Transcranial Doppler Ultrasound (TCD)

Transcranial Doppler ultrasound has been used to estimate cerebral blood flow velocity (CBFv) under a variety of conditions including orthostasis, Valsalva maneuver, etc. It has been used in functional form to interrogate the various branches of the Circle of Willis to localize and lateralize stroke and has been used to demonstrate that chronic orthostatic intolerance and POTS involve marked changes in cerebral blood flow velocity which appear to coincide with the onset of hyperpnea and often dyspnea.  We use a pulse range-gated 2 MHz probe focused by a plastic lens (Multigon TCD System 500M) via the anterior transtemporal approach to insonate the left and right middle cerebral artery (MCA). Data are synchronized with SGP, IPG, HR, and BP data through the DATAQ A/D interface. If the diameter of the MCA is relatively unchanged throughout an experiment, and if changes in maximum flow velocity can be substituted for changes in average velocity (the usual assumption which can be demonstrated for pulsatile laminar flow regimes) then changes in flow velocity reflect relative changes in flow. Changes in the MCA are often taken to be reasonably representative of overall cerebral blood flow changes if changes are global. The quantity [(Mean arterial pressure at heart level) (.776* height of the MCA above the right atrium)] estimates the mean arterial pressure at the MCA. Autoregressive modeling of mean BP and CBFv  following the same principles used in obtaining any transfer function can be used to estimate cerebral autoregulation capability.

 

The transcranial Doppler probe is placed on the left anterior temporal area to insonate the middle cerebral artery (MCA).
A typical TCD signal is shown in the upper panel with corresponding arterial pressure signal shown in the lower panel.;
 

 


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Peripheral Vascular Properties Measured by Strain Gauge Plethysmography (SPG)
Laser Doppler Flowmetry (LDF)
Indicator Techniques to Measure Blood Volume and Cardiac Output
Heart Rate and Blood Pressure
Near Infrared Spectroscopy
Microneurography and Muscle Sympathetic Nerve Activity (MSNA)
Transcranial Doppler Ultrasound (TCD)
Impedance Plethysmography (IPG)
Skeletal Muscle Pump