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(Chest. 1999;116:30-39.)
© 1999 American College of Chest Physicians

Effect of Lung Volume Reduction Surgery on Bony Thorax Configuration in Severe COPD*

Yaroslav Lando, MD; Philip Boiselle, MD, FCCP; Daniel Shade, MD; John M. Travaline, MD; Satoshi Furukawa, MD and Gerard J. Criner, MD, FCCP

* From the Division of Pulmonary and Critical Care Medicine (Drs. Lando, Shade, Travaline, and Criner), and the Departments of Surgery (Dr. Furukawa), and Radiology (Dr. Boiselle), Temple University School of Medicine, Philadelphia, PA.

Correspondence to: Gerard J. Criner, MD, FCCP, Division of Pulmonary and Critical Care Medicine, Temple University School of Medicine, 3401 North Broad St, Philadelphia, PA 19140; e-mail: criner{at}astro.ocis.temple.edu


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: Hyperinflation in patients with severe COPD is associated with an increased anteroposterior (AP) rib cage diameter. We sought to determine whether bilateral lung volume reduction surgery (LVRS) affects bony thorax configuration.

Design: Prospective of clinical data collection before and after LVRS.

Setting: Tertiary-care university medical center.

Patients: We measured multiple AP and transverse thoracic diameters, by using plain chest roentgenograms (CXRs) in 25 patients (11 men, 14 women), and thoracic CT scans in 14 patients (7 men, 7 women), preoperatively and 3 months postoperatively. A subgroup of 7 patients (reference data) also had CXR thoracic diameter measurements made, using films obtained previously within a year of their presurgical evaluation. Another subgroup of 10 patients had CT scan measurements also made 12 months postoperatively.

Measurements and results: CXR dimensions were taken at the level of the manubrium sterni (M) and thoracic T7 and T11 levels. CT dimensions were taken at T4, T6, T8, and T10 levels. At each level, left (L), midsagittal (C), and right (R) AP and maximal transverse diameters were measured. The sum of the three AP diameters (Total) was used for calculations. Patients also underwent tests such as spirometry, lung volumes, diffusing capacity of the lung for carbon monoxide, 6-min walk distance (6MWD), and transdiaphragmatic pressures during maximum static inspiratory efforts (Pdimax sniff) measured before and 3 months after LVRS. Patients were (mean ± SD) 58 ± 8 years old, with severe COPD and hyperinflation (FEV1, 0.68 ± 0.23 L; FVC, 2.56 ± 7.3 L; and total lung capacity [TLC], 143 ± 22% predicted). After LVRS, AP diameters were reduced at thoracic level T7 (from 24.2 ± 2.0 cm to 23.3 ± 2.2 cm, p = 0.0002), and transverse diameters were reduced at T7 (from 26.8 ± 1.9 cm to 26.4 ± 1.7 cm, p = 0.001) and T11 (from 29.9 ± 2.2 cm to 29.5 ± 2.2 cm, p = 0.03), as measured using the CXR. In contrast, thoracic diameters were similar in subjects with CXRs before LVRS and within 1 year before evaluation. CT-measured AP diameters were significantly reduced 3 months after LVRS at T6, (from 48.8 ± 6.0 cm to 46.7 ± 5.4 cm, p = 0.02), T8 (from 54.2 ± 7.0 cm to 52.3 ± 6.5 cm, p = 0.004), and T10 (from 53.8 ± 7.5 cm to 51.2 ± 8.0 cm, p = 0.001), but not at T4. These AP diameter reductions directly correlated with the postoperative reductions in TLC and residual volume, and also with the increases in Pdimax sniff and 6MWD after LVRS. The reduction in AP diameters at thoracic levels T8 and T10 seen 3 months after LVRS remained stable at 12-month follow-up, whereas those measured at T6 lost statistical significance. CT-measured transverse diameters were unchanged at all levels after LVRS.

Conclusions: We conclude that LVRS decreases mid-to-lower AP rib cage diameter as assessed by CXR and thoracic CT. Although transverse diameters were reduced on CXR, the magnitude was small and was not confirmed with CT. After LVRS, AP diameter reductions are most likely the result of reduction in lung volume, and they are associated with improvements in diaphragm strength and exercise endurance.

Key Words: bony thorax • COPD • emphysema • lung volume reduction surgery • thoracic diameters


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The concept of structural changes of the bony thorax leading to hyperinflation in COPD originated in the early 20th century.1 Traditionally, it has been believed that patients with COPD accommodate an increased lung volume by expanding the anteroposterior (AP) diameter of their rib cage, thus resulting in a "barrel-chest" configuration.2 This observation has been demonstrated in animal and human subjects.3 4 5 6

This alteration of the bony thorax can have detrimental implications for respiratory mechanics. The hyperinflated thorax of an emphysematous patient passively shortens the diaphragm to a suboptimal operating length and reduces its area of apposition with the rib cage, thus placing it at a mechanical disadvantage to generate force. The enlarged rib cage may also contribute to an impairment in chest wall elastic recoil.7

Because roentgenographic indices correlate well with airflow obstruction in COPD patients,8 9 we thought that by lessening the severity of obstruction, there would be changes in bony thorax configuration. It has been shown that lung volume reduction surgery (LVRS) improves spirometry, lung volumes, and diaphragm strength in select patients with severe COPD.10 11 12 Also, two recent studies evaluated lung volume and thoracic dimensions after LVRS.13 14 They suggested that lung height and coronal diameter are reduced shortly after LVRS, as measured by plain chest roentgenograms (CXRs),13 and that all thoracic dimensions during expiration are decreased after LVRS, as measured by MRI.14 To date, it has not been determined whether these changes in thoracic dimensions after LVRS maintain long-term stability, or whether they are significant enough to improve respiratory mechanics (ie, respiratory muscle function).

The purpose of this investigation is to determine whether (1) the configuration of the bony thorax in patients with severe COPD is altered after LVRS, as measured by plain CXRs and CT scans; and (2) the postoperative improvements in hyperinflation correlate with improvements in respiratory mechanics.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Patient Selection
Our study was performed with 25 consecutive patients who underwent LVRS at Temple University Hospital. All patients enrolled in our LVRS program had severe emphysema, were on optimal medical therapy (bronchodilators, inhaled and/or oral corticosteroids, home oxygen therapy, and comprehensive outpatient pulmonary rehabilitation), and were clinically stable with no evidence of acute respiratory symptoms. They had no evidence of kyphoscoliosis or history of chest trauma, did not reveal any thoracic or parenchymal abnormalities on routine CXR other than those consistent with the diagnosis of COPD, and fulfilled the inclusion criteria shown in Table 1 . All patients signed informed consent, as approved by our Institutional Review Board for Human Research.


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  		Table 1. Inclusion and Exclusion Criteria for LVRS*

 
All patients had plain CXRs, CT scans, routine pulmonary function tests, and 6-min walk distance test (6MWD) done within 3 weeks before LVRS. CXRs were available in 25 patients and CT scans in 14 patients at 3 months after LVRS. Seven of the above patients had plain CXRs done previously, within a year before their baseline presurgical evaluation. These were analyzed and compared with the preoperative and postoperative data. Also, a subgroup of patients (n = 10) had CT scans obtained 1 year after surgery, and these too were analyzed and compared with the preoperative and 3-month postoperative LVRS data.

Physiologic Measurements
Pulmonary Function Testing: Pulmonary function testing was performed with a plethysmograph (System 6200 Autobox DL Plethysmograph; SensorMedics Corp; Yorba Linda, CA) using American Thoracic Society guidelines.15 FVC, FEV1, and FEV1/FVC ratio were measured. Thoracic gas volumes were measured in a body plethysmograph. All postbronchodilator pulmonary function data are reported in absolute numbers and as percent of normal predicted values.15 The 6MWD test (the total distance that the patient was able to walk in 6 min in a closed corridor) was also recorded.16

Diaphragm Strength: In addition to routine pulmonary function testing, eight patients also had measurement of maximal transdiaphragmatic pressure before and 3 months after LVRS. Transdiaphragmatic pressure (Pdi) was measured, as previously described,17 18 by two balloon-tipped catheters placed into the distal esophagus (endoesophageal pressure [pleural pressure]) and stomach (gastric pressure), and connected to pressure transducers (100 ± 5 cm H2O) [Validyne; Ventura, CA]. The pressure waveforms were continuously displayed on a strip-chart recorder (ES 1000; Gould; Dayton, OH). Pdi was calculated as the difference in end-inspiratory and end-expiratory values.

Pdi during maximum static inspiratory effort (sniff maneuvers) (Pdimax sniff) was determined by having each patient perform three to six maximal sniff maneuvers. After each patient could reproducibly perform several maximal efforts, a total of three values, all within 5%, were averaged and reported. All measurements were performed from functional residual capacity (FRC) by monitoring the endoesophageal pressure waveform, with patients seated in the upright position.

Surgical Technique
LVRS was performed via median sternotomy with biapical and upper lobe stapling resection in all but three patients who had only lower lobes operated on. The goal of resection was to remove 20 to 40% of the volume of each lung. High-resolution chest CT and quantitative ventilation-perfusion scans were used preoperatively to target lung regions with the worst emphysema (ie, areas of greatest gas trapping with poorest perfusion). At the end of the operation, chest tubes were placed and managed in the conventional manner.

Radiologic Measurements
Rib Cage Dimensions: Rib cage dimensions were measured by using two methods: plain AP and lateral CXRs, and chest CT scans. These studies were performed within 3 weeks before LVRS and 3 months after LVRS. Seven patients had undergone CXRs previously, within a year of their preoperative evaluation, and 10 patients underwent CT scans 1 year after surgery.

Plain CXR: The plain CXRs were performed at maximal inspiration, with each patient standing upright with the chest against a wall and arms away from the sides. Patients were asked to maintain an erect position. The following measurements were taken (Fig 1 ): (1) transverse diameter (on AP view) at the levels of the manubrium sterni and the 7th and 11th thoracic vertebral bodies (T7, T11); (2) AP diameter (on lateral view) using a vertical reference line drawn tangentially to the posterior aspect of vertebral bodies T6 through T9. A parallel vertical line was drawn at the most posterior aspect of patient's back (thoracic soft tissue). Three horizontal AP diameter measurements were taken from this line to the posterior aspect of the sternum, at the same levels as the transverse diameter measurements (as modified from Walsh et al19 ).



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  		Figure 1. Thoracic diameter measurements on the AP and lateral CXRs. A to B, C to D, and E to F represent the transverse diameters at the levels of the manubrium sterni, T7, and T11, respectively. G to H, I to J, and K to L represent the AP diameters at the levels of the manubrium sterni, T7, and T11, respectively.

 
CT Scan: The CT scans were obtained with the GE Highlight Advantage scanner (General Electric Corp; Milwaukee, WI) or the Picker PQ 5000 scanner (Picker Corp; Cleveland, OH). Scan thickness was 10 mm and scanning time was 1 s. Scans were obtained at the level of the pedicles of the 4th, 6th, 8th, and 10th thoracic vertebrae. All scans were obtained at full inspiration, with patients holding their breath in supine position, and arms positioned parallel to the longitudinal axis of the body. At each aforementioned vertebral level, the AP diameter was measured from the anterior aspect of the vertebral body to the posterior aspect of the sternum (AP midsagittal). The maximal AP diameter of the right and left hemithoraces (AP right and left) and the maximal transverse diameter were measured as well (Fig 2 ) (taken from Cassart et al6 ).



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  		Figure 2. Thoracic diameter measurements on the chest CT scan. Lines 1, 2, and 3 represent midsagittal, left, and right AP diameters, respectively. Line 4 represents the transverse diameter.

 
Data Analysis
All the measurements were made in centimeters and were rounded off to the nearest 0.1 cm. Each diameter represents the maximal internal thoracic diameter at a particular level. Every measurement was obtained independently by two investigators and the variability in each measurement between the two investigators was < 0.1 cm. Values reported represent the average of two independently obtained measurements at each level. Both investigators were blinded to the physiologic data.

All data are expressed as mean ± SD, except where otherwise noted. Statistical analysis was performed using two-tailed paired Student's t test to compare preoperative with postoperative values. Repeated measures analysis of variance was used to compare preoperative measurements with those at 3 and 12 months after LVRS. Linear regression analyses with Pearson correlation were used to evaluate correlations between roentgenographic and physiologic measurements. Values of p < 0.05 were considered statistically significant. All statistical analyses were conducted using a commercially available computer software program (Sigmastat, version 1.0; Jandel Corp; San Rafael, CA).


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Patient Characteristics
Baseline characteristics of 25 patients in the study cohort are shown in Table 2 . Patients were 58 ± 8 years old, and 14 were females. All patients were functionally limited, designated as New York Heart Association class III or IV. The majority were oxygen dependent, had a significant smoking history, had hyperinflation with severe airflow obstruction, and had abnormal gas exchange. All patients finished 8 weeks of outpatient pulmonary rehabilitation before LVRS. All preoperative baseline data were taken after completion of rehabilitation.


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  		Table 2. Baseline Characteristics in All 25 COPD Patients

 
Physiologic Data
Results of lung function studies (spirometry, lung volumes, 6MWD) and diaphragm strength (Pdimax sniff) at baseline and 3 months after LVRS can be seen in Table 3 . All patients had severe airflow obstruction, moderate to severe hyperinflation, and decreased exercise tolerance. At 3 months after LVRS, FEV1 improved to 0.87 ± 0.29 L (p < 0.001), total lung capacity (TLC) decreased to 6.6 ± 1.4 L (p < 0.001), and 6MWD increased to 330 ± 84 m (p < 0.001). There was also a significant improvement in mean Pdimax sniff (p < 0.0001).


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  		Table 3. Physiologic Data Before and 3 Months After Lung Volume Reduction Surgery*

 
Roentgenographic (Plain Film) Data
Seven of the 25 patients had plain CXRs done previously within a year of their baseline presurgical evaluation. Table 4 demonstrates the rib cage dimensions in these seven patients, measured using plain CXRs, done previously within a year before evaluation for LVRS (controls) and during preoperative assessment. There was no significant change at any thoracic level in AP or transverse rib cage dimensions when preoperative measurements were compared with control films; however, the sample size is relatively small to detect a significant difference.


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  		Table 4. Control Subjects' Rib Cage Dimensions on Prior Examination and Immediately Before LVRS (Using Plain CXR; N = 7)*

 
This contrasts with the significant reductions in thoracic dimensions seen 3 months after LVRS. Table 5 demonstrates rib cage dimensions measured using plain CXRs preoperatively and 3 months after LVRS. Compared with baseline, there were significant reductions in AP diameter at the levels of the manubrium and at T7, but not at T11. There were also significant reductions in transverse diameter at T7 and at T11; however, no change was seen at the level of the manubrium. Although the magnitude of these changes is small, and similar to the changes between the baseline and preoperative values in Table 4 , the larger number of patients evaluated at 3 months compared with baseline accounts for the significance of these changes.


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  		Table 5. Rib Cage Dimensions Before and 3 Mo After LVRS (Using Plain CXR; N = 25)*

 
Roentgenographic (Thoracic CT) Data
Table 6 demonstrates rib cage dimensions measured using thoracic CT scans preoperatively and 3 months after LVRS. Compared with baseline, there was no significant postoperative change in maximal transverse diameter at all levels measured. The AP diameter, on the other hand, decreased significantly at the level of the mid-to-lower thorax. Although there was no change at T4, there were significant AP diameter reductions demonstrated at the T6, T8, and T10 levels.


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  		Table 6. Rib Cage Dimensions Before and 3 Mo After LVRS (Using Thoracic CT Scans; N = 14)*

 
Correlations
To evaluate the clinical significance of the above findings, the described changes in thoracic dimensions after LVRS were correlated with physiologic parameters. Figure 3 shows a potential mechanism for postoperative change in thoracic dimensions, by demonstrating correlations between the percent change in total lung capacity and the percent change in AP diameter of the lower rib cage, measured using the plain CXR (at T11) and the CT scan (at T8 and T10). Significant positive correlations were found between the postoperative reduction in total lung capacity and the decrease in AP diameter of the lower rib cage, as measured by plain CXR (r = 0.57, p = 0.03), and as measured by CT at T8 (r = 0.69, p = 0.01) and at T10 (r = 0.64, p = 0.03).



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  		Figure 3. Correlations between the percent change in TLC after LVRS and the percent change in AP diameter of the lower rib cage, measured on CXR (at T11) and on CT scan (at T8 and T10). This demonstrates that the post-LVRS reduction in lower AP diameter is directly related to reduction in lung volume.

 
Positive correlations were also found between the postoperative reduction in residual volume (RV) and the decrease in AP diameter of the lower rib cage (Fig 4 ), but did not quite reach statistical significance, as measured by plain CXR (r = 0.47, p = 0.07), and by CT at T8 (r = 0.48, p = 0.1) and at T10 (r = 0.36, p = 0.2).



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  		Figure 4. Correlations between the percent change in RV after LVRS and the percent change in AP diameter of the lower rib cage, measured on CXR (at T11) and on CT scan (at T8 and T10). This demonstrates that the post-LVRS reduction in lower AP diameter is directly related to reduction in lung volume.

 
To evaluate the potential significance of a decreased thoracic AP diameter after LVRS on diaphragm strength, correlations with Pdimax sniff were made in eight patients who had transdiaphragmatic pressure measured (Fig 5 ). A strong relationship was observed between the postoperative decrease in AP diameter of the lower rib cage and the postoperative increase in diaphragm strength (r = 0.75, p = 0.03).



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  		Figure 5. Correlations between the percent change in AP diameter of the lower rib cage on CXR (at T11) after LVRS and the percent change in diaphragm strength (Pdimax sniff). This demonstrates that the post-LVRS reduction in lower AP diameter directly affects improvement in diaphragm strength.

 
The potential significance of a decreased thoracic AP diameter on exercise endurance was also evaluated. Figure 6 correlates the percent change in AP diameter of the lower rib cage after LVRS, measured using plain CXR (at T11), and the percent change in distance walked during a 6MWD test. Again, a strong relationship is seen between the postoperative decrease in AP diameter of the lower rib cage and the postoperative increase in the distance walked in 6 min (r = 0.68, p = 0.01).



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  		Figure 6. Correlations between the percent change in AP diameter of the lower rib cage on CXR (at T11) after LVRS and the percent change in 6MWD. This demonstrates that the post-LVRS reduction in lower AP diameter directly affects improvement in performance during a 6MWD test.

 
Long-term Stability
To determine whether the reductions in the mid-to-lower AP thoracic diameter initially observed 3 months after LVRS remained stable with time, a subgroup of 10 patients had thoracic CT scans also repeated 1 year after LVRS, and the same rib cage measurements were made. Table 7 demonstrates these measurements preoperatively, and 3 and 12 months after LVRS. The AP diameter reductions initially seen 3 months after LVRS at T8 and T10 remained stable at 12 months; however, at T6 the reduction was no longer statistically significant. In these patients, FEV1 (36 vs 31% predicted) and TLC (109 vs 120% predicted) were no different at 12 months compared with 3 months after LVRS (p = 0.06 and 0.09, respectively).


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  		Table 7. AP Thoracic Diameter at T6, T8, and T10 Before, 3, and 12 Months After LVRS (Using Thoracic CT Scans) (No. = 10)*

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Our data confirm findings of prior investigations that LVRS improves spirometry, lung volumes, and diaphragm strength in select patients with severe COPD.10 11 12 They also demonstrate that LVRS alters the configuration of the bony thorax in these patients. Small but significant reductions in lower AP rib cage dimension are seen 3 months after LVRS, and are maintained at 1 year of follow-up. This configurational change significantly correlates with increases in diaphragm strength and exercise endurance, and may be the result of a postoperative reduction in lung volume.

It has been shown clearly in animal and human subjects that structural changes of the bony thorax occur in emphysema.3 4 5 6 In hamsters, Snider and Sherter3 were able to demonstrate by roentgenogram a marked increase in the AP diameter of an emphysematous animal (compared with normal animals) 1 year after induction of emphysema. Likewise, Thomas et al4 showed significantly greater circumference, AP, transverse, and rostral-caudal dimensions of the thorax in emphysematous hamsters (compared with control animals) 6 months after induction of emphysema.

In humans, Gilmartin and Gibson,5 using plain roentgenograms and linearized magnetometers, found an increased AP diameter at FRC in patients with COPD. In addition, Cassart et al,6 using CT scans, demonstrated that COPD patients have a more circular configuration of their bony thorax (compared with controls) because of increases in AP diameter.

Roentgenographic indexes have been shown to correlate well with airflow obstruction in COPD patients.8 9 Simon et al8 assessed CXRs of 101 patients with chronic airflow obstruction and found good correlations between roentgenographic and pulmonary function abnormalities. Flattened diaphragm, increased retrosternal airspace, and roentgenographic estimation of TLC were all highly specific for having an FEV1 < 1 L. Similarly, using 189 CXRs of patients with COPD, Burki and Krumpelman9 demonstrated that a depressed level of the diaphragmatic dome, increased retrosternal airspace, and decreased transverse diameter of the heart all correlated with the degree of airflow obstruction.

To address whether postoperative changes in the bony thorax configuration actually improve respiratory mechanics, one may use the model of COPD patients undergoing lung transplantation.20 21 22 In patients with COPD undergoing single-lung transplantation, Brunsting et al20 demonstrated a correlation between lung volume and spirometry and concluded that "chest wall factors" determine postoperative pulmonary function. Scott et al21 found the physiologic improvements after single-lung transplantation in patients with COPD to be related to increases in lung elastic recoil and suggested that these findings implied a postoperative reduction in chest wall distention. Guignon et al22 demonstrated the opposite effect on thoracic dimensions in heart-lung transplant recipients for cystic fibrosis, with a persistent increase in FRC after transplantation, and concluded that the persistent hyperinflation was owing to the AP rib cage expansion. The persistent hyperinflation may have been related to the en bloc insertion used during heart-lung implantation, which differs from the technique of single- or double-lung transplantation.

Recently, two studies looked at lung volumes and thoracic dimensions after LVRS.13 14 Takasugi et al13 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,14 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.11 23 24 25 26 27 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.19 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.

Another potential limitation of our study is the lack of control for median sternotomy. Although we had internal controls to assure that no significant changes in the bony thorax occurred with time, we were unable to control for possible changes that can occur after median sternotomy without LVRS. We know that after median sternotomy there is a reduction in rib cage and spine motion that contributes to a restrictive chest wall process.28 The reduction in the bony thorax dimensions that we measured, however, correlated with RV and TLC, suggesting that the changes were not attributable to the effect of median sternotomy alone.

There are several strengths of our study design. It is a controlled, prospective study, in which two independent investigators made measurements using two roentgenographic modalities, coupled with a 12-month follow-up period. The seven patients whose measurements served as reference data helped solidify our results by demonstrating that the small improvements in thoracic cage configuration found postoperatively were not merely caused by variations in two roentgenograms taken at different times. To further strengthen the standard chest film findings, CT scan measurements were obtained as well. The CT measurements confirmed the AP diameter reductions measured on plain roentgenograms and strengthened their significance; however, they did not confirm the small transverse diameter changes seen with plain films. This difference presumably reflects the better resolution of CT measurements compared with plain roentgenogram measurements. Unlike plain roentgenograms, CT images are not hampered by superimposition of soft tissues. We repeated the CT measurements 12 months postoperatively and demonstrated stability of the lower thoracic AP diameter reductions seen 3 months after LVRS.

In conclusion, we evaluated by CXR the bony thorax of select COPD patients undergoing bilateral LVRS. Using two techniques, we demonstrated that a change in rib cage configuration occurs after LVRS, especially in the lower AP axis. This improvement in thoracic shape remained stable for a 12-month follow-up period. Although the demonstrated changes are small, they likely occur in all three dimensions, and are probably underestimated with two-dimensional measurements. The strong correlations between the roentgenographic bony thorax changes and physiologic measurements suggest a possible mechanism for improvement in respiratory mechanics after LVRS, and suggest that bony thorax configuration may be an important factor affecting diaphragm pressure generation.


   Acknowledgements
 
ACKNOWLEDGMENT: We acknowledge the efforts of Physical Therapy, Respiratory Therapy, and the Nursing Staff in the care of these patients. We also thank Darlene Macon for secretarial assistance.


   Footnotes
 
Abbreviations: AP = anteroposterior; CXR = chest roentgenogram; FRC = functional residual capacity; LVRS = lung volume reduction surgery; NYHA = New York Heart Association; Pdi = transdiaphragmatic pressure; Pdimax sniff = transdiaphragmatic pressure during maximum static inspiratory effort; RV = residual volume; 6MWD = 6-min walk distance; TLC = total lung capacity

Received for publication July 17, 1998. Accepted for publication January 14, 1999.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Kerley, P (1936) Discussion on emphysema. Proc R Soc Med 29,1307-1324
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  11. O'Donnell, DE, Webb, KA, Bertley, JC, et al (1996) Mechanisms of relief of exertional breathlessness following unilateral bullectomy and lung volume reduction surgery in emphysema. Chest 110,18-27[Abstract/Free Full Text]
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