The COVID-19 infection, a current worldwide health concern, manifests as an alveolar-interstitial pneumonia with unknown long-term evolution. It is also associated with vascular dysfunction and shows a vascular remodeling with a changed balance between small- and large-caliber vessels. In this study, we question the existence of residual vascular alteration in post-acute sequelae of COVID-19 (PASC) by investigating possible associations between vascular remodeling biomarkers extracted from CT and functional, radiological and morphological parameters. The used vascular biomarkers concern the blood volume ratio of vessels with cross-section area inferior to 5 mm2 versus vessels of crosssection area inferior to 50 mm2 (BV5/BV50), an index of local peripheral vascular density and a peripheral composite vascular remodeling index, both measured in the antero-postero-lateral lung periphery (excluding mediastinal region). As a functional parameter, diffusing capacity of the lung for carbon monoxide (DLCO) is a measure depending on the vascular perfusion and the amount of interstitial thickening, a decreased DLCO value suggesting altered vascular perfusion. Imaging biomarkers can be extracted from the analysis of perfusion lung scintigraphy or CT scan. Some of them are included in our study. Radiological features include CT attenuation as a measure of persistence of ground glass opacity and development of changes suggestive to look for fibrosis, such as reticulations. As additional morphological parameter, lung deformation observed between inspiration/expiration maneuvers may be suggestive of the presence of reticulations inducing lung stiffness and breathing deficiency. The investigation of associations between vascular remodeling biomarkers obtained from CT and the above functional, radiological and morphological parameters revealed moderate to strong correlations highlighting the ability to capture the persistence of vascular alterations in PASC in relation with the development of fibrotic patterns, which is a promising direction for future research.
Fibrosing idiopathic interstitial pneumonia (fIIP) is a subclass of interstitial lung diseases, which leads to fibrosis in a continuous and irreversible process of lung function decay. Patients with fIIP require regular quantitative follow-up with CT and several image biomarkers have already been proposed to grade the pathology severity and try to predict the evolution. Among them, we cite the spatial extent of the diseased lung parenchyma and airway and vascular remodeling markers. COVID-19 (Cov-19) presents several similarities with fIIP and this condition is moreover suspected to evolve to fIIP in 10-30% of severe cases. Note also that the main difference between Cov-19 and fIIP is the presence of peripheral ground glass opacities and less or no amount of fibrosis in the lung, as well as the absence of airway remodeling. This paper proposes a preliminary study to investigate how existing image markers for fIIP may apply to Cov-19 phenotyping, namely texture classification and vascular remodeling. In addition, since for some patients, the fIIP/Cov-19 follow-up protocol imposes CT acquisitions at both full inspiration and full expiration, this information could also be exploited to extract additional knowledge for each individual case. We hypothesize that taking into account the two respiratory phases to analyze breathing parameters through interpolation and registration might contribute to a better phenotyping of the pathology. This preliminary study, conducted on a reduced number of patients (eight Cov-19 of different severity degrees, two fIIP patients and one control), shows a great potential of the selected CT image markers.
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