What is the minimum amount of time that blood must take for pulmonary capillary transit for equilibration of O2 to occur across the alveolar-capillary membrane?
a. 0.15 sec
b. 0.25 sec
c. 0.35 sec
d. 0.45 sec
ANS: B
If blood flow increases, such as during heavy exercise, capillary transit time can decrease to as low as 0.25 sec. Even this short timeframe is adequate to ensure that equilibration takes place, as long as no other factors impair diffusion. However, in the presence of a diffusion limitation, rap-id blood flow through the pulmonary circulation can result in inadequate oxygenation.
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