Diffusing capacity for nitric oxide: Reference values and dependence on alveolar volume

SummaryNitric oxide (NO) has a much stronger affinity for hemoglobin than carbon monoxide (CO); therefore, the DLNO (diffusing capacity for NO) is less influenced by changes in capillary blood volume than the DLCO (diffusing capacity for CO), and represents the true membrane diffusing capacity.We measured the combined single breath DLNO/DLCO in 124 healthy subjects, and generated reference equations for the DLNO and KNO. In a subset of 21 subjects the measurements were performed on different inspiratory levels.The reference equation for DLNO in females is 53.47*H(height)0.077*A(age)-48.28(RSD5.22)53.47*H(height)0.077*A(age)-48.28(RSD5.22) and for males 59.84*H-0.25*A-44.20(RSD6.3959.84*H-0.25*A-44.20(RSD6.39). Reference equations for KNO in females is -2.03*H-0.025*A+11.52(RSD0.48)-2.03*H-0.025*A+11.52(RSD0.48) and for males -0.15*H-0.045*A+9.47(RSD0.65)-0.15*H-0.045*A+9.47(RSD0.65). The KCO (DLCO/VA) increases when VA (alveolar volume) decreases, probably due to an increase of blood volume per unit lung volume.The DLNO was much stronger related to the VA, the KNO was almost independent of VA. Because of the relative independence of the KNO on VA, the KNO appears to be a much better index for the diffusion capacity per unit lung volume (transfer coefficient) than the KCO.