The significance of moment analysis of spirogram

: In order to assess the significance of moment analysis of transit times on spirograms, we investigated the characteristics of this analysis and the distribution of mechanical time constants of the lung derived from this method. Assuming the log-normal distribution of time constants, mu is the mean and sigma is the standard deviation of the natural logarithms of the time constants. The normal value for mu was -0.64 +/- 0.41 and for sigma was 1.54 +/- 0.42 (mean +/- 1 S.D.) in 94 normal males. The smoking habits enhanced the response of sigma on age-effect, but did not enhance the response of V25/HT. Compared with the normal group, excessive sigma was observed in the patients with bronchial asthma, pulmonary emphysema and interstitial lung disease. Mu was especially greater in the patients with the former two diseases. In bronchial asthma, mu decreased and forced expiratory volume in 1 second (FEV 1.0) increased after inhalation of salbutamol, but these did not always correlate. Mu correlated with some clinical conditions. Moment analysis was available on the volume-time profile of quiet breathing with good reproducibility. The first moment (alpha 1) and standardized first moment (alpha 1') showed an increase in bronchial asthma and pulmonary emphysema, and decreased with treatment in bronchial asthma. It was concluded that the moment analysis of transit times on spirogram is useful as an index of time-course aspects of expiration.