The surface area of the lungs is about 75 m2, and the thickness of the alveolar

Question

The surface area of the lungs is about 75 m2, and the thickness of the alveolar diffusion layer is about 0.5 micrometers. The P02 in alveolar air is 100 mmHg, while the Po2 of venous blood is 40 mmHg. The diffusion coefficient of O2 in water is about 1.5x10-5 cm2s-1. The solubility of O2 is given by Henry's law as [O2]= 0.024 P02 ; here [O2] is expressed in ml O2 at STPD per ml of water and P02 is in atmospheres. Only the dissolved O2 diffuses. What is the initial rate of O2 diffusion from the aggregate alveoli to the blood?

Explanation / Answer

To measure diffusion rate we use following formula.

Vgas = D x (A/t) x (P1 - P2)

Where Vgas is the rate of diffusion of gas, D is the diffusion coefficient, A is the lung’s surface area, t is the thickness, and P is the partial pressure; here P1 is the alveolar air pressure and P2 is the venous O2 pressure.

Now by putting the all values from the question in the equation (convert all values into centimeters),

Vgas = 1.2 x 10-5 cm2s-1 x (75 x 104 cm2/ 0.5x 10-4 cm) x (100 mmHg– 40mmHg)

Vgas = 10800 x 103 cm3 mmHg s-1

Vgas = 10.8 cm3 mmHg s-1

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