Computed tomographic measures of pulmonary vascular morphology in smokers and their clinical implications

Abstract

Rationale: Angiographic investigation suggests that pulmonary vascular remodeling in smokers is characterized by distal pruning of the blood vessels.

Objectives: Using volumetric computed tomography scans of the chest we sought to quantitatively evaluate this process and assess its clinical associations.

Methods: Pulmonary vessels were automatically identified, segmented, and measured. Total blood vessel volume (TBV) and the aggregate vessel volume for vessels less than 5 mm(2) (BV5) were calculated for all lobes. The lobe-specific BV5 measures were normalized to the TBV of that lobe and the nonvascular tissue volume (BV5/T(issue)V) to calculate lobe-specific BV5/TBV and BV5/T(issue)V ratios. Densitometric measures of emphysema were obtained using a Hounsfield unit threshold of -950 (%LAA-950). Measures of chronic obstructive pulmonary disease severity included single breath measures of diffusing capacity of carbon monoxide, oxygen saturation, the 6-minute-walk distance, St George's Respiratory Questionnaire total score (SGRQ), and the body mass index, airflow obstruction, dyspnea, and exercise capacity (BODE) index.

Measurements and main results: The %LAA-950 was inversely related to all calculated vascular ratios. In multivariate models including age, sex, and %LAA-950, lobe-specific measurements of BV5/TBV were directly related to resting oxygen saturation and inversely associated with both the SGRQ and BODE scores. In similar multivariate adjustment lobe-specific BV5/T(issue)V ratios were inversely related to resting oxygen saturation, diffusing capacity of carbon monoxide, 6-minute-walk distance, and directly related to the SGRQ and BODE.

Conclusions: Smoking-related chronic obstructive pulmonary disease is characterized by distal pruning of the small blood vessels (<5 mm(2)) and loss of tissue in excess of the vasculature. The magnitude of these changes predicts the clinical severity of disease.

Figure 1.

(Top) Coronal images of a never-smoker (left) and smoker with Global Initiative for Chronic Obstructive Lung Disease 4 chronic obstructive pulmonary disease (right). (Middle) Volumetric reconstructions of the pulmonary vasculature that are color-coded based on vessel radii. (Bottom) Distribution of blood vessel volume as a function of the cross-sectional area (CSA) of the vessels. Plots are color-coded based on vessel size as shown in the volumetric models of the vasculature. The larger peaks in the plots in the CSA range of 0–10 mm² suggest that most intraparenchymal blood vessel volume is within the vessels whose CSA is 0–10 mm². All plots are the same scale. Note the effect of emphysema on the size of the blood vessel volume peak in the 0–10 mm² CSA range.

Figure 2.

Summary profiles for the blood vessel volume as a function of blood vessel cross-sectional area (CSA; square millimeter) for all 359 smokers in the range 0–20 mm². Results are provided for each lobe. The color-coded line represents the median profile and the dotted lines the 25th and 75th percentile. The figure inserts for each plot represent an enhanced view of the blood vessel volume distribution in the range of 0–70 mm².