Lung function measured by impulse oscillometry and spirometry following eucapnic voluntary hyperventilation

The efficacy of impulse oscillometry (IOS) to measure airway calibre change is not fully established.

To evaluate lung function change after eucapnic voluntary hyperventilation (EVH), and to compare IOS indices with spirometric maximal expiratory flow measurements.

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.

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%.

IOS is an acceptable measure to determine AHR and can supplement spirometry in lung function evaluation.