The effect of deep inspiration on methacholine induced bronchoconstriction

Jang, An Soo

Abstract

BACKGROUND: Deep inspiration not only has a bronchodilatory effect but also a bronchopro- tective effect. We compared the 2-min tidal breathing method and the five-breath dosimeter method to evaluate effect of deep inspiration on airway narrowing during methacholine provocation tests (MPT) in normal subjects.
METHODS
Eleven normal volunteers (seven males and four females) inhaled five doses of methacholine (25mg/ml) at 5-min intervals during the 2-min tidal breathing method and the five-breath dosimeter method. MPT was cross-overly performed by the two methods. On first visit, a questionnaire for symptoms, allergy skin test, spirometry, and MPT (2-min tidal breathing and five-breath dosimeter method) were performed. On second visit, pulmonary function tests and methacholine challenge using the 25mg/mL dose were performed on two separate days at the same time each day. The perception of dyspnea during methacholine challenge was scored using modified Borg scale. The recovery time from maximal decrease in FEV1 to baseline FEV1 was checked without using bronchodilator after MPT.
RESULTS
The maximal decreases in FEV1 and FVC during the 2-min tidal breathing method were 38.8+/-5.3% and 27.8+/-5.1%, respectively. The maximal decreases in FEV1 and FVC during the five-breath dosimeter method were 16.5+/-6.1% and 14.2+/-4.9%, respectively. Score on Borg scale during the 2-min tidal breathing method at methacholine dose 1 was from 0.5 to 7. The FEV1 and FVC at methacholine dose 1, 2, 3, 4, 5 showed significantly greater decreases during the 2-min tidal breathing method compared to those during the five-breath dosimeter method. There was significant correlation between maximal decrease in FEV1 during the five-breath dosimeter method and recovery time from decrease in FEV1 to baseline FEV1 (r=0.82; p<0.01). A significant correlation (r=0.79; p<0.05) was found between decrease in FEV1 at methacholine dose 1 during the 2-min tidal breathing method and perception score.
CONCLUSION
These observations indicate that the continuous generation method produces more bronchoconstriction than the dosimeter method for delivering methacholine aerosol during MPT, suggesting inhibition of deep inspiration enhances methacholine induced airway narro- wing in normal subjects.