Pulse oximeter

• US 20020198442A1
• Filed: 05/02/2002
• Published: 12/26/2002
• Est. Priority Date: 05/03/2001
• Status: Active Grant

• Current Assignee: Instrumentarium Dental Incorporated (Envista Holdings Corporation)
• Original Assignee: Instrumentarium Dental Incorporated (Envista Holdings Corporation)
• Inventors: Huiku, Matti, Rantala, Borje, Muuranta, Erno, Spoof, Markku
• Granted Patent: US 6,963,767 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence

Abstract

The invention relates to pulse oximeters used to measure blood oxygenation. The current trend towards lower power consumption has brought a problem of erroneous readings caused by intrachannel crosstalk, i.e. errors due to the coupling of undesired capacitive, inductive, or conductive (resistive) pulse power from the emitting side of the pulse oximeter directly to the detecting side of the oximeter. The pulse oximeter of the invention is therefore provided with means for detecting whether intrachannel crosstalk is present and whether it will cause erroneous results in the oxygenation measurements. The pulse oximeter is preferably further provided with means for eliminating intrachannel crosstalk which are adapted to control the measurement so that measurement signals can be obtained which are substantially void of crosstalk components.

Claims

1. A method for detecting the validity of measurement circumstances in connection with a monitoring device intended for determining the amount of at least one light absorbing substance in a subject, the monitoring device comprising

emitters for emitting radiation at a minimum of two wavelengths,

driving means for activating said emitters, and

a detector for receiving said radiation at said wavelengths and for producing an electrical signal in response to the radiation, the method comprising the steps of

driving an emitter by a drive signal having predetermined characteristics,

analyzing the electrical signal traveling from the direction of said detector in order to detect whether a crosstalk component caused by electric power coupled directly from said drive signal is present, and

taking predetermined measures when a crosstalk component is detected.

2. A method according to claim 1, wherein said analyzing step includes sampling the electrical signal and analyzing the samples obtained.

3. A method according to claim 2, wherein said sampling step includes

sampling the electrical signal by a synchronous detector, taking one sample per each pulse of the electrical signal, and

shifting the sampling moments so that samples of the pulses are obtained at different points for ascertaining the waveform of the pulses.

4. A method according to claim 2, wherein said sampling step includes sampling the electrical signal by an A/D converter, taking a plurality of samples per each pulse of the electrical signal.

5. A method according to claim 3 or 4, wherein the step of taking the predetermined measures includes generating a measurement signal essentially void of said crosstalk component.

6. A method according to claim 5, wherein said generating step includes removing the crosstalk component mathematically.

7. A method according to claim 5, wherein said generating step includes

adjusting the sampling moments on the basis of said samples in order to allow the crosstalk component to disappear from the electrical signal and

generating the measurement signal by sampling the electrical signal at the adjusted sampling moments.

8. A method according to claim 5, wherein said generating step includes

adjusting the pulse width of the drive signal and

generating the measurement signal by sampling the electrical signal resulting from the drive signal with the adjusted pulse widths.

9. A method according to claim 5, wherein said generating step includes changing the configuration of an amplifier stage amplifying the electrical signal.

10. A method according to claim 5, wherein said generating step includes grounding the shield of a cable containing the electrical signal.

11. A method according to claim 1, wherein said analyzing step includes determining the type of the crosstalk.

12. A method according to claim 1, wherein the step of taking the predetermined measures includes producing a warning of impending measurement errors when the electrical signal fulfils predetermined criteria.

13. A method according to claim 12, wherein

the drive signal comprises voltage pulses, the amplitude of which is insufficient to activate said at least one emitter, and

said producing step includes creating the warning when the amplitude of the electrical signal exceeds a predetermined threshold during said voltage pulses.

14. A method according to claim 12, wherein the drive signal includes current pulses of different amplitudes.

15. A method according to claim 14, further comprising the steps of

storing the values of the electrical signal corresponding to said different amplitudes and

estimating the value of the electrical signal corresponding to zero amplitude,

wherein the warning is generated when the estimated value exceeds a predetermined threshold value.

16. A method according to claim 14, further comprising the step of modulating the AC component of the current pulses, the warning being generated when the AC to DC ratio of the electrical output signal deviates essentially from that of the drive signal.

17. A method according to claim 14, further comprising changing of the DC level of the drive signal.

18. A method according to claim 12, wherein

the drive signal comprises a voltage pulse, the amplitude of which is sufficient to activate said at least one emitter, and

said driving step includes preventing current from flowing through said at least one emitter during said pulse, thereby preventing the emitter from generating radiation,

the warning being produced when the amplitude of the electrical signal exceeds a predetermined threshold during said pulse.

19. A method according to claim 1, wherein the amount of at least one light absorbing substance is determined in the blood of a subject.

20. A method according to claim 12, wherein the warning is given to the device itself.

21. A method according to claim 12, wherein the warning is given to a user of the device.

22. A method according to claim 1, wherein the monitoring device is a pulse oximeter.

24. An apparatus according to claim 23, further comprising crosstalk elimination means for generating a measurement signal essentially void of a crosstalk component.

25. An apparatus according to claim 23, wherein

the sampling means comprise a synchronous detector adapted to take one sample per each pulse of the electrical signal, and

the crosstalk elimination means are adapted to adjust the sampling moment so that the samples are obtained at pulse points where the crosstalk component is substantially negligible.

26. An apparatus according to claim 23, wherein

the sampling means comprise an A/D converter taking a plurality of samples per each pulse of the electrical signal, and

the crosstalk detection means and the crosstalk elimination means are introduced into the signal processing means.

27. An apparatus according to claim 23, wherein the driving means comprise

a current drive adapted to output current pulses for activating the emitters, and

a voltage drive adapted to output voltage pulses the amplitude of which is insufficient to activate the emitters.

28. An apparatus according to claim 23, wherein

the driving means are adapted to (1) supply voltage to one lead of an emitter and (2) simultaneously prevent current from flowing through said emitter, thereby preventing the emitter from generating radiation.

29. An apparatus according to claim 28, wherein the driving means are adapted to disconnect another lead of said emitter, thereby preventing current from flowing.

30. An apparatus according to claim 23, said apparatus being a non-invasive monitoring device, preferably a pulse oximeter.

23. An apparatus for non-invasively determining the amount of at least one light absorbing substance in a subject, the apparatus comprising

emitters for emitting radiation at a minimum of two different wavelengths,

driving means for activating said emitters,

a detector for receiving said radiation at said wavelengths and producing an electrical signal in response to the radiation,

sampling means for sampling the electrical signal, whereby a sampled signal is obtained,

signal processing means for determining said amount by processing the sampled signal, and

crosstalk detection means for analyzing whether a direct electric crosstalk component is present in the electrical signal, the direct electric crosstalk component being caused by electric power coupled directly from said driving means to said electrical signal.