Use of transcutaneous oxygen tension, arterial oxygen saturation, and respiratory resistance to assess the response to inhaled methacholine in asthmatic children and normal adults.

Respiratory resistance (Rrs6), transcutaneous oxygen tension (PtcO2), and oxygen saturation (SaO2) were measured during methacholine challenge in 15 asthmatic children and six normal adults. During bronchoconstriction, induced by a wide range of inhaled methacholine concentrations (0.5-256 g/l), the rise in Rrs6 was reflected by a fall in PtcO2 in all subjects. Although there was a significant mean fall in SaO2 at maximum bronchoconstriction there was no consistent relation between changes in SaO2 and Rrs6. The inhaled dose of methacholine causing a 40% increase in Rrs6 (PD40Rrs6) and a 20% fall in PtCO2 (PD20PtcO2) was calculated for each subject. There was no significant difference in mean PD40Rrs6 and PD20PtcO2, and the relation between the two was similar in the asthmatic children and the normal adults. It was therefore concluded that the measurement of PtcO2, but not SaO2, during methacholine challenge can be used for the assessment of bronchial responsiveness, and that it could prove particularly useful for children too young to cooperate with lung function tests.