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Updated: Aug 20, 2025

Author Spotlight: Unveiling the Polyfunctionality and Heterogeneity in Immune Responses
Published on: March 8, 2024
COVID-19 Demonstrates That Inflammation Is a Hyperviscous State
Gregory D Sloop1, Gheorghe Pop2, Joseph J Weidman3
1Pathology, Idaho College of Osteopathic Medicine, Meridian, USA.
Insights
Severe COVID-19 causes blood hyperviscosity and hyperfibrinogenemia, increasing thrombosis risk and decreasing tissue perfusion. This contributes to organ damage and long-COVID symptoms.
Area of Science:
- Hematology
- Virology
- Pathophysiology
Background:
- Severe coronavirus disease-2019 (COVID-19) complications are linked to blood hyperviscosity.
- Hyperviscosity arises from elevated fibrinogen levels, creating a syndrome affecting various blood flow conditions.
- This condition increases thrombosis risk and impairs tissue perfusion.
Purpose of the Study:
- To elucidate the mechanisms by which COVID-19-induced hyperviscosity contributes to disease severity and long-term effects.
- To explore the role of viral genetic factors in triggering hyperviscosity and immune responses.
Main Methods:
- Review of existing literature on COVID-19 pathophysiology, focusing on hematological changes.
- Analysis of the severe acute respiratory syndrome coronavirus 2 genome for specific genetic sequences.
- Correlation of hyperviscosity markers with clinical outcomes and organ-specific damage in COVID-19 patients.
Main Results:
- COVID-19-associated hyperviscosity significantly increases arterial and venous thrombosis risk, counteracting anticoagulation.
- Reduced tissue perfusion due to hyperviscosity leads to lung, heart, and brain damage, including hypoxemia, myocarditis, and demyelination.
- Viral genetic factors, specifically oligonucleotide sequences, activate innate immunity, elevating fibrinogen and contributing to pathology.
Conclusions:
- Blood hyperviscosity is a critical factor in severe COVID-19 pathogenesis, driving thrombosis and organ dysfunction.
- Hyperviscosity contributes to long-COVID symptoms through mechanisms like capillary rarefaction and endothelial damage.
- Targeting hyperviscosity and associated immune activation may offer therapeutic strategies for COVID-19 and its sequelae.
Abstract:
Many of the complications of severe coronavirus disease-2019 (COVID-19) are caused by blood hyperviscosity driven by marked hyperfibrinogenemia. This results in a distinctive hyperviscosity syndrome which affects areas of high and low shear. A change in blood viscosity causes a threefold inverse change in blood flow, which increases the risk of thrombosis in both arteries and veins despite prophylactic anticoagulation. Increased blood viscosity decreases perfusion of all tissues, including the lungs, heart, and brain. Decreased perfusion of the lungs causes global ventilation-perfusion mismatch which results in silent hypoxemia and decreased efficacy of positive pressure ventilation in treating pulmonary failure in COVID-19. Increased blood viscosity causes a mismatch in oxygen supply and demand in the heart, resulting in myocarditis and ventricular diastolic dysfunction. Decreased perfusion of the brain causes demyelination because of a sublethal cell injury to oligodendrocytes. Hyperviscosity can cause stasis in capillaries, which can cause endothelial necrosis. This can lead to the rarefaction of capillary beds, which is noted in "long-COVID." The genome of the virus which causes COVID-19, severe acute respiratory syndrome coronavirus 2, contains an extraordinarily high number of the oligonucleotide virulence factor 5'-purine-uridine-uridine-purine-uridine-3', which binds to toll-like receptor 8, hyperactivating innate immunity. This can lead to a marked elevation in fibrinogen levels and an increased prevalence of neutrophil extracellular traps in pulmonary failure, as seen in COVID-19 patients.
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