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      An in silico analysis of oxygen uptake of a mild COPD patient during rest and exercise using a portable oxygen concentrator

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          Oxygen treatment based on intermittent-flow devices with pulse delivery modes available from portable oxygen concentrators (POCs) depends on the characteristics of the delivered pulse such as volume, pulse width (the time of the pulse to be delivered), and pulse delay (the time for the pulse to be initiated from the start of inhalation) as well as a patient’s breathing characteristics, disease state, and respiratory morphology. This article presents a physiological-based analysis of the performance, in terms of blood oxygenation, of a commercial POC at different settings using an in silico model of a COPD patient at rest and during exercise. The analysis encompasses experimental measurements of pulse volume, width, and time delay of the POC at three different settings and two breathing rates related to rest and exercise. These experimental data of device performance are inputs to a physiological-based model of oxygen uptake that takes into account the real dynamic nature of gas exchange to illustrate how device- and patient-specific factors can affect patient oxygenation. This type of physiological analysis that considers the true effectiveness of oxygen transfer to the blood, as opposed to delivery to the nose (or mouth), can be instructive in applying therapies and designing new devices.

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          Most cited references 22

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          Daily Step Count Predicts Acute Exacerbations in a US Cohort with COPD

          Background COPD is characterized by variability in exercise capacity and physical activity (PA), and acute exacerbations (AEs). Little is known about the relationship between daily step count, a direct measure of PA, and the risk of AEs, including hospitalizations. Methods In an observational cohort study of 169 persons with COPD, we directly assessed PA with the StepWatch Activity Monitor, an ankle-worn accelerometer that measures daily step count. We also assessed exercise capacity with the 6-minute walk test (6MWT) and patient-reported PA with the St. George's Respiratory Questionnaire Activity Score (SGRQ-AS). AEs and COPD-related hospitalizations were assessed and validated prospectively over a median of 16 months. Results Mean daily step count was 5804±3141 steps. Over 209 person-years of observation, there were 263 AEs (incidence rate 1.3±1.6 per person-year) and 116 COPD-related hospitalizations (incidence rate 0.56±1.09 per person-year). Adjusting for FEV1 % predicted and prednisone use for AE in previous year, for each 1000 fewer steps per day walked at baseline, there was an increased rate of AEs (rate ratio 1.07; 95%CI = 1.003–1.15) and COPD-related hospitalizations (rate ratio 1.24; 95%CI = 1.08–1.42). There was a significant linear trend of decreasing daily step count by quartiles and increasing rate ratios for AEs (P = 0.008) and COPD-related hospitalizations (P = 0.003). Each 30-meter decrease in 6MWT distance was associated with an increased rate ratio of 1.07 (95%CI = 1.01–1.14) for AEs and 1.18 (95%CI = 1.07–1.30) for COPD-related hospitalizations. Worsening of SGRQ-AS by 4 points was associated with an increased rate ratio of 1.05 (95%CI = 1.01–1.09) for AEs and 1.10 (95%CI = 1.02–1.17) for COPD-related hospitalizations. Conclusions Lower daily step count, lower 6MWT distance, and worse SGRQ-AS predict future AEs and COPD–related hospitalizations, independent of pulmonary function and previous AE history. These results support the importance of assessing PA in patients with COPD, and provide the rationale to promote PA as part of exacerbation-prevention strategies.
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            Asthma-COPD Overlap.

             Peter Barnes (2016)
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              Ventilation-perfusion inequality in chronic obstructive pulmonary disease.

              A multiple inert gas elimination method was used to study the mechanism of impaired gas exchange in 23 patients with advanced chronic obstructive pulmonary disease (COPD). Three patterns of ventilation-perfusion (Va/Q) inequality were found: (a) A pattern with considerable regions of high (greater than 3) VA/Q, none of low (less than 0.1) VA/Q, and essentially no shunt. Almost all patients with type A COPD showed this pattern, and it was also seen in some patients with type B. (b) A pattern with large amounts of low but almost none of high VA/Q, and essentially no shunt. This pattern was found in 4 of 12 type B patients and 1 of type A. (c) A pattern with both low and high VA/Q areas was found in the remaining 6 patients. Distributions with high VA/Q areas occurred mostly in patients with greatly increased compliance and may represent loss of blood-glow due to alveolar wall destruction. Similarly, well-defined modes of low VA/Q areas were seen mostly in patients with severe cough and sputum and may be due to reduced ventilation secondary to mechanical airways obstruction or distortion. There was little change in the VA/Q distributions on exercise or on breathing 100% O2. The observed patterns of VA/Q inequality and shunt accounted for all of the hypoxemia at rest and during exercise. There was therefore no evidence for hypoxemia caused by diffusion impairment. Patients with similar arterial blood gases often had dissimilar VA/Q patterns. As a consequence the pattern of VA/Q inequality could not necessarily be inferred from the arterial PO2 and PCO2.

                Author and article information

                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
                29 September 2016
                : 11
                : 2427-2434
                [1 ]Medical R&D, Air Liquide Santé International, Centre de Recherche Paris-Saclay, Les Loges-en-Josas, France
                [2 ]Department of Mechanical Engineering, Lafayette College, Easton, PA, USA
                [3 ]Physique de la Matière Condensée, CNRS, Ecole Polytechnique, Palaiseau
                [4 ]Centre de Mathématiques et de leurs Applications, CNRS, UniverSud, Cachan
                [5 ]Centre Explor!, Air Liquide Healthcare, Gentilly, France
                [6 ]Valley Inspired Products, Inc, Apple Valley, MN, USA
                [7 ]Department of Mechanical Engineering, University of Alberta, Edmonton, AB, Canada
                Author notes
                Correspondence: Ira Katz, Medical R&D, Air Liquide Santé International, Centre de Recherche Paris-Saclay, 1 Chemin de la Porte des Loges, BP126, 78354 Jouy en Josas, France, Tel +33 1 39 07 65 11, Fax +33 1 39 37 61 99, Email ira.katz@
                © 2016 Katz et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( 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.

                Original Research

                Respiratory medicine

                pulsed delivery, efficiency, respiratory physiology, respiratory disease


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