PURPOSE: Forced Oscillation (FO) provides indices of peripheral airway obstruction (frequency dependence of resistance [f-d R] and low frequency reactance); but resistance (R) measured by occlusion or airflow perturbation devices (APD) has hitherto measured R at only a single frequency. We used APD to measure R at 5 and 15 Hz (R5 and R15) to correlate with FO measures of f-d R and low frequency reactance area (AX) and thereby to determine if APD reflects peripheral airway obstruction in patients with asthma or COPD (obstructive airway disease, OAD).
METHODS: In 219 adult patients with OAD, we compared FO measures using Impulse Oscillometry (IOS) and APD measurements R5 and R15 during clinical followup of OAD. We correlated APD f-d R (R5-R15) with IOS f-d R, and with IOS integrated low frequency reactance (AX). We also compared the effects of known airflow leak on IOS and APD parameters.
RESULTS: APD R5 correlated closely with IOS R5 (r = 0.87) but underestimated IOS R5 at R values > 6 cm H2O/L/s, (slope of APD R5 vs IOS R5 = 0.71). APD f-d R correlated well with IOS f-d R (r = 0.76, slope = 0.68)and with IOS AX, (r = 0.74). Known airflow leaks through holes drilled in microbial filters caused a 12-15% decrease in IOS R5 and R15, and a 4-7% decrease in APD R5 and R15.
CONCLUSION: We conclude that APD R measured at 5 and 15 Hz can reflect IOS indices of peripheral airway obstruction in patients with asthma or COPD. APD appears to be less sensitive to airflow leak in front of the patients’ mouth.
CLINICAL IMPLICATIONS: APD is small, inexpensive and portable and provides airflow resistance during quiet breathing and an index of peripheral airway obstruction. APD may serve as a convenient substitute for FO or IOS in screening patients for OAD and monitoring changes in OAD.
DISCLOSURE: Michael Goldman, None.