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      Outcome measures of the 6 minute walk test: relationships with physiologic and computed tomography findings in patients with sarcoidosis

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          Abstract

          Background

          We assessed the relationship between physiologic parameters, computed tomography patterns, 6 minute walk distance (6MWD) and the distance-saturation product [DSP; defined as the product of the 6MWD and the lowest oxygen saturation during the 6 minute walk test (6MWT)]. In addition, we investigated factors affecting 6MWD in patients with pulmonary sarcoidosis.

          Methods

          We performed a retrospective study of patient demographics, treatment, pulmonary function, 6MWT, echocardiography and computed tomography results.

          Results

          Fifty nine patients were included in this study. Their mean+standard deviation age was 47.5 years + 12.5 years, and 42 (71.2%) were female. Mean pulmonary function parameters for forced vital capacity (FVC), forced expiratory volume in 1 second (FEV 1) and total lung capacity (TLC) results, as percentages of predicted values, were 77.6 ± 22.2, 77.1 ± 22.8 and 78.7 ± 16.1, respectively. Comparison of the DSP with distance walked revealed a significant correlation with factors underlying reduced 6MWD, including gender, pulmonary function indices, partial pressure of oxygen (PaO 2), and Borg dyspnea score. Other factors were significantly associated with DSP but not distance; these included lung fibrosis (p = 0.02), pulmonary hypertension (p = 0.01) and systemic therapy (p = 0.04). Backward elimination stepwise multiple regression analysis revealed that gender, and FEV 1 were independent predictors of 6MWD, but FEV 1 was more strongly related when DSP applied [DSP, R 2 = 0.53, p = 0.02; distance, R 2 = 0.45, p < 0.0001].

          Conclusion

          Our findings reveal that, compared to 6MWD alone, the DSP is correlated with a greater number of factors associated with reduced 6MWT performance. Therefore, the DSP may be a useful indicator of functional status in patients with sarcoidosis. Additional large-scale studies are warranted to validate our findings.

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          Most cited references29

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          Statement on sarcoidosis. Joint Statement of the American Thoracic Society (ATS), the European Respiratory Society (ERS) and the World Association of Sarcoidosis and Other Granulomatous Disorders (WASOG) adopted by the ATS Board of Directors and by the ERS Executive Committee, February 1999.

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            Clinical correlates and prognostic significance of six-minute walk test in patients with primary pulmonary hypertension. Comparison with cardiopulmonary exercise testing.

            The six-minute walk test is a submaximal exercise test that can be performed even by a patient with heart failure not tolerating maximal exercise testing. To elucidate the clinical significance and prognostic value of the six-minute walk test in patients with primary pulmonary hypertension (PPH), we sought (1) to assess the relation between distance walked during the six-minute walk test and exercise capacity determined by maximal cardiopulmonary exercise testing, and (2) to investigate the prognostic value of the six-minute walk test in comparison with other noninvasive parameters. The six-minute walk test was performed in 43 patients with PPH, together with echocardiography, right heart catheterization, and measurement of plasma epinephrine and norepinephrine. Symptom-limited cardiopulmonary exercise testing was performed in a subsample of patients (n = 27). Distance walked in 6 min was significantly shorter in patients with PPH than in age- and sex-matched healthy subjects (297 +/- 188 versus 655 +/- 91 m, p < 0. 001). The distance significantly decreased in proportion to the severity of New York Heart Association functional class. The distance walked correlated modestly with baseline cardiac output (r = 0.48, p < 0.05) and total pulmonary resistance (r = -0.49, p < 0. 05), but not significantly with mean pulmonary arterial pressure. In contrast, the distance walked correlated strongly with peak V O(2) (r = 0.70, p < 0.001), oxygen pulse (r = 0.57, p < 0.01), and V E-VCO(2) slope (r = -0.66, p < 0.001) determined by cardiopulmonary exercise testing. During a mean follow-up period of 21 +/- 16 mo, 12 patients died of cardiopulmonary causes. Among noninvasive parameters including clinical, echocardiographic, and neurohumoral parameters, only the distance walked in 6 min was independently related to mortality in PPH by multivariate analysis. Patients walking < 332 m had a significantly lower survival rate than those walking farther, assessed by Kaplan-Meier survival curves (log-rank test, p < 0.01). These results suggest that the six-minute walk test, a submaximal exercise test, reflects exercise capacity determined by maximal cardiopulmonary exercise testing in patients with PPH, and it is the distance walked in 6 min that has a strong, independent association with mortality.
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              Glossary of terms for CT of the lungs: recommendations of the Nomenclature Committee of the Fleischner Society.

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                Author and article information

                Journal
                BMC Pulm Med
                BMC Pulmonary Medicine
                BioMed Central
                1471-2466
                2010
                9 August 2010
                : 10
                : 42
                Affiliations
                [1 ]Pulmonary Davison, Department of Medicine, King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia
                [2 ]Department of Family & Community Medicine, King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia
                [3 ]Pulmonary Medicine, Department of Medicine, Riyadh Military Hospital, Riyadh, Saudi Arabia
                [4 ]Pulmonary Medicine, King Abdulaziz Medical City, Riyadh, Saudi Arabia
                [5 ]College of Medicine and Research Center, King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia
                Article
                1471-2466-10-42
                10.1186/1471-2466-10-42
                2924267
                20696064
                3f3a6d24-f489-4db1-9d96-daa2d0f24de4
                Copyright ©2010 Alhamad et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 28 July 2009
                : 9 August 2010
                Categories
                Research Article

                Respiratory medicine
                Respiratory medicine

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