Parenchymal emphysema measured by CT lung density correlates with lung function in patients with bullous disease

Abstract

In subjects with chronic obstructive pulmonary disease (COPD) computed tomographic (CT) lung density correlates with direct pathological measurements of the size of the distal airspaces, as well as with measurements of airflow limitation and impairment of the diffusing capacity. Thus, CT lung density can be used to quantify emphysema in life. We wanted to assess the use of CT scanning to detect and measure the extent of bullous lung, and to quantify the severity of emphysema in the non-bullous areas of the lungs. In patients with bullous emphysema (21 males and 2 females; aged 31-69 yrs; forced expiratory volume in one second (FEV1) 14-84% predicted; volume corrected diffusing capacity of the lungs for carbon monoxide (DLCO/VA) 17-114% predicted). CT lung density was measured in electromagnetic imaging (EMI) units. The extent of bullous emphysema correlated poorly with all respiratory function measurements. In contrast, the severity of emphysema in the non-bullous parts of the lungs, expressed as either the mean EMI number, or the EMI number of the lowest 5th percentile of the CT lung density histogram, correlated well with measurements of airflow limitation and diffusing capacity. Our findings, thus, suggest that in patients with bullae the major determinant of respiratory function is the severity of the emphysema in non-bullous lung, and that the extent of the bullae has less functional importance. We therefore suggest that CT scanning is useful in the assessment of patients with bullous disease, since it not only accurately defines the extent and site of the bullae, but also assesses the severity of emphysema in the non-bullous regions of the lungs, a factor which may influence respiratory function and the outcome of surgical intervention.