Imaging Pulmonary Blood Vessels and Ventilation-Perfusion Mismatch in COVID-19

Abstract

COVID-19 hypoxemic patients although sharing a same etiology (SARS-CoV-2 infection) present themselves quite differently from one another. Patients also respond differently to prescribed medicine and to prone Vs supine bed positions. A severe pulmonary ventilation-perfusion mismatch usually triggers moderate to severe COVID-19 cases. Imaging can aid the physician in assessing severity of COVID-19. Although useful for their portability X-ray and ultrasound serving on the frontline to evaluate lung parenchymal abnormalities are unable to provide information about pulmonary vasculature and blood flow redistribution which is a consequence of hypoxemia in COVID-19. Advanced imaging modalities such as computed tomography, single-photon emission tomography, and electrical impedance tomography use a sharp algorithm visualizing pulmonary ventilation-perfusion mismatch in the abnormal and in the apparently normal parenchyma. Imaging helps to access the severity of infection, lung performance, ventilation-perfusion mismatch, and informs strategies for medical treatment. This review summarizes the capacity of these imaging modalities to assess ventilation-perfusion mismatch in COVID-19. Despite having limitations, these modalities provide vital information on blood volume distribution, pulmonary embolism, pulmonary vasculature and are useful to assess severity of lung disease and effectiveness of treatment in COVID-19 patients.

Diagnostic importance of lung perfusion/ventilation scans in the evaluation of pulmonary embolism in COVID-19 patients: systematic review of the literature

“…Three studies (Bahloul, Goetz, Tipre) observed tracheobronchial uptake [16,27,38] which was a unique finding in COVID-19 patients most likely due to tracheobronchial inflammation.…”

“…The perfusion SPECT of COVID-19 patients also revealed novel findings, such as tracheobronchial uptake in ventilation SPECT, as described by Bahloul et al ., Goetz et al ., and Tipre [16,27,38].…”

“…(1) Reverse mismatch Bajc, Burger, Cobes, Goetz, Tipre, Bonnefoy, and Venegas discovered reversed mismatch patterns in their study [17,18,20,21,27,38,39]. This was attributed to non-segmental diversion of perfusion from ventilated areas (shunt perfusion) in Bajc et al study.…”

“…(2) Matched perfusion defects Matched perfusion defects on SPECT images were found in Cobes, Evboumwan, Kurkowska, Sajal, Tipre, Bonnefoy, and Venegas studies [18,21,24,28,34,38,39]. This pattern can virtually rule out pulmonary embolism as the culprit in the location of these abnormalities.…”

Quantitative assessment of ventilation-perfusion relationships with gallium-68 positron emission tomography/computed tomography imaging in lung cancer patients

“…Given the basic physiologic principle that gas exchange is the primary function of the lungs and previous work demonstrating an association between D LCO and toxicity [23] , [24] , [25] , [26] , V/Q imaging may serve as a better imaging biomarker for planning and improve toxicity prediction compared to imaging of ventilation or perfusion alone. Furthermore, V/Q imaging offers opportunities for applications in pulmonary medicine, such as early detection and phenotyping of COPD [27] , assessment of severity of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and response to therapy [28] .…”