COVID-19: 3 reasons for hypoxia

This is really one of the many confusing aspects of how the novel coronavirus attacks the lungs and other parts and organs of the body. It is still unclear how the virus causes “silent hypoxia” – abnormally low oxygen levels in the body, which can irreparably damage various vital organs. Some brain damage associated with COVID-19 perfectly illustrates the possible effects of this hypoxia. Here, with computer models and analysis of patient data, the Boston bioengineers with their colleagues at the University of Vermont provide an early understanding of this process.

Hypoxia is sometimes silent, why?

Despite dangerously low oxygen levels, many COVID-19 patients have no symptoms of shortness of breath or difficulty breathing. The ability of hypoxia to deal damage silently is why it is referred to here as “silent”. In coronavirus patients, the infection is thought to damage the lungs first, rendering some parts unable to function normally. These tissues no longer infuse oxygen into the bloodstream, causing this silent hypoxia.

Hypoxia in its pulmonary phase does not always appear on imaging: Dr. Bela Suki, professor of biomedical engineering and co-author of the study, recounts her experience of COVID patients with blood oxygen levels “incompatible with life” and yet showed few or no signs of abnormalities on lung scan.

A domino effect? To better understand the causes of silent hypoxia, the team used computer models and tested 3 scenarios that could explain how and why the lungs stop supplying oxygen to the bloodstream. The researchers conclude that it is most likely a combination of several biological mechanisms that contribute to more systemic hypoxia.

Normally, the lungs provide gas exchange, supplying oxygen to every cell in the body when we inhale and eliminating carbon dioxide every time we exhale. Healthy lungs keep oxygenated blood at a level between 95 and 100%, and if this level drops below 92%, the need for additional oxygen begins to arise.

When our lungs don’t collect enough oxygen due to damage caused by an infection, blood vessels in these areas constrict, forcing blood to flow through oxygen-filled lung tissues, which then circulates to the rest. from the body.

1. In some COVID patients, however, the lungs lose this ability to restrict blood flow to already damaged tissues. The result is very low levels of oxygen throughout the body;
2. second observation: when the blood vessel walls are inflamed due to the COVID-19 disease, tiny blood clots too small to be detected can form inside the lungs. These micro-clots also contribute to silent hypoxia, but, the researchers say, they probably wouldn’t be enough on their own to bring down such low oxygen levels;
3. Finally, COVID-19 appears to interfere with the normal air-to-blood flow ratio that the lungs need to function normally. This same deregulation occurs in many respiratory diseases, such as asthma, and may be a possible contributor to silent hypoxia.

Overall, this work reveals 3 factors involved in severe hypoxia in COVID-19 patients: response of the lungs to oxygen flow, possible micro-clots within the lungs and deregulation of the air / blood flow ratio. Researchers are calling for a better examination of how the combination of these 3 factors can vary from patient to patient in order to make more informed clinical choices.

Because every patient responds differently to this virus and it is essential that doctors understand all the possible reasons why a patient’s blood oxygen may be reduced, in order to be able to choose the appropriate treatment (ventilation, Medicines to “restrict” “blood vessels, remove clots or correct this air-to-blood flow relationship.