Real-time moment analysis of pulmonary nitrogen washout.

A real-time moment analysis was applied to multibreath nitrogen-washout dynamics of the lung. Because the analysis accounts for breathing pattern variations, subjects could perform the washout with spontaneous breathing. The real-time digital processing of the nitrogen and flow signals incorporates filtering, delay compensation, and corrections for the effects of gas composition and temperature changes. In our study, moment analysis of the multibreath washout was evaluated for 37 subjects: 6 normal nonsmokers, 4 "normal" smokers, 6 asthmatics, 12 with diffuse interstitial disease, and 9 with chronic obstructive pulmonary disease. Moments were computed from end-tidal and breath-averaged nitrogen fractions. The ratio of 1st-to-0th moments was found to yield distinctions among subjects with different degrees of ventilation inhomogeneity, even between normal nonsmokers and "normal" smokers. With minimal computational facilities, this moment analysis not only provides a sensitive index of ventilatory dysfunction, but also a cost-effective tool.