Changes in Cross-Sectional Area and Transverse Diameter of the Heart on Inspiratory and Expiratory Chest CT: Correlation with Changes in Lung Size and Influence on Cardiothoracic Ratio Measurement

Abstract

ObjectiveThe aim of this study was to investigate physiological changes in cardiac area and diameters between inspiratory and expiratory chest computed tomography (CT), and to assess their correlation with lung size change and influence on cardiothoracic ratio (CTR) measurements.Materials and MethodsThe institutional review board of our institution approved this study, and informed consent was waived. Forty-three subjects underwent inspiratory and expiratory chest CT as part of routine clinical care. On both inspiratory and expiratory scans, lung volumes and maximum lung diameters (transverse and vertical directions) were measured. The maximum cardiac cross-sectional area (CSA) and the maximum transverse cardiac diameter were measured on both scans, and the CT-based CTR was calculated. Changes in the lung and cardiac measurements were expressed as the expiratory/inspiratory (E/I) ratios. Comparisons between inspiratory and expiratory measurements were made by the Wilcoxon signed-rank test. Correlations between the E/I ratios of lung and heart measurements were evaluated by Spearman’s rank correlation analysis.ResultsCardiac CSA and transverse cardiac diameter was significantly larger on expiratory than on inspiratory CT (p < 0.0001). Significant negative correlations were found between the E/I ratios of these cardiac measurements and the E/I ratios of lung volume and vertical lung diameter (p < 0.01). CT-based CTR was significantly larger on expiration than on inspiration (p < 0.0001).ConclusionsHeart size on chest CT depends on the phase of ventilation, and is correlated with changes in lung volume and craniocaudal lung diameter. The CTR is also significantly influenced by ventilation.

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

“…In the current study, we used dynamic-ventilation CT to demonstrate that smokers without obvious airflow limitation have an incremental change in heart size during expiration, consistent with previous reports of non-COPD patients. 20 In subjects without airflow limitation, a rapid reduction in intrathoracic pressure during inspiration leads to an increase in venous return and an increase in right-sided cardiac volume. Meanwhile, reduced pulmonary venous return due to blood pooling in the lung parenchyma causes a reduction in left-sided cardiac volume.…”

“…At each frame of the dynamic-ventilation CT, the cardiac CSA was measured semi-automatically by research software that had the same function as the CT scanner console. Based on a previously published method, 20 the following process was repeated in each subject: first, a threshold was set using Hounsfield units (HU) to exclude the pericardial fat pad (from 0 to 300 HU); second, at each time frame, all images that contained the heart were identified and the maximum cardiac CSA was determined; third, the boundary of the heart was traced and the maximum cardiac CSA was recorded.…”

“…Similar to previous studies that calculated the CT-based CTR, 20 , 30 the CTR was defined as the maximum transverse cardiac diameter divided by the maximum transverse lung diameter. For each patient, inspiratory CTR, expiratory CTR, and the difference between inspiratory and expiratory CTR (ΔCTR = expiratory CTR − inspiratory CTR) were obtained.…”

“…19 However, dynamic changes in heart size throughout the respiratory cycle are unknown. Tomita et al 20 reported that the cardiac cross-sectional area (CSA) is significantly larger on expiratory computed tomography (CT) than on inspiratory CT in patients without severe airflow limitation and that the increase in heart size from the inspiratory to expiratory phase is correlated with the degree of expiration and the upward movement of the diaphragm. Patients with COPD have increased intrathoracic pressure during expiration, 21 which is tightly correlated with decreased venous return, decreased cardiac transmural filling pressure, and decreased cardiac output.…”

Evaluating Cardiomegaly by Radiological Cardiothoracic Ratio as Compared to Conventional Echocardiography

“…They showed that the cardiac diameter, but not the CTR, was significantly correlated with the left ventricular size, the well-known predictor of cardiovascular morbidity and mortality. However, there are several studies that emphasize the utility of CTR in different entities [27][28][29][30][31]. Even CTR values that are within normal limits were found to have clinical implication.…”