What is a "diffusion capacity lung" test or "DCLO" test?
A diffusion capacity lung test is a specialized test that helps us understand the health of the alveolar-capillary membrane. Now remember that the alveolus is a thin membrane that allows for oxygen and CO2 to move across this membrane. Well this membrane is tested best by the diffusion capacity, and there are several ways of doing diffusion capacity but they all require that you inhale a minute amount of carbon monoxide. Carbon monoxide moves across the alveolar-capillary membrane in such a way that it is not blocked at all by, it's not blocked at all by its diffusion ability. It is rapidly absorbed across the membrane into the red blood cells, but if that membrane becomes diseased it will in some way then limit the ability of the carbon monoxide to move, to move across. So that the only thing that is a variable there is the state of health of the alveolar-capillary membrane. Now, if in, like, for instance, emphysema, emphysema is a disease where these alveoli fuse together. Where you used to have one aveloli you now have--you used to have two, you now have one. The surface area of two alveoli is greater than the surface area of one when you combine those two together, and so you'll start to lose diffusion capacity because the surface area is being lost, and that's what emphysema does--one of the many things it does--to damage your lung. So diffusion capacities will help you not only help you establish the health of the alveolar-capillary membrane using the inhalation of carbon dioxide--not enough to poison you of course, but just minute amounts--and it'll also tell you about the size of your alveolar-capillary membrane as an aggregate whole. Are you losing surface area? We lose surface area as we age naturally, however, we'll not lose it as fast as if you are a significant smoker who then develops emphysema and then start to lose surface area, and that'll be picked up by diffusion capacity.
