Tidal breathing pulmonary function (TBPF) tests are easy to obtain in infants but their inharent variability is a major concern for clinical use. We hypothesized that intra-test variability of various parameters of TBPF tests is <10%. TBPF tests were performed on ninteen infants (mean age 5±2.8 mo) with bronchiolitis, with 2600 Neonatal/Pediatric Pul Testing System (Sensor Medics, Cal.) in a standardized fashion. Nebulized albuterol(0.15mg/kg) and saline were given 6 hours apart in a randomized, double blind, cross over design. We have performed pre and post test with each aerosol. For each TBPF test we have selected four near identical flow-volume loops and average of 4 loops was taken. Coefficient of variation (CV) was calculated for the four loops. TBPF tests done before each aerosol were analysed for the purpose of present study. Infants were sedated with chloral hydrate (50mg/kg p.o.). Mean CV ± SD for VT (expiratory tidal volume in ml), PTEF (peak tidal expiratory flow in ml/sec), V-PT (% of Vt to PTEF), T-PT (% of expiratory time to PTEF), and TEF10, TEF25, TEF50 (tidal expiratory flow rates at 10, 25, and 50% of VT) are given in the table. All values given here are mean CV of nineteen subjects with ± SD. We found low intra-test coefficients of variation for VT(3.6 & 3.8), PTEF (3 & 3.8), and TEF50 (5.1 & 6.6). Tidal flows at lower lung volumes (eg. TEF10) were more variable than at higher lung volumes (p < 0.001with TEF50 and p< 0.0006 with PTEF). Inspite of similar VT and PTEF, the flow-volume loops exhibited highly variable V-PT(25.5 & 26.4), T-PT (26.6 & 28.1) ratios(P< 0.00001 compared with PTEF). Reproducibility of various aspects of flow-volume loops was not similar. Variability of the measurements was <10% only with VT, PTEF, TEF50, and TEF25. We conclude that the effect of bronchodilators on measurements of V-PT, T-PT, and TEF10 from a flow-volume loop should be interpreted with caution, taking into consideration for the inharent variability of those measurements.

Table 1
Full size table