Dynamic Hyperinflation in COPD Patients: Is It Related to Emphysema and Airway Morphology in Inspiration and Expiration Thoracic CT?

PURPOSE Dynamic hyperinflation (DH), progressive airtrapping during exercise, is related to dyspnea in COPD patients. A subgroup of COPD patients divided over all GOLD stages suffer from dynamic hyperinflation. This study relates automatically extracted measures of airway morphology, airtrapping and emphysema to dynamic hyperinflation. METHOD AND MATERIALS As part of a research study, eighteen COPD patients underwent low dose CT (64x0.75mm, Siemens Sensation 64) at full inspiration and expiration. Using a portable ergo-spirometry system (Oxycon Mobile) to measure operational lung volume during activities of daily life, the study population was divided into ten patients suffering from DH and eight non-DH. Research software (Diagnostic Image Analysis Group, Nijmegen, The Netherlands; Fraunhofer MEVIS, Bremen, Germany) automatically segmented the lungs and airways in both the inspiration and expiration scans. As measures for emphysema, the percentages of lung volume below -950 HU (IN-950) and the 15th percentile of the cumulative histogram (PD15) were computed in inspiration scans. As a quantification of air-trapping, the percentages of lung volume below -856 HU were computed in expiration scans (EX-856). Airway morphology was extracted from the inspiration scans as the wall area percentage at airways with a circumference of 10mm (Pi10), computed using regression on all cross-sectional airway measurements. Means and standard deviations for each measurement are reported for the two groups. RESULTS The means and standard deviations of the measurements for the DH and non-DH groups were 19.7 A-A?A 1/2 8.6% and 14.6 A-A?A 1/2 10.5% for IN-950, -956 A-A?A 1/2 15 HU and -945 A-A?A 1/2 23 HU for PD15, 47.2 A-A?A 1/2 13.7% and 35.1 A-A?A 1/2 10.9% for EX-856, and 48.0 A-A?A 1/2 6.9% and 40.7 A-A?A 1/2 9.3% for Pi10, respectively. The differences between the DH and non-DH group are thus more pronounced for EX-856 and Pi10 than for IN-950 and PD15. CONCLUSION Quantitative measurements from inspiration and expiration CT scans related to airway morphology appear to be more informative for distinguishing COPD patients suffering from dynamic hyperinflation from non-hyperinflators than emphysema related measurements. CLINICAL RELEVANCE/APPLICATION Understanding the underlying pathways of hyperinflation is important for the management of COPD since reduction of dynamic hyperinflation is strongly correlated with less dyspnea complaints.