Electronic processor for pulse oximeter

• US 5,348,004 A
• Filed: 03/31/1993
• Issued: 09/20/1994
• Est. Priority Date: 03/31/1993
• Status: Expired due to Term

• Current Assignee: Nellcor Incorporated (Medtronic Plc)
• Original Assignee: Nellcor Incorporated (Medtronic Plc)
• Inventors: Hollub, Seth D.
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US08/040,839
• Time in Patent Office: 538 Days
• Field of Search: 128/633-634, 128/664-667, 356/39-41
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: G05B 19/0423 Input/output
• CPC Class Codes: G05B 2219/25249 Counter, timer plus microprocessor for real time, jitter
• CPC Class Codes: G05B 2219/2657 Blood, urine analyzer

Abstract

An electronic processor for calculating in vivo blood oxygenation concentration levels using pulsed light that eliminates both requirements for comparing photosensor signal amplitudes with analog/digital circuit dynamic ranges and also adjusting electronic processor parameters. The invention uses monolithic a/d converters with expanded capacity and a microcontroller/processor with a pulse control module to synchronize switching in an oversampling demodulator with pulsing of light sources to overcome prior circuitry limitations that consumed substantial central processor capacity.

Claims

1. An oximeter including a light emitting means and a photosensor means for converting received pulses of light from said light emitting means to an electrical signal having a dynamic range directly related to amplitudes of received pulses of light, said oximeter further comprising:

an analog-to-digital converter means for providing digitized signals accurately representative of amplitudes of received pulses of light; and

,

filter means; and

an oversampling demodulator means for providing a switched and filtered electrical signal from said photosensor means to said analog-to-digital converter means, said oversampling demodulator means including switching means for alternately connecting said electrical signal from said photosensor means to ground and to said filter means, said filter means having a cutoff frequency below both cycle rates for said electrical signal from photosensor means and switching rates of said switching means.

2. An oximeter according to claim 1 further including a pulse control module means for providing timing signals to control pulsing of light from said light emitting means and for also synchronizing said switching means for switching of said electrical signal with pulsing of light from said light emitting means.

3. An oximeter according to claim 2 further including

a readout means;

and

a central processor unit means which sends initial timing signals to said pulse control module means and display signals, responsive to said digitized signals from said analog-to-digital converter means, to said readout means, said central processor unit means sends no other signals for control of circuits used in said oximeter.

4. An oximeter including a light emitting means and a photosensor means for converting received pulses of light from said light emitting means to an electrical signal having a dynamic range directly related to amplitudes of received pulses of light, said oximeter further comprising:

an analog-to-digital converter means for providing digitized signals accurately representative of amplitudes of received pulses of light;

filter means;

an oversampling demodulator means for providing a switched and filtered electrical signal from said photosensor means to said analog-to-digital converter means;

a queued serial input module means for receiving digitized signals from said analog-to-digital converter means;

a central processor unit means; and

a random access memory means;

said queued serial input module means having an interface with said central processor unit means through said random access memory means.

5. A pulse oximeter including a central processor unit means for calculating oxygen saturation in blood, said pulse oximeter further comprising:

a light emitting means and a photosensor means for converting received pulses of light from said light emitting means to an electrical signal having a dynamic range directly related to amplitudes of received pulses of light;

an analog-to-digital converter means for providing digitized signals accurately representative of amplitudes of received pulses of light;

filter means; and

an oversampling demodulator means for providing a switched and filtered electrical signal from said photosensor means to said analog-digital converter means;

said oversampling demodulator means includes switching means for alternately connecting said electrical signal from said photosensor means to ground and to said filter means, said filter means having a cutoff frequency below both cycle rates for said electrical signal from said photosensor means and switching rates of said switching means.

6. Pulse oximeter according to claim 5 further including a pulse control module means for providing timing signals to control pulsing of light from said light emitting means and for also synchronizing said switching means for switching of said electrical signal with pulsing of light from said light emitting means.

7. A pulse oximeter including a central processor unit means for calculating oxygen saturation in blood, said pulse oximeter further comprising:

a light emitting means and a photosensor means for converting received pulses of light from said light emitting means to an electrical signal having a dynamic range directly related to amplitudes of received pulses of light;

an analog-to-digital converter means for providing digitized signals accurately representative of amplitudes of received pulses of light;

filter means; and

an oversampling demodulator means for providing a switched and filtered electrical signal from said photosensor means to said analog-digital converter means;

a queued serial input module means for receiving digitized signals from said analog-to-digital converter means; and

a random access memory means providing an interface for said queued serial input module means with said central processor unit means.

8. A method for measuring electrical pulse signal amplitudes produced from energy sensor means that have received energy from energy emitter means for digital processing using at least one analog-to-digital converter means without having to compare a first dynamic range for said electrical pulse signal amplitudes with a second dynamic range for said analog-to-digital converter means and then adjust gain of at least one amplifier to have said first dynamic range be within said second dynamic range, including the steps of:

amplifying said electrical pulse signal amplitudes using an input amplifier means;

switching said amplified electrical pulse signal amplitudes between ground and a filter means;

filtering said switched electrical pulse signal amplitudes through said filter means having a cutoff frequency below both cycle rates for said electrical pulse signal from said energy sensor means and switching rates used to switch said electrical pulse signal amplitudes;

providing a timing signal from a pulse control module means to control pulsing of energy from said energy emitter means and for also synchronizing said switching of said electrical signal with pulsing of said light; and

,

digitizing signals output from said filter means using said analog-digital converter means.

9. The method as defined in claim 8 further including the step of:

inputting said digitized signals output from said analog-to-digital converter means to a queued serial input module means having an interface with a central processor unit means through a random access memory means.

10. A pulse energy measuring system including an energy emitting means and an energy sensor means for converting received energy from said energy emitting means to an electrical signal, said pulse energy measuring system further comprising:

filter means;

switching means for alternately connecting said electrical signal from said energy sensor means to ground and to said filter means, said filter means having a cutoff frequency below both cycle rates for said electrical signal from said energy sensor means and switching rates of said switching means;

timing means for producing a timing signal that controls pulsing of energy received by said energy sensor means and that also synchronizes switching of said switching means with pulsing of energy received by said energy sensor means; and

analog/digital converter means for converting analog signals from said filter means to digital signals.

11. A pulse energy measuring system according to claim 10 further comprising at least two of said energy emitting means.

12. A pulse energy measuring system according to claim 10 wherein said switching rates of said switching means are at least two times faster than said cycle rates of electrical signals from said energy sensor means.

13. A pulse energy measuring system according to claim 10 further comprising a microcontroller/processor means including said timing means, a queued input means for receiving digitized output from said analog/digital converter means, a random access memory means and a central processor means wherein said central processor means is interconnected with said timing means and said queued input means through said random access memory means.

14. An oximeter including a light emitting means and a photosensor means for converting received light from said light emitting means to an electrical signal, said oximeter further comprising:

switching means for alternately connecting said electrical signal from said photosensor means to ground and to said filter means, said filter means having a cutoff frequency below both cycle rates for said electrical signal from said photosensor means and switching rates of said switching means;

timing means for producing a timing signal that controls pulsing of light received by said photosensor means and that also synchronizes switching of said switching means with pulsing of light received by said photosensor means; and

,

analog/digital converter means for converting analog signals from said filter means to digital signals.

15. A oximeter according to claim 14 further comprising at least two of said light emitting means.

16. An oximeter according to claim 14 further comprising at least two of said filter means and at least two of said switching means that are synchronized with pulsing of said light received by said photosensor means using timing signals from said timing means, and each of said switching means being connected to one of said filter means having cutoff frequencies below both cycle rates for said electrical signal from said photosensor means and switching rates of said connected switching means.

17. An oximeter according to claim 14 wherein said switching rates of said switching means are at least ten times faster than said cycle rates of electrical signals from said photosensor means.

18. An oximeter according to claim 14 wherein said cutoff frequency of said filter means is less than 20 Hz.

19. An oximeter according to claim 14 further comprising a microcontroller/processor means including said timing means, a queued input means for receiving digitized output from said analog/digital converter means, a random access memory means and a control processor means wherein said central processor means is interconnected with said timing means and said queued input means through said random access memory means.

20. A method for measuring electrical pulse signal amplitudes produced from energy sensor means that have received energy from an energy emitter means, said method including the steps of:

switching said electrical pulse signal between ground and filter means;

filtering said switched electrical pulse signal through said filter means having a cutoff frequency below both cycle rates for said electrical pulse signal from said energy sensor means and switching rates used to switch said electrical pulse signal;

providing a timing signal to control pulsing of energy from said energy emitter means and to also synchronize said switching of said electrical pulse signal with pulsing of said energy; and

,

digitizing signals output from said filter means.

21. The method as defined in claim 20 wherein said switching rates are at least ten times faster than said cycle rates.

22. A method for pulsed in vivo measurement of blood oxygenation saturation levels using at least one light source means and a photosensor means, including the steps of:

switching electrical signals from said photosensor means between ground and a filter means;

filtering said switched electrical signal through said filter means having a cutoff frequency below both cycle rates for said electrical signal from said photosensor means and switching rates used to switch said electrical signal;

providing a timing signal to control pulsing of light from said light source means and for also synchronizing said switching of said electrical signal with pulsing of said light; and

,

digitizing signals output from said filter means.

23. The method as defined in claim 22 wherein said switching rates are at least two times faster than said cycle rates.