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

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          Abstract

          Purpose

          The aims of this study were to evaluate dynamic changes in heart size during the respiratory cycle using four-dimensional computed tomography (CT) and to understand the relationship of these changes to airflow limitation in smokers.

          Materials and methods

          A total of 31 smokers, including 13 with COPD, underwent four-dimensional dynamic-ventilation CT during regular breathing. CT data were continuously reconstructed every 0.5 s, including maximum cross-sectional area (CSA) of the heart and mean lung density (MLD). Concordance between the cardiac CSA and MLD time curves was expressed by cross-correlation coefficients. The CT-based cardiothoracic ratio at inspiration and expiration was also calculated. Comparisons of the CT indices between COPD patients and non-COPD smokers were made using the Mann–Whitney test. Spearman rank correlation analysis was used to evaluate associations between CT indices and the forced expiratory volume in 1 s (FEV 1.0) relative to the forced vital capacity (FVC).

          Results

          Cardiac CSA at both inspiration and expiration was significantly smaller in COPD patients than in non-COPD smokers ( P<0.05). The cross-correlation coefficient between cardiac CSA and MLD during expiration significantly correlated with FEV 1.0/FVC (ρ=0.63, P<0.001), suggesting that heart size decreases during expiration in COPD patients. The change in the cardiothoracic ratio between inspiration and expiration frames was significantly smaller in COPD patients than in non-COPD smokers ( P<0.01).

          Conclusion

          Patients with COPD have smaller heart size on dynamic-ventilation CT than non-COPD smokers and have abnormal cardiac compression during expiration.

          Related collections

          Most cited references 34

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          Chronic obstructive pulmonary disease as a risk factor for cardiovascular morbidity and mortality.

          Chronic obstructive pulmonary disease and other disorders, associated with reduced lung function, are strong risk factors for cardiovascular events, independent of smoking. Overall, when the lowest quintile of lung function, as measured by FEV1 is compared with the highest quintile, the risk of cardiovascular mortality increases by approximately 75% in both men and women. Having symptoms of chronic bronchitis alone increases the risk of coronary deaths by 50%. Reduced ratio of FEV1 to FVC by itself is a modest independent risk factor for coronary events, increasing the risk by 30%. However, if patients have ventricular arrhythmias, the risk of coronary events is increased twofold, suggesting that the cardiotoxic effects of obstructive airways disease are amplified in those who have underlying cardiac rhythm disturbances. In general, for every 10% decrease in FEV1, all-cause mortality increases by 14%, cardiovascular mortality increases by 28%, and nonfatal coronary event increases by almost 20%. These data indicate that chronic obstructive pulmonary disease is a powerful, independent risk factor for cardiovascular morbidity and mortality.
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            Decreasing cardiac chamber sizes and associated heart dysfunction in COPD: role of hyperinflation.

            Little is known about the role of abnormal lung function in heart size and heart dysfunction in patients with COPD. We studied the relationship of lung function with heart size and heart dysfunction and associated consequences for 6-min walk distance (6MWD) in patients with COPD of different severitites. In 138 patients with COPD (Global Initiative for Obstructive Lung Disease [GOLD] I-IV), we measured the size of all cardiac chambers, left ventricular diastolic dysfunction (relaxation and filling), and global right ventricular dysfunction (Tei-index) by echocardiography. We also measured lung function (spirometry, body plethysmography, and diffusion capacity) and 6MWD. The size of all cardiac chambers decreased with increasing GOLD stage. Overall, moderate relationships existed between variables of lung function and cardiac chamber sizes. Static hyperinflation (inspiratory-to-total lung capacity ratio [IC/TLC], functional residual capacity, and residual volume) showed stronger associations with cardiac chamber sizes than airway obstruction or diffusion capacity. IC/TLC correlated best with cardiac chamber sizes and was an independent predictor of cardiac chamber sizes after adjustment for body surface area. Patients with an IC/TLC 0.25. An impaired left ventricular diastolic filling pattern was independently associated with a reduced 6MWD. An increasing rate of COPD severity is associated with a decreasing heart size. Hyperinflation could play an important role regarding heart size and heart dysfunction in patients with COPD.
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              Contractile properties of the human diaphragm during chronic hyperinflation.

              In patients with chronic obstructive pulmonary disease (COPD) and hyperinflation of the lungs, dysfunction of the diaphragm may contribute to respiratory decompensation. We evaluated the contractile function of the diaphragm in well-nourished patients with stable COPD, using supramaximal, bilateral phrenic-nerve stimulation, which provides information about the strength and inspiratory action of the diaphragm. In eight patients with COPD and five control subjects of similar age, the transdiaphragmatic pressure generated by the twitch response to phrenic-nerve stimulation was recorded at various base-line lung volumes, from functional residual capacity to total lung capacity, and during relaxation and graded voluntary efforts at functional residual capacity (twitch occlusion). At functional residual capacity, the twitch transdiaphragmatic pressure ranged from 10.9 to 26.6 cm of water (1.07 to 2.60 kPa) in the patients and from 19.8 to 37.1 cm of water (1.94 to 3.64 kPa) in the controls, indicating considerable overlap between the two groups. The ratio of esophageal pressure to twitch transdiaphragmatic pressure, an index of the inspiratory action of the diaphragm, was -0.50 +/- 0.05 in the patients, as compared with -0.43 +/- 0.02 in the controls (indicating more efficient inspiratory action in the patients than in the controls). At comparable volumes, the twitch transdiaphragmatic pressure and esophageal-to-transdiaphragmatic pressure ratio were higher in the patients than in normal subjects, indicating that the strength and inspiratory action of the diaphragm in the patients were actually better than in the controls. Twitch occlusion (a measure of the maximal activation of the diaphragm) indicated near-maximal activation in the patients with COPD, and the maximal transdiaphragmatic pressure was 106.9 +/- 13.8 cm of water (10.48 +/- 1.35 kPa). The functioning of the diaphragms of the patients with stable COPD is as good as in normal subjects at the same lung volume. Compensatory phenomena appear to counterbalance the deleterious effects of hyperinflation on the contractility and inspiratory action of the diaphragm in patients with COPD. Our findings cast doubt on the existence of chronic fatigue of the diaphragm in such patients and therefore on the need for therapeutic interventions aimed at improving diaphragm function.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                1176-9106
                1178-2005
                2017
                26 October 2017
                : 12
                : 3123-3131
                Affiliations
                [1 ]Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Nishihara, Japan
                [2 ]Department of Radiology, China-Japan Friendship Hospital, Beijing, People’s Republic of China
                [3 ]Department of Radiology, Ohara General Hospital, Fukushima, Japan
                [4 ]Department of Radiology, Shiga University of Medical Science, Otsu, Japan
                [5 ]Department of Radiology, St Marianna University School of Medicine, Kawasaki, Japan
                Author notes
                Correspondence: Tsuneo Yamashiro, Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa 903-0215, Japan, Tel +81 98 895 1162, Fax +81 98 895 1420, Email clatsune@ 123456yahoo.co.jp
                Article
                copd-12-3123
                10.2147/COPD.S145599
                5661839
                © 2017 Xu et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Categories
                Original Research

                Respiratory medicine

                heart, copd, computed tomography, ventilation, emphysema

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