Competition for Intrathoracic Space Reduces Lung Capacity in Patients With Chronic Heart Failure
Chronic heart failure is a progressive disease resulting in severe morbidity and mortality. Interestingly, certain resting measures of cardiac function (ie, ejection fraction [EF]) correlate poorly with exercise tolerance, and thus it is clear that chronic heart failure becomes a systemic disorder, influencing a number of organ systems that may contribute to activity intolerance. Because the pulmonary system lies in series with the heart, accepts nearly all of the cardiac output, and is exposed to similar intratho-racic pressure changes, it would be expected that changes in cardiac structure and function may have adverse consequences on the pulmonary system. Most studies suggest mild-to-moderate changes in the pulmonary system with chronic heart failure, including both restrictive and obstructive changes as well as a reduction in lung diffusing capacity. Causes for changes in lung function remain unclear but have been thought to be related to respiratory muscle weakness, chronic pulmonary hypertension, and changes in lung fluid balance. Another possible contributor to the changes in pulmonary function relates to the progressive cardiac enlargement within a closed thoracic cavity. Such changes in cardiac volume would result in primarily restrictive lung changes manifested as reductions in total lung volume as well as vital capacity.” review
Previous studies have reported marked changes in cardiac size as heart failure progresses. Such changes in cardiac size could clearly “steal” volume from the lungs, as the lungs are more compliant than the heart. Previously, we reduced lung volumes in healthy adults by 40% through chest wall strapping in order to increase the competition for intrathoracic space between the heart and lungs. Despite the marked reductions in lung volumes, there was relatively little impact on cardiac function. These findings are consistent with the much higher lung compliance as compared to the heart. To date, few studies have closely examined the relationship between cardiac size and the alterations in lung volume within a closed thoracic cavity in the chronic heart failure population. The purpose of this study was to examine the relationship between the radiographically determined thoracic, cardiac, and lung volumes in heart failure patients as compared to control participants without known cardiovascular disease. We hypothesized that the increased competition for intrathoracic space caused by changes in cardiac volume associated with chronic heart failure contributes significantly to the restrictive pulmonary changes observed in this population, and that these changes are associated with severity of chronic heart failure.