Spectrum analysis in ultrasonic Doppler blood flow monitoring: experience in its application to deeply situated vessels.

Ultrasonic Doppler monitoring of pulsatile flow patterns in the major systemic arteries has been rendered possible by the development of intravenous and intra-esophageal probes, thereby obviating major surgery or arterial catheterization. The information provided by Doppler flow signals obtained in this way is considerably enhanced by the use of spectrum analysis. The advantages include immunity from interference from noise or extraneous signals, the separation of two or more superimposed flow signals, and superposition of pressure and flow signals for time correlation and comparison.