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      SaO 2 as a predictor of exercise-induced hypoxemia in chronic obstructive pulmonary disease at moderate altitude

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          Abstract

          Background

          Given the high prevalence of chronic obstructive pulmonary disease (COPD) in Bogota (2630 m above the sea), screening methods are required for COPD patients who develop exercise-induced hypoxemia (EIH).

          Objective

          The objective was to measure the productive capacity of basal oxygen saturation for the detection of EIH during the 6-min walking test (6MWT) in patients diagnosed with COPD in a hospital in Bogotá.

          Design

          This was a cross-sectional, retrospective study.

          Population

          Patients diagnosed with COPD with SaO 2≥88% who attended the Pneumology Section of the FSFB for a 6MWT between 2013 and 2017 were included in the study.

          Measurements

          Age, sex, anthropometric data, SaO 2, SaO 2 during 6MWT, and spirometry were evaluated.

          Results

          Ninety-two patients with EIH and 32 patients without EIH were studied. Statistically significant differences were found in SaO 2, minimum SaO 2 during 6MWT, and BMI (90.8% vs 93%, 80.3% vs 88.9%, and 26.7 kg/m 2 vs 23.8 kg/m 2, respectively). FEV1 was without statistically significant differences (74.1% vs 78.6%). The ROC curve showed a better cut-off point for detecting EIH with basal SaO 2≤92% (sensitivity 76.1%, specificity 62.5%, NPV 47.6%, and PPV 85.4%) and SaO 2≤94% as the best sensitivity point (sensitivity 94.6%, specificity 15.6%, NPV 76.3%, and PPV 50%).

          Conclusion

          SaO 2 is not a good screening test for EIH in COPD patients at moderate altitude.

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          Most cited references 22

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          The 6-min walk distance in healthy subjects: reference standards from seven countries.

          The 6-min walk distance (6MWD) predicted values have been derived from small cohorts mostly from single countries. The aim of the present study was to investigate differences between countries and identify new reference values to improve 6MWD interpretation. We studied 444 subjects (238 males) from seven countries (10 centres) ranging 40-80 yrs of age. We measured 6MWD, height, weight, spirometry, heart rate (HR), maximum HR (HR(max)) during the 6-min walk test/the predicted maximum HR (HR(max) % pred), Borg dyspnoea score and oxygen saturation. The mean ± sd 6MWD was 571 ± 90 m (range 380-782 m). Males walked 30 m more than females (p < 0.001). A multiple regression model for the 6MWD included age, sex, height, weight and HR(max) % pred (adjusted r² = 0.38; p < 0.001), but there was variability across centres (adjusted r² = 0.09-0.73) and its routine use is not recommended. Age had a great impact in 6MWD independent of the centres, declining significantly in the older population (p < 0.001). Age-specific reference standards of 6MWD were constructed for male and female adults. In healthy subjects, there were geographic variations in 6MWD and caution must be taken when using existing predictive equations. The present study provides new 6MWD standard curves that could be useful in the care of adult patients with chronic diseases.
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            Distance and oxygen desaturation during the 6-min walk test as predictors of long-term mortality in patients with COPD.

            The distance walked in the 6-min walk test (6MWT) predicts mortality in patients with severe COPD. Little is known about its prognostic value in patients with a wider range of COPD severity, living in different countries, and the potential additional impact of oxygen desaturation measured during the test. We enrolled 576 stable COPD outpatients in Spain and the United States and observed them for at least 3 years (median, 60 months). We measured FEV1, body mass index, Pao2, Charlson comorbidity score, 6-min walk distance (6MWD), and oxygen saturation by pulse oximetry (Spo2) during the 6MWT. Desaturation was defined as a fall in Spo2 > or = 4% or Spo2 < 90%. Regression analysis helped determine the association between these variables and all-cause and respiratory mortality. The 6MWD was a good predictor of all-cause and respiratory mortality primarily in patients with FEV1 < 50% of predicted (p < 0.001) after adjusting for all covariates. Patients with desaturation during the 6MWT had a higher mortality rate than patients without desaturation (67% vs 38%, p < 0.001). Oxygen desaturation predicted mortality (relative risk, 2.63; 95% confidence interval, 1.53 to 4.51; p < 0.001) but with less power than Pao2 at rest. The 6MWD helps predict mortality primarily in patients with severe COPD. Although the oxygen desaturation profile during the 6MWT improves the predictive ability of the 6MWD, it appears to be of less relevance than in other lung diseases and than the resting Pao2.
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              Pathophysiology of dyspnea in chronic obstructive pulmonary disease: a roundtable.

              Effective management of dyspnea in chronic obstructive pulmonary disease (COPD) requires a clearer understanding of its underlying mechanisms. This roundtable reviews what is currently known about the neurophysiology of dyspnea with the aim of applying this knowledge to the clinical setting. Dyspnea is not a single sensation, having multiple qualitative descriptors. Primary sources of dyspnea include: (1) inputs from multiple somatic proprioceptive and bronchopulmonary afferents, and (2) centrally generated signals related to inspiratory motor command output or effort. Respiratory disruption that causes a mismatch between medullary respiratory motor discharge and peripheral mechanosensor afferent feedback gives rise to a distressing urge to breathe which is independent of muscular effort. Recent brain imaging studies have shown increased limbic system activation in response to various dyspneogenic stimuli and emphasize the affective dimension of this symptom. All of these mechanisms are likely instrumental in exertional dyspnea causation in COPD. Increased central motor drive (and effort) is required to increase ventilation during activity because the inspiratory muscles become acutely overloaded and functionally weakened. Abnormal dynamic ventilatory mechanics and excessive chemostimulation during exercise also result in a widening disparity between escalating central neural drive and restricted thoracic volume displacement. This neuromechanical uncoupling may form the basis for the distressing sensation of unsatisfied inspiration. Interventions that alleviate dyspnea in COPD do so by improving ventilatory mechanics, reducing central neural drive, or both-thereby partially restoring neuromechanical coupling of the respiratory system. Self-management strategies address the affective aspect of dyspnea and are essential to successful treatment.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                COPD
                copd
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove
                1176-9106
                1178-2005
                29 August 2019
                2019
                : 14
                : 1951-1958
                Affiliations
                [1 ]Pneumology Department, Santafé De Bogotá Foundation, Los Andes University , Bogotá, Colombia
                [2 ]Epidemiology, Research Group: Medicina Comunitaria, El Bosque University , Bogotá, Colombia
                Author notes
                Correspondence: Carlos Ernesto Lombo Moreno Epidemiology, Research group: Medicina Comunitaria, El Bosque University , Transversal 58 a No. 103b – 22, Bogotá, ColombiaTel +57 310 873 9897Email clombo1149@gmail.com
                Article
                207467
                10.2147/COPD.S207467
                6718247
                © 2019 Acero Colmenares and Lombo Moreno.

                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. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Figures: 2, Tables: 2, References: 25, Pages: 8
                Categories
                Original Research

                Respiratory medicine

                screening, oximetry, walk test, altitude, copd

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