Review and Evaluation of Range-Gated, Pulsed, Echo-Doppler

The need for a quantitative transcutaneous method of volume-blood-flow measurement is clinically significant. Many methods of blood-flow detection and measurement have been tried, from plethysmography to nuclear magnetic resonance. These techniques lack the capability required to sense flow at a particular location. Ultrasonic Doppler techniques have the capability to overcome many of the limitations of these methods. Knowing the current amount of oxygen being supplied to the patient's tissues is a factor which can assist the clinician in the management of the patient. Volume blood flow may be one of the best indicators of available oxygen. It is also an indicator of the heart's ability to function as a pump to maintain normal body processes. Other factors of blood flow may have clinical significance. The velocity profile in the vessels affected by arterial occlusive disease may be an important variable to determine the state of the patient. Techniques were evaluated for the use of pulsed Doppler for blood-flow measurements, vessel dimensions, and velocity profiles. Until the development of pulse Doppler equipment, the use of ultrasonics was primarily qualitative. Doppler signals were previously processed and recorded as analog waveforms and the clinician based his conclusions on listening to the detected Doppler's signals. Currently available pulsed Doppler equipment are not flowmeters but velocity detectors. Velocity profiles were measured on blood flow in water-tank models to study the relationships between measured velocity and true flow and between measured velocity and hematocrit levels. The data indicate that the pulsed Doppler system can be pre-calibrated to measure quantitatively blood flow in water-tank models. Its application in clinical use requires further evaluation.