Transit time analysis of the forced expiratory spirogram in growth.

In the search for more sensitive indicators of airway obstruction Fish et al. (Am. Rev. Respirat. Diseases 109: 700, 1974) have proposed a transit time analysis of the forced expiratory spirogram. In this method the forced vital capacity (FVC) is divided into volumes of air and each volume is assigned a transit time; the nature of the FVC can be described by the transit times' mean, standard deviation, and index of skewness. In a group of 48 healthy nonsmoking subjects between the ages of 9 and 22 yr we found that all three quantities decreased with increasing age. This demonstrates an improvement in the function of the peripheral airways with lung growth. In contrast to the increase in flow rates with lung growth, none of this improved function can be attributed to increased lung volume.