FACTORS AFFECTING OXYGEN-SATURATION DURING METHACHOLINE CHALLENGE IN A MIXED POPULATION

Bronchial challenge with methacholine or histamine is associated with a reduction in arterial oxygen tension, which can be appreciable. In t his study, oxygen saturation was monitored during methacholine challen ge in subjects with and without respiratory disease, over a wide age r ange, in order to identify factors predicting a large fall in saturati on during the challenge. Two hundred and twenty subjects aged 24-86 ye ars were included, comprising 15 healthy adult volunteers, and 205 adu lts from a random sample of the local adult population taking part in a survey of bronchial responsiveness. Subjects with ischaemic heart di sease or baseline FEV(1) <60% predicted were excluded. Methacholine ch allenge was performed by the Newcastle Dosimeter technique; oxygen sat uration (SaO(2)) was monitored using a pulse oximeter and finger probe . Of the 220 subjects, 27% were current smokers and 39 . 5% were ex-sm okers; 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 t hat fall in saturation during methacholine challenge is related to bas eline FEV(1), baseline SaO(2), log of total methacholine dose inhaled, and fall in FEV(1) during challenge. Change in saturation was not rel ated to subject age, smoking history, reported asthma or bronchitis, o r the presence of respiratory symptoms. Methacholine challenge produce s a significant fall in oxygen saturation, but this is not greater in subjects who are old or have low baseline saturation.