Why COVID-19 lacks oxygen without shortness of breath
Some people suffer from COVID-19 from what is known as quiet shortness of breath (silent hypoxaemia), which is characterized by a life-threatening and asymptomatic lack of oxygen. It is extremely confusing that despite the lack of oxygen, the human body’s alarm system should simply fail. A new study has now clearly shown what causes COVID-19 quiet breathing.
Researchers at the University of Boston and the University of Vermont jointly investigated the causes of silent respiratory distress COVID-19 in their study. The results of the study were published in the English-language journal Nature Communications.
What causes quiet breathing?
To date, the causes of COVID-19 silent hypoxaemia are unclear. Recent results suggest that at least some of the problems are lung problems. With this disorder, more blood is pumped into the broken rather than the intact areas of the lungs. In addition, existing blood clots and insufficient blood flow disrupt oxygen exchange, the researchers report.
Oxygen deficiency without typical symptoms?
There are people who suffer from COVID-19, who do not have a cough or shortness of breath and no signs of extensive lung damage, but who still have a dangerous lack of oxygen. Existing oxygen saturations in the blood sometimes reach such low values that the affected people actually have to disappear.
Can COVID-19 disable the critical alarm system?
“We didn’t know that something like this was physiologically possible at all,” the study’s author, Professor Bela Suki of Boston University, told a press release. Normally, carotid artery sensors alert the brain as soon as the actual balance of carbon dioxide and oxygen in the blood is no longer correct. It is this alarm system that appears to be partially deactivated when COVID-19 occurs. The reasons for this were unclear.
Viral infection is thought to affect the respiratory center in the brain, among other consequences. This area of the brain causes shortness of breath when there is a lack of oxygen, experts explain.
SARS-CoV-2 can enter the brain
Other studies have already shown that SARS-CoV-2 can enter the nose and olfactory system in the brain, where coronavirus can also be detected in parts of the brainstem. There is also a breathing center in this area.
Why does shortness of breath occur at an early stage?
The researchers were also interested in why silent shortness of breath occurs especially in the early stages of COVID-19. At this stage of the disease, the lungs usually appear to be only slightly attacked. “These patients have hypoxemia, although their lung CT scans show only minimal areas with impaired ventilation,” explains Professor Suki. The study group used patient data and computer simulations to study what happens in the lungs in this case.
Improper lung control?
Experts assumed that blood flow control in the lungs may be incorrect. Usually, the feedback mechanism ensures that the venous blood flows mainly to the place where the air exchange works well. When the areas of the lungs are poorly ventilated due to inflammation or injury, the blood vessels in that area narrow. With this so-called hypoxic vasoconstriction, the blood is mainly diverted to the still intact area, and the blood is adequately supplied with oxygen, the researchers explain.
COVID-19 no hypoxic vasoconstriction?
This diversion does not seem to work properly for some people with COVID-19. In the affected individuals, the blood vessels in the damaged lung areas no longer shrink. This prevents the blood flow from being diverted. “Failure to do so could lead to a significant disproportion between breathing and oxygen exchange in the lungs,” said Professor Suki.
Lung lesions were simulated in a lung model
The study team used a biophysical lung model to see if such a malfunction could explain the lack of oxygen in the affected person. In this model, experts reduced air supply to lung tissue by 17 percent. These effects are comparable to the lung damage caused by COVID-19 at an early stage, the researchers explain. The team then simulated various circulatory and oxygen exchange scenarios during the investigation.
What Causes Reduced Oxygen Uptake?
It has been found that if the veins in the affected areas of the lungs remain open or even dilate rather than contract, this can significantly reduce the uptake of oxygen into the blood. However, the observed effect is not sufficient to explain the abnormally low oxygen saturation in some people with COVID-19, experts explain.
However, there is another factor that can cause hypoxemia. COVID-19 disease has also been shown to disrupt gas exchange in healthy areas of the lungs.
Causes of gas exchange disturbances
Possible causes include blood clots and embolism in the small veins of the lungs. “If such thrombotic emboli occur in the early stages of COVID-19, they may increase pulmonary malnutrition and hypoxemia,” the study group explains.
Inconsistency between ventilation and perfusion
There is also an imbalance between the actual amount of oxygen in the still intact alveoli and the blood’s ability to absorb this breathing gas. In this case, experts talk about the discrepancy between ventilation and perfusion. Possible causes include inflammation of the walls of the vessels, but also insufficient blood flow and blood pressure in the lung capillaries.
The coronavirus not only directly attacks the lung cells
According to the study group, this suggests that coronavirus infection not only directly attacks lung cells, but also disrupts the regulation of lung function in several ways. This explains why oxygen deficiency occurs even in people whose lungs actually appear intact, the researchers conclude.
“People react very differently to this virus,” explains Professor Suki. For this reason, it is especially important to find out all the possible causes of dangerous oxygen deficiency. According to experts, this could help determine the right treatment for COVID-19 patients. (how to)
Information about the author and source
This text meets the requirements of specialist medical literature, medical guidelines and current research and has been reviewed by medical professionals.
- Jacob Herrman, Vitor Mori, Jason HT Bates, Bel Suki: Modeling pulmonary perfusion abnormalities to explain early COVID-19 hypoxemia, Nature Communications (veröffentlicht 28.09.2020), Nature Communications
- Boston University: Three reasons why COVID-19 can cause silent hypoxia (veröffentlicht 08.10.2020), Boston University
This article is for general guidance only and should not be used for self-diagnosis or self-treatment. He cannot replace a visit to the doctor.