METHOD AND APPARATUS FOR MEASURING BLOOD VOLUME

• US 20080269581A1
• Filed: 04/23/2008
• Published: 10/30/2008
• Est. Priority Date: 04/24/2007
• Status: Abandoned Application

• Current Assignee: Scisense Inc. (Measurement Innovations Corp.)
• Original Assignee: Scisense Inc. (Measurement Innovations Corp.)
• Inventors: Wood, Kim, Plouf, Peter, Hodgson, P. Chad
• Application Number:
  US12/108,434
• Publication Number:
  US 20080269581A1
• Time in Patent Office: Days
• US Class Current: 600/345
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2560/0252 using ambient temperature
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/02055 Simultaneously evaluating both cardiovascular condition and temperature
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61B 5/6852 Catheters
• CPC Class Codes: G01F 22/00 Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for

Abstract

In one aspect, a conductance catheter is provided for measuring the volume of a fluid. The conductance catheter comprises a series of electrodes and a circuit to compensate for variations in sensitivity of the electrodes in the catheter. In another aspect, a resistivity sensor is provided for determining the resistivity of a fluid. The sensor comprises a series of electrodes spaced such that the total distance between endmost electrodes does not exceed the diameter of the catheter deploying the sensor.

Claims

1. A sensing tip for measuring the volume of a fluid comprising one or more electrodes for measuring said volume and a resistivity sensor disposed on said tip in communication with said fluid to incorporate a current measurement of resistivity during measurement of said volume.

2. The sensing tip according to claim 1 wherein said resistivity sensor comprises a series of resistivity electrodes spaced from each other such that a total distance between endmost ones of said resistivity electrodes does not exceed the diameter of said sensing tip.

3. The sensing tip according to claim 2 wherein said resistivity electrodes are diametrically spaced.

4. The sensing tip according to claim 2 wherein said resistivity electrodes are axially spaced.

5. The sensing tip according to claim 1 configured for continuously obtaining said measurement of resistivity.

6. A system for measuring volume of a fluid comprising a sensing tip having a plurality of pairs of electrodes, each pair of electrodes being connected to a circuit to compensate for variations in sensitivity of respective pairs of electrodes according to the positioning of said respective pairs along said sensing tip.

7. The system according to claim 6 wherein said circuit comprises individual gain and offset circuits to adjust the strength of a respective signal.

8. The system according to claim 7 comprising an output for displaying said respective signal to facilitate adjustment of said gain and offset circuits.

9. The system according to claim 6 comprising a control box for calibrating said sensing tip, said control box including a gain and offset circuit for each pair of electrodes to adjust the strength of a respective signal;

and a monitor for displaying said respective signal to facilitate adjustment of said gain and offset circuits.

10. The system according to claim 9 wherein said control box obtains a resistivity measurement from said sensing tip and incorporates a value of resistivity into a calibration measurement.

11. The system according to claim 9 comprising a plurality of cuvettes for containing fluids of differing properties.

12. A method for calibrating a sensing tip used for measuring volume of a fluid comprising inserting said sensing tip into a plurality of cuvettes containing fluids having differing properties, and when in each well, said method comprises:

obtaining a plurality of conductance signals using a plurality of electrodes on said sensing tip;

adjusting said conductance signals to compensate for variations is sensitivity of said pairs of electrodes due to the positioning of said electrodes along said sensing tip;

obtaining a measurement of resistivity; and

using said conductance signals and said measurement of resistivity to calibrate said sensing tip.

13. The method according to claim 12 wherein said differing properties comprises differing volumes and said measurement of resistivity is obtained using a resistivity measurement on said sensing tip.

14. The method according to claim 12 wherein volume measurements obtained by said sensing tip are calibrated according to a linear relationship.

15. The method according to claim 12 wherein said differing properties comprises differing known values of conductance and said method comprises providing a segmental output that is proportional to the conductance of the fluid in the respective cuvette.

16. A method for positioning a sensing tip disposed in a ventricle comprising obtaining an excitation waveform generated by one pair of electrodes disposed on said sensing tip;

obtaining a conductance waveform sensed by another pair of electrodes disposed on said sensing tip;

comparing said waveforms to determine a phase shift between said waveforms; and

adjusting said positioning until said phase shift is deemed acceptable.

17. The method according to claim 16 wherein said comparing comprises superimposing said waveforms to provide a visual indication of said phase shift.

18. The method according to claim 16 wherein said phase shift is determined by comparing zero-crossings of said waveforms.

19. The method according to claim 16 performed in real time while said sensing tip is measuring volume of fluid in said ventricle.

20. The method according to claim 16 performed during a calibration operation.