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Happy hypoxia: Researchers find what causes blood oxygen levels to drop in many Covid-19 patients

Patients with low blood oxygen levels may experience symptoms like shortness of breath and chest pain. Shutterstock

Silent hypoxemia or happy hypoxia is an unusual Covid-19 complication that has most baffled the scientific and medical community.

Written by Longjam Dineshwori |Updated : December 31, 2020 8:05 AM IST

It's been a year now since the Covid-19, the disease caused by the novel coronavirus, emerged in China's Wuhan city. But many questions still remain unanswered. Although most Covid-19 patients have mild to moderate symptoms, the disease can cause severe medical complications in some people. Common complications of Covid-19 include pneumonia, acute respiratory distress syndrome, acute cardiac injury, arrhythmia, septic shock, acute liver injury, secondary infection, and acute kidney injury. Some COVID-19 patients are also experiencing unusual complications, like Guillain barre syndrome, lacy purple rashes and "silent hypoxemia" or "happy hypoxia".

Happy hypoxia is one of the physiopathological characteristics of Covid-19 that has most baffled the scientific and medical community.

Why is it called happy hypoxia?

For a normal person, the blood oxygen saturation level (the amount of hemoglobin carrying oxygen) is around 95 percent or more. Hypoxemia is a condition in which the blood saturation levels drop below 94 percent.

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Patients with blood oxygen levels below 90 percent, which is considered too low, may experience symptoms like shortness of breath and chest pain. They may need oxygen therapy. If blood oxygen levels continue to fall, their organs may shut down, which could be life threatening. However, despite low blood oxygen levels, some Covid-19 patients do not feel any symptoms and feel fine, until eventually, they collapse. This unusual phenomenon gave rise to the term "silent hypoxemia" or "happy hypoxia." Patients with this condition often suffer a sudden imbalance, reaching a critical state that can be fatal.

Cause of happy hypoxia found

Researchers and doctors have been trying to understand the causes of happy hypoxia in Covid-19 patients. Now, researchers from the University of Seville in Spain have come up with an explanation for the condition.

They say that infection in carotid bodies by SARS-CoV-2, the virus responsible for the pandemic, may be the cause of the decreased blood oxygen levels in many Covid-19 cases. Carotid bodies are sensory organs located on either side of the neck next to the carotid artery. They detect the drop in blood oxygen and send signals to the brain to stimulate the respiratory centre.

In their study, detailed in the journal Function, the researchers suggest that infection of this carotid body by SARS-CoV-2 in the early stages of the disease could alter its ability to detect blood oxygen levels, resulting in the silent drop in oxygen in the arteries.

They have also found a high presence of the enzyme ECA2, the protein the coronavirus uses to infect human cells, in the carotid body.

The hypothesis support the use of activators of the carotid body independent of the oxygen sensing mechanism as respiratory stimulants in patients with Covid-19.

With inputs from IANS

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