Diversity of respiratory impedance based on quantitative computed tomography in patients with COPD

Figures & data

Figure 1 Correlation between AWT-Pi10 and percentage of low attenuation volume (LAV%) in 174 patients with COPD.

Notes: ◆: Bronchodilator response using 200 μg salbutamol of FEV₁ ≥200 mL and 12% from baseline values. ◇: bronchodilator response using 200 μg salbutamol of FEV₁ <200 mL and 12% from baseline values. Horizontal line shows mean + 2SD of LAV% in the asymptomatic smokers. Vertical line shows mean + 2SD of AWT-Pi10 in the asymptomatic smokers.
Abbreviations: NCT, normal by computed tomography; AD, airway-dominant; ED, emphysema-dominant; FEV₁, forced expiratory volume in 1 second; AWT, airway wall thickness.

Table 1 Clinical characteristics of patients with the NCT, AD, ED, and mixed phenotypes

	NCT phenotype (n=36)	AD phenotype (n=49)	ED phenotype (n=58)	Mixed phenotype (n=31)
Age, years	71.3±1.5	70.1±1.2	71.6±0.9	73.3±1.1
Gender
Male, n (%)	36 (100%)	47 (95.9%)	56 (96.6%)	30 (96.8%)
Female, n (%)	0 (0%)	2 (4.1%)	2 (3.4%)	1 (3.2%)
Body mass index, kg/m^2	23.0±0.5	23.6±0.5	20.7±0.4**,$$	21.5±0.6$
Brinkman index, pack-years	58.7±5.6	55.6±4.6	59.8±2.9	62.2±5.8
Chest CT findings
AWT-Pi10	3.69±0.06	4.94±0.05**	3.75±0.05$$	4.90±0.08**,‡‡
WA%, %	59.9±0.9	73.8±0.8**	61.3±0.8$$	75.2±0.9**,‡‡
LAV%, %	1.04±0.15	0.87±0.11	16.29±1.43**,$$	12.36±1.88**,$$
Pulmonary function
VC, % predicted	88.41±2.44	90.00±1.68	95.74±2.00	92.82±2.87
FVC, % predicted	85.36±2.42	86.51±1.71	95.40±2.29*,$	86.31±3.28‡
FEV1, % predicted	65.76±2.10	60.80±1.66	58.60±1.95	49.04±2.66**,**,$,‡
FEV1/FVC, %	61.71±0.79	56.79±1.27	49.23±1.29**,$$	45.40±1.98**,$$
FRC, % predicted	92.21±2.52	98.31±3.24	108.22±3.40**	107.97±3.44**
RV, % predicted	138.59±4.32	142.26±5.72	162.93±6.78*,$	168.67±6.17**,$$
TLC, % predicted	104.55±2.20	106.79±2.03	117.97±2.56**,$$	116.73±2.61**,$
DLCO, % predicted	71.21±2.74	76.50±2.88	53.58±3.11**,$$	54.95±3.83**,$$
DLCO/VA, % predicted	94.28±3.31	100.29±3.73	63.16±2.81**,$$	67.65±4.58**,$$
delta N2, %N2/L	2.99±0.31	3.02±0.26	4.31±0.33*,$$	4.34±0.76

Note: Values are presented as mean ± standard error of the mean;

** p<0.01

* p<0.05 versus the NCT phenotype

$$ p<0.01

$ p<0.05 versus the AD phenotype

‡‡ p<0.01,

‡ p<0.05 versus the ED phenotype.

Abbreviations: NCT, normal by computed tomography; AD, airway-dominant; ED, emphysema-dominant; AWT, airway wall thickness; WA%, percentage of wall area; LAV%, percentage of low-attenuation volume; VC, vital capacity; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; FRC, functional residual capacity; RV, residual volume; TLC, total lung capacity; DLCO, diffusing capacity of lung for carbon monoxide; DLCO/VA, diffusing capacity of lung for carbon monoxide/alveolar volume.

Figure 2 Response to short-acting β₂ agonists in patients with the NCT, AD, ED, and mixed phenotypes.

Note: Values are mean ± standard error of the mean.
Abbreviations: NCT, normal by computed tomography; AD, airway-dominant; ED, emphysema-dominant; FEV₁, forced expiratory volume in 1 second.

Table 2 Respiratory impedance in patients with the NCT, AD, ED, and mixed phenotypes

	AD phenotype (n=36)	AD phenotype (n=49)	ED phenotype (n=58)	Mixed phenotype (n=31)
Whole breath
R5 (cmH2O/L/s)	2.87±0.20	4.32±1.44**	3.16±0.14$$	4.15±0.18**,‡‡
R20 (cmH2O/L/s)	2.31±0.14	3.38±0.17**	2.43±0.09$$	3.14±0.75**,‡‡
R5–R20 (cmH2O/L/s)	0.60±0.08	0.94±0.10*	0.73±0.07	1.01±0.07**
X5 (cmH2O/L/s)	−0.95±0.16	−1.97±0.20**	−1.12±0.13$$	−2.12±0.26**,‡‡
Fres (Hz)	11.37±0.79	16.14±0.79**	13.36±0.76	17.90±0.97**,‡‡
ALX (cmH2O/L/s Hz)	6.08±1.42	15.63±2.08**	8.42±1.25$	17.95±2.93**,‡‡
Expiratory phase
R5 (cmH2O/L/s)	3.11±0.23	4.66±0.24**	3.50±0.16$$	4.51±0.21**,‡‡
R20 (cmH2O/L/s)	2.43±0.15	3.51±0.20**	2.60±0.11$$	3.29±0.14**,‡‡
R5–R20 (cmH2O/L/s)	0.60±0.10	1.15±0.11**	0.90±0.07	1.22±0.10**
X5 (cmH2O/L/s)	−1.12±0.22	−2.63±0.32**	−1.46±0.19$	−2.93±0.42**,‡‡
Fres (Hz)	12.24±0.94	18.14±0.97**	14.82±0.89	20.32±1.22**,‡‡
ALX (cmH2O/L/s Hz)	7.78±1.99	22.54±3.34**	11.96±1.97	26.91±5.01**,‡
Inspiratory phase
R5 (cmH2O/L/s)	2.62±0.18	3.97±0.19**	2.81±0.13$$	3.77±0.17**,‡‡
R20 (cmH2O/L/s)	2.19±0.13	3.24±0.15**	2.26±0.09$$	2.98±0.14**,‡‡
R5–R20 (cmH2O/L/s)	0.43±0.07	0.73±0.11*	0.56±0.07	0.80±0.06**
X5 (cmH2O/L/s)	−0.75±0.11	−1.30±0.12**	−0.79±0.08$$	−1.31±0.14**,‡‡
Fres (Hz)	10.50±0.69	14.14±0.71**	11.90±0.63	15.48±0.77**,‡‡
ALX (cmH2O/L/s Hz)	4.16±0.90	8.72±1.12**	4.80±0.63$$	8.99±1.20**,‡‡
Differences between inspiratory and expiratory phases
ΔR5 (cmH2O/L/s)	−0.49±0.09	−0.69±0.14	−0.69±0.09	−0.74±0.12
ΔR20 (cmH2O/L/s)	−0.24±0.05	−0.27±0.10	−0.34±0.05	−0.32±0.08
ΔR5–R20 (cmH2O/L/s)	−0.25±0.05	−0.42±0.07	−0.35±0.05	−0.42±0.06
ΔX5 (cmH2O/L/s)	0.39±0.14	1.33±0.26	0.67±0.14	1.61±0.35**,‡
ΔFres (Hz)	−1.74±0.49	−4.01±0.60	−2.92±0.46	−4.84±0.64**
ΔALX (cmH2O/L/s Hz)	−3.74±1.33	−13.82±2.72	−6.83±1.49	−17.92±4.32**,‡

Notes: Values are presented as the mean ± standard error of the mean;

** p<0.01

* p<0.05 versus the NCT phenotype

$$ p<0.01

$ p<0.05 versus the AD phenotype;

‡‡ p<0.01

‡ p<0.05 versus the ED phenotype.

Abbreviations: NCT, normal by computed tomography; AD, airway-dominant; ED, emphysema-dominant; Fres, resonant frequency; ALX, low-frequency reactance area.

Table 3 Correlation between the respiratory impedance and the degree of airway wall thickness, emphysema, and reversibility of airway obstruction in patients with COPD (n=174)

	AWT-Pi10		WA%		LAV%		ΔFEV1		% change in FEV1
	r	p-value	r	p-value	r	p-value	r	p-value	r	p-value
Whole breath
R5	0.460	<0.001	0.518	<0.001	0.001	0.992	0.259	<0.001	0.323	<0.001
R20	0.440	<0.001	0.484	<0.001	−0.052	0.496	0.221	0.003	0.279	<0.001
R5–R20	0.283	<0.001	0.339	<0.001	0.083	0.277	0.200	0.008	0.262	<0.001
X5	−0.452	<0.001	−0.507	<0.001	−0.042	0.584	−0.251	<0.001	−0.387	<0.001
Fres	0.430	<0.001	0.482	<0.001	0.195	0.010	0.208	0.006	0.340	<0.001
ALX	0.409	<0.001	0.469	<0.001	0.106	0.167	0.234	0.002	0.370	<0.001
Expiratory phase
R5	0.441	<0.001	0.478	<0.001	0.033	0.667	0.215	0.004	0.267	<0.001
R20	0.408	<0.001	0.435	<0.001	−0.024	0.752	0.166	0.028	0.213	0.005
R5–R20	0.323	<0.001	0.363	<0.001	0.119	0.119	0.214	0.005	0.256	<0.001
X5	−0.431	<0.001	−0.479	<0.001	−0.079	0.303	−0.226	0.003	−0.359	<0.001
Fres	0.441	<0.001	0.480	<0.001	0.209	0.006	0.192	0.011	0.328	<0.001
ALX	0.397	<0.001	0.447	<0.001	0.129	0.091	0.218	0.004	0.348	<0.001
Inspiratory phase
R5	0.449	<0.001	0.528	<0.001	−0.039	0.611	0.293	<0.001	0.367	<0.001
R20	0.456	<0.001	0.517	<0.001	−0.083	0.278	0.274	<0.001	0.343	<0.001
R5–R20	0.218	0.004	0.290	<0.001	0.052	0.494	0.183	0.016	0.228	0.003
X5	−0.430	<0.001	−0.493	<0.001	0.057	0.453	−0.280	<0.001	−0.397	<0.001
Fres	0.381	<0.001	0.446	<0.001	0.161	0.034	0.214	0.005	0.330	<0.001
ALX	0.369	<0.001	0.444	<0.001	0.016	0.837	0.245	0.001	0.367	<0.001
Differences between inspiratory and expiratory phases
ΔR5	−0.144	0.058	−0.089	0.242	0.129	0.089	0.051	0.504	0.068	0.371
ΔR20	−0.057	0.456	−0.001	0.992	0.105	0.169	0.148	0.052	0.174	0.022
ΔR5–R20	−0.207	0.006	−0.170	0.025	0.120	0.116	−0.085	0.267	−0.083	0.275
ΔX5	0.351	<0.001	0.383	<0.001	−0.128	0.093	0.157	0.039	0.274	0.000
ΔFres	−0.337	<0.001	−0.326	<0.001	0.186	0.014	−0.084	0.271	−0.190	0.012
ΔALX	−0.356	<0.001	−0.387	<0.001	0.145	0.057	−0.169	0.026	−0.284	<0.001

Note: Values are presented as the mean ± standard error of the mean.

Abbreviations: Fres, resonant frequency; ALX, low-frequency reactance area; AWT, airway wall thickness; WA%, percentage of wall area; LAV%, percentage of low-attenuation volume; FEV₁, forced expiratory volume in 1 second.

Figure 3 Correlation between respiratory impedance and the degree of airway wall thickness on chest CT in patients with COPD (n=174).

Abbreviations: WA%, percentage of wall area; CT, computed tomography; AWT, airway wall thickness.