DOPPLER BLOOD FLOW SYSTEM AND METHOD USING SPECIAL ZERO FLOW RATE ANALYSIS

摘要

A Doppler blood flow system and method in which an ultrasonic wave (16) is reflected off of red blood cells (24) in blood flowing in tubing (20). The reflected ultrasonic wave (26) is digitally processed in the frequency domain. The flow rate of the blood is directly related to the average frequency of the Doppler signal. Because the Doppler blood flow system calculates flow rate solely on the basis of frequency, a special case exists at zero rate of flow where the received signal is not a valid Doppler flow signal, but rather purely noise. The noise at zero flow rate is random and will not have an average frequency which is unique to zero flow. The Doppler blood flow system and method must invoke a special case determination of when a zero flow condition in order to accurately provide a blood flow rate. The system utilizes a method of determining the rate of flow of a fluid containing particles flowing through a tube. An ultrasonic signal is transmitted through the tube at an oblique angle thereto. The ultrasonic signal which has been reflected off of the particles contained in the fluid is received as a received ultrasonic signal. The rate of flow of the fluid is calculated from the received ultrasonic signal using Doppler techniques. Whether the special case of the value of the rate of flow being equal to zero exists is determined and the value of the rate of flow is set equal to zero for the special case.