INTRODUCTION

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Recent reports indicate that lung volume reduction surgery (LVRS) is effective in producing short-term physiological improvement in patients with severe emphysema. This improvement is characterized by increased airflow, reduction in residual volume, and improved gas exchange with increased oxygenation (1, 2). These changes are likely induced by improved lung mechanics following resection of bullous lung tissue, resulting in increased elastic recoil of the lung (3). Such changes lead to documented improvement in dyspnea indices and exercise tolerance. Improvement in exercise tolerance generally has been reported by increments in the 6 min walk test. A recent review of the current status of lung volume reduction surgery by Naunheim and Ferguson (4) compiles reported results in a total of 1,331 emphysema patients, derived from 16 studies published in the literature describing results following LVRS. Seven of those studies reported increased exercise tolerance measured by increments in the distance endured over a 6 min walk test. The reported increments ranged from 14% (5) to 104% (6) following surgery. The duration of these observed benefits is currently unknown, but Cooper and collaborators have reported significant increments in 6 min walk distances up to a year after lung volume reduction surgery, and these increments are comparable to those observed among recipients of single- and double-lung transplantation (7). The original work of Brantigan (8) and collaborators reported cases in which subjective relief of dyspnea lasted for over 5 yr, although there was no objective data reported concerning exercise tolerance.

These beneficial changes have been reported with lung reduction performed bilaterally via sternotomy (1) or by using thoracoscopic volume reduction unilaterally (9) or bilaterally (10). Laser techniques for lung reduction, combined with stapled resection of lung tissue, have also resulted in physiologic improvements in emphysematous patients, but improvement has been greater among patients subjected to surgical resection than those receiving laser ablation alone (11).

When postoperative spirometry has been analyzed, most attention has been directed toward expiratory flows. Little information is available documenting changes occurring in inspiratory flows after lung reduction surgery. Likewise, only limited information is available on the effects of this surgery on exercise capacity. O'Donnell and co-workers have suggested that reduction in breathlessness following LVRS is related to reduction in end-expiratory lung volume (EELV) and diminished mechanical constraints on tidal breathing (12). Improved ventilatory mechanics, including inspiratory capacity, have been proposed as mechanisms responsible for lessened dyspnea. Gelb, McKenna, and colleagues have shown that improvements in spirometric variables following LVRS may be related to increased elastic recoil of the lungs with decreased chest wall recoil pressures (13). We hypothesized that reduced breathlessness and improved exercise capacity following LVRS are related to increased inspiratory as well as expiratory flows.

We studied 25 patients with end-stage emphysema who underwent unilateral thoracoscopic lung volume reduction surgery (TLVRS). This was a simple observational study; each subject's variables were compared before and after surgery. Measures of inspiratory and expiratory flows were compared along with changes in exercise capacity measured during a symptom-limited cardiopulmonary stress test on a bicycle ergometer. These measurements were initially obtained after preoperative pulmonary rehabilitation but before unilateral TLVRS, and then repeated within 6 mo after surgery.

	METHODS

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Patients Selection

All patients had an established diagnosis of severe emphysema with significant air trapping and impaired diffusion capacity. Patients with chronic bronchitis were excluded, as well as those patients with severe hypercapnia (resting Pa_CO2 > 55 mm Hg) or with significant pulmonary hypertension (mean pulmonary artery pressure > 35 mm Hg). All patients were screened to rule out left ventricular failure or active coronary artery disease. Patients underwent at least 6 wk of pulmonary rehabilitation before surgery. Patients selected for this clinical research signed an informed written consent. The protocol followed in the study was approved by the St. Louis University institutional review board.

The patients undergoing TLVRS demonstrated distinct target areas for surgical resection. These areas were characterized by well-defined zones of decreased or absent perfusion matched by poor ventilation and trapping of inhaled radiotracers during delayed expiratory phases. The lung with the least differential perfusion (i.e., largest perfusion defects) was selected for surgery.

Pulmonary Function Tests

All patients had complete pulmonary function studies including spirometry, lung volumes, diffusing capacity, and maximal respiratory pressures. Spirometry was performed using either a flow-based system (Sensormedics 2200, Yorba Linda, CA) or a volume-based system (Collins GS, Braintree, MA). All tests met American Thoracic Society (ATS) criteria for acceptability and reproducibility (14). Spirometric values are reported as absolute values (L or L/s) and as a percent of predicted (15). Maximal voluntary ventilation (MVV) reported was the largest value from duplicate (within 10%) 12 s maneuvers. Inspiratory flows were measured from acceptable forced inspiratory flow-volume maneuvers. Maximal values for forced inspiratory volume in one second (FIV₁), peak inspiratory flow (PIF), and forced inspiratory flow at 50% of the curve (FIF_50%) were recorded even if they came from separate efforts. All reported values were taken before bronchodilator challenge because all these patients were already on maximal bronchodilator medical therapy at the time of assessment. For follow-up, each patient was retested using the same equipment and protocols as employed preoperatively.

Functional residual capacity (FRC) was measured by gas dilution techniques (helium dilution) and using a constant volume plethysmograph (Collins Body Plethysmograph, Braintree, MA). Total lung capacity (TLC), residual volume (RV), and RV/TLC ratio were calculated using the FRC values determined by gas dilution and plethysmography. Lung volumes are reported in L and percent of predicted (16, 17).

Diffusing capacity for carbon monoxide (DL_CO) was measured using the single breath technique following the guidelines of the ATS (18). These DL_CO values are reported as the absolute value and as percent of predicted (19). All DL_CO values were corrected for hemoglobin (Hb) and carboxyhemoglobin (COHb) as recommended by the ATS.

Arterial blood gases were obtained with each patient breathing room air at rest. All specimens were analyzed using a Radiometer ABL520 (Radiometer America, Westlake, OH).

Exercise Tests

Exercise tests were performed on an electronically braked cycle ergometer (Sensormedics 800 S). Patients pedaled up to a symptom-limited maximum. All variables were measured first while patients were semirecumbent, then when they were sitting upright on the cycle ergometer. Two minutes of unloaded pedaling (approximately 10 W) was followed by 2 min at 25 W. Workload was then increased by 25 W at 2-min intervals. Gas was sampled at the mouth and analyzed using a breath-by-breath metabolic measurement system (Sensormedics 2900c). Minute ventilation, tidal volume (VT), respiratory rate (RR), and expiratory time (ET) were measured by averaging data from the last 30 s of each exercise interval. Inspiratory time (IT) was calculated from expiratory time and respiratory rate. The ratio of inspiratory to total cycle time (TI/Ttot) was calculated as IT/(IT + ET). Mean inspiratory (I) and expiratory (E) flows at maximal exercise were calculated from VT and IT and ET, respectively. The Dyspneic Index was measured using measured maximum E divided by MVV, expressed as a percentage [(E/MVV)100] to estimate ventilatory impairment (20) and assess breathing reserve during exercise (21). Breathlessness is usually present when the dyspneic index exceeds 50%, in patients with severe obstructive lung diseases whose E max meets or exceeds the MVV, reflecting complete utilization of ventilatory capacity for short periods of exercise (22). Most patients required supplementary oxygen for exercise. The decision to use oxygen was made based on the patients' history (whether they were already on continuous oxygen therapy), or when the resting arterial blood gases obtained on room air showed resting hypoxemia. Oxygen was supplied using a blender and 120 L meteorologic balloon. Gas was blended to achieve fractional inspired concentrations of 0.25-0.35 and delivered via a high-flow flowmeter. Flow to the reservoir balloon was adjusted to match the subjects' ventilation at each exercise level. At the beginning of oxygen breathing, each patients' oxygen consumption (O₂) was monitored until it stabilized and the respiratory quotient (RQ) was within the normal physiologic range.

Measurement of Dyspnea

Severity of preoperative dyspnea was evaluated using scores as described by Mahler and collaborators (23). A baseline dyspnea index (BDI) for each of three different categories was measured: functional impairment, magnitude of effort, and magnitude of task. Each category rated dyspnea in five possible scores ranging from 0 (severe) to 4 (unimpaired). The ratings for each category were added to form a baseline focal score (BFS), where the worst possible degree of dyspnea equalled a score of 0, and a patient completely free of dyspnea scored 12 points.

Postoperatively, changes in dyspnea for each category were measured using the transition dyspnea index (TDI). These categories were rated in 7 possible grades ranging from 3 (major deterioration) to +3 (major improvement). The ratings of each category were added to form a transition focal score (TFS), which ranged from a minimum of 9 to a maximum of +9 (largest possible improvement). A score of 0 indicated no change from the preoperative status.

Surgical Technique

Unilateral TLVRS was performed using a 0 degrees, 10 mm rigid thoracoscope with a one-chip camera. Three to four trocar port sites were fashioned, each measuring approximately 2 cm. The target area of the lung was identified, lifted with a sponge forceps, and excised using an endoscopic stapling device (Endo GIA 60 or EZ45 Endostapler; Ethicon Endosurgery Inc., Cincinnati, OH). Bovine pericardium was not routinely used to buttress the staple line. An average of 56 ± 12 g of lung tissue was excised. The resected lung was removed through the anterior trocar sites. All patients were extubated in the operating room regardless of the degree of hypercapnia during surgery. Postoperative pain management included intercostal nerve blocks (0.5% bupivacaine with epinephrine) over the ribs encompassing the trocar sites. Subsequently, ketorolac and small doses of intravenous morphine sulfate were administered during the first 48 h. Thereafter, pain management was accomplished via oral analgesics. All patients had insertion of two or three 28 French chest tubes connected to a water-sealed chest drainage system. Occasional use of negative water suction was required. Chest tubes remained in place until all air leaks subsided.

All data reduction and statistics were performed using Lotus 123 version 4.01 (Lotus Development Corp., Cambridge, MA). Descriptive statistics are reported as mean ± standard deviation. All pre- and postoperative measures were compared using paired, two-tailed t tests.

Subjects selected for this report were the first 25 consecutive cases in our series of a total of 75 patients who completed pulmonary function and exercise studies 3-6 mo postoperatively. This group, who received unilateral TLVRS, had completed preoperative pulmonary function tests, exercise test, 6 min walk tests, and questionnaires regarding subjective evaluation of dyspnea. They completed the same profile postoperatively.

	RESULTS

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Characteristics of the population studied are contained in Table 1. All patients had smoking-induced emphysema, except for three subjects diagnosed with alpha-1 antitrypsin deficiency. The mean age of the group was 60 yr. Two patients were younger than 50 yr, three older than 70, and the rest from 50 to 70 yr. They had normal height and weight. This group had severe dyspnea. The mean BDI for functional impairments was 1.0 ± 0.63; for magnitude of effort, 1.16 ± 0.54; and for magnitude of task, 1.20 ± 0.57. The mean BFS for the group was 3.36 ± 1.47. These results are consistent with severe dyspnea and functional impairment, with cessation of most or all usual activities due to shortness of breath. Severe dyspnea occurred with minimal effort and with activities such as standing or walking.

Following surgery, these patients required chest tubes for a median 6 d; eight patients required chest tubes for longer than 7 d. Median length of hospital stay was 7 d. Nineteen patients (76%) did not develop any postoperative complications. Three patients developed minor complications (delayed pneumothorax in one, urinary retention due to previously present prostatic disease in another, and severe purulent bronchitis in the third). Three patients suffered significant complications. One patient developed postoperative bleeding from the thoracic wall where a trocar was previously inserted, requiring repeated thoracoscopy with a "mini" thoracotomy to remove clots and cauterize the bleeding source. A second patient had a large persistent air leak requiring a second thoracoscopy to repair a 1-mm hole near the staple line. A third patient who was recovering well from thoracic surgery developed an acute abdomen due to a perforated peptic ulcer, requiring laparotomy and surgical closure. All cases recovered well. The presence of significant postoperative complications was not necessarily associated with poor functional outcome. The patient complicated by a perforated peptic ulcer postoperatively was among those who later showed the largest improvement.

Baseline data of pulmonary function and gas exchange is contained in Table 2. These patients showed severe expiratory airflow obstruction by an average FEV₁ of 28.4% (median 26%), with severe limitation in their MVV (median 25% of normal), severe air trapping evidenced by RV larger than 200% of normal, and markedly impaired diffusion capacity. Their baseline data shows relatively less impairment of inspiratory flows, with FIV₁ and peak inspiratory flows proportionally larger than their equivalent expiratory flows (FEV₁ and PEF). The resting arterial blood gases with patients breathing room air are shown. Most patients had mild to moderate hypoxemia, with a mean Pa_O2 of 66 mm Hg and 91% oxygen saturation. The mean AaPO₂ gradient was increased. The distance walked over a 6 min walk test ranged from 343 to 1,400 ft.

Details related to this group's baseline exercise capacity are contained in Table 3. These patients demonstrated severe functional aerobic impairment by severely reduced O₂ max (9.71 ml/kg/min). Their main limitation was ventilatory, as shown by inability to increase their maximum E. The E max averaged 82% of the MVV (E/MVV ratio or Dyspneic Index), which is consistent with severe ventilatory limitation during exercise (22). In addition, this group showed an elevated dead space ratio at rest (mean 0.40), which remained elevated with exercise (mean 0.35). Due to their ventilatory limitation, most patients ceased exercising even before reaching anaerobic threshold. Their baseline room air hypoxemia (shown in Table 2) was compensated by supplemental oxygen. These patients widened their already abnormal resting alveolar arterial oxygen gradient during exercise, as a manifestation of impaired gas exchange.

Table 4 shows changes in pulmonary function tests and resting arterial blood gases of these patients after unilateral TLVRS. These patients were evaluated within 6 mo (4.2 ± 0.8 mo, ranging from 3 to 6 mo). The group showed significant increases in FVC, FEV₁, FIV₁, PEF, MVV, MEP, Pa_O2, and Sa_O2. There was significant reduction in RV (16% decrease after surgery). The changes were accompanied by improved gas exchange characterized by significantly higher resting Pa_O2and Sa_O2 levels. Figure 1 illustrates four significant physiological changes that followed TLVRS. These were the changes most significantly correlated with subjective scores reflecting improved dyspnea (TFS). The mean increment in FEV₁ was 35 ± 28%, the mean increment in Pa_O2 was 9.7 ± 11 mm Hg, the mean increment in MVV was 10 ± 11 L/min, and the mean reduction in Dyspneic Index [(E/MVV)100] was -15%. Thirteen of 25 patients achieved more than 25% improvement in FEV₁, 11 patients increased their baseline Pa_O2 by more than 10 mm Hg, and 13 patients improved MVV by at least 10 L/min. Eighteen patients showed reduced Dyspneic Index. However, one patient experienced reduced FEV₁, two patients developed worsening resting Pa_O2, and four had lower MVV values than preoperatively. Seven subjects showed an increased Dyspneic Index during exercise.

View larger version (44K): [in this window] [in a new window]   Figure 1.   Left upper panel shows the 25 patients sorted in ascending order by change in FEV1 following TLVRS. Surgery produced a mean 35% increase in FEV1. One patient showed a 1.5% reduction in FEV1 after surgery, eight patients showed an increase < 15%, and the remaining sixteen patients had an increase > 15%. Seven of those patients showed large increases (> 50% increase in FEV1). Right upper panel shows the 25 patients sorted according to changes in resting PaO2 after TLVRS, breathing room air. Two patients showed reduction in PaO2 and three patients were unchanged after surgery. Nine patients increased their PaO2 < 10 mm Hg and 11 patients increased their resting PaO2 > 10 mm Hg. The mean increment was 9.7 mm Hg for the group. Left lower panel shows patients sorted according to change in MVV. Five patients showed no improvement or worsening after TLVRS. Six patients showed increases < 10 L/min, and 13 patients > 10 L/min for a mean increase of 10 L/min for the group. Right lower panel depicts patients sorted by change in [( E/MVV)100] the Dyspneic Index. Seven patients had increased Dyspneic Index during maximum exercise following TLVRS, while 18 patients showed decreased Dyspneic Index ranging from 0.2% to 84%. The mean change in Dyspneic Index for the group was 15%.

These results were associated with improvement in subjective feeling of dyspnea. The transition dyspnea index (TDI) for functional impairment increased an average of 1.72 ± 0.7 points; for magnitude of effort, by 2.12 ± 0.8; and for magnitude of task, by 2.28 ± 0.7. The mean Transition Focal Store (sum of TDI) was 6.12 ± 2 points. These scores reflect moderate improvement in functional status, allowing patients to return to most activities with only moderate restrictions. Scores indicate that patients felt able to do things with fewer pauses and perform distinctly greater effort without shortness of breath. Figure 2 illustrates the postoperative TFS of these 25 patients, representing the subjective changes in dyspnea.

View larger version (35K): [in this window] [in a new window]   Figure 2.   The 25 patients sorted incrementally according to their Transition Factor Scores (TFS) obtained from adding Transition Dyspnea Indices (TDI) for functional impairment, magnitude of effort, and magnitude of task, following TLVRS. Possible TFS scores range from 9 (severe worsening in three categories of TDI) to +9 points, representing maximum improvement in the three categories. A score of 0 represents no change from baseline. No patient reported subjectively worsening in dyspnea from baseline. Twenty-two patients reported a TFS of +5 points or better. The mean score for the group was 6.12 ± 2, ranging from 1 to 9 points.

Table 5 shows changes in exercise capacity (O₂, E max, VT, respiratory rate) and the pattern of exercise ventilation (TI / Ttot, mean inspiratory and expiratory flows) before and after lung reduction. There was significant increase in exercise tolerance; the duration of exercise increased from 4.43 ± 1.71 min preoperatively to 5.71 ± 1.83 min after surgery (p < 0.001). The mean preoperative maximum workload tolerated was 37.1 ± 19 W compared to 52.4 ± 21 W after surgery. The O₂ max increased significantly to 11.8 ± 3 ml/kg/min (p < 0.01). Maximal exercise ventilation (E max in L/min) also increased significantly from 24.4 ± 11 to 28.5 ± 10.3 (p < 0.001). The increased E max was accomplished solely by an increased VT from 951 ± 330 ml to 1,145 ± 367 ml (p < 0.001). Respiratory rate during maximal exercise was unchanged after surgery. Similarly, there were no changes in expiratory or inspiratory times. The ratio TI / Ttot also remained the same. The increase in E max and VT was accomplished by significantly increasing mean inspiratory and mean expiratory flows from 0.89 ± 0.41 to 1.06 ± 0.42 L/s and from 0.77 ± 0.37 to 0.90 ± 0.32 L/s respectively (p < 0.01). Increased exercise capacity was also manifested by a significant increase in the distance walked in the 6 min walk test, which increased from 934 ± 297 to 1,071 ± 241 ft (p = 0.01). The Dyspneic Index decreased from a mean of 82% preoperatively to 72% after TLVRS, indicating significantly larger breathing reserve and less ventilatory impairment to exercise, even when these variables were measured at a higher workload.

We evaluated the correlation between TFS as an index reflecting the subjective impression of dyspnea relief with the change produced by reduction surgery in different variables measured at rest and during exercise. The changes induced by surgery were calculated by subtracting postoperative from preoperative values. Only few variables correlated significantly with TFS: the change in FEV₁ (L/min) showed a correlation coefficient (r) equal to 0.44 (p < 0.05), and the percent change in FEV₁ following surgery had r = 0.46 (p < 0.05). The change in Pa_O2 also correlated with TFS, showing r = 0.50 (p < 0.05). The highest correlation occurred between the change in MVV and TFS (r = 0.57, p < 0.01). The change induced by surgery in FIV₁, FVC, E max, O₂ max, and 6 min walk distance did not correlate significantly with the subjective sensation of improving dyspnea, as measured by the TFS. The only variable measured during exercise that correlated significantly with TFS was the Dyspneic Index, showing r = 0.50 (p < 0.05).

	DISCUSSION

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Lung volume reduction surgery produces significant dyspnea relief for many patients with severe emphysema. Associated with this subjective improvement, most patients will achieve a variable degree of physiological improvement evidenced by increased airflows and decreased residual volume. Many patients will also have improved exercise capacity. The exact mechanism of the subjective improvement is not precisely defined. None of the 25 patients in this group reported subjective worsening after surgery. Twenty-two out of 25 (88%) had improvement in the Transition Focal Score of 5 points or more, in a scale where the maximum improvement possible is 9 points (mean score = 6 ± 2 points). Most patients demonstrated an increase in either expiratory or inspiratory airflow (FEV₁, FIV₁) or MVV maneuvers. The relationship between subjective changes and objective improvement in physiological parameters is not well defined. Certainly there is no single measurable pulmonary function parameter showing precise and strong correlation with subjective reduction in dyspnea.

The change in MVV following surgery was the variable that correlated best with the subjective improvement in dyspnea scores. The correlation coefficient, although significant, was not extremely high (r = 0.57). An increased MVV as seen in this group of patients may be related to multiple factors. Increased effort, improved respiratory muscle strength, increased lung volume, higher respiratory rate, or improved flows are all possible explanations. Although subjects in the study may have increased their effort, MVV maneuvers were routinely compared to FEV₁ · 35 to assure that each patient was giving a maximal effort. We did not observe an improvement in inspiratory muscle strength as measured by the MIP. Expiratory muscle function, as measured by MEP, did show a minor yet statistically significant increment in this group and may be associated with some of the improvement in MVV. Similarly, the increase in FVC and associated decrease in RV may account for improvement in MVV. The highly significant improvement in inspiratory and expiratory flows during maximal exercise suggests that a similar pattern might be observed during performance of the MVV. Except for the Dyspneic Index, the measured variables during exercise did not correlate with subjective scores of improved dyspnea.

In carefully chosen subjects, unilateral thoracoscopic resection of lung tissue on the side with the largest perfusion defects produces significant reduction in residual volume, as shown in our patients. This reduction in residual volume is accompanied by increased FVC, making the overall change in TLC minimal and nonsignificant. Baseline pulmonary function tests of this group show that these patients with severe emphysema had much greater impairment in expiratory flows than in inspiratory efforts (FEV₁ = 0.80 ± 0.33 L versus FIV₁ = 2.26 ± 0.82 L). This finding is not unexpected, since the dynamic airway compression disrupts expiratory flow much more than inspiratory flow. A similar pattern was present with PIF and PEF. These patients achieved a significant improvement in expiratory airflow, as previously discussed. We also observed a parallel improvement in inspiratory airflow, reflected in the significant increase in FIV₁. The mean percent increment in FEV₁ was 35% for the group, while the FIV₁ increased by a mean of 21%. The increase in both flows produced the 40% average increment in MVV.

Improved oxygenation is likely secondary to better ventilation or perfusion matching. Two patients showed postoperative Pa_O2 values lower than preoperative values. Three patients showed postoperative values equal to the preoperative level. The remaining 20 cases had improved oxygenation, and 11 of them had an increase in Pa_O2 larger than 10 mm Hg. We chose to exclude patients with significant hypercapnia from this study; consequently, we did not see any significant changes in resting Pa_CO2 values following surgery. Other groups that have included patients with higher baseline Pa_CO2 values have shown improved resting ventilation with significant reduction in Pa_CO2. Inclusion of hypercapnic patients for lung reduction surgery, however, has been recognized as a high risk factor for morbidity and mortality (5).

Our results compare favorably with those reported for bilateral LVRS. Cooper and coworkers (1, 2) have reported a 52% increment in FEV₁ among 84 patients evaluated 3 mo after bilateral LVRS via sternotomy, which is a larger improvement than our patients experienced after unilateral surgery. Likewise, they reported an average 33% reduction in RV compared to 16% in our series. Despite these larger changes, their average increase in Pa_O2 3 mo after surgery was 8 mm Hg, and the increase in 6 min walk test was 13%, both comparable to the early results achieved by our patients subjected to unilateral surgery. Recent studies report the same magnitude of improvement among patients subjected to bilateral LVRS, regardless of whether the surgery was performed via sternotomy or thoracoscopically (10). The latter group underwent bilateral surgery in either staged procedures or simultaneously. In this series, survival rates were better for patients undergoing thoracoscopic surgery when compared to the sternotomy group. Further studies will be necessary to define whether the type of surgical procedure has a real impact in functional outcome, morbidity, and mortality. Furthermore, benefits of performing simultaneous bilateral thoracoscopic surgery compared to unilateral procedures followed by later contralateral surgery will need to be investigated. Not every patient with emphysema and severe air trapping will show well defined bilateral target zones amenable to surgery. Some patients have a defined unilateral pattern of decreased perfusion and air trapping, where one lung is markedly worse than the other. For these patients, a unilateral thoracoscopic procedure should be the best approach.

Observations made during exercise test were important. These patients demonstrated an increased exercise capacity not only by a significant increment in the 6 min walk, but also by achieving a significantly higher O₂ max and by tolerating higher workloads. The average increase in O₂ max was 27% over baseline (2.12 ± 3 ml/kg/min, or an average increment of 111 ml O₂/min).

Improvement in O₂ max was achieved largely through a significant increase in E. Increased ventilation was achieved exclusively by larger tidal volumes during maximal exercise. Respiratory rates at maximal tolerated workloads were unchanged. This pattern seems to differ from the data of O'Donnel and colleagues (12). However, their group reported reduced respiratory frequency at a standardized work rate, not at maximum tolerable workload. In our patients, both inspiratory and expiratory flows increased at maximal exercise, allowing generation of larger VT. The relative changes in inspiratory and expiratory flows were similar, so expiratory and inspiratory times remained constant. This results in a TI / Ttot ratio unchanged from baseline. Increased inspiratory and expiratory flows with no change in the timing of the ventilatory phases suggests that lung reduction alters the pressure-volume characteristics of the lung. Increased lung recoil and decreased chest wall recoil following lung reduction have been postulated as potential contributors to improvement in airway conductance (13). Our findings are consistent with this concept that lung reduction alters the pressure-volume characteristics of the lungs and thorax, allowing increased exercise tolerance. This increased exercise tolerance with generation of larger VT and E was achieved while the E/MVV ratio or Dyspneic Index decreased significantly from 82% ± 22 to 72% ± 16 (p = 0.04), consistent with reduction in the severity of ventilatory impairment. Long-term follow-up of this group will be necessary to determine the duration of these physiological changes.

In summary, early follow-up of 25 patients who completed pulmonary function tests and cardiopulmonary stress tests after unilateral TLVRS is reported. In this observational study, there was significant improvement in static measures of expiratory and inspiratory flows with significant reduction in RV. These patients also achieved substantial improvement in oxygenation. These improvements were accompanied by an increased exercise tolerance, decreased ventilatory limitation to exercise, and reduced sensation of dyspnea. Increased maximal ventilation was accomplished by increased inspiratory and expiratory flows and the resulting increased VT with no change in the timing of the breathing cycle.

The subjective improvement in dyspnea observed in this group correlated best with the change in MVV following surgery. Measured changes in exercise capacity did not correlate with subjective scores indicating improved dyspnea. A randomized prospective trial is necessary to better elucidate the mechanisms for improvement following lung reduction surgery.