Membrane based oxygenators are frequently used as a heartlun

Membrane based oxygenators are frequently used as a heart-lung device in medical applications. The partial pressure of oxygen in venous blood is 53 mbar.

(1) Estimate the driving force with air as feed gas at 1 atm.

(2) In a heart-lung device, generally higher partial oxygen feed pressures are supplied. (i.e., partial oxygen feed pressure=0.9 atm.) A 100-micron silicone membrane with an oxygen permeability of 550 Barrers and a carbon dioxide permeability of 3000 Barrers is used for the oxygen and carbon dioxide transfer. Calculate the oxygen flux.

(3) Calculate the membrane area is 250 cm^3 (STP) of oxygen is required per minute.

(4) The carbon dioxide pressure in the supply gas is negligible and the venous carbon dioxide pressure is 60 mbar. The carbon dioxide production rate is 200 cm^3 (STP)/min. Is the area calculated in (3) above sufficient to remove the carbon dioxide from the blood?

Solution

1)

The driving force is the difference in PO₂ across the blood vessel walls. The partial pressure of venous blood is given as 53mBar and the feed gas or air is at 1 atm.

53 Bars = 52.3 atmospheres

1 bar = 0.9869 atm

53*10^-3*0.9869 = 0.052atm

The difference between 0.052 atm and 1 atm is 0.948atm which is the driving force mentioned in the question.

2)

Oxygen flux = diffusion coefficient of oxygen (0.9/100microns)

1micron = 10^-6m and 100 microns is 10^-4m

D of oxygen through permeable silicon rubber is 16*10^6 cm²/s

Flux = - 16*10^6*10^-4 (0.9/10^-4)

Flux = 144*10^6 atm/m

3)

Diffusivity of oxygen = 16*10^2 m²/s

Flux = 250 cm³/60sec

1sec-0.9atm-1600 m²

60secs – 250atm – area ?

=(1600*0.9)/(60*200) = 0.12 m² is the membrane area required for the given volume of oxygen to diffuse.

4)

Yes, the above area is sufficient for the carbondioxide to diffuse from blood.

Diffusivity of carbon-dioxide = 11*10^2 m²/s

Flux = 200 cm³/60sec

1sec-59.2*10^-3 atm-11*10^2 m²

60 secs– 200atm – area ?

= (1.1*59.2)/(60*200) = 0.00427 m² is the area required by the carbondioxide to move from blood.