lower altitude

26. Exercise in a Hyperbaric Environment Pressure underwater is greater than at sea level, i.e., a hyperbaric environment. As pressure increases, gas volume decreases (Boyles’ Law). w Descent—external pressure increases and air already in the body compresses. • Ascent—air taken in at depth expands. If breath is held while ascending, lungs may overdistend leading to spontaneous pneumothorax (lungs collapse) Medical Problems: • Barotrauma – tissue injury caused by changing pressure • Gas toxicity – CO, O2, CO2 • Decompression sickness – N2 bubble formation during ascent

27. WATER DEPTH AND AIR VOLUME

28. Cardiovascular Responses to Immersion w Cardiovascular workload decreases w Plasma volume increases w Heart rate decreases (even more in cold water) w At a given exercise effort, heart rate is lower

29. OXYGEN UPTAKE AND HEART RATE

30. Ventilation during Diving Maximal expiratory flow rate Brooks et al., Exercise Physiology, 2000

31. VO2 during Diving VO2 during swimming at 30 m/min at increasing depths Brooks et al., Exercise Physiology, 2000

32. Key Points Breath-Hold Diving w Urge to breathe is due to build-up of arterial CO2. w Gases in lungs can reduce to no smaller than residual volume. w Depth limit is determined by the TLV:RV ratio. w Individuals with larger TLV:RV ratios can dive deeper than those with smaller ratios.

33. w Scuba equipment includes: – Tank(s) of highly compressed air, – First-stage regulator valve to reduce air pressure for breathing, – Second-stage regulator that releases air at pressure equal to the water, and – One-way breathing valve. Key Points Scuba Diving w A self-contained underwater breathing apparatus (scuba) pressurizes the air breathed underwater. w The length of a dive depends on the diver's depth.

34. OPEN-CIRCUIT-DEMAND SCUBA GEAR

35. Depth Total pressure PO2 PN2 (m) (mmHg) (mmHg) (mmHg) 0 760 159 600 10 1,520 318 1,201 20 2,280 477 1,802 30 3,040 636 2,402 Effects of Water Depth on the Partial Pressure of Inspired Oxygen (PO2) and Nitrogen (PN2)

36. PNEUMOTHORAX AND EMBOLI FORMATION

37. HEALTH RISKS OF HYPERBARIC CONDITIONS

38. Oxygen Toxicity (Poisoning) w PO2 values exceed 318 mmHg w Visual distortion, rapid and shallow breathing, and convulsions w Tissues are not able to remove O2 from hemoglobin w Hemoglobin is then not able to remove CO2 w High PO2 causes vasoconstriction to cerebral vessels

39. Decompression Sickness w Results from ascending too rapidly w Aching in elbows, shoulders, and knees, can cause emboli in blood w Nitrogen bubbles become trapped in body w Treat by placing diver in recompression chamber w Prevent by using chart showing time to ascend from various depths

40. DECOMPRESSION DURING DIVING

41. Hyperbaric (Recompression) Chamber

42. Saturation Diving The Navy uses a technique called saturation diving to enable divers to stay at great depths for long periods of time. At a given depth, the amount of nitrogen that can dissolve in the body tissues is limited. By staying in a pressurized environment for 24 hours, the body tissues become saturated, after which the tissues do not absorb any more inactive gas for as long as the diver stays at that depth.

43. Nitrogen Narcosis w Nitrogen acts like anaesthetic gas (N2O – “laughing gas”) w Similar to alcohol intoxication w Depth and pressure increases worsen it w Also called rapture of the deep

44. Microgravity Environments w 1 g is the standard acceleration produced by gravity. w Microgravity describes conditions where gravitational force is less than 1 g. w Microgravity is used to describe conditions in space that aren't always 0 g. wThe effects of microgravity on the body are similar to the effects of detraining and aging.

45. Physiological Alterations from Microgravity w Muscle atrophies and strength decreases w Cross-sectional areas of ST and FT fibers decrease wBone mineral content in weight-bearing bones decreases* w Plasma volume decreases w Transient cardiac output and arterial blood pressure increases • Weight decreases (nearly 50% from fluid loss) • Orthostatic stress upon return to earth: failure to maintain blood pressure because of pooling of blood in the legs

46. Effects on Skeletal Muscle of Bed Rest Versus Space Flight Changes in cross-sectional area in fibers after 30 days of bed rest

47. Bone Mineral Changes in Cosmonauts during Spaceflight Bone mineral changes in the radius, a non-weight-bearing bone

48. Bone Mineral Changes in Cosmonauts during Spaceflight Bone mineral changes in the tibia, a weight-bearing bone

49. . MICROGRAVITY AND VO2MAX 3 astronauts in Skylab 4 – increased because they actually increased their exercise training while in space

50. Exercise as a Countermeasure to Detrimental Effects of Space Travel Research shows that exercise during space-flight may be an effective countermeasure to prepare astronauts for successful adaptation on return to earth. The type and amount of exercise that produces the best results is still under debate. Because of this, a number of exercise physiologists are leaders in NASA-related research into countermeasures to the deterioration that occurs during space travel. Example is Dr. Sue Bloomfield and in our department.