A size-based emphysema severity index: robust to the breath-hold-level variations and correlated with clinical parameters

Figures & data

Table 1 Demographic and clinical characteristics of study subjects

Characteristic	Value
Number of subjects	100 (males: 97, females: 3)
Age (years), mean ± SD (range)	67±7.8 (48–84)
Body mass index (kg/m^2), mean ± SD	23±3.6
Smoking amount (pack-years), mean ± SD (range)	42±22 (14–108)
GOLD stage, stage: subjects (n)	I: 4, II: 44, III: 44, and IV: 8
Post-BD FEV1 (%pred), mean ± SD	51±16
cDLCO (%pred), mean ± SD	73±30
SGRQ score, mean ± SD	34.8±18.9
6MWD (m), mean ± SD	446±99

Abbreviations: GOLD, Global Initiative for Chronic Obstructive Lung Disease; BD, bronchodilator; FEV₁, forced expiratory volume in 1 second; cDLCO, corrected diffusing capacity of the lungs for carbon monoxide to hemoglobin; pred, predicted; SGRQ, St George’s Respiratory Questionnaire; 6MWD, 6-minute-walk-test distance.

Figure 1 Emphysematous holes identified and measured in volumetric CT of a subject during inspiration and expiration.

Notes: (A) Inspiratory CT image of a subject, showing low-attenuation masks (>−950 HU; EI_ins% 13.79). (B) Low-attenuation masks of expiratory CT of the same subject (EI_exp% 1.57). (C) Three-dimensional visualization of emphysematous holes in A with size-based color coding. (D) Three-dimensional visualization of emphysematous holes in B with size-based color coding. (E) Distributions of emphysematous hole sizes in inspiratory and expiratory CT scans of the same subject as in A–D on cumulative log–log scale. The size distribution followed a power law with exponents D_ins =4.70 (R²=0.97) and D_exp =4.90 (R²=0.96).
Abbreviations: CT, computed tomography; HU, Hounsfield units; EI, emphysema index; ins, inspiration; exp, expiration; D, power-law exponents.

Figure 2 Effects of inspiration and expiration on (A) EI%s and (B) Ds.

Abbreviations: EI, emphysema index; D, power-law exponent.

Figure 3 Bland–Altman plots of the robustness of D and EI% to breath-hold levels.

Notes: (A) EI% measured during inspiratory and expiratory CT scans; the mean difference was 9.8%. (B) D measured during inspiratory and expiratory CT scans; the mean difference was 0.022.
Abbreviations: EI, emphysema index; CT, computed tomography; SD, standard deviation; D, power-law exponents; ins, inspiration; exp, expiration.

Table 2 Associations of D_ins with post-BD FEV₁ (%pred), cDLCO (%pred), 6MWD, SGRQ score, and EI_ins%

Indices	Pearson’s correlation coefficients with Dins (ρ-values)
Post-BD FEV1 (%pred)	0.47 (ρ<0.0001)
cDLCO (%pred)	0.59 (ρ<0.0001)
6MWD	0.34 (ρ=0.0004)
SGRQ score	−0.38 (ρ=0.0001)
EIins %	−0.77 (ρ<0.0001)

Abbreviations: BD, bronchodilator; FEV₁, forced expiratory volume in 1 second; cDLCO, corrected diffusing capacity of the lungs for carbon monoxide to hemoglobin; 6MWD, 6-minute-walk-test distance; SGRQ, St George’s Respiratory Questionnaire; EI, emphysema index; D, power-law exponents; ins, inspiration; exp, expiration; pred, predicted.

Figure S1 EI% differences (A) were affected by the lung volume changes but D differences (B) were not.

Abbreviations: EI, emphysema index; D, power-law exponents; ins, inspiration; exp, expiration; V, lung volume.