Hypoxia can also make people healthier

 　　German climbers Dujemovitz and Hansen are no strangers to hypoxia, having climbed eight of the world's tallest mountains together. But when they entered the hypoxic chamber at the German Aerospace Center in May 2018, they were actually climbing a career-high. During the 16-day test, the air they breathed had an oxygen concentration lower than that at the base camp of Mount Everest at an altitude of 5,200 meters, and in 4 days it was even as low as the oxygen content at an altitude of 7,112 meters. The "death zone" above 8,000 meters, above which a lack of oxygen impairs climbers' judgment and increases their risk of heart disease and stroke, is only a hundred steps away.

　　Time and time again, the experimenters who observed them worried about whether they would hold on, but they did. Dujemovitz and Hansen proved through this experiment that healthy people can tolerate prolonged hypoxia. This paves the way for a more ambitious experiment: testing whether hypoxia can be safely used as a therapy to treat certain diseases.

Should there be more or less oxygen?

　　This may sound strange. After all, our organs and tissues need oxygen. In hospitals, many critically ill patients have oxygen inhalation devices at the bedside. After a heart attack or stroke, patients often require frequent oxygen to ensure tissue does not die. The ventilator, which has been widely used in the new coronary pneumonia epidemic that has swept the world, is to inhale more oxygen for severely ill patients with new coronary pneumonia.

　　However, it's surprising how "resilient" our bodies are: breathing in more oxygen treats some diseases, and breathing in less seems to treat others.

　　In 2019, the Nobel Prize in Physiology and Medicine was awarded to three scientists who discovered a protein called "hypoxia-inducible factor" in liver cells. This protein multiplies when oxygen is deficient in the blood, activating hundreds of genes and biochemical reactions to help the body cope with the lack of oxygen. This is our body's long-evolved physiological response to adapt to changes in the oxygen content of the air.

　　At least some of these responses appear to be beneficial. It has long been found that exposure to high altitudes helps treat conditions ranging from asthma to high blood pressure. In addition, people who lived at high altitudes for a long time were healthier on average than those in the plains. They had lower rates of diabetes, cardiovascular disease and certain types of cancer, such as breast and lymphoma.

　　But these findings run counter to how we traditionally think about hypoxia. As we all know, people living in low altitudes traveling to high altitude areas often trigger what is called altitude sickness: rapid heartbeat, high blood pressure, nausea, headaches, difficulty concentrating, and even swelling of the brain and lungs Waterlogging, causing death.

Hypoxia promotes regeneration of heart, blood vessels and nerves

　　How to explain this paradox? Scientists have taken inspiration from animal studies.

　　In 2017, Hersam Sadik and his colleagues at Texas Southwestern Medical Center reported a curious finding. They kept the mice in a sealed box with a slowly decreasing oxygen concentration and noticed that if the mice breathed air with only 7% oxygen (at sea level, the oxygen concentration is 21%, At a concentration of 7 percent, roughly equivalent to the concentration at the summit of Mount Everest), their cardiomyocytes begin to grow and divide. This is surprising because, in general, adult mammalian hearts often fail to regenerate -- which is why heart disease is not easily treatable.

　　Sadik knew that the mammalian heart was regenerating in utero, but lost its ability to regenerate shortly after birth. He speculates that the loss of the heart's ability to regenerate may be related to environmental changes in the fetus from hypoxia to no hypoxia. Because while in the womb, although fetuses get oxygen from their mothers through the placenta, their hearts grow to a large extent in the absence of oxygen; and when they croak and begin to learn to breathe, the heart is in in a normal oxygen supply environment.

　　From the above mouse experiments, Sadik speculates that this process may be reversible: by carefully reducing the oxygen concentration, mature cardiomyocytes can be prompted to return to their embryonic form and begin to grow and divide, thereby allowing the heart to regenerate Ability is restored to a certain extent.

　　Evidence suggests that hypoxia not only regenerates the heart, but also stimulates the growth of blood vessels around the heart. This helps explain why people living at high altitudes have a lower risk of cardiovascular disease.

　　Hypoxia also appears to stimulate regeneration and repair of nerve pathways between the brain and spinal cord. Scientists gave a group of patients who had lost the ability to walk due to spinal cord injury and had to rely on a ventilator to maintain their lives. air), after a period of time, their walking ability was restored to a certain extent.

　　This intermittent hypoxia therapy also appears to be effective in treating neurodegenerative diseases. The principle is the same as above, hypoxia can stimulate the regeneration of nerve cells.

German mountaineering female athlete Nancy Hansen trains in an oxygen-deficient airtight laboratory.

hypoxia can also lose weight

　　The benefits of hypoxia therapy may not end there. One area of ​​interest is weight loss. It has long been found that people who live in mountains are less likely to be obese, and people who climb regularly tend to lose weight.

　　Of course, mountain people or climbers tend to be more physically active, which is one of the reasons. But researchers say that's not the whole story.

　　In 1985, the U.S. Army simulated a 40-day mountaineering expedition in a hypoxia chamber. Six volunteers were kept in a hypoxic chamber. Oxygen levels in the chamber gradually decrease to levels at the summit of Mount Everest. During this period, volunteers are guaranteed to be warm and free to eat meals and snacks. If they are happy, they can also exercise. By the end of the experiment, the volunteers lost an average of 7.5 kilograms.

　　A similar situation was observed when the researchers recruited a group of obese men to live at an altitude of 2,650 meters for a week. Although they didn't do any exercise and ate as much as they wanted, they lost an average of about 1.3kg over the course of a week.

　　Unfortunately, the weight loss in these trials was temporary. By the time they returned to living in a normoxic environment, the weight returned.

　　The researchers believe that hypoxia induces weight loss in two ways. First, lack of oxygen stimulates the body to produce more leptin. Leptin is a hormone that makes us feel full. More leptin makes a person feel less hungry, in which case fewer calories are eaten. Second, lack of oxygen also increases our metabolic rate and therefore burns more calories.

　　At the end of the day, hypoxia is a double-edged sword: beneficial in some cases, but undeniably detrimental in others. For example, in people with sleep apnea, lack of oxygen can certainly be detrimental. Sleep apnea causes breathing to stop repeatedly at night for up to several minutes, and many people then develop diabetes. This may be due to the disturbance of glucose metabolism caused by hypoxia.

　　Clearly, more experiments are needed to see whether hypoxia can be used as a safe therapy. The human trials of Dujemovitz and Hansen showed that healthy people can tolerate hypoxia with no real risk, and then it needs to be shown that there is no risk for heart disease patients. A few days ago, the German Aerospace Center has recruited volunteers suffering from heart disease to participate in the next hypoxia experiment.

Extended reading

dangerous happy hypoxia

　　Since the outbreak of the new crown pneumonia epidemic, doctors have been puzzled by a symptom that some seriously ill patients are showing: their blood oxygen levels are alarmingly low, almost to the point of life support, and yet they do not seem to have any breathing difficulties, able to speak normally. Their lungs initially continued to expel carbon dioxide, which even made them feel good. This symptom is called "happy hypoxia".

　　We do not yet know why this symptom occurs. Some speculate that this may be a manifestation of the damage to the nerves of the new coronavirus. A preliminary study in October 2020 showed that the new coronavirus can invade the brain and cause it to age.

　　Happy hypoxia is dangerous in the onset of COVID-19. The reduction in inhaled oxygen is directly associated with an increase in mortality from COVID-19. Therefore, monitoring the oxygen content in the blood is an important measure to monitor the development of the disease.