Lung diffusing capacity

Everyone in the safety field knows that carbon monoxide is the “silent killer.” So, you might find it interesting that CO is used in an important test of lung function—the test for lung diffusing capacity. That is, how well do the lungs transfer gases to and from the bloodstream? (Oxygen and carbon dioxide)

Carbon monoxide is used in this test because of the blood hemoglobin’s extreme affinity for this compound. In fact, the affinity of CO for deoxyhemoglobin is about 200 times greater than that of O2. In clinical practice, the patient inhales a known volume of test gas that usually contains 10% helium, 0.3% carbon monoxide, 21% oxygen, and the remainder nitrogen. Other mixtures that include methane and neon are also used.

The idea is that the CO breathed in minus the CO breathed out will equal the amount absorbed by the blood.

For the test, the patient inhales the test gas and holds his or her breath for 10 seconds. The patient exhales to wash out a conservative overestimate of mechanical and anatomic dead space. Subsequently, an alveolar sample is collected. DLCO (Diffusing capacity of the lung for carbon monoxide) is calculated from the total volume of the lung, breath-hold time, and the initial and final alveolar concentrations of carbon monoxide. The exhaled helium concentration is used to calculate a single-breath estimate of total lung capacity and the initial alveolar concentration of carbon monoxide.

That hemoglobin has such an affinity for deadly carbon monoxide has little to do with biology, and more to do with the basic chemistry of iron (in the heme) and the carbon monoxide molecule.

We’ve handled this application for years, including some long term contracts with lung diffusion instrument manufacturers.

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