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Intrasubject between-day variability of PD20 methacholine assessed by the dosimeter inhalation test
G Balzano1, I Delli Carri, C Gallo
1Department of Pneumology and Respiratory Allergy, Cardarelli Hospital, Italy.
Abstract:
The intrasubject between-day variability of the methacholine inhalation test (MIT) was estimated in a group of 30 patients (15 males, mean age 29 yr), representative of a wide range of degrees of nonspecific bronchial responsiveness (from normal to severely increased). In each patient, an MIT with the dosimeter method was carried out on three separate occasions within one week, keeping as constant as possible both the technical and patient-related factors (FEV1 within +/- 5 percent, no recent airway inflammation) and independently from operator-related factors (three tests, three different operators blinded with regard to previous MIT results). On each occasion, twofold increasing doses of methacholine were given from 6.25 to 3,200 micrograms as cumulative doses, at five-minute intervals by means of a dosimeter Me.far MB3 (nebulization time 0.8 +/- 0.2s, output 5 +/- 0.2 microliters/puff). The FEV1 was measured initially and 1.5 and 3 minutes after each inhalation. The test was continued until either a fall of 20 percent or more in FEV1 was obtained or the last dose was reached. The results were expressed in terms of PD20, ie, the dose of methacholine producing a 20 percent fall in FEV1. Under these carefully controlled conditions, the 95 percent confidence intervals (as based on a single determination) corresponded to +/- 0.22 on a log10 scale or, in a more meaningful way, +/- 1.66 fold-difference in PD20 from one visit to the other.
Insights
The methacholine inhalation test (MIT) shows a consistent intrasubject variability, with a 95% confidence interval of 1.66-fold difference in PD20. This finding is crucial for accurately assessing bronchial responsiveness.
Area of Science:
- Pulmonary Medicine
- Respiratory Physiology
Background:
- Nonspecific bronchial hyperresponsiveness is a key feature of asthma.
- The methacholine inhalation test (MIT) is widely used to assess bronchial responsiveness.
- Understanding the test's variability is essential for accurate clinical interpretation.
Purpose of the Study:
- To estimate the intrasubject between-day variability of the methacholine inhalation test (MIT).
- To quantify the reliability of PD20 measurements in assessing bronchial responsiveness.
Main Methods:
- 30 patients with varying degrees of bronchial responsiveness underwent three MITs within one week.
- A dosimeter method delivered increasing cumulative doses of methacholine.
- Forced expiratory volume in 1 second (FEV1) was measured to determine the provocative dose 20 (PD20).
Main Results:
- Under controlled conditions, the 95% confidence intervals for PD20 showed a 1.66-fold difference between visits.
- This indicates a degree of variability in test results even with standardized procedures.
Conclusions:
- The methacholine inhalation test demonstrates moderate intrasubject variability.
- The findings provide valuable data for interpreting changes in bronchial responsiveness over time.