Why do some people faint when they see blood?

Some people may experience dizziness and fainting when they see blood. According to cardiovascular experts, this may be a special physiological reflex, fainting due to parasympathetic nerve reflex.

Many people have felt dizzy, pale, and fainted when they saw blood or an open wound bleeding. According to Master, Doctor Ngo Hang Vinh, Head of the Department of Cardiology 2, Xuyen A General Hospital, Ho Chi Minh City, fainting is defined as a state of transient loss of consciousness due to cerebral ischemia, which occurs quickly and recovers completely. It is necessary to distinguish it from pseudo-fainting (also known as fainting), which is due to exhaustion due to other diseases, low blood pressure, but there is no loss of consciousness like fainting.

There are some diseases that have symptoms of loss of consciousness similar to fainting, causing confusion in concept and classification. These are neurological diseases such as generalized epilepsy causing apnea, brain hypoxia causing loss of consciousness, or cerebrovascular accident, or diseases that cause sudden cardiac arrest and death that can be saved, or toxic diseases that cause coma... These diseases cause prolonged loss of consciousness and can leave neurological sequelae, unlike fainting which is completely self-recovery.

According to Dr. Ngo Hang Vinh, fainting is divided into three main groups: cardiac fainting, postural hypotension, and parasympathetic reflex fainting. For example, a person with an arrhythmia that is too fast or too slow for a few seconds can cause fainting and spontaneous recovery, or when changing from lying to standing position suddenly causes severe hypotension and fainting, or due to parasympathetic reflex in situations of neuralgia, abdominal pain, or excessive fear.

Fainting at the sight of blood, this is a type of fainting due to parasympathetic nerve reflex.

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Causes of fainting when seeing blood

In the case of fainting when seeing blood, this is a type of fainting due to parasympathetic reflex with a similar mechanism as above. When a person sees blood and is afraid, the sympathetic nervous system is first activated, causing rapid heart rate and palpitations, but the parasympathetic nervous system will also be activated to balance it out. If the parasympathetic reflex is too strong, it will cause a slow heart rate and sudden dilation of blood vessels, causing fainting.

With these diseases, when medical examination will not see physical damage in the cardiovascular and nervous system, but the problem is due to dysfunction of sympathetic and parasympathetic nervous regulation. These patients can often have symptoms of hypotension when standing for a long time, possibly accompanied by fainting.

"Fainting at the sight of blood, or neurally mediated fainting, is generally benign. However, as mentioned above, many cardiovascular neuropathies can cause similar symptoms, which can be confusing. Therefore, patients need to see a cardiologist or neurologist for in-depth examination of underlying cardiovascular diseases such as cardiomyopathy, myocardial ischemia, dangerous arrhythmias, valvular heart disease, epilepsy, cerebrovascular disease, etc.," Dr. Vinh shared.

Source: https://thanhnien.vn/vi-sao-mot-so-nguoi-de-ngat-khi-thay-mau-185251027234105736.htm