WO2003011127A1 - Optoelectronic blood analytical apparatus - Google Patents

Optoelectronic blood analytical apparatus Download PDF

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Publication number
WO2003011127A1
WO2003011127A1 PCT/GB2002/003370 GB0203370W WO03011127A1 WO 2003011127 A1 WO2003011127 A1 WO 2003011127A1 GB 0203370 W GB0203370 W GB 0203370W WO 03011127 A1 WO03011127 A1 WO 03011127A1
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WO
WIPO (PCT)
Prior art keywords
light
frequencies
analytical apparatus
attenuation
photosensitive means
Prior art date
Application number
PCT/GB2002/003370
Other languages
French (fr)
Inventor
Geoffrey Richard Mathews
Veronica Mary Mathews
Original Assignee
The Electrode Company Limited
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 The Electrode Company Limited filed Critical The Electrode Company Limited
Publication of WO2003011127A1 publication Critical patent/WO2003011127A1/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
    • A61B5/1455—Measuring 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
    • A61B5/14551—Measuring 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

Definitions

  • Pulse oximetry is a widely used technique for determining the level of oxygen saturation of a subject's blood.
  • the technique involves measuring, at two or more pre- determined frequencies, the level of attenuation of light transmitted through or reflected from a human or animal body part (the transmission technique typically being applied to an ear lobe or finger) and comparing those measurements with pre- stored, experimentally and/or theoretically derived reference data to provide an estimate of the level of oxygen saturation
  • a typical pulse oximetry apparatus comprises a monitor and a sensor, the sensor comprising a pair of light emitters, such as a pair of light emitting diodes (LEDs) , for transmitting light, at red and infra-red frequencies respectively, through a body part .
  • a pair of light emitters such as a pair of light emitting diodes (LEDs)
  • an analytical apparatus comprising: a light source for transmitting light through a test medium at at least two different frequencies; means for calculating a ratio of the respective levels of attenuation of the light transmitted through the test medium at each of said two frequencies; a memory storing, for different combinations of transmission frequencies, experimentally and/or theoretically derived reference data corresponding to different attenuation ratios at those frequencies; and photosensitive means, preferably a spectrometer, for measuring at least one parameter of the light emitted by the light source to obtain appropriate data from the memory.
  • the photosensitive means are used to identify said two frequencies from respective peaks in the spectrum of the light emitted by the light source, to obtain, from the memory, stored data corresponding to the calculated attenuation ratios at the two frequencies identified.
  • the apparatus does not require means for varying the drive current applied to the light source to adjust the frequency of the light emitted therefrom.
  • the level of attenuation of the light emitted at each of said two frequencies may be measured either by the photosensitive means or by some further photosensitive means, such as one or more photodiodes.
  • the photosensitive means may be arranged to receive light from the light source, either before or after that light has been transmitted through the test medium.
  • the light source preferably comprises a pair of light emitters, such as a pair of light emitting diodes, arranged to emit light at the first and the second of said two frequencies respectively.
  • the light source is arranged to emit a range of frequencies of light
  • the photosensitive means are used to measure the level of attenuation of the light emitted at each of two chosen frequencies within that range, to obtain, from the memory, stored data corresponding to the calculated attenuation ratios at each of the chosen frequencies .
  • the light source may comprise a plurality of light emitters, such as a pair of light emitting diodes, arranged to emit light at the first and the second of said two frequencies respectively.
  • a single light emitter e.g. a white- light emitter
  • the test medium comprises a human or animal body part and the apparatus is arranged such that the attenuation ratio is calculated from attenuation measurements taken over a period of time (to take into account the pulsatile nature of the subject's oxygenated arterial blood flow), the stored data preferably comprising a set of experimentally and/or theoretically derived values of the level of oxygenation of the subject's blood.
  • Conventional pulse oximetry apparatus assume a substantially uniform rate of venous blood flow when deriving an estimate of blood oxygenation. However, it can be shown that, in certain circumstances, venous blood flow can have a pulsatile component which can effect the accuracy of the blood oxygenation estimate.
  • the undesirable influence of noise factors, such as pulsatile or irregular venous blood flow, on the analytical accuracy of the apparatus is preferably reduced by measuring the level of light attenuation at at least one reference frequency, in addition to said two frequencies .
  • attenuation measurements may also or otherwise be taken at more than said, two frequencies, to simultaneously identify and/or quantify a plurality of constituents of the test medium which, with a subject's blood as the test medium, might include carboxyhaemoglobin, bilirubin, methaemoglobin or sickle-cell haemoglobin.
  • Figure 1 is a schematic view of a first embodiment of analytical apparatus in accordance with the present invention
  • Figure 2 is a graph showing the relationship between the level of oxygen saturation of a subject's blood and a ratio of the levels of attenuation of light transmitted through a body part from red and infra-red light emitters respectively.
  • Figure 3 is a schematic view of a second embodiment of analytical apparatus in accordance with the present invention.
  • Figure 4 is a schematic view of a third embodiment of analytical apparatus in accordance with the present invention.
  • Figure 5 is a schematic view of a fourth embodiment of analytical apparatus in accordance with the present invention.
  • an analytical apparatus comprising a pair of light emitting diodes (LEDs) 2,4 arranged to transmit red and infra-red light respectively, through a subject's finger 6, to a photo-detector (PD) 8.
  • LEDs light emitting diodes
  • PD photo-detector
  • the PD 8 provides, as output, respective measurements corresponding to the levels of attenuation of the red and infra-red light through the finger 6.
  • Processing means (not shown) derive a ratio of the two attenuation measurements and obtain from a memory a pre-stored, experimentally and/or theoretically derived estimate of the level of oxygen saturation (Sa0 2 ) of the subject's blood for that particular attenuation ratio.
  • reference data is stored for only a single pair of emission frequencies.
  • Figure 2 shows a set of standard reference data, in the form of a so- called R-curve, relating blood oxygen content to the attenuation of red and infra-red light at frequencies of 665nm and 900nm respectively.
  • the apparatus of Figure 1 overcomes this problem by storing respective R-curves for a large variety of combinations of red and infra-red frequencies and by providing a miniature spectrometer 10 for analyzing the spectrum of the light transmitted by the two LEDs 2,4, to select an appropriate R- curve for those LEDs .
  • a portion of the light emitted by the LEDs 2,4 is collected prior to being transmitted through the subject's finger 6 and channeled to the spectrometer 10 by a fibre-optic light guide 12.
  • the apparatus of Figure 3 operates in substantially the same manner as that of Figure 1, except that the fibre-optic light guide 12 is instead arranged to collect a portion of the light which has already passed through the subject's finger 6, thereby taking into account any scattering of the light which might occur as the light travels through the finger.
  • the spectrometer 10 serves both to select an appropriate R-curve (according to the respective emission frequencies of the two LEDs 2,4) and to provide measurements of the respective levels of attenuation at each of those frequencies, for obtaining an appropriate estimate of blood oxygenation from the selected curve.
  • the red and infra-red LEDs 2,4 are replaced by a single, large-bandwidth light- emitter 14 and the spectrometer 10 serves to provide attenuation measurements at any two chosen frequencies within that bandwidth, which measurements may then be used to obtain a blood oxygenation estimate from an R-curve stored in memory for the chosen frequencies.
  • the analytical apparatus thus described do not require any complicated feedback means for controlling the frequencies of light emitted by their light emitters and can each be used to obtain light attenuation measurements over a range of frequencies using one or more light emitter (s) .

Abstract

An analytical apparatus comprising a light source (2, 4) for transmitting light through a test medium (6), a memory storing reference data and photosensitive means (10) for measuring at least one parameter of the light emitted by the light source (2, 4) to obtain appropriate data from the memory.

Description

OPTOELECTRONIC BLOOD ANALYSING APPARATUS
Pulse oximetry is a widely used technique for determining the level of oxygen saturation of a subject's blood.
The technique involves measuring, at two or more pre- determined frequencies, the level of attenuation of light transmitted through or reflected from a human or animal body part (the transmission technique typically being applied to an ear lobe or finger) and comparing those measurements with pre- stored, experimentally and/or theoretically derived reference data to provide an estimate of the level of oxygen saturation
(Sa02) of the subject's blood.
A typical pulse oximetry apparatus comprises a monitor and a sensor, the sensor comprising a pair of light emitters, such as a pair of light emitting diodes (LEDs) , for transmitting light, at red and infra-red frequencies respectively, through a body part .
However, a serious problem arises where the frequency of light emitted from one or other of the light emitters deviates from its expected value, so that the attenuation measurements no longer correspond with the experimentally and/or theoretically derived reference data. This problem becomes particularly acute at the low values of blood oxygen saturation, where the accuracy of estimates are most critical. A deviation of the frequency of light emitted by a light emitter from its expected value might, for example, result from an incorrect light emitter having been selected during the assembly of the sensor, from manufacturing tolerances in the formation of the light emitter, from the complete failure of the light emitter, from a gradual degradation in the performance of the light emitter over a period of time, or from a change in the ambient conditions
(such as the temperature) under which the sensor is operated.
It has been proposed to overcome this limitation of existing apparatus by providing means for adjusting the drive current supplied to each light emitter (and thus the frequency of its emitted light) to achieve a desired emission frequency for that emitter.
However, such an arrangement is only of limited use, as firstly, only a small degree of correction can be achieved by varying the drive current, before other performance characteristics of a light emitter are effected. Secondly, the degree of correction achieved might not be that predicted theoretically. Thirdly, the correction is usually applied during the manufacture of an apparatus, which is therefore still vulnerable to subsequent changes in the emission frequency of a light emitter thereof.
It is a first object of the present invention to provide an arrangement which obviates the requirement for varying the drive current supplied to a light emitter of an analytical apparatus, to regulate the frequency of its emitted light.
It is a second object of the present invention to provide an analytical apparatus wherein a single light emitter may be used to obtain light attenuation measurements over a range of frequencies.
In accordance with the present invention, there is provided an analytical apparatus comprising: a light source for transmitting light through a test medium at at least two different frequencies; means for calculating a ratio of the respective levels of attenuation of the light transmitted through the test medium at each of said two frequencies; a memory storing, for different combinations of transmission frequencies, experimentally and/or theoretically derived reference data corresponding to different attenuation ratios at those frequencies; and photosensitive means, preferably a spectrometer, for measuring at least one parameter of the light emitted by the light source to obtain appropriate data from the memory. In a first preferred embodiment of the present invention, the photosensitive means are used to identify said two frequencies from respective peaks in the spectrum of the light emitted by the light source, to obtain, from the memory, stored data corresponding to the calculated attenuation ratios at the two frequencies identified.
Thus, the apparatus does not require means for varying the drive current applied to the light source to adjust the frequency of the light emitted therefrom. In this case, the level of attenuation of the light emitted at each of said two frequencies may be measured either by the photosensitive means or by some further photosensitive means, such as one or more photodiodes. In the former case, the photosensitive means may be arranged to receive light from the light source, either before or after that light has been transmitted through the test medium.
The light source preferably comprises a pair of light emitters, such as a pair of light emitting diodes, arranged to emit light at the first and the second of said two frequencies respectively.
In a second preferred embodiment of the present invention, the light source is arranged to emit a range of frequencies of light, and the photosensitive means are used to measure the level of attenuation of the light emitted at each of two chosen frequencies within that range, to obtain, from the memory, stored data corresponding to the calculated attenuation ratios at each of the chosen frequencies .
In this case, the light source may comprise a plurality of light emitters, such as a pair of light emitting diodes, arranged to emit light at the first and the second of said two frequencies respectively.
Alternatively, a single light emitter, e.g. a white- light emitter, may be used to obtain attenuation measurements within a range of frequencies. Preferably the test medium comprises a human or animal body part and the apparatus is arranged such that the attenuation ratio is calculated from attenuation measurements taken over a period of time (to take into account the pulsatile nature of the subject's oxygenated arterial blood flow), the stored data preferably comprising a set of experimentally and/or theoretically derived values of the level of oxygenation of the subject's blood.
Conventional pulse oximetry apparatus assume a substantially uniform rate of venous blood flow when deriving an estimate of blood oxygenation. However, it can be shown that, in certain circumstances, venous blood flow can have a pulsatile component which can effect the accuracy of the blood oxygenation estimate.
In the apparatus according to the present invention, the undesirable influence of noise factors, such as pulsatile or irregular venous blood flow, on the analytical accuracy of the apparatus is preferably reduced by measuring the level of light attenuation at at least one reference frequency, in addition to said two frequencies . It will be appreciated that attenuation measurements may also or otherwise be taken at more than said, two frequencies, to simultaneously identify and/or quantify a plurality of constituents of the test medium which, with a subject's blood as the test medium, might include carboxyhaemoglobin, bilirubin, methaemoglobin or sickle-cell haemoglobin.
Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a first embodiment of analytical apparatus in accordance with the present invention;
Figure 2 is a graph showing the relationship between the level of oxygen saturation of a subject's blood and a ratio of the levels of attenuation of light transmitted through a body part from red and infra-red light emitters respectively. Figure 3 is a schematic view of a second embodiment of analytical apparatus in accordance with the present invention;
Figure 4 is a schematic view of a third embodiment of analytical apparatus in accordance with the present invention; and
Figure 5 is a schematic view of a fourth embodiment of analytical apparatus in accordance with the present invention.
Referring to Figure 1, an analytical apparatus is shown comprising a pair of light emitting diodes (LEDs) 2,4 arranged to transmit red and infra-red light respectively, through a subject's finger 6, to a photo-detector (PD) 8.
The PD 8 provides, as output, respective measurements corresponding to the levels of attenuation of the red and infra-red light through the finger 6. Processing means (not shown) derive a ratio of the two attenuation measurements and obtain from a memory a pre-stored, experimentally and/or theoretically derived estimate of the level of oxygen saturation (Sa02) of the subject's blood for that particular attenuation ratio. In conventional apparatus, reference data is stored for only a single pair of emission frequencies. For example, Figure 2 shows a set of standard reference data, in the form of a so- called R-curve, relating blood oxygen content to the attenuation of red and infra-red light at frequencies of 665nm and 900nm respectively.
It will be appreciated that in a conventional apparatus using reference data for only a single pair of emission frequencies, any deviation in the frequency of light emitted by either the red or the infra-red LED 2,4 will result in an incorrect estimation of the subject's blood oxygenation level.
The apparatus of Figure 1 overcomes this problem by storing respective R-curves for a large variety of combinations of red and infra-red frequencies and by providing a miniature spectrometer 10 for analyzing the spectrum of the light transmitted by the two LEDs 2,4, to select an appropriate R- curve for those LEDs .
In the apparatus of Figure 1, a portion of the light emitted by the LEDs 2,4 is collected prior to being transmitted through the subject's finger 6 and channeled to the spectrometer 10 by a fibre-optic light guide 12.
The apparatus of Figure 3 operates in substantially the same manner as that of Figure 1, except that the fibre-optic light guide 12 is instead arranged to collect a portion of the light which has already passed through the subject's finger 6, thereby taking into account any scattering of the light which might occur as the light travels through the finger.
In the apparatus of Figure 4, the spectrometer 10 serves both to select an appropriate R-curve (according to the respective emission frequencies of the two LEDs 2,4) and to provide measurements of the respective levels of attenuation at each of those frequencies, for obtaining an appropriate estimate of blood oxygenation from the selected curve.
In the apparatus of Figure 5, the red and infra-red LEDs 2,4 are replaced by a single, large-bandwidth light- emitter 14 and the spectrometer 10 serves to provide attenuation measurements at any two chosen frequencies within that bandwidth, which measurements may then be used to obtain a blood oxygenation estimate from an R-curve stored in memory for the chosen frequencies. The analytical apparatus thus described do not require any complicated feedback means for controlling the frequencies of light emitted by their light emitters and can each be used to obtain light attenuation measurements over a range of frequencies using one or more light emitter (s) .

Claims

Claims
1) An analytical apparatus comprising: a light source for transmitting light through a test medium at at least two different frequencies; means for calculating a ratio of the respective levels of attenuation of the light transmitted through the test medium at each of said two frequencies; a memory storing, for different combinations of transmission frequencies, experimentally and/or theoretically derived reference data corresponding to different attenuation ratios at those frequencies; and photosensitive means, for measuring at least one parameter of the light emitted by the light source to obtain appropriate data from the memory.
2) An analytical apparatus as claimed in Claim 1, wherein the photosensitive means are used to identify said two frequencies from respective peaks in the spectrum of the light emitted by the light source, to obtain, from the memory, stored data corresponding to the calculated attenuation ratios at the two frequencies identified.
3) An analytical apparatus as claimed in Claim 2, wherein the level of attenuation of the light emitted at each of said two frequencies is measured by the photosensitive means .
4) An analytical apparatus as claimed in Claim 3, wherein the photosensitive means are arranged to receive light from the light source before that light has been transmitted through the test medium.
5) An analytical apparatus as claimed in Claim 3, wherein the photosensitive means are arranged to receive light from the light source after that light has been transmitted through the test medium.
6) An analytical apparatus as claimed in Claim 2 , wherein the level of attenuation of the light emitted at each of said two frequencies is measured by further photosensitive means.
7) An analytical apparatus as claimed in Claim 6, wherein said further photosensitive means comprise one or more photodiodes
8) An analytical apparatus as claimed in any of Claims 2 to 7 , wherein the light source comprises a pair of light emitters, arranged to emit light at the first and the second of said two frequencies respectively.
9) An analytical apparatus as claimed in Claim 8, wherein said light emitters comprise a pair of light emitting diodes.
10) An analytical apparatus as claimed in Claim 1, wherein the light source is arranged to emit a range of frequencies of light, and the photosensitive means are used to measure the level of attenuation of the light emitted at each of two chosen frequencies within that range, to obtain, from the memory, stored data corresponding to the calculated attenuation ratios at each of the chosen frequencies.
11) An analytical apparatus as claimed in Claim 10, wherein the light source comprises a plurality of light emitters, arranged to emit light at the first and the second of said two frequencies respectively.
12) An analytical apparatus as claimed in Claim 11, wherein said light emitters comprise a pair of light emitting diodes.
13) An analytical apparatus as claimed in Claim 10, wherein a single light emitter is used to obtain attenuation measurements within a range of frequencies.
14) An analytical apparatus as claimed in Claim 13, wherein said single light emitter comprises a white light emitter.
15) An analytical apparatus as claimed in any preceding claim, wherein the test medium comprises a human or animal body part and the apparatus is arranged such that the attenuation ratio is calculated from attenuation measurements taken over a period of time (to take into account the pulsatile nature of the subject's oxygenated arterial blood flow), the stored data preferably comprising a set of experimentally and/or theoretically derived values of the level of oxygenation of the subject's blood.
16) An analytical apparatus as claimed in any preceding claim, wherein the undesirable influence of noise factors on the analytical accuracy of the apparatus is reduced, by measuring the level of . light attenuation at at least one reference frequency, in addition to said two frequencies.
17) An analytical apparatus as claimed in any preceding claim, wherein attenuation measurements are taken at more than said two frequencies, to simultaneously identify and/or quantify a plurality of constituents of the test medium.
18) An analytical apparatus as claimed in any preceding claim, wherein said photosensitive means comprise a spectrometer.
PCT/GB2002/003370 2001-08-02 2002-07-23 Optoelectronic blood analytical apparatus WO2003011127A1 (en)

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GB0118966A GB2382406B (en) 2001-08-02 2001-08-02 Analytical apparatus
GB0118966.1 2001-08-02

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US7684842B2 (en) 2006-09-29 2010-03-23 Nellcor Puritan Bennett Llc System and method for preventing sensor misuse
US8219170B2 (en) 2006-09-20 2012-07-10 Nellcor Puritan Bennett Llc System and method for practicing spectrophotometry using light emitting nanostructure devices
US8265724B2 (en) 2007-03-09 2012-09-11 Nellcor Puritan Bennett Llc Cancellation of light shunting
US8280469B2 (en) 2007-03-09 2012-10-02 Nellcor Puritan Bennett Llc Method for detection of aberrant tissue spectra
US8315685B2 (en) 2006-09-27 2012-11-20 Nellcor Puritan Bennett Llc Flexible medical sensor enclosure
US8600469B2 (en) 2005-09-29 2013-12-03 Covidien Lp Medical sensor and technique for using the same
US8965473B2 (en) 2005-09-29 2015-02-24 Covidien Lp Medical sensor for reducing motion artifacts and technique for using the same
US9010634B2 (en) 2009-06-30 2015-04-21 Covidien Lp System and method for linking patient data to a patient and providing sensor quality assurance
US9066660B2 (en) 2009-09-29 2015-06-30 Nellcor Puritan Bennett Ireland Systems and methods for high-pass filtering a photoplethysmograph signal
WO2017129633A1 (en) * 2016-01-25 2017-08-03 Prediktor Medical As Calibrating the output of a light-emitting diode
US9895068B2 (en) 2008-06-30 2018-02-20 Covidien Lp Pulse oximeter with wait-time indication
CN110811639A (en) * 2019-11-06 2020-02-21 浙江清华柔性电子技术研究院 Total bilirubin detection patch and total bilirubin detection system

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Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8600469B2 (en) 2005-09-29 2013-12-03 Covidien Lp Medical sensor and technique for using the same
US8965473B2 (en) 2005-09-29 2015-02-24 Covidien Lp Medical sensor for reducing motion artifacts 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
US7684842B2 (en) 2006-09-29 2010-03-23 Nellcor Puritan Bennett Llc System and method for preventing sensor misuse
US8265724B2 (en) 2007-03-09 2012-09-11 Nellcor Puritan Bennett Llc Cancellation of light shunting
US8280469B2 (en) 2007-03-09 2012-10-02 Nellcor Puritan Bennett Llc Method for detection of aberrant tissue spectra
US9895068B2 (en) 2008-06-30 2018-02-20 Covidien Lp Pulse oximeter with wait-time indication
US9010634B2 (en) 2009-06-30 2015-04-21 Covidien Lp System and method for linking patient data to a patient and providing sensor quality assurance
US9066660B2 (en) 2009-09-29 2015-06-30 Nellcor Puritan Bennett Ireland Systems and methods for high-pass filtering a photoplethysmograph signal
US9649071B2 (en) 2009-09-29 2017-05-16 Nellcor Puritan Bennett Ireland Systems and methods for high-pass filtering a photoplethysmograph signal
WO2017129633A1 (en) * 2016-01-25 2017-08-03 Prediktor Medical As Calibrating the output of a light-emitting diode
CN107926093A (en) * 2016-01-25 2018-04-17 普雷迪科特医疗有限公司 Calibrate the output of light emitting diode
CN107926093B (en) * 2016-01-25 2020-10-30 普雷迪科特医疗有限公司 Method and apparatus for calibrating output intensity of light emitting diode in photoelectric sensor
CN110811639A (en) * 2019-11-06 2020-02-21 浙江清华柔性电子技术研究院 Total bilirubin detection patch and total bilirubin detection system
CN110811639B (en) * 2019-11-06 2023-11-21 浙江清华柔性电子技术研究院 Total bilirubin detection patch and total bilirubin detection system

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