Factors affecting oxygen saturation during methacholine challenge in a mixed population

Abstract

Listen

Translate article

Bronchial challenge with methacholine or histamine is associated with a reduction in arterial oxygen tension, which can be appreciable. In this study, oxygen saturation was monitored during methacholine challenge in subjects with and without respiratory disease, over a wide age range, in order to identify factors predicting a large fall in saturation during the challenge. Two hundred and twenty subjects aged 24–86 years were included, comprising 15 healthy adult volunteers, and 205 adults from a random sample of the local adult population taking part in a survey of bronchial responsiveness. Subjects with ischaemic heart disease or baseline FEV 1 <60% predicted were excluded. Methacholine challenge was performed by the Newcastle Dosimeter technique; oxygen saturation (SaO 2) was monitored using a pulse oximeter and finger probe. Of the 220 subjects, 27% were current smokers and 39·5% were ex-smokers; 26% reported asthma or bronchitis. Mean baseline FEV 1 was 100% predicted; mean baseline saturation was 97%. Mean fall in saturation was 3·2% (range 0–17·5%). Multiple regression analysis revealed that fall in saturation during methacholine challenge is related to baseline FEV 1, baseline SaO 2, log of total methacholine dose inhaled, and fall in FEV 1 during challenge. Change in saturation was not related to subject age, smoking history, reported asthma or bronchitis, or the presence of respiratory symptoms. Methacholine challenge produces a significant fall in oxygen saturation, but this is not greater in subjects who are old or have low baseline saturation.