Recently, two studies looked at lung volumes and thoracic dimensions after LVRS. Takasugi et al evaluated plain roentgenograms of 35 patients with COPD, and found post-LVRS reductions in vertical lung height and transverse diameter at the level of the aortic arch. No changes in AP diameters were found, and only the left lung height reduction correlated with a physiologic measurement (FEV1). Gierada et al, using MRI in eight patients with COPD, found post-LVRS decreases in expiratory lung height and AP diameter at the level of the diaphragm. They also showed correlations between measurements of lung volumes by MRI and body plethysmography, but failed to demonstrate whether the MRI-measured alterations after LVRS have a relationship to the plethysmography-measured reduced lung volume.
Our results are somewhat different from these studies for the following reasons: (1) all our measurements were referenced to the bony thorax to minimize errors of respiratory variation; (2) we made CT scan measurements to minimize any technical difficulties encountered in measuring plain films; (3) all initial postoperative measurements were made 3 months after LVRS, allowing enough time for any remodeling to occur, and were correlated with plethysmography-measured lung volumes; (4) we used percent change instead of absolute change for all calculations, to help minimize the influence of sex and body size; (5) we showed convincing long-term stability of the rib cage changes found at initial evaluation; and (6) we showed significant correlations between the roentgenographic alterations and the physiologic improvements after LVRS.
There is a significant body of literature now available demonstrating impressive reductions in lung volumes after LVRS and their association with improvements in respiratory mechanics and exercise tolerance.- Our findings are consistent with this literature and suggest that a reduction in lung volume decreases bony thorax dimensions and may contribute to the improvement observed in respiratory mechanics.
There are several limitations of our study. First, although plain roentgenograms and CT scans were obtained with patients following instructions to maintain a maximal inspiration, we used no objective monitoring to assure a maximal inspiration. Second, our methodology for AP diameter measurements on plain CXRs differs slightly from that described by Walsh et al. They had each patient stand against a vertical rigid backboard lined by an aluminum strip for reference. Not having such a setup, we used a vertical reference line, drawn tangentially to the posterior aspects of vertebral bodies T6 through T9, thus maintaining reference to the bony thorax. This should not have had a significant influence on our results, since all comparisons were made in the same individuals studied repeatedly, rather than in different groups of individuals examined at separate study points.