Competition for Intrathoracic Space Reduces Lung Capacity in Patients With Chronic Heart Failure: Conclusion
This muscle fiber atrophy is associated with significant reductions in tissue force generation, thus limiting resting tonality and potentially contributing the upward crescent shape of the diaphragm. Another potential contributor to the increased diaphragm volume includes ascites. Mutoh and col-leagues have shown, using a piglet model, a 40% reduction in TLC as a result of increased abdominal volume through a surgically implanted water-filled balloon. Although this relationship has yet to be fully examined in humans, the majority of the heart failure patients in the present study were clinically stable and did not have apparent ascites or otherwise significant abdominal distension.
Importantly, a potential limitation to this study is the use of a single equation to estimate pulmonary blood and parenchymal tissue volumes in control subjects and patients with chronic heart failure. Understandably, the use of a single prediction equation may have a tendency to slightly underestimate actual volumes in this population. Until recently, pulmonary fluid accumulation was thought to be a chronic process occurring as a result of cardiac contractile insufficiency leading to elevated left atrial pressure, increased pulmonary venous pressure, and concomitant distension of the pulmonary vasculature, coupled with generalized central and peripheral fluid accumulation and retention. buy birth control pills online
However, data suggest that pulmonary edema may be an acute process of fluid redistribution, often developing more rapidly over a few hours. Because the lung blood and parenchymal volumes were only a small fraction of the total volumes studied and each of the chronic heart failure patients in this study were receiving optimally managed medical therapy and were hemodynamically stable at the time of the radiograph measures, we feel this estimate provides sufficient information to draw relevant conclusions regarding cardiac and pulmonary measurements and does not detract from the relationships presented. It is also likely that if the pulmonary blood volume was slightly elevated in parallel to disease severity, we in fact may have slightly underestimated the cardiac effect on lung volume.
Another potential limitation to this study is the retrospective nature of the radiograph analysis. This retrospective portion of the study was conducted on data from patients who volunteered to participate in a prospective study examining the effects of cardiopulmonary interactions in heart failure patients. Although the analysis remains retrospective, all of the available participants who met the inclusion criteria were utilized in this analysis thus minimizing potential bias.
Posteroanterior and lateral chest radiographs are common clinical procedures for patients with heart failure. By using volumetric analysis of radiographs, estimates can be made of changes in cardiac, lung, diaphragm, and total thoracic volume. The changes observed in cardiac size within a closed thoracic cavity may pose significant constraints on the lung, resulting in significant reductions in lung volumes and resulting in the restrictive breathing pattern often reported in heart failure patients. In addition, the cardiomegaly associated changes in lung function may contribute to the inspiratory load, limit the encroachment on the inspiratory reserve volume during times of increased ventilatory demand, and contribute to symptoms of dyspnea.