Implantable flow sensor apparatus and method

• US 5,598,847 A
• Filed: 12/28/1994
• Issued: 02/04/1997
• Est. Priority Date: 12/28/1994
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Renger, Herman L.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US08/365,265
• Time in Patent Office: 769 Days
• Field of Search: 128/691, 128/692, 128/698, 128/713, 128/736, 73/204.11, 73/204.13, 73/204.23, 73/861
• US Class Current: 600/504
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/6876 Blood vessel
• CPC Class Codes: A61B 5/6884 Clamps or clips
• CPC Class Codes: G01F 1/6886 Pyroelectric elements

Abstract

An implantable blood flow sensor for measuring a blood flow rate through a blood vessel within a person'"'"'s body. The flow sensor includes a rigid cylindrical tube, sized to fit within the blood vessel, a heater attached to the tube, and a pyroelectric detector located within the tube. A predetermined amount of heat energy is produced by the heater and the pyroelectric detector monitors the resultant temperature change and generates a temperature signal based on the temperature change. A processor generates a data signal, based on the temperature change, that indicates the blood flow rate through the blood vessel or artery. The rigid tube protects the pyroelectric detector from external forces that may produce unwanted signals due to piezoelectric effects. Additionally, the heater may be incorporated into one of the electrodes of the pyroelectric detector as a serpentine path in the electrode that forms a resistive heating element. Also, a switch may be provided that prevents induced voltage signals caused by currents through the heater from reaching the processor.

Claims

1. An implantable flow sensor for measuring a rate of fluid flow within a fluid path, comprising:

a rigid tube sized to fit within the fluid path and to allow the fluid to flow along the tube;

a heater located within the tube and adapted to produce a predetermined amount of heat energy to increase the temperature of fluid within the fluid path;

a first pyroelectric detector adapted to detect changes in temperature caused by the heat energy and to generate a temperature signal based on the temperature change, wherein the first pyroelectric detector is coaxially located within the tube such that external forces applied to the tube are not transferred to the first pyroelectric detector; and

a processor that generates a data signal, based on the temperature signal, that indicates the fluid flow rate within the fluid path.

2. An implantable flow sensor, as defined in claim 1, wherein the heater is a resistance heating element.

3. An implantable flow sensor, as defined in claim 2, wherein:

the first pyroelectric detector includes first and second electrodes spaced apart from each other by a pyroelectric material, and

the first electrode is configured to serve as the resistive heating element.

4. An implantable flow sensor, as defined in claim 3, wherein the first electrode is etched in a serpentine path on one surface of the pyroelectric detector, to form the resistive heating element.

5. An implantable flow sensor, as defined in claim 1, wherein:

the rigid tube has a cylindrical shape.

6. An implantable flow sensor, as defined in claim 1, further comprising a second pyroelectric detector that operates in conjunction with the first pyroelectric detector to measure the direction of fluid flow.

7. An implantable flow sensor for measuring a rate of fluid flow within a fluid path, comprising:

a rigid tube sized to fit within the fluid path to allow the fluid to flow along the tube;

a pyroelectric detector, formed of a relatively thin sheet of pyroelectric material coaxially located within the tube and attached to an inside surface of the tube such that external forces applied to the tube are not transferred to the pyroelectric detector, wherein the pyroelectric detector detects changes in temperature and generates a temperature signal based on the temperature change, the pyroelectric detector having a first detector electrode sandwiched between the tube surface and one surface of the pyroelectric material and having a second detector electrode that is etched in a serpentine path on the other surface of the pyroelectric detector to form a heater;

an electrical power source that is switchably connected to the heater for a predetermined time period to cause the heater to produce a predetermined amount of heat energy;

an amplifier having an input terminal that receives the temperature signal from the pyroelectric detector allowing the amplifier to buffer the received temperature signal and produce a data signal that indicates the fluid flow rate within the fluid path; and

a switch connected to the input terminal of the amplifier and configured to operate during the predetermined time period so that stray signals produced by currents through the heater are not received by the amplifier.

8. A blood flow sensor for measuring a flow rate of blood pumped by a person'"'"'s heart through a blood vessel and for supplying a data signal indicating the measured blood flow rate to an implantable heart pacemaker, comprising:

a rigid cylindrical tube sized to fit within the blood vessel and to allow the blood to flow along the tube;

a heater located within the tube and adapted to produce a predetermined amount of heat energy to increase the temperature of blood within the blood vessel;

a first pyroelectric detector coaxially located within the tube and adapted to detect changes in temperature caused by the heat energy and to generate a temperature signal based on the temperature change; and

a processor that generates the data signal, based on the temperature signal, that indicates the blood flow rate through the blood vessel.

9. A method for measuring a rate of fluid flow within a fluid path, comprising:

providing a rigid tube sized to fit within the fluid path and to allow the fluid to flow along the tube;

heating the fluid and tube by supplying a predetermined quantity of heat energy; and

providing a first pyroelectric detector coaxially located within the tube that detects changes in temperature caused by the heating and generates a temperature signal based on the temperature change, wherein external forces applied to the tube are not transferred to the first pyroelectric detector; and

processing the temperature signal to generate a data signal that indicates the fluid flow rate within the fluid path.

10. A method for measuring a rate of fluid flow within a fluid path as defined in claim 9, wherein:

the step of providing a first pyroelectric detector comprises providing first and second electrodes spaced apart from each other by a pyroelectric material; and

the step of the heating the fluid and tube comprises using the first electrode to heat the fluid and tube.

11. A method for measuring a rate of fluid flow within a fluid path, as defined in claim 9, wherein the first electrode is etched in a serpentine path on the surface of the pyroelectric detector to form the resistive heating element.

12. A method for measuring a rate of fluid flow within a fluid path, as defined in claim 9, further comprising, providing a second pyroelectric detector that operates in conjunction with the first pyroelectric detector to measure the direction of fluid flow.

13. An implantable flow sensor for measuring a rate of fluid flow within a fluid path, comprising:

a rigid tube sized to fit within the fluid path and to allow fluid to flow along the tube;

a heater adapted to increase the temperature of fluid within the fluid path; and

a pyroelectric detector coaxially located within the tube such that external forces applied to the tube are not transferred to the pyroelectric detector, the pyroelectric detector adapted to detect changes in temperature and to generate a temperature signal based on the temperature change.

14. An implantable flow sensor for measuring a rate of fluid flow within a fluid path, comprising:

a rigid tube sized to fit within the fluid path to allow fluid flow a fluid path; and

a pyroelectric detector, formed of a relatively thin sheet of pyroelectric material attached to a surface of the tube, wherein the pyroelectric detector detects changes in temperature and generates a temperature signal based on the temperature change, the pyroelectric detector having a first detector electrode sandwiched between the tube surface and one surface of the pyroelectric material and having a second detector electrode that is etched in a serpentine path on the other surface of the pyroelectric detector to form a heater, wherein the pyroelectric detector is coaxially located within the tube such that external forces applied to the tube are not transferred to the pyroelectric detector.