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      Functional respiratory imaging: heterogeneity of acute exacerbations of COPD

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          Abstract

          Background

          Exacerbations of COPD are a major burden to patients, and yet little is understood about heterogeneity. It contributes to the current persistent one-size-fits-all treatment. To replace this treatment by more personalized, precision medicine, new insights are required. We assessed the heterogeneity of exacerbations by functional respiratory imaging (FRI) in 3-dimensional models of airways and lungs.

          Methods

          The trial was designed as a multicenter trial of patients with an acute exacerbation of COPD who were assessed by FRI, pulmonary function tests, and patient-reported outcomes, both in the acute stage and during resolution.

          Results

          Forty seven patients were assessed. FRI analyses showed significant improvements in hyperinflation (a decrease in total volume at functional residual capacity of −0.25±0.61 L, p≤0.01), airway volume at total lung capacity (+1.70±4.65 L, p=0.02), and airway resistance. As expected, these improvements correlated partially with changes in the quality of life and in conventional lung function test parameters. Patients with the same changes in pulmonary function differ in regional disease activity measured by FRI.

          Conclusion

          FRI is a useful tool to get a better insight into exacerbations of COPD, and significant improvements in its indices can be demonstrated from the acute phase to resolution even in relatively small groups. It clearly visualizes the marked variability within and between individuals in ventilation and resistance during exacerbations and is a tool for the assessment of the heterogeneity of COPD exacerbations.

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          Most cited references 21

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          The connection between chronic obstructive pulmonary disease symptoms and hyperinflation and its impact on exercise and function.

           B. D. Cooper (2006)
          Forced expiratory volume in 1 second (FEV1) has served as an important diagnostic measurement of chronic obstructive pulmonary disease (COPD) but has not been found to correlate with patient-centered outcomes such as exercise tolerance, dyspnea, or health-related quality of life. It has not helped us understand why some patients with severe FEV1 impairment have better exercise tolerance compared with others with similar FEV1 values. Hyperinflation, or air trapping caused by expiratory flow limitation, causes operational lung volumes to increase and even approach the total lung capacity (TLC) during exercise. Some study findings suggest that a dyspnea limit is reached when the end-inspiratory lung volume encroaches within approximately 500 mL of TLC. The resulting limitation in daily physical activity establishes a cycle of decline that includes physical deconditioning (elevated blood lactic acid levels at lower levels of exercise) and worsening dyspnea. Hyperinflation is reduced by long-acting bronchodilators that reduce airways resistance. The deflation of the lungs, in turn, results in an increased inspiratory capacity. For example, the once-daily anticholinergic bronchodilator tiotropium increases inspiratory capacity, 6-minute walk distance, and cycle exercise endurance time, and it decreases isotime fatigue or dyspnea. Pulmonary rehabilitation and oxygen therapy both reduce ventilatory requirements and improve breathing efficiency, thereby reducing hyperinflation and improving exertional dyspnea. Thus, hyperinflation is directly associated with patient-centered outcomes such as dyspnea and exercise limitation. Furthermore, therapeutic interventions--including pharmacotherapy and lung volume--reduction surgery--that reduce hyperinflation improve these outcomes.
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            Validation of computational fluid dynamics in CT-based airway models with SPECT/CT.

            To compare the results obtained by using numerical flow simulations with the results of combined single photon emission computed tomography (SPECT) and computed tomography (CT) and to demonstrate the importance of correct boundary conditions for the numerical methods to account for the large amount of interpatient variability in airway geometry. This study was approved by all relevant institutional review boards. All patients gave their signed informed consent. In this study, six patients with mild asthma (three men; three women; overall mean age, 46 years ± 17 [standard deviation]) underwent CT at functional residual capacity and total lung capacity, as well as SPECT/CT. CT data were used for segmentation and computational fluid dynamics (CFD) simulations. A comparison was made between airflow distribution, as derived with (a) SPECT/CT through tracer concentration analysis, (b) CT through lobar expansion measurement, and (c) CFD through flow computer simulation. Also, the heterogeneity of the ventilation was examined. Good agreement was found between SPECT/CT, CT, and CFD in terms of airflow distribution and hot spot detection. The average difference for the internal airflow distribution was less than 3% for CFD and CT versus SPECT/CT. Heterogeneity in ventilation patterns could be detected with SPECT/CT and CFD. This results of this study show that patient-specific computer simulations with appropriate boundary conditions yield information that is similar to that obtained with functional imaging tools, such as SPECT/CT. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100322/-/DC1. © RSNA, 2010
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              The clinical importance of dynamic lung hyperinflation in COPD.

              Lung hyperinflation commonly accompanies expiratory flow-limitation in patients with Chronic Obstructive Pulmonary Disease (COPD) and contributes importantly to dyspnea and activity limitation. It is not surprising, therefore, that lung hyperinflation has become an important therapeutic target in symptomatic COPD patients. There is increasing evidence that acute dynamic increases in lung hyperinflation, under conditions of worsening expiratory flow-limitation and increased ventilatory demand (or both) can seriously stress cardiopulmonary reserves, particularly in patients with more advanced disease. Our understanding of the physiological mechanisms of dynamic lung hyperinflation during both physical activity and exacerbations in COPD continues to grow, together with an appreciation of its serious negative mechanical and sensory consequences. In this review, we will discuss the basic pathophysiology of COPD during rest, exercise and exacerbation so as to better understand how this can be pharmacologically manipulated for the patient's benefit. Finally, we will review current concepts of the mechanisms of symptom relief and improved exercise endurance following pharmacological lung volume reduction.
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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
                2018
                30 May 2018
                : 13
                : 1783-1792
                Affiliations
                [1 ]Department of Respiratory Medicine, Medical Centre Leeuwarden, Leeuwarden, the Netherlands
                [2 ]Department of Pulmonary Diseases, University Medical Center Groningen, Groningen Research Institute for Asthma and COPD, University of Groningen, the Netherlands
                [3 ]Department of Pulmonary Diseases, Antwerp University Hospital, Antwerp, Belgium
                [4 ]FLUIDDA nv, Kontich, Belgium
                [5 ]GlaxoSmithKline R&D, Stevenage, UK
                [6 ]Faculty of Medicine, National Heart & Lung Institute, Imperial College London, London, UK
                [7 ]Department of Experimental and Clinical Medicine, Section of Respiratory Medicine, University of Florence, Florence, Italy
                Author notes
                Correspondence: Wouter H van Geffen, Department of Respiratory Medicine, Medical Centre Leeuwarden, Henri Dunantweg 2, 8934 AD Leeuwarden, the Netherlands, Tel +31 58 286 6666, Email wouter.van.geffen@ 123456znb.nl
                Article
                copd-13-1783
                10.2147/COPD.S152463
                5985851
                © 2018 van Geffen 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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                Original Research

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