Figures
- FIGURE 1
Functional residual capacity measured by controlled breathing (FRCCB) and free breathing (FRCFB) protocols. a) There was strong correlation between the protocols (r=0.96, p<0.0001). b) Bland–Altman plot showing good agreement between the protocols (mean difference (95% limits of agreement) −0.009 (−0.592, 0.555) L, p=0.75).
- FIGURE 2
Functional residual capacity measured by controlled breathing (FRCCB) and free breathing (FRCFB) protocols versus the gold-standard body plethysmography (FRCpleth). There was good correlation between FRC measured by both protocols and FRCpleth (r=0.86 and r=0.92, respectively, p<0.0001 for both). MBNW: multiple breath nitrogen washout.
- FIGURE 3
Lung clearance index measured by controlled breathing (LCICB) and free breathing (LCIFB) protocols. a) There was strong correlation between the protocols (r=0.82, p<0.0001). b) Bland–Altman plot showing that free breathing produced a higher LCI compared to controlled breathing (mean difference (95% limits of agreement) 0.21 (−0.44, 0.87), p=0.003)). There was a trend towards proportional bias confirmed by linear regression (p=0.07).
- FIGURE 4
Ventilation heterogeneity in conducting airways measured by controlled breathing (ScondCB) and free breathing (ScondFB) protocols. a) There was no significant correlation between the protocols (r=0.16, p=0.44). b) Bland–Altman plot showing high between-protocol variability (mean difference (95% limits of agreement) 0.0002 (−0.03, 0.03 L−1, p=0.94)). There was no evidence of proportional bias, regardless of outliers (p=0.83).
- FIGURE 5
Ventilation heterogeneity in distal/intra-acinar airways measured by controlled breathing (SacinCB) and free breathing (SacinFB) protocols. a) There was relatively poor correlation between the protocols (r=0.33, p=0.11). b) Bland–Altman plot showing that free breathing produced higher Sacin compared to controlled breathing (mean difference (95% limits of agreement) 0.03 (−0.045, 0.103) L−1, p<0.0005)). There was also significant proportional bias confirmed by linear regression (p=0.002). The between-protocol difference in Sacin (SacinFB–SacinCB) was predicted by the between-protocol differences in c) tidal volume (VTFB−VTCB, regression p=0.004) and d) respiratory rate (RRFB−RRCB, regression p=0.009). One participant was excluded from Sacin analyses due to negative value in one trial.
Tables
- TABLE 1
Participant characteristics, lung function and multiple-breath nitrogen washout (MBNW) parameters
Whole group Repeatability subgroup Females/males n 11/16 6/9 Age years median (range) 34 (19–65) 30 (23–41) BMI kg·m−2 24.6±3.4 25.1±4.2 Lung function FEV1 % predicted# 105±14 101±30 FEV1/FVC % 83±6 84±5 TLCpleth % predicted¶ 101±23 107±11 FRCpleth % predicted¶ 97±27 104±20 MBNW parameters Controlled breathing FRCCB L 2.94±0.89 2.96±0.88 LCICB 6.49±0.47 6.39±0.36 ScondCB L−1 0.019±0.011 0.025±0.012 SacinCB L−1 0.056±0.020 0.061±0.022 VT mL 1124±37 1127±37 VT/FRCMBNW 0.40±0.16 0.42±0.15 RR breaths·min−1 10.2±0.89 9.86±1.0 Free breathing FRCFB L 2.92±0.86 3.00±0.87 LCIFB 6.70±0.59 6.57±0.57 ScondFB L−1 0.019±0.012 0.018±0.014 SacinFB L−1 0.085±0.039 0.091±0.041 VT mL 880±324 912±304 VT/FRCMBNW 0.31±0.12 0.32±0.14 RR breaths·min−1 12.3±3.53 13.6±3.10 Data are presented as mean±sd unless otherwise stated. For the repeatability subgroup, results are from the first visit. BMI: body mass index; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; TLC: total lung capacity; FRC: functional residual capacity; LCI: lung clearance index; Scond: conductive zone ventilation heterogeneity; Sacin: acinar zone ventilation heterogeneity; VT: mean tidal volume across measurements; RR: respiratory rate; pleth: body plethysmography; CB: controlled breathing protocol; FB: free breathing protocol. #: reference equations for predicted values from Quanjer et al. [13]; ¶: reference equations for predicted values from Quanjer et al. [14].
- TABLE 2
Within- and between-session variability for the controlled and free breathing protocols
Within-session CoV Between-session difference 95% LOA Between-session ICC Controlled breathing FRCCB L 3.0±1.9% −0.02±0.47 −0.94–0.91 0.927 LCICB 2.4±1.7% 0.13±0.34 −0.53±0.79 0.849 ScondCB L−1 −0.003±0.009 −0.021–0.015 0.867 SacinCB L−1 −0.002±0.02 −0.039–0.034 0.828 Free breathing FRCFB L 3.9±2.4% −0.04±0.026 −0.54–0.47 0.979 LCIFB 3.1±2.2% 0.15±0.51 −0.84–1.14 0.704 ScondFB L−1 0.006±0.016 −0.026–0.038 0.411 SacinFB L−1 0.003±0.054 −0.103–0.109 0.278 Data are presented as mean±sd unless otherwise stated. Mean differences are Visit 2 minus Visit 1. CoV: coefficient of variation; 95% LOA: 95% limits of agreement; ICC: intra-class correlation coefficient; FRC: functional residual capacity; LCI: lung clearance index; Scond: conducting airways ventilation heterogeneity; Sacin: distal/intra-acinar airways ventilation heterogeneity.
Supplementary Material
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Supplementary material 00435-2020.SUPPLEMENT
