Feeling "chest tightness, shortness of breath"? Please don't breathe deeply!

This is the 4577th article of Da Yi Xiao Hu

If the human body is hypoxic, the oxygen content in the arterial blood decreases and the carbon dioxide content increases, the brain will send out warning signals, and the human body will produce hypoxia reactions - chest tightness, shortness of breath, and sometimes accompanied by panic - so we will increase the amplitude of breathing and speed up the breathing rate (healthy adults usually breathe about 12-20 times per minute) to inhale more oxygen and expel more carbon dioxide to compensate for hypoxia and relieve the symptoms of dyspnea, and even involuntarily breathe with a big mouth. Because there are many patients who repeatedly experience symptoms such as "hypoxia" and "difficulty in breathing" in a resting state (or when the amount of activity is very small) and go to the hospital for treatment, after examination and doctor's evaluation, there is no obvious tissue or organ damage that is sufficient to cause hypoxia and dyspnea; the "dyspnea" of this type of patients has another characteristic: the harder they breathe and the faster their breathing rate, the symptoms of chest tightness, shortness of breath, and panic will not only not be relieved, but often worsen, and they will also experience dizziness, cold sweats, numbness of the lips and limbs, and even tetany, hallucinations, and temporary loss of consciousness, and they are sent to the hospital for emergency treatment. This type of stress-induced acute hyperventilation reaction is not uncommon in the emergency room. The brain mistakenly sends out an "oxygen deficiency" warning signal, causing the body to feel "difficulty breathing" and increase the frequency and amplitude of breathing. The concentration of O2 in the blood exceeds the physiological needs of the human body, while the CO2 concentration continues to decrease (hyperventilation), leading to respiratory alkalosis; when the blood concentration of CO2 drops significantly in a short period of time, severe acute respiratory alkalosis will cause the above-mentioned series of acute neurological, muscular and mental reactions.

As for why the brain sends out false hypoxia signals, the mechanism is relatively complex and the research conclusions are not yet completely clear. The disorder of the regulation function of the autonomic nervous system (sympathetic-vagus nerve) is one of the most commonly mentioned mechanisms, but it is far more than that. The causes of this "false hypoxia" are often related to anxiety, stress, strong emotional stimulation, etc.; recently, many people who have been "healthy" after being infected with the new coronavirus have also shown this non-pathological "false hypoxia" performance. They have been "healthy" for as short as one month and as long as more than half a year. Although there is no substantial damage to the functions of organs such as the heart and lungs, they will experience chest tightness, shortness of breath, and palpitations from time to time. Some of these patients feel that their daily activities or physical exercise have not exceeded the past, but they are more prone to "breathlessness" than before, and the blood oxygen saturation is normal. They can only sigh that "the physical strength is much worse than before!"

Let us imagine a scene like this: an ancient hunter is hunting a hare not far away in the forest. He gently pulls the bow and holds his breath for several seconds while aiming at the target. The reason for holding his breath temporarily is to make as little sound as possible so as not to disturb the prey with sensitive hearing, and also to maintain the stability of the aiming action; when the arrow leaves the string and hits the prey, the hunter can't help but take a deep breath or two.

Humans have long formed a physiological mechanism for stress. Sometimes when we are in a state of high concentration and mental tension, we will hold our breath for a few seconds until the brain senses an increase in the carbon dioxide concentration and a decrease in the oxygen concentration in the blood. It then sends out a "hypoxia" warning signal. We will immediately resume our breathing because of "chest tightness", and breathe more vigorously to compensate for the hypoxia caused by the suspension of breathing.

Some in-depth studies have found that if we are under high stress and high tension for a long time and need to constantly concentrate on certain points, the above-mentioned "short-term breath holding - hypoxia warning - compensatory deep breathing" situation will occur repeatedly at irregular intervals, making the breathing rhythm and amplitude irregular; further, if we are often under high stress and high tension for a long time, in order to adjust this irregular breathing rhythm of repeatedly "interrupting breathing and then compensating breathing", our brain will lower the warning value of CO2 concentration in the blood, that is, increase the sensitivity to hypoxia, so the breathing rate increases and the ventilation volume increases to respond to possible "hypoxia" in advance; however, under the repeated stimulation of continuous high-pressure state, the brain continues to lower the warning value of blood CO2 concentration, and its sensitivity to hypoxia continues to increase.

Thus, on the one hand, the human body maintains a faster breathing rate and a larger ventilation volume, so that the oxygen concentration in the blood is continuously maintained at a high level and the carbon dioxide concentration is continuously at a low level. The mild respiratory alkalosis caused by this continuous hyperventilation causes the human body to experience palpitations (increased heart rate), increased sweating (sympathetic nerve excitement), headaches (cerebral vasoconstriction, increased cerebral blood flow), chest tightness (repeated "false hypoxia" signals due to increased sensitivity to hypoxia), anxiety, irritability, etc.; not only that, some people will involuntarily form the habit of breathing through their mouths, which is also to obtain a larger ventilation volume. The long-term habit of breathing through the mouth will not only cause an increase in pathogenic anaerobic bacteria colonizing the nasal mucosa, dehydration of the respiratory mucosa, and obstruction of airway secretion excretion, but also increase snoring during sleep and the risk of obstructive sleep apnea.

On the other hand, on the basis of hyperventilation and mild respiratory alkalosis caused by continuous anxiety, tension and high pressure, once new or greater factors that may cause stress appear (such as strong emotional fluctuations, new stressors, environmental stimulation, extreme fatigue or significant physical discomfort caused by acute diseases, etc.), the body's "pseudo-hypoxia" reaction will be aggravated, and the situation mentioned at the beginning of this article may occur: continuous increase in breathing amplitude and frequency - the feeling of "hypoxia" is more obvious - more large breaths - severe hyperventilation and respiratory alkalosis and a series of acute complications. As for whether the "pseudo-hypoxia" symptoms such as chest tightness and shortness of breath in some new crown "healthy" people are related to the above mechanism, further research is needed, but repeated excessive breathing is also not helpful in relieving symptoms.

In short, our bodies will be misled by "hypoxia" signals due to the combined effects of some factors and physiological mechanisms. As long as it is determined through scientific evaluation that chest tightness and shortness of breath are not true hypoxia reactions caused by pathological factors, it is even more important to avoid breathing too quickly and too much. Excessive ventilation caused by "big breaths" not only does not help improve symptoms, but may also trigger a series of more serious symptoms.

So how should we respond?

1. Combine work and rest, and "relax and work at the same time", avoid being in a state of tension and high pressure for a long time, and try to relieve negative emotions, pressure and other stimuli in time by diverting attention and communicating effectively.

2. Maintaining a moderate amount and appropriate intensity of aerobic exercise and practicing traditional health exercises (such as Ba Duan Jin, Tai Chi, etc.) can help regulate autonomic nervous function, improve the body's "anti-stress" ability, and reduce the chance of "false hypoxia" in the body.

3. "Slow breathing" exercises can be used to relieve symptoms such as chest tightness, shortness of breath, and palpitations caused by "false hypoxia", and reduce excessive breathing caused by "false hypoxia" and the damage it causes to the body. The key points are: ① Choose a quiet and comfortable environment as much as possible to relax the body and mind; ② Breathe through the nasal cavity, not with your mouth open; ③ Make the inhalation and exhalation movements gentle and even, and slow down the breathing frequency (no more than 10 times per minute). Practice for more than 10 minutes each time. It can also be used as a relaxation exercise during breaks between work and study.

Author: Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine

Emergency Department He Miao