Repeatability of lung function tests during methacholine challenge in wheezy infants

Abstract

Background-The repeatability of lung function tests and methacholine inhalation tests was evaluated in recurrently wheezy infants over a one month period using the rapid thoracic compression technique. Methods-Eighty one wheezy, symptom free infants had pairs of methacholine challenge tests performed one month apart. Maximal flow at functional residual capacity (V̇maxFRC) and transcutaneous oxygen tension (PtcO2) were measured at baseline and after methacholine inhalation. Provocative doses of methacholine causing a 15% fall in Ptco2 (PD15PtcO2) or a 30% fall in V̇maxFRC (PD30V̇maxFRC) were determined. Results-Large changes in V̇maxFRC were measured from T1 to T2 with a mean difference between measurements (T2- T1) of 7 (113) ml/s and a 95% range for a single determination for V̇maxFRC of 160 ml/s. The mean (SD) difference between pairs of PD30V̇maXFRC measurements was 0.33 (1.89) doubling doses with a 95% range for a single determination of 2.7 doubling doses. Repeatability of PD15Ptco2 was similar. A change of 3.7 doubling doses of methacholine measured on successive occasions represents a significant change. Conclusions-Baseline V̇maxFRC values are highly variable in wheezy, symptom free infants. Using either V̇maxFRC or Ptco2 as the outcome measure for methacholine challenges provided similar repeatability. A change of more than 3.7 doubling doses of methacholine is required for clinical significance.