Effects of deep inspiration (DI) on respiratory impedance measured by impulse oscillometry (IOS)

Abstract Rationale Deep inspiration (DI) normally causes a decrease of bronchomotor tone; but in some asthmatic subjects, DI has been shown to cause increased bronchomotor tone. Methods This study measured effects of DI by forced oscillation using IOS, in 29 patients evaluated for allergic rhinitis and asthma. Triplicate 30 sec IOS tests of quiet breathing, and a 60 sec IOS test with DI between 30-35 sec were done before and after nebulized levalbuterol including resistance at 5Hz (R5) and low frequency reactance (AX). Routine spirometry was performed after each set of IOS tests. Results Baseline small airway inflammation (increased AX) was associated with increased bronchoconstrictor response (increased impedance) to DI; and levalbuterol inhalation was associated with decreased bronchoconstrictor response to DI, irrespective of spirometry. Conclusions We conclude that concurrent airway inflammation and baseline bronchomotor tone modulate the response to DI in asthmatic subjects, irrespective of spirometric results.