Replacement of Helium by Argon for Measurement of Carbon Monoxide Diffusing Capacity of lung

Diffusion capacity for carbon monoxideof the lung (D_LCO_(SB)) of 118 normal subjectsand 48 patients was measured by using threedifferent gas mixtures respectively: (a) 10％He, 0.3％CO, 21％O_2 and the remainder N_2,(b)10％ Ar, 0.3％CO, 21％O_2 and the remain-der N_2; (C) 10％ He, 10％ Ar, 0.3％ CO, 21％O_2 and the remainder N_2. The results wereextremely close with each other (r= 0.99, P<0.0005). The date also showed that the concentra-