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Original Research: COPD |

The 6-Min Walk Distance, Peak Oxygen Uptake, and Mortality in COPD* FREE TO VIEW

Claudia G. Cote, MD; Victor Pinto-Plata, MD, FCCP; Kyra Kasprzyk; Luis J. Dordelly; Bartolome R. Celli, MD, FCCP
Author and Funding Information

*From the Division of Pulmonary and Critical Care (Dr. Cote), Bay Pines Veterans Affairs Medical Center, Bay Pines, FL; Division of Pulmonary, Critical Care and Sleep Medicine (Drs. Pinto-Plata and Celli), St. Elizabeth’s Medical Center, Boston, MA; and The Bay Pines Research Foundation (Ms. Kasprzyk and Mr. Dordelly), Bay Pines, FL.

Correspondence to: Claudia G. Cote, MD, Pulmonary and Critical Care Medicine, Bay Pines VA Health Care System, 10,000 Bay Pines Blvd, Bay Pines, FL 33744; e-mail: claudia.cote@med.va.gov



Chest. 2007;132(6):1778-1785. doi:10.1378/chest.07-2050
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In patients with COPD, the maximal oxygen uptake (V̇o2) measured at peak exercise and the 6-min walk distance (6MWD) have been associated with survival; however, no study has compared the strength of the association in the same patients. In this study, we compared the association between the 6MWD and peak V̇o2 and mortality in 365 patients with COPD. Patients’ cardiopulmonary cycle ergometry test results and 6MWD were determined at entry, and patients were followed up for a mean period of 67 months. There were 171 deaths. Compared with survivors, nonsurvivors were older (mean [± SD] age, 67.9 ± 8 vs 65.9 ± 8 years, respectively; p = 0.008), had worse mean FEV1 (36.5 ± 12 vs 42.6 ± 14 L, respectively; p = 0.02), had lower mean peak V̇o2 (9.8 ± 3 vs 11.8 ± 3.6 mL/Kg/min, respectively; p < 0.0001), lower mean 6MWD (312 ± 104 vs 377 ± 95 m, respectively; p < 0.0001), and lower mean exercise minute ventilation (37.4 ± 12 vs 42.3 ± 13 L/min, respectively; p = 0.004). Univariate analysis showed that peak V̇o2 and 6MWD as well as comorbidity, FEV1, and body mass index were associated with death. Logistic regression analysis with mortality as the dependent variable revealed that 6MWD (hazard ratio [HR], 0.996; 95% confidence interval [CI], 0.993 to 0.999; p < 0.01) had a stronger association than the peak V̇o2 (HR, 0.971; 95% CI, 0.959 to 1.000; p = 0.050) with mortality. This study shows the 6MWD is as good predictor of mortality as the peak V̇o2 in patients with COPD.

Figures in this Article

There has been great interest in evaluating the role of exercise testing in patients with COPD. Exercise testing is used to explore the mechanisms of dyspnea12 and its response to treatment.3In addition, the maximal oxygen uptake (V̇o2) measured at peak exercise helps to predict survival in patients undergoing lung resection.5 In one report,6peak V̇o2 proved to be a better predictor of mortality than FEV1 and health-related quality of life in a cohort of patients with COPD. However, the determination of peak V̇o2 requires relatively complex equipment and certain expertise that is not available to most clinicians. Further, some patients with very advanced heart or lung disease cannot undergo a CPET.7

An alternative to formal laboratory exercise testing is the use of simple field tests that can provide related information, such as the 6-min walk distance (6MWD) test. Over the last decade, it has gained acceptance because it is simple and reliable, and because it has been standardized.8Due to its simplicity, the 6MWD test has been used as a tool to evaluate the effect of pulmonary rehabilitation and the change in functional exercise capacity.9The results of the 6MWD test are a good predictor of mortality in patients with COPD completing rehabilitation10or being evaluated in pulmonary clinics.11 In those studies, the timed walk proved to be a better predictor of mortality than more conventional tests, such as the pulmonary function test, and the patient’s nutritional status, as represented by the body mass index (BMI).

There is a significant but modest correlation between the peak V̇o2 and the 6-min walk distance (6MWD).1213 However, no study has yet compared the predictive value for mortality of peak V̇o2 with that of the 6MWD in patients with COPD. It is entirely possible that the two tests share common characteristics but may have different predictive power for different outcomes. Indeed, two studies15 of patients with primary pulmonary hypertension showed that the 6MWD was a better predictor of mortality than the peak V̇o2, as determined by a formal cardiopulmonary exercise test (CPET). If this proved to be true in patients with COPD, their caregivers would have a simple tool that could provide valuable information regarding the prognosis of those patients.

We therefore designed this prospective study to compare the capacity of the peak V̇o2 and the 6MWD in predicting mortality in patients with COPD and aimed to identify the thresholds associated with this outcome. The patients included in this study were part of a larger study16 designed to evaluate the role of the respiratory and systemic manifestations of COPD.

Patients

The 365 consecutive patients with symptomatic COPD had been recruited to the body-mass index, airflow obstruction, dyspnea, and exercise capacity (BODE) protocol at the Bay Pines Veterans Administration Health Care System (n = 278) and St. Elizabeth’s Medical Center (n = 87) between 1994 and 2005. The human research committees approved the study, and all of the patients gave informed consent. The study enrollment criteria were as follows: smoking history of > 10 pack-years; diagnosis of COPD; FEV1/FVC ratio of < 0.70; and response to bronchodilator of < 12% or 200 mL. The patients were part of a larger cohort, the results of which have been reported earlier.16The cohort consisted primarily of patients attending pulmonary clinics, which had no contraindications for pulmonary rehabilitation, had been clinically stable for 6 weeks prior to entry into the study, and were able to perform all of the required tests. The CPET and the 6MWD were performed on separate days. Comorbidity was determined with the Charlson score.17

Pulmonary Function and Exercise Tests

The FEV1 and FEV1/FVC were calculated following American Thoracic Society recommendations.18 The results were expressed as absolute and percent predicted values. Lung volumes were obtained using body plethysmography.

The 6MWD test was completed as recommended by the American Thoracic Society.8 Oxygen saturation was continuously monitored. Supplemental O2 was provided to 121 patients (33%) to maintain arterial oxygen saturation at > 90%. The inclusion or exclusion of these patients in the analysis did not modify any of the results.

Exercise ergometry was performed using a 1-min incremental protocol.19 Patients started with a 2-min period of unloaded pedaling at 60 cycles per minute, followed by a loading rate increment of 10 W/min. The patients were encouraged to cycle until discomfort or exhaustion for at least 2 min. Heart rate was monitored with a 12-lead ECG, and BP was measured with the cuff technique. Minute ventilation (V̇e) and its components were measured using a pneumotachograph. The concentrations of expired oxygen and carbon dioxide were analyzed breath by breath. These measures and flow signals were integrated to yield 30-s averages of V̇e, tidal volume, respiratory rate, V̇o2, carbon dioxide output, and gas exchange ratio. The predicted maximal V̇o2 was calculated using standard equations.,19Maximal voluntary ventilation was directly determined > 12 s. The heart rate reserve was calculated as the predicted maximal heart rate (maximal heart rate = 220 beats/min − age) minus the observed peak heart rate. Dyspnea was measure as per the modified Medical Research Council (MMRC) dyspnea scale.20

Statistical Analysis

For continuous variables, the data are presented as the mean ± SD and range. The differences in physical characteristics, pulmonary function test results, and exercise parameters were evaluated using t tests for independent variables. Receiver operating characteristic (ROC) curves were used to identify the best sensitivities and specificities for both 6MWD and peak V̇o2 to determine survival in COPD patients. The Pearson correlation test was used to assess the relationship between the 6MWD and peak V̇o2 and other clinical variables. Mortality was evaluated over time using Kaplan-Meier analysis. Differences in death rate at different 6MWD thresholds were evaluated by the log-rank test. Univariate and logistic regression analyses were used to investigate the relationship between the clinical variables and mortality. A probability value of < 0.05 was considered to be significant. Statistical analysis was completed with a commercial software package (GB Stat; St. Louis, MO).

The clinical characteristics of the 365 patients studied are shown in Table 1 . As expected, the patients had important airflow limitation, were mostly men, and the group included patients with a wide range of COPD severity.

There were 171 deaths (47%) over the study period (mean period, 66.7 ± 29 months; range, 3 to 121 months). The mean time to death for nonsurvivors was 43 ± 24 months. The majority of patients (50%) died from respiratory failure. However, 9% of deaths were due to cardiovascular disease, 18% were due to lung cancer, and 23% were due to other causes. The mean Charlson comorbidity index for the group was 4.86 ± 2.7. There were significant differences between survivors and nonsurvivors in most of the variables evaluated. The differences are summarized in Table 2 . The nonsurvivors were older than survivors (mean age, 68 ± 8 vs 66 ± 8 years, respectively; p = 0.008), had more severe airflow limitation (mean FEV1, 1.1 ± 0.4 vs 1.3 ± 0.51 L, respectively; p = 0.0001), and had lower mean exercise capacity (mean peak V̇o2, 9.8 ± 3 vs 11.8 ± 3.6 mL/kg/min, respectively; p < 0.0001), 6MWD (313 ± 104 vs 378 ± 95 m, respectively; p < 0.0001), and ventilatory capacity (mean V̇e, 37 ± 13 vs 42.1 ± 3 L/min, respectively; p = 0.004). However, nonsurvivors and survivors achieved similar peak exercise heart rates (119 ± 16 vs 122 ± 18, respectively; p = 0.056). We found significant differences among patients dying from COPD vs those dying from other causes. Overall, patients dying from COPD had worse exercise capacity. The differences are summarized in Table 3 .

The correlation between 6MWD and peak V̇o2 is shown in Figure 1 ; this correlation, as well as those with other variables, is shown in Table 4 . The 6MWD was strongly associated with watts (r = 0.60; p < 0.0001) and MMRC dyspnea scale score (r = −0.52; p < 0.0001). The peak V̇o2 correlated best with FEV1 percent predicted (r = 0.46; p < 0.0001), MMRC dyspnea scale (r = −0.38; p < 0.0001), and, as expected, with watts (r = 0.64; p < 0.0001).

The univariate analysis showed that mortality was significantly associated with 6MWD, peak V̇o2, maximum workload, Charlson index, BMI, FEV1 percent predicted, and MMRC dyspnea scale score. The results of the logistic regression analysis with mortality as the dependent variable and those variables with the best correlation in the univariate analysis are summarized in Table 5 . In this analysis, the 6MWD was a better predictor of all-cause mortality than the peak V̇o2. 6MWD (hazard ratio [HR], 0.996; 95% confidence interval [CI], 0.993 to 0.999; p < 0.0001) vs V̇o2 (HR, 0.971; 95% CI, 0.959 to 1.000; p = 0.050). BMI also contributed to the model (HR, 0.92; 95% CI, 0.904 to 0.943; p = 0.0013) while age almost reached statistical significance (HR, 1.031; 95% CI, 0.995 to 1.068; p < 0.08). The FEV1 (p = 0.24), peak heart rate (p = 0.58), and V̇e (p = 0.42) did not contribute to the mortality prediction model. The percentage of the deviance explained by the model was 17.1 (p < 0.0000). The exclusion or inclusion of the small number of women did not affect these results.

We constructed ROC curves to determine the best specificity and sensitivity for both the 6MWD and the V̇o2 max as percent predicted value. For the 6MWD, the value identified was 350 m (specificity, 68.6; sensitivity, 64.5), while for the peak V̇o2 the identified threshold was 41% of the predicted value (specificity, 63.3%; sensitivity, 63.3%). Using these thresholds, the area under the curve was 0.68 for the 6MWD and 0.66 for the peak V̇o2 (Fig 2 ). Kaplan-Meier survival analysis for the two modalities of testing is shown in Figure 3 . We found no significant differences between the survival of patients walking > 350 m (survival rate, 66%) and achieving > 41% of their predictive value for the peak V̇o2 (survival rate, 65%). On the other hand, the survival of patients walking < 350 m was 39% compared to those achieving < 41% of their peak V̇o2 (survival rate, 43%). The best χ2 value was seen with the 6MWD test. Further stratification of the 6MWD test by 100 m showed an exponential increase in mortality with patients walking < 250 m having a 5-year survival rate of only 26% (Fig 4 ).

This prospective study shows that in patients with a wide range of COPD severity, the 6MWD is as good a predictor, if not a better one, of all-cause mortality as the peak V̇o2 obtained during a formal CPET. COPD is the fastest-rising major cause of death in the United States, and its prevalence is increasing rapidly.21The severity of the disease has classically been assessed using a single physiologic value, the FEV1. Although the FEV1 is a good indicator of disease severity, as the disease advances the FEV1 loses some of its predictive power for outcomes such as dyspnea,22 health status,23 and mortality.1011 Our group has recently demonstrated24that in advance Global Initiative for Chronic Obstructive Lung Disease stages of COPD, patients show a greater loss in exercise capacity than in FEV1 percent predicted. The walking distance then becomes a better indicator of progression of disease. Several studies26 have shown that in some patients with COPD decreased muscle mass and peripheral muscle dysfunction develop, which likely contributes to poor exercise performance. Indeed, such findings indicate a systemic compromise, and conversely weight loss and a low BMI have emerged as important predictors of mortality in patients with COPD.2728 The BODE index, an integrated multidimensional tool that incorporates FEV1 percent predicted, the 6MWD, dyspnea score, and BMI, has proven to be a more powerful predictor of mortality in patients with this disease than the FEV1.,16 However, performance in a formal CPET was not evaluated in any of those studies.

Peak V̇o2, determined during a CPET, has gained acceptance as a predictor of mortality in patients being evaluated for lung resection4,29as well as in patients with severe heart disease.30 In addition, Oga and colleagues6 have shown that in patients with COPD peak V̇o2 measured during a CPET is a better predictor of mortality than FEV1 and health status. Using this same argument, it seems reasonable that a simple walk test might similarly have an overall predictive capacity, even if it was not expected to be as accurate as that provided by the formal CPET. To our surprise, the 6MWD performed as well if not better than the peak V̇o2 in predicting mortality in our cohort. At first glance, both of these tests represent a function of exercise capacity, but they may provide slightly different information. Indeed, in our patients there was a modest but significant correlation between peak V̇o2 and 6MWD (r = 0.48), a finding that has been reported in other studies,12,31 evaluating the correlation between the two tests. Interestingly, the patients reported by Oga and coworkers6 overall had higher exercise capacity than the patients reported on here. Although no direct comparisons have been made between the exercise capacity in patients from different countries with different exercise habits, we have consistently reported a lower 6MWD in patients from the United States compared with patients from Spain.24 The reasons for these differences remain to be explored.

We have previously shown that patients who are unable to perform a CPET are 11 times more likely to die after undergoing lung resection than those completing the CPET independent of the achieved peak V̇o2.7 This observation suggests that an inability to exercise is indicative of important vital compromise; it also helps to explain the intrinsic predictive power of exercise per se. However, the difference between the 6MWD and peak V̇o2 during CPET was not due to the lower number of patients in the CPET group because all of our patients completed both tests and, therefore, were able to exercise. Thus, the better predictive value of the 6MWD is unrelated to which patients could complete this test but not the CPET.

Perhaps the way in which the tests are conducted influences the information obtained. Peak V̇o2 is measured toward the end of a predetermined, progressively increasing load protocol that may not be sustainable for sicker patients. A similar observation has been reported by two different groups1415 in patients with primary pulmonary hypertension in whom the 6MWD was a better predictor of mortality than the peak V̇o2. It is possible, and indeed probable, that during CPET symptoms of shortness of breath and/or leg fatigue develop in patients with COPD before the theoretically possible peak V̇o2 is achieved and that they stop exercising because of intolerable symptoms. Indeed, patients with COPD rarely reach a true plateau of maximal V̇o2 during CPET.,1,32Furthermore, the development of leg fatigue and not ventilatory limitation in patients with COPD has been documented by Pepin et al, administering bronchodilators to increase the ventilatory ceiling of patients with severe COPD.33The 6MWD involves an activity that all of the patients are familiar with; in addition, the patients are asked to attempt to cover the maximal distance in 6 min. Thus, they are allowed to pace themselves as opposed to having a fixed predetermined load. The patients seem to comply with these instructions and perform to the best of their capacity. Indeed, a recent report by Casas and colleagues34 has shown that patients with COPD walk at a pace that is close to their maximally tolerable exercise capacity. Their patients tried to walk as fast as they could without becoming fatigued. This cannot be done during the CPET, where the load is increased progressively until symptoms force discontinuation of the test.

Our study has some limitations. Perhaps the most important one is that the patients included in the study were only those attending specialized centers and were felt to be at need for pulmonary rehabilitation; therefore, they may not represent the larger population of patients with COPD. However, the wide range of airflow obstruction does represent patients with COPD of the degree seen by clinicians. Second, we only included patients capable of performing both tests. Thus, the results may not apply to patients with conditions that limit the ability to walk; other factors (such as response to arm ergometry) may be more predictive of mortality in those patients than the inability to walk. It could also be argued that the peak V̇o2 is a better test in patients where the presence of important cardiac involvement is not an exclusion criterion. However, data from studies involving patients with congestive heart failure35 also support the value of the 6MWD to predict mortality. Finally, the population consisted mainly of men. We admit this to be a limitation; however, in the studies by Miyamoto et al14and Barst et al15 of patients with primary pulmonary hypertension, where a large proportion of patients were women, the 6MWD still proved to be a better predictor of mortality than peak V̇o2. In addition, excluding the women from our study did not affect any of the results. We hope that further studies will include more women to extend our findings.

We must caution about overgeneralizing the results reported here. Our purpose was not to promote the substitution of a formal CPET for the 6MWD test. The CPET remains an extremely powerful tool that can provide information on the nature of the cardiopulmonary response to an exercise, or can help formulate an accurate prescription of exercise training or the response to pharmacologic therapy.18 Indeed, the 6MWD provides much less mechanistic information. Perhaps this field test should be used as a complement to an exercise test and can find a role in the wider practice of everyday pulmonary medicine.

In summary, this study shows that in patients with a wide range of COPD severity, the 6MWD test is as good a predictor of mortality, if not a better one, than the peak V̇o2 obtained in a CPET. Further, the results suggest that the 6MWD test is a simple and useful test that can provide important information about a patient’s functional capacity and overall prognosis, and could become an easy test to include in the assessment of patients with COPD.

Abbreviations: BMI = body mass index; BODE = body-mass index, airflow obstruction, dyspnea, and exercise capacity; CI = confidence interval; CPET = cardiopulmonary exercise test; HR = hazard ratio; MMRC = modified Medical Research Council; ROC = receiver operating characteristic; 6MWD = 6-min walk distance; V̇e = minute ventilation; V̇o2 = oxygen uptake

The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Table Graphic Jump Location
Table 1. Baseline Characteristics
Table Graphic Jump Location
Table 2. Baseline Differences in Resting and Exercise Variables Between Survivors and Nonsurvivors in 365 Patients With COPD*
* 

Values are given as the mean ± SD, unless otherwise indicated.

Table Graphic Jump Location
Table 3. Differences in Exercise Variables Between Patients Dying From COPD and COPD Patient Dying From Any Other Cause*
* 

MVV = maximal voluntary ventilation.

 

p < 0.05.

Figure Jump LinkFigure 1. There was a modest (r = 0.48) but significant (p < 0.0001) correlation between the 6MWD and the peak V̇o2.Grahic Jump Location
Table Graphic Jump Location
Table 4. Correlations Between the 6MWD and Peak V̇o2 With Other Clinical and Physiologic Variables
* 

p < 0.05.

Table Graphic Jump Location
Table 5. Multivariate Analysis To Investigate the Most Important Factors Predicting Death in the Patients With COPD*
* 

Percentage of deviance explained by the model, 17.1 (p < 0.0000).

Figure Jump LinkFigure 2. Diagnostic testing of the predictive value of the 6MWD test and the maximal V̇o2 (VO2M) for survival in COPD by ROC curves. The values identified the best thresholds for both tests. NS = not significant.Grahic Jump Location
Figure Jump LinkFigure 3. Kaplan Meier curves for the 6MWD test and the V02 max as percent of predicted. The thresholds shown for the 2 groups were taking from the values determined from the ROC curves. The number of survivors at each time point in years is shown for each test. FU = follow-up.Grahic Jump Location
Figure Jump LinkFigure 4. Kaplan-Meier curves for patients walking > 350 m, between 250 and 349 m and < 250 m. Survival decreased by 20% for each one hundred meter difference in the 6MWD test.Grahic Jump Location
Montes de Oca, M, Rassulo, J, Celli, B (1996) Respiratory muscle function and cardiopulmonary response to exercise in severe COPD.Am J Respir Crit Care Med154,1284-1289. [PubMed]
 
O’Donnell, DE, Lam, M, Webb, KA Spirometric correlates of improvement in exercise performance after anticholinergic therapy in chronic obstructive pulmonary disease.Am J Respir Crit Care Med1999;160,542-549. [PubMed]
 
Belman, MJ, Botnick, WC, Shin, JW Inhaled bronchodilators reduce dynamic hyperinflation during exercise in patients with chronic obstructive pulmonary disease.Am J Respir Crit Care Med1996;153,967-975. [PubMed]
 
Weisman, I Cardiopulmonary exercise testing in the preoperative assessment for lung resection surgery.Semin Thorac Cardiovasc Surg2001;13,116-125. [PubMed] [CrossRef]
 
Bolliger, C, Perruchoud, A Functional evaluation of the lung resection candidate.Eur Respir J1998;11,198-212. [PubMed]
 
Oga, T, Nishimura, K, Tsukino, M, et al Analysis of the factors related to mortality in chronic obstructive pulmonary disease: role of exercise capacity and health status.Am J Respir Crit Care Med2002;167,544-549. [PubMed]
 
Epstein, SK, Faling, LJ, Daly, BD, et al Inability to perform bicycle ergometry predicts increased morbidity and mortality after lung resection.Chest1995;107,311-316. [PubMed]
 
American Thoracic Society.. American Thoracic Society statement: guidelines for the six-minute walk test.Am J Respir Crit Care Med2002;166,111-117. [PubMed]
 
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Pinto-Plata, V, Cote, CG, Cabral, HJ, et al The 6-minute walk distance: change over time and value as predictor of survival in severe COPD.Eur Respir J2004;23,28-33. [PubMed]
 
Montes de Oca, M, Ortega, M, Lezama, J, et al Enfermedad pulmonar obstructiva crónica: evaluación de la tolerancia al ejercicio utilizando tres tipos diferentes de prueba de esfuerzo.Arch Bronconeumol2001;37,69-74. [PubMed]
 
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Barst, RJ, Langleben, D, Frost, A, et al Sitaxsestan therapy for pulmonary hypertension.Am J Respir Crit Care Med2004;169,441-447. [PubMed]
 
Celli, B, Cote, C, Marin, J, et al The body mass index, airflow obstruction, dyspnea, and exercise capacity index in chronic obstructive pulmonary disease.N Engl J Med2004;350,1005-1012. [PubMed]
 
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Lauer, M, Snader, C Using exercise test to prognosticate patients with heart failure: which parameter should we measure?Cardiol Clin2001;19,573-581. [PubMed]
 
Swinburn, CR, Wakefield, JM, Jones, PW Performance, ventilation, and oxygen consumption in three different types of exercise test in patients with chronic obstructive lung disease.Thorax1985;40,581-586. [PubMed]
 
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Figures

Figure Jump LinkFigure 1. There was a modest (r = 0.48) but significant (p < 0.0001) correlation between the 6MWD and the peak V̇o2.Grahic Jump Location
Figure Jump LinkFigure 2. Diagnostic testing of the predictive value of the 6MWD test and the maximal V̇o2 (VO2M) for survival in COPD by ROC curves. The values identified the best thresholds for both tests. NS = not significant.Grahic Jump Location
Figure Jump LinkFigure 3. Kaplan Meier curves for the 6MWD test and the V02 max as percent of predicted. The thresholds shown for the 2 groups were taking from the values determined from the ROC curves. The number of survivors at each time point in years is shown for each test. FU = follow-up.Grahic Jump Location
Figure Jump LinkFigure 4. Kaplan-Meier curves for patients walking > 350 m, between 250 and 349 m and < 250 m. Survival decreased by 20% for each one hundred meter difference in the 6MWD test.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Baseline Characteristics
Table Graphic Jump Location
Table 2. Baseline Differences in Resting and Exercise Variables Between Survivors and Nonsurvivors in 365 Patients With COPD*
* 

Values are given as the mean ± SD, unless otherwise indicated.

Table Graphic Jump Location
Table 3. Differences in Exercise Variables Between Patients Dying From COPD and COPD Patient Dying From Any Other Cause*
* 

MVV = maximal voluntary ventilation.

 

p < 0.05.

Table Graphic Jump Location
Table 4. Correlations Between the 6MWD and Peak V̇o2 With Other Clinical and Physiologic Variables
* 

p < 0.05.

Table Graphic Jump Location
Table 5. Multivariate Analysis To Investigate the Most Important Factors Predicting Death in the Patients With COPD*
* 

Percentage of deviance explained by the model, 17.1 (p < 0.0000).

References

Montes de Oca, M, Rassulo, J, Celli, B (1996) Respiratory muscle function and cardiopulmonary response to exercise in severe COPD.Am J Respir Crit Care Med154,1284-1289. [PubMed]
 
O’Donnell, DE, Lam, M, Webb, KA Spirometric correlates of improvement in exercise performance after anticholinergic therapy in chronic obstructive pulmonary disease.Am J Respir Crit Care Med1999;160,542-549. [PubMed]
 
Belman, MJ, Botnick, WC, Shin, JW Inhaled bronchodilators reduce dynamic hyperinflation during exercise in patients with chronic obstructive pulmonary disease.Am J Respir Crit Care Med1996;153,967-975. [PubMed]
 
Weisman, I Cardiopulmonary exercise testing in the preoperative assessment for lung resection surgery.Semin Thorac Cardiovasc Surg2001;13,116-125. [PubMed] [CrossRef]
 
Bolliger, C, Perruchoud, A Functional evaluation of the lung resection candidate.Eur Respir J1998;11,198-212. [PubMed]
 
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    Print ISSN: 0012-3692
    Online ISSN: 1931-3543