Implantable flow sensor apparatus and method

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.

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.

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.

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.