Flow measurement system

• US 4,781,525 A
• Filed: 07/17/1987
• Issued: 11/01/1988
• Est. Priority Date: 07/17/1987
• Status: Expired due to Term

• Current Assignee: Terumo Cardiovascular Systems Corporation (Terumo Corporation)
• Original Assignee: 3M Company
• Inventors: Hubbard, Lloyd C., Clausen, Earl W.
• Primary Examiner(s): Garrett, Robert E.
• Assistant Examiner(s): Kwon, John T.
• Application Number:
  US07/074,549
• Time in Patent Office: 473 Days
• Field of Search: 415/26, 415/30, 415/17, 417/22, 417/63
• US Class Current: 415/30
• CPC Class Codes: A61M 1/3663 Flow rate transducers; Flow integrators
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 60/113 in other functional devices, e.g. dialysers or heart-lung machines
• CPC Class Codes: A61M 60/148 in line with a blood vessel using resection or like techniques, e.g. permanent endovascular heart assist devices
• CPC Class Codes: A61M 60/232 Centrifugal pumps
• CPC Class Codes: A61M 60/38 Blood oxygenation
• CPC Class Codes: A61M 60/416 transmitted directly by the motor rotor drive shaft
• CPC Class Codes: A61M 60/554 of blood pressure
• CPC Class Codes: G01F 1/80 operating by measuring pressure, force, momentum, or frequency of a fluid flow to which a rotational movement has been imparted
• CPC Class Codes: G01N 11/14 by using rotary bodies, e.g. vane G01N11/16 takes precedence

Abstract

Blood flow rate in a motor driven centrifugal blood pump is measured indirectly and non-invasively by sensing a first parameter representative of pump RPM and a second parameter representative of motor torque. The blood flow rate is computed as a function of the first and second parameters. By measuring the second parameter in a zero flow condition while the motor is being driven at a known RPM, a viscosity calibration factor is determined which is used, together with the first and second parameters in the calculation of flow rate.

Claims

1. A method of indirectly and noninvasively measuring blood flow in an outlet line connected to a motor driven centrifugal blood pump of a type having an inlet, and outlet connected to the outlet line, a housing, and an impeller which is rotated by the motor to pump blood from the inlet to the outlet, the method comprising:

sensing a first parameter to provide a first signal representative of pump impeller RPM;

sensing a second parameter to provide a second signal representative of motor torque;

computing a blood flow rate in the outlet line as a function of the first and second signals; and

displaying a representation of the blood flow in the outlet line.

2. The method of claim 1 and further comprising:

determining a viscosity factor representative of viscosity of the blood; and

wherein the computing of a blood flow rate is a function of the viscosity factor.

4. The method of claim 1 wherein a motor which drives the pump is a DC electric motor and wherein the second parameter is a DC drive current to the DC electric motor.

5. The method of claim 1 wherein computing a blood flow rate comprises:

storing a plurality of RPM dependent tables which relate motor torque and blood flow rate;

selecting one of the tables based upon the first signal; and

determining a blood flow rate based upon the table selected and the second signal.

3. A method of indirectly and noninvasively measuring blood flow from a motor driven centrifugal blood pump, the method comprising:

sensing a first parameter to provide a first signal representative of pump RPM;

sensing a second parameter to provide a second signal representative of motor torque;

causing the pump to operate at a selected RPM;

clamping an outlet line from the pump to reduce blood flow to zero;

sensing the second parameter while the blood flow is zero and the pump is operating;

computing a viscosity factor representative of viscosity of the blood based upon the second signal as produced while the blood flow is zero and the pump is operating; and

computing a blood flow rate as a function of the first and second signals and the viscosity factor.

6. In a centrifugal blood pump system which includes a centrifugal blood pump having an inlet, an outlet, a housing and an impeller;

a motor which causes the impeller to rotate; and

means for controlling the motor to produce a selected RPM of the impeller;

the improvement comprising;

means for producing a first signal representative of RPM;

means for producing second signal representative of motor torque;

means for producing a third signal representative of blood flow rate from the outlet as a function of the first and second signals; and

means for displaying a representation of the blood flow rate from the outlet as a function of the third signal.

7. The invention of claim 6 and further comprising:

means for storing a viscosity factor; and

wherein the means for producing the third signal uses the viscosity factor.