Asynchrony in respiratory movements between the pulmonary lobes in patients with COPD: continuous measurement of lung density by 4-dimensional dynamic-ventilation CT

Figures & data

Figure 1 Example of continuous mean lung density measurements in the right upper lobe using PhyZiodynamics software (Ziosoft Inc., Minato-ku, Tokyo, Japan).

Note: A spherical volume of interest (VOI) with a fixed volume (10 mm in radius) is placed and the center point of the VOI is tracked throughout the dynamic computed tomography (also see Supplementary materials).

Table 1 Clinical characteristics of 32 subjects

	Mean ± SD	(Range)
Gender (female:male)	(4:28)	–
Age (years)	70±12	(36 to 84)
Smoking index (pack-years)	46±21	(2 to 100)
Smoking status (ex-smoker:current smoker)	(16:16)	–
FEV1.0/FVC	0.73±0.12	(0.41 to 0.92)

Abbreviation: FEV_1.0/FVC, forced expiratory volume in one second/forced vital capacity.

Table 2 Measurements of lung density and correlations to FEV_1.0/FVC

	Density measurement		Correlation to FEV1.0/FVC
	Mean ± SD	(Range)	Coefficient (ρ)	P-value
Dynamic-ventilation CT
Inspiratory-MLD (HU)
Right lung	−874.9±38.1	(−941.7 to −814.8)	0.62	<0.001
Left lung	−866.9±38.6	(−953.5 to −809.9)	0.45	<0.01
RUL	−909.3±34.3	(−959.8 to −836.2)	0.52	<0.01
RML	−908.8±38.1	(−987.5 to −828.1)	0.44	<0.05
RLL	−861.6±58.0	(−969.5 to −728.0)	0.49	<0.01
LUL	−907.8±41.9	(−1,021.4 to −818.2)	0.51	<0.01
LLL	−866.9±62.4	(−971.8 to −733.5)	0.42	<0.05
Expiratory-MLD (HU)
Right lung	−809.4±57.6	(−937.6 to −704.7)	0.78	<0.0001
Left lung	−799.4±60.5	(−917.6 to −684.3)	0.74	<0.0001
RUL	−861.7±49.3	(−946.8 to −751.5)	0.70	<0.0001
RML	−862.2±47.7	(−945.9 to −765.5)	0.59	<0.001
RLL	−777.1±86.6	(−936.2 to −625.1)	0.56	<0.001
LUL	−855.6±61.6	(−1,003.4 to −731.9)	0.67	<0.0001
LLL	−788.5±86.9	(−960.2 to −641.4)	0.60	<0.001
Helical CT
LAV% (%)
Whole lung	10.8±14.8	(0 to 52.0)	−0.73	<0.0001

Abbreviations: FEV_1.0/FVC, forced expiratory volume in one second/forced vital capacity; LAV%, percentage low attenuation volume (<−950 HU); LLL, left lower lobe; LUL, left upper lobe; MLD, mean lung density; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe.

Table 3 Cross-correlation coefficients between two MLD curves of the right and left lungs and those of paired lung lobes and their correlations to FEV_1.0/FVC

Pairs – MLD curves	Cross-correlation coefficient		Correlation to FEV1.0/FVC
	Mean ± SD	(Range)	Coefficient (ρ)	P-value
Right – left lungs	0.954±0.049	(0.798 to 0.996)	0.66	<0.0001
RUL – RLL	0.784±0.366	(−0.791 to 0.993)	0.67	<0.0001
RUL – RML	0.823±0.428	(−0.984 to 0.999)	0.61	<0.001
RML – RLL	0.707±0.495	(−0.968 to 0.996)	0.72	<0.0001
LUL – LLL	0.842±0.298	(−0.460 to 0.997)	0.60	<0.001
RUL – LUL	0.928±0.160	(0.183 to 0.999)	0.60	<0.001
RLL – LLL	0.801±0.324	(−0.610 to 0.998)	0.73	<0.0001
Average of six lobar pairs	0.814±0.259	(0.065 to 0.994)	0.80	<0.0001

Abbreviations: FEV_1.0/FVC, forced expiratory volume in one second/forced vital capacity; LLL, left lower lobe; LUL, left upper lobe; MLD, mean lung density; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe.

Figure 2 Mean lung density (MLD) time curves of the right and left lungs.

Notes: In a smoker without COPD (A), the two MLD curves are comparable, suggesting that both lungs move simultaneously (cross-correlation coefficient [CCC] =0.982). In contrast, in a COPD patient (B), the right and left MLD curves are uneven and not well-matched, suggesting the occurrence of asynchronous lung movements (CCC =0.798).
Abbreviations: FEV_1.0/FVC, forced expiratory volume in one second/forced vital capacity; LAV%, percentage low attenuation volume (<−950 HU).

Figure 3 Mean lung density (MLD) time curves of three lung lobes in the right lung.

Notes: In a smoker without COPD (A), the three MLD time curves of the three lung lobes have similar shapes, which indicates synchronous respiratory movements of the lobes (cross-correlation coefficient [CCC] of three pairs =0.975–0.996). A larger change in MLD in the lower lobe than in the upper and middle lobes suggests that respiratory volume changes mainly occur in the lower lobe in this subject. In a severe COPD patient (B), the three MLD time curves are unmatched, resulting in uncertain inspiratory/expiratory movements. Note that nearly opposite MLD curves of the middle and lower lobes are observed (CCC =−0.135), suggesting that asynchronized respiratory airflow exists in this patient.

Abbreviations: FEV_1.0/FVC, forced expiratory volume in one second/forced vital capacity; LAV%, percentage low attenuation volume (<−950 HU); RUL, right upper lobe; RML, right middle lobe; RLL, right lower lobe.

Figure 4 Correlation between spirometric value (FEV_1.0/FVC) and mean cross-correlation coefficient (CCC) from six pairs of lung lobes.

Note: Most smokers without COPD have CCC larger than 0.9, suggesting that respiratory movement is uniform and synchronized among lung lobes in non-COPD smokers.
Abbreviation: FEV_1.0/FVC, forced expiratory volume in one second/forced vital capacity.

Table 4 Correlation between cross-correlation coefficient of paired MLD curves and emphysema index of the whole lung

Pairs – MLD curves	Correlation to LAV% (whole lung)
	Coefficient (ρ)	P-value
Right – left lungs	−0.44	<0.05
RUL – RLL	−0.40	<0.05
RUL – RML	−0.63	<0.001
RML – RLL	−0.54	<0.01
LUL – LLL	−0.31	NS
RUL – LUL	−0.52	<0.01
RLL – LLL	−0.43	<0.05
Average of six lobar pairs	−0.54	<0.01

Abbreviations: LAV%, percentage low attenuation volume (<−950 HU); LLL, left lower lobe; LUL, left upper lobe; MLD, mean lung density; NS, not significant; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe.