S43 Repeatability of impulse oscillometry in patients with severe asthma

IntroductionImpulse oscillometry (IOS) has advantages over spirometry especially where accurate forced volumetric measurements may be difficult. The coefficient of variation (CV) is commonly used as a measure of precision and repeatability and can also be utilised to assess variability between different devices that perform similar tasks irrespective of units of measurement. Biological variability (BV), a measurement of natural fluctuation, is calculated as the within subject one sided 97.5% CI. Its value can be used as a surrogate for the minimal change that must be exceeded for a clinically significant treatment effect to occur.AimTo assess the medium term within subject CVs and BVs for IOS (Jaeger Masterscreen) and spirometry.MethodsData on 42 poorly controlled severe asthma patients attending clinic who underwent no change in treatment between two timepoints (T1 and T2) were retrospectively evaluated.ResultsThe mean baseline demographic data were as follows: gender (F/M) 27/15; age 53 years; FEV187%; FEF25–7551%; R5 158%; ACQ 2.1; 4 exacerbations requiring OCS in past year; mean BDP equivalent ICS dose of 1850µg and mean duration between T1 vs T2 11 months. No significant differences were detected for spirometry, IOS and ACQ between T1 and T2. Table 1 depicts the mean within subject% changes with two-sided 95%CI, CVs with two-sided 95%CI and BVs with one sided 97.5%CI. The within subject BV in ACQ was 0.6 units which is similar to the conventional MCID value of 0.5. Thus, BV values for spirometry and IOS could perhaps be interpreted as the change required for a clinically meaningful response in severe asthma patients. Hence for AX a change ≥0.39 kPa/L is required to represent a clinically meaningful response.Abstract S43 Table 1Mean within subject% change, coefficient of variation and biological variability in pulmonary function between timepoints Mean% change (95% CI ) Mean CV (95% CI ) Biological Variability (97.5% CI ) FEV1 4% (-2 – 10.1) 10.1% (6.7 – 13.5) 0.15 L FEF25–75 6.9% (-5.2 - 19) 20.3% (14.1 – 26.5) 0.21 L/s FVC 3.3% (-0.8 – 7.1) 6.9% (4.6 – 9.2) 0.15 L R5 -1.8% (-12.7 – 10.9) 16.1% (11.6 – 20.6) 0.07 kPa/L/s R20 4.8% (-2.4 – 11.9) 12.5% (9.2 – 15.8) 0.03 kPa/L/s AX -12.2% (-39.6 – 15.8) 39.2% (28.9 – 49.6) 0.39 kPa/L Fres -0.6% (-9.1 – 7.9) 14% (9.4 – 18.5) 1.5 Hz AX = area under the reactance curve; Fres = resonance frequency; R5 = resistance at 5Hz; R20 = resistance at 20Hz; Within subject biological variability was calculated as a one-