反射性暈厥

Reflex syncope is a brief loss of consciousness due to a neurologically induced drop in blood pressure and/or heart rate. An affected person may experience sweating, vision loss, or ringing in the ears before passing out. Sometimes, patients may have convulsions while losing consciousness. Complications of reflex syncope include injuries from falls.

There are three types of reflex syncope:

  1. Vasovagal syncope: Vasovagal syncope is usually triggered by the sight of blood, pain, emotional stress, or standing for long periods of time.
  2. Situational syncope: Situational syncope is usually triggered by urinating, swallowing, or coughing.
  3. Carotid sinus syncope: Carotid sinus syncope is caused by pressure on the carotid sinus in the neck.

The underlying mechanism involves the nervous system slowing the heart rate and dilating blood vessels, causing low blood pressure and thus not enough blood flowing to the brain. Diagnosis is made based on symptoms and after ruling out other possible causes.

Reflex syncope attacks can resolve without special treatment. Preventing attacks includes avoiding triggers. Drinking enough fluids, salt, and exercise may also help. If this is not enough to treat vasovagal syncope, medications such as midodrine or fludrocortisone can be tried. Sometimes, a cardiac pacemaker can be used for treatment. Reflex syncope affects at least one in 1,000 people each year. It is the most common type of syncope, accounting for more than 50% of all cases.

Signs and symptoms

Vasovagal syncope attacks often occur repeatedly, often when a susceptible person is exposed to a specific trigger. Before losing consciousness, individuals often experience early signs or symptoms such as dizziness, nausea, feeling extremely hot or cold, ringing in the ears, feeling uncomfortable, blurred thoughts, confusion, mild inability to speak or form words, weakness, and visual disturbances. Examples include lights that appear too bright, blurred or tunnel vision, dark cloud-like spots in vision, and feelings of nervousness. Symptoms may become more severe in the seconds to minutes before losing consciousness. It usually occurs when a person is sitting or standing.

When people lose consciousness, they fall, and when in this position, effective blood flow to the brain is immediately restored, allowing the person to regain consciousness. If the person is not lying completely flat or supine, and the head is still higher than the torso, blood cannot return to the brain quickly, which may lead to a state similar to an epileptic seizure. The neurons in the body will discharge and shut down, usually causing slight muscle twitching. But mostly it was still pretty intense.

Physiological states of the autonomic nervous system resulting in loss of consciousness may last for several minutes, so

  • If the patient tries to sit or stand after waking up, they may pass out again
  • The patient may feel nauseous, pale, and sweat for several minutes or hours

reason

Reflex syncope occurs due to triggering factors due to dysfunction of heart rate and blood pressure regulatory mechanisms. When the heart rate slows or the blood pressure drops, a lack of blood supply to the brain can cause fainting.

vasovagal nerve

Typical triggers include:

  • standing for long periods of time
  • emotional stress
  • pain
  • bloody scene
  • fear of needles
  • Time-varying magnetic fields (i.e., transcranial magnetic stimulation)

situational

  • After or during urination (urinary syncope)
  • Straining, such as having a bowel movement
  • cough
  • swallow
  • lift heavy objects

carotid sinus

Press on a certain part of the neck. This may occur when wearing a tight collar, shaving, or turning your head.

pathophysiology

Regardless of the trigger, the mechanisms of syncope in various vasovagal syncope syndromes are similar. The nucleus of the solitary tract in the brainstem is directly or indirectly activated by triggering stimulation, causing the tone of the parasympathetic nervous system (vagus nerve) to simultaneously increase and the tone of the sympathetic nervous system to weaken.

This results in a series of hemodynamic responses:

  • On the one hand is the cardioinhibitory response, characterized by a decrease in heart rate (negative chronotropic effect) and contractility (negative inotropic effect), leading to a reduction in cardiac output severe enough to cause loss of consciousness. This response is thought to be primarily due to increased parasympathetic tone.
  • On the other side is the vasodepressor response, caused by a drop in blood pressure (as low as 80/20) without much change in heart rate. This phenomenon occurs due to vasodilation, possibly as a result of reduced tone of the sympathetic nervous system.
  • Most patients with vasovagal syncope respond somewhere between these two extremes.

One explanation for these physiological responses is the Bezold-Jarisch reflex.

Vasovagal syncope may be part of an evolved response, specifically the fight-or-flight response.

diagnosis

In addition to the mechanisms mentioned above, many other medical conditions can cause syncope. Proper diagnosis of loss of consciousness is difficult. The core of the diagnosis of vasovagal syncope depends on a clear description of the typical pattern of triggers, symptoms, and time course.

Differentiating dizziness, seizures, vertigo, and hypoglycemia from other causes is relevant.

In patients with recurrent vasovagal syncope, diagnostic accuracy can usually be improved with one of the following diagnostic tests:

  • Tilt table test
  • Implantable loop recorder
  • Holter monitor or event monitor
  • Ultrasound heart test
  • electrophysiology studies

treat

Treatment of reflex syncope focuses on avoidance of triggering factors, restoration of blood flow to the brain during the impending attack, and measures to interrupt or prevent the pathophysiological mechanisms described above.

lifestyle changes

  • The cornerstone of treatment is avoiding triggers known to cause the person to faint. However, research shows that people experience significantly less vasovagal syncope through exposure-based exercises with a therapist if the trigger is mental or emotional. However, if the trigger is a specific drug, then avoidance is the only treatment.
  • A technique called "tensioning" may also be useful for people who have fainted from exposure to blood. The technique is accomplished by tightening the skeletal muscles for approximately 15 seconds when exposure occurs, and then slowly releasing them. Then repeat every 30 seconds for several minutes.
  • Since vasovagal syncope can cause a drop in blood pressure, it is disadvantageous to relax the entire body as a means of escape. Before the injection, a person can move or cross their legs and tighten their leg muscles to prevent a significant drop in blood pressure.
  • Prior to a known triggering event, affected individuals may increase salt and fluid consumption to increase blood volume. Sports drinks or drinks containing electrolytes may help.
  • People should know how to respond to further episodes of syncope, especially if they have prodromal symptoms: They should lie down and raise their legs, or at least lower their head to increase blood flow to the brain. At the very least, at the first onset of symptoms, the patient should try to move to a "safe" place, perhaps with a buffer, to prevent loss of consciousness. Positioning yourself in a position that minimizes the impact of a fall or collapse is ideal. A "safe" zone should be nearby because time is of the essence and these symptoms often climax within minutes, leading to loss of consciousness. If the patient loses consciousness, he should be placed in the recovery position. Tight clothes should be loose fitting. If the irritant is known, it should be eliminated if possible (eg the cause of the pain).
  • Wearing graded compression stockings may help.

drug

Certain medications may also help:

  • Beta-blockers (beta-adrenergic antagonists) were once the most commonly used drugs; however, various studies have shown that they are ineffective and they are no longer used. Additionally, they may cause syncope by lowering blood pressure and heart rate.
  • Medications that may be effective include: CNS stimulants fludrocortisone, midodrine, SSRIs (such as paroxetine or sertraline), disopyramide, and atropine or adrenaline in medical settings where syncope is expected white.
  • For people with cardiodepressant vasovagal syncope, permanent pacemaker implantation may be beneficial and even therapeutic.

Types of long-term treatment for vasovagal syncope include .

  • Preload proxy
  • vasoconstrictor
  • anticholinergic drugs
  • negative cardiotonic drugs
  • central agent
  • Machinery
  • Stopping medications known to lower blood pressure may help, but stopping antihypertensive medications can also be dangerous for some people. Taking antihypertensive medications may worsen

prognosis

A brief loss of consciousness usually does not cause lasting harm to health. Reflex syncope can also occur in otherwise healthy people for a number of possible reasons, usually something as trivial as standing on one's legs for an extended period of time.

The main risk with vasovagal syncope, or dizziness due to vertigo, is the risk of injury from falling while unconscious. Medication may prevent future vasovagal reactions; however, for some people, medication is not effective and they continue to experience fainting.

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