<s>[INST] context: Carotid duplex scan Neurocardiogenic syncope is also called vasovagal syncope or vasodepressor syncope. It is considered to be an abnormality in the complex neurocardiovascular interactions responsible for maintaining systemic and cerebral perfusion. Under normal circumstances, upright posture causes venoul polling and a transient decrease in aerial pressure, resulting in unloading of baroreceptors. Reflex augumentation of sympathetic activity and parasympathetic withdrawl results in peripheral aerial vasoconstriction, venoconstriction and an increase in hea rate and contractility. These adaptive mechanisms serve to maintain normal systemic and cerebral perfusion. Individuals susceptible to neurocardiogenic syncope are unable to maintain the adaptive neurocardiovascular response to upright posture for prolonged periods. In these patients due to incompletely understood mechanisms the cardiopulmonary mechanoreceptors are stimulated resulting in increased neural stimulus to vasomotor centre. This results in reflex paradoxical vasodilation and bradycardia. The final result is hypotension, cerebral hypopeifusion, cerebral hypoxia and syncope. Diagnosis of neurocardiogenic syncope : Tilt table study It is used to evaluate patients with neurocardiogenic syncope. In a tilt table study the patient is strapped to a table which is then mechanically tilted to an upright position. While monitoring the pulse, blood pressure, electrocardiogram and sometimes blood oxygen saturation, the patient is left in a 'motionless standing position' for 20 to 30 minutes. When the patient's syncope is reproduced during the test a "positive" tilt table study is said to have occurred. During an upright tilt, a patient's cardiovascular system has to adjust itself in order to prevent a significant poion of the blood volume from pooling in the legs. These adjustments consists of a mild increase in hea rate and a constriction of blood vessels in the legs. When a normal individual is placed in an upright tilt, these cardiovascular adjustments occur very quickly, and there is no significant drop in the blood pressure. However, in patients with neurocardiogenic syncope, these adjustments do not occur. Carotid sinus massage In patients with neurocardiogenic syncope, the symptoms can be elicited by carotid sinus massage. Ohostatic blood pressure recording Supine and upright blood pressure monitoring should be done in all patients with neurocardiogenic syncope. Carotid duplex scan Carotid duplex scan is a non-invasive study to estimate the presence and severity of carotid narrowing due to atherosclerosis. In neurocardiogenic syncope, no organic cause is present, so carotid duplex scan has no role. [/INST] question: Neurocardiagenic syncope, the least useful investigation is : | options: A: Tilt table B: Carotid sinus massage C: Carotid duplex scan D: Ohostatic blood pressure recording | answer: C </s>