Complexity of Terminal Airspace Geometry Assessed by Lung Computed Tomography in Normal Subjects and Patients with Chronic Obstructive Pulmonary Disease

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 96; no. 16; pp. 8829 - 8834
• Main Authors: Mishima, Michiaki, Hirai, Toyohiro, Itoh, Harumi, Nakano, Yasutaka, Sakai, Hiroaki, Muro, Shigeo, Nishimura, Koichi, Oku, Yoshitaka, Chin, Kazuo, Ohi, Motoharu, Nakamura, Takashi, Jason H. T. Bates, Alencar, Adriano M., Suki, Bèla
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 03.08.1999; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Airspace; Biological Sciences; Cardiovascular disease; Chronic obstructive pulmonary disease; Computed tomography; Computerized axial tomography; Emphysema; Forced Expiratory Volume; Fractals; Geometry; Humans; Lung - diagnostic imaging; Lung - physiology; Lung - physiopathology; Lung Diseases, Obstructive - diagnostic imaging; Lung Diseases, Obstructive - physiopathology; Lungs; Medical research; Physical Sciences; Physiology; Power laws; Pulmonary alveoli; Reference Values; Respiratory Function Tests; Size distribution; Tomography; Tomography, X-Ray Computed - methods; Vital Capacity
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.16.8829

Increases in the low attenuation areas (LAA) of chest x-ray computed tomography images in patients with chronic obstructive pulmonary disease (COPD) have been reported to reflect the development of pathological emphysema. We examined the statistical properties of LAA clusters in COPD patients and in healthy subjects. In COPD patients, the percentage of the lung field occupied by LAAs (LAA%) ranged from 2.6 to 67.6. In contrast, LAA% was always <30% in healthy subjects. The cumulative size distribution of the LAA clusters followed a power law characterized by an exponent D. We show that D is a measure of the complexity of the terminal airspace geometry. The COPD patients with normal LAA% had significantly smaller D values than the healthy subjects, and the D values did not correlate with pulmonary function tests except for the diffusing capacity of the lung. We interpret these results by using a large elastic spring network model and find that the neighboring smaller LAA clusters tend to coalesce and form larger clusters as the weak elastic fibers separating them break under tension. This process leaves LAA% unchanged whereas it decreases the number of small clusters and increases the number of large clusters, which results in a reduction in D similar to that observed in early emphysema patients. These findings suggest that D is a sensitive and powerful parameter for the detection of the terminal airspace enlargement that occurs in early emphysema.