Gas Exchange and Transport

1. Gas Exchange and Transport McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

2. Concentration and Partial Pressure of Respired Gases • Partial pressure = Percentage of concentration of specific gas × Total pressure of a gas • Dalton’s law • Total pressure = Sum of partial pressure of all gases in a mixture McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

3. Ambient Air • O2 = 20.93% = ~ 159 mm Hg PO2 • CO2 = 0.03% = ~ 0.23 mm Hg PCO2 • N2 = 79.04% = ~ 600 mm Hg PN2 McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

4. Tracheal Air • Water vapor reduces the PO2 in the trachea about 10 mm Hg to 149 mm Hg. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

5. Alveolar Air • Alveolar air is altered by entry of CO2. • Average alveolar PO2 = 103 mm Hg McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

6. Movement of Gas in Air and Fluids • Henry’s law • Gases diffuse from high pressure to low pressure. • Diffusion rate depends upon • Pressure differential • Solubility of the gas in the fluid McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

7. Pressure Differential • The difference in the pressure of specific gases from the capillary blood to the alveoli dictates the direction of diffusion. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

8. Solubility • CO2 is about 25 times more soluble than O2. • CO2 and O2 are both more soluble than N2. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

9. Gas Exchange in Lungs & Tissues • Exchange of gases between lungs and blood and gas movement at the tissue level progress passively by diffusion, depending on their pressure gradients. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

10. Gas Exchange in the Lungs • PO2 in alveoli ~ 100 mm Hg • PO2 in pulmonary capillaries ~ 40 mm Hg • Result: O2 moves into pulmonary capillaries • PCO2 in pulmonary capillaries ~ 46 mm Hg • Average arterial blood gases equal • PO2 100 mm Hg • PCO2 40 mm Hg McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

11. Pulmonary Disease • Gas transfer capacity may be impaired by • Thickening of membrane • Reduction in surface area McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

12. Gas Transfer in Tissues • Pressure gradients cause diffusion of O2 into and CO2 out of tissues. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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14. Transport of O2 in the Blood • Two mechanisms exist for O2 transport • Dissolved in plasma • Combined with hemoglobin McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

15. Oxygen in Physical Solution • For each 1 mm Hg increase, 0.003 mL O2 dissolves into plasma. • This results in ~ 3 mL of O2/liter blood. • With 5 L total blood volume = 15 mL dissolved O2 • Dissolved O2 establishes the PO2 of the blood. • Regulates breathing • Determines loading of hemoglobin McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

16. Oxygen Combined with Hemoglobin • Each of four iron atoms associated with hemoglobin combines with one O2 molecule. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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18. Oxygen-Carrying Capacity of Hb • Each gram of Hb combines with 1.34 mL O2. • With normal Hb levels, each dL of blood contains about 20 mL O2. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

19. Anemia Affects Oxygen Transport • Volume percent (vol%) refers to the milliliters of oxygen extracted from a 100-mL sample of whole blood. • Human blood carries O2 at 14 vol%. • Iron deficiency anemia reduces O2 carrying capacity considerably. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

20. PO2 and Hb Saturation • Oxyhemoglobin dissociation curve illustrates the saturation of Hb with oxygen at various PO2 values • Percent saturation = 12 vol% / 20 vol% × 100 = 60% McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

21. PO2 in the Lungs • Hb ~ 98% saturated under normal conditions • Increased PO2 doesn’t increase saturation. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

22. PO2 in Tissues • At rest • PO2 = 40 mm Hg • Venous blood carries ~ 70% of the O2 content of arterial blood. • Venous blood carries 15 mL O2 per dL blood. • Tissues have extracted 5 mL O2 per dL blood. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

23. Arteriovenous O2 Difference • The a- O2 difference shows the amount of O2 extracted by tissues. • During exercise a- O2 difference increases up to 3 times the resting value. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

24. Bohr Effect • Conditions creating the Bohr effect • Increased PCO2 • Increased temperature • Increased 2,3-DPG • Decreased pH • Cause a shift to the right of the oxyhemoglobin dissociation curve McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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27. RBC 2,3-DPG • 2,3-DPG is a byproduct of glycolysis/ • RBCs contain no mitochondria. • Rely on glycolysis • 2,3-DPG increases with intense exercise and may increase due to training. • Helps deliver O2 to tissues McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

28. Myoglobin, The Muscle’s O2 Store • Myoglobin is an iron-containing globular protein in skeletal and cardiac muscle. • Stores O2 intramuscularly • Myoglobin contains only 1 iron atom. • O2 is released at low PO2. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

29. CO2 Transport • Three mechanisms • Bound to Hb • Dissolved in plasma • Plasma bicarbonate McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

30. CO2 in Physical Solution • ~ 5% CO2 is transported as dissolved CO2. • The dissolved CO2 establishes the PCO2 of the blood. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

31. CO2 Transport as Bicarbonate • CO2 in solution combines with water to form carbonic acid. • Carbonic anhydrase • Zinc-containing enzyme within red blood cell • Carbonic acid ionizes into hydrogen ions and bicarbonate ions. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

32. CO2 Transport as Carbamino Compounds • CO2 reacts directly with amino acid mq to form carbamino compounds. • Haldane Effect: Hb interaction with O2 reduces its ability to combine with CO2. • This aids in releasing CO2 in the lungs. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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