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      The Efficiency Index (EFFi), based on volumetric capnography, may allow for simple diagnosis and grading of COPD

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          Abstract

          Background

          Spirometry, the main tool for diagnosis and follow-up of COPD, incompletely describes the disease. Based on volumetric capnography (VCap), an index was developed for the diagnosis and grading of COPD, aimed as a complement or alternative to spirometry.

          Methods

          Nine non-smokers, 10 smokers/former smokers without COPD and 54 smokers/former smokers with COPD were included in the study. Multiple breath washout of N 2 and VCap were studied with Exhalyzer D during tidal breathing. VCap was based on signals for flow rate and CO 2 and was recorded during one breath preceding N 2 washout. Efficiency Index (EFFi) is the quotient between exhaled CO 2 volume and the hypothetical CO 2 volume exhaled from a completely homogeneous lung over a volume interval equal to 15% of predicted total lung capacity.

          Results

          EFFi increased with increased Global initiative for chronic Obstructive Lung Disease (GOLD) stage and the majority of subjects in GOLD 2 and all subjects in GOLD 3 and 4 could be diagnosed as having COPD using the lower 95% confidence interval of the healthy group. EFFi also correlated with N 2 washout (r=−0.73; p<0.001), forced expiratory volume in 1 second (r=0.70; p<0.001) and diffusion capacity for carbon oxide (r=0.69; p<0.001).

          Conclusion

          EFFi measures efficiency of tidal CO 2 elimination that is limited by inhomogeneity of peripheral lung function. EFFi allows diagnosis and grading of COPD and, together with FEV 1, may explain limitation of physical performance. EFFi offers a simple, effortless and cost-effective complement to spirometry and might serve as an alternative in certain situations.

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          Most cited references 22

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          Clinical Significance of Symptoms in Smokers with Preserved Pulmonary Function.

          Currently, the diagnosis of chronic obstructive pulmonary disease (COPD) requires a ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) of less than 0.70 as assessed by spirometry after bronchodilator use. However, many smokers who do not meet this definition have respiratory symptoms.
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            Reference spirometric values using techniques and equipment that meet ATS recommendations.

            Forced expiratory volumes and flows were measured in 251 healthy nonsmoking men and women using techniques and equipment that meet American Thoracic Society (ATS) recommendations. Linear regression equations using height and age alone predict spirometric parameters as well as more complex equations using additional variables. Single values for 95% confidence intervals are acceptable and should replace the commonly used method of subtracting 20% to determine the lower limit of normal for a predicted value. Our study produced predicted values for forced vital capacity and forced expiratory volume in one second that were almost identical to those predicted by Morris and associates (1) when the data from their study were modified to be compatible with the back extrapolation technique recommended by the ATS. The study of Morris and colleagues was performed at sea level in rural subjects, whereas ours was performed at an altitude of 1,400 m in urban subjects. Either the present study or the study of Morris and co-workers, modified to back extrapolation, could be recommended for predicting normal values.
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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.
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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
                27 June 2018
                : 13
                : 2033-2039
                Affiliations
                [1 ]Respiratory Medicine and Allergology, Department of Clinical Sciences, Skåne University Hospital, Lund University, Lund, Sweden, linnea.jarenback@ 123456med.lu.se
                [2 ]Clinical Physiology, Department of Clinical Sciences, Skåne University Hospital, Lund University, Lund, Sweden
                Author notes
                Correspondence: Linnea Jarenbäck, Respiratory Medicine and Allergology, Department of Clinical Sciences, Skåne University Hospital, Lund University, BMC, D12, 221 84 Lund, Sweden, Tel +46 46 175 277, Email linnea.jarenback@ 123456med.lu.se
                Article
                copd-13-2033
                10.2147/COPD.S161345
                6029593
                © 2018 Jarenbäck 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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