Variability of breath-by-breath tidal volume and its characteristics in normal and diseased subjects. Ventilatory monitoring with electrical impedance pneumography.

To assess clinical significance of breath-by-breath variation of tidal volume and its distribution pattern displayed as a histogram, continuous measurement of tidal volume was made with electrical impedance pneumography for about 60 minutes. Subjects were composed of 26 normal male and 46 patients including 17 patients with restrictive lung disease and 29 patients with obstructive lung disease. To evaluate variation of tidal volume quantitatively, coefficient of variance (C.V.) was used. In comparison to the normal pattern of distribution (C.V. = 26.0 +/- 7.5%, mean +/- S.D.), patients with restrictive lung disease showed extremely narrow pattern of the distribution and significantly smaller C.V. (17.5 +/- 4.6% in old pulmonary tuberculosis, P less than 0.005 and 18.9 +/- 9.3% in pneumonitis, P less than 0.025). Whereas, patients with obstructive lung disease showed widespread pattern of the distribution and significantly greater C.V. (43.2 +/- 13.0% in pulmonary emphysema with hypercapnia, 33.0 +/- 7.5% in normocapnia and 35.8 +/- 9.4% in asthmatic attack, P less than 0.005). In all the patients with bronchial asthma after the treatment, the extremely widespread pattern of histogram was returned toward the normal one and the C.V. was decreased (22.4 +/- 6.4%). It was suggested that the distribution pattern of tidal volume was affected by the change of clinical condition, and was well correlated to the pathophysiological process related to restrictive or obstructive lung disease. We conclude that analysis of tidal volume distribution by the histogram is one of the useful approach to manage patients with respiratory diseases.