[A preliminary study of the chord and specific time constants in 342 healthy children]

Using Knudson's method, the chord time constant, tau ch, tau ch75, tau ch50, tau ch25, and specific time constant, S tau, 1/V75, 1/V50, 1/V25, at high, middle and low lung volumes were calculated from V75, V50 and V25 of the MEFV curves measured previously from 342 healthy children of 3-6 years of age in a nursery. The multiple stepwise regression equation were built with age, height and FVC as independent variables by the IBM-XT/PC computer. The result showed that the S tau corrected by volume from tau ch could reflect the time required for change of unit lung volume more precisely than tau ch owing to the elimination of the influence of lung volume. The S tau was shortened with the increase of age, and was negatively correlate with age and FVC. These facts reflected the growth of lung elastic pressure (PLel) and airway conductance (Gaw) with the increase of age. The prolongation of S tau with the decay of lung volume just reflected the decrease of PLel and Gaw with the decay of lung volume. No regular changes of tau h were observed with age and lung volume. Probably, it was concerned with the complexity of factors affecting the tau ch.