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

Nitric oxide (NO) is a novel indicator gas for investigating alveolar capil lary gas exchange conditions. In clinical practice, pulmonary gas uptake is determined by measuring the single-breath diffusing capacity (D-L.NO). Dif ferent algorithms are employed to calculate D-L.NO. TO compare the accuracy of those most commonly used, we per-Formed single-breath experiments on 12 artificially ventilated rabbits. In each animal four manoeuvres, executing breath-holds: of 2, 4, 6 and 8 a, were carried out. In each case we admini stered 55 mi of an indicator gas mixture containing 0.05% NO. Alveolar gas was analysed by respiratory mass spectrometry. The two algorithms fur calcu lating D-L,D-NO based on the conventional solution of the breath-holding eq uation [Ogilvie et al. (1957) J Clin Invest 36:1-17 and Jones and Meade (19 61) Q J Exp Physiol 46:131-143], were compared with the three-equation tech nique [Graham ct al. (1980) IEEE Trans Biomed Eng 27:221-227] as the refere nce. The deviation between D-L.NO calculated from the conventional methods and the reference decreased linearly with increasing duration of NO uptake (Deltat). The mean deviations declined from 16.6% (Jones and Meade) or 7.7% (Ogilvie) at Deltat=4 a to 5.7% (Jones and Meade) or 2.4% (Ogilvie) at Del tat=10 s. The larger mean values are due to the conventional solution where three-tenths of the inflation time is subtracted ft om dt. These findings qualify the common prediction that the latter method yields D-L,D-NO values of the highest accuracy. We therefore recommend Ogilvie's procedure if the three-equation technique cannot be employed.