Reflex syncope entities

Reflex syncope is a brief loss of consciousness due to a neurologically induced drop in blood pressure and/or a decrease in heart rate. Before an affected person passes out, there may be sweating, a decreased ability to see, or ringing in the ears. Occasionally, the person may twitch while unconscious
Reflex syncope is divided into three types:
1. Vasovagal: Typically triggered by seeing blood, pain, emotional stress, or prolonged standing.
2. Situational: Triggered by urination, swallowing, or coughing
3. Carotid sinus: Due to pressure on the carotid sinus in the neck

Before losing consciousness, the individual frequently experiences early signs or symptoms such as
Lightheadedness
Nausea
Feeling of being extremely hot or cold (accompanied by sweating)
Ringing in the ears
Uncomfortable feeling in the heart
Fuzzy thoughts, confusion, a slight inability to speak or form words
Visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, black cloud-like spots in vision
Nervousness

Reflex syncope occurs in response to a trigger due to dysfunction of the heart rate and blood pressure regulating mechanism.
When heart rate slows or blood pressure drops, the resulting lack of blood to the brain causes fainting.

Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes.
The nucleus tractus solitarii of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous
- Enhancement of parasympathetic nervous system (vagal) tone
- Withdrawal of sympathetic nervous system tone.

This results in a spectrum of hemodynamic responses:

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.
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 dilation of the blood vessels, probably as a result of withdrawal of sympathetic nervous system tone.
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.

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

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