Carotid Sinus is also called carotid bulb. The human anatomy states that carotid sinus is the dilation of internal carotid artery at its point of origin, the common carotid artery bifurcation. The pressure is monitored by various sensitive receptors and nerve endings that are an integral part of Carotid artery.
There are innumerable barorecptors present inside the carotid sinus and are known to function as sampling area for different homeostatic related mechanisms that contribute in maintaining blood pressure. The Hearing sinus nerve which is an extension of cranial nerve IX or glossopharyngeal nerve innervates the carotid sinus baroreceptors. The synapses of of glossophyarngeal nerve occur in nucleus tractus solitaries or NTS. This NTS is placed inside the brainstem medulla. With the help of hypothalamus, the NTS amends the sympathetic and parasympathetic or vagal neuron activities inside the pons and medulla. These vagal neurons further organize the heart and blood vessels autonomic control. The aortic nerve or nerve of Cyon innervates the aortic arch baroreceptors and then meets the CN X or vagus nerve. It further joins the NTS.
The carotid sinus mostly suffers due to unsteady hemodynamics i.e. reversal or recirculation of flow or low wall shear stress. That is why we often find atherosclerotic plaques attacking carotid sinus. Many times these plaques are very large and highly unstable and can influence ischemic strokes, carotid endarterectomies, transient ischemic attacks and also lead to prophylaxis. The carotid sinus has been known to react over sensitively at times to stimulation triggered manually. This condition is also termed as carotid sinus hypersensitivity, carotid sinus syndrome or carotid sinus syncope. In this condition, manual stimulation has been found to cause huge shift in blood pressure or heart rate. Carotid sinus syndrome makes one loose consciousness temporarily and at times is accompanied by convulsive seizures depending upon the intensity of the carotid sinus reflex due to the pressure building up in either or both carotid sinuses.
Diagnosis of carotid sinus syncope is the main reason behind carotid sinus massage. It is also used for distinguishing supraventricular tachycardia (SVT) from ventricular tachycardia. It is used as a therapy for SVT, just as valsalva maneuver. Although its effects are comparatively much less than the pharmaceutical management doses of verapamil or adenosine it is preferred more to stable hemodyanmically unstable patients.
Carotid sinus reflex death uses application of manual stimulation to carotid sinus which leads to strong impulses in glossopharyngeal or Vagus nerve and can result in terminal cardiac arrest. Hence it is also termed as mechanism of death. In most of the death cases due to strangulation, hanging or erotic asphyxiation carodic sinus reflex is the reason of death, but the conclusions mostly are controversial in such cases. This reflex can also influence the other death causing factors like decreasing heart rate and/ or blood pressure. This is more common in old age or in patients with carotid sinus hypersensitivity.