WO2006083180A1 - Ambient light auto-zero circuit for photo-optical physiological monitoring equipment - Google Patents
Ambient light auto-zero circuit for photo-optical physiological monitoring equipment Download PDFInfo
- Publication number
- WO2006083180A1 WO2006083180A1 PCT/NZ2005/000027 NZ2005000027W WO2006083180A1 WO 2006083180 A1 WO2006083180 A1 WO 2006083180A1 NZ 2005000027 W NZ2005000027 W NZ 2005000027W WO 2006083180 A1 WO2006083180 A1 WO 2006083180A1
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- WO
- WIPO (PCT)
- Prior art keywords
- signal
- photo
- power reduction
- processed
- feedback circuit
- Prior art date
- Legal status (The legal status 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 status listed.)
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/02—Details
- G01J1/08—Arrangements of light sources specially adapted for photometry standard sources, also using luminescent or radioactive material
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/4204—Photometry, e.g. photographic exposure meter using electric radiation detectors with determination of ambient light
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/55—Specular reflectivity
-
- 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 or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue
- A61B5/14532—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue for measuring glucose, e.g. by tissue impedance measurement
-
- 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 or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue
- A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/06—Illumination; Optics
- G01N2201/064—Stray light conditioning
Definitions
- photo-optical medical monitoring equipment means equipment designed to receive signals from sensors incorporating light emitting diodes, said sensors being connected to or associated with a subject, to monitor one or more physiological parameters of that subject.
- the term includes sensors, monitors, and adapters in the related field
- a wide range of physiological monitoring equipment is currently available, for monitoring one or more of a number of different physiological parameters Typically these devices are used for medical monitoring Medical monitoring equipment often has the ability to record the analysis of signals from sensors, and include an alarm system to alert medical staff of undesirable or dangerous changes in the patient's condition
- a sensor designed to sense the selected physiological parameter is attached to the patient and is connected to a monitor by a cable
- the l ⁇ ght-source(s) of the sensor shine through or into the target site Transmitted or reflected light falling on a photo-detector component of the sensor causes the photo-detector to generate an electrical signal corresponding to the physiological parameter being sensed
- the electrical signal is transmitted directly or digitised and transmitted to the monitor by various means including, but not limited to, a conducting wire or infrared, radio- frequency, or fibre-optic connections
- Photo-optical sensors require power to operate, and even relatively low-power light sources are often the major element in a sensor power budget Therefore, the light source power consumption becomes a limiting factor in continuous operational performance life-time for physiological monitoring devices with finite power supplies such as, but not limited to, batteries or solar cells This limitation is particularly important in the burgeoning field of portable sensors, sensor adapters, and portable monitors
- the light source is therefore typically switched on and off rapidly during operation to minimise the power consumption
- the term light' as herein used includes the electromagnetic frequencies from far infra-red through visible light to extreme ultraviolet
- the photo-detector measures the light transmitted or reflected by the target site, and the ambient light falling on the sensor This ambient light falling on the photo-detector increases the electrical signal from the photo-detector which can obscure the electrical signal representing the physiological parameter being measured, making it more difficult to obtain an accurate reading, this ambient light signal can therefore be considered noise
- the ambient light signal increases the overall magnitude of the electrical signal from the photo-detector and can therefore increase the power required to process and transmit the signal to the monitor
- a further object of the invention is to reduce the relative magnitude of the ambient light component in the photo-detector signal thus increase the dynamic range of the analogue to digital converter by maximising the signal to noise ratio
- the present invention provides a power reduction circuit for photo-optical physiological monitoring equipment adapted to be used to measure one or more physiological properties of a patient at preset intervals by illuminating a portion of the patient with one or more light sources, which produces a reflected or transmitted modified light signal representative of the physiological property being measured, the modified light signal is detected by a photo-sensor which produces a raw output signal, which includes an ambient light component, that is representative of the modified light signal, characterised in that the power reduction circuit includes i an adding unit adapted to produce a processed signal by adding the raw output signal to a second signal, ii a first signal buffer adapted to retain the processed signal, in a processing unit which further processes the processed signal, iv an isolating switch which is controlled by the processing unit and is connected to the first signal buffer, said isolating switch being adapted to reversibly connect the first signal buffer to a feed back circuit, v said feedback circuit is adapted to generate the second signal from the processed signal, and includes a second signal buffer, which is adapted
- the feedback circuit includes a high frequency filter before the second signal buffer
- the power reduction circuit includes additional signal processing circuitry in the feedback circuit or photo-detector output
- the second signal can be further processed prior to the adding unit
- a method of using the power reduction circuit includes the following steps in order a the isolating switch is opened by the processing unit, isolating the feedback circuit and locking the second signal level in the second signal buffer, b the or each light source is turned on, c the raw output signal is added to the second signal, generating the processed signal, d the or each light source is turned off, e the isolating switch is closed
- FIG. 1 is a block diagram of the invention
- FIG. 2 is a flowchart showing the steps involved in an active measurement cycle using the invention
- Figure 3 is a block diagram of a second embodiment of the invention which includes additional filters in the feedback circuit
- Figure 4 is a flowchart showing the steps involved in a further embodiment of the invention that carries out a second active measurement cycle using a second light source shortly after a first active measurement cycle with a first light source
- the invention includes a photo-detector (3), a light source (1), an adder (4), a first signal buffer (5) and a processing unit (8), all connected in series in that order
- the light source (1) is adapted to illuminate a portion of a subject (2) for a period of time, the light from the light source (1 ) interacts with the portion of the subject (2) and is modified
- the photo-detector (3) is adapted to respond to certain properties of this modified light and generate an output signal whose properties are dependent upon the ambient light and modified light received
- the output signal is transmitted to the adder (4) which combines it with a second signal producing an adder signal
- the first signal buffer (5) is adapted to retain the adder signal for a period of time prior to further processing
- the invention further includes an isolating switch (9), which is adapted to be controlled by the processing unit (8), and a feedback circuit (13)
- the isolating switch (9) is connected at a point between the first signal buffer (5) output and the processing unit
- the feedback circuit (13) includes a high frequency filter (10), a second signal buffer (11) and an inverting amplifier (12), connected in that order in series wherein
- the high frequency filter (10) is adapted to remove the high frequency noise from the first signal buffer (5) output signal, generating a filtered signal which is transmitted to the second signal buffer (11), ii the second signal buffer (11) is adapted to retain the filtered signal for processing by the inverting amplifier (12), Hi the inverting amplifier (12) is adapted to invert and amplify the filtered signal from the second signal buffer (11) generating the second signal which is then transmitted to the adder (4)
- the output signal, prior to the light source (1) being turned on, is representative of the ambient light impinging on the photo-detector (3) During this time the isolating switch
- an active measurement cycle (20) is commenced and the isolating switch (9) is opened
- the second signal buffer (11) retains the filtered signal stored at that time, and the second signal is fixed at a level representative of the ambient light level immediately prior to the active measurement cycle (20) being commenced
- the light source (1) is turned on and the photo-detector generates an output signal containing ambient light and modified light components
- the output signal from the photo-detector (3) during the active measurement cycle (20) is added to the second signal (which is representative of the ambient light level prior to the measurement cycle), so that the resulting adder signal is effectively free from the ambient light component
- the adder signal is then transmitted via the first signal buffer (5) to the processing unit (8) for further processing. Once the further processing, which may involve multiple reading of the first signal buffer (5), has been completed the processing unit (8) turns the light source (1 ) off and closes the isolating switch (9) completing the active measurement cycle (20).
- one or more additional signal filters (14) are placed in the feedback circuit (13), and the output signal is pre-processed prior to the adder (4).
- a second active measurement cycle (2) is undertaken shortly after the first using a different frequency light source (1 ).
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- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- General Health & Medical Sciences (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Pathology (AREA)
- Biophysics (AREA)
- Medical Informatics (AREA)
- Analytical Chemistry (AREA)
- Immunology (AREA)
- Chemical & Material Sciences (AREA)
- Sustainable Development (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- Biochemistry (AREA)
- Molecular Biology (AREA)
- Surgery (AREA)
- Animal Behavior & Ethology (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
- Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)
Abstract
A power reduction circuit for photo-optical physiological monitoring equipment adapted to measure a physiological property of a patient by illuminating a portion of the patient with one or more light sources producing a modified light signal which is detected by a photo-sensor, generating a raw output signal which includes an ambient light component, characterized in that the power reduction circuit includes: ii. An adding unit that produces a processed signal by adding the raw output signal to a second signal; ii a first signal buffer to store the processed signal; iii a processing unit; iv an isolating switch to control a feed back circuit; v an inverting amplifier, which amplifies and inverts a stored processed signal generating the second signal; such that the processed signal generated when the isolating switch is open, during the measurement of the desired physiological property, is effectively free of the ambient light component.
Description
TITLE AMBIENT LIGHT AUTO-ZERO CIRCUIT FOR PHOTO-OPTICAL PHYSIOLOGICAL MONITORING EQUIPMENT
Technical Field The present invention relates to photo-optical medical monitoring equipment As used herein, the term "photo-optical medical monitoring equipment" means equipment designed to receive signals from sensors incorporating light emitting diodes, said sensors being connected to or associated with a subject, to monitor one or more physiological parameters of that subject The term includes sensors, monitors, and adapters in the related field
A wide range of physiological monitoring equipment is currently available, for monitoring one or more of a number of different physiological parameters Typically these devices are used for medical monitoring Medical monitoring equipment often has the ability to record the analysis of signals from sensors, and include an alarm system to alert medical staff of undesirable or dangerous changes in the patient's condition
Background Art
In the most commonly used types of photo-optical physiological monitoring equipment, a sensor designed to sense the selected physiological parameter is attached to the patient and is connected to a monitor by a cable In use, the lιght-source(s) of the sensor shine through or into the target site Transmitted or reflected light falling on a photo-detector component of the sensor causes the photo-detector to generate an electrical signal corresponding to the physiological parameter being sensed The electrical signal is transmitted directly or digitised and transmitted to the monitor by various means including, but not limited to, a conducting wire or infrared, radio- frequency, or fibre-optic connections
Photo-optical sensors require power to operate, and even relatively low-power light sources are often the major element in a sensor power budget Therefore, the light source power consumption becomes a limiting factor in continuous operational performance life-time for physiological monitoring devices with finite power supplies such as, but not limited to, batteries or solar cells This limitation is particularly important in the burgeoning field of portable sensors, sensor adapters, and
portable monitors The light source is therefore typically switched on and off rapidly during operation to minimise the power consumption It should be noted that the term light' as herein used includes the electromagnetic frequencies from far infra-red through visible light to extreme ultraviolet
During the time the light source is on, the photo-detector measures the light transmitted or reflected by the target site, and the ambient light falling on the sensor This ambient light falling on the photo-detector increases the electrical signal from the photo-detector which can obscure the electrical signal representing the physiological parameter being measured, making it more difficult to obtain an accurate reading, this ambient light signal can therefore be considered noise In addition, the ambient light signal increases the overall magnitude of the electrical signal from the photo-detector and can therefore increase the power required to process and transmit the signal to the monitor
In the past, physiological monitoring devices have had comparatively large power supplies such as mains supply or large batteries With the recent development of very small portable and wireless monitoring devices and adapters it has become desirable to avoid these energy sources This has meant that the portable monitoring device often has a short operational life before the battery must be recharged or replaced This recharging or replacing disturbs the subject and may mean that valuable monitoring data is lost during the changeover Therefore means for achieving significant power savings need to be implemented to extend the useful operational life In a wireless device, (including but not limited to infrared or radiofrequency connections), the electrical signal has to be digitised prior to transmission, and the power required to digitise the electrical signal is dependent upon its magnitude Thus reducing the magnitude of the ambient light signal relative to the physiological signal prior to digitisation conserves overall power consumption extends the useful operational life
Disclosure of Invention
It is therefore an object of the present invention to provide a means to reduce the power consumption of photo-optical physiological monitoring equipment, by using an auto-zero circuit to reduce the relative magnitude of the ambient light component of the photo-detector signal, without significantly reducing the performance specification
for the equipment A further object of the invention is to reduce the relative magnitude of the ambient light component in the photo-detector signal thus increase the dynamic range of the analogue to digital converter by maximising the signal to noise ratio
The present invention provides a power reduction circuit for photo-optical physiological monitoring equipment adapted to be used to measure one or more physiological properties of a patient at preset intervals by illuminating a portion of the patient with one or more light sources, which produces a reflected or transmitted modified light signal representative of the physiological property being measured, the modified light signal is detected by a photo-sensor which produces a raw output signal, which includes an ambient light component, that is representative of the modified light signal, characterised in that the power reduction circuit includes i an adding unit adapted to produce a processed signal by adding the raw output signal to a second signal, ii a first signal buffer adapted to retain the processed signal, in a processing unit which further processes the processed signal, iv an isolating switch which is controlled by the processing unit and is connected to the first signal buffer, said isolating switch being adapted to reversibly connect the first signal buffer to a feed back circuit, v said feedback circuit is adapted to generate the second signal from the processed signal, and includes a second signal buffer, which is adapted to retain the level of the processed signal inside the feedback circuit, and an inverting amplifier, which amplifies and inverts the processed signal in the second signal buffer generating the second signal,
wherein the processed signal generated when the isolating switch is open, during the measurement of the desired physiological property, is effectively free of the ambient light component
Preferably the feedback circuit includes a high frequency filter before the second signal buffer In a further preferred form there is more than one frequency filtering stage included in the feedback circuit
Preferably the power reduction circuit includes additional signal processing circuitry in the feedback circuit or photo-detector output
Preferably the second signal can be further processed prior to the adding unit
Preferably a method of using the power reduction circuit includes the following steps in order a the isolating switch is opened by the processing unit, isolating the feedback circuit and locking the second signal level in the second signal buffer, b the or each light source is turned on, c the raw output signal is added to the second signal, generating the processed signal, d the or each light source is turned off, e the isolating switch is closed
Brief Description of Drawings
Figure 1 is a block diagram of the invention
Figure 2 is a flowchart showing the steps involved in an active measurement cycle using the invention
Figure 3 is a block diagram of a second embodiment of the invention which includes additional filters in the feedback circuit
Figure 4 is a flowchart showing the steps involved in a further embodiment of the invention that carries out a second active measurement cycle using a second light source shortly after a first active measurement cycle with a first light source
Best Mode for Carrying out the Invention
Referring to Figure 1 , the invention includes a photo-detector (3), a light source (1), an adder (4), a first signal buffer (5) and a processing unit (8), all connected in series in that order The light source (1) is adapted to illuminate a portion of a subject (2) for a period of time, the light from the light source (1 ) interacts with the portion of the subject (2) and is modified The photo-detector (3) is adapted to respond to certain properties of this modified light and generate an output signal whose properties are dependent upon the ambient light and modified light received The output signal is transmitted to the adder (4) which combines it with a second signal producing an adder signal The
first signal buffer (5) is adapted to retain the adder signal for a period of time prior to further processing
The invention further includes an isolating switch (9), which is adapted to be controlled by the processing unit (8), and a feedback circuit (13) The isolating switch (9) is connected at a point between the first signal buffer (5) output and the processing unit
(8) The feedback circuit (13) includes a high frequency filter (10), a second signal buffer (11) and an inverting amplifier (12), connected in that order in series wherein
i the high frequency filter (10) is adapted to remove the high frequency noise from the first signal buffer (5) output signal, generating a filtered signal which is transmitted to the second signal buffer (11), ii the second signal buffer (11) is adapted to retain the filtered signal for processing by the inverting amplifier (12), Hi the inverting amplifier (12) is adapted to invert and amplify the filtered signal from the second signal buffer (11) generating the second signal which is then transmitted to the adder (4)
The output signal, prior to the light source (1) being turned on, is representative of the ambient light impinging on the photo-detector (3) During this time the isolating switch
(9) is closed and the second signal is representative of, and varies with, the ambient light level
Referring to Figure 2, when a physiological measurement of the subject is to be undertaken, an active measurement cycle (20) is commenced and the isolating switch (9) is opened When the isolating switch (9) is opened the second signal buffer (11) retains the filtered signal stored at that time, and the second signal is fixed at a level representative of the ambient light level immediately prior to the active measurement cycle (20) being commenced
The light source (1) is turned on and the photo-detector generates an output signal containing ambient light and modified light components The output signal from the photo-detector (3) during the active measurement cycle (20) is added to the second signal (which is representative of the ambient light level prior to the measurement cycle), so that the resulting adder signal is effectively free from the ambient light component The adder signal is then transmitted via the first signal buffer (5) to the
processing unit (8) for further processing. Once the further processing, which may involve multiple reading of the first signal buffer (5), has been completed the processing unit (8) turns the light source (1 ) off and closes the isolating switch (9) completing the active measurement cycle (20).
In a second embodiment, as shown in Figure 3, one or more additional signal filters (14) are placed in the feedback circuit (13), and the output signal is pre-processed prior to the adder (4).
In a further embodiment, as shown in Figure 4, a second active measurement cycle (2) is undertaken shortly after the first using a different frequency light source (1 ).
Claims
1 A power reduction circuit for photo-optical physiological monitoring equipment adapted to be used to measure one or more physiological properties of a patient at preset intervals by illuminating a portion of the patient with one or more light sources, which produces a reflected or transmitted modified light signal representative of the physiological property being measured, the modified light signal is detected by a photo-sensor which produces a raw output signal, which includes an ambient light component, that is representative of the modified light signal, characterised in that the power reduction circuit includes i an adding unit adapted to produce a processed signal by adding the raw output signal to a second signal, ii a first signal buffer adapted to retain the processed signal, Mi a processing unit which further processes the processed signal, iv an isolating switch which is controlled by the processing unit and is connected to the first signal buffer, said isolating switch being adapted to reversibly connect the first signal buffer to a feed back circuit, v said feedback circuit is adapted to generate the second signal from the processed signal, and includes a second signal buffer, which is adapted to retain the level of the processed signal inside the feedback circuit, and an inverting amplifier, which amplifies and inverts the processed signal in the second signal buffer generating the second signal,
wherein the processed signal generated when the isolating switch is open, during the measurement of the desired physiological property, is effectively free of the ambient light component
2 The power reduction circuit as claimed in claim 1 wherein the feedback circuit includes a high frequency filter before the second signal buffer
3 The power reduction circuit as claimed in claim 1 wherein the feedback circuit includes more than one frequency filtering stage in the feedback circuit
4 The power reduction circuit as claimed in claim 1 wherein the feedback circuit includes additional signal processing circuitry
5. The power reduction circuit as claimed in claim 1 wherein the feedback circuit includes additional signal processing circuitry for the photo-detector output.
6. The power reduction circuit as claimed in claim 1 wherein the second signal can be further processed prior to the adding unit
7. A method of using the power reduction circuit as claimed in claim 1 which includes the following steps in order: a. the isolating switch is opened by the processing unit, isolating the feedback circuit and locking the second signal level in the second signal buffer; b. the or each light source is turned on; c. the raw output signal is added to the second signal, generating the processed signal; d. the or each light source is turned off; e. the isolating switch is closed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NZ53808205A NZ538082A (en) | 2005-02-04 | 2005-02-04 | Ambient light auto-zero circuit for photo-optical physiological monitoring equipment |
| NZ538082 | 2005-02-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2006083180A1 true WO2006083180A1 (en) | 2006-08-10 |
Family
ID=36777498
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/NZ2005/000027 Ceased WO2006083180A1 (en) | 2005-02-04 | 2005-02-24 | Ambient light auto-zero circuit for photo-optical physiological monitoring equipment |
Country Status (2)
| Country | Link |
|---|---|
| NZ (1) | NZ538082A (en) |
| WO (1) | WO2006083180A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9241676B2 (en) | 2012-05-31 | 2016-01-26 | Covidien Lp | Methods and systems for power optimization in a medical device |
| US9241643B2 (en) | 2012-05-31 | 2016-01-26 | Covidien Lp | Methods and systems for power optimization in a medical device |
| US9351688B2 (en) | 2013-01-29 | 2016-05-31 | Covidien Lp | Low power monitoring systems and method |
| US9560994B2 (en) | 2008-03-26 | 2017-02-07 | Covidien Lp | Pulse oximeter with adaptive power conservation |
| US9775528B2 (en) | 2014-06-30 | 2017-10-03 | Koninklijke Philips N.V. | Photoplethysmography sensor apparatus and method |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4258719A (en) * | 1978-12-04 | 1981-03-31 | Hughes Aircraft Company | Heart rate measurement system |
| US4781195A (en) * | 1987-12-02 | 1988-11-01 | The Boc Group, Inc. | Blood monitoring apparatus and methods with amplifier input dark current correction |
| US5954644A (en) * | 1997-03-24 | 1999-09-21 | Ohmeda Inc. | Method for ambient light subtraction in a photoplethysmographic measurement instrument |
| US6381479B1 (en) * | 1999-12-17 | 2002-04-30 | Date-Ohmeda, Inc. | Pulse oximeter with improved DC and low frequency rejection |
-
2005
- 2005-02-04 NZ NZ53808205A patent/NZ538082A/en unknown
- 2005-02-24 WO PCT/NZ2005/000027 patent/WO2006083180A1/en not_active Ceased
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4258719A (en) * | 1978-12-04 | 1981-03-31 | Hughes Aircraft Company | Heart rate measurement system |
| US4781195A (en) * | 1987-12-02 | 1988-11-01 | The Boc Group, Inc. | Blood monitoring apparatus and methods with amplifier input dark current correction |
| US5954644A (en) * | 1997-03-24 | 1999-09-21 | Ohmeda Inc. | Method for ambient light subtraction in a photoplethysmographic measurement instrument |
| US6381479B1 (en) * | 1999-12-17 | 2002-04-30 | Date-Ohmeda, Inc. | Pulse oximeter with improved DC and low frequency rejection |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9560994B2 (en) | 2008-03-26 | 2017-02-07 | Covidien Lp | Pulse oximeter with adaptive power conservation |
| US9241676B2 (en) | 2012-05-31 | 2016-01-26 | Covidien Lp | Methods and systems for power optimization in a medical device |
| US9241643B2 (en) | 2012-05-31 | 2016-01-26 | Covidien Lp | Methods and systems for power optimization in a medical device |
| US9517018B2 (en) | 2012-05-31 | 2016-12-13 | Covidien Lp | Methods and systems for power optimization in a medical device |
| US9538961B2 (en) | 2012-05-31 | 2017-01-10 | Covidien Lp | Methods and systems for power optimization in a medical device |
| US9351688B2 (en) | 2013-01-29 | 2016-05-31 | Covidien Lp | Low power monitoring systems and method |
| US9775528B2 (en) | 2014-06-30 | 2017-10-03 | Koninklijke Philips N.V. | Photoplethysmography sensor apparatus and method |
Also Published As
| Publication number | Publication date |
|---|---|
| NZ538082A (en) | 2007-03-30 |
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