Computer quantification of “angle of collapse” on maximum expiratory flow volume curve for diagnosing asthma-COPD overlap syndrome

Figures & data

Figure 1 Example of the measurement of AC.

Notes: (A) The data points and the optimal couple of regression lines of the descending branch of the maximum expiratory flow volume curve. (B) The MSE of each couple of regression lines. The red point represents the couple of regression line with lowest MSE, which was defined as the optimal couple of regression lines.
Abbreviations: AC, angle of collapse; MSE, mean square error.

Table 1 Participants’ characteristics

	Controls (n=392)	Asthma (n=151)	COPD (n=173)	P-value
Age, years	57.5±11.4	58.2±9.4***	65.1±9.1*	<0.01a
Sex, female/male	189/203	81/70	34/139	<0.01b
BMI, kg/m^2	24.74±3.64	25.5±3.9***	22.8±4.2*,#	<0.01a
Smoking, pack-years	0	12.1±21.8	31.8±25.8	<0.01c
Current/former/never smoker	0/0/392	28/23/100	73/71/29	<0.01b
FEV1, % predicted	102.3±12.6	65.1±22.5*	45.2±16.2*,#	<0.01a
FVC, % predicted	106.2±13.7	88.5±18.1*	72.4±16.1*,#	<0.01a
VC, % predicted	104.8±13.2	88.9±17.1*	76.4±15.2*,#	<0.01a
FEV1/FVC, %	80.65±4.6	60.5±13.9*	50.6±12.0*,#	<0.01a
EI, %	NA	6.2±6.8	13.8±11.8	<0.01c
AC	165.5±9.0	147.6±12.9*	135.1±14.2*,#	<0.01a

Notes: Data are presented as mean ± standard deviation.

* P<0.01 and

*** P>0.05 vs controls;

# P<0.01 vs asthma patients.

a Analysis of Kruskal–Wallis test.

b Analysis of chi-square test.

c Analysis of Mann–Whitney U test.

Abbreviations: AC, angle of collapse; BMI, body mass index; EI, emphysema index; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; NA, not applicable; VC, vital capacity.

Table 2 AC of patients with different degree of airflow limitation and EI

	High EI		Low EI		P-value
	N	AC	N	AC
FEV1.0/FVC >0.7	0	NA	51	159.1±8.8	NA
GOLD I–II	28	140.2±11.0	89	148.4±7.04	<0.001
GOLD III–IV	94	125.2±10.9	62	139.4±8.50	<0.001

Note: Data are presented as mean ± standard deviation.

Abbreviations: AC, angle of collapse; EI, emphysema index; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease; NA, not applicable.

Table 3 The comparison between high and low EI patients with airflow limitation

	High EI patients (n=50)	Low EI patients (n=50)	P-value
Age, years	65.4±9.1	62.9±9.5	0.191a
Sex, female/male	10/40	16/34	0.254b
BMI, kg/m^2	21.6±4.0	24.8±3.4	<0.001a
Smoking, pack-years	35.1±27.4	21.5±22.6	0.008a
FEV1, % predicted	45.3±17.2	47.7±14.2	0.447a
FVC, % predicted	78.4±19.8	71.4±14.2	0.045a
VC, % predicted	80.8±18.8	75.4±13.7	0.104a
EI, %	20.6±10.2	4.2±2.8	<0.001a
AC, degrees	129.8±13.3	141.4±9.5	<0.001a

Notes: Data are presented as mean ± standard deviation.

a Analysis of Mann–Whitney U test.

b Analysis of chi-square test.

Abbreviations: AC, angle of collapse; BMI, body mass index; EI, emphysema index; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; NA, not applicable; VC, vital capacity.

Figure 2 AC of patients with high and low EI.

Notes: (A) Patient with high EI, FEV_1.0, % =44.9%, EI =27.8%, AC =122.5°; (B) patient with low EI, FEV_1.0, % =44.5%, EI =6%, AC =149.57°.
Abbreviations: AC, angle of collapse; EI, emphysema index; FEV₁, forced expiratory volume in 1 second.

Table 4 Relationship between pulmonary function parameters and emphysema index in univariate correlation analysis

	r	P-value
AC, degrees	−0.666	<0.001
FEV1.0/FVC, %	−0.615	<0.001
FEV1.0, % predicted	−0.496	<0.001
FVC, % predicted	−0.269	<0.001
VC, % predicted	−0.214	<0.001

Abbreviations: AC, angle of collapse; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; VC, vital capacity.

Table 5 Relationship between pulmonary function parameters and emphysema index in multiple regression analysis

	r	P-value
Model	0.686	0.022
AC, degrees	−0.357	<0.001
FEV1.0/FVC, %	−0.203	<0.001
FEV1.0, % predicted	0.138	<0.001

Abbreviations: AC, angle of collapse; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity.

Table 6 The AUC of ROC curve of AC and other pulmonary function parameters

	AUC	95% CI
AC	0.876	0.835–0.909
FEV1.0/FVC, %	0.863	0.821–0.899
FEV1.0, % predicted	0.809	0.761–0.850
FVC, % predicted	0.652	0.597–0.703
VC, % predicted	0.646	0.591–0.698

Abbreviations: AC, angle of collapse; AUC, area under the curve; CI, confidence interval; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; ROC, receiver-operating characteristic curve; VC, vital capacity.

Figure 3 The receiver-operating characteristic curve of angle of collapse for diagnosing high emphysema index.