Measurements of resistance by the interrupter technique and of transcutaneous partial pressure of oxygen in young children during methacholine challenge

Measurement of bronchial airway responsiveness requires noninvasive techniques in young children. The study was designed to examine the changes in resistance as measured using the interrupter technique (Rint) at the dose of methacholine (M) that induced a fall in transcutaneous partial pressure in O 2 (P tc O 2 ) ≥ 20% (PD 20 P tc O 2 ) in young children. Rint was calculated using the linear back‐extrapolation method (Rint L ) and the end‐interrupter method (Rint EI ). Twenty‐two children (mean age, 5.2 ± 1.1 years; range, 3.4 – 7.1 years) with nonspecific respiratory symptoms (mainly chronic cough, n = 17) were tested. P tc O 2 , Rint L , and Rint EI were measured before the test, after saline challenge (baseline (B)), after each dose of M delivered by a dosimeter, and after bronchodilator (BD) inhalation. P tc O 2 decreased significantly during M challenge, from 85 ± 6 mmHg (B) to 62 ± 9 mmHg ( P  < 0.05), and increased after BD inhalation, to 82 ± 8 mmHg. Rint L and Rint EI increased significantly during M challenge, from 0.94 ± 0.2 KPa/L/s and 1.11 ± 0.19 KPa/L/s (B) to 1.27 ± 0.35 KPa/L/s and 1.47 ± 0.37 KPa/L/s, respectively ( P  < 0.05), and decreased after BD inhalation to 0.80 ± 0.17 KPa/L/s and 0.95 ± 0.18 KPa/L/s, respectively. Nineteen of 22 children reached the PD 20 P tc O 2 at a dose of M ranging from 50–400 μg. At the PD 20 P tc O 2 , significant changes in Rint L and Rint EI (sensitivity index (SI) ≥ 2) were found in 79% and 63% of children, respectively. We conclude that: 1) M challenge using P tc O 2 is safe in young children; and 2) our findings are not in favor of the use of Rint as the only indicator of bronchial reaction in young children during M challenge. Pediatr Pulmonol. 2001; 31:238–246. © 2001 Wiley‐Liss, Inc.