Figures
- FIGURE 1
Comparison of standard (uncorrected) and corrected multiple breath nitrogen washout (MBNW) parameters in health. There were strong correlations between uncorrected and corrected functional residual capacity (FRC) (r=0.99 and p<0.0001) (a), lung clearance index (LCI) (r=0.94 and p<0.0001) (b), Scond (r=0.86, p<0.0001) (c) and Sacin (r=0.98, p<0.0001) (d). Bland–Altman plots show that sensor correction results in a lower FRC (mean difference (95% limits of agreement) (−0.25 (−0.46, −0.04), p<0.0001) (e), lower LCI (−0.71 (−1.14– −0.28), p<0.0001) (f), higher Scond (0.002 (−0.007–0.012), p=0.027) (g), but no change in Sacin (−0.0009 (−0.006–0.004), p=0.08) (h). There was also significant proportional bias confirmed by linear regression for FRC (p<0.0001), LCI (p<0.007) and Scond (p=0.0009). Sacin: distal/intra-acinar airways ventilation heterogeneity; Scond: conducting airways ventilation heterogeneity.
- FIGURE 2
Comparison of standard (uncorrected) and corrected multiple breath nitrogen washout (MBNW) parameters in asthma. There were strong correlations between uncorrected and corrected functional residual capacity (FRC) (r=0.99 and p<0.0001) (a), lung clearance index (LCI) (r=0.98 and p<0.0001) (b), Scond (r=0.94, p<0.0001) (c) and Sacin (r=0.98, p<0.0001) (d). Bland–Altman plots show that sensor correction results in a lower FRC (mean difference (95% limits of agreement) (−0.22 (−0.38–0.06), p<0.0001) (e), lower LCI (−0.71 (−1.24– −0.18), p<0.0001) (f), higher Scond (0.004 (−0.006–0.014), p=0.003) (g) and lower Sacin (−0.002 (−0.007–0.003), p=0.003) (h). There was also significant proportional bias confirmed by linear regression for FRC (p=0.02) and LCI (p=0.01). Sacin: distal/intra-acinar airways ventilation heterogeneity; Scond: conducting airways ventilation heterogeneity.
- FIGURE 3
Comparison of standard (uncorrected) and corrected multiple breath nitrogen washout (MBNW) parameters in smokers. There were strong correlations between uncorrected and corrected functional residual capacity (FRC) (r=0.99 and p<0.0001) (a), lung clearance index (LCI) (r=0.97 and p<0.0001) (b), Scond (r=0.93, p<0.0001) (c) and Sacin (r=0.99, p<0.0001) (d). Bland–Altman plots show that sensor correction results in a lower FRC (mean difference (95% limits of agreement) (−0.28 (−0.50– −0.06), p<0.0001) (e), lower LCI (−0.65 (−1.16– −0.13), p<0.0001) (f), higher Scond (0.009 (−0.006–0.025), p=0.0004) (g) and lower Sacin (−0.004 (−0.015–0.006), p=0.008) (h). There was also significant proportional bias confirmed by linear regression for FRC (p=0.04), LCI (p=0.03) and Scond (p=0.01). The uncorrected value is the reference. Absolute differences were calculated as corrected – uncorrected. Sacin: distal/intra-acinar airways ventilation heterogeneity; Scond: conducting airways ventilation heterogeneity.
- FIGURE 4
Normalised phase III slope (SnIII) versus lung turnover (TO) graphs in health (a), asthma (b) and smokers (c). Open squares represent corrected values (with sensor correction) and solid circles uncorrected values. Scond is calculated as the slope of the plot of SnIII versus lung TO, between TO 1.5 and 6. Corrected SnIII values are increased resulting in larger Scond as calculated between TO 1.5 and 6 in all three patient groups. The change in SnIII in the first breath was minimal, explaining the minimal effects seen in Sacin post-correction. SnIIIms: slope of alveolar phase (phase III) normalised by mean slope concentration.
Tables
- TABLE 1
Participant demographics and lung function
Health Asthma Smokers Participants (n) 27 20 16 Males/females (n) 16/11 4/16 12/4 Age (years) 34 (19–65) 43 (24–78)¶ 43 (27–54)+ BMI (kg·m−2) 24.6±3.4 25.5±4.3 27.4±6.4 Smoking history (pack-years) 19.3±8.6 Lung function FEV1 (% predicted) 105.0±14 89.2±19¶ 98.8±11§ FVC (% predicted) 105.0±15 97.7±20 105.5±11 FEV1/FVC (%) 83±6.0 74±8.4¶ 76±6.0+ TLC (% predicted) 101±23 103±18 108±11 FRCpleth (% predicted) 97.0±27 97.0±17 109.1±19 DLCO (% predicted) 102±13 99±15 90±12+ FRCMBNW (L)# 2.94±0.89 2.62±0.72 2.93±0.84 LCI (TO)# 6.49±0.47 7.23±1.04¶ 7.05±0.82+ Scond (L−1)# 0.019±0.011 0.033±0.018¶ 0.038±0.019§ Sacin (L−1)# 0.056±0.020 0.086±0.049 0.095±0.037+,§ Data are presented as mean±sd or median (interquartile range) unless otherwise stated. BMI: body mass index; DLCO: diffusing capacity of the lung for carbon monoxide; FEV1: forced expiratory volume in 1 s; FRC: functional residual capacity; FVC: forced vital capacity; LCI: lung clearance index; MBNW: multiple breath nitrogen washout; Sacin: distal/intra-acinar airways ventilation heterogeneity; Scond: conducting airways ventilation heterogeneity; TLC: total lung capacity; TO: lung turnover. #Corrected, controlled breathing protocol values used. ¶p<0.05 health versus asthma. +p<0.05 health versus smokers. §p<0.05 asthma versus smokers.
- TABLE 2
Effects of sensor correction on main MBNW parameters
Parameter Standard Corrected Mean difference
(95% CI) absoluteMean difference
(95% CI) relativep-value Health FRC (L) 3.19±0.98 2.94±0.89 −0.25 (−0.29– −0.21) −7.7 (−8.4– −7.0) <0.0001 LCI (TO) 7.20±0.58 6.49±0.47 −0.71 (−0.80– −0.63) −9.8 (−10.8– −8.8) <0.0001 Scond (L−1) 0.017±0.009 0.019±0.011 0.002 (0.0003–0.004) 11.1 (−1.4–23.5) 0.03 Sacin (L−1) 0.057±0.020 0.056±0.020 −0.0009 (−0.002–0.0001) −1.8 (−4.0–0.44) 0.08 Asthma FRC (L) 2.84±0.76 2.62±0.72 −0.22 (−0.26– −0.18) −8.0 (−9.2– −6.8) <0.0001 LCI (TO) 7.94±1.19 7.23±1.04 −0.71 (−0.84– −0.58) −8.8 (−10.0– −7.6) <0.0001 Scond (L−1) 0.029±0.016 0.033±0.018 0.004 (0.001–0.006) 14.0 (4.2–23.9) 0.003 Sacin (L−1) 0.088±0.049 0.086±0.049 −0.002 (−0.003– −0.0008) −2.9 (−4.9– −0.9) 0.003 Smokers FRC (L) 3.19±0.91 2.93±0.84 −0.28 (−0.34– −0.22) −8.4 (−10.2– −6.7) <0.0001 LCI (TO) 7.69±0.96 7.05±0.82 −0.65 (−0.78– −0.51) −8.3 (−9.7– −6.8) <0.0001 Scond (L−1) 0.029±0.015 0.038±0.019 0.009 (0.005–0.013) 36.0 (19.8–52.2) 0.0004 Sacin (L−1) 0.10±0.040 0.095±0.037 −0.004 (−0.007– −0.001) −4.8 (−8.9– −0.71) 0.008 Effects of sensor correction on main MBNW parameters. Data are presented as mean±sd unless otherwise stated. FRC: functional residual capacity; LCI: lung clearance index; MBNW: multiple breath nitrogen washout; Sacin: distal/intra-acinar airways ventilation heterogeneity; Scond: conducting airways ventilation heterogeneity; TO: lung turnover. The standard (uncorrected) value is the reference. Absolute difference is calculated as corrected – standard. Relative difference is calculated as corrected – standard/standard × 100.
- TABLE 3
Effects on within- and between-session repeatability in health
Within-session CoV Between-session difference Between-session 95% LoA Between-session ICC Uncorrected FRC (L) 3.3±2.9% −0.03±0.52 −1.04–0.98 0.931 LCI (TO) 2.5±2.4% 0.06±0.47 −0.86–0.98 0.812 Scond (L−1) – −0.001±0.011 −0.017–0.015 0.836 Sacin (L−1) – −0.003±0.018 −0.037–0.031 0.835 Corrected FRC (L) 3.0±1.9% −0.02±0.47 −0.94–0.91 0.927 LCI (TO) 2.4±1.7% 0.13±0.34 −0.53–0.79 0.849 Scond (L−1) – −0.003±0.009 −0.021–0.015 0.867 Sacin (L−1) – −0.002±0.02 −0.039–0.034 0.828 Data are presented as mean±sd unless otherwise stated. Mean differences are visit 2 minus visit 1. 95% LoA: 95% limits of agreement; CoV: coefficient of variation; FRC: functional residual capacity; ICC: intra-class correlation coefficient; LCI: lung clearance index; Sacin: distal/intra-acinar airways ventilation heterogeneity; Scond: conducting airways ventilation heterogeneity; TO: lung turnover.
