Simultaneous blood flow and hematocrit sensor

• US 20080058630A1
• Filed: 08/31/2007
• Published: 03/06/2008
• Est. Priority Date: 09/01/2006
• Status: Active Grant

• Current Assignee: Proteus Digital Health, Inc. (Otsuka Holdings Company Limited)
• Original Assignee: Proteus Digital Health, Inc. (Otsuka Holdings Company Limited)
• Inventors: Robertson, Timothy
• Granted Patent: US 8,172,762 B2
• Time in Patent Office: Days
• US Class Current: 600/368
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/026 Measuring blood flow A61B3/1233, A61B3/1241 take precedence
• CPC Class Codes: A61B 5/14535 for measuring haematocrit

Abstract

Embodiments of the present invention provide blood flow sensors that can be used for measurement of various physiological parameters under a wide array of conditions. In some embodiments, the blood flow sensor can be implanted into a blood vessel and left in place indefinitely and will unobtrusively measure and record data as the patient engages in regular daily activities. The data can later be read out by a clinician using a suitable interface. In other embodiments, the data is collected and analyzed within a data collection device implanted in or attached to the patient'"'"'s body, and the collection device can report to the patient on an ongoing basis or in the form of alerts issued when conditions requiring medical intervention are detected.

Claims

1. An implantable blood flow sensor comprising:

a substrate sized and shaped to be implantable in a blood vessel of a body of a patient;

a pair of current-flow terminals disposed on a top surface of the substrate and arranged to be placed in flowing blood;

a current source fabricated on the substrate and configured to transfer charge between the current-flow terminals;

a pair of sense electrodes disposed on the top surface of the substrate between the current-flow terminals and separated by a distance S; and

a detection circuit fabricated on the substrate configured to detect a potential difference between the sense electrodes, the potential difference correlating to a resistivity of flowing blood, and to produce an output signal at an output node, the output signal correlating to the potential difference.

2. The implantable blood flow sensor of claim 1 further comprising:

a transmitter unit coupled to the output node of the detection circuit and configured to transmit the output signal to a data collector.

3. The implantable blood flow sensor of claim 2 wherein the transmitter unit is configured to transmit via quasi-electrostatic coupling into a conductive tissue of the body of the patient.

4. The implantable blood flow sensor of claim 2 wherein the transmitter is fabricated on the substrate.

5. The implantable blood flow sensor of claim 1 further comprising a power supply unit configured to supply power to the current source and the detection circuit.

6. The implantable blood flow sensor of claim 5 wherein the power supply unit is further configured to receive power via a quasi-electrostatic coupling to a conductive tissue of the body.

7. The implantable blood flow sensor of claim 1 wherein the distance S is less than 10 microns.

8. The implantable blood flow sensor of claim 7 wherein the distance S is between about 6 and about 8 microns.

9. The implantable blood flow sensor of claim 7 wherein the detection circuit is further configured to detect discrete potential variations resulting from passage of individual red blood cells.

10. The implantable blood flow sensor of claim 9 wherein the discrete potential variations are used to extract a measurement of hematocrit.

11. A method of measuring a physiological parameter, the method comprising:

implanting a blood flow sensor in a blood vessel in a body of a patient, the blood flow sensor being configured to measure a resistivity of blood in the blood vessel and to report the measured resistivity;

communicably coupling a data collector to the blood flow sensor, wherein the data collector is implanted in or attached to the patient'"'"'s body;

operating the blood flow sensor to measure the resistivity and report the measured resistivity to the data collector; and

processing the measured resistivity to extract a physiological parameter.

12. The method of claim 11 wherein the blood flow sensor is configured to communicate wirelessly using quasi-electrostatic coupling to a conductive tissue of the body of the patient.

13. The method of claim 12 wherein the data collector comprises a pacemaker can configured to detect quasi-electrostatic signals propagating in the body of the patient.

14. The method of claim 12 wherein the data collector comprises a wearable unit including electrodes attachable to the patient'"'"'s skin and configured to detect quasi-electrostatic signals propagating in the body of the patient.

15. The method of claim 11 wherein the blood flow sensor is operated while the patient is away from a medical clinic.

16. The method of claim 11 wherein the extracted physiological parameter corresponds to a blood flow velocity.

17. The method of claim 11 wherein the extracted physiological parameter corresponds to hematocrit.

18. The method of claim 11 wherein the extracted physiological parameter corresponds to a stroke volume.

19. The method of claim 11 further comprising:

triggering a remedial action based on the extracted physiological parameter.

20. The method of claim 19 wherein the remedial action includes releasing a medication into the patient'"'"'s body.

21. The method of claim 19 wherein the remedial action includes alerting the patient to seek medical attention.