Simultaneous measurement of pulmonary diffusing capacity for carbon monoxide and nitric oxide

In Europe and America, the newly-developed, simultaneous measurement of diffusing capacity for CO (DLCO) and NO (DLNO) has replaced the classic DLCO measurement for detecting the pathophysiological abnormalities in the acinar regions. However, simultaneous measurement of DLCO and DLNO is currently not used by Japanese physicians. To encourage the use of DLNO in Japan, the authors reviewed aspects of simultaneously-estimated DLCO and DLNO from previously published manuscripts. The simultaneous DLCO-DLNO technique identifies the alveolocapillary membrane-related diffusing capacity (membrane component, DM) and the blood volume in pulmonary microcirculation (VC); VC is the principal factor constituting the blood component of diffusing capacity (DB,DB=θ·VC where θ is the specific gas conductance for CO or NO in the blood). As the association velocity of NO with hemoglobin (Hb) is fast and the affinity of NO with Hb is high in comparison with those of CO, θNO can be taken as an invariable simply determined by diffusion limitation inside the erythrocyte. This means that θNO is independent of the partial pressure of oxygen (PO2). However, θCO involves the limitations by diffusion and chemical reaction elicited by the erythrocyte, resulting in θCO to be a PO2-dependent variable. Furthermore, DLCO is determined primarily by DB (∼77%), while DLNO is determined equally by DM (∼55%) and DB (∼45%). This suggests that DLCO is more sensitive for detecting microvascular diseases, while DLNO can equally identify alveolocapillary membrane and microcirculatory abnormalities.