Vasovagal response

Vasovagal episode
Classification and external resources
File:Gray793.png Vagus nerve
ICD-10	R55.
ICD-9	780.2
DiseasesDB	13777
MeSH	D019462

A vasovagal episode or vasovagal response or vasovagal attack (also called neurocardiogenic syncope) is a malaise mediated by the vagus nerve. When it leads to syncope or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.

There are a number of different syncope syndromes which all fall under the umbrella of vasovagal syncope. The common element among these conditions is the central mechanism leading to loss of consciousness. The differences among them are in the factors that trigger this mechanism.

Signs and symptoms

Among people with vasovagal episodes, the episodes are typically recurrent, usually happening when the person is exposed to a specific trigger. The initial episode often occurs when the person is a teenager, then recurs in clusters throughout his or her life. Prior to losing consciousness, the individual frequently experiences a prodrome of symptoms such as lightheadedness, nausea, the feeling of being extremely hot (accompanied by sweating), ringing in the ears (tinnitus), uncomfortable feeling in the heart, fuzzy thoughts, a slight inability to speak/form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, and sometimes a feeling a nervousness can occur as well. These last for at least a few seconds before consciousness is lost (if it is lost), which typically happens when the person is sitting up or standing. When sufferers pass out, they fall down (unless this is impeded); and when in this position, effective blood flow to the brain is immediately restored, allowing the person to wake up. Short of fainting a person may experience an almost undescribable weak and tired feeling resulting from a lack of oxygen to the brain due to a sudden drop in blood pressure. Tabor's describes this as the "feeling of impending death" caused by expansion of the aorta, drawing blood from the head and upper body.

The autonomic nervous system's physiologic state (see below) leading to loss of consciousness may persist for several minutes, so:

1. If sufferers try to sit or stand when they wake up, they may pass out again;
2. The person may be nauseated, pale, and sweaty for several minutes.

Cause

Typical triggers for vasovagal episodes include:

• Prolonged standing or upright sitting, particularly when standing with legs in a locked position for long periods of time—avoidance of long-term locking of one's legs in the standing position is taught in the military as well as in marching bands and drill teams.
• Standing up very quickly
• Stress
• Any painful or unpleasant stimuli, such as:
  • Venepuncture
  • Acupuncture
  • Hitting your funny bone
  • Experiencing medical procedures with local anesthesia
  • Post-surgical pain when standing up or moving too abruptly after the procedure
  • Giving or receiving a needle immunization
  • Watching someone give blood
  • Watching someone experience pain
  • Watching or experiencing medical procedures
  • Sight of blood
  • Occasions of slight discomfort, such as dental and eye examinations
  • Hyperthermia, a prolonged exposure to heat
  • High temperature, either in the environment or due to exercise
  • High pressure on or around the chest area after heavy exercise
• Arousal or stimulants, e.g. sex
• Sudden onset of extreme emotions
• Hunger
• Nausea or vomiting
• Dehydration
• Urination ('micturition syncope') or defecation, having a bowel movement ('defecation syncope')
• Abdominal straining or 'bearing down'
• Swallowing ('swallowing syncope') or coughing ('cough syncope')
• Random onsets due to nerve malfunctions
• Pressing upon certain places on the throat, sinuses, and eyes, also known as vagal reflex stimulation when performed clinically
• Water colder than 10 Celsius (50° F), or ice that comes in contact with the face, that stimulates the mammalian diving reflex
• High altitude
• Use of certain drugs that affect blood pressure, such as amphetamine
• Intense laughter

Pathophysiology

Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. In it, the nucleus tractus solitarius of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of parasympathetic nervous system (vagal) tone and withdrawal of sympathetic nervous system tone.

This results in a spectrum of hemodynamic responses:

1. On one end of the spectrum is the cardioinhibitory response, characterized by a drop in heart rate (negative chronotropic effect) and in contractility (negative inotropic effect) leading to a decrease in cardiac output that is significant enough to result in a loss of consciousness. It is thought that this response results primarily from enhancement in parasympathetic tone.
2. On the other end of the spectrum is the vasodepressor response, caused by a drop in blood pressure (to as low as 80/20) without much change in heart rate. This phenomenon occurs due to vasodilation, probably as a result of withdrawal of sympathetic nervous system tone.
3. The majority of people with vasovagal syncope have a mixed response somewhere between these two ends of the spectrum.

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

Diagnosis

In addition to the mechanism described above, a number of other medical conditions may cause syncope. Making the correct diagnosis for loss of consciousness is one of the most difficult challenges that a physician can face. The core of the diagnosis of vasovagal syncope rests upon a clear description by the patient of a typical pattern of triggers, symptoms, and time course. It is also pertinent to differentiate lightheadedness, seizures, vertigo and hypoglycemia as other causes.

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

1. A tilt table test
2. Implantation of an insertable loop recorder
3. A Holter monitor or event monitor
4. An echocardiogram
5. An electrophysiology study

Treatment

Treatment for vasovagal syncope focuses on avoidance of triggers, restoring blood flow to the brain during an impending episode, and measures that interrupt or prevent the pathophysiologic mechanism described above.

• The cornerstone of treatment is avoidance of triggers known to cause syncope in that person. However, new development in psychological research has shown that patients show great reductions in vasovagal syncope through exposure-based exercises with therapists.
• Because vasovagal syncope causes a decrease in blood pressure, relaxing the entire body as a mode of avoidance isn't favorable. A patient can cross his/her legs and tighten leg muscles to keep blood pressure from dropping so drastically before an injection.
• Before known triggering events, the patient may increase consumption of salt and fluids to increase blood volume. Sports and energy drinks may be particularly helpful.
• Discontinuation of medications known to lower blood pressure may be helpful, but stopping antihypertensive drugs can also be dangerous. This process should be managed by an expert.
• Patients should be educated on how to respond to further episodes of syncope, especially if they experience prodromal warning signs: they should lie down and raise their legs; or at least lower their head to increase blood flow to the brain. If the individual has lost consciousness, he or she should be laid down with his or her head turned to the side. Tight clothing should be loosened. If the inciting factor is known, it should be removed if possible (for instance, the cause of pain).
• Wearing graded compression stockings may be helpful.
• There are certain orthostatic training exercises which have been proven to improve symptoms in people with recurrent vasovagal syncope.
• Certain medications may also be helpful:
  • Beta blockers (β-adrenergic antagonists) were once the most common medication given; however, they have been shown to be ineffective in a variety of studies and are thus no longer prescribed.
  • Other medications which may be effective include: fludrocortisone, midodrine, SSRIs such as paroxetine or sertraline, disopyramide, and, in health-care settings where a syncope is anticipated, atropine.
• For people with the cardioinhibitory form of vasovagal syncope, implantation of a permanent pacemaker may be beneficial or even curative.

Prognosis

Vasovagal syncope is rarely life-threatening in itself, but is mostly associated with injuries from falling while having an episode.

See also

• Vagus reflex
• Vagovagal reflex
• Roemheld Syndrome

External links

• Dysautonomia Information Network
• Dysautonomia Youth Network of America, Inc.
• Seattle Community Network Autism - Information regarding syncope
• 12 More Pages-Live & Cope with Dysautonomia

ar:إغماء وعائي مبهمي tr:Vazovagal senkop