Lung diffusing capacity for nitric oxide measured by two commercial devices: a randomised crossover comparison in...

In Europe, two commercial devices are available to measure combined single-breath diffusing capacity of the lung for nitric oxide (D _LNO) and carbon monoxide (D _LCO) in one manoeuvre. Reference values were derived by pooling datasets from both devices, but agreement between devices has not been established. We conducted a randomised crossover trial in 35 healthy adults (age 40.0±15.5 years, 51% female) to compare D _LNO (primary end-point) between MasterScreen™ (Vyaire Medical, Mettawa, IL, USA) and HypAir (Medisoft, Dinant, Belgium) devices during a single visit under controlled conditions. Linear mixed models were used adjusting for device and period as fixed effects and random intercept for each participant. Difference in D _LNO between HypAir and MasterScreen was 24.0 mL·min^-1·mmHg^-1 (95% CI 21.7-26.3). There was no difference in D _LCO (-0.03 mL·min^-1·mmHg^-1, 95% CI -0.57-0.12) between devices while alveolar volume (V _A) was higher on HypAir compared to MasterScreen™ (0.48 L, 95% CI 0.45-0.52). Disparity in the estimation of V _A and the rate of NO uptake (K_NO=D _LNO/V _A) could explain the discrepancy in D _LNO between devices. Disparity in the estimation of V _A and the rate of CO uptake (K_CO=D _LCO/V _A) per unit of V _A offset each other resulting in negligible discrepancy in D _LCO between devices. Differences in methods of expiratory gas sampling and sensor specifications between devices likely explain these observations. These findings have important implications for derivation of D _LNO reference values and comparison of results across studies. Until this issue is resolved, reference values, established on the respective devices, should be used for test interpretation.