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In diving, the syndrome known as 'carotid sinus reflex' usually occurs through a dilation or widening of the internal carotid artery in the neck.
Swelling can happen due to any form of stimulation to the carotid sinus artery. But, the most common cause is an excessively tight fitting exposure suit neck seal.
The carotid sinus baroreceptor is situated in the neck. It's an important organ for maintaining suitable blood pressure.
It is hypersensitive to various sources of pressure and to other kinds of external stimulation.
If the carotid has a condition of hypersensitivity, the detrimental effects may be triggered by accident.
For example, certain daily activities like shaving the neck or looking up may be enough to cause an attack of syncope.
As a result, it can lead to a rapid change in blood pressure and a lower than normal heart rate function (sometimes with dizzy spells, falling over, and a loss of consciousness).
Carotid sinus hypersensitivity is a potentially dangerous response condition and is normally the cause of dizziness and more.
Scuba divers should avoid wearing a tight-fitting wetsuit or dry suit neck seal because it will exert excess pressure at the side of the neck. This is why some divers call it the "tight collar syndrome".
It could also follow a rapid ascent in a dry suit, especially after a blowup with a large bubble of air collecting under the neck seal, which fails to give. In fact, carotid sinus syndrome symptoms may also be combined with pulmonary barotrauma.