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One of the signature symptoms of the transition from mild to severe after infection with the new coronary virus is shortness of breath, which significantly reduces oxygen levels in the patient's blood, known as hypoxemia.
the patient's blood oxygen levels return to normal, oxygen absorption is a commonly used respiratory support during treatment.
, however, a new study suggests that such treatments, commonly used in people with respiratory diseases, can have unintended consequences in unexpected ways.
In a paper published today in the journal Science Translational Medicine, researchers at the University of Michigan School of Medicine found that bacteria in the lungs are quickly affected by high concentrations of oxygen and play an important role in lung damage.
"People often think that the lungs should be relatively clean and bacteria-resistant, but we now know that bacteria in the lungs need to be ecologically balanced like gut bacteria, " he said.
study's first author, Dr. Shanna Ashley.
Although we live without oxygen, scientists have long found in animal experiments that inhaling too much oxygen can lead to damage to the lungs and is clinically associated with increased mortality, severe lung damage and pneumonia.
" oxygen is actually a strong pulmonary toxin.
Professor Robert Dickson, who led the study, said: "If I put healthy mice in 100 per cent oxygen, they would die within five days and suffer severe lung damage similar to that suffered by patients with new coronary pneumonia or other lung damage.
in the Respiratory and Critical Care Medicine Department, where the team is based, patients often need to continue receiving high levels of oxygen therapy.
therefore, it is important to understand how oxygen used in treatment can cause harm and why some patients are more prone to misfortune.
researchers studied 1,500 critically ill patients who had been on ventilators for more than 24 hours.
they tested bacteria in a patient's lung sample and found significant differences in the types of bacteria in different samples, which were related to the concentration of oxygen inhaled by the patient.
specifically, patients with high oxygen concentrations (FiO2?gt;55%) had a much higher proportion of Staphylococcus ale in their bacterial cultures than other bacteria.
the bacteria is very oxygen-resistant and is a common cause of lung infections in intensive care units (ICU).
different types of bacteria have different tolerances to oxygen, so the researchers speculate that the oxygen provided to patients may affect the composition of bacteria in their respiratory tracts.
researchers designed a set of experiments to analyze the composition of lung bacteria in mice using 16S rRNA sequencing.
they divided healthy mice into two groups and exposed them to high-oxygen and normal-oxygen environments.
"As we predicted, when we provide high levels of oxygen, the lung microbiotics of healthy mice change rapidly," Dr. Ashley said.
" three days later, oxygen-resistant staphylococcus became the most abundant bacteria in the lungs of mice.
, the scientists then answered the key question of "chicken first or eggs first" in the study: Does a change in lung microbiome cause lung damage, or does a damaged lung alter the composition of bacteria? The researchers first looked at when it happened: the response of mice inhaling high concentrations of oxygen was that the composition of the lung bacteria had changed in just one day, and lung damage could be detected by day three.
relative time, lung microbiota is destroyed before lung damage occurs.
, the degree of change in lung bacteria in mice was closely related to the severity of pneumonia in mice in high oxygen environments.
to further confirm the role of lung bacteria in lung damage caused by high oxygen, researchers conducted a key experiment in sterile mice.
inhaled high concentrations of oxygen for the same 72 hours, but no lung damage occurred in sterile mice.
think this is an unusual discovery!" he said. Professor Dickson said: 'Compared to the normal mice in the control group, sterile mice had the same genetic genes and received the same amount of oxygen, but their lungs were protected.
" fully demonstrates that microorganisms play an important role in lung damage.
," Dr. Ashley added.
that, can antibiotics protect patients who receive oxygen therapy? Critically ill patients often use antibiotics while inhaling oxygen, but the researchers note that the problem is not that simple.
" bacteria are not all good or all bad, which is why we have to dig out the mechanism behind it.
are far from specific, and we need to take a more targeted approach to bacteria," the study authors note.
the study strongly demonstrates in animals how different oxygen concentrations can cause lung damage, the researchers caution against changing clinical practice prematurely based on these findings.
" how much oxygen is provided to critically ill patients is a complex issue and one that requires in-depth study.
, "I hope that the results of randomized controlled trials will be followed by better decisions."
"