Alveolar-capillary membrane diffusion measurement by nitric oxide inhalation in heart failure

BACKGROUND: In heart failure, lung diffusion is reduced, it correlates with prognosis and exercise capacity, and it is a therapy target. DESIGN: Diffusion is measured as CO total diffusion (DLCO), which has two components: membrane diffusion (Dm) and capillary volume, the latter related to CO and O2 competition for hemoglobin. DLCO needs to be corrected for hemoglobin. Diffusion can also be measured with NO (DLNO), which has a very high affinity for hemoglobin, and thus, the resistance of hemoglobin being trivial, it directly represents Dm. Therefore, Dm is directly calculated from DLNO through a correction factor. DLNO has never been measured in heart failure. The study aims at determining, in heart failure, DLNO, Dm correction factor, and whether DmNO provides Dm estimates comparable to DmCO. METHODS: We measured DLCO, DmCO by multi-maneuver Roughton-Forster method, and DLCO and DLNO by single-breath maneuver in 50 heart failure and 50 healthy subjects. RESULTS: DLCO was 21.9 ± 4.8 ml/mmHg per min and 16.8 ± 5.1 in healthy subjects and heart failure subjects, respectively (p < 0.001). DLNO was 88.6 ± 20.5 ml/mmHg per min and 72.5 ± 22.3, respectively (p < 0.001). The correction factors to obtain Dm from DLNO were 2.68 (entire population), 2.63 (healthy subjects) and 2.75 (heart failure subjects). DmCO and DmNO were 34.7 ± 10.9 ml/mmHg per min and 33.8 ± 7.6 in healthy subjects and 25.9 ± 2.0 and 26.4 ± 8.1 in heart failure subjects. CONCLUSIONS: DLNO and DmNO measurements are feasible in heart failure. DmCO and DmNO provide comparable results. The correction factor to calculate Dm from DLNO in heart failure is 2.75, which is little different from the 2.63 value we observed in healthy subjects.