Relationship between Extent of Pulmonary Emphysema by High-resolution Computed Tomography and Lung Elastic Recoil in Patients with Chronic Obstructive Pulmonary Disease

Abstract

We investigated the relationship between the extent of pulmonary emphysema, assessed by quantitative high-resolution computed tomography (HRCT), and lung mechanics in 24 patients with chronic obstructive pulmonary disease (COPD). The extent of emphysema was quantified as the relative lung area with CT numbers < -950 Hounsfield Units (HU). Patients with COPD had severe airflow obstruction (FEV(1) 35 +/- 15% pred) and severe reduction of CO diffusion constant (DCO/VA 37 +/- 19% pred). Maximal static elastic recoil pressure (Pst(max)) averaged 54 +/- 24% predicted, and the exponential constant K of pressure-volume curves was 258 +/- 116% predicted. Relative lung area with CT numbers < -950 HU averaged 21 +/- 11% (range 1 to 38%). It showed a highly significant negative correlation with DCO/VA (r = -0.84, p < 0.0001), a weak correlation with FEV(1)% predicted, and no correlation with either Pst(max) or constant K. A significant relationship was found between the natural logarithm of K and the full width at half maximum of the frequency distribution of CT numbers, taken as an index of the heterogeneity of lung density (r = 0.68, p < 0.0005). We conclude that currently used methods of assessing the extent of emphysema by HRCT closely reflect the reduction of CO diffusion constant, but cannot predict the elastic properties of the lung tissue.

Tumour necrosis factor family genes in a phenotype of COPD associated with emphysema

“…In an attempt to narrow the phenotype choice to COPD-associated pulmonary emphysema, a severe reduction of DL,CO was used as an inclusion criterion. FEV1 % pred is weakly related to the extent of emphysema [24,33,34], suggesting that flow obstruction in severe COPD is not totally accounted for by the extent of emphysema. Reduction of DL,CO is more strongly correlated with the severity of emphysema, as assessed by high-resolution computed tomography analysis [24], reflecting the reduction of the alveolar-capillary surface, although with some limitations [24,35].…”

“…The first group of subjects consisted of 63 consecutive male patients with history of COPD, diagnosed according to the American Thoracic Society (ATS) guidelines [22] and characterised by significant impairment in diffusing capacity for carbon monoxide (DL,CO), a functional abnormality known to be associated with pulmonary emphysema [23,24]. These patients were recruited in two clinical centres, 33 in Pavia and 30 in Gussago, both located in Northern Italy, based on a common protocol requiring forced expiratory volume in one second (FEV1) v50% pred, v12% reversible, FEV1/forced vital capacity (FVC)v70% pred, and DL,COv50% pred.…”

“…The mean¡SD FEV1 reversibility in these subjects was 4¡4. The low level of DL,CO in the COPD group (37¡12% pred) allowed them to be defined as affected by moderate-to-severe COPD (Stage II-III) associated with pulmonary emphysema [23,24].…”

Imaging phenotypes of chronic obstructive pulmonary disease

“…The relationship between extent of emphysema on quantitative CT and the presence of pathologic emphysema is well established. Quantitative CT of emphysematous destruction consists of mean lung density, emphysema index, low end percentiles, and other measures (32)(33)(34)(35)(36). Different thresholds have been investigated in the literature for thick and thin slices, ranging from À770 HU to À980 HU, revealing good correlation to pulmonary function test and pathology (22,(32)(33)(34)(36)(37)(38)(39).…”

Airflow Limitation and Airway Dimensions in Chronic Obstructive Pulmonary Disease

“…Thin-section computed tomography (CT) has been used to quantify emphysema by detecting low attenuation areas (LAA), and the role of CT in diagnosing emphysema, including subclinical emphysema (2,3), has been well established (4)(5)(6)(7)(8)(9). However, airflow limitation evaluated by forced expiratory volume in 1 s (FEV 1 ) does not necessarily have a good correlation with the severity of emphysema as evaluated by CT (10), because small airway disease appears to contribute more significantly to the airflow limitation in COPD (1,(11)(12)(13)(14).…”