Faint

Syncope is a transient loss of consciousness caused by reduced cerebral blood supply. Stopping blood flow to the brain for only 6 seconds (for example, with a sharp narrowing of the vessels during a bright emotion) guarantees a fainting, even count, as well as an overall decrease in oxygen supply to the brain by 20% over a short period of time (for example, in very stuffy rooms where we absorb significantly less oxygen).

The brain uses 20% of all oxygen, which enters the circulatory system, but still occupies only 2% of body weight, that is, the brain consumes more oxygen than any other organ. Therefore, it is especially sensitive to a sharp lack of oxygen and, in the case of such, decides to simply turn off and "wait out" until better times. When the supply of oxygen with blood resumes, the brain returns to its usual state.

Syncope can also occur if the normal level of oxygen in the blood is exceeded. See Hyperventilation in the lungs of man.

2023: What happens in the body during fainting. Scientific explanation

On November 1, 2023, American scientists from the University of California at Los Angeles released the results of a study giving an idea of ​ ​ what happens in the human body during fainting. Experts have identified a previously unknown group of sensory neurons that are involved in this process.

It is estimated that about 40% of people worldwide lose consciousness at least once in their lives. This condition can be provoked by heat, hunger or just a type of blood. In addition to the long-standing observation that fainting occurs as a result of decreased blood flow in the brain, the mechanism of the process remained a mystery. This is partly because researchers tend to focus on the isolated study of either the heart or the brain. In the new work, the researchers took a comprehensive approach.

UCLA scientists find out what happens in the human body during fainting

Scientists have discovered a group of sensory neurons called NPY2R VSNs that connect the heart to the brain stem. By combining high-resolution ultrasound imaging with optogenetics, the researchers stimulated these neurons in mice while tracking the animals' heart rate, blood pressure, breathing and eye movements. After activating the VSN, NPY2R rodents, which had previously moved freely, quickly fainted. At the same time, the mice showed all signs of syncope in humans: dilation of pupils, rolling of the eyes, a decrease in heart rate, blood pressure, respiratory rate and blood flow to the brain.

Now we know that there are receptors in the heart that turn it off when triggered, "said neurologist Jan Gert van Dijk, one of the authors of the work.

To better understand what happens inside the brain during fainting, the researchers used electrodes to record the activity of thousands of neurons from different brain regions in mice when the animals fainted. Activity decreased in all areas except one particular hypothalamic zone. Blocking this area resulted in longer episodes of unconsciousness.^[1]

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