Changes and discordances during methacholine challenge between interrupter resistance (Rint) and transcutaneous partial pressure of oxygen (PtcO2)

Responsive childrenNonresponsive children
Subjects n207
Changes in PtcO2 %−25.4±4.8−13.4±8.4
Changes Rintinsp %+49.1±29.6+13.2±11.4
Change Rintexp %+34.3±27.9+8.8±17.4
Discordance between Rintinsp and PtcO2 n (%, 95% CI)11 (55, 34–74)0 (0, 0–35)
Rint increase <35% at PD20PtcO2 n6
Rint increase ≥35% before PD20PtcO2 n5
Discordance between PD35Rintinsp+SpO2,3%
and PtcO2 n
Discordance between Rintexp and PtcO2 n (%, 95% CI)16 (80, 58–92)3 (42, 16–75)
Rint increase <35% at PD20PtcO2 n100
Rint increase ≥35% before PD20PtcO2 n63
Discordance between PD35Rintexp+ SpO2,3%
and PtcO2 n
  • Data are presented as mean±sd percentage of post-diluent values unless otherwise stated. Changes are at the provocative dose of methacholine causing a 20% decrease in PtcO2 (PD20PtcO2) in responsive children and at the last dose of methacholine in nonresponsive children. Discordances between Rint and PtcO2 changes were assessed at every steps of the test. Rint changes are more or less than 35% increase from the post-diluent value (PD35Rint). Rintinsp: inspiratory interrupter resistance; Rintexp: expiratory interrupter resistance; PD35Rintinsp: provocative dose of methacholine causing a 35% decrease in Rintinsp; SpO2,3%: at least 3% decrease in transcutaneous saturation of oxygen from the post-diluent value; PD35Rintexp: provocative dose of methacholine causing a 35% decrease in Rintexp.