Electronic processor for pulse oximeters

• US 5,676,141 A
• Filed: 09/19/1995
• Issued: 10/14/1997
• Est. Priority Date: 03/31/1993
• Status: Expired due to Term

• Current Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Hollub, Seth D.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/525,591
• Time in Patent Office: 756 Days
• Field of Search: 128/633, 128/664, 128/665, 128/666, 356/41
• 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 apparatus for measuring the concentration of blood constituents in which the architecture of the electronic processor reduces the amount of controller processing time required for tasks such as data acquisition and generation of system control signals. A demodulator is coupled to a probe for converting a first electrical signal to digital data. An interface is coupled to the demodulator for receiving the digital data and generating interrupts when a first amount of the digital data has been received. A buffer memory is coupled to the interface for storing the digital data. A controller having a controller memory (in specific embodiments, a CPU having a CPU memory) is also coupled to the buffer memory. The controller transfers the digital data from the buffer memory to the controller memory in response to the interrupts. The controller then processes the digital data to calculate the blood oxygen concentration.

Claims

1. An apparatus for calculating arterial oxygen concentration using an electrical signal generated by a probe, comprising:

at least one demodulator coupled to the probe for converting the electrical signal to digital data;

a queued serial module coupled to said demodulator and configured to generate an interrupt signal only after multiple bytes of digital data have been received from said demodulator;

a controller coupled to said queued serial module to receive said multiple bytes of digital data in response to said interrupt signal and for processing the digital data to calculate the arterial oxygen concentration; and

a control signal generator coupled to the controller and a drive circuit for driving a source of electromagnetic radiation in the probe, the control signal generator for generating a drive signal for the drive circuit, the drive signal being generated without intervention by the controller after the control signal generator is initialized by the controller;

wherein the control signal generator also generates a gating signal for gating the electrical signal to facilitate synchronous detection, the gating signal being generated without intervention by the controller after the control signal generator is initialized by the controller.

2. The apparatus of claim 1 wherein the electrical signal comprises a plurality of phases, each phase corresponding to a period during which a particular type of electromagnetic radiation is being received by a sensor in the probe, and wherein the at least one demodulator comprises:

at least one analog-to-digital converter for receiving the electrical signal and sampling each phase a plurality of times, thereby generating a plurality of samples for each phase, the at least one analog-to-digital converter converting the samples from each phase to first digital data; and

a logic circuit coupled to the at least one analog-to-digital converter for filtering the first digital data from each phase, thereby increasing a signal-to-noise ratio, the logic circuit generating the digital data.

3. An apparatus for calculating arterial oxygen concentration using an electrical signal generated by a probe, comprising:

at least one demodulator coupled to the probe for converting the electrical signal to digital data;

a controller coupled to the at least one demodulator for processing the digital data to calculate the arterial oxygen concentration; and

a control signal generator coupled to the controller and a drive circuit for driving a source of electromagnetic radiation in the probe, the control signal generator for generating a drive signal for the drive circuit, the drive signal being generated without intervention by the controller after the control signal generator is initialized by the controller;

wherein the control signal generator also generates a gating signal for gating the electrical signal to facilitate synchronous detection, the gating signal being generated without intervention by the controller after the control signal generator is initialized by the controller;

wherein the at least one demodulator comprises an analog-to-digital converter having a dynamic range, and the electrical signal has an amplitude range, the dynamic range being sufficient to cover the amplitude range without clipping, thereby eliminating a need to manipulate the amplitude range of the electrical signal.

4. The apparatus of claim 3 wherein the analog-to-digital converter converts the electrical signal into serial digital data having a resolution of at least 18 bits.

5. An apparatus for calculating arterial oxygen concentration using a first electrical signal generated by a probe, comprising:

at least one demodulator coupled to the probe for converting the first electrical signal to digital data;

an interface coupled to the demodulator for receiving the digital data and generating interrupts when a plurality of samples of the digital data has been received;

a buffer memory coupled to the interface for storing the digital data; and

a controller having a controller memory, the controller being coupled to the buffer memory, the controller transferring the digital data from the buffer memory to the controller memory in response to the interrupts, the controller for processing the digital data to calculate the arterial oxygen concentration.

6. The apparatus of claim 5, further comprising a control signal generator coupled to the controller and a drive circuit for driving a source of electromagnetic radiation in the probe, the control signal generator for generating a drive signal for the drive circuit, and for generating a gating signal for gating the first electrical signal to facilitate synchronous detection, the drive and gating signals being generated without intervention by the controller after the control signal generator is initialized by the controller.

7. The apparatus of claim 6 wherein the interface, the buffer memory, the controller, and the control signal generator are part of one integrated circuit.

8. The apparatus of claim 5 wherein the first electrical signal comprises a plurality of phases, each phase corresponding to a period during which a particular type of electromagnetic radiation is being received by a sensor in the probe, and wherein the at least one demodulator comprises:

at least one analog-to-digital converter for receiving the first electrical signal and sampling each phase a plurality of times, thereby generating a plurality of samples for each phase, the at least one analog-to-digital converter converting the samples from each phase to first digital data; and

a logic circuit coupled to the at least one analog-to-digital converter for filtering the first digital data from each phase, thereby increasing a signal-to-noise ratio, the logic circuit generating the digital data.

9. An apparatus for calculating arterial oxygen concentration using a first electrical signal generated by a probe, comprising:

at least one demodulator coupled to the probe for converting the first electrical signal to digital data, said demodulator including

an analog switch coupled to the probe for intermittently switching the first electrical signal to ground, thereby generating a switched electrical signal,

a filter coupled to the analog switch for filtering the switched electrical signal, thereby generating a filtered electrical signal, and

an analog-to-digital converter coupled to the filter for converting the filtered electrical signal to the serial digital data;

an interface coupled to the demodulator for receiving the digital data and generating interrupts when a first amount of the digital data has been received;

a buffer memory coupled to the interface for storing the digital data; and

a controller having a controller memory, the controller being coupled to the buffer memory, the controller transferring the digital data from the buffer memory to the controller memory in response to the interrupts, the controller for processing the digital data to calculate the arterial oxygen concentration.

10. A method for calculating arterial oxygen concentration using a first electrical signal generated by a probe, the first electrical signal comprising a plurality of phases, each phase corresponding to a period during which a particular type of electromagnetic radiation is being received by a sensor in the probe, the method comprising the steps of:

sampling each phase of the first electrical signal a plurality of times, thereby generating a plurality of samples for each phase;

converting the samples from each phase to first digital data;

averaging the first digital data from each phase, thereby generating average digital data for each phase, and increasing a signal-to-noise ratio for each phase;

generating second digital data for each phase from the average digital data; and

calculating the arterial oxygen concentration by analyzing the second digital data.

11. The method of claim 10 wherein at least three phases of at least one electrical signal cycle comprise a first phase corresponding to a first electromagnetic radiation, a second phase corresponding to ambient background radiation, and a third phase corresponding to a second electromagnetic radiation, and wherein the step of generating second digital data comprises:

subtracting the filtered digital data for the second phase from the filtered digital data for the first phase to produce second digital data for the first phase; and

subtracting the filtered digital data for the second phase from the filtered digital data for the third phase to produce second digital data for the third phase.

12. An apparatus for calculating oxygen concentration using a first electrical signal generated by a probe, the first electrical signal comprising a plurality of phases, each phase corresponding to a period during which a particular type of electromagnetic radiation is being received by a sensor in the probe, the apparatus comprising:

a demodulator for receiving the first electrical signal and sampling each phase a plurality of times, thereby generating a plurality of samples for each phase, the demodulator converting the samples from each phase to first digital data;

a logic circuit coupled to the demodulator for filtering the first digital data from each phase, thereby generating filtered digital data for each phase and increasing a signal-to-noise ratio for each phase, the logic circuit generating second digital data from the filtered digital data; and

a controller coupled to the logic circuit for calculating the arterial oxygen concentration by analyzing the second digital data;

wherein at least three phases of at least one first electrical signal cycle comprise a first phase corresponding to a first electromagnetic radiation, a second phase corresponding to a second electromagnetic radiation, and a third phase corresponding to ambient background radiation, and wherein the logic circuit is for subtracting the filtered digital data for the third phase from the filtered digital data for the first phase to produce second digital data for the first phase, and subtracting the filtered digital data for the third phase from the filtered digital data for the second phase to produce second digital data for the second phase.

13. The apparatus of claim 12 wherein the demodulator comprises an analog-to-digital converter having a dynamic range, and the first electrical signal has an amplitude range, the dynamic range being sufficient to cover the amplitude range, thereby eliminating a need for the controller to manipulate the amplitude range of the first electrical signal.