Search

Measurement of bronchial reactivity is widely used in epidemiological surveys. Histamine has been compared with methacholine inhalation challenge in two samples of adults from a small town to determine which is the better agent for use in community studies. Increasing doses of histamine and methacholine were given, up to a maximum of 4 and 12 mumol respectively, according to the method of Yan et al, the provocative dose of agonist causing a 20% fall in FEV1 (PD20) being measured. More subjects had a measurable PD20 with methacholine than with histamine, both in a random sample of 108 subjects (25 v 11 subjects, p less than 0.01) and in an additional 95 subjects selected because of wheeze in the last 12 months (67 v 48 subjects, p less than 0.01). Side effects were mild with both agents but histamine caused voice change in more subjects (21% v 11%). Repeatability was assessed in a further group of subjects with wheeze in the last year. The 95% range for a single estimation of PD20 in subjects with a measured PD20 on at least one occasion was +/- 2.5 doubling doses for histamine (n = 25) and +/- 2.1 doubling doses for methacholine (n = 33). Thus methacholine has advantages over histamine for community studies of bronchial reactivity as it is possible to use doses that produce more PD20 measurements with fewer side effects. [ABSTRACT FROM PUBLISHER]

Epidemiological problems arising from the absence of an agreed definition of asthma have led to the use of bronchial reactivity tests in community surveys of asthma prevalence. Since only a minority of the general population will develop bronchoconstriction in response to the dose of histamine considered acceptable for use in the community it is important to make maximum use of the data available. Several methods for summarising the information in the dose-response curve obtained from a histamine challenge test have been compared. A standardised histamine challenge test was administered to 797 subjects selected from two communities, and a repeat test to 106 subjects. The test was well accepted. For most subjects FEV1 rose initially after administration of histamine (median rise 100 ml), so maximum FEV1 was used as the baseline from which the 20% fall to achieve a PD20 was calculated. In order to use all the data rather than just two points on the FEV1-log dose graph, PD20 was estimated by means of curve fitting, and the values were compared with PD20 from linear interpolation. An exponential curve was found to fit the data well. Extrapolation from the maximum dose of 4 mumol up to 8 mumol was allowed in the estimation of PD20 by both methods. The curve fitting method gave slightly more reproducible PD20 values than did linear interpolation, and also gave more estimates in the range 0.03-8 mumol. The repeatability of PD20 compared well with that of asthmatic subjects tested in a clinical environment. Curve fitting has an advantage over linear interpolation in large community studies, for which analysis of data by computer is essential. [ABSTRACT FROM AUTHOR]

The bronchial response to inhaled histamine has been suggested as an epidemiological tool for assessing the prevalence of asthma, though the exact relationship between reactivity and asthma is unknown. Tests of bronchial reactivity to histamine were carried out in 511 subjects aged 18-64 years, randomly selected from the population in two areas of the South of England, who had returned questionnaires on respiratory symptoms. Bronchial reactivity to less than or equal to 8 mumol histamine was present in 14% and was associated with positive skin test responses to common allergens and with smoking history. Both of these relationships were in turn dependent on age, skin sensitivity being the more important determinant of reactivity in the young and smoking the more important in older subjects. Bronchial reactivity was least prevalent in the 35-44 year age group. No independent effect on reactivity of sex, social class, or area of residence was detected, and no significant effect from recent respiratory tract infections. Interpretation of the bronchial response to histamine in selected groups of subjects must take account of age, atopic state, and smoking history. [ABSTRACT FROM AUTHOR]