The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

COMPARISON OF TWO METHODS FOR MONITORING AIRWAY RESPONSIVENESS BEFORE AND AFTER THE ADMINISTRATION OF METHACHOLINE.

K. McDonald1, C. D. Mottram1, B. Kettler1, H. Renner1, S. Johnson1, P. Scanlon1

The most common method for measuring airway responsiveness to the administration of methacholine is spirometry, specifically, the change in forced expiratory volume in one second (FEV1). Spirometry requires a maximal forced expiratory effort by the subject, which is repeated numerous times during a testing session. Impulse oscillometry is another method for measuring airway function. It only requires the subject to breath quietly for 20-30 seconds through a mouthpiece. We compared the change in FEV1 against the change in resistance (R5) and reactance (X5), as measured with impulse oscillometry, after the administration of methacholine.

Methods: A convenience sample of fifty one subjects (age 18-80 yrs, M-23, F-28) were recruited. They were referred for methacholine challenge (MC). Testing was performed using calibrated laboratory equipment. The MC was conducted according to the laboratory’s standard operating procedure. Impulse oscillometry was performed prior to spirometry for all measurements.   All subjects were able to perform acceptable and repeatable spirometry and IOS maneuvers.

Results: There was a good correlation among the post-methacholine % change values for spirometry and IOS parameters: FEV1 % chg -11%; R5 (resistance) % chg 32%; X5 (reactance) % chg 93%. The % change in reactance (X5) correlated with the change in FEV1 (r = 0.47 p<0.001). 11 subjects met the ATS criteria for a positive methacholine response (20% decline in FEV1). 10 of these 11 subjects were identified with a change in reactance >100%. Using this criterion, an additional subset of 12 subjects was “reactance positive” but “spirometry negative”.

Conclusion: Impulse oscillometry shows potential as a method for evaluating airway responsiveness. In comparison with spirometry IOS identified 10 of 11 subjects who were “spirometry positive”. An additional subset of subjects were “reactance positive”, but “spirometry negative”. Further study is needed to characterize these subjects. Performing IOS does not require a deep breath maneuver, which may have an effect on airway caliber. Mayo Clinic IRB 07-001700


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