Question

Explain the physiological mechanism of diffusion of oxygen, how could you measure the diffusing capacity of the patient, how it might be affected by the disease, and which conditions from the vital signs may be affecting even more the already impaired mechanism of diffusion  

Answer 1

The diffusion of gases take place from higher concentration to a lower concentration.

Alveoli have a higher partial pressure of oxygen (pO2 is 104mmHg) while in the pulmonary capillary it is about pO2 40mmHg because of a difference of pressure gradient oxygen diffuse from alveoli to capillary and from Red blood cell to other cells.

Diffusion capacity:

It is the volume of gas diffuses through the respiratory membrane per minute for a pressure gradient of 1 mmHg.

This test is done to access the perfusion capacity of the lung.

Single breath technique.

We give a dilute mixture of CO patient inspire it and hold the breath for 10 sec.

The amount of CO taken up by the RBC is determined by infrared.

DLCO	CO/ml/min/mmhg
	PaCO-PcCO.

PaCO -partial pressure of carbon monoxide at the alveolar end.

PcCO-partial pressure of carbon monoxide at the capillary end.

Carbon monoxide (CO) has a higher affinity to hemoglobin, so we use it to calculate the diffusion capacity of the lung.

DLO2 (diffusion capacity of oxygen ) is 21ml/min/mmHg.

Which is DLCO×1.23, it means the diffusion capacity of oxygen is 1.23 times more than the diffusion capacity of

carbon monoxide.

It decreases diffusion of oxygen in various diseases such as emphysema, sarcoidosis, pulmonary fibrosis it is because of an increase in the thickness of the respiratory membrane.

while during the exercise or in the supine position the diffusion of gases is increased because of the increase in blood flow.