In: Anatomy and Physiology
If the pulmonary capillary partial pressure of a gas equilibrates with that in the alveolus before the blood leaves the capillary (gas diffusing from the alveolar space to the capillary):
a. its transfer is said to be perfusion limited
b. its transfer is said to be diffusion limited
c. increasing the cardiac output will not increase the amount of of gas diffusing across the alveolar-capillary barrier
d. increasing the alveolar partial pressure of the gas will not increase the amount of the gas diffusing across the alveolar-capillary barrier
e. None of the above
Ans:- a). its transfer is said to be perfusion limited.
Because as partial press of gas becomes equal in alveoli and pulmonary capillary before leaving the alveoli, that means pressure gradient of gas is not a limiting factor i.e diffusion is not a limiting factor . To increase the gas transport rate of perfusion of gas must be increased.
Hence there is perfusion limited transfer.
For eg if 5 works can load coal in a train fully before next cartage comes. And if the workers are very effective. Then to increase the rate of coal transport u will have to increase the speed of coming cartage in which coal is being filled.
In diffusion-limited gas exchange, the gas will diffuse as long as the partial pressure gradient is maintained. In perfusion-limited gas exchange, the partial pressure gradient is not maintained and blood flow must be increased in order to increase the amount of gas transported.
Option c) is wrong because if cardiac out put will increase then rate of perfusion is also increased and gas exchange will also increase.