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Researchers in Spain Suggest COVID-19 Infection of Oxygen-Sensing Carotid Body May Be Cause of “Silent Hypoxemia” Observed in Many COVID-19 Patients; Carotid Body Activators Might Prove Useful in Treatment, If Hypothesis Confirmed

One of the physiopathological characteristics of COVID-19 that has most baffled the scientific and medical community is what is known as "silent hypoxemia" or "happy hypoxia." Patients suffering this phenomenon, the causes of which are still unknown, have severe pneumonia with markedly decreased arterial blood oxygen levels (known as hypoxemia). However, they do not report dyspnea (subjective feeling of shortness of breath) or increased breathing rates, which are usually characteristic symptoms of people with hypoxemia from pneumonia or any other cause. Patients with "silent hypoxemia" often suffer a sudden imbalance, reaching a critical state that can be fatal. Normally, individuals (healthy or sick) with hypoxemia report a feeling of shortness of breath and a higher breathing rate, thus increasing the body's uptake of oxygen. This reflex mechanism depends on the carotid body. This small organ, located on either side of the neck next to the carotid artery, detects the drop in blood oxygen and sends signals to the brain to stimulate the respiratory center. A group of researchers from the Seville Institute of Biomedicine - IBiS/University Hospitals Virgen del Rocío y Macarena/CSIC/University of Seville, led by Dr. Javier Villadiego, Dr. Juan José Toledo-Aral, and Dr. José López-Barneo, specialists in the physiopathological study of the carotid body, have suggested in the journal Function, that "silent hypoxemia" in COVID-19 cases could be caused by this organ (carotid body) being infected by the coronavirus (SARS-CoV-2). The open-access Function article was published online on November 23, 2020 and is titled “Is Carotid Body Infection Responsible for Silent Hypoxemia in COVID-19 Patients?” This hypothesis, which has attracted the interest of the scientific community for its novelty and possible therapeutic significance, comes from experiments that have revealed a high presence of the enzyme ECA2 (calcium-transporting ATPase 2, endoplasmic reticulum-type), a protein that helps coronavirus infect human cells, in the carotid body.

In patients with COVID-19, the coronavirus circulates in the blood. Therefore, researchers suggest that infection of the human carotid body by SARS-CoV-2 in the early stages of the disease could alter its ability to detect blood oxygen levels, resulting in an inability to "notice" the drop in oxygen in the arteries. If this hypothesis, which is currently being tested in new experimental models, is confirmed, this would justify the use of activators of the carotid body, independent of the oxygen sensing mechanism, as respiratory stimulants in patients with COVID-19.

[News release] [Function article]

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Graphic image showing carotid body position relative to vascular & nervous systems. (Credit: Elsevier).