Transit-time analysis of the forced expiratory spirogram during clinical remission in juvenile asthma

The mean transit time (MTT), coefficient of variation (CoV), and index of skewness (IoS) of transit times of the forced expiratory flow/time curve have been compared with maximal mid-expiratory flow (MMEF), flow at 75, 50, and 25% of vital capacity (V75, V50, and V25), and the ratio of forced expiratory volume in 1 second (FEV1) to vital capacity (VC) in 51 asthmatic children judged on clinical grounds to be in remission. In 19 children all eight indices were normal. Of the remaining 32, MTT was normal in 5, V50 in 11, V75 in 12, and FEV1/VC and MMEF in 13 each. MTT was significantly more sensitive in detecting abnormality when other indices were normal, and abnormalities in MTT were of significantly greater magnitude when present. In 12 patients with at least one abnormal index given salbutamol aerosol, MTT was not more sensitive than MMEF, V25, FEV1/VC, or V50 in detecting change.