System and method for determining the flow rate of blood in a vessel using doppler frequency signals

A system for determining flow rate of blood in a hemodialysis access which communicates the blood between two locations of a patient, the system comprising:

• an external dialysis circuit in communication with the blood in the access, the circuit comprising an inlet for diverting the blood from the access into the circuit, and an outlet for returning the blood from the circuit into the access, wherein the access has a flow rate (QD) downstream from the inlet and before the outlet, and a flow rate (QA) upstream from the inlet;
• a pump disposed between the inlet and the outlet, the pump pumping the diverted blood in the circuit and returning the diverted blood into the access using a pump flow rate;
• an ultrasonic sensor in communication with the blood in the access downstream from the inlet and before the outlet, the ultrasonic sensor sensing the downstream flow rate (QD) and generating at least two downstream Doppler frequency signals including a first downstream Doppler frequency signal when the pump has a first pump flow rate and a second downstream Doppler frequency signal when the pump has a second pump flow rate;
• and
• a processor connected to the ultrasonic sensor and the pump, the processor determining the upstream flow rate (QA) when the pump has a selected pump flow rate first and second downstream Doppler frequency signals and the selected pump flow rate.

A system for determining flow rate of blood in a vessel which communicates the blood between two locations of a patient, the system comprising:

• an intravascular catheter in communication with the blood in the vessel, the catheter having an inlet for diverting the blood from the vessel into the catheter and an outlet for returning the blood from the catheter into the vessel, wherein the vessel has a flow rate (QD) downstream from the inlet and before the outlet, and a flow rate (QA) upstream from the inlet;
• a pump connected to the catheter, the pump pumping the diverted blood in the catheter and returning the blood into the vessel using a pump flow rate;
• an ultrasonic sensor in communication with the blood in the vessel downstream from the inlet and before the outlet, the ultrasonic sensor sensing the downstream flow rate (QD) and generating at least two downstream Doppler frequency signals including a first downstream Doppler frequency signal when the pump has a first pump flow rate and a second downstream Doppler frequency signal when the pump has a second pump flow rate;
• and
• a processor connected to the ultrasonic sensor and the pump, the processor determining the upstream flow rate (QA) when the pump has a selected pump flow rate from the first and second downstream Doppler frequency signals and the selected pump flow rate.

A method for determining flow rate of blood in a vessel which communicates the blood between two locations of a patient, the method comprising:

• providing a conduit in communication with the blood in the vessel, the conduit having a diversion point;
• diverting the blood from the vessel at the diversion point of the conduit, wherein the vessel has a flow rate (QA) upstream from the diversion point and a flow rate (QD) downstream from the diversion point;
• pumping the diverted blood into the conduit at a pump flow rate;
• sensing the downstream flow rate (QD) and generating at least two downstream Doppler frequency signals including a first downstream Doppler frequency signal when pumping the diverted blood into the conduit at a first pump flow rate and a second downstream Doppler frequency signal when pumping the diverted blood into the conduit at a second pump flow rate;
• selecting a selected pump flow rate;
• and
• processing the first and second downstream Doppler frequency signals and the selected pump flow rate to determine the upstream flow rate (QA).