Transit time analysis of the forced expiratory spirogram in male smokers

Transit time analysis has been proposed as a simple and sensitive method for detecting slowing and non-uniformity of lung emptying in airway disease. We have measured the first moment (alpha 1, mean transit time) and second moment (alpha 2) about the origin of the forced expiratory spirogram in 202 men (53 non-smokers, 149 regular smokers). Values of alpha 1 and square root alpha 2 (calculated from the first 6 s of expiration) increased with age in both smokers and non-smokers and were significantly greater in older smokers than in non-smokers. The rate of increase in alpha 1 and square root alpha 2 was most rapid in smokers between 24 and 36 years. Changes in alpha 1 were closely related to changes in FEV1/FVC ratio. Values of square root alpha 2 were frequently slightly increased in young smokers and in older smokers without definite abnormality of FEV1/FVC or alpha 1, probably because square root alpha 2 is more strongly influenced by the final part of the spirogram. Problems persist in determining the best method for expressing abnormality in square root alpha 2, in allowing for premature termination of the spirogram and for assessing dispersion of transit times. We conclude that square root alpha 2 demonstrates abnormalities not detected by alpha 1, in many young smokers and in older smokers with no or only slight increase in alpha 1. Once alpha 1 is definitely increased, measuring square root alpha 2 provides little additional information.(ABSTRACT TRUNCATED AT 250 WORDS)