3.2.2 short- and mid-term repeatability
Short-term repeatability of LCI and FRC was assessed in sixteen children with CF and is summarized in Supplemental Table 1. Average LCI in children with CF was lower when analyzed in Spiroware 3.3.1 (LCI 9.4 (SD 1.8) vs. 10.8 (2.2)). In general, repeatability of MBW measurements was similar when analyzed in Spiroware 3.2.1 and 3.3.1. Variability between measurements expressed as CV% increased slightly in Spiroware 3.3.1 (LCI: 4.2 vs 3.7; FRC 3.7 vs 3.6). Also when expressing relative differences between measurements, the upper limit of normal (95% quantile) increased marginally (9.1 vs 8.4%).
Mid-term repeatability of LCI measurements was assessed in 12 healthy children and 23 children with CF, results are summarized in Supplemental Table 1. Mean (SD) LCI in healthy children was 6.8 (0.4) when assessed in Spiroware 3.2.1 and 6.1 (0.3) in Spiroware 3.3.1, in children with CF mean (SD) LCI was 11.6 (2.6) and 9.7 (2.2) in Spiroware 3.2.1 and 3.3.1, respectively. Repeatability indices were similar when assessed in Spiroware 3.2.1 and 3.3.1. While variability tended to be lower in healthy children when analyzed in Spiroware 3.3.1 (CV% 3.4 vs 4.4) this was the opposite in children with CF (CV% 9.6 (3.3.1) vs 8.1 (3.2.1). Similarly, when assessing relative changes between visits, the upper limit of normal (95% quantile) was lower in healthy children in Spiroware 3.3.1 compared to 3.2.1 but higher in children with CF in 3.3.1 (Supplemental Table 1). While we found within-subject between test standard deviation to be independent of the magnitude of LCI for both Spiroware settings (Supplemental Figure 1), within-subject within-test standard deviation was associated with the magnitude of LCI for both settings (Spiroware 3.2.1: R2= 0.3 (p<0.001); 3.3.1: R2= 0.2 (p<0.001).
3.2.3 validity