Photoplethysmographic instrument

• US 6,360,113 B1
• Filed: 12/17/1999
• Issued: 03/19/2002
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: Datex-Ohmeda Incorporated (General Electric Company)
• Original Assignee: Datex-Ohmeda Incorporated (General Electric Company)
• Inventors: Dettling, Allen
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US09/465,858
• Time in Patent Office: 823 Days
• Field of Search: 600/310, 600/322, 600/323, 600/330, 600/336
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

The pulse oximeter instrument of the present invention includes switched gain, channel rotation and bootstrap amplification features. In one embodiment, a time-division multiplexed gain circuit is provided in receiver circuitry and is equipped with a switched gain amplifier to faciliate the use of a fixed light source drive and otherwise improve the signal processing characteristics of the instrument. Signal processing is further enhanced via use of a transimpedance amplifier and bootstrap amplifier interconnected across one or more photodiodes. The apparatus time division multiplexes (TDM) the optical input channels to customize the gain response of the apparatus to the variable characteristics of each input channel. Thus, the channel-specific error sources are determined and precisely eliminated from the input data. The channels may also be rotated in subsequent signal conditioning that entails demultiplexing/multiplexing.

Claims

1. An apparatus for noninvasively measuring components of arterial blood in a patient, comprising:

a plurality of light emitting devices for emitting light of predetermined spectral content to illuminate a site on said patient that is perfused with arterial blood;

light detector means for receiving a portion of said light that is transmitted by the illuminated site;

amplifying means having a settable gain for separately amplifying a plurality of time-divided signal portions of a multiplexed detection signal indicative of said transmitted light received by the light detector means, wherein each of said plurality of time-divided signal portions includes a first subportion corresponding with activation of a corresponding one of said plurality of light emitting devices and a second subportion corresponding with a sequential dark time during which all of said plurality of light emitting devices are inactive.

2. The apparatus of claim 1, further comprising:

monitoring means for monitoring an amplitude of said multiplexed detection signal and for providing a control signal to set the gain of the amplifying means, wherein the amplitude of said multiplexed detection signal is maintained within a predetermined range.

3. The apparatus of claim 2, wherein:

said plurality of light emitting devices are sequentially activatable and deactivatable so that said multiplexed detection signal comprises a corresponding said plurality of time-divided signal portions; and

said control signal is provided to separately set the gain of said amplifying means in relation to each of said plurality of time-divided signal portions.

4. The apparatus of claim 3, further comprising:

signal rotating means for receiving a first ordered signal corresponding with said multiplexed detection signal and for rotating a sequential order of said plurality of time-divided signal portions to provide a re-ordered signal.

5. The apparatus of claim 1, wherein said amplifying means comprises:

a first amplifier for maintaining a substantially zero bias across the detector means.

6. The apparatus of claim 5, wherein said first amplifier comprises:

a non-inverting operational amplifier having a first input interconnected to an input of said detector means and a second input interconnected to an output of said detector means.

7. The apparatus of claim 5, wherein said amplifier means further comprises:

a second amplifier for presenting a substantially zero impedance load to the detector means.

8. The apparatus of claim 7, wherein;

said detector means includes a photodiode;

said first amplifier includes a non-inverting operational amplifier having a first input interconnected to an input of said photodiode and a second input interconnected to an output of said photodiode; and

said second amplifier includes an inverting operational amplifier having a first input interconnected to an output of said photodiode and a second input interconnected to a virtual ground and to said photodiode output.

9. The apparatus of claim 8, wherein said amplifying means further comprises:

a switching means for receiving said control signal and providing a predetermined gain signal to said second input of the inverting operational amplifier.

10. The apparatus of claim 2, further comprising:

a fixed drive means for providing fixed drive signals to sequentially activate each of said plurality of light emitting devices.

11. A method for noninvasively measuring components of arterial blood in a patient using a plurality of light emitting devices, each of which generates a beam of light of predetermined wavelength, to illuminate a site on said patient that is perfused with arterial blood, said method comprising the steps of:

applying fixed drive signals to activate said plurality of light emitting devices;

producing a multiplexed analog signal comprising a plurality of time-divided signal portions, using a light detector, indicative of an intensity of a portion of the light that is transmitted by said illuminated site, wherein each of said plurality of time-divided signal portions includes a first subportion corresponding with activation of a corresponding one of said plurality of light emitting devices and a second subportion corresponding with a sequential dark time during which all of said plurality of light emitting devices are inactive;

separately amplifying each of said plurality of time-divided signal portions of said multiplexed analog signal using an amplifier having a settable gain; and

monitoring an amplitude corresponding with said amplified time-divided signal portions to provide a control signal to set the gain of said amplifier, wherein said monitoring an amplitude comprises subtracting said second subportion from said first subportion.

12. The method of claim 11, wherein said applying step includes sequentially activating each of said plurality of light emitting devices seriatim so that said multiplexed analog signal comprises a plurality of time-divided signal portions, and wherein the amplifying step comprises:

separately setting the gain of said amplifier in relation to each of said plurality of time-divided signal portions.

13. The method of claim 12, wherein each of said plurality of time-divided signal portions includes a first subportion corresponding with activation of a corresponding one of said plurality of light emitting devices and a second subportion corresponding with a sequential dark time during which all of said plurality of light emitting devices are inactive, and wherein said amplifying step includes maintaining said separately set gain the first and second subportions of each of the plurality of time-divided signal portions.

14. The method of claim 12, further comprising:

rotating a first ordering of said plurality of time-divided signal portions to provide a second ordering thereof.

15. The method of claim 11, wherein said amplifying step comprises:

maintaining a substantially zero bias across the light detector.

16. The method of claim 11 wherein said amplifying step further comprises:

presenting a substantially zero impedance to the light detector.

17. An apparatus for noninvasively measuring components of arterial blood in a patient, comprising:

a plurality of light-emitting devices for sequentially emitting light of a predetermined spectral content to illuminate a site on a patient that is perfused with arterial blood;

light detector means for receiving a portion of said light that is transmitted by the illuminated site; and

signal rotating means for receiving a detection signal indicative of the light received by the detection means, wherein the detection signal comprises a plurality of portions each corresponding with a different one of the plurality of light sources, and wherein said rotating means rotates the order of the detection signal portions, in accordance with a predetermined ordering scheme to provide a reordered signal.

18. The apparatus of claim 17, further comprising:

demultiplexing means for providing each of said plurality of detector signal portions to said rotating means in corresponding separate channels; and

multiplexing means for receiving each of a plurality of portions of said reordered signal from said rotating means and multiplexing said rotated signal portions.

19. The apparatus of claim 17, further comprising:

amplifying means having a settable gain for amplifying said detection signal.

20. An apparatus for noninvasively measuring components of arterial blood in a patient, comprising:

at least one light emitting device for emitting light of a predetermined spectral content to illuminate a site on said patient that is perfused with arterial blood;

a detector means for receiving a portion of said light that is transmitted by the illuminated site; and

amplifying means for amplifying a detection signal indicative of said transmitted light received by the photodiode, and including a first amplifier for maintaining a substantially zero bias across the detector means.

21. The apparatus of claim 20, wherein said first amplifier comprises:

a non-inverting operational amplifier having a first input interconnected to an input of said detector means and a second input interconnected to an output of said detector means.

22. The apparatus of claim 21, wherein said amplifying means further includes a second amplifier for presenting a substantially zero impedance load to the detector means.

23. The apparatus of claim 22, wherein said second amplifier includes an inverting operational amplifier having a first input interconnected to an output of said photodiode and a second input interconnected to a virtual ground and to said photodiode output.