Computed tomography based estimates of regional gas and tissue volume of the lung in supine subjects with chronic airflow limitation or fibrosing alveolitis.

Abstract

Twelve patients with chronic airflow limitation and 12 patients with a histological diagnosis of fibrosing alveolitis were studied. The calculated mean (SD) tissue volume of a single lung at total lung capacity was 467 (91) ml in the patients with alveolitis, which was 43% (14%) more than predicted for healthy people of the same age, sex, and height. The tissue volume of a single lung at total lung capacity was 436 (82) ml in the patients with chronic airflow limitation, which was 26% (21%) more than predicted. At residual volumes the tissue contents of the fibrotic and the obstructed lungs changed very little (to 407 (84) ml and 433 (84) ml respectively). This allowed tissue volume to be used as a marker of position within the lung, to match inspiratory and expiratory slices and to calculate regional ventilation. In both groups local ventilation was diminished and more variable than in healthy lungs-that is, in the mid 70% of lung volume the local residual volume to total gas volume ratios (RV/TGV) were 32% (10%) in the fibrotic group and 66% (14%) in the group with chronic airflow limitation, compared with 23% (5%) in healthy subjects. As expected, the fibrotic lungs were much denser (0-246 (0036) g/ml) and the lungs with chronic airflow obstruction were less dense (0-114 (0-026) g/ml) than were healthy lungs (0-126 (0-017) g/ml).We have previously shown that computed tomography could measure the total gas and tissue volumes and the regional vital capacities and residual volumes of the lungs in healthy men.' The aim of the present study was to discover how well computed tomography could recover the same volumes in patients with lung disease. MethodsWe studied 12 patients with chronic airflow limitation and 12 patients with fibrosing alveolitis. They were chosen from larger groups of patients with probable emphysema or fibrosis in whom computed tomography had been performed for clinical reasons. Their scans, which were stored on magnetic tape, were selected for more detailed study retrospectively, on the basis of clinical, radiographic, functional, and (in the case of fibrosing alveolitis) histological confirmation of the diagnosis.

Distribution of Lung Density and Mass in Patients With Emphysema as Assessed by Quantitative Analysis of CT

“…The groups of emphysema patients with high M and normal M had a slightly positive but nonsignificant craniocaudal gradient of D between the apex and 80% lung height, whereas the group with low M had an absence of gradient (Fig 3, middle, b). Although the gradient of D observed at low lung volume 9,10,23 in healthy subjects as well as in emphysema patients has been shown to be reduced with lung inflation at TLC, our observations indicated that this gradient might be abolished even at FRC in emphysema patients who have severe, destructive losses of lung tissue.…”

“…Although there are numerous reports on the ventrodorsal gradient of D, few studies have been devoted to the craniocaudal density gradient of human lungs in subjects with emphysema. 9,10 To our knowledge, the interrelationship between both the severity and extent of emphysema (Xt) and the distributions of tissue mass and air volume in this gradient have not been investigated previously.…”

Lung volumes and forced ventilatory flows

“…Detailed information about (regional) lung volumes and lung density can be oblained from computed tomography, single-photon emission computed tomography and magnetic resonance inlaging [200][201][202][203], bul tl1ese techniques for determining lung volumes are still at an experimental stage. 4 Bronchodilator response and serial measurements…”

Sources of Variation in Quantitative Computed Tomography of the Lung

“…Other investigators showed that at suspended inspiration a density gradient could be measured within the gravity plane that compared very favourably to pleural pressure gradients that had been described using inhaled radioactive Xenon 3,4 . Importantly, these and other studies have shown that as disease develops the density of the lung changes and that these density changes are related to lung function 5,6 . Therefore, the superior resolution of CT images and the ability to obtain quantitative information helped propel CT densitometry analysis into the mainstream such that CT became a popular and central part of many lung structure/function studies in health and disease.…”