Datex-ohmeda, Inc.

General Electric Company

Datex&thgr;ohmeda, Inc.

Date-ohmeda, Inc.

Mark A Norris

D Alan Hanna

Donald W Heckel

Matti Veli Tapani Huiku

Christopher Hicks

Scott James Charles Light

An initialization module in a pulse oximeter accommodates a variety of different probes and a variety of operating parameters as well as providing for interrogation of various probe circuits for detection of probe faults. Probe fault detection for the red and infrared LED circuits of the probe is implemented using an adaptive algorithm that is dependent on the drive settings or signals applied to the LED circuits. A configurable circuit is used to provide multiple initialization values relating to a calibration circuit of the probe for improved fault detection. Additionally, potential faults with respect to the photodetector circuit of a probe are identified based on monitoring drawn by an output by the photodetector.

System for detecting potential probe malfunction conditions in a pulse oximeter

A photoplethysmographic system and method is provided for filtering a photoplethysmographic (pleth) signal to reduce the effects of noise in the signal. The system and method utilize a combination of frequency, time and/or magnitude information, to identify and separate transient signal components within a pleth signal from repeating signal components within the pleth signal. Typically, signal components of interest repeat over a period that corresponds with a patient's heartbeat. Such periodically repeating signals may be identified as stationary signals/objects within a frequency and time-based analysis. In contrast, motion artifacts or other sources of noise are often isolated (i.e., non-repeating) transient events and may be identified as non-stationary objects in a frequency and time-based analysis. Data associated with identified transient events may be filtered from or otherwise removed from a given signal. In this regard, a pleth signal may be cleansed prior to its use for, e.g., blood analyte determinations.

Wavelet transform of a plethysmographic signal

A detector signal in a pulse oximeter is prefiltered, prior to processing so as to determine a physiological parameter value, so as to reduce the effects of artifact in the signal. An exemplary prefilter multiplies signal amplitude values by a quantitude that is inversely proportional to a substantially current amplitude so as to reduce the amplitude of large amplitude sections typically associated with artifact. In one implementation, the quantity is a ratio of an amplitude associated with a clean section of the signal by some exponential factor of a substantially current amplitude. In this manner, artifact affected portions of the signal are deemphasized in subsequent analyses.

System for prefiltering a plethysmographic signal

A method for use in operating a signal attenuation measurement device used to obtain a physiological parameter of a patient and an apparatus for use in determining at least one physiological parameter relating to a patient from at least first and second signals transmitted to a patient tissue site and attenuated thereby are provided. In accordance with the method and apparatus of the present invention, the first and second signals are multiplexed using frequency orthogonal code division multiplexed excitation waveforms. This allows for both relatively good source separation of the signals and whitening of external noise.

Simultaneous signal attenuation measurements utilizing frequency orthogonal random codes

An oversampling pulse oximeter includes an analog to digital converter with a sampling rate sufficient to take multiple samples per source cycle. In one embodiment, a pulse oximeter () includes two or more light sources () driven by light source drives () in response to drive signals from a digital signal processing unit (). The source drives () may drive the sources () to produce a frequency division multiplex signal. The optical signals transmitted by the light sources () are transmitted through a patient's appendage () and impinge on a detector (). The detector () provides an analog current signal representative of the received optical signals. An amplifier circuit () converts the analog current signal to an analog voltage signal in addition to performing a number of other functions. The amplifier circuit () outputs an analog voltage signal which is representative of the optical signals from the sources (). This analog voltage signal is received by a fast A/D converter () which samples the analog voltage signal to generate a digital voltage signal which can be processed by the digital signal processing unit (). The fast A/D converter () operates at a rate sufficient to take multiple samples per source cycle and may have a sampling frequency, for example, of over 41 kHz. The digital signal processing unit () implements software for averaging the samples over a source cycle for improved measurement consistency, improved signal to noise ratio and reduced A/D converter word length.

Oversampling pulse oximeter

An oximeter has an op-amp with a first input, a second input, and an output, the first input being directly connected to a reference voltage. A switch has an input connected to the output of the op-amp, and has a plurality of switch outputs. A transistor has a control input connected to one of the plurality of outputs, and has a current source terminal and a supply terminal. A diode is connected to the current source terminal of the transistor. The supply terminal of the transistor is connected both to the second input of the op-amp and to a second one of the plurality of switch outputs. The switch is thereby in a feedback loop of the op-amp, effecting a feedback-controlled switch for switching the diode on and off.

Feedback-controlled LED switching

A system and method of reducing cross talk in pulse oximetry signals that are attenuated by a patient tissue site are provided. In one embodiment, Red and IR LEDs of a pulse oximeter are separately excited ( ) and the respective Red and IR data vectors output by the detector are measured ( ). The Red and IR data vectors are normalized ( ). Red to IR and IR to Red cross talk vectors are computed ( ). Red and IR demodulation vectors are obtained by subtracting ( ) the respective Red and IR cross talk vectors from the respective normalized Red and IR data vectors. The demodulation vectors are normalized ( ), scaled ( ), and the magnitudes of the Red and IR signal components are obtained by computing ( ) the dot product of the composite signal data vector with the normalized and scaled Red demodulation and IR demodulation vectors, respectively.

Reduced cross talk pulse oximeter

An oversampling pulse oximeter includes an analog to digital converter with a sampling rate sufficient to take multiple samples per source cycle. In one embodiment, a pulse oximeter ( ) includes two mor more light sources ( ) driven by light source drives ( ) in response to drive signals from a digital signal processing unit ( ). The source drives ( ) may drive the sources ( ) to produce a frequency division multiplex signal. The optical signals transmitted by the light sources ( ) are transmitted through a patient's appendage ( ) and impinge on a detector ( ). The detector ( ) provides an analog current signal representative of the received optical signals. An amplifier circuit ( ) converts the analog current signal to an analog voltage signal in addition to performing a number of other functions. The amplifier circuit ( ) outputs an analog voltage signal which is representative of the optical signals from the sources ( ). This analog voltage signal is received by a fast A/D converter ( ) which samples the analog voltage signal to generate a digital voltage signal which can be processed by the digital signal processing unit ( ). The fast A/D converter ( ) operates at a rate sufficient to take multiple samples per source cycle and may have a sampling frequency, for example, of over 41 kHz. The digital signal processing unit ( ) implements software for averaging the samples over a source cycle for improved measurement consistency, improved signal to noise ratio and reduced A/D converter word length.

A method of producing a diode drive current in an oximeter includes sensing at least a part of a current passing through the diode and converting the sensed current to a sensed voltage, inputting the sensed voltage to a feedback amplifier for stabilizing the current passing through the diode, and eliminating an offset voltage across inputs of the feedback amplifier. A pulse oximeter includes a diode for emitting light flashes, a feedback amplifier having inputs, a feedback capacitor, and an output, the feedback amplifier stabilizing a current passing through the diode, a nulling amplifier having inputs, a nulling capacitor, and an output, the nulling amplifier charging and discharging the feedback capacitor until the inputs of the feedback amplifier are at a same voltage. The operation may include synchronizing an elimination of input offset voltages of the feedback and nulling amplifiers with on or off state of diode current.

Oximeter with nulled op-amp current feedback

An oximeter diode-driving device has a diode, a transistor operative to controllably connect current to the diode, a current sensing resistor that senses at least part of the current, a feedback amplifier operative to control the connecting of current by the transistor according to the current sensed by the current sensing resistor, and an inductor disposed in series with the current sensing resistor. A method of driving a current through the diode of an oximeter includes driving a current through the diode by connecting the current to the diode, controlling the connecting using a feedback type amplifier, the feedback type amplifier having a current source that uses a current-limiting resistor, and adding phase lead to a current passing through the current-limiting resistor.

Ferrite stabilized LED drive

A photoplethysmographic system and method is provided to identify compatible sensors to monitors and/or for determining sensor attributes. The improved system includes a signal generation means for providing an interrogation signal, an identifying means coupled between a first and second sensor terminal operable to produce multiple outputs upon application of the interrogation signal in two modes of operation, and a processor to interpret the outputs. When the interrogation signal is applied to a sensor terminal in a first mode, a first output is obtained. Upon applying the same interrogation signal to the sensor terminal in a second mode, a second output is obtained. The first and second outputs may then be utilized by the processor comprising, for example, a photoplethysmographic monitor to yield enhanced sensor information. The disclosed method may be carried out utilizing the inventive photoplethysmographic system.

Diode detection circuit

Differential values, for use in blood oxygenation calculations, are determined based on multiple sample values for each channel of an oximetry system, each such value constituting a data point. In one implementation, each of these data points is defined by a sample window ( and ), where the window includes, for example, 7-10 data points. That is, the data points within window ( or ) are used to establish a differential value nominally associated with the data sample about which the window is centered. The differential value is calculated based on a mathematical model such as a weighted linear regression analysis. In this manner, output may be provided on a sample-by-sample basis while mitigating noise sensitivity.

Method and apparatus for determining pulse oximetry differential values

A pulse oximeter ( ) includes two or more light sources ( ) for transmitting optical signals through an appendage ( ) of patient. The sources ( ) are operated to transmit code division multiplexed (CDM) signals. That is, the sources ( ) are driven by drives ( ) in response to signals from a digital processing unit ( ) such that the sources ( ) are modulated using different code sequences. The code sequences are preferably non-periodic and may be orthogonal to one another. The use of such CDM signals provides certain advantages related to noise reduction.

Simultaneous signal attenuation measurements utilizing code division multiplexing

A system for providing an improved DC and low frequency signal rejection in a photoplethysmographic measurement instrument is disclosed. The system is used in a measurement instrument which includes at least two signal sources ( ) for transmitting light signals at least at two wavelengths through a tissue of a test subject and a detector ( ) for converting light signals transmitted through the tissue into a detector output signal. The system includes a DC restoration ( ) which removes DC and low frequency signal components from the detector output signal prior to amplification thereof so as to avoid saturating amplified output signal with the low frequency signal component. The DC restoration ( ) is configured to continuously remove low frequency signal component from the detector signal during dark intervals when the signal sources are deactivated, as well as during light intervals when one of the signal sources is activated. In one embodiment, the DC restoration is embodied in the form of a DC restoration circuit ( ) which comprises a transimpedance amplifier ( ) which receives the detector output signal and produces an amplifier output signal ( ) and an integrator feedback loop ( ) which receives the amplified output signal and produces a bias current, wherein the bias current is used to subtract DC and low frequency signal components from the detector output signal prior to amplification of the detector signal by the amplifier.

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Boulder, CO, United States of America

Mark A Norris