54. ALVEOLAR-CAPILLARY DIFFUSION: MAN 



Part I: PULMONARY CAPILLARY O2 PRESSURE 



Mixed venous blood enters the pulmonary capillaries with p02 of 40 mm Hg. Blood normally requires about 0.7 5 

 seconds to pass through the capillaries, at the end of which time its p02 has risen to almost 100 mm Hg. The p02 

 of arterial blood is lower because of venous-to-arterial shunts. 



p02 mm Hg 

 100 



80 — 



Alveolar p02 



60 — 



40 -1 



I Pulm. 

 ^^ ~ Artery 



Pulm. 

 Veins 



Systemic 

 Arteries 



0.15 



0.30 



0.45 



0.60 



0.75 



I -^ Time (sec) in pulm. capillaries — 



Reference : Comroe, J. H., Jr., Forster, R. E.. 11, DuBois, A. B., Briscoe, W. A., and Carlsen, E., "The Lung, 

 Chicago: The Year Book Publishers, Inc., 1956. 



Part II: END- AND MEAN CAPILLARY O2 PRESSURE 



The graphic and tabular presentation illustrates different rates at which venous blood may be oxygenated in pulmo- 

 nary capillaries, depending upon the diffusing capacity of the lung. Alveolar p02 in each case is 100 mm Hg. 



p02 mm Hg 

 100 



80 — 



Alveolar p02 



60 



40 



0.15 0.30 0.45 0.60 0.75 



Time (sec) in pulm. capillaries — 



Reference : Comroe, J. H., Jr., Forster, R. E., II, DuBois, A. B., Briscoe, W. A., and Carlsen, E., "The Lung, 

 Chicago: The Year Book Publishers, Inc., 1956. 



53 



