Adequateness of impulse oscillometry (IOS) reference values in the Swedish CArdioPulmonary bioImage Study (SCAPIS)

Abstract

IOS assess the mechanical properties of the respiratory system. The method is sensitive to identify early changes, but adequate reference values are needed for clinical use.

Therefore we studied how the producer’s recommended reference values (Vogel 1994) fit individuals from SCAPIS. Furthermore, we evaluated the burden of respiratory symptoms in relation to abnormal IOS.

IOS was done in 5036 (51% female) individuals aged 50-64 years from the Uppsala center of SCAPIS. Values above 95th percentile for resistance at 5 Hz (R5) and lower values than 5th percentile for reactance at 5 Hz (X5) were used to defined cut-offs for impaired R5 and X5 in healthy, never smokers (n=1887, 46% female).

The prevalence of impaired R5 and X5 was 10 and 11.4%, respectively, of the general population, while corresponding numbers using the Vogel were 5.8% and 3.7%. Subjects with R5 normal according to Vogel, but impaired according to SCAPIS (n=170) had a higher burden of wheeze (12.0% vs 5.8%,) dyspnea (14.9% vs 6.3%), and self-reported asthma (12.3% vs 7.9%) compared to subjects with normal R5 according to both Vogel and SCAPIS (n=3426) (all p<0.05). Similar findings were found for X5 for wheeze (13.5% vs 6.4%) and asthma (11.3% vs 8.1%) (all p<0.05).

Using the producer’s recommended reference values, fewer individuals will have an impaired lung function measured by IOS, compared to population-defined normal range in SCAPIS. Individuals with abnormal IOS according to SCAPIS, but normal according to producer’s reference values, have a higher burden of respiratory disease. This suggests clinical implications of choosing adequate reference equations.