One of the most baffling characteristics of COVID-19 is silent hypoxemia or ‘happy hypoxia’. Patients exhibit markedly decreased arterial blood oxygen levels. They do not report dyspnoea or increased breathing rate. Patients with “silent hypoxemia” often suffer a sudden imbalance, reaching a critical state that can be life-threatening. Usually, patients 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 bodies. These small organs, located on either side of the neck next to the carotid artery, detect the drop in blood oxygen, and send 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/the University of Seville has suggested that that the silent hypoxemia could be caused by this organ being infected with SARS-CoV-2. This comes from experiments that have revealed a high presence of the enzyme ACE2 in the carotid body.
This protein is used by the SARS-CoV-2 virus to gain entry into the cells. 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 silent hypoxemia.
Ref link: https://academic.oup.com/function/article/2/1/zqaa032/5998649