Piezoelectric sensor in a living organism for fluid pressure measurement

• US 20040060362A1
• Filed: 09/24/2003
• Published: 04/01/2004
• Est. Priority Date: 10/24/2000
• Status: Active Grant

• Current Assignee: St. Jude Medical AB (Abbott Laboratories)
• Original Assignee: St. Jude Medical AB (Abbott Laboratories)
• Inventors: Nilsson, Kenth, Ljungstrom, Karin, Lidman, Johan, Kjellmann, Charlotte
• Granted Patent: US 6,886,411 B2
• Time in Patent Office: Days
• US Class Current: 73/754
• CPC Class Codes: A61B 2090/064 for measuring force, pressure or mechanical tension
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61M 2025/0002 with a pressure sensor at the distal end
• CPC Class Codes: G01L 9/06 of piezo-resistive devices
• CPC Class Codes: G01L 9/08 by making use of piezoelectric devices , i.e. electric circuits therefor

Abstract

The invention relates to a fluid pressure sensor for a lead (18) or catheter preferably intended to be placed in a living organism, such as the heart of a human being, said sensor comprising a piezoelectric element (4, 10, 11, 14) delivering an electric signal when subjected to a pressure variation, said piezoelectric element (4, 10, 11, 14) being designed to exhibit circumferential sensitivity and being disposed on at least parts of the outer surface of a rigid annular or tubular supporting structure (2). The rigidity of said sensor is such that the signal from the sensor relating to the pressure transferred to the sensor through an ongrowth of for instance tissue on the sensor would be at least 90% of the signal from the sensor without the ongrowth.

Claims

1. A fluid pressure sensor for a lead (18) or catheter preferably intended to be placed in a living organism, such as the heart of a human being, said sensor comprising a piezoelectric element (4,10,11,14) delivering an electric signal when subjected to a pressure variation, said piezoelectric element (4,10,11,14) being designed to exhibit circumferential sensitivity and being disposed on at least parts of the outer surface of a rigid annular or tubular supporting structure (2), characterized in that the rigidity of said sensor is such that

a) the charge generated by said sensor when said sensor is covered by a 1 mm thick layer of a silicon elastomer having a modulus of elasticity of at least 1.49 MPa (as measured with 6% deformation of the material) and is immersed in distilled water at 20°

C. to a depth of 50 mm in a pressure chamber and subjected to an increase of pressure amounting to 2 kPa, is at least 90% of the charge generated by said sensor when immersed into distilled water at 20°

C. to a depth of 50 mm in a pressure chamber and subjected to an increase of pressure of 2 kPa but not covered with said silicon elastomer layer,

b) the amplitude of the signal from said sensor when said sensor is covered by a 1 mm thick layer of said specific, commercially available silicon elastomer and is immersed in distilled water at 20°

C. to a depth of 50 mm in a pressure chamber and subjected to a pressure increase varying sinusoidally between 0 and 2 kPa at a frequency increasing from 1 to 30 Hz over the entire frequency range between 1 and 30 Hz does not deviate more than 3 dB from the amplitude of the signal obtained from said sensor when said sensor is immersed in distilled water at 20°

C. to a depth of 50 mm in a pressure chamber and subjected to a pressure increase varying sinusoidally between 0 and 2 kPa at a frequency increasing from 1 to 30 Hz but not covered by said silicon elastomer.

2. The sensor according to claim 1, characterized in that the piezoelectric element is formed as a layer (4) of piezoelectric material on the outer surface of said supporting structure (2).

3. The sensor according to claim 1, characterized in that the piezoelectric element is formed as strips (14) of piezoelectric material distributed at interspaces around the outer surface of the supporting structure (2).

4. The sensor according to claim 1, characterized in that the piezoelectric element is formed of a tube (11) or ring of piezoelectric material, positioned around said rigid supporting structure (2).

5. The sensor according to any of claims 1 through 4, characterized in that said supporting structure (2) also is formed of a piezoelectric material.

6. The sensor according to claim 5, characterized in that said supporting structure (2) is formed of a piezoelectric material different from the material in the piezoelectric layer (4, 10, 11, 14)

7. The sensor according to any of the claims 1 through 4, characterized in that said supporting structure (2) is formed of titanium, titanium alloy, titanium nitride, platinum, platinum alloy, niobium, niobium alloy, tantalum, tantalum alloy or carbon.

8. The sensor according to any of the claims 1 through 7, characterized in that said supporting structure (2) comprises a rigid tube or ring.

9. The sensor according to any of the claims 1 through 8, characterized in that layers of conductive material (6,13) are arranged in contact with the piezoelectric element (4,10,14) to form its electrodes, said layers comprising titanium, titanium alloy, titanium nitride, platinum, platinum alloy, carbon, niobium, niobium alloy, tantalum or tantalum alloy.

10. The sensor according to claim 8, characterized in that a low input impedance charge amplifier (8) is connected to the electrodes (6,13) of the piezoelectric element (4,10,11,14) to measure charge signals generated by the piezoelectric element when subjected to pressure variations.

11. A lead comprising a fluid pressure sensor according to any one of claims 1-10 characterized in that said piezoelectric element is formed as an annular or tubular rigid body (11).

12. The lead according to claim 11, characterized in that said lead is a bipolar lead and in that the sensor (20) is mounted coaxially with the lead, between the inner and outer insulating layers of the lead (18).