[Replacement of helium by argon in the measurement of the carbon monoxide diffusing capacity of the lung]

Carbon monoxide diffusing capacity of the lung (DLco) of 118 normal subjects and 48 patients was measured by using three different gas mixtures respectively: (1) 10% He, 0.3% CO, 21% O2 and the remainder N2; (2) 10% Ar, 0.3% CO, 21% O2 and the remainder N2; (3) 10% He, 10% Ar, 0.3% CO, 21% O2 and the remainder N2. The results were extremely close with each other, value was 0.99 (P less than 0.0005). These results indicate for the first time that the much cheaper and easy-available gas-argon can be used instead of the very expensive helium for measurement of DLco.