Hyperinflated lungs compress the heart during expiration in COPD patients: a new finding on dynamic-ventilation computed tomography

Figures & data

Table 1 Clinical characteristics of the 31 study subjects

Characteristics	Mean ± SD	Range
Gender (female:male)	5:26
Age (years)	72±10	39–86
Smoking status (ex-smoker:current smoker)	15:16
Smoking index (pack-years)	47±11	2–100
FEV1.0/FVC	0.71±0.13	0.41–0.92

Abbreviations: FEV_1.0, forced expiratory volume in 1 s; FVC, forced vital capacity; SD, standard deviation.

Table 2 CT-based indices in COPD patients versus non-COPD smokers

CT indices	COPD patients	Non-COPD smokers	P-value
Dynamic-ventilation CT
Cardiac CSAInsp (cm^2)	69.1±10.3	78.7±8.2	<0.05
Cardiac CSAExp (cm^2)	68.2±15.0	84.6±10.2	<0.01
CTRInsp (%)	46.7±4.4	49.7±4.9	NS
CTRExp (%)	47.9±4.7	54.3±4.5	<0.001
ΔCTR (%)	1.2±2.0	4.6±2.7	<0.01
E/I ratio – CTR	1.03±0.04	1.10±0.06	<0.01
Helical CT
LAV%	23.9±16.9	4.5±5.2	<0.001
LV (L)	5.1±0.9	4.4±0.8	<0.05
LV/BSA	3.3±1.1	2.6±1.0	<0.001

Note: Data are expressed as mean ± SD.

Abbreviations: BSA, body surface area; CSA, cross-sectional area; CT, computed tomography; CTR, cardiothoracic ratio; ΔCTR, difference between CTR_Exp and CTR_Insp; E/I, expiratory/inspiratory; Exp, expiratory; Insp, inspiratory; LAV%, percent low attenuation volume; LV, lung volume; NS, not significant; SD, standard deviation.

Figure 1 A 39-year-old male current smoker without COPD underwent dynamic-ventilation CT for preoperative analysis of parietal pleural adhesion caused by a benign rib tumor.

Notes: His FEV_1.0/FVC was 0.92. Inspiratory (A) and expiratory phases (B) (both shown in coronal view, MIP images) demonstrated an increase in heart size during expiration, mainly due to diaphragm elevation.

Abbreviations: CT, computed tomography; FEV_1.0, forced expiratory volume in 1 s; FVC, forced vital capacity; MIP, maximum intensity projection.

Figure 2 A 70-year-old male with COPD underwent dynamic-ventilation CT to evaluate central airway abnormalities.

Notes: His FEV_1.0/FVC was 0.55. The shape of the right atrium was normal during the inspiratory phase (A) but was severely compressed (arrows) during the expiratory phase, probably due to the emphysematous right middle lobe (B).
Abbreviations: CT, computed tomography; FEV_1.0, forced expiratory volume in 1 s; FVC, forced vital capacity.

Table 3 CCC between the maximum cardiac CSA and MLD on dynamic-ventilation CT

CCC measurements	CCC between cardiac CSA and MLD		Correlation with FEV1.0/FVC
	Mean ± SD	Range	Coefficient (ρ)	P-value
Entire respiratory phase	0.14±0.62	−0.87 to 0.99	0.56	<0.01
Expiratory phase only	0.25±0.57	−0.79 to 0.94	0.63	<0.001

Note: The expiratory phase was defined from the peak inspiratory frame to the peak expiratory frame on the continuous MLD curve (5–12 frames).

Abbreviations: CCC, cross-correlation coefficient; CSA, cross-sectional area; CT, computed tomography; FEV_1.0, forced expiratory volume in 1 s; FVC, forced vital capacity; MLD, mean lung density; SD, standard deviation.

Figure 3 Measurements of MLD and maximum cardiac CSA.

Notes: A non-COPD smoker (as shown in Figure 1) showed similar time curves (A), suggesting that cardiac CSA decreased with inspiration and increased with expiration (CCC of all frames =0.987). The cardiac CSA measurements were performed on axial CT images Video S1. In a severe COPD patient (as shown in Figure 2), measurements of MLD and maximum cardiac CSA demonstrated almost opposite shapes (B), suggesting that the heart size increased during inspiration and decreased during expiration. The CCC of the entire cycle was −0.392, and that of the expiratory frames (frame no 6–13 in this case) was −0.723. CT images are available from Video S2.
Abbreviations: CCC, cross-correlation coefficient; CSA, cross-sectional area; CT, computed tomography; HU, Hounsfield unit; MLD, mean lung density.

Table 4 Correlations between the CTR on dynamic-ventilation CT and FEV_1.0/FVC

CTR measurements	CTR measurements		Correlation with FEV1.0/FVC
	Mean ± SD	Range	Coefficient (ρ)	P-value
CTRInsp (%)	48.5±4.8	39.0 to 60.1	0.28	NS
CTRExp (%)	51.6±5.5	41.0 to 64.0	0.59	<0.001
ΔCTR (%)	3.2±2.9	−2.7 to 11.3	0.58	<0.001

Abbreviations: CT, computed tomography; CTR, cardiothoracic ratio; ΔCTR, difference between CTR_Exp and CTR_Insp; Exp, expiratory; FEV_1.0, forced expiratory volume in 1 s; FVC, forced vital capacity; Insp, inspiratory; NS, not significant; SD, standard deviation.