1. Copyright © 2006 by Elsevier, Inc. Determinants of Diffusion Rate of Diffusion = (P 1 -P 2 ) * Area * Solubility Distance * MW Pressure Gradient Area Distance Solubility and MW are fixed

2. Copyright © 2006 by Elsevier, Inc. Changes in Alveolar Gas Composition Figure 39-3; Guyton & Hall

3. Copyright © 2006 by Elsevier, Inc. Partial Pressure of Oxygen in Alveoli Figure 39-4: Guyton & Hall

4. Copyright © 2006 by Elsevier, Inc. Partial Pressure of CO 2 in Alveoli Figure 39-5; Guyton & Hall

5. Copyright © 2006 by Elsevier, Inc. Alveolar and Blood Gases P O 2 = 100 P CO 2 = 40 P CO 2 = 45 P O 2 = 40 P O 2 = 100 P O 2 = 159 P CO 2 = 0 PO2 = 149 PCO2 = 0

6. Copyright © 2006 by Elsevier, Inc. Diffusion Capacity Oxygen Diff capacity 21 ml/min/mmHg * gradient of 11 mmHg 230 ml/min diffusion of oxygen 0 20 40 60 80 100 120 00.250.50.75 Pulmonary Capillary Length % Po 2 in blood

7. Copyright © 2006 by Elsevier, Inc. Diffusion Capacity Carbon Dioxide –Diff capacity 400 ml/min/mm Hg * gradient < 1 mmHg –200 ml/min diffusion of carbon dioxide 40 41 42 43 44 45 46 0 0.20.40.60.8 Pulmonary Capillary Length % blood Pco 2

8. Copyright © 2006 by Elsevier, Inc. Ventilation/Perfusion Relationship between adequate flow and adequate ventilation Defined as V/Q V/Q = (4 L/min)/ (5 L/min) = 0.8

9. Copyright © 2006 by Elsevier, Inc. Ventilation/Perfusion pO 2 =? pCO 2 =? pO 2 =? pCO 2 =? pO 2 =? pCO 2 =? Shunt Normal Dead space V/Q = 0 V/Q =  Figure 39-11; Guyton & Hall

10. Copyright © 2006 by Elsevier, Inc. Regional Gas Exchange Va/Q Bottom lung Top lung blood flow ventilation Blood flow and ventilation are not evenly matched

11. Copyright © 2006 by Elsevier, Inc. Ventilation/Perfusion Physiologic shunt –Va/Q < normal –low ventilation Physiologic dead space –Va/Q > normal –wasted ventilation Abnormalities –Upper lung Va/Q ~ 2.5 –Lower lung Va/Q ~.5