Asthma is one the most common obstructive lung diseases. Asthma is diagnosed based on clinical exam (respiratory symptoms) and lung function testing. For evaluation, spirometry and body plethysmography are most commonly used. For certain populations (the elderly and children) performing these tests can be very challenging and exhausting.
Impulse oscillometry (IOS) represents a new concept of evaluating lung function. This method is simple and requires minimal effort from the subject's part; in contrast to spirometry, oscillometry is measured during regular breathing. With the aim to verify a simpler method of evaluating lung function, parameters of impulse oscillometry were compared to spirometry and body plethysmography parameters during metacholine challenge testing. In our study we included 102 patients aged 18 to 65 years.
We performed a statistical analysis of the specificity and sensitivity of impulse oscillometry parameters in comparison with that of standard spirometry and an evaluation of the magnitude of correlation between parameters measured with impulse oscillometry and those measured with spirometry and body plethysmography during metacholine challenge testing. We graded the correlation between results obtained with body plethysmography and impulse oscillometry using the Bland-Altman method. Considering our results, impulse oscillometry was shown to have a 97.4% sensitivity and 36.5% specificity in determining bronchial hypersensitivity. We determined that the magnitude of correlation between parameters of spirometry (ΔFEV1) and impulse oscillometry (ΔR5, ΔR20, ΔR5-ΔR20) varies. In evaluating the magnitude of correlation, ΔFEV1, which is the most important factor in provocation testing showed a moderate negative correlation with ΔR5 (rs = 0,58) and with ΔR5-ΔR20 (rs = 0,37). The correlation between ΔFEV1 and ΔFres (rs = 0,49). A positive, moderate correlation was observed between ΔFEV1 and ΔX5 (rs = 0,59); the correlation between ΔFEV1 and ΔR20 (rs = 0,05) was weak. A strong correlation was observed between body plethysmography ΔRV and spirometry (ΔFEV1) (rs = 0,78). The magnitude of correlation between body plethysmography ΔRV and impulse oscillometry was strong in respect to ΔRaw with a correlation between ΔRaw and ΔR5 of rs = 0,63 whereas the correlation between ΔRaw and ΔR20 was weak with a value of rs = 0,24.
We can conclude that there is a moderate correlation between impulse oscillometry and spirometry for certain parameters (ΔR5, ΔR5-ΔR20 and ΔX5) as with body plethysmography. Results obtained with impulse oscillometry at (ΔR5) compared to those of body plethysmography (ΔRaw) were 0,14 kPa/(L/s) higher; at (ΔR20), ΔRaw was higher by 0,1 kPa/(L/s). We estimated that the correlation between methods for measuring individual parameters is satisfactory.