WO1997049330A1 - Motion artifact resistant oximeter using three wavelengths - Google Patents

Motion artifact resistant oximeter using three wavelengths Download PDF

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Publication number
WO1997049330A1
WO1997049330A1 PCT/US1997/011263 US9711263W WO9749330A1 WO 1997049330 A1 WO1997049330 A1 WO 1997049330A1 US 9711263 W US9711263 W US 9711263W WO 9749330 A1 WO9749330 A1 WO 9749330A1
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WO
WIPO (PCT)
Prior art keywords
optical signals
individual
signal
optical
signals
Prior art date
Application number
PCT/US1997/011263
Other languages
French (fr)
Inventor
David M. Shemwell
Andrew J. W. Brown
Marc A. Norsen
Original Assignee
Falcon Medical, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Falcon Medical, Inc. filed Critical Falcon Medical, Inc.
Priority to AU35832/97A priority Critical patent/AU3583297A/en
Publication of WO1997049330A1 publication Critical patent/WO1997049330A1/en

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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6813Specially adapted to be attached to a specific body part
    • A61B5/6825Hand
    • A61B5/6826Finger
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/145Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
    • A61B5/1455Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
    • A61B5/14551Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/683Means for maintaining contact with the body
    • A61B5/6838Clamps or clips
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/72Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7203Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
    • A61B5/7207Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/314Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N21/3151Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths using two sources of radiation of different wavelengths

Definitions

  • the present invention relates to pulse oximetry, and more particularly, to apparatus and methods for pulse oximetry measurements.
  • pulse oximeters which use a combination of two light emitting diodes (LEDs), one red and one infrared, are used to monitor the patient functional blood oxygen saturation (SaC ⁇ ) .
  • the probe portion of the pulse oximeter is designed to be disposable.
  • the design of current art reusable probe normally consists of a clamshell type plastic housing for enclosing one of the patient's fingers.
  • the LED emitters are usually situated in the part of the housing designed to cover the fingernail, and the detector (usually a photodiode) is situated in the portion of the housing designed to cover the pad of the fingertip.
  • the electrical cable which transmits the signals back to the pulse oximeter monitor usually emanates from the part of the housing on the dorsal side of the clamshell housing.
  • the emitter and detector components are usually embedded in a sandwich of plastic layers which contain the wires and LED detectors which are laminated to a layer of tape.
  • the disposable probe is wrapped around the fingertip and the tape is wrapped to adhere to both the finger and the outside of the probe.
  • the end of the patient's finger is nearly immobilized by the tape/probe structure. The purpose of this immobilization is to reduce fmger motion and thus reduce motion artifact. This system is not comfortable for the patient and is ineffective m reducing motion artifact.
  • the invention is an apparatus for performing blood oximetry measurements in the body of an individual.
  • the apparatus including a transmit signal circuit, an optical signal circuit, a probe, and a signal processing circuit.
  • the transmit signal circuit produces an electrical transmit signal.
  • the optical signal circuit receives the electrical transmit signal and produces at least first, second and third optical signals in response thereto.
  • the at least first, second and third optical signals include optical energy at distinct optical wavelengths.
  • the probe receives the at least first, second and third optical signals and transmits the at least first, second and third optical signals through a portion of the body of the individual.
  • the probe also receives the at least first, second and third optical signals after transmission through the portion of the body of the individual and produces at least first, second and third transmission signals m response to the transmitted at least first, second and third optical signals.
  • the signal processing circuit receives the at least first, second and third transmission signals and produces an indication of blood oximetry measurements in the body of the individual in response thereto, regardless of whether the at least first, second and third optical signals are produced when the probe moves relative to the portion of the body of the individual.
  • the invention is an apparatus for performing blood oximetry measurements m the body of an individual in the presence of ambient light conditions.
  • the apparatus includes a transmit signal circuit, an optical signal circuit, a probe, and a signal processing circuit.
  • the transmit signal circuit produces an electrical transmit signal.
  • the optical signal circuit receives the electrical transmit signal and produces at least first, second and third optical signals in response thereto. Each of the at least first, second and third optical signals includes optical energy at a distinct optical wavelength.
  • the probe receives the at least first, second and third optical signals and transmits the at least first, second and third optical signals through a portion of the body of the individual.
  • the probe also receives the at least first, second and third optical signals after transmission through the portion of the body of the individual and produces at least first, second and third transmission signals in response to the transmitted at least first, second and third optical signals.
  • the signal processing circuit receives the at least first, second and third transmission signals and produces therefrom a system of eguations representative of the relationships among the at least first, second and third transmission signals as a function of the SaO , the system or equations being solvable to produce an unambiguous measurement of the SaO .
  • the invention is an apparatus for performing blood oximetry measurements m the body of an individual m the presence of ambient light conditions.
  • the apparatus includes a transmit signal circuit, an optical signal circuit, d probe, and a signal processing circuit.
  • the transmit signal circuit produces an electrical transmit signal.
  • the optical signal circuit receives the electrical transmit signal and produces at least first, second and third optical signals in response thereto. Each of the at least first, second and third optical signals include optical energy at a distinct optical wavelength.
  • the probe receives the at least first, second and third optical signals and transmits the at least first, second and third optical signals through a portion of the body of the individual.
  • the probe also receives the at least first, second and third optical signals after transmission through the portion of the body of the individual, and produces at least one transmission signal in response to the transmitted at least first, second and third optical signals.
  • the presence of variable ambient light conditions affects all of the transmitted at least first, second and third optical signals equally and, hence, can easily be removed by signal processing techniques described herein.
  • the signal processing circuit receives the at least first, second and third transmission signals and produces an indication of blood oximetry measurements in the body of the individual, regardless of whether the at least first, second and third optical signals are produced when the probe moves relative to the portion of the body of the individual.
  • Figure 1 is a graph of the absorption coefficient of blood as a function of wavelength of light.
  • Figure 2 is a graph of the alternating current (AC) signal as a runction of time.
  • Figure 3 is a block diagram or a preferred embodiment of the invention.
  • the motion artifact reduction that is accomplished through this invention is independent of the probe design and instead relies on the process of using three independent wavelengths of light specifically to remove common mode signal variation-induced motion artifact. It is not unknown to use a variety of wavelengths of light in a pulse oximeter. However, in previous cases the introduction of the additional wavelength was done m order to examine blood gases other than oxygen. However, it is believed that the use of three wavelengths to provide a motion reference is unique to this invention.
  • the three sources of the wavelengths of light are lasers, which allow the source to be located remote from the finger via a fiber optic pathway, and allow for much more precise spectral separation of the sources.
  • the present invention specifically uses three independent wavelengths, together with conventional associated mathematical analysis, to eliminate or significantly reduce artifacts in the pulse oximetry measurement caused by common mode variations m the detected intensity of the investigating wavelengths.
  • This common mode variation is the major component of motion artifacts in current art pulse oximetry.
  • the measurement of this invention may be made with virtually any three wavelengths, but superior performance and enhanced practicality encourages certain wavelength choices.
  • Figure 1 is a graph of the absorption coefficient of blood as a function of wavelength of light, and shows a typical set of three laser wavelengths superimposed over the respective absorption curves 10 and 20 for oxygenated and deoxygenated hemoglobin.
  • Three laser diode wavelengths (635 nm, 670 nm, 780 nm) are indicated m Figure 1. These three wavelengths are flashed on for short periods of time in cyclic sequence m a manner similar to that of a current production pulse oximeter.
  • wavelengths 21, 22 are in the red portion of the spectrum and the third wavelength 23 is in the infrared portion of the spectrum.
  • a typical pulse format would turn on the source of wavelength 21 from 100 to 200 microseconds, wait a similar amount of time, then turn on the source of wavelength 22 similarly, then repeat the entire sequence for wavelength 23. When recorded over time it can be seen that the absorption of each wavelength is modulated by the pressure waves of the heartbeat.
  • the three wavelengths 21, 22, and 23 shown are common, but other wavelengths could be used as will be understood by those skilled in the art (indeed virtually any set of three independent wavelengths can be used, although some wavelengths are more optimal than others) .
  • the three independent lasers or light emitting diodes, LEDs
  • a detector which may be an optical fiber or a photodiode.
  • a typical absorption curve showing the AC component of absorption schematically is shown in Figure 2.
  • Figure 2 is a graph of the alternating current (AC) signal as a function of time.
  • the detector is moved rhythmically with a repetition rate similar to a human pulse rate it is very easy to provoke an erroneous reading in a present-day production pulse oximeter. This is the case because the movement due to the pressure pulse causes a rhythmic variation in the signal intensity, such as that shown in Figure 2.
  • Typical curves showing the heartbeat caused variations and the common mode motion variations are shown schematically in Figure 2.
  • the pulse oximeter monitor can misinterpret them as heartbeat variations and produce the wrong answer.
  • Sophisticated monitors can be controlled by software that allows the monitor to infer the existence of motion and thus ignore the bad data.
  • no current monitor is immune to common mode rhythmic motions of the detector and emitter complex.
  • FIG. 3 is a block diagram of a preferred embodiment of the invention.
  • the three light signals each show a time-varying amplitude modulation which is caused when the pressure waves of the heartbeat produce an expansion of the body at the measurement site.
  • the block diagram in Figure 3 shows the process by which three wavelengths are used to eliminate common mode motion artifact.
  • the data is gathered by the standard pulse oximetry technique, and then subjected to mathematical analysis to solve for the three unknowns (oxygenated- deoxygenated blood, scattering and absorption of all other sources, and common mode signal variations), m the presence of the three measured quantities.
  • the signals representing the data are processed to represent normalized values and then the resulting signals are ratioed m order to form a single index which determines SaO in the presence of common mode signal variations which affect the measurements at all three wavelengths, such as motion artifact.
  • the techniques of using measurements due to the three different wavelengths of light will recognize the techniques of using measurements due to the three different wavelengths of light as methods of inverting the measurement system's equation matrix. There are many specific methods which will allow such a solution. Even m the case where the equations are not linear, they can be solved by, for example, developing a linear approximation or by the use of calibration tables.
  • FIG. 3 shows a functional block diagram of the current invention.
  • the overall apparatus 100 includes signal production and analysis circuitry 102, signal conduits 104 and a pulse oximetry probe 106.
  • the signal production and analysis circuitry 102 can be included in a single enclosure 108 (as shown) or may be distributed as necessary and as will be appreciated by those skilled in the electronic circuitry arts.
  • the signal conduits 104 carry signals between the signal production and analysis circuitry 102 and the pulse oximetry probe 106.
  • the signal conduits 104 can carry electrical signals (in which case they will be electrical conductors, such as stranded copper wires) or they can carry optical signals (in which case they will be optical conductors, such as optical fibers) .
  • the signal production and analysis circuitry 102 can include a transmit signal circuit 110 that produces an electrical transmit signal.
  • the electrical transmit signal is received by an optical signal circuit 112 over a line 114.
  • the optical signal circuit 112 produces optical signals at three different wavelengths in response to the electrical transmit signal. Each of the three different wavelengths is produced by a separate source 116,, 116.>, and 116 * . And then directed onto a first conduit 118 (which may be an optical fiber bundle) that carries the optical signals at the three different wavelengths to the pulse oximetry probe 106.
  • the three wavelength sources 116,, 116v, and 116 are shown as laser diodes which, in the preferred embodiment, are located in the enclosure 108. It is also possible that the three separate wavelength sources could be located at the site of the pulse oximetry probe 106, where they would respond to electrical signals carried by the first conduit 118 to the pulse oximetry probe 106. In either case, the three wavelength sources 116,, 116-, and 116, could be LEDs rather than laser diodes.
  • the signal conduits 104 can be detachable from the pulse oximetry probe 106 at a connector 120. This enables the pulse oximetry probe 106 to be discarded or reprocessed for reuse, if desired. The detachable portion of the pulse oximetry probe 106 is usually connected to the patient's finger 122.
  • the three wavelength sources 116,, 116 , and 116 are pulsed sequentially by the transmit signal circuit 110, and the three wavelengths of light from the three wavelength sources transit the tip of the finger 122, after leaving an emitter 124.
  • This light is received at a detector site 124, which may be either a fiber optic or a photodetector such as a photodiode.
  • Signals, either optical or electronic, from the detector site 124 are transmitted through a return conduit 126 to the enclosure 108 for processing by a signal processing circuit 128.
  • the signal processing circuit 128 performs the mathematical equivalent of inverting the matrix of three equations in three signals to produce a common mode error-free pulse oximetry reading. As discussed above, one such mathematical method is via production of the super-ratio of signals.
  • the signals received through the return conduit 126 are amplified by an amplifier 130 and then portions of the signals are sent to first and second ratio circuits 132 and 134.
  • the first ratio circuit 132 produces the ratio of the magnitude of the first red wavelength signal to the magnitude of the infrared wavelength signal.
  • the second ratio circuit 134 produces the ratio of the magnitude of the second red wavelength signal to the magnitude of the infrared wavelength signal. Signals representing these two ratios are then conducted to a final signal processing circuit 136 over respective signal lines 138 and 140.
  • the final signal processing circuit 136 uses the signals carrying the two ratios and dedicated electronic circuitry (including a properly programmed microprocessor and calibration tables, as desired) to produce signals that indicate the current value of SaO / or the presence of a common mode artifact on the conventional display 138.
  • the super-ratio measurement method can be used as a noise reduction technique, or as a check on the accuracy of the direct three wavelength measurement.
  • the display 138 may choose the most optimal value, via additional processing in the final signal processing circuit 136 under any given circumstance.

Abstract

A method and apparatus for making motion artifact-resistant pulse oximeter measurements using three wavelengths of light, and a method for its use. Light energy production circuits (112) produce pulses of at least three distinct wavelengths of light, such as through laser diodes. The pulses are cyclically transmitted through a portion of a patient's body, such as a finger (122), and signals representing the amount of light at the three distinct wavelengths are transmitted to signal processing circuits (128). The signal processing circuits produce signals indicative of the blood oxygen saturation levels of the patient's blood and of the presence of motion artifacts.

Description

Description
MOTION ARTIFACTRESISTANTOXIMETER USINGTHREEWAVELENGTHS
Technical Field
The present invention relates to pulse oximetry, and more particularly, to apparatus and methods for pulse oximetry measurements.
Background of the Invention
In current clinical practice pulse oximeters which use a combination of two light emitting diodes (LEDs), one red and one infrared, are used to monitor the patient functional blood oxygen saturation (SaC^) . In many cases the probe portion of the pulse oximeter is designed to be disposable. The design of current art reusable probe normally consists of a clamshell type plastic housing for enclosing one of the patient's fingers. The LED emitters are usually situated in the part of the housing designed to cover the fingernail, and the detector (usually a photodiode) is situated in the portion of the housing designed to cover the pad of the fingertip. The electrical cable which transmits the signals back to the pulse oximeter monitor usually emanates from the part of the housing on the dorsal side of the clamshell housing.
In the case of disposable probes the emitter and detector components are usually embedded in a sandwich of plastic layers which contain the wires and LED detectors which are laminated to a layer of tape. In use, the disposable probe is wrapped around the fingertip and the tape is wrapped to adhere to both the finger and the outside of the probe. After application of the probe, the end of the patient's finger is nearly immobilized by the tape/probe structure. The purpose of this immobilization is to reduce fmger motion and thus reduce motion artifact. This system is not comfortable for the patient and is ineffective m reducing motion artifact.
Summary of the Invention
According to one aspect, the invention is an apparatus for performing blood oximetry measurements in the body of an individual. The apparatus including a transmit signal circuit, an optical signal circuit, a probe, and a signal processing circuit. The transmit signal circuit produces an electrical transmit signal. The optical signal circuit receives the electrical transmit signal and produces at least first, second and third optical signals in response thereto. The at least first, second and third optical signals include optical energy at distinct optical wavelengths. The probe receives the at least first, second and third optical signals and transmits the at least first, second and third optical signals through a portion of the body of the individual. The probe also receives the at least first, second and third optical signals after transmission through the portion of the body of the individual and produces at least first, second and third transmission signals m response to the transmitted at least first, second and third optical signals. The signal processing circuit receives the at least first, second and third transmission signals and produces an indication of blood oximetry measurements in the body of the individual in response thereto, regardless of whether the at least first, second and third optical signals are produced when the probe moves relative to the portion of the body of the individual.
In accordance with a second aspect, the invention is an apparatus for performing blood oximetry measurements m the body of an individual in the presence of ambient light conditions. The apparatus includes a transmit signal circuit, an optical signal circuit, a probe, and a signal processing circuit. The transmit signal circuit produces an electrical transmit signal. The optical signal circuit receives the electrical transmit signal and produces at least first, second and third optical signals in response thereto. Each of the at least first, second and third optical signals includes optical energy at a distinct optical wavelength. The probe receives the at least first, second and third optical signals and transmits the at least first, second and third optical signals through a portion of the body of the individual. The probe also receives the at least first, second and third optical signals after transmission through the portion of the body of the individual and produces at least first, second and third transmission signals in response to the transmitted at least first, second and third optical signals. The signal processing circuit receives the at least first, second and third transmission signals and produces therefrom a system of eguations representative of the relationships among the at least first, second and third transmission signals as a function of the SaO , the system or equations being solvable to produce an unambiguous measurement of the SaO .
According to another aspect, the invention is an apparatus for performing blood oximetry measurements m the body of an individual m the presence of ambient light conditions. The apparatus includes a transmit signal circuit, an optical signal circuit, d probe, and a signal processing circuit. The transmit signal circuit produces an electrical transmit signal. The optical signal circuit receives the electrical transmit signal and produces at least first, second and third optical signals in response thereto. Each of the at least first, second and third optical signals include optical energy at a distinct optical wavelength. The probe receives the at least first, second and third optical signals and transmits the at least first, second and third optical signals through a portion of the body of the individual. The probe also receives the at least first, second and third optical signals after transmission through the portion of the body of the individual, and produces at least one transmission signal in response to the transmitted at least first, second and third optical signals. The presence of variable ambient light conditions affects all of the transmitted at least first, second and third optical signals equally and, hence, can easily be removed by signal processing techniques described herein. The signal processing circuit receives the at least first, second and third transmission signals and produces an indication of blood oximetry measurements in the body of the individual, regardless of whether the at least first, second and third optical signals are produced when the probe moves relative to the portion of the body of the individual.
Brief Description of the Drawings
Figure 1 is a graph of the absorption coefficient of blood as a function of wavelength of light.
Figure 2 is a graph of the alternating current (AC) signal as a runction of time. Figure 3 is a block diagram or a preferred embodiment of the invention.
Detailed Description of the Preferred Embodiment of the Invention The motion artifact reduction that is accomplished through this invention is independent of the probe design and instead relies on the process of using three independent wavelengths of light specifically to remove common mode signal variation-induced motion artifact. It is not unknown to use a variety of wavelengths of light in a pulse oximeter. However, in previous cases the introduction of the additional wavelength was done m order to examine blood gases other than oxygen. However, it is believed that the use of three wavelengths to provide a motion reference is unique to this invention. In the preferred embodiment, the three sources of the wavelengths of light are lasers, which allow the source to be located remote from the finger via a fiber optic pathway, and allow for much more precise spectral separation of the sources. The present invention specifically uses three independent wavelengths, together with conventional associated mathematical analysis, to eliminate or significantly reduce artifacts in the pulse oximetry measurement caused by common mode variations m the detected intensity of the investigating wavelengths. This common mode variation is the major component of motion artifacts in current art pulse oximetry. In principle, the measurement of this invention may be made with virtually any three wavelengths, but superior performance and enhanced practicality encourages certain wavelength choices. Figure 1 is a graph of the absorption coefficient of blood as a function of wavelength of light, and shows a typical set of three laser wavelengths superimposed over the respective absorption curves 10 and 20 for oxygenated and deoxygenated hemoglobin. Three laser diode wavelengths (635 nm, 670 nm, 780 nm) are indicated m Figure 1. These three wavelengths are flashed on for short periods of time in cyclic sequence m a manner similar to that of a current production pulse oximeter.
It is particularly advantageous if two of the wavelengths 21, 22 are in the red portion of the spectrum and the third wavelength 23 is in the infrared portion of the spectrum. In addition it is more practical for a production pulse oximeter system for the three wavelengths chosen to correspond to red and infrared wavelengths that are available from production laser diode sources. A typical pulse format would turn on the source of wavelength 21 from 100 to 200 microseconds, wait a similar amount of time, then turn on the source of wavelength 22 similarly, then repeat the entire sequence for wavelength 23. When recorded over time it can be seen that the absorption of each wavelength is modulated by the pressure waves of the heartbeat.
The three wavelengths 21, 22, and 23 shown are common, but other wavelengths could be used as will be understood by those skilled in the art (indeed virtually any set of three independent wavelengths can be used, although some wavelengths are more optimal than others) . The three independent lasers (or light emitting diodes, LEDs) are then strobed in the standard fashion known m the present art, and the light which has transmitted through the patient's finger is received by a detector which may be an optical fiber or a photodiode. A typical absorption curve showing the AC component of absorption schematically is shown in Figure 2. Figure 2 is a graph of the alternating current (AC) signal as a function of time. If the detector is moved rhythmically with a repetition rate similar to a human pulse rate it is very easy to provoke an erroneous reading in a present-day production pulse oximeter. This is the case because the movement due to the pressure pulse causes a rhythmic variation in the signal intensity, such as that shown in Figure 2.
Typical curves showing the heartbeat caused variations and the common mode motion variations are shown schematically in Figure 2. When the motion-caused variations are rhythmic m nature, the pulse oximeter monitor can misinterpret them as heartbeat variations and produce the wrong answer. Sophisticated monitors can be controlled by software that allows the monitor to infer the existence of motion and thus ignore the bad data. However, no current monitor is immune to common mode rhythmic motions of the detector and emitter complex.
This rhythmic signal variation is the same for all wavelengths in use. Unfortunately an equal variation of signals in a current production pulse oximeter also corresponds to a blood oxygen saturation of about 85°, therefore current production pulse oximeters have a hard time discriminating between motion and an 85u blood oxygen saturation condition of a patient. With three wavelengths there is never a physiologically viable condition where all three measurements will vary equally, due to blood oxygen saturation levels. This is the fundamental basis of this invention. Figure 3 is a block diagram of a preferred embodiment of the invention. When assessed as functions of time, the three light signals each show a time-varying amplitude modulation which is caused when the pressure waves of the heartbeat produce an expansion of the body at the measurement site. In addition, there may be amplitude variations caused by motions of the receiver and detectors.
The block diagram in Figure 3 shows the process by which three wavelengths are used to eliminate common mode motion artifact. In general, the data is gathered by the standard pulse oximetry technique, and then subjected to mathematical analysis to solve for the three unknowns (oxygenated- deoxygenated blood, scattering and absorption of all other sources, and common mode signal variations), m the presence of the three measured quantities.
In one embodiment, the signals representing the data are processed to represent normalized values and then the resulting signals are ratioed m order to form a single index which determines SaO in the presence of common mode signal variations which affect the measurements at all three wavelengths, such as motion artifact. Those skilled in the relevant mathematical arts will recognize the techniques of using measurements due to the three different wavelengths of light as methods of inverting the measurement system's equation matrix. There are many specific methods which will allow such a solution. Even m the case where the equations are not linear, they can be solved by, for example, developing a linear approximation or by the use of calibration tables. Those skilled in the arts will recognize that all such methods are equivalent or close approximations to the first method (using ratios of measurements) via the Uniqueness Theorem of Linear Systems. Therefore all equivalent mathematical techniques should be considered within the purview of this invention. The normalized ratio, once calculated, is related to the patient' s blood oxygen saturation through a calibration curve and is displayed on a conventional monitor.
In addition to the foregoing method, it is possible, using the three wavelengths, to make two independent two wavelength measurements of SaO... Motion would be revealed as a discrepancy between the two measurements. This additional method can be used to check the results from the first method and to reduce random or systematic non-common mode noise in the final determined value of SaO-, which may be displayed on a monitor. These additional measurements are optional.
Figure 3 shows a functional block diagram of the current invention. The overall apparatus 100 includes signal production and analysis circuitry 102, signal conduits 104 and a pulse oximetry probe 106. The signal production and analysis circuitry 102 can be included in a single enclosure 108 (as shown) or may be distributed as necessary and as will be appreciated by those skilled in the electronic circuitry arts. The signal conduits 104 carry signals between the signal production and analysis circuitry 102 and the pulse oximetry probe 106. The signal conduits 104 can carry electrical signals (in which case they will be electrical conductors, such as stranded copper wires) or they can carry optical signals (in which case they will be optical conductors, such as optical fibers) .
In the event that the signal conduits 104 are optical conductors, the signal production and analysis circuitry 102 can include a transmit signal circuit 110 that produces an electrical transmit signal. The electrical transmit signal is received by an optical signal circuit 112 over a line 114. The optical signal circuit 112 produces optical signals at three different wavelengths in response to the electrical transmit signal. Each of the three different wavelengths is produced by a separate source 116,, 116.>, and 116*. And then directed onto a first conduit 118 (which may be an optical fiber bundle) that carries the optical signals at the three different wavelengths to the pulse oximetry probe 106.
The three wavelength sources 116,, 116v, and 116, are shown as laser diodes which, in the preferred embodiment, are located in the enclosure 108. It is also possible that the three separate wavelength sources could be located at the site of the pulse oximetry probe 106, where they would respond to electrical signals carried by the first conduit 118 to the pulse oximetry probe 106. In either case, the three wavelength sources 116,, 116-, and 116, could be LEDs rather than laser diodes. If desired, the signal conduits 104 can be detachable from the pulse oximetry probe 106 at a connector 120. This enables the pulse oximetry probe 106 to be discarded or reprocessed for reuse, if desired. The detachable portion of the pulse oximetry probe 106 is usually connected to the patient's finger 122.
The three wavelength sources 116,, 116 , and 116, are pulsed sequentially by the transmit signal circuit 110, and the three wavelengths of light from the three wavelength sources transit the tip of the finger 122, after leaving an emitter 124. This light is received at a detector site 124, which may be either a fiber optic or a photodetector such as a photodiode. Signals, either optical or electronic, from the detector site 124 are transmitted through a return conduit 126 to the enclosure 108 for processing by a signal processing circuit 128.
The signal processing circuit 128 performs the mathematical equivalent of inverting the matrix of three equations in three signals to produce a common mode error-free pulse oximetry reading. As discussed above, one such mathematical method is via production of the super-ratio of signals. The signals received through the return conduit 126 are amplified by an amplifier 130 and then portions of the signals are sent to first and second ratio circuits 132 and 134. The first ratio circuit 132 produces the ratio of the magnitude of the first red wavelength signal to the magnitude of the infrared wavelength signal. The second ratio circuit 134 produces the ratio of the magnitude of the second red wavelength signal to the magnitude of the infrared wavelength signal. Signals representing these two ratios are then conducted to a final signal processing circuit 136 over respective signal lines 138 and 140. The final signal processing circuit 136 uses the signals carrying the two ratios and dedicated electronic circuitry (including a properly programmed microprocessor and calibration tables, as desired) to produce signals that indicate the current value of SaO/ or the presence of a common mode artifact on the conventional display 138.
Other equivalent methods of mathematical reduction in the final signal processing circuit 136 will be known to those skilled in the relevant arts. For example, the super-ratio measurement method can be used as a noise reduction technique, or as a check on the accuracy of the direct three wavelength measurement. The display 138 may choose the most optimal value, via additional processing in the final signal processing circuit 136 under any given circumstance.
While the foregoing is a detailed description of the preferred embodiment of the invention, there are many alternative embodiments of the invention that would occur to those skilled m the art and which are within the scope of the present invention. Accordingly, the present invention is to be determined by the following claims.

Claims

Claims
1. An apparatus for performing blood oximetry measurements in the body of an individual, the apparatus comprising: a transmit signal circuit to produce an electrical transmit signal; an optical signal circuit to receive the electrical transmit signal and to produce at least first, second and third optical signals in response thereto, the at least first, second and third optical signals including optical energy at at least three distinct optical wavelengths; a probe receiving the at least first, second and third optical signals, transmitting the at least first, second and third optical signals through a portion of the body of the individual, receiving the at least first, second and third optical signals after transmission through the portion of the body of the individual, and producing at least first, second and third transmission signals m response to the transmitted at least first, second and third optical signals; and a signal processing circuit to receive the at least first, second and third transmission signals and to produce an indication of blood oximetry measurements in the body of the individual in response thereto, regardless of whether the at least first, second and third optical signals are modified when the probe moves relative to the portion of the body of the individual .
2. The apparatus of claim 1 wherein the optical signal circuit comprises diode lasers for producing the at least first, second and third optical signals.
3. The apparatus of claim 1 wherein the at least first, second and third optical signals include an infrared signal, a first red signal and a second red signal.
4. The apparatus of claim 3, wherein the signal processing circuit makes a first measurement of SaO. by processing the infrared signal and the first red signal, and makes a second measurement of Sa02 by processing the infrared signal and the second red signal, the apparatus further comprising a motion artifact detection circuit to receive the first and second measurements of SaO; and to compare the first and second measurements of SaO_> to detect a motion artifact, the apparatus further including a detection signal circuit to produce a detection signal if a motion artifact is detected.
5. The apparatus of claim 1, wherein the signal processing circuit makes a first measurement of SaO by processing the first and second optical signals, and makes a second measurement of SaO by processing the second and third optical signals, the apparatus further comprising a motion artifact detection circuit to receive the first and second measurements of SaO and to compare the first and second measurements of SaO to detect a motion artifact, the apparatus further including a detection signal circuit to produce a detection signal if a motion artifact is detected.
6. The apparatus of claim 1, wherein the signal processing circuit produces an indication of blood oximetry measurements m the body of the individual by processing the at least first, second and third optical signals substantially concurrently.
7. An apparatus for performing blood oximetry measurements in the body of an individual in the presence of ambient light conditions, the apparatus comprising: a transmit signal circuit to produce an electrical transmit signal; an optical signal circuit to receive the electrical transmit signal and to produce at least first, second and third optical signals in response thereto, each of the at least first, second and third optical signals including optical energy at a distinct optical wavelength; a probe receiving the at least first, second and third optical signals, transmitting the at least first, second and third optical signals through a portion of the body of the individual, receiving the at least first, second and third optical signals after transmission through the portion of the body of the individual, and producing at least one transmission signal m response to the transmitted at least first, second and third optical signals, the at least one transmission signal being unaffected by the presence of the ambient light conditions; and a signal processing circuit to receive the at least first, second and third transmission signals and to produce an indication of blood oximetry measurements in the body of the individual, regardless of whether the at least first, second and third optical signals are modified when the probe moves relative to the portion of the body of the individual.
8. An apparatus for performing blood oximetry measurements m the body of an individual m the presence of ambient light conditions, the apparatus comprising: a transmit signal circuit to produce an electrical transmit signal; an optical signal circuit to receive the electrical transmit signal and to produce at least first, second and third optical signals in response thereto, each of the at least first, second and third optical signals including optical energy at a distinct optical wavelength; a probe receiving the at least first, second and third optical signals, transmitting the at least first, second and third optical signals through a portion of the body of the individual, receiving the at least first, second and third optical signals after transmission through the portion of the body of the individual, and producing at least first, second and third transmission signals in response to the transmitted at least first, second and third optical signals; and a signal processing circuit to receive the at least first, second and third transmission signals and to produce therefrom a system of equations representative of the relationships among the at least first, second and third transmission signals as a function of the SaO , the system of equations being solvable to produce an unambiguous measurement of the SaO?.
9. An apparatus for performing blood oximetry measurements in the body of an individual, the apparatus comprising: transmit signal circuit means for producing an electrical transmit signal; optical signal circuit means for receiving the electrical transmit signal and producing at least first, second and third optical signals in response thereto, the at least first, second and third optical signals including optical energy at at least three distinct optical wavelengths; probe means for receiving the at least first, second and third optical signals, for transmitting the at least first, second and third optical signals through a portion of the body of the individual, for receiving the at least first, second and third optical signals after transmission through the portion of the body of the individual, and for producing at least first, second and third transmission signals m response to the transmitted at least first, second and third optical signals; and signal processing circuit means for receiving the at least first, second and third transmission signals and for producing an indication of blood oximetry measurements m the body of the individual in response thereto, regardless of whether the at least first, second and third optical signals are modified when the probe moves relative to the portion of the body of the individual.
10. A method for performing blood oximetry measurements in the body of an individual, the method comprising the steps of: a) producing an electrical transmit signal; b) receiving the electrical transmit signal; c) producing at least first, second and third optical signals m response to the electrical transmit signal, the at least first, second and third optical signals including optical energy at distinct optical wavelengths; d) transmitting the at least first, second and third optical signals through a portion of the body of the individual; e) receiving the at least first, second and third optical signals after transmission through the portion of the body of the individual; f) producing at least first, second and third transmission signals in response to the transmitted at least first, second and third optical signals; g) receiving the at least first, second and third transmission signals; and h) producing an indication of blood oximetry measurements in the body of the individual m response to the at least first, second and third transmission signals, regardless of whether the at least first, second and third optical signals are modified when the probe moves relative to the portion of the body of the individual.
PCT/US1997/011263 1996-06-27 1997-06-27 Motion artifact resistant oximeter using three wavelengths WO1997049330A1 (en)

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US08/670,155 1996-06-27

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EP1013218A3 (en) * 1998-12-25 2001-06-06 Mitsui Mining & Smelting Co., Ltd. Blood sugar value measuring method and apparatus
DE10321338A1 (en) * 2003-05-13 2004-12-02 MCC Gesellschaft für Diagnosesysteme in Medizin und Technik mbH & Co. KG Method and device for determining blood components using the method of ratiometric absolute pulse spectroscopy
US7277741B2 (en) * 2004-03-09 2007-10-02 Nellcor Puritan Bennett Incorporated Pulse oximetry motion artifact rejection using near infrared absorption by water
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US7684842B2 (en) 2006-09-29 2010-03-23 Nellcor Puritan Bennett Llc System and method for preventing sensor misuse
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US10076276B2 (en) 2008-02-19 2018-09-18 Covidien Lp Methods and systems for alerting practitioners to physiological conditions

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Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1013218A3 (en) * 1998-12-25 2001-06-06 Mitsui Mining & Smelting Co., Ltd. Blood sugar value measuring method and apparatus
DE10321338A1 (en) * 2003-05-13 2004-12-02 MCC Gesellschaft für Diagnosesysteme in Medizin und Technik mbH & Co. KG Method and device for determining blood components using the method of ratiometric absolute pulse spectroscopy
US7277741B2 (en) * 2004-03-09 2007-10-02 Nellcor Puritan Bennett Incorporated Pulse oximetry motion artifact rejection using near infrared absorption by water
US9351674B2 (en) 2005-03-03 2016-05-31 Covidien Lp Method for enhancing pulse oximetry calculations in the presence of correlated artifacts
US8965473B2 (en) 2005-09-29 2015-02-24 Covidien Lp Medical sensor for reducing motion artifacts and technique for using the same
US8600469B2 (en) 2005-09-29 2013-12-03 Covidien Lp Medical sensor and technique for using the same
US8219170B2 (en) 2006-09-20 2012-07-10 Nellcor Puritan Bennett Llc System and method for practicing spectrophotometry using light emitting nanostructure devices
US8315685B2 (en) 2006-09-27 2012-11-20 Nellcor Puritan Bennett Llc Flexible medical sensor enclosure
US10022058B2 (en) 2006-09-28 2018-07-17 Covidien Lp System and method for pulse rate calculation using a scheme for alternate weighting
US7684842B2 (en) 2006-09-29 2010-03-23 Nellcor Puritan Bennett Llc System and method for preventing sensor misuse
WO2008042147A3 (en) * 2006-09-29 2008-05-22 Nellcor Puritan Bennett Llc Symmetric led array for pulse oximetry
WO2008042147A2 (en) * 2006-09-29 2008-04-10 Nellcor Puritan Bennett Llc Symmetric led array for pulse oximetry
US8280469B2 (en) 2007-03-09 2012-10-02 Nellcor Puritan Bennett Llc Method for detection of aberrant tissue spectra
US8265724B2 (en) 2007-03-09 2012-09-11 Nellcor Puritan Bennett Llc Cancellation of light shunting
US10076276B2 (en) 2008-02-19 2018-09-18 Covidien Lp Methods and systems for alerting practitioners to physiological conditions
US11298076B2 (en) 2008-02-19 2022-04-12 Covidien Lp Methods and systems for alerting practitioners to physiological conditions
US8862194B2 (en) 2008-06-30 2014-10-14 Covidien Lp Method for improved oxygen saturation estimation in the presence of noise
US9895068B2 (en) 2008-06-30 2018-02-20 Covidien Lp Pulse oximeter with wait-time indication
US8930145B2 (en) 2010-07-28 2015-01-06 Covidien Lp Light focusing continuous wave photoacoustic spectroscopy and its applications to patient monitoring
US9833146B2 (en) 2012-04-17 2017-12-05 Covidien Lp Surgical system and method of use of the same
US9924896B2 (en) 2014-06-23 2018-03-27 Koninklijke Philips N.V. Device, system and method for determining the concentration of a substance in the blood of a subject

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