Diagnostic Ability of Impulse Oscillometry in Diagnosis of Chronic Obstructive Pulmonary Disease

Figures & data

Figure 1. Flow-chart describing the study population.

Table 1. Baseline characteristics of subjects. (N = 147).

Clinical characteristics	COPD (n = 67)	Chronic smokers (n = 50 )	Healthy subjects (n = 30)	p-value
Male n (%)	58 (86.6)	45 (90.0)	25 (83.3)	0.693
Age (year)	68.2 ± 8.3	69.1 ± 9.2	68.5 ± 8.1	0.869
Height (cm)	158.7 ± 7.2	159.7 ± 6.2	159.7 ± 6.8	0.631
Body weight (kg)	56.9 ± 12.9	56.6 ± 12.3	58.9 ± 9.7	0.698
Body mass index (km/m^2)	22.5 ± 4.5	22.1 ± 4.2	22.9 ± 2.6	0.672
Smoking status n (%)^a				1.000
Non-smoker	0 (0.0)	0 (0.0)	23 (76.7)
Current-smoker	4 (6.0)	3 (6.0)	0 (0.0)
Ex-smoker	63 (94.0)*	47 (94.0)*	7 (23.3)
Smoking pack-years^b	31.7 ± 24.4*	33.2 ± 20.4*	0.92 ± 1.74	0.726
Signs and symptoms (yes), n (%)
Cough^a	38 (56.7)	34 (68.0)	NA	0.252
Phlegm^a	25 (37.0)	19 (38.0)	NA	1.000
Dyspnea^a	56 (83.6)	34 (68.0)	NA	0.075
Emphysematous change in CXR (yes)^a	21 (31.3)	4 (8.0)	NA	0.003
Age of symptom onset (year)^b	66.2 ± 8.9	67.9 ± 9.8	NA	0.336
Duration of symptoms (month) (Median, IQR)^c	6 (2-12)	3 (1-12)	NA	0.025
Comorbidity n (%)
Cardiovascular disease^a	42 (62.7)*	29 (58.0)*	7 (23.3)	0.703
Metabolic disease^a	11 (16.4)*	19 (38.0)*	0 (0.0)	0.010
Neuromuscular disease^a	7 (10.4)	1 (2.0)	0 (0.0)	0.135

Note: Data are mean ± standard deviation (SD) unless otherwise stated; ^ap-value from exact test comparing COPD and chronic smokers; ^bp-value from t-test comparing COPD and chronic smokers; ^c, p-value from Mann-Whitney U test comparing COPD and chronic smokers; *, p < 0.001 compared with healthy subjects group.

Abbreviations: CXR, chest X-rays; IQR, interquartile range.

Table 2. Spirometric data of subjects.

Spirometry data (Pre-bronchodilator)	COPD (n = 67)	Chronic smokers (n = 50 )	Healthy subjects (n = 30)	p-value
FEV1 (L)^a	1.29 ± 0.44*	1.96 ± 0.49*	2.29 ± 0.56	<0.001
%predicted of FEV1^a	55.9 ± 16.6*	84.6 ± 14.3*	99.0 ± 16.4	<0.001
FVC (L)^a	2.29 ± 0.65*	2.59 ± 0.64	2.89 ± 0.58	0.039
%predicted of FVC^a	79.6 ± 17.9*	89.3 ± 16.0*	99.8 ± 12.9	0.006
FEV1/FVC (%)^a	55.9 ± 9.3*	76.2 ± 7.4	78.1 ± 5.4	<0.001
FEF25-75% (L/sec)^a	0.58 ± 0.25*	1.69 ± 0.74*	2.16 ± 0.77	<0.001

Note: Data are mean ± standard deviation (SD); ^a, p-value from ANOVA with Bonferroni adjustment compared between COPD and chronic smokers; *, p < 0.001 compared healthy subjects group from ANOVA with Bonferroni adjustment.

Abbreviations: FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second; FEF25-75%, forced expiratory flow at 25-75% of FVC; L, liter.

Table 3. IOS parameters of subjects.

IOS parameters	COPD (n = 67)	Chronic smokers (n = 50 )	Healthy subjects (n = 30)	p-value
Z5 (cmH2O/L/s)^a	5.53 ± 2.05*	3.54 ± 0.96	3.22 ± 0.78	<0.001
R5 (cmH2O/L/s)^a	4.96 ± 1.71*	3.32 ± 0.91	3.06 ± 0.72	<0.001
R20 (cmH2O/L/s)^a	3.16 ± 1.03*	2.61 ± 0.71	2.58 ± 0.64	0.002
R5 - R20 (cmH2O/L/s)^a	1.79 ± 1.05*	0.71 ± 0.47	0.48 ± 0.26	<0.001
X5 (cmH2O/L/s)^a	−2.36 ± 1.34*	−1.18 ± 0.46	−0.99 ± 0.40	<0.001
Fres (Hz)^a	23.50 ± 5.48*	16.65 ± 4.05*	13.93 ± 2.70	<0.001
AX (cmH2O/L)^a	21.14 ± 14.76*	6.36 ± 4.44	3.51 ± 2.01	<0.001

Note: Data are mean ± standard deviation (SD); ^a, p-value from ANOVA with Bonferroni adjustment compared between COPD and chronic smokers; *, p < 0.001 compared healthy subjects group from ANOVA with Bonferroni adjustment.

Abbreviations: Z5, impedance at 5 hertz; R5, resistance at 5 Hz; R20, resistance at 20 Hz, R5-R20; heterogeneity of resistance between R5 and R20; Fres, resonant frequency; X5, reactance at 5 Hz; AX, area under reactance curve between 5 Hz and resonant frequency.

Figure 2. Receiver operating characteristic curves illustrating the performance of IOS variables in diagnosis of COPD using the ratio of FEV₁/FVC < LLN (A) and the ratio of FEV₁/FVC < 0.7 (B) between COPD and chronic smokers.

Note: AuROC from score based ROC.

Figure 3. Receiver operating characteristic curves illustrating the performance of IOS variables in diagnosis of COPD using the ratio of FEV₁/FVC < LLN (A) and the ratio of FEV₁/FVC < 0.7 (B) between COPD and normal subjects.

Note: AuROC from score based ROC.

Table 4. Diagnostic performances of IOS parameters for diagnosis of COPD using the ratio of FEV₁/FVC < LLN and the ratio of FEV₁/FVC < 0.7 between COPD and chronic smokers.

IOS variable	Cutoff value	Sensitivity	Specificity	+ LR	- LR	AUC
Diagnosis of COPD using the ratio of FEV1/FVC < LLN
AX (cmH2O/L)	≥8.66	79.1	78.0	3.60	0.27	0.79
Fres (Hz)	≥19.48	70.1	78.0	3.19	0.38	0.74
R5 – R20 (cmH2O/L/s)	≥1.00	70.1	78.0	3.19	0.38	0.74
Z5 (cmH2O/L/s)	≥3.88	82.1	66.0	2.41	0.27	0.74
R5 (cmH2O/L/s)	≥3.68	79.1	68.0	2.47	0.31	0.74
X5 (cmH2O/L/s)	≤−1.33	79.1	66.0	2.33	0.32	0.73
R20 (cmH2O/L/s)	≥2.72	67.2	64.0	1.87	0.51	0.66
Combined AX ≥ 8.66 and Fres ≥ 19.48		67.2	84.0	4.20	0.39	0.76
Combined AX ≥ 8.66 and R5 – R20 ≥ 1.00		68.7	82.0	3.81	0.38	0.75
Diagnosis of COPD using the ratio of FEV1/FVC < 0.7
AX (cmH2O/L)	≥8.66	80.6	86.7	6.04	0.22	0.84
R5 – R20 (cmH2O/L/s)	≥1.00	72.2	86.7	5.42	0.32	0.79
Z5 (cmH2O/L/s)	≥3.88	83.3	73.3	3.13	0.23	0.78
R5 (cmH2O/L/s)	≥3.68	80.6	75.6	3.30	0.26	0.78
Fres (Hz)	≥19.46	72.2	82.2	4.06	0.34	0.77
X5 (cmH2O/L/s)	≤−1.33	80.6	73.3	3.02	0.27	0.77
R20 (cmH2O/L/s)	≥2.72	68.1	68.9	2.19	0.46	0.68
Combined AX ≥ 8.66 and R5 – R20 ≥ 1.00		66.7	88.9	6.00	0.38	0.78

Note: AUC from cut off based ROC.

Abbreviations: AUC, area under the curve; Z5, impedance at 5 hertz; R5, resistance at 5 Hz; R20, resistance at 20 Hz, R5-R20; heterogeneity of resistance between R5 and R20; Fres, resonant frequency; X5, reactance at 5 Hz; AX, area under reactance curve between 5 Hz and resonant frequency; + LR, positive likelihood ratio; - LR, negative likelihood ratio.

Figure 4. Receiver operating characteristic curves illustrating the performance of IOS variables in diagnosis of COPD using the ratio of FEV₁/FVC < LLN between COPD based on median %predicted of FEV₁ (A; %predicted of FEV₁ ≥ median value of group, B; % predicted of FEV₁ < median value of group) and chronic smokers.

Note: AuROC from score based ROC.

Table 5. Diagnostic performances of IOS parameters for diagnosis of COPD using the ratio of FEV₁/FVC < LLN between COPD (based on the median FEV₁) and chronic smokers.

IOS variable	Cutoff value	Sensitivity	Specificity	+ LR	- LR	AUC
COPD with % predicted of FEV1 ≥ median value of group (53.9%)
AX (cmH2O/L)	≥ 8.66	64.7	78.0	2.94	0.45	0.71
X5 (cmH2O/L/s)	≤ −1.33	73.5	66.0	2.16	0.40	0.70
Z5 (cmH2O/L/s)	≥ 3.91	73.5	66.0	2.16	0.40	0.70
R5 (cmH2O/L/s)	≥ 3.68	70.6	68.0	2.21	0.43	0.69
Fres (Hz)	≥ 17.26	76.5	60.0	1.91	0.39	0.68
R5 – R20 (cmH2O/L/s)	≥ 0.84	70.6	60.0	1.76	0.65	0.65
R20 (cmH2O/L/s)	≥ 2.72	64.7	64.0	1.80	0.55	0.64
COPD with % predicted of FEV1 < median value of group (53.9%)
R5 – R20 (cmH2O/L/s)	≥ 1.50	87.9	96.0	21.97	0.13	0.92
AX (cmH2O/L)	≥ 11.84	93.9	88.0	7.83	0.07	0.91
Fres (Hz)	≥ 22.42	90.9	92.0	11.36	0.10	0.91
Z5 (cmH2O/L/s)	≥ 4.56	81.8	88.0	6.82	0.21	0.85
R5 (cmH2O/L/s)	≥ 4.16	75.8	76.0	3.16	0.32	0.76
X5 (cmH2O/L/s)	≤ −1.34	84.8	66.0	2.50	0.23	0.75
R20 (cmH2O/L/s)	≥ 2.72	69.7	64.0	1.94	0.47	0.67

Note: AUC from cut off based ROC.

Abbreviations: AUC, area under the curve; Z5, impedance at 5 hertz; R5, resistance at 5 Hz; R20, resistance at 20 Hz, R5-R20; heterogeneity of resistance between R5 and R20; Fres, resonant frequency; X5, reactance at 5 Hz; AX, area under reactance curve between 5 Hz and resonant frequency; + LR, positive likelihood ratio; - LR, negative likelihood ratio.

Table 6. IOS parameters of subjects in our study compared to previous studies.

IOS parameters	COPD		Chronic smokers		Healthy subjects
	Our study	Previous studies	Our study	Previous studies	Our study	Previous studies
R5 (cmH2O/L/s)	4.86	3.26-4.99^[9,19,20]	3.20	3.05-3.16^[9,20]	3.06	2.75-3.36^[19,20]
R20 (cmH2O/L/s)	3.14	2.34-3.06^[9,18-20]	2.56	2.45-2.55^[9,20]	2.58	2.54-2.65^[19,20]
R5-R20(cmH2O/L/s)	1.71	0.81-1.93^[9,19,20]	0.64	0.61-1.71^[9,20]	0.48	0.20-0.71^[19,20]
X5 (cmH2O/L/s)	−2.26	−1.02- −2.95^[9,14,15,19,20]	−1.10	−0.81- −0.92^[9,20]	−0.99	−0.82- −1.02^[14,15,19,20]
Fres (Hz)	23.07	20.7-25.5^[15,18-20]	16.13	12.1-14.37^[14,20]	13.92	11.21-15.70^[14,15,19,20]
AX (cmH2O/L)	19.76	18.4-20.25^[18,20]	5.48	2.03-3.47^[9,20]	3.51	1.93-3.87^[9,20]

Abbreviations: R5, resistance at 5 Hz; R20, resistance at 20 Hz, R5-R20; heterogeneity of resistance between R5 and R20; Fres, resonant frequency; X5, reactance at 5 Hz; AX, area under reactance curve between 5 Hz and resonant frequency.