Carotid sinus

In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carotid sinus extends from the bifurcation to the "true" internal carotid artery.[1] The carotid sinus is sensitive to pressure changes in the arterial blood at this level. It is the major baroreception site in humans and most mammals.

Carotid sinus
Arteries of the neck. The carotid sinus is at the origin of the internal carotid artery.
Details
Arterycarotid artery
Nervebranch of glossopharyngeal nerve to carotid sinus
Identifiers
Latinsinus caroticus
MeSHD002346
TAA12.2.04.008
FMA50094
Anatomical terminology

Structure

The carotid sinus is the reflex area of the carotid artery, consisting of baroreceptors which monitor blood pressure.

Function

The carotid sinus contains numerous baroreceptors which function as a "sampling area" for many homeostatic mechanisms for maintaining blood pressure. The carotid sinus baroreceptors are innervated by the sinus nerve of Hering, which is a branch of the glossopharyngeal nerve (CN IX). The neurons which innervate the carotid sinus centrally project to the solitary nucleus in the medulla of the brainstem. The solitary nucleus indirectly modulates the activity of sympathetic and parasympathetic neurons in the medulla and pons through the hypothalamus. These neurons then regulate the autonomic control of the heart and blood vessels. The aortic arch baroreceptors are innervated by the aortic nerve (Nerve of Cyon), which combines with CN X (vagus nerve) and travels to the NTS.

Clinical significance

It is a sensitive site of the body because stimulation can drive large-scale reflex effects throughout the body. This can be used therapeutically in treatment of resistant hypertension[2] by baroreflex activation. Physical assault at this point, producing massive baroreflex activation can cause dramatic falls in blood pressure and cerebral ischemia.

Disease

The carotid sinus often has atherosclerotic plaques because of disturbed hemodynamics (low wall shear stress, flow reversal/recirculation).[3] Since these plaques, if large and unstable, predispose to ischemic strokes and transient ischemic attacks, carotid endarterectomies are frequently done for prophylaxis.

The carotid sinus can be oversensitive to manual stimulation, a condition known as carotid sinus hypersensitivity, carotid sinus syndrome or carotid sinus syncope, in which manual stimulation causes large changes in heart rate and/or blood pressure. This classically presents as a patient who has "fainted" (actually a presyncope) on several occasions while shaving, or in some other way coming into contact with their carotid sinus.

Carotid sinus syndrome is a temporary loss of consciousness that sometimes accompanies convulsive seizures because of the intensity of the carotid sinus reflex when pressure builds in one or both carotid sinuses.[4]

Treatment of resistant hypertension

Stimulation of baroreceptors at the carotid sinus can be used to treat resistant hypertension via activation of the baroreflex. A pacemaker-like device can be implanted to electrically stimulate the receptors chronically, which is found to lower blood pressure by 15-25 mmHg.[2]

Massage
See also: vagal maneuver and Czermak-Hering test

Massage of the carotid sinus, carotid sinus massage is used to diagnose carotid sinus syncope and is sometimes useful for differentiating supraventricular tachycardia (SVT) from ventricular tachycardia. Like the valsalva maneuver, it is a therapy for SVT.[5] It is less effective than pharmaceutical management of SVT with verapamil or adenosine[6] though is still the preferred first line of treatment in a hemodynamically stable patient[7]

Carotid sinus reflex death

Carotid sinus reflex death is a potential etiology[8] of sudden death in which manual stimulation of the carotid sinus allegedly causes strong glossopharyngeal nerve (Vagus nerve is for aortic arch baroreceptors) impulses leading to terminal cardiac arrest. Carotid sinus reflex death has been pointed out as a possible cause of death in cases of strangulation, hanging and autoerotic strangulation, but such deductions remain controversial. However, medical literature is replete with studies examining the use of carotid sinus massage as a diagnostic and therapeutic examination tool. In studies of thousands of uses on elderly patients, there were no complications of death or bradycardic events requiring treatment or resuscitation, even though this age group is more likely to be symptomatic from carotid sinus stimulation.[8] A carotid massage can also possibly dislodge a thrombus, or some plaque. This could lead to any number of life-threatening effects, including stroke.[9]

In martial arts and self defense

Stimulation of the carotid sinus via a slap or a strike, to induce (usually temporary, but sometimes lethal) loss of consciousness is a theatrical self-defense technique, and is often taught in martial arts such as karate.[10]

See also

References
  1. S., Pellerito, John; F., Polak, Joseph (2012). Introduction to vascular ultrasonography. Saunders/Elsevier. ISBN 9781437714173. OCLC 797855544.
  2. Scheffers, IJ; Kroon, AA; Schmidli, J; Jordan, J; Tordoir, JJ; Mohaupt, MG; Luft, FC; Haller, H; Menne, J; Engeli, S; Ceral, J; Eckert, S; Erglis, A; Narkiewicz, K; Philipp, T; de Leeuw, PW (5 October 2010). "Novel baroreflex activation therapy in resistant hypertension: results of a European multi-center feasibility study". Journal of the American College of Cardiology. 56 (15): 1254–8. doi:10.1016/j.jacc.2010.03.089. PMID 20883933.
  3. Glagov S, Zarins C, Giddens DP, Ku DN. Hemodynamics and atherosclerosis. Insights and perspectives gained from studies of human arteries. biod degradable Arch Pathol Lab Med. 1988 Oct;112(10):1018-31. PMID 3052352
  4. Wallbach, M; Koziolek, MJ (9 November 2017). "Baroreceptors in the carotid and hypertension-systematic review and meta-analysis of the effects of baroreflex activation therapy on blood pressure". Nephrology, Dialysis, Transplantation. doi:10.1093/ndt/gfx279. PMID 29136223.
  5. Lim SH, Anantharaman V, Teo WS, Goh PP, Tan AT. Comparison of treatment of supraventricular tachycardia by Valsalva maneuver and carotid sinus massage. Ann Emerg Med. 1998 Jan;31(1):30-5. doi:10.1016/S0196-0644(98)70277-X PMID 9437338
  6. Ballo P, Bernabo D, Faraguti SA. Heart rate is a predictor of success in the treatment of adults with symptomatic paroxysmal supraventricular tachycardia. Eur Heart J. 2004 Aug;25(15):1310-7. doi:10.1016/j.ehj.2004.05.011 PMID 15288158
  7. American Heart Association. Tachycardia algorithm. Advanced Cardiac Life Support Provider Manual (2007).
  8. Darrell L. Ross, Ted Chan Sudden Deaths in Custody
  9. Passig, K. Carotid sinus reflex death - a theory and its history. URL last accessed February 28, 2006.
  10. "Carotid Sinus strike/slap as an effective self defense technique". Full Potential Martial Arts. Retrieved 30 May 2015.

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