Carotid sinus

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Carotid sinus
Gray513.png
Arteries of the neck. The carotid sinus is at the origin of the internal carotid artery.
Details
Artery Carotid artery
Nerve Branch of glossopharyngeal nerve to carotid sinus
Identifiers
Latin sinus caroticus
MeSH D002346
TA98 A12.2.04.008
A12.2.06.003
TA2 4367
FMA 50094
Anatomical terminology

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.

Contents

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 carotid sinus nerve, which is a branch of the glossopharyngeal nerve (CN IX). [2] [3] 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, Ludwig nerve), 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 [4] by baroreflex activation. Physical assault at this point, producing massive baroreflex activation can cause dramatic falls in blood pressure and cerebral ischemia. This is the mechanism of baroreflex activation therapy.

Disease

The carotid sinus often has atherosclerotic plaques because of disturbed hemodynamics (low wall shear stress, flow reversal/recirculation). [5] Since these plaques, if large and unstable, predispose to ischemic strokes and transient ischemic attacks, carotid endarterectomies are frequently done for prophylaxis.

Carotid sinus hypersensitivity

The carotid sinus baroreceptor can be oversensitive to manual stimulation from the pressure applied at the carotid sinus at the carotid bifurcation. It is a condition known as 'carotid sinus hypersensitivity' (CSH), 'carotid sinus syndrome' or 'carotid sinus syncope', in which manual stimulation causes large changes in heart rate and blood pressure, which can result in bradycardia, vasodilation, and hypotension. 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. Denervation is performed as treatment for this. [6] [7]

Usually older patients with syncope and unexplained falls often have coexisting conditions such as carotid sinus hypersensitivity, orthostatic hypotension, and vasovagal syncope. [7] [8]

Carotid sinus syndrome

Carotid sinus syndrome (CSS) 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. [9]

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. [4]

Massage

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 treatment for acute SVT. [10] It is less effective than pharmaceutical management of SVT with verapamil or adenosine, [11] but it is still the preferred first line of treatment in a hemodynamically stable patient. [12]

Carotid sinus reflex death

Carotid sinus reflex death is a potential etiology 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. Medical literature examining the use of carotid sinus massage involving brief gentle pressure of the carotid sinus in therapeutic settings as a diagnostic and therapeutic examination tool have reported few potentially fatal complications. [13] [14] [15] [16] [17] A carotid massage can also possibly dislodge a thrombus, or some plaque. This could lead to any number of life-threatening effects, including stroke.

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 self-defense technique, and is often taught in martial arts such as karate. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Vagus nerve</span> Main nerve of the parasympathetic nervous system

The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right vagus nerves, each containing about 100,000 fibres—but they are typically referred to collectively as a single subsystem.

Baroreceptors are sensors located in the carotid sinus and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that a proper blood pressure can be maintained.

<span class="mw-page-title-main">Glossopharyngeal nerve</span> Cranial nerve IX, for the tongue and pharynx

The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.

<span class="mw-page-title-main">Valsalva maneuver</span> Technique for equalising pressure in the middle ears

The Valsalva maneuver is performed by a forceful attempt of exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut while expelling air, as if blowing up a balloon. Variations of the maneuver can be used either in medical examination as a test of cardiac function and autonomic nervous control of the heart, or to clear the ears and sinuses when ambient pressure changes, as in scuba diving, hyperbaric oxygen therapy, or air travel.

<span class="mw-page-title-main">Palpitations</span> Perceived cardiac abnormality in which ones heartbeat can be felt

Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.

<span class="mw-page-title-main">Carotid body</span> Anatomical structure

The carotid body is a small cluster of chemoreceptor cells and supporting sustentacular cells situated at bifurcation of each common carotid artery in its adventitia.

<span class="mw-page-title-main">Solitary nucleus</span> Sensory nuclei in medulla oblongata

The solitary nucleus is a series of sensory nuclei forming a vertical column of grey matter in the medulla oblongata of the brainstem. It receives general visceral and/or special visceral inputs from the facial nerve, glossopharyngeal nerve and vagus nerve ; it receives and relays stimuli related to taste and visceral sensation. It sends outputs to various parts of the brain, such as the hypothalamus, thalamus, and reticular formation. Neuron cell bodies of the SN are roughly somatotopically arranged along its length according to function.

Cushing reflex is a physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing's triad of increased blood pressure, irregular breathing, and bradycardia. It is usually seen in the terminal stages of acute head injury and may indicate imminent brain herniation. It can also be seen after the intravenous administration of epinephrine and similar drugs. It was first described in detail by American neurosurgeon Harvey Cushing in 1901.

<span class="mw-page-title-main">Baroreflex</span> Homeostatic mechanism in the body

The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure causes the heart rate to decrease. Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels. Their function is to sense pressure changes by responding to change in the tension of the arterial wall The baroreflex can begin to act in less than the duration of a cardiac cycle and thus baroreflex adjustments are key factors in dealing with postural hypotension, the tendency for blood pressure to decrease on standing due to gravity.

<span class="mw-page-title-main">Paroxysmal supraventricular tachycardia</span> Medical condition

Paroxysmal supraventricular tachycardia (PSVT) is a type of supraventricular tachycardia, named for its intermittent episodes of abrupt onset and termination. Often people have no symptoms. Otherwise symptoms may include palpitations, feeling lightheaded, sweating, shortness of breath, and chest pain.

<span class="mw-page-title-main">Carotid sinus nerve</span>

The carotid branch of the glossopharyngeal nerve is a small branch of the glossopharyngeal nerve that innervates the carotid sinus, and carotid body.

Reflex bradycardia is a bradycardia in response to the baroreceptor reflex, one of the body's homeostatic mechanisms for preventing abnormal increases in blood pressure. In the presence of high mean arterial pressure, the baroreceptor reflex produces a reflex bradycardia as a method of decreasing blood pressure by decreasing cardiac output.

The Bezold–Jarisch reflex involves a variety of cardiovascular and neurological processes which cause hypopnea, hypotension and bradycardia in response to noxious stimuli detected in the cardiac ventricles. The reflex is named after Albert von Bezold and Adolf Jarisch Junior. The significance of the discovery is that it was the first recognition of a chemical (non-mechanical) reflex.

The Nicoladoni–Branham sign is named after Carl Nicoladoni, who first noticed the phenomenon of the pulse slowing in a patient with right arm phlebarteriectasia when the brachialis artery proximal to it was compressed. In modern medicine, the sign is elicited when pressure is applied to an artery proximal to an arteriovenous fistula and said to be positive if the following occurs:

The vasomotor center (VMC) is a portion of the medulla oblongata. Together with the cardiovascular center and respiratory center, it regulates blood pressure. It also has a more minor role in other homeostatic processes. Upon increase in carbon dioxide level at central chemoreceptors, it stimulates the sympathetic system to constrict vessels. This is opposite to carbon dioxide in tissues causing vasodilatation, especially in the brain. Cranial nerves IX and X both feed into the vasomotor centre and are themselves involved in the regulation of blood pressure.

<span class="mw-page-title-main">Syncope (medicine)</span> Transient loss of consciousness and postural tone

Syncope, commonly known as fainting or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching. Psychiatric causes can also be determined when a patient experiences fear, anxiety, or panic; particularly before a stressful event, usually medical in nature. When consciousness and muscle strength are not completely lost, it is called presyncope. It is recommended that presyncope be treated the same as syncope.

A vagal maneuver is an action used to stimulate the parasympathetic nervous system by activating the vagus nerve. The vagus nerve is the longest nerve of the autonomic nervous system and helps regulate many critical aspects of human physiology, including heart rate, blood pressure, sweating, and digestion through the release of acetylcholine. Common maneuvers that activate the vagus nerve include the Valsalva maneuver and carotid sinus massage, which can serve diagnostic or therapeutic functions.

A choke-out is a hand-to-hand combat tactic involving the use of a chokehold to cause syncope, or temporary loss of consciousness, at which point the choke is released. Common chokeholds in grappling used to accomplish a choke-out include the rear naked choke, arm triangle, triangle choke, and the guillotine.

The Czermak–Hering test is a vagal maneuver consisting of the application of external digital pressure to the carotid sinus. The test is performed at the patient's bedside by imposing moderate pressure with the fingers, repeatedly massaging the left or the right carotid arteries.

<span class="mw-page-title-main">Baroreflex activation therapy</span>

Baroreflex activation therapy is an approach to treating high blood pressure and the symptoms of heart failure. It uses an implanted device to electrically stimulate baroreceptors in the carotid sinus region. This elicits a reflex response through the sympathetic and vagal nervous systems that reduces blood pressure.

References

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