Strain Analysis in Patients at High-Risk for COPD Using Four-Dimensional Dynamic-Ventilation CT

Figures & data

Table 1 Basic Clinical Characteristics and Imaging Measurements of Study Groups

Parameters		COPD (n=35)	Non-COPD (n=18)	t/z/χ^2	P
Demographics
Age (y)		60.66±11.46	55.39±9.74	−1.664	NS
No. of Male		27(77.14%)	9(50%)	4.020	0.045
No. of Ex-/current smoker		24(68.57%)	4(22.22%)	10.247	0.001
BMI		23.62±2.97	26.51±3.90	3.009	0.004
Spirometry
FVC (L)		3.45±1.10	3.57±1.13	0.364	NS
FEV1 (L)		2.23±0.89	2.88±0.94	2.449	0.018
FEV1/FVC*		65.78±9.85	80.57±4.50	−5.597	<0.001
PEF (L)		6.60±2.45	8.25±1.99	2.465	0.017
MMEF75% (L/S)		4.11±2.24	7.10±2.16	4.662	<0.001
MMEF50% (L/S)		1.74±0.96	3.65±1.40	5.842	<0.001
MMEF25% (L/S)		0.48±0.26	1.08±0.56	−4.077	<0.001
MMEF25-75% (L/S)		1.26±0.71	2.81±1.21	−4.508	<0.001
Imaging measurements
Static CT	LD index (%)*	7.50±13.90	5.30±15.55	−1.146	NS
	TLV (mL)	4710.80±1036.03	3499.11±1498.99	−2.892	0.004
Dynamic-ventilation CT	PSmax-all*	150.57±168.39	626.00±584.17	−4.658	<0.001
	PSmean-all*	14.02±23.98	65.93±106.48	−4.320	<0.001
	Speedmax-all*	18.30±18.78	49.87±37.53	−4.104	<0.001
	PSmax2s*	62.22±76.96	205.34±131.47	−3.794	<0.001
	PSmean2s*	6.25±9.23	18.52±42.12	−4.432	<0.001
	Speedmax2s*	14.10±14.05	45.05±38.29	−4.157	<0.001

Notes: *Data are expressed as medians ± interquartile range. Except where indicated, data are means ± standard deviation. Strain-related parameters of the whole expiration phase: PS_max-all, PS_mean-all, Speed_max-all. Strain-related parameters of the first 2s of expiration phase: PS_max2s, PS_mean2s, Speed_max2s.

Abbreviations: COPD, chronic obstructive pulmonary disease; BMI, body mass index; FVC, forced vital capacity; FEV₁, forced expiratory volume at 1 second; PEF, peak expiratory flow; MMEF, maximum mid-expiratory flow; NS, no significant; LD index, low density index, defined as the percent low attenuation (<-950 Hounsfield units) volume of the whole lung; TLV, total lung volume.

Figure 1 Lung volume-frame curve.

Figure 2 Schematic diagram of strain analysis.

Table 2 Correlations Between CT Measurements and Spirometry

CT Measurement		Correlation Coefficients (ρ)
		FVC	FEV1	FEV1/FVC	PEF	MMEF75%	MMEF50%	MMEF25%	MMEF25-75%
Dynamic-ventilation CT	PSmax-all	0.121 (NS)	0.237 (NS)	0.450 (P <0.001)	0.251 (NS)	0.396 (P =0.003)	0.397 (P =0.003)	0.420 (P =0.002)	0.410 (P =0.002)
	PSmean-all	0.208 (NS)	0.354 (P =0.004)	0.614 (P <0.001)	0.340 (P =0.013)	0.514 (P <0.001)	0.543 (P <0.001)	0.569 (P <0.001)	0.591 (P <0.001)
	Speedmax-all	−0.026 (NS)	0.187 (NS)	0.679 (P <0.001)	0.262 (NS)	0.436 (P =0.001)	0.438 (P =0.001)	0.364 (P =0.007)	0.467 (P <0.001)
	PSmax2s	0.122 (NS)	0.324 (P =0.018)	0.621 (P <0.001)	0.354 (P =0.004)	0.585 (P <0.001)	0.547 (P <0.001)	0.542 (P <0.001)	0.564 (P <0.001)
	PSmean2s	0.264 (NS)	0.431 (P =0.001)	0.652 (P <0.001)	0.456 (P =0.001)	0.616 (P <0.001)	0.612 (P <0.001)	0.597 (P <0.001)	0.643 (P <0.001)
	Speedmax2s	−0.023 (NS)	0.193 (NS)	0.687 (P <0.001)	0.275 (P =0.046)	0.467 (P <0.001)	0.455 (P =0.001)	0.371 (P =0.006)	0.475 (P <0.001)
Static CT	LD index	−0.094 (NS)	−0.210 (NS)	−0.370 (P =0.006)	−0.047 (NS)	−0.231 (NS)	−0.337 (P =0.013)	−0.338 (P =0.004)	−0.336 (P =0.014)

Notes: Strain-related parameters of the whole expiration phase: PS_max-all, PS_mean-all, Speed_max-all. Strain-related parameters of the first 2s of expiration phase: PS_max2s, PS_mean2s, Speed_max2s.

Abbreviations: FVC, forced vital capacity; FEV₁, forced expiratory volume at 1 second; PEF, peak expiratory flow; MMEF, maximum mid-expiratory flow; NS, no significant. LD index, low density index, defined as the percent low attenuation (<-950 Hounsfield units) volume of the whole lung.

Table 3 Strain-Related Parameters in COPD Patients with Different Severity of Airflow Restriction

Strain-Related Parameters		GOLD I (n=19)	GOLD II–IV (n=16)	Z	P
Whole expiration	PSmax-all	186.89±218.86	62.21±118.82	−2.782	0.005
	PSmean-all	18.70±27.86	8.17±21.64	−1.788	NS
	Speedmax-all	21.99±22.66	11.77±20.73	−2.053	0.04
First 2s of expiration	PSmax2s	75.58±149.96	52.97±92.92	−1.126	NS
	PSmean2s	7.08±8.22	3.68±15.35	−0.966	NS
	Speedmax2s	16.58±24.58	10.97±17.56	−1.722	NS

Abbreviations: COPD, chronic obstructive pulmonary disease; GOLD, Global Initiative for Chronic Obstructive Lung Disease; NS, no significant.

Table 4 Cut-off Values and Corresponding Diagnostic Rate for Strain-Related Parameters

Strain-Related Parameters		Cut-off value	Accuracy	Sensitivity	Specificity
Whole expiration	PSmax-all	378.76	69.91	54.29	100
	PSmean-all	38.46	81.13	82.86	77.78
	Speedmax-all	27.09	81.13	77.14	88.89
First 2s of expiration	PSmax2s	65.48	86.79	94.29	72.22
	PSmean2s	13.18	83.02	85.71	77.78
	Speedmax2s	23.34	83.02	80.00	88.89

Figure 3 Receiver-operating characteristic curve for strain-related parameters in distinguishing COPD patients from non-COPD ones.