Total Respiratory Resistance and Reactance as a Measurement of Response to Bronchial Challenge with Histamine

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Abstract
The potential of the forced oscillation technique to detect the airway response on histamine bronchial challenge tests was compared with that of FEV1 and plethysmographic SGaw. In 53 subjects with a history of episodic wheezing and a normal baseline airway resistance, we carried out bronchial challenges with successively doubling concentrations of histamine until FEV1 had dropped by 15% or more or a concentration of 16 mg/ml histamine was reached. For the baseline values, a mean within-subject coefficient of variation was found of 2.8% for FEV1, 7.4% for SGaw, 8.7% for the oscillatory respiratory conductance at 6 Hz (1/Rrs6), and 7.7% for the mean oscillatory respiratory conductance (between 2 and 26 Hz) (1/Rrs). The latter coefficients allow the calculation of the following threshold values: PD15FEV1, PD40SGaw, PD47 1/Rrs6, and PD42 1/Rrs. The probability of exceeding these levels by chance is virtually zero. Histamine challenge caused significant absolute changes in Rrs at 6 Hz (Rrs6), in mean level of Rrs and of respiratory reactance (Xrs), in slope of Rrs and Xrs versus frequency, and in mean curvature of Rrs-frequency curve. A multivariate analysis of the differences between prechallenge and postchallenge values showed that the parameters with the best sensitivity to detect the effect of histamine were, in decreasing order: the relative change of SGaw, of 1/Rrs6, of 1/Rrs, of FEV1, of FVC, and of 1/Vtg, followed by the absolute change of Xrs and of the average slope of the Rrs-frequency relationship.(ABSTRACT TRUNCATED AT 250 WORDS)