REPEATABILITY OF LUNG-FUNCTION TESTS DURING METHACHOLINE CHALLENGE INWHEEZY INFANTS

Background-The repeatability of lung function tests and methacholine i nhalation 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 chal lenge tests performed one month apart. Maximal flow at functional resi dual capacity ((V)over dot maxFRC) and transcutaneous oxygen tension ( Ptco(2)) were measured at baseline and after methacholine inhalation. Provocative doses of methacholine causing a 15% fall in Ptco(2) (PD(15 )Ptco(2)) or a 30% fall in (V)over dot maxFRC (PD30(V)over dot maxFRC) were determined. Results-Large changes in (V)over dot maxFRC were mea sured from T-1 to T-2 with a mean difference between measurements (T-2 -T-1) of 7 (113) ml/s and a 95% range for a single determination for ( V)over dot maxFRC of 160 ml/s. The mean (SD) difference between pairs of PD30(V)over dot maxFRC measurements was 0.33 (1.89) doubling doses with a 95% range for a single determination of 2.7 doubling doses. Rep eatability of PD(15)Ptco(2) was similar. A change of 3.7 doubling dose s of methacholine measured on successive occasions represents a signif icant change. Conclusions-Baseline (V)over dot maxFRC values are highl y variable in wheezy, symptom free infants. Using either (V)over dot m axFRC or Ptco(2) as the outcome measure for methacholine challenges pr ovided similar repeatability. A change of more than 3.7 doubling doses of methacholine is required for clinical significance.