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      Usefulness of the 6-minute walk test as a screening test for pulmonary arterial enlargement in COPD

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          Abstract

          Purpose

          Pulmonary hypertension and exercise-induced oxygen desaturation (EID) influence acute exacerbation of COPD. Computed tomography (CT)-detected pulmonary artery (PA) enlargement is independently associated with acute COPD exacerbations. Associations between PA to aorta (PA:A) ratio and EID in patients with COPD have not been reported. We hypothesized that the PA:A ratio correlated with EID and that results of the 6-minute walk test (6MWT) would be useful for predicting the risk associated with PA:A >1.

          Patients and methods

          We retrospectively measured lung function, 6MWT, emphysema area, and PA enlargement on CT in 64 patients with COPD. The patients were classified into groups with PA:A ≤1 and >1. Receiver-operating characteristic curves were used to determine the threshold values with the best cutoff points to predict patients with PA:A >1.

          Results

          The PA:A >1 group had lower forced expiratory volume in 1 second (FEV 1), forced vital capacity (FVC), FEV 1:FVC ratio, diffusion capacity of lung carbon monoxide, 6MW distance, and baseline peripheral oxygen saturation (SpO 2), lowest SpO 2, highest modified Borg scale results, percentage low-attenuation area, and history of acute COPD exacerbations ≤1 year, and worse BODE (Body mass index, airflow Obstruction, Dyspnea, and Exercise) index results ( P<0.05). Predicted PA:A >1 was determined for SpO 2 during 6MWT (best cutoff point 89%, area under the curve 0.94, 95% confidence interval 0.88–1). SpO 2 <90% during 6MWT showed a sensitivity of 93.1, specificity of 94.3, positive predictive value of 93.1, negative predictive value of 94.3, positive likelihood ratio of 16.2, and negative likelihood ratio of 0.07.

          Conclusion

          Lowest SpO 2 during 6MWT may predict CT-measured PA:A, and lowest SpO 2 <89% during 6MWT is excellent for detecting pulmonary hypertension in COPD.

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          Most cited references 22

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          Pulmonary hypertension in COPD.

          Mild-to-moderate pulmonary hypertension is a common complication of chronic obstructive pulmonary disease (COPD); such a complication is associated with increased risks of exacerbation and decreased survival. Pulmonary hypertension usually worsens during exercise, sleep and exacerbation. Pulmonary vascular remodelling in COPD is the main cause of increase in pulmonary artery pressure and is thought to result from the combined effects of hypoxia, inflammation and loss of capillaries in severe emphysema. A small proportion of COPD patients may present with "out-of-proportion" pulmonary hypertension, defined by a mean pulmonary artery pressure >35-40 mmHg (normal is no more than 20 mmHg) and a relatively preserved lung function (with low to normal arterial carbon dioxide tension) that cannot explain prominent dyspnoea and fatigue. The prevalence of out-of-proportion pulmonary hypertension in COPD is estimated to be very close to the prevalence of idiopathic pulmonary arterial hypertension. Cor pulmonale, defined as right ventricular hypertrophy and dilatation secondary to pulmonary hypertension caused by respiratory disorders, is common. More studies are needed to define the contribution of cor pulmonale to decreased exercise capacity in COPD. These studies should include improved imaging techniques and biomarkers, such as the B-type natriuretic peptide and exercise testing protocols with gas exchange measurements. The effects of drugs used in pulmonary arterial hypertension should be tested in chronic obstructive pulmonary disease patients with severe pulmonary hypertension. In the meantime, the treatment of cor pulmonale in chronic obstructive pulmonary disease continues to rest on supplemental oxygen and a variety of measures aimed at the relief of airway obstruction.
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            Clinical and Radiologic Disease in Smokers With Normal Spirometry.

            Airflow obstruction on spirometry is universally used to define chronic obstructive pulmonary disease (COPD), and current or former smokers without airflow obstruction may assume that they are disease free.
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              Severe pulmonary hypertension and chronic obstructive pulmonary disease.

              Severe pulmonary hypertension occurs occasionally in patients with chronic obstructive pulmonary disease (COPD), but no detailed description of these patients is available. To identify and characterize patients with COPD and severe pulmonary hypertension. Retrospective study of 27 patients with COPD with severe pulmonary hypertension (pulmonary artery mean pressure [Ppa], > or = 40 mm Hg) among 998 patients who underwent right heart catheterization between 1990 and 2002 as part of a workup for chronic respiratory failure during a period of disease stability. Of the 27 patients, 16 had another disease capable of causing pulmonary hypertension. The remaining 11 (11 of 998, 1.1%) patients had COPD as the only cause of pulmonary hypertension, with a median Ppa of 48 mm Hg (interquartile range, 46-50). They had an unusual pattern of cardiopulmonary abnormalities with mild to moderate airway obstruction, severe hypoxemia, hypocapnia, and a very low diffusing capacity for carbon monoxide (p < 0.01 compared with a control group of patients with COPD). Exertional dyspnea was more severe (p < 0.01) and survival was shorter (p = 0.0026) than in the control subjects. Severe pulmonary hypertension is uncommon in patients with COPD. When it occurs, another cause must be sought. COPD with severe pulmonary hypertension and no other possible cause shares features with pulmonary vascular diseases, such as idiopathic pulmonary hypertension.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                1176-9106
                1178-2005
                2016
                22 November 2016
                : 11
                : 2869-2875
                Affiliations
                [1 ]Department of Community Health Sciences, Kobe University Graduate School of Health Sciences
                [2 ]Department of Rehabilitation
                [3 ]Department of Respiratory Medicine, Kobe City Medical Center West Hospital, Kobe
                [4 ]Department of Rehabilitation, Sapporo Nishimaruyama Hospital, Sapporo, Japan
                Author notes
                Correspondence: Yutaro Oki, Department of Community Health Sciences, Kobe University Graduate School of Health Sciences, 7-10-2 Tomogaoka, Suma-ku, Kobe, Hyogo 654-0142, Japan, Tel +81 90 2513 1497, Fax +81 78 796 4526, Email yutaro.oki@ 123456gmail.com
                Article
                copd-11-2869
                10.2147/COPD.S114497
                5126000
                © 2016 Oki et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

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