Pulse oximeter sensor with piece-wise function

• US 20020035318A1
• Filed: 04/16/2001
• Published: 03/21/2002
• Est. Priority Date: 04/17/2000
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Fein, Michael E., Mannheimer, Paul D., Porges, Charles E.
• Granted Patent: US 6,801,797 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 2562/085 combined with means for recording calibration data
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

A memory in a sensor is used to store multiple coefficients for a physiological parameter. In one embodiment, not only are the sensor'"'"'s specific calibration coefficients stored in a memory in the sensor for the formula to determine oxygen saturation, but multiple sets of coefficients are stored. The multiple sets apply to different ranges of saturation values to provide a better fit to occur by breaking the R to SpO2 relationship up into different pieces, each described by a different function. The different functions can also be according to different formulas for determining oxygen saturation.

Claims

1. A patient monitoring sensor comprising:

a sensor element for providing signals corresponding to a measured physiological parameter; and

a memory storing coefficients for use in a formula for determining said physiological parameter, said coefficients including

a first set of coefficients for use with a first formula for a first range of values associated with the signals, and

a second set of coefficients for use with either said first formula or a second formula for a second range of the values.

2. The patient monitoring sensor of claim 1 wherein said sensor is an oximeter sensor, and further comprising:

a light emitter for directing light at a patient; and

a light detector mounted to receive light from said patient.

3. The patient monitoring sensor of claim 2 wherein the values are either saturation values or ratiometric values.

4. The patient monitoring sensor of claim 2 wherein each set of coefficients comprises at least two coefficients.

5. The patient monitoring sensor of claim 2 wherein said coefficients correspond to a mean wavelength of said light emitter.

6. The patient monitoring sensor of claim 2 further comprising at least a third set of coefficients stored in said memory for a third range of said saturation values.

7. The patient monitoring sensor of claim 2 wherein said memory further comprises a second value indicating a breakpoint between said first and second ranges.

9. The oximeter system of claim 7 wherein said specified level is stored in said oximeter sensor.

10. The oximeter system of claim 7 wherein said specified level is other than 70 percent.

12. The oximeter sensor of claim 10 wherein said coefficients are dependent on a mean wavelength of said light emitter.

13. The oximeter sensor of claim 10 wherein said memory further stores a value indicating a signal breakpoint between said first and second sets of coefficients.

14. The oximeter sensor of claim 10 wherein said first and second sets of coefficients are used in the same formula.

15. The oximeter sensor of claim 10 wherein said first and second sets of coefficients are used in different formulas.

8. An oximeter system comprising:

an oximeter sensor;

an oximeter in communication with said oximeter sensor, said oximeter including an upper ratiometric signal value or saturation range and a lower ratiometric signal value or saturation range

a processor programmed to calculate oxygen saturations, for saturations or ratiometric signal values below a specified level, using a non-linear formula with coefficients.

11. An oximeter sensor comprising:

a light emitter for directing light at a patient;

a light detector mounted to receive light from said patient; and

a memory storing coefficients for use in at least one formula for determining oxygen saturation, said coefficients including at least a first set of coefficients and a second set of coefficients.

16. The oximeter sensor of claim 14 wherein said different formulas are nonlinear formulas.

17. The oximeter sensor of claim 14 wherein said different formulas are linear formulas.

19. The oximeter sensor of claim 17 wherein the values are either saturation values or ratiometric values.

20. The oximeter sensor of claim 17 wherein said coefficients are dependent on a mean wavelength of said light emitter.

21. The oximeter sensor of claim 17 wherein said first and second sets of coefficients are used in the same formula.

18. An oximeter sensor comprising:

a light emitter for directing light at a patient;

a light detector mounted to receive light from said patient; and

a memory storing coefficients for use in a formula for determining oxygen saturation, said coefficients including a first set of coefficients and a second set of coefficients,

said memory further storing an indication of a saturation for use in selecting between said first and second sets of coefficients.

22. An oximeter sensor comprising:

a light emitter for directing light at a patient;

a light detector mounted to receive light from said patient; and

a memory storing a plurality of values of oxygen saturation or ratio-of-ratio values used to determine oxygen saturation, said plurality of values corresponding to a mean wavelength of said light emitter.

23. The sensor of claim 22 wherein said values are usable for interpolation.

24. An oximeter system comprising:

an oximeter sensor comprising

a light emitter for directing light at a patient;

a light detector mounted to receive light from said patient; and

a memory storing a plurality of values of oxygen saturation or signal ratiometric values used to determine oxygen saturation, said plurality of values being dependent on a mean wavelength of said light emitter; and

an oximeter in communication with said oximeter sensor for receiving said plurality of values and a light detector signal, said oximeter being programmed to determine oxygen saturation from said light detector signal by fitting said oxygen saturation to a curve defined by said values stored in said memory.