Associations of pulmonary microvascular blood volume with per cent emphysema and CT emphysema subtypes in the community: the MESA Lung study

Abstract

Background: Pulmonary microvasculature alterations are implicated in emphysema pathogenesis, but the association between pulmonary microvascular blood volume (PMBV) and emphysema has not been directly assessed at scale, and prior studies have used non-specific measures of emphysema.

Methods: The Multi-Ethnic Study of Atherosclerosis Lung Study invited participants recruited from the community without renal impairment to undergo contrast-enhanced dual-energy CT. Pulmonary blood volume was calculated by material decomposition; PMBV was defined as blood volume in the peripheral 2 cm of the lung. Non-contrast CT was acquired to assess per cent emphysema and novel CT emphysema subtypes, which include the diffuse emphysema subtype and small-airways-related combined bronchitic-apical emphysema subtype. Generalised linear regression models included age, sex, race/ethnicity, body size, smoking, total lung volume and small airway count.

Results: Among 495 participants, 53% were never-smokers and the race/ethnic distribution was 35% white, 31% black, 15% Hispanic and 18% Asian. Mean PMBV was 352±120 mL; mean per cent emphysema was 4.95±4.75%. Lower PMBV was associated with greater per cent emphysema (-0.90% per 100 mL PMBV, 95% CI: -1.29 to -0.51). The association was of larger magnitude in participants with 10 or more pack-years smoking and airflow obstruction, but present among participants with no smoking history or airflow limitation, and was specific to the diffuse CT emphysema subtype (-1.48% per 100 mL PMBV, 95% CI: -2.31 to -0.55).

Conclusion: In this community-based study, lower PMBV was associated with greater per cent emphysema, including in participants without a smoking history or airflow limitation, and was specific to the diffuse CT emphysema subtype.

Keywords: Emphysema.

Figure 1.

Contrast-enhanced, DECT scans showing pulmonary blood masks and 3-dimensional and 2-dimensional reconstructions of pulmonary microvascular blood volume in representative participants with low and high percent emphysema. Participants from the lowest and highest quintile percent emphysema are shown. Pulmonary microvascular blood volume, or volume of blood in the peripheral 2cm peel of lung parenchyma, is demonstrated in red on pulmonary blood volume maps (top) and on 3-dimensional reconstructions of the lungs (middle), and axial 2-dimensional sections (bottom) of dual energy CT images. Participants are female nonsmokers with age and BMI within 1 SD of the population mean.

Figure 2.

Generalized additive models of the associations between pulmonary microvascular blood volume and percent pulmonary microvascular blood volume on DECT and percent emphysema on CT. Top panel (A) shows the association between pulmonary microvascular blood volume and percent emphysema adjusted for age, sex, height, race/ethnicity, weight, smoking status, pack-years, educational attainment, study site, total lung volume and small airway count. P<0.001, P-nonlinearity = 0.348 Bottom panel (B) shows the association between percent pulmonary microvascular blood volume and percent emphysema adjusted for age, sex, height, race/ethnicity, weight, smoking status, pack-years, educational attainment, study site and small airway count. P<0.001, P-nonlinearity = 0.015 Note: Dashed lines represent 95% confidence intervals.