The relationship between resistance, pressure, and flow can be expressed by Ohm’s law: flow = pressure/resistance. Introduction to Basic Cerebrovascular Hemodynamics In this article, we will review TCD testing as a procedure and discuss its clinical applications of special interest to the primary care physician. It is currently under-utilized in part due to the lack of awareness about the diagnostic usefulness of this test. Transcranial Doppler (TCD) is a noninvasive ultrasound device that allows real-time evaluation of the intracranial cerebral circulation. Its use in neurology was first reported in 1982, 1 and since then, its convenience and growing range of uses have made it an attractive tool to evaluate the cerebrovascular tree in patients with neurovascular disorders. The pressure to contain increasing medical cost will likely result in increased utilization of this test in future.Ĭhristian Johann Doppler, a mathematician, physician, and astronomer, first described the Doppler principle in 1843. TCD is underused as a clinical tool despite well established indications. TCD with micro-bubble enhancement has comparable sensitivity to transesophageal echocardiogram in detecting right-to-left atrial cardiac shunts. It is useful for the evaluation of occlusive intracranial vascular lesions with many emerging indications in the management of ischemic stroke. Screening of children with sickle cell disease to assess and prevent ischemic strokes and monitoring for vasospasm after subarachnoid hemorrhage are well established, evidenced based utilizations of TCD. It can be repeated multiple times and can be used for continuous monitoring if needed. It is inexpensive, safe, and reliable when compared with other techniques. Transcranial Doppler (TCD) is a diagnostic tool that can be used at bedside to assess the cerebral vasculature noninvasively.
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