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Mechanical ventilation gas exchange 2
This document discusses gas exchange and transport in the human body. It covers the partial pressures and concentrations of oxygen and carbon dioxide in ambient air, tracheal air, and alveolar air. It describes how these gases diffuse between the alveoli and pulmonary capillaries based on pressure gradients. Oxygen is transported in the blood both dissolved in plasma and bound to hemoglobin, while carbon dioxide is transported through dissolution, binding to hemoglobin, and as bicarbonate ions. Factors like pulmonary disease, anemia, exercise and the Bohr effect impact gas exchange and transport.
Mechanical ventilation gas exchange 2
- 1. hosam m atefp Mechanical ventilation:gas exchange Hosam m. Atef;MD SUEZ CANAL UNIVERSITY
- 2. p Concentration and PartialPressure 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 hosam m atef
- 3. hosam m atefp Ambient Air • O2 = 20.93% = ~ 159 mm Hg PO2 • CO2 = 0.03% = ~ 0.23 mm Hg PCO2 • N2 = 79.04% = ~ 600 mm Hg PN2
- 4. hosam m atefp Tracheal Air • Water vapor reduces the PO2 in the trachea about 10 mm Hg to 149 mm Hg.
- 5. hosam m atefp Alveolar Air • Alveolar air is altered by entry of CO2. • Average alveolar PO2 = 103 mm Hg
- 6. hosam m atefp 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
- 7. hosam m atefp Pressure Differential • The difference in the pressure of specific gases from the capillary blood to the alveoli dictates the direction of diffusion.
- 8. hosam m atefp Solubility • CO2 is about 25 times more soluble than O2. • CO2 and O2are both more soluble than N2.
- 9. hosam m atefp Gas Exchange • Exchange of gases between lungs and blood and gas movement at the tissue level progress passively by diffusion, depending on their pressure gradients.
- 10. hosam m atefp 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
- 11. hosam m atefp Pulmonary Disease • Gas transfer capacity may be impaired by – Thickening of membrane – Reduction in surface area
- 12. hosam m atefp Gas Transfer in Tissues • Pressure gradients cause diffusion of O2 into and CO2 out of tissues.
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- 14. hosam m atefp Transport of O2 in the Blood • Two mechanisms exist for O2 transport – Dissolved in plasma – Combined with hemoglobin
- 15. hosam m atefp 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
- 16. hosam m atefp Oxygen Combined with Hemoglobin • Each of four iron atoms associated with hemoglobin combines with one O2 molecule.
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- 18. hosam m atefp 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.
- 19. hosam m atefp 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.
- 20. hosam m atefp 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%
- 21. hosam m atefp PO2 in the Lungs • Hb ~ 98% saturated under normal conditions • Increased PO2 doesn’t increase saturation.
- 22. hosam m atefp 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.
- 23. hosam m atefp 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. v v
- 24. hosam m atefp Bohr Effect • Conditions creating the Bohr effect – Increased PCO2 – Increased temperature – Increased 2,3-DPG – Decreased pH • Shift to the right of the oxyhemoglobin curve
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- 27. hosam m atefp 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 O to tissues
- 28. hosam m atefp 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.
- 29. hosam m atefp CO2 Transport • Three mechanisms – Bound to Hb – Dissolved in plasma – Plasma bicarbonate
- 30. hosam m atefp CO2 in Physical Solution • ~ 5% CO2 is transported as dissolved CO2. • The dissolved CO2 establishes the PCO2of the blood.
- 31. hosam m atefp 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.
- 32. hosam m atefp 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.
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