Pathomorphological changes in pulmonary vessels at different terms of lethal outcomes of patients with COVID-19
Objective: to study the pathomorphological changes in the vessels of the lungs at diﬀerent times of death in patients with COVID-19. Material and methods: autopsy protocols of 40 deaths from COVID-19 with histological, histochemical examination, and photoregistration. To determine the degree of pulmonary vascular lesions, the authors developed and applied a semi-quantitative assessment scale for the sign based on counting the aﬀected lung vessels in 10 ﬁelds of view, expressed as a percentage: no sign - (0%), weak sign + (1-25%), moderate sign ++ (26-50%), expressed sign +++ (51-75%), highly expressed sign ++++ (76-100%). Results: during the ﬁrst 14 days of the disease, stasis and swelling of individual endotheliocytes were noted in the vessels of the microvasculature. A fter 15-21 days of the development of COVID-19, signs of alterations in endothelial cells and microthrombosis were observed in microvessels. A fter 22-28 days of the disease, the phenomena of repair and hyperplasia of endothelial cells were detected. At diﬀerent times of the development of the disease in the lung tissue, the phenomena of acute respiratory distress syndrome, interstitial pneumonia, and focal pneumoﬁbrosis were observed. Conclusions: the authors believe that COVID-19 is associated with a progressive microvascular endotheliopathy in the lungs which is characterized by swelling, alteration, and later, by hyperplasia, and regeneration of endothelial cells in combination with microthrombosis. Destructive changes in the walls of the microvessels of the lungs have superﬁcial character without the destruction of the reticular frame and basal membranes. Endotheliopathy, microthrombus formation of microvessels of the lungs, and interstitial pneumonia create a vicious circle of severe respiratory failure, which must be taken into account in the clinic to correct the treatment of patients with COVID-19.