"Pulmonary Vascular Morphology Associated with Gas Exchange in Systemic Sclerosis without Lung Fibrosis"

Zhiwei Zhai, Marius Staring, Maarten K. Ninaber, Jeska de Vries-Bouwstra, Anne A. Schouffoer, Lucia J. Kroft, Jan Stolk and Berend C. Stoel

Abstract

Purpose: Gas exchange in systemic sclerosis (SSc) is known to be affected by fibrotic changes in the pulmonary parenchyma. However, SSc patients without detectable fibrosis can still have impaired gas transfer. We aim to investigate whether pulmonary vascular changes could partly explain a reduction in gas transfer of systemic sclerosis (SSc) patients without fibrosis.

Materials and Methods: We selected 77 patients, whose visual CT scoring showed no fibrosis. Pulmonary vessels were detected automatically in CT images and their local radii were calculated. The frequency of occurrence for each radius was calculated, and from this radius histogram two imaging biomarkers (α and β) were extracted, where α reflects the relative contribution of small vessels compared to large vessels and β represents the vessel tree capacity. Correlations between imaging biomarkers and gas transfer (DLCOc %predicted) were evaluated with Spearman's correlation. Multivariable stepwise linear regression was performed with DLCOc %predicted as dependent variable and age, BMI, sPAP, FEV1 %predicted, TLC %predicted, FVC %predicted, α, β, voxel size and CT-derived lung volume as independent variables.

Results: Both α and β were significantly correlated with gas transfer (R=-0.29, p-value=0.011 and R=0.32, p-value=0.004, respectively). The multivariable step-wise linear regression analysis selected sPAP (coefficient=-0.78, 95%CI=[-1.07, -0.49], p-value<0.001), β (coefficient=8.6, 95%CI=[4.07, 13.1], p-value<0.001) and FEV1 %predicted (coefficient=0.3, 95%CI=[0.12, 0.48], p-value=0.001) as significant independent predictors of DLCOc %predicted (R=0.71, p-value<0.001).

Conclusions:In SSc patients without detectable pulmonary fibrosis, pulmonary vascular morphology is associated with gas transfer, indicating that impaired gas exchange is associated with vascular changes.

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