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Chronic obstructive pulmonary disease (COPD) can be seen as a complex desease which is
far from being fully understood despite its high socio-economic relevance. One important
aspect in the course of the disease are acute exacerbations, which contribute substantially to morbidity and mortality of COPD, but exacerbations are just like COPD itself heterogenous in terms of cause, occurence, frequency and influence on the individual course of the
Apart from well established function tests, computed tomography CT can deliver information on the dominant characteristic of an individual with COPD and additionally provides valuable knowledge about distribution pattern and heterogeneity of changes.
The main goal of this work was to find possible parameters in CT data that serve as an independent predictor for exacerbation frequency in COPD. Besides that, measurement parameters in CT should be tested for possible correlation with measurements of well established pulmonary function tests.
Between 2010 and 2011, 43 patients diagnosed with COPD were included retrospectively, who had had a multislice CT exam as well as at least one functional test (body plethymography, 6 minute walk test, blood gas analysis) within the same stay in hospital.
For every patient, documented exacerbations between 2006 and 2014 were recorded. From CT data sets, global and lobe-based density values of the lung were acquired using the prototype software Mevis Pulmo 3D (including among others: low attenuation volume LAV2, mean lung density MLD and the peak value of the lung density histogram Pk). From lobe based measurements the difference betweeen maximum and minimum
values were taken as measure of emphysema heterogeneity.
As surrogate of bronchi obstruction, the bronchial wall thickness in CT was measured semiautomatically using the software AirwayInspector. From those measurements the pi10-value, the wall thickness of an ideal bronchus with an internal perimeter of 10mm, was computed for every patient.
As most important measurement parameters in body plethysmography, the absolute and normalized 1 second forced exspirational volume LF_FEV1 respectively LF_FEV1%Soll and airway resistance LF_Rspez resp. LF_Respez%Soll were chosen. Main parameter in 6 minute walk test was the distance covered 6MWT_Strecke.
In respect to the main goal of this work, using stepwise regression exacerbation frequency ExFreq was found to correlate to the global low attenuation volume LAV2 (p=0,014) as well as the emphysema heterogeneity based on measuring the peak of the density histogram het_Pk (p=0,002).
To my knowledge, so far only few studies have tested a correlation between exacerbation frequency and emphysema index, not all of them confirming the findings of this work. Comparable studies which examined an influence of emphysema heterogeneity on exacerbation frequency could not be found in literature search at all. Therefore these results deserve to be confirmed in further tests. A significant inverse correlation was found between emphysema index LAV2 in CT and forced expiratory volume in 1 second LF_FEV1, a finding confirmed in multiple other studies. Some markers of Emphysema heterogeneity showed an inverse correlation with forced expiratory volume in 1 second LF_FEV1 and a positive correlation with airway resistance LF_Rspez, but other markers failed showing the same, therefore such correlation could not be show for sure in this work. Clearly shown was an inverse correlation between emphysema heterogeneity and the 6 minute walk distance 6MWT_Strecke. Studies examining emphysema heterogeneity and its effects were rare findings compared to studies concerning global emphysema, most of them dealing with a very limited number of patients too, but in general they could confirm the findings of this work. A significant correlation of bronchi wall thickness in CT and results of conventional pulmonary function tests could not be found, which is contrary to the results of several other studies. But compared to measuring emphysema, measurments of bronchi wall thickness seem to be a
lot more difficult, error-prone and less reliable at least concerning the software used in this study. The prototype software used for emphysema quantification in this study proved to deliver reliable, plausible and reproducable results. Based on such results, a better understandig of changes in COPD and their contribution to the course of the disease is to be expected.