Correspondence between forced oscillation and body plethysmography during bronchoprovocation with carbachol in children

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Abstract
We compared dose–response curves obtained with the forced oscillation technique (FOT) and with body plethysmography during bronchoprovocation in children. In 40 stable asthmatic children (age, 5–16 yr) we performed challenges with doubling concentrations of inhaled carbachol (0.15–10 mg/mL) until specific airway resistance SRaw had increased by 100% (PC100SRaw). The FOT-response was assessed by total respiratory system resistance (Rrs, cmH2O·1−1·s) and reactance (Xrs, cmH2O·1−1·s) from 8 to 26 Hz, expressed as mean Rrs (Rrs), mean Xrs (Xrs), Rrs at 8 Hz (Rrs8), and mean slope of Rrs (dRrs/df). Dose–response curves were analyzed for threshold concentrations (TC) causing a 3 SD change from baseline and sensitivity indices (SI) defined as differences between baseline and postchallenge values (at PC100SRaw) divided by baseline SD. Median TC of Rrs8, Rrs, Xrs, dRrs/df, and SRaw was 0.21, 0.30, 0.34, 0.41, and 0.42 mg/mL, respectively, indicating a slightly higher sensitivity for FOT. Median SI values of SRaw and Xrs (12.0 and 8.2; difference n.s.) were significantly higher than those of the other parameters. Multiple regression analysis revealed only the absolute change of Xrs (ΔXrs), baseline Rrs and age as significantly (P < 0.001) correlated with the percentage change of SRaw (Δ%SRaw). Best correlation (r = 0.86) with Δ%SRaw was found for the function: FOT score = −102.5 · ΔXrs · exp(−0.196 · Rrs + 0.038 · age). Provocative concentrations estimated by this FOT score differed from PC100SRaw by less than one (two) concentration steps in 34 (40) out of 40 children. We conclude that FOT is as sensitive as plethysmography during bronchoprovocation and that with the FOT score practically equivalent dose–response curves to those of SRaw can be obtained in children. Pediatr Pulmonol 1990; 8:280-288.