How to calculate the single-breath nitric oxide diffusing capacity in rabbits

Abstract.

Nitric oxide (NO) is a novel indicator gas for investigating alveolar capillary gas exchange conditions. In clinical practice, pulmonary gas uptake is determined by measuring the single-breath diffusing capacity (D _L,NO). Different algorithms are employed to calculate D _L,NO. To compare the accuracy of those most commonly used, we performed single-breath experiments on 12 artificially ventilated rabbits. In each animal four manoeuvres, executing breath-holds of 2, 4, 6 and 8 s, were carried out. In each case we administered 55 ml of an indicator gas mixture containing 0.05% NO. Alveolar gas was analysed by respiratory mass spectrometry. The two algorithms for calculating D _L,NO based on the conventional solution of the breath-holding equation [Ogilvie et al. (1957) J Clin Invest 36:1–17 and Jones and Meade (1961) Q J Exp Physiol 46:131–143], were compared with the three-equation technique [Graham et al. (1980) IEEE Trans Biomed Eng 27:221–227] as the reference. The deviation between D _L,NO calculated from the conventional methods and the reference decreased linearly with increasing duration of NO uptake (Δt). The mean deviations declined from 16.6% (Jones and Meade) or 7.7% (Ogilvie) at Δt=4 s to 5.7% (Jones and Meade) or 2.4% (Ogilvie) at Δt=10 s. The larger mean values are due to the conventional solution where three-tenths of the inflation time is subtracted from Δt. These findings qualify the common prediction that the latter method yields D _L,NO values of the highest accuracy. We therefore recommend Ogilvie's procedure if the three-equation technique cannot be employed.