Background: The efficacy of impulse oscillometry (IOS) to measure airway calibre change is not fully established.
Objectives: To evaluate lung function change after eucapnic voluntary hyperventilation (EVH), and to compare IOS indices with spirometric maximal expiratory flow measurements.
Methods: Twenty subjects (10 airway hyperresponsive [AHR+] and 10 normal [AHR--]) underwent IOS and spirometry before and for 15 min after 6 min EVH (inhaling 5% CO2, 21% O2, balance N2) at a target ventilation of 30 times the baseline value of the forced expiratory volume in 1 s (FEV1) at 20 degrees C. AHR+ was defined by a fall in FEV1 of 10% or greater from baseline after a provoking challenge. Airway resistance at 5 Hz (R5), reactance at 5 Hz, resonant frequency (Fres), area of reactance integrated from 5 Hz to Fres (AX), and FEV1 were determined.
Results: No baseline spirometry values correlated with falls in FEV1. Baseline R5 and AX values correlated with peak falls in FEV1 (r= -0.51 and -0.46, respectively; P< 0.05). AHR+ subjects demonstrated greater per cent peak falls in FEV1 than did AHR- subjects following EVH (30.6 +/- 14.0% versus 7.5 +/- 2.6%, respectively; P<0.05). Changes in R5, Fres, reactance and AX were greater for AHR+ subjects than for AHR- subjects and correlated with a fall in FEV1 (r= -0.74, -0.70, 0.69 and -0.73, respectively; P<0.05). At a designated specificity of 80%, the per cent change in R5 (50% or greater) and post-EVH AX (12 cm H2O/L or greater) yielded sensitivities to a 10% fall in FEV1 of 90%.
Conclusion: IOS is an acceptable measure to determine AHR and can supplement spirometry in lung function evaluation.