Sensor verification via forward voltage measurement

Abstract

A device for measuring oxygen saturation is disclosed. The device includes circuitry configured to measure a first forward voltage across an anode and a cathode of a first light-emitting diode (LED) when a first current is applied, and to measure a second forward voltage across an anode and a cathode of a second light-emitting diode (LED) when a second current is applied. The circuitry is further configured to determine a difference in the measured forward voltages based on a comparison of the first and second forward voltages, and to determine that the first and second LEDs are valid based on a difference in the calibrated forward voltages and the measured forward voltages. In response to determining that the first and second LEDs are valid, the circuitry is configured to determine an oxygen saturation level.

Description

[0001] This application claims priority to U.S. patent application Ser. No. 16 / 857,695, filed on April 24, 2020, and entitled “SENSOR VERIFICATION THROUGH FORWARD VOLTAGE MEASUREMENTS,” and U.S. patent application Ser. No. 17 / 082,944, filed on October 28, 2020, and entitled “SENSOR VERIFICATION THROUGH FORWARD VOLTAGE MEASUREMENTS,” the entire contents of each of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to determining blood oxygen saturation with a physiological monitor, and more particularly, to determining regional blood oxygen saturation with a regional oximeter or other medical device. Background Art

[0003] The oximeter can output a small light beam that passes through the blood and measure the absorption of the small light beam to estimate the oxygen saturation level in the blood. For example, blood with a relatively high oxygen saturation level may absorb more light at a specific wavelength than blood with a relatively low oxygen saturation level. Therefore, the oximeter can determine that the oxygen saturation level in the blood increases as less light at a specific wavelength is received after passing through the blood. Summary of the Invention

[0004] Generally speaking, the present disclosure relates to devices, systems, and techniques for verifying oximeters through forward voltage measurement. For example, a device can measure the forward voltage of a light-emitting diode (LED) used to measure oxygen saturation. In this example, the device can compare the measured forward voltage of the LED to the value used during calibration. In this way, the device can verify that it is consistent with the calibration value, helping to ensure the correct construction and / or accuracy of the sensor device.

[0005] In one example, a device for measuring oxygen saturation includes a memory configured to store a calibrated forward voltage difference; circuitry configured to: apply a first current from an anode of a first light-emitting diode to a cathode of the first light-emitting diode; measure a first forward voltage across the anode and cathode of the first light-emitting diode while applying the first current; apply a second current from an anode of a second light-emitting diode to a cathode of the second light-emitting diode; measure a second forward voltage across the anode and cathode of the second light-emitting diode while applying the second current; determine a difference in the measured forward voltages based on a comparison of the first and second forward voltages; determine that the first and second light-emitting diodes are valid based on the calibrated forward voltage difference and the measured forward voltage difference; and, in response to the determination that the first and second light-emitting diodes are valid, determine an oxygen saturation level using the first and second light-emitting diodes and output an indication of the oxygen saturation level.

[0006] In another example, a method for measuring oxygen saturation includes: applying, by circuitry, a first current from an anode of a first light-emitting diode to a cathode of the first light-emitting diode; measuring, by the circuitry, a first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode while applying the first current; applying, by the circuitry, a second current from an anode of a second light-emitting diode to a cathode of the second light-emitting diode; measuring, by the circuitry, a second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode while applying the second current; determining, by the circuitry, a difference in the measured forward voltages based on a comparison of the first forward voltage and the second forward voltage; determining, by the circuitry, that the first light-emitting diode and the second light-emitting diode are valid based on the difference in calibrated forward voltages and the difference in the measured forward voltages; and in response to determining that the first light-emitting diode and the second light-emitting diode are valid, determining, by the circuitry, an oxygen saturation level using the first light-emitting diode and the second light-emitting diode and outputting, by the circuitry, an indication of the oxygen saturation level.

[0007] In one example, a system for measuring oxygen saturation includes: a sensor device including a first light emitting diode and a second light emitting diode; an oximetry device including: a memory configured to store a calibrated forward voltage difference; and a circuit system configured to: apply a first current from an anode of the first light emitting diode to a cathode of the first light emitting diode; measure a first forward voltage across the anode and cathode of the first light emitting diode while applying the first current; apply a second current from the anode of the second light emitting diode to the cathode of the first light emitting diode; and the cathode of the second light emitting diode; measuring a second forward voltage across the anode of the second light emitting diode and the cathode of the second light emitting diode when applying the second current; determining a difference in the measured forward voltages based on a comparison of the first forward voltage and the second forward voltage; determining that the first light emitting diode and the second light emitting diode are valid based on the difference in the calibrated forward voltages and the difference in the measured forward voltages; and in response to the determination that the first light emitting diode and the second light emitting diode are valid, determining an oxygen saturation level using the first light emitting diode and the second light emitting diode and outputting an indication of the oxygen saturation level. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a conceptual block diagram illustrating an exemplary regional oximetry device.

[0009] Figure 2 is a conceptual block diagram illustrating an exemplary regional oximetry device configured to monitor a patient's autoregulatory state.

[0010] Figure 3 is a conceptual diagram illustrating an exemplary graphical user interface including self-adjustment information presented on a display.

[0011] Figure 4 is a conceptual diagram illustrating an exemplary first sensor device according to techniques described herein.

[0012] Figure 5 is a conceptual diagram illustrating an exemplary second sensor device according to techniques described herein.

[0013] Figure 6 is a flow chart illustrating an example technique for measuring oxygen saturation in accordance with the techniques described herein. DETAILED DESCRIPTION

[0014] An oximeter may refer to a medical device configured to determine the oxygen saturation of an analyzed tissue. For the purposes of this disclosure, an oximeter may be defined as a device that measures factors other than oxygen content. For example, an oximeter may measure other characteristics and chemical composition of blood, such as carbon monoxide. In some examples, an oximeter may be used solely to measure a subject's photoplethysmogram for pulse rate determination. Examples of oximeters may include, for example, a pulse oximeter, a regional oximeter, a CO-oximeter, or other photometric measurement devices. A pulse oximeter may be configured to estimate the oxygen saturation of blood. A regional oximeter may be configured to estimate the oxygen saturation of a region of tissue of a subject (e.g., a human patient). For example, a regional oximeter may be configured to estimate the regional oxygen saturation of hemoglobin in a region of the subject's tissue by determining a differential absorption value for each of two or more wavelengths of light received at two different locations on the subject's body. For each wavelength of light, the regional oximeter may compare the amount of light absorbed by the subject's tissue in a first region with the amount of light absorbed by the subject's tissue in a second region to obtain a differential absorption value. Sensor devices may include regional oximeters and pulse oximeters.

[0015] An oximeter (e.g., a pulse oximeter, a regional oximeter, etc.) can include a sensor device that is placed at a location on the patient, such as on a fingertip, toe, forehead or earlobe, cerebral cortex, or, in the case of a newborn, on a foot, hand, or another location. The oximeter can use a light source to pass light through blood-perfused tissue and photoelectrically sense the absorption of light in the tissue. Other suitable sensor locations can include, for example, the neck to monitor carotid artery pulsatile flow, the wrist to monitor radial artery pulsatile flow, the inner side of a patient's thigh to monitor femoral artery pulsatile flow, the ankle to monitor tibial artery pulsatile flow, around or in front of the ear, a location with strong pulsatile arterial flow, or other locations.

[0016] The oximeter can be configured to output a photon signal that interacts with tissue at one or more wavelengths that are attenuated by blood by an amount representative of the concentration of a blood component. The oximeter can be configured to generate the photon signal at red and infrared (IR) wavelengths. The oximeter can estimate the oxygen saturation of hemoglobin in arterial blood based on the intensities of the photon signal at the red wavelength and the photon signal at the infrared wavelength.

[0017] The light-emitting diode (LED) of the oximeter can be manufactured to output a photon signal at a specific wavelength within a certain manufacturing tolerance. For example, a first LED can output a first photon signal (e.g., red light) within a first wavelength range (e.g., 630 nm to 700 nm) within a first manufacturing tolerance of 5%. In this example, a second LED can output a second photon signal (e.g., infrared light) within a second wavelength range (e.g., 700 nm to 1200 nm) within a second manufacturing tolerance of 5%. Although various examples described herein refer to LEDs that can output relatively low-intensity light, in some examples, the LED may include a device that outputs a relatively intense beam of infrared radiation (e.g., a laser diode), a vertical cavity surface emitting laser, or another device that emits light using at least one p-type junction and at least one n-type junction. Furthermore, although the examples described herein may refer to devices that emit light (e.g., LEDs, laser diodes, etc.), similar techniques can be used with devices that receive light (e.g., photodiodes).

[0018] To account for manufacturing tolerances, some oximeters may use calibration information established for each sensor. For example, some oximeters may be configured to store calibration information about the oximeter's LEDs in a memory (e.g., EEPROM). This calibration information can help account for manufacturing tolerances of the LEDs, which may shift the wavelength of light emitted by the LEDs. However, when an oximeter configured with calibration information for a specific set of LEDs is used with LEDs having different manufacturing tolerances, the oximetry measurement may produce incorrect measurements.

[0019] According to the techniques of this disclosure, a device (e.g., an oximeter) can be configured to verify (e.g., validate) that an LED used by the device to determine blood oxygen saturation values ​​complies with stored calibration information (e.g., is within a range defined by the calibration information). Verifying that the LED complies with the calibration information indicates that the LED is verified for use in determining oxygen levels (e.g., the measurement should be accurate).

[0020] In some examples, a device may determine the forward voltage across each of the LEDs as a way to ensure that the LEDs used by the device comply with calibration information (e.g., are within the range defined by the calibration information). However, relying solely on forward voltage can have drawbacks. For example, varying cable resistance can significantly alter the measured forward voltage across the LEDs. Therefore, to account for cable resistance, some examples may use four-terminal sensing, where additional leads are placed on each side of the LED to help reduce the impact of cable resistance, which increases system complexity and cost.

[0021] Rather than always using calibration information to determine blood oxygen saturation values ​​or relying on four-terminal sensing, a device (e.g., an oximeter) can use the difference in forward voltages of LEDs to verify that the LEDs used by the device correspond to the calibration information (e.g., that conditions are met to confirm that the LEDs will provide accurate measurements). During calibration, the device can measure a first forward voltage across the LED in response to a positive current and a second forward voltage across the LED in response to a negative current that has the same magnitude as the positive current (e.g., the device measures the first and second forward voltages using opposite polarity currents of the same magnitude). In some examples, the device can perform only a single measurement of the first forward voltage. However, in some examples, the device can perform more than one forward voltage measurement, each at a different corresponding current. For example, during calibration, the device can measure a first forward voltage at a first current, a first forward voltage at a second current that is different from the first current (e.g., greater than, less than, etc.), and so on. In this example, the device can store the difference between the calibrated first and second forward voltages ("calibrated ΔVF") in memory along with the calibration information for the LEDs. After calibration, the device may measure a first forward voltage in response to a positive current and a second forward voltage in response to a negative current, and generate a difference between the measured first forward voltage and the second forward voltage ("measured ΔVF"). If the measured ΔVF and the calibrated ΔVF are within a certain tolerance, the device may determine that the LED in service of the device (e.g., an oximeter) is consistent with the calibration information and is therefore verified. In response to determining that the LED in service of the device is valid, the device may use the LED to determine the oxygen saturation level based on the calibration information. If the measured ΔVF and the calibrated ΔVF are not within a certain tolerance, the device may determine that the LED in service of the device is inconsistent with the calibration information and may therefore determine that the LED in service of the device is not verified. In response to determining that the LED in service of the device is not verified, the device will not determine the oxygen saturation level. In this way, the device can be verified to be consistent with the calibration value to help ensure the correct construction and accuracy of the device.

[0022] In some examples, a device (e.g., an oximeter) can use the measured ΔVF to detect the LED temperature. The device can match the measured ΔVF with the ΔVF stored in a specific table entry. The device can determine that the temperature at the LED corresponds to the temperature in the specific table entry. In some examples, the device can use the ΔVF as an encryption key to encrypt and decrypt information in memory (e.g., calibration information).

[0023] Figure 1 is a conceptual block diagram illustrating an exemplary regional oximetry device 100. Figure 1The example of FIG. 100 describes a regional oximetry device, but the techniques described herein for verifying light-emitting diodes can be used in other devices, such as, for example, a pulse oximetry device, a CO-oximeter device, or another oximeter device. Regional oximetry device 100 includes processing circuitry 110, memory 120, a user interface 130, a display 132, sensing circuitry 140, 141, and 142, and sensing devices 150, 151, and 152. In some examples, regional oximetry device 100 can be configured to determine and display a patient's brain autoregulatory state, for example, during a medical procedure or for longer-term monitoring (such as monitoring prenatal infants, children, or adults). A clinician can receive information about the patient's brain autoregulatory state via display 132 and adjust treatment or therapy to suit the patient based on the brain autoregulatory state information. Although regional oximetry device 100 is described as an exemplary device herein, other devices can calculate blood pressure and / or use blood pressure for other physiological monitoring purposes and perform similar compensation processes for blood pressure that experiences sudden changes in measured blood pressure values.

[0024] Processing circuitry 110 and other processors, processing circuits, controllers, control circuitry, etc. described herein may include one or more processors. Processing circuitry 110 may include any combination of integrated circuits, discrete logic circuitry, analog circuitry (such as one or more microprocessors), digital signal processors (DSPs), application specific integrated circuits (ASICs), or field programmable gate arrays (FPGAs). In some examples, processing circuitry 110 may include multiple components, such as any combination of one or more microprocessors, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry and / or analog circuitry.

[0025] For example, the memory 120 may be configured to store measurements of blood pressure, oxygen saturation, blood volume, other physiological parameters, relationships between blood pressure and physiological parameters, MAP values, rSO2 values, COx values, BVS values, HVx values, and / or values ​​of the lower limit of autoregulation (LLA) and / or the upper limit of autoregulation (ULA). The memory 120 may also be configured to store data such as thresholds for detecting sudden changes in blood pressure, previous LLA and ULA values, and / or other physiological parameters, as well as expected values ​​for the physiological parameters. The memory 120 may also be configured to store data such as threshold levels for physiological parameters, thresholds for blood pressure, and / or thresholds for signal quality metrics. The thresholds or other data may remain constant throughout use of the device 100 and across multiple patients, or these values ​​may change over time. The memory 120 may store a difference in forward voltage for verifying the calibration of the sensing device 150.

[0026] Memory 120 may store program instructions, which may include one or more program modules that may be executed by processing circuit system 110. When executed by processing circuit system 110, such program instructions may cause processing circuit system 110 to provide the functionality assigned to it herein. For example, memory 120 may store instructions on how to determine a sudden change in measured blood pressure, calculate ULA and LLA values, and present information to a user via user interface 130. The program instructions may be embodied in software, firmware, and / or RAMware. Memory 120, as well as other memory devices described herein (e.g., Figure 2 The memory 220 shown) may include any volatile, nonvolatile, magnetic, optical, circuit system, or electrical medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other digital medium.

[0027] The user interface 130 and / or the display 132 may be configured to present information to a user (e.g., a clinician). The user interface 130 and / or the display 132 may be configured to present a graphical user interface to the user, wherein each graphical user interface may include an indication of the value of one or more physiological parameters of the subject. For example, the processing circuit system 110 may be configured to present a blood pressure value, other physiological parameter values ​​(e.g., heart rate), and an indication of the patient's brain autoregulatory state via the display 132. In some examples, if the processing circuit system 110 determines that the patient's brain autoregulatory state is impaired, the processing circuit system 110 may present a notification (e.g., a warning) indicating the impaired brain autoregulatory state via the display 132. As another example, the processing circuit system 110 may present an estimate of the patient's regional oxygen saturation (rSO2), an estimate of blood oxygen saturation (SpO2) determined by the processing circuit system 110, pulse rate information, respiratory rate information, blood pressure, any other patient parameter, or any combination thereof via the display 132.

[0028] The user interface 130 and / or display 132 may include a monitor, a cathode ray tube display, a flat panel display (such as a liquid crystal (LCD) display), a plasma display or a light emitting diode (LED) display, a personal digital assistant, a mobile phone, a tablet computer, a laptop computer, any other suitable display device, or any combination thereof. The user interface 130 may also include a device for projecting audio to the user, such as a speaker. The processing circuit system 110 may be configured to present a visual, auditory, or somatosensory notification (e.g., an alarm signal) indicating the patient's self-regulation status via the user interface 130. The user interface 130 may include or may be part of any suitable device for conveying such information, including a computer workstation, a server, a desktop computer, a laptop computer, a handheld computer, a mobile device, etc. In some examples, the processing circuit system 110 and the user interface 130 may be part of the same device or supported within a housing (e.g., a computer or a monitor).

[0029] Sensing circuit systems 140, 141, and 142 may be configured to receive physiological signals sensed by respective sensing devices 150, 151, and 152 and transmit the physiological signals to processing circuit system 110. Sensing devices 150, 151, and 152 may include any sensing hardware configured to sense physiological parameters of a patient, such as, but not limited to, one or more electrodes, an optical receiver, a blood pressure cuff, and the like. Sensing circuit systems 140, 141, and 142 may convert the physiological signals into usable signals for processing circuit system 110, such that processing circuit system 110 is configured to receive the signals generated by sensing circuit systems 140, 141, and 142. Sensing circuit systems 140, 141, and 142 may receive signals indicative of physiological parameters from the patient, such as, but not limited to, blood pressure, regional oxygen saturation, heart rate, and respiration. Sensing circuit systems 140, 141, and 142 may include, but are not limited to, blood pressure sensing circuit systems, oxygen saturation sensing circuit systems, heart rate sensing circuit systems, temperature sensing circuit systems, electrocardiogram (ECG) sensing circuit systems, electroencephalogram (EEG) sensing circuit systems, or any combination thereof. In some examples, sensing circuit systems 140, 141, and 142 and / or processing circuit system 110 may include signal processing circuit systems, such as analog-to-digital converters.

[0030] Oxygen saturation sensing device 150 is a regional oxygen saturation sensor configured to generate an oxygen saturation signal indicative of the oxygen saturation of blood within the venous, arterial, and / or capillary vascular systems within a region of a patient. For example, oxygen saturation sensing device 150 may be configured to be placed on a patient's forehead and may be used to determine the oxygen saturation of the patient's blood within the venous, arterial, and / or capillary vascular systems of a region below the patient's forehead (e.g., in the cerebral cortex).

[0031] Oxygen saturation sensing device 150 may include an emitter 160 and a detector 162. Emitter 160 may include at least two light emitting diodes (LEDs), each configured to emit light of a different wavelength, such as red light and near-infrared light. In some examples, optical drive circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may provide an optical drive signal to drive emitter 160 and cause emitter 160 to emit light. In some examples, the LEDs of emitter 160 emit light within a wavelength range of approximately 600 nanometers (nm) to approximately 1000 nm. In a specific example, one LED of emitter 160 is configured to emit light at a wavelength of approximately 730 nm, and another LED of emitter 160 is configured to emit light at a wavelength of approximately 810 nm. In other examples, light of other wavelengths may also be used.

[0032] The detector 162 may include a first detection element positioned relatively “close” to (e.g., on the proximal side of) the emitter 160 and a second detection element positioned relatively “far” from (e.g., on the distal side of) the emitter 160. Figure 1 , these multiple detectors are shown as a single detector). The intensity of light at multiple wavelengths may be received at both "near" and "far away" detector 162. For example, if two wavelengths are used, the two wavelengths may be compared at each location and the resulting signals may be compared to arrive at a regional saturation value that, when light is transmitted through a certain area of ​​the patient (e.g., the patient's skull), is related to additional tissue (tissue other than the tissue through which light received at the "far away" detector passed, such as brain tissue) as the light is transmitted through. Surface data from the skin and skull may be subtracted to generate a regional oxygen saturation signal of the target tissue over time. The oxygen saturation sensing device 150 may provide the regional oxygen saturation signal to the processing circuit system 110 or any other suitable processing device to enable estimation of the patient's autoregulatory state.

[0033] The blood pressure sensing device 151 and the oxygen saturation sensing device 150 can each be placed on the same or different parts of the patient's body. For example, the blood pressure sensing device 151 and the oxygen saturation sensing device 150 can be physically separated from each other and placed separately on the patient. As another example, the blood pressure sensing device 151 and the oxygen saturation sensing device 150 can, in some cases, be part of the same sensor or supported by a single sensor housing. For example, the blood pressure sensing device 151 and the oxygen saturation sensing device 150 can be part of an integrated blood pressure determination system configured to non-invasively measure blood pressure (e.g., based on time delays in the PPG signal) and regional oxygen saturation. One or both of the blood pressure sensing device 151 or the oxygen saturation sensing device 150 can be further configured to measure other parameters, such as hemoglobin, respiratory rate, respiratory effort, heart rate, saturation pattern detection, response to stimulation (such as the bispectral index (BIS)), or electromyographic (EMG) response to electrical stimulation, etc. Although Figure 1 An exemplary regional oximetry device 100 is shown in FIG. Figure 1 The components shown are not intended to be limiting. Additional or alternative components and / or implementations may be used in other examples.

[0034] The blood pressure sensing device 151 can be any sensor or device configured to obtain a patient's blood pressure (e.g., arterial blood pressure). In one example, the blood pressure sensing device 151 can include or be connected to a probe configured to be inserted into the patient's blood pressure. In another example, the blood pressure sensing device 151 can include a blood pressure cuff for non-invasively monitoring blood pressure or an arterial line for invasively monitoring blood pressure (e.g., a pressure probe configured to be placed in an artery or vein). In some examples, the blood pressure sensing device 151 can include one or more pulse oximetry sensors. In some such cases, the patient's blood pressure can be obtained by processing the time delay between two or more characteristic points within a single plethysmography (PPG) signal obtained from a single pulse oximetry sensor.

[0035] Processing circuit system 110 can be configured to receive one or more physiological signals generated by sensing devices 150, 151, and 152 and sensing circuit systems 140, 141, and 142. The physiological signals may include a signal indicating blood pressure, a signal indicating oxygen saturation, and / or a signal indicating the patient's blood volume. Processing circuit system 110 can be configured to determine a relationship between the patient's blood pressure value and a physiological parameter of the patient, such as a related index (e.g., COx, hemoglobin volume index (HVx)), an oxygen saturation value, a blood volume value, a gradient-based metric of two or more physiological parameters, and / or another physiological parameter. Processing circuit system 110 can determine the gradient-based metric by determining the corresponding gradients of the signals of the physiological parameters and determining whether the corresponding gradients converge to a consistent value.

[0036] Processing circuitry 110 may be configured to determine blood pressure values ​​at which physiological parameters are less than or greater than one or more threshold values. As an example, processing circuitry 110 may determine an estimate of the lower limit of brain autoregulation (LLA) based on the lowest blood pressure value at which the expected COx value is less than a threshold value, such as 0.5, 0.4, 0.3, 0.2, 0.1, or 0.0 (e.g., where 1.0 indicates full correlation and 0.0 indicates no correlation between blood pressure and rSO2). Thus, processing circuitry 110 may determine estimates of brain autoregulatory limits (e.g., LLA and ULA) based on blood pressure and rSO2. Regional oximetry device 100 may omit blood pressure and / or blood volume circuitry. For example, regional oximetry device 100 may omit sensing circuitry 141 and / or sensing device 151. In some examples, regional oximetry device 100 may omit sensing circuitry 142 and sensing device 152. In some examples, regional oximetry device 100 may include only circuitry for determining oxygen saturation levels.

[0037] According to the techniques of this disclosure, a device such as regional oximetry device 100 may include memory circuitry (e.g., memory 120) configured to store a calibrated forward voltage difference. Device 100 may also include processing circuitry (e.g., processing circuitry 110) configured to apply a first current from the anode of a first light-emitting diode (e.g., a first LED of emitter 160) to the cathode of the first light-emitting diode. For example, light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may apply the first current (e.g., a positive current) to emitter 160 to cause the first current to flow through the first light-emitting diode (e.g., a light-emitting diode configured to emit red light). While applying the first current, voltage measurement circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may measure a first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode. For example, light driving circuitry (eg, within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may measure an indication of a voltage output at terminals of a source supplying the first current when the first current is applied.

[0038] The light driving circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may apply a second current from the anode of a second light-emitting diode (e.g., a second LED of emitter 160) to the cathode of the second light-emitting diode. For example, the light driving circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may apply a second current (e.g., a negative current) to emitter 160 so that the second current flows through the second light-emitting diode (e.g., a light-emitting diode configured to emit infrared light). While applying the second current, the voltage measuring circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may be configured to measure a second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode. For example, the light driving circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may measure an indication of a voltage output at a terminal of a source supplying the second current.

[0039] Processing circuit system 110 may be configured to determine a difference in the measured forward voltage based on a comparison of the first forward voltage and the second forward voltage. For example, processing circuit system 110 may subtract the absolute value of the first forward voltage and the absolute value of the second forward voltage to generate the difference in the measured forward voltage. Processing circuit system 110 may be configured to determine that the first light emitting diode and the second light emitting diode are valid based on the difference in the calibrated forward voltage and the difference in the measured forward voltage. For example, processing circuit system 110 may determine that the first light emitting diode and the second light emitting diode are valid in response to determining that the difference between the difference in the calibrated forward voltage and the difference in the measured forward voltage is less than a threshold value. The threshold value may be a user-configurable value.

[0040] Processing circuitry 110 may be configured to determine the oxygen saturation level using the first and second LEDs in response to determining that the first and second LEDs are valid. For example, processing circuitry 110 may determine the oxygen saturation level in the subject's tissue only in response to determining that the first and second LEDs are valid. Processing circuitry 110 may refrain from determining the oxygen saturation level in the subject's tissue in response to determining that the first and second LEDs are not validated. For example, processing circuitry 110 may output an error code on display 132 in response to determining that the first and second LEDs are not validated.

[0041] In the above examples, processing circuitry 110, light driving circuitry, and voltage measurement circuitry are described as performing exemplary techniques, where the light driving circuitry and voltage measurement circuitry may be part of processing circuitry 110, sensing device 150, and / or sensing circuitry 140. However, any one or any combination of processing circuitry 110, sensing circuitry 140, and / or sensing device 150 may be configured to perform the exemplary techniques. For example, the exemplary techniques may be performed by circuitry, and examples of circuitry include any one or any combination of processing circuitry 110, sensing circuitry 140, and / or sensing device 150.

[0042] Figure 2 is a conceptual block diagram illustrating an exemplary regional oximetry device 200 configured to monitor a patient's autoregulatory state. Figure 2 The example of describes a regional oximetry device, but the techniques described herein for verifying light emitting diodes can be used in other devices, such as, for example, a pulse oximetry device. Figure 2 In the example shown, the regional oximetry device 200 is coupled to the sensing device 250, and the regional oximetry device and the sensing device may be collectively referred to as a regional oximetry system, each of which generates and processes physiological signals of a subject. The regional oximetry device 200 and the sensing device 250 may be Figure 1 In some examples, the sensing device 250 and the regional oximetry device 200 may be part of an oximeter. Figure 2 As shown, the regional oximetry device 200 includes a back-end processing circuit system 214, a user interface 230, an optical drive circuit system 240, a front-end processing circuit system 216, a control circuit system 245, and a communication interface 290. The regional oximetry device 200 is communicatively coupled to the sensing device 250. The regional oximetry device 200 is Figure 1 In some examples, the regional oximetry device 200 may also include a blood pressure sensor and / or a blood volume sensor (e.g., Figure 1 sensing devices 151 and 152).

[0043] exist Figure 2 In the example shown, the sensing device 250 includes a light source 260, a detector 262, and a detector 263. The light source 260 may be Figure 1 Detectors 262 and 263 may be Figure 110. In some examples, sensing device 250 may include more than two detectors. Light source 260 may be configured to emit a photon signal of light having two or more wavelengths (e.g., up to four or more wavelengths, more than four wavelengths, etc.) (e.g., red and infrared (IR), or light of another wavelength) into the subject's tissue. For example, light source 260 may include a red light emitting light source and an IR light emitting light source (e.g., a red and IR LED) for emitting light into the subject's tissue to generate a physiological signal. In some examples, the red wavelength may be between about 600nm and about 700nm, and the IR wavelength may be between about 800nm ​​and about 1000nm. Other wavelengths of light may be used in other instances. Light source 260 may include any number of light sources having any suitable characteristics. In an example where a sensor array is used instead of sensing device 250, each sensing device may be configured to emit a single wavelength. For example, a first sensing device may emit only red light, while a second sensing device may emit only IR light. In some examples, light source 260 can be configured to emit two or more wavelengths of near-infrared light (e.g., wavelengths between 600 nm and 1000 nm) into the tissue of a subject. In some examples, light source 260 can be configured to emit four wavelengths of light (e.g., 724 nm, 770 nm, 810 nm, and 850 nm) into the tissue of a subject. In some examples, the subject can be a medical patient.

[0044] As used herein, the term "light" may refer to energy generated by a radiation source and may include one or more of ultrasonic, radio, microwave, millimeter wave, infrared, visible light, ultraviolet, gamma ray, or X-ray electromagnetic radiation. Light may also include any wavelength within the radio, microwave, infrared, visible light, ultraviolet, or X-ray spectrum, and any suitable wavelength of electromagnetic radiation may be suitable for use with the present technology. Detectors 262 and 263 may be selected to be specifically sensitive to a selected target energy spectrum of light source 260.

[0045] Detectors 262 and 263 can be configured to detect the intensity of near-infrared light of multiple wavelengths. In some examples, detectors 262 and 263 can be configured to detect the intensity of light at red and IR wavelengths. In some examples, a detector array can be used, and each detector in the array can be configured to detect the intensity of a single wavelength. In operation, light can enter detector 262 after passing through the subject's tissue, including skin, bone, and other superficial tissues (e.g., non-brain tissue and superficial brain tissue). Light can enter detector 263 after passing through the subject's tissue, including skin, bone, other superficial tissues (e.g., non-brain tissue and superficial brain tissue) and deep tissues (e.g., deep brain tissue). Detectors 262 and 263 can convert the intensity of received light into an electrical signal. Light intensity can be directly related to the absorption and / or reflection of light in the tissue. That is, when more light at a certain wavelength is absorbed or reflected, less light of that wavelength is received from the tissue by detectors 262 and 263.

[0046] For example, detector 262 and / or detector 263 may determine a first intensity of a first received photon signal corresponding to a first output photon signal (e.g., red light) output by a first light emitting diode of light source 260. More specifically, processing circuitry (e.g., light driver circuitry 240) may be configured to drive the first light emitting diode of light source 260 to output the output photon signal toward the tissue of the subject and receive the first received photon signal from detector 262 and / or detector 263 after the first output photon signal is transmitted through the tissue of the subject. Similarly, detector 262 and / or detector 263 may determine a second intensity of a second received photon signal corresponding to a second output photon signal (e.g., infrared light) output by a second light emitting diode. More specifically, processing circuitry (e.g., light driver circuitry 240) may be configured to drive the second light emitting diode of light source 260 to output the second output photon signal toward the tissue of the subject and receive the second received photon signal from detector 262 and / or detector 263 after the second output photon signal is transmitted through the tissue of the subject.

[0047] After converting the received light into electrical signals, detectors 262 and 263 may transmit the detection signals to regional oximetry device 200, which may process the detection signals and determine a physiological parameter (e.g., based on the absorption of red and IR wavelengths in the subject's tissue at the two detectors). For example, regional oximetry device 200 may determine an oxygen saturation level based on a first intensity of the first received photon signal and a second intensity of the second received photon signal. More specifically, processing circuitry 210 may estimate a first wavelength of the first output photon signal based on calibration information stored in memory 220. For example, processing circuitry 210 may estimate the first wavelength of the first output photon signal to be equal to a first wavelength identified in the calibration information stored in memory 220. In some cases, processing circuitry 210 may estimate the first wavelength of the first output photon signal to be equal to a first wavelength identified in the calibration information stored in memory 220, which corresponds to an estimated operating temperature at light-emitting diode 260 (e.g., the first light-emitting diode).

[0048] Similarly, processing circuitry 210 may estimate a second wavelength of the output second output photon signal based on the calibration information stored in memory 220. For example, processing circuitry 210 may estimate the second wavelength of the second output photon signal to be equal to the second wavelength identified in the calibration information stored in memory 220. In some cases, processing circuitry 210 may estimate the second wavelength of the second output photon signal to be equal to the second wavelength identified in the calibration information stored in memory 220, which corresponds to an estimated operating temperature at light-emitting diode 260 (e.g., a second light-emitting diode).

[0049] In this example, processing circuitry 210 may determine the oxygen saturation level based on the first wavelength of the first output photon signal and the second wavelength of the second output photon signal. For example, processing circuitry 210 may determine the oxygen saturation level by matching the absorption amount of the first wavelength (e.g., the amplitude difference between the emitted light and the received light) and the absorption amount of the second wavelength in a table and outputting the corresponding oxygen saturation levels of the absorption of the first wavelength and the absorption of the second wavelength.

[0050] Processing circuitry 210 may output an indication of the oxygen saturation level. For example, processing circuitry 210 may store the indication of the oxygen saturation level (e.g., a numerical value indicating the oxygen saturation level) for storage at memory 220. Processing circuitry 210 may output the indication of the oxygen saturation level (e.g., a numerical value indicating the oxygen saturation level) to user interface 230 for output on display 232. Processing circuitry 210 may output the indication of the oxygen saturation level (e.g., a numerical value indicating the oxygen saturation level) to communication interface 290 for storage and / or output at one or more external or implanted devices.

[0051] Processing circuitry 210 may decrypt the calibration information stored in memory 220. For example, processing circuitry 210 may use the difference in the measured forward voltages as an encryption key to encrypt the calibration information stored in memory 220. Thus, processing circuitry 210 may use the difference in the measured forward voltages as a key to decrypt the encrypted calibration information. In this way, processing circuitry 210 may help ensure that the calibration information stored in memory 220 is used in a secure manner.

[0052] In some examples, one or more of the detection signals may be pre-processed by sensing device 250 before being transmitted to regional oximetry device 200. Additional exemplary details for determining oxygen saturation based on optical signals may be found in commonly assigned U.S. Patent No. 9,861,317, issued January 9, 2018, and entitled “Methods and Systems for Determining Regional Blood Oxygen Saturation,” which is incorporated herein by reference in its entirety.

[0053] The control circuitry 245 may be coupled to the light driver circuitry 240, the front-end processing circuitry 216, and the back-end processing circuitry 214 and may be configured to control the operation of these components. In some examples, the control circuitry 245 may be configured to provide timing control signals to coordinate their operation. For example, the light driver circuitry 240 may generate one or more light drive signals based on the timing control signals provided by the control circuitry 245, and the one or more light drive signals may be used to turn the light source 260 on and off. The front-end processing circuitry 216 may use the timing control signals to operate synchronously with the light driver circuitry 240. For example, the front-end processing circuitry 216 may synchronize the operation of the analog-to-digital converter and the demultiplexer with the light drive signals based on the timing control signals. In addition, the back-end processing circuitry 214 may use the timing control signals to coordinate its operation with the front-end processing circuitry 216.

[0054] As discussed above, the light drive circuit system 240 can be configured to generate a light drive signal that is provided to the light source 260 of the sensing device 250. The light drive signal can, for example, control the intensity of the light source 260 and control the timing of when the light source 260 is turned on and off. In some examples, the light drive circuit system 240 provides one or more light drive signals to the light source 260. In the case where the light source 260 is configured to emit two or more wavelengths of light, the light drive signal can be configured to control the operation of each wavelength of light. The light drive signal can include a single signal, or can include multiple signals (e.g., one signal for each wavelength of light).

[0055] Front-end processing circuitry 216 can perform any suitable analog conditioning of the detector signal. The conditioning can include any type of filtering (e.g., low-pass, high-pass, band-pass, notch, or any other suitable filtering), amplification, performing operations on the received signal (e.g., taking derivatives, averaging), performing any other suitable signal conditioning (e.g., converting a current signal into a voltage signal), or any combination thereof. The conditioned analog signal can be processed by an analog-to-digital converter of circuitry 216, which can convert the conditioned analog signal into a digital signal. Front-end processing circuitry 216 can operate on the analog or digital form of the detector signal to separate different signal components. Front-end processing circuitry 216 can also perform any suitable digital conditioning on the detector signal, such as low-pass, high-pass, band-pass, notch, averaging, or any other suitable filtering, amplification, performing operations on the signal, performing any other suitable digital conditioning, or any combination thereof. Front-end processing circuitry 216 can reduce the number of samples in the digital detector signal. In some examples, front-end processing circuitry 216 can also remove dark or ambient effects on the received signal.

[0056] Backend processing circuitry 214 may include processing circuitry 210 and memory 220. Processing circuitry 210 may include components of analog or digital electronic components and may be configured to execute software that may include an operating system and one or more application programs, as described herein for example. Figure 1 The processing circuitry 210 may receive and further process the physiological signals received from the front-end processing circuitry 216. For example, the processing circuitry 210 may determine one or more physiological parameter values ​​based on the received physiological signals. For example, the processing circuitry 210 may calculate one or more of regional oxygen saturation, blood oxygen saturation (e.g., arterial, venous, or both), pulse rate, respiratory rate, respiratory effort, blood pressure, hemoglobin concentration (e.g., oxygenated, deoxygenated, and / or total), any other suitable physiological parameters, or any combination thereof.

[0057] Processing circuitry 210 may perform any suitable signal processing on the signal, such as any suitable bandpass filtering, adaptive filtering, closed-loop filtering, any other suitable filtering, and / or any combination thereof. Processing circuitry 210 may also receive input signals from additional sources not shown. For example, processing circuitry 210 may receive an input signal from user interface 230 containing information about a treatment being provided to the subject. Processing circuitry 210 may use the additional input signal in any of its determinations or operations performed based on backend processing circuitry 214 or regional oximetry device 200.

[0058] Processing circuitry 210 is an example of processing circuitry 110 and is configured to perform the techniques of this disclosure. For example, processing circuitry 210 may be configured to determine a measured forward voltage difference based on a comparison of a first forward voltage of a first LED of light source 260 and a second forward voltage of a second LED of light source 260. For example, processing circuitry 210 may subtract the absolute value of the first forward voltage from the absolute value of the second forward voltage to generate the measured forward voltage difference. Processing circuitry 210 may be configured to determine that the first and second LEDs of light source 260 are valid based on the calibrated forward voltage difference and the measured forward voltage difference. For example, processing circuitry 210 may determine that the first and second LEDs of light source 260 are valid in response to determining that the difference between the calibrated forward voltage difference and the measured forward voltage difference is less than a predetermined threshold. Processing circuitry 210 may be configured to determine the oxygen saturation level using the first and second LEDs of light source 260 in response to determining that the first and second LEDs are valid.

[0059] Memory 220 may include any suitable computer-readable medium capable of storing information that can be interpreted by processing circuitry 210. In some examples, memory 220 may store reference absorption curves, reference sets, determined values ​​(such as blood oxygen saturation, pulse rate, blood pressure, fiducial locations or characteristics), initialization parameters, any other determined values, or any combination thereof in a memory device for later retrieval. Memory 220 may also store thresholds for detecting sudden changes in blood pressure, etc. Backend processing circuitry 214 may be communicatively coupled to user interface 230 and communication interface 290.

[0060] Memory 220 may store a calibrated forward voltage difference for the LEDs of light source 260. For example, during calibration of sensing device 250, device 200 (e.g., one or more of light driver circuitry 240, front-end processing circuitry 216, back-end processing circuitry 214, etc.) may generate a calibrated forward voltage difference for the LEDs of light source 260. For example, device 200 may determine the calibrated forward voltage difference based on a comparison of a first forward voltage of a first LED of light source 260 and a second forward voltage of a second LED of light source 260 during calibration of sensing device 250. For example, processing circuitry 210 may subtract the absolute value of the first forward voltage during calibration of sensing device 250 from the absolute value of the second forward voltage during calibration of sensing device 250 to generate the calibrated forward voltage difference.

[0061] During calibration of sensing device 250, device 200 or another device (e.g., a calibration device) may generate calibration information. For example, device 200 or the calibration device may generate an indication of a first wavelength output by a first light-emitting diode of light source 260 and an indication of a second wavelength output by a second light-emitting diode of light source 260. Memory 220 may store the calibration information based on the indication of the first wavelength output by the first light-emitting diode of light source 260 and the indication of the second wavelength output by the second light-emitting diode of light source 260. In some examples, device 200 may encrypt the calibration information. As used herein, calibration information may include information for accounting for manufacturing tolerances of light source 260, such as, for example, but not limited to, the wavelengths output by the light-emitting diodes of light source 260. For example, device 200 may encrypt the calibration information based on the difference in calibrated forward voltages. For example, device 200 may encrypt the calibration information using the difference in calibrated forward voltages as an encryption key.

[0062] In some examples, the user interface 230 may include an input device 234, a display 232, and a speaker 236. The user interface 230 is Figure 1 An example of the user interface 130 is shown, and the display 232 is Figure 1 An example of a display 132 is shown. The user interface 230 may include, for example, any suitable device, such as one or more medical devices (e.g., a medical monitor that displays various physiological parameters, a medical alarm, or any other suitable medical device that displays physiological parameters or uses the output of the backend processing 214 as input), one or more display devices (e.g., a monitor, a personal digital assistant (PDA), a mobile phone, a tablet computer, a clinician workstation, any other suitable display device, or any combination thereof), one or more audio devices, one or more memory devices, one or more printing devices, any other suitable output device, or any combination thereof.

[0063] Input device 234 may include one or more of any type of user input device, such as a keyboard, mouse, touch screen, buttons, switches, microphone, joystick, touchpad, or any other suitable input device or combination of input devices. In other examples, input device 234 may be a pressure-sensitive or presence-sensitive display included as part of display 232. Input device 234 may also receive commands for selecting sensing device 250, blood pressure sensor 250 ( Figure 2 ) or the model of the blood pressure processing equipment. In some examples, the processing circuit system 210 may determine the presentation type of the display 232 based on the user input received by the input device 234.

[0064] In some examples, the subject may be a medical patient, and the display 232 may present a list of values ​​that may be generally applicable to the subject, such as, for example, an oxygen saturation signal indicator, a blood pressure signal indicator, a COx signal indicator, a COx value indicator, and / or an autoregulation status indicator. The display 232 may also be configured to present additional physiological parameter information. Figure 3 The graphical user interface 300 is shown as a graphical user interface that can be used under the control of the processing circuit system 210 via Figure 2 2. In some examples, user interface 230 includes speaker 236 configured to generate and provide audible sounds that can be used in various examples, such as, for example, when a physiological parameter of the patient is not within a predetermined normal range and / or when processing circuit system 210 determines that the sensed blood pressure value may be due to non-physiological reasons (such as due to blood pressure sensor device 151 ( Figure 1 ) of the blood pressure probe is moved) and is inaccurate.

[0065] The communication interface 290 can enable the regional oximetry device 200 to exchange information with other external devices or implanted devices. The communication interface 290 can include any suitable hardware, software, or both that can allow the regional oximetry device 200 to communicate with electronic circuitry, devices, networks, servers or other workstations, displays, or any combination thereof. For example, the regional oximetry device 200 can receive MAP (or other blood pressure measurement) values ​​and / or oxygen saturation values ​​from an external device via the communication interface 290.

[0066] The components of regional oximetry device 200 shown and described as separate components are shown and described for illustrative purposes only. In some examples, the functionality of some of the components may be combined in a single component. For example, the functionality of front-end processing circuitry 216 and back-end processing circuitry 214 may be combined in a single processor system. Furthermore, in some examples, the functionality of some of the components of regional oximetry device 200 shown and described herein may be divided across multiple components. For example, some or all of the functionality of control circuitry 245 may be performed in front-end processing circuitry 216, back-end processing circuitry 214, or both. In other examples, the functionality of one or more components may be performed in a different order or may not need to be performed. In some examples, all components of regional oximetry device 200 may be implemented in processor circuitry.

[0067] In the above examples, processing circuitry 210, light driver circuitry 240, front-end processing circuitry 216, and voltage measurement circuitry are described as performing exemplary techniques, wherein light driver circuitry 240, front-end processing circuitry 216, and voltage measurement circuitry may be part of processing circuitry 210. However, any one or any combination of processing circuitry 210, light driver circuitry 240, front-end processing circuitry 216, and voltage measurement circuitry may be configured to perform the exemplary techniques. For example, the exemplary techniques may be performed by circuitry, and examples of circuitry include any one or any combination of processing circuitry 210, light driver circuitry 240, front-end processing circuitry 216, and voltage measurement circuitry.

[0068] Figure 3 An exemplary graphical user interface 300 including self-adjustment information presented on a display is shown. Figure 3 is processed by the processing circuit system 110 Figure 1 The display 132 is shown or the processing circuit system 210 is shown Figure 2 An example of a presentation performed on display 232 is shown. Although Figures 3 to 5 Compared to the regional oximetry device 100 ( Figure 1 ) is described with respect to processing circuitry 110, but in other examples, processing circuitry 210, 214, and / or 216 ( Figure 2 ) executable Figures 3 to 5 any part of the technology.

[0069] The graphical user interface 300 can be configured to display various information related to blood pressure, oxygen saturation, COx index, brain autoregulatory limits, and / or brain autoregulatory status. As shown, the graphical user interface 300 can include an oxygen saturation signal indicator 310, a blood pressure signal indicator 320, and a COx signal indicator 330. The graphical user interface 300 can also include a COx value indicator 340, an autoregulatory status indicator 350, and autoregulatory limit indicators 360 and 370.

[0070] The blood pressure signal indicator 320 can present a set of MAP values ​​determined by the processing circuitry 110 of the regional oximetry device 100. The MAP values ​​can be based on measured blood pressure values, but in other examples, raw measured blood pressure values ​​can be displayed (e.g., to illustrate changes in the intracardiac circulation). In some examples, the blood pressure signal indicator 320 can present the MAP values ​​as discrete points over time or in a table. The blood pressure signal indicator 320 can also present the MAP values ​​as a moving average of discrete points or as a waveform. The blood pressure signal indicator 320 can also present the MAP values ​​as a single value (e.g., a number) representing the current MAP value. The oxygen saturation signal indicator 310 and the COx signal indicator 330 can also present the rSO2 value and COx value, respectively, as discrete points, in a table, as a moving average, as a waveform, and / or as a single value. In other examples, data from two or more of the oxygen saturation signal indicator 310, the blood pressure signal indicator 320, or the COx signal indicator 330 can be combined on a single graph.

[0071] COx signal indicator 330 may present a set of correlation coefficients determined by processing circuitry 110. Processing circuitry 110 may determine the correlation coefficients as a function of the oxygen saturation value presented in oxygen saturation signal indicator 310 and the MAP value presented in blood pressure signal indicator 320. In some examples, a COx value equal to or close to one indicates that the patient's brain autoregulatory state is impaired, as shown by autoregulatory state indicator 350.

[0072] COx value indicator 340 shows the COx value determined by processing circuitry 110. Figure 3 In the example of FIG, , the COx value is shown as 0.8 and may change over time. A COx value of 0.8 may be used by the processing circuit system 110 to determine that the patient's brain autoregulation state is impaired. The processing circuit system 110 may be configured to present the most recently determined COx value as the COx value in the COx value indicator 340. To determine the patient's brain autoregulation state for presentation in the autoregulation state indicator 350, the processing circuit system 110 may determine whether the most recent MAP value shown in the blood pressure signal indicator 320 is between the brain autoregulation limits presented in the limits of the autoregulation indicators 360 and 370. The processing circuit system 110 may present text, such as "intact" or "impaired," in the autoregulation state indicator 350. The processing circuit system 110 may also present a color, such as green (e.g., for intact brain autoregulation) or red (e.g., for impaired brain autoregulation) to help help the user understand the patient's autoregulation state.

[0073] In some examples, processing circuitry 110 may present the limits of autoregulation indicators 360 and / or 370 in terms of blood pressure, e.g., in millimeters of mercury (mmHg). Processing circuitry 110 may determine the limits of brain autoregulation (LLA and ULA) for presentation in indicators 360 and 370 based on a relationship between the patient's blood pressure and another physiological parameter of the patient. For example, indicator 360 may highlight when the LLA has been exceeded, or may highlight when the ULA has been exceeded. In other examples, a single indicator may present the type of limit that the MAP value has exceeded. If the LLA or ULA changes, processing circuitry 110 may control user interface 300 to change the respective value based on any change in the value of the LLA or ULA.

[0074] In some examples, processing circuit system 110 determines the brain's autoregulatory state for presentation in autoregulatory state indicator 350 by comparing the most recently determined MAP value to the brain's autoregulatory limit. For example, if processing circuit system 110 estimates an LLA of 50 mmHg and determines a MAP value of 40 mmHg, processing circuit system 110 may determine that the patient's brain's autoregulatory state is impaired or incomplete. In response to determining that the MAP value is less than or equal to the estimate of the LLA for more than a predetermined period of time, processing circuit system 110 may output a notification in autoregulatory state indicator 350 as text, color, flashing, and / or any other suitable visual or audible manner.

[0075] Figure 4 An example of a sensor device 450 according to the techniques described herein is shown. The sensor device 450 may be Figure 1 The sensor device 150 and / or Figure 2 4. LED 460A and LED 460B (collectively referred to as "LEDs") may form an example of light source 260. Although Figure 4 Compared to the regional oximetry device 100 ( Figure 1 ), but in other examples, other devices may perform Figure 4 For example, processing circuitry 210, 214, and / or 216 (either alone or in combination with processing circuitry 110) Figure 2 ) executable Figure 4 In some examples, light emitting diode 460 may include a laser diode, a vertical cavity surface emitting laser, or another device that emits light. In some examples, light emitting diode 460 may additionally or alternatively include a photodiode or another device that detects light (e.g., red light, infrared light, etc.).

[0076] exist Figure 4In the example of , LED 460A may be configured to emit red light, and LED 460B may be configured to emit infrared light. However, in some examples, LED 460A may be configured to emit infrared light, and LED 460B may be configured to emit red light. In addition, LED 460 may be configured to emit light at wavelengths other than red and infrared. Figure 4 In the example of FIG, LEDs 460 are arranged in an anti-parallel configuration. For example, the anode of LED 460B can be coupled to the cathode of LED 460A, and the cathode of LED 460B can be coupled to the anode of LED 460A.

[0077] Cable resistance 464, which may represent the ohmic resistance between sensor device 450 and a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.), may have a resistance of several ohms, which may bias the forward voltage reading of LED 460. The oximetry device may be configured to improve measurement accuracy by using very small currents to help reduce voltage errors generated by cable resistance 464. For simplicity, the series resistance of LED 460A and LED 460B is represented by cable resistance 464. Cable resistance 464 may include only the resistance in the cable. In some examples, cable resistance 464 may include one or more of the cable resistance and resistive losses from one or more connectors, one or more wire bond pads, one or more printed circuit board (PCB) traces, one or more extension cables, one or more sensor cables, the bulk resistance of LED 460A, the bulk resistance of LED 460B, and / or other resistances.

[0078] According to the techniques of this disclosure, a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.) can be configured to utilize an anti-parallel configuration of LEDs (e.g., red-emitting diode 460A and infrared-emitting diode 460B arranged in an anti-parallel configuration) to reduce or eliminate voltage errors generated by cable resistance 464. For example, a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.) can include memory circuitry (e.g., memory 120, memory 220, etc.) configured to store the difference in calibrated forward voltages. The device can also include processing circuitry (e.g., processing circuitry 110, backend processing circuitry 210, etc.) configured to apply a first current 470 from the anode of LED 460A to the cathode of LED 460A. For example, light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) can apply a first current 470 (e.g., a positive current) to cause first current 470 to flow through LED 460A. For example, light driver circuitry can apply first current 470 from a first terminal 474 through a first cable (e.g., represented by a first portion of cable resistance 464) to an anode of LED 460A, from the anode of LED 460A to a cathode of LED 460A, and from the cathode of LED 460A through a second cable (e.g., represented by a second portion of cable resistance 464) to a second terminal 476.

[0079] When first current 470 is applied, processing circuitry can measure a first forward voltage across the anode of LED 460A and the cathode of LED 460A. For example, light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) can measure an indication of a voltage output at first terminal 474 and second terminal 476 of a source supplying first current 470. While cable resistance 464 is shown as being disposed only between terminal 474 and the anode of LED 460A, in some examples, cable resistance can additionally or alternatively be disposed anywhere between terminal 476 and terminal 474. Similarly, cable resistance 464 can include one or more of cable resistance and resistive losses from one or more connectors, one or more wire bond pads, one or more printed circuit board (PCB) traces, one or more extension cables and one or more sensor cables, the bulk resistance of LED 460A, the bulk resistance of LED 460B, and / or other resistances.

[0080] The light driving circuitry (e.g., within sensing device 150, sensing circuitry 140, processing circuitry 110, etc.) can apply a second current 472 from the anode of LED 460B to the cathode of LED 460B. For example, the light driving circuitry (e.g., within sensing device 150, sensing circuitry 140, processing circuitry 110, etc.) can apply a second current 472 (e.g., a negative current) to cause the second current 472 to flow through LED 460B. For example, the light driving circuitry can apply the second current 472 from the second terminal 476 through the second cable (e.g., represented by the second portion of cable resistance 464) to the anode of LED 460B, from the anode of LED 460B to the cathode of LED 460B, and from the cathode of LED 460B through the first cable (e.g., represented by the first portion of cable resistance 464) to the first terminal 474.

[0081] When the second current is applied, the processing circuitry can be configured to measure a second forward voltage across the anode of light emitting diode 460B and the cathode of light emitting diode 460B. For example, light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, processing circuitry 110, etc.) can measure an indication of the voltage output at first terminal 474 and second terminal 476 of the source supplying second current 472.

[0082] Processing circuitry 110 may apply first current 470 with a current magnitude and a positive polarity (e.g., flowing from −Vf to +Vf) such that first current 470 flows from the anode of light-emitting diode 460A to the cathode of light-emitting diode 460A. In this example, processing circuitry 110 may apply second current 472 with a current magnitude and a negative polarity (e.g., flowing from +Vf to −Vf) such that second current 472 flows from the anode of light-emitting diode 460B to the cathode of light-emitting diode 460B.

[0083] Using the same current amplitude and measuring the forward voltage of LED 460A and then reversing the current to measure the forward voltage of LED 460B can result in the two forward voltage measurements having an equivalent current*cable-resistance measurement error. Therefore, subtracting the Vf of LED 460A from the Vf of LED 460B (or vice versa) can "cancel" any errors in cable resistance 464. That is, while both the Vf of LED 460A and the Vf of LED 460B vary with different values ​​of cable resistance 464, the difference in the measured forward voltages of LEDs 460 can remain constant for different cable resistance levels. In this way, cable resistance 464 can be canceled to validate sensor device 450.

[0084] Additionally, the forward voltage measurement can be correlated to the wavelength of light emitted by LED 460 (e.g., via Planck's equation). In this way, a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.) can verify that LED 460 has the correct wavelength used in calibration. Using this highly accurate measurement of ΔVf, the device can measure the temperature of LED 460 to ensure the LED is not at an undesirable temperature. When in contact with the patient's skin, the device can measure the temperature of LED 460 with sufficient accuracy to measure the placement of a sensor device (e.g., sensor device 150, sensor device 250, etc.) through changes in the temperature of LED 460. In some examples, the device can use the forward voltage information to generate an encryption key, for example, to decrypt stored calibration information.

[0085] Figure 5 is a conceptual diagram illustrating an exemplary second sensor device according to the techniques described herein. Sensor device 550 may be Figure 1 The sensor device 150 and / or Figure 2 LED 560A and LED 560B (collectively, “LED 560”), LED 580A and LED 580B (collectively, “LED 580”), and LED 582A and LED 582B (collectively, “LED 582”) may each form an example of light source 260. Although Figure 5 Compared to the regional oximetry device 100 ( Figure 1 ), but in other examples, other devices may perform Figure 5 For example, processing circuitry 210, 214, and / or 216 (either alone or in combination with processing circuitry 110) Figure 2 ) executable Figure 5 In some examples, light emitting diodes 560, 580, 582 may include a laser diode, a vertical cavity surface emitting laser, or another device that emits light, or any combination thereof. In some examples, light emitting diodes 560, 580, 582 may additionally or alternatively include a photodiode or another device that detects light (e.g., red light, infrared light, etc.). Although Figure 5 The example includes 6 LEDs, but the example may include fewer LEDs (e.g., 2 LEDs or 4 LEDs) or more LEDs (e.g., 8 LEDs, 10 LEDs, etc.).

[0086] exist Figure 5In the example of FIG, one LED in each pair of LEDs 560, 580, 582 may be configured to emit red light, and one LED in each pair of LEDs 560, 580, 582 may be configured to emit infrared light. However, in some examples, one or more of LEDs 560, 580, 582 may be configured to emit light at wavelengths other than red and infrared. Figure 5 In the example of FIG, each pair of LEDs 560, 580, and 582 is arranged in an anti-parallel configuration. For example, the anode of LED 560B can be coupled to the cathode of LED 560A, and the cathode of LED 560B can be coupled to the anode of LED 560A.

[0087] First terminal 574, second terminal 575, and third terminal 576 can each represent a connection to an oximetry device (e.g., oximetry device 100) using one or more cables, extension cables, one or more connectors, one or more wire bond pads, or other resistive components. Although not shown, sensor device 550 can include resistive losses due to, for example, cable resistance, one or more connectors, one or more wire bond pads, one or more printed circuit board (PCB) traces, one or more extension cables and one or more sensor cables, bulk resistance of light-emitting diodes 560, 580, 582, and / or other resistive losses.

[0088] According to the techniques of this disclosure, a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.) can be configured to utilize an anti-parallel configuration of LEDs (e.g., light-emitting diodes 560, 580, 582 arranged in an anti-parallel configuration) to reduce or eliminate voltage errors generated by resistance in sensor device 550. For example, a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.) can include memory circuitry (e.g., memory 120, memory 220, etc.) configured to store the difference in calibrated forward voltages. The following examples refer to light-emitting diode 560, however, any pair of light-emitting diodes (e.g., light-emitting diode 580, light-emitting diode 582, etc.) can be used.

[0089] The device may also include processing circuitry (e.g., processing circuitry 110, backend processing circuitry 210, etc.) configured to apply a first current from the anode of light-emitting diode 560A to the cathode of light-emitting diode 560A. While applying the first current, the processing circuitry may measure a first forward voltage across the anode of light-emitting diode 560A and the cathode of light-emitting diode 560A. For example, light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, and / or processing circuitry 110) may measure an indication of the voltage output at first terminal 574 and second terminal 575.

[0090] The light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, processing circuitry 110, etc.) may apply a second current from the anode of light-emitting diode 560B to the cathode of light-emitting diode 560B. While applying the second current, the processing circuitry may be configured to measure a second forward voltage across the anode of light-emitting diode 560B and the cathode of light-emitting diode 560B. For example, the light driver circuitry (e.g., within sensing device 150, sensing circuitry 140, processing circuitry 110, etc.) may measure an indication of the voltage output at first terminal 574 and second terminal 575.

[0091] Processing circuitry 110 may apply a first current with a current magnitude and a positive polarity (e.g., flowing from first terminal 574 to second terminal 575) such that the first current flows from the anode of light-emitting diode 560A to the cathode of light-emitting diode 560A. In this example, processing circuitry 110 may apply a second current with a current magnitude and a negative polarity (e.g., flowing from second terminal 575 to first terminal 574) such that the second current flows from the anode of light-emitting diode 560B to the cathode of light-emitting diode 560B.

[0092] Using the same current amplitude and measuring the forward voltage of LED 560A and then reversing the current to measure the forward voltage of LED 560B can result in these two forward voltage measurements having an equivalent current * resistance measurement error. Therefore, subtracting the Vf of LED 560A from the Vf of LED 560B (or vice versa) can "cancel" any errors in the resistance of sensor device 550. That is, while both the Vf of LED 560A and the Vf of LED 560B vary with different values ​​of the resistance of sensor device 550, the difference in the measured forward voltage of LED 560 can remain constant for different resistance levels. In this way, the resistance losses of sensor device 550 can be canceled to verify sensor device 550.

[0093] Additionally, the forward voltage measurement can be correlated to the wavelength of light emitted by LEDs 560, 580, 582 (e.g., via Planck's equation). In this way, a device (e.g., regional oximetry device 150, regional oximetry device 250, etc.) can verify that LEDs 560, 580, 582 have the correct wavelength used in calibration. Using this highly accurate measurement of ΔVf, the device can measure the temperature of LEDs 560, 580, 582 to ensure the LEDs are not at an undesirable temperature. When in contact with a patient's skin, the device can measure the temperature of LEDs 560, 580, 582 with sufficient accuracy to measure the placement of a sensor device (e.g., sensor device 150, sensor device 250, etc.) based on changes in the temperature of LEDs 560, 580, 582. In some examples, the device can use the forward voltage information to generate an encryption key, for example, to decrypt stored calibration information.

[0094] Figure 6 is a flow chart illustrating an exemplary technique for measuring oxygen saturation according to the techniques described herein. Figure 6 Compared to the regional oximetry device 100 ( Figure 1 ), but in other examples, other devices may perform Figure 6 For example, the circuit system may include one or more of the processing circuit system 110, the oxygen saturation sensing circuit system 140, the sensing device 150, the optical drive circuit system, the control circuit system, the front-end processing circuit system, the back-end processing circuit system, and / or other circuit systems. Figure 6 is described using sensor device 450, but Figure 6 The technology can be applied to other sensor devices, such as e.g. Figure 5 Sensor device 550. In some examples, the first light emitting diode and / or the second light emitting diode may include a laser diode, a vertical cavity surface emitting laser, or another device that emits light. In some examples, the first light emitting diode and / or the second light emitting diode may additionally or alternatively include a photodiode or another device that detects light (e.g., red light, infrared light, etc.).

[0095] exist Figure 6In an example of FIG. 5 , the circuit system may apply a first current from an anode of a first light-emitting diode to a cathode of the first light-emitting diode (602). For example, the circuit system may apply first current 470 from an anode of light-emitting diode 460A to a cathode of light-emitting diode 460A. While applying the first current, the circuit system may measure a first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode (604). For example, the circuit system may measure a first forward voltage across the anode of light-emitting diode 460A and the cathode of light-emitting diode 460A while applying the first current 470.

[0096] The circuit system may apply a second current from the anode of the second light-emitting diode to the cathode of the second light-emitting diode (606). For example, the circuit system may apply second current 472 from the anode of light-emitting diode 460B to the cathode of light-emitting diode 460B. While applying the second current, the circuit system may measure a second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode (608). For example, the circuit system may measure a first forward voltage across the anode of light-emitting diode 460B and the cathode of light-emitting diode 460B while applying the second current 472.

[0097] The circuit system may determine a difference in the measured forward voltages based on a comparison of the first forward voltage and the second forward voltage (610). The circuit system may determine that the first LED and the second LED are valid based on the difference in the calibrated forward voltages and the difference in the measured forward voltages (612). In response to determining that the first LED and the second LED are valid, the circuit system may use the first LED and the second LED to determine an oxygen saturation level and output an indication of the oxygen saturation level (614).

[0098] The following are examples of the descriptions herein.

[0099] Embodiment 1: A device for measuring oxygen saturation, the device comprising: a memory configured to store a calibrated forward voltage difference; circuitry configured to: apply a first current from an anode of a first light-emitting diode to a cathode of the first light-emitting diode; measure a first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode while applying the first current; apply a second current from an anode of a second light-emitting diode to a cathode of the second light-emitting diode; measure a second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode while applying the second current; determine a difference in the measured forward voltages based on a comparison of the first forward voltage and the second forward voltage; determine that the first light-emitting diode and the second light-emitting diode are valid based on the calibrated forward voltage difference and the measured forward voltage difference; and in response to the determination that the first light-emitting diode and the second light-emitting diode are valid, determine an oxygen saturation level using the first light-emitting diode and the second light-emitting diode and output an indication of the oxygen saturation level.

[0100] Example 2. An apparatus according to Example 1, wherein, to apply the first current, the circuit system is configured to apply the first current with a current amplitude and with a positive polarity so that the first current flows from the anode of the first light-emitting diode to the cathode of the first light-emitting diode; and wherein, to apply the second current, the circuit system is configured to apply the second current with the current amplitude and with a negative polarity so that the second current flows from the anode of the second light-emitting diode to the cathode of the second light-emitting diode.

[0101] Embodiment 3. An apparatus according to any combination of embodiments 1 to 2, wherein, to determine that the first light-emitting diode and the second light-emitting diode are valid, the circuit system is configured to determine that the difference between the calibrated forward voltage difference and the measured forward voltage difference is less than a threshold.

[0102] Embodiment 4. The device of any combination of Embodiments 1 to 3, wherein the anode of the second light-emitting diode is coupled to the cathode of the first light-emitting diode, and the cathode of the second light-emitting diode is coupled to the anode of the first light-emitting diode.

[0103] Embodiment 5. An apparatus according to any combination of embodiments 1 to 4, wherein, to apply the first current, the circuit system is configured to apply the first current from a first terminal to the anode of the first light-emitting diode through a first cable, from the anode of the first light-emitting diode to the cathode of the first light-emitting diode, and from the cathode of the first light-emitting diode to a second terminal through a second cable; and wherein, to measure the first forward voltage, the circuit system is configured to measure the voltage across the first terminal and the second terminal when the first current is applied.

[0104] Example 6. An apparatus according to Example 5, wherein, to apply the second current, the circuit system is configured to apply the second current from the second terminal to the anode of the second light-emitting diode through the second cable, from the anode of the second light-emitting diode to the cathode of the second light-emitting diode, and from the cathode of the second light-emitting diode to the first terminal through the first cable; and wherein, to measure the second forward voltage, the circuit system is configured to measure the voltage across the first terminal and the second terminal when the second current is applied.

[0105] Embodiment 7. The apparatus of any combination of Embodiments 1 to 6, wherein, to determine the oxygen saturation level, the circuit system is configured to: determine a first intensity of a first received photon signal corresponding to a first output photon signal output using the first light-emitting diode; determine a second intensity of a second received photon signal corresponding to a second output photon signal output using the second light-emitting diode; and determine the oxygen saturation level based on the first intensity of the first received photon signal and the second intensity of the second received photon signal.

[0106] Example 8. An apparatus according to Example 7, wherein, in order to determine the first intensity of the first received photon signal, the circuit system is configured to drive the first light-emitting diode to output the first output photon signal to the tissue of the subject and to receive the first received photon signal from a first detector after the first output photon signal is transmitted through the tissue of the subject; and wherein, in order to determine the second intensity of the second received photon signal, the circuit system is configured to drive the second light-emitting diode to output the second output photon signal to the tissue of the subject and to receive the second received photon signal from a second detector after the second output photon signal is transmitted through the tissue of the subject.

[0107] Embodiment 9. The apparatus of any combination of Embodiments 7 to 8, wherein the memory is further configured to store calibration information, and wherein the determination of the oxygen saturation level is also based on the calibration information.

[0108] Example 10. The apparatus of Example 9, wherein, to determine the oxygen saturation level, the circuit system is configured to: estimate a first wavelength of the first output photon signal based on the calibration information; estimate a second wavelength of the output second output photon signal based on the calibration information; and wherein the determination of the oxygen saturation level is also based on the first wavelength of the first output photon signal and the second wavelength of the second output photon signal.

[0109] Embodiment 11. The apparatus of any combination of Embodiments 9-10, wherein the circuitry is configured to decrypt the calibration information based on a difference in the measured forward voltages.

[0110] Embodiment 12. The device of any combination of Embodiments 1 to 11, wherein the first light emitting diode is configured to emit red light; and wherein the second light emitting diode is configured to emit infrared light.

[0111] Embodiment 13. The apparatus of any combination of Embodiments 1 to 12, wherein the circuitry is configured to estimate a temperature at one or more of the first light emitting diode or the second light emitting diode based on a difference in the measured forward voltages.

[0112] Embodiment 14. A method for measuring oxygen saturation, the method comprising: applying, by circuitry, a first current from an anode of a first light-emitting diode to a cathode of the first light-emitting diode; measuring, by the circuitry, a first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode while applying the first current; applying, by the circuitry, a second current from an anode of a second light-emitting diode to a cathode of the second light-emitting diode; measuring, by the circuitry, a second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode while applying the second current; determining, by the circuitry, a difference in the measured forward voltages based on a comparison of the first forward voltage and the second forward voltage; determining, by the circuitry, that the first light-emitting diode and the second light-emitting diode are valid based on the difference in calibrated forward voltages and the difference in measured forward voltages; and in response to determining that the first light-emitting diode and the second light-emitting diode are valid, determining, by the circuitry, an oxygen saturation level using the first light-emitting diode and the second light-emitting diode and outputting, by the circuitry, an indication of the oxygen saturation level.

[0113] Embodiment 15. A method according to embodiment 14, wherein applying the first current includes applying the first current with a current amplitude and with a positive polarity so that the first current flows from the anode of the first light-emitting diode to the cathode of the first light-emitting diode; and wherein applying the second current includes applying the second current with the current amplitude and with a negative polarity so that the second current flows from the anode of the second light-emitting diode to the cathode of the second light-emitting diode.

[0114] Embodiment 16. A method according to any combination of embodiments 14 to 15, wherein determining that the first light-emitting diode and the second light-emitting diode are valid includes determining that the difference between the calibrated forward voltage difference and the measured forward voltage difference is less than a threshold.

[0115] Embodiment 17. The method of any combination of Embodiments 14 to 16, wherein the anode of the second light-emitting diode is coupled to the cathode of the first light-emitting diode, and the cathode of the second light-emitting diode is coupled to the anode of the first light-emitting diode.

[0116] Embodiment 18. A method according to any combination of Embodiments 14 to 17, wherein applying the first current includes applying the first current from a first terminal to the anode of the first light-emitting diode through a first cable, from the anode of the first light-emitting diode to the cathode of the first light-emitting diode, and from the cathode of the first light-emitting diode to a second terminal through a second cable; and wherein measuring the first forward voltage includes measuring the voltage across the first terminal and the second terminal when the first current is applied.

[0117] Embodiment 19. A method according to embodiment 18, wherein applying the second current includes applying the second current from the second terminal through the second cable to the anode of the second light-emitting diode, from the anode of the second light-emitting diode to the cathode of the second light-emitting diode, and from the cathode of the second light-emitting diode through the first cable to the first terminal; and wherein measuring the second forward voltage includes measuring the voltage across the first terminal and the second terminal when the second current is applied.

[0118] Embodiment 20. A system for measuring oxygen saturation, the system comprising: a sensor device comprising a first light emitting diode and a second light emitting diode; an oximetry device comprising: a memory configured to store a calibrated forward voltage difference; circuitry configured to: apply a first current from an anode of the first light emitting diode to a cathode of the first light emitting diode; while applying the first current, measure a first forward voltage across the anode of the first light emitting diode and the cathode of the first light emitting diode; apply a second current from an anode of the second light emitting diode to a cathode of the second light emitting diode; while applying the second current, measure a second forward voltage across the anode of the second light emitting diode and the cathode of the second light emitting diode; determine a difference in the measured forward voltages based on a comparison of the first forward voltage and the second forward voltage; determine that the first light emitting diode and the second light emitting diode are valid based on the calibrated forward voltage difference and the measured forward voltage difference; and in response to the determination that the first light emitting diode and the second light emitting diode are valid, determine an oxygen saturation level using the first light emitting diode and the second light emitting diode and output an indication of the oxygen saturation level.

[0119] Embodiment 21. A device for measuring oxygen saturation, the device comprising: a memory configured to store a calibrated forward voltage difference; and circuitry configured to: determine a measured forward voltage difference based on a first forward voltage at a first light-emitting diode and a second forward voltage at a second light-emitting diode; determine that the first light-emitting diode and the second light-emitting diode are valid based on the calibrated forward voltage difference and the measured forward voltage difference; and in response to the determination that the first light-emitting diode and the second light-emitting diode are valid, determine an oxygen saturation level using the first light-emitting diode and the second light-emitting diode and output an indication of the oxygen saturation level.

[0120] Embodiment 22. An apparatus according to embodiment 21, wherein the circuit system is configured to: apply a first current having a positive polarity with a current amplitude such that the first current flows from the anode of the first light-emitting diode to the cathode of the first light-emitting diode; measure the first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode when the circuit system applies the first current; apply a second current having a negative polarity with the current amplitude such that the second current flows from the anode of the second light-emitting diode to the cathode of the second light-emitting diode; and measure the second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode when the circuit system applies the second current.

[0121] Embodiment 23. An apparatus according to any combination of embodiments 21 to 22, wherein, to determine that the first light-emitting diode and the second light-emitting diode are valid, the circuit system is configured to determine that the difference between the calibrated forward voltage difference and the measured forward voltage difference is less than a threshold.

[0122] Embodiment 24. The device of any combination of Embodiments 21 to 23, wherein the anode of the second light-emitting diode is coupled to the cathode of the first light-emitting diode, and the cathode of the second light-emitting diode is coupled to the anode of the first light-emitting diode.

[0123] Embodiment 25. An apparatus according to any combination of Embodiments 21 to 24, wherein the circuit system is configured to apply a first current from a first terminal to an anode of the first light-emitting diode through a first cable, from the anode of the first light-emitting diode to the cathode of the first light-emitting diode, and from the cathode of the first light-emitting diode to a second terminal through a second cable; and measure the first forward voltage, wherein, to measure the first forward voltage, the circuit system is configured to measure a voltage across the first terminal and the second terminal when the circuit system applies the first current.

[0124] Embodiment 26. An apparatus according to embodiment 25, wherein the circuit system is configured to apply a second current from the second terminal to the anode of the second light-emitting diode through the second cable, from the anode of the second light-emitting diode to the cathode of the second light-emitting diode, and from the cathode of the second light-emitting diode to the first terminal through the first cable; and measure the second forward voltage, wherein, in order to measure the second forward voltage, the circuit system is configured to measure the voltage across the first terminal and the second terminal when the circuit system applies the second current.

[0125] Embodiment 27. An apparatus according to any combination of embodiments 21 to 26, wherein, to determine the oxygen saturation level, the circuit system is configured to: determine a first intensity of a first received photon signal corresponding to a first output photon signal output using the first light-emitting diode; determine a second intensity of a second received photon signal corresponding to a second output photon signal output using the second light-emitting diode; and determine the oxygen saturation level based on the first intensity of the first received photon signal and the second intensity of the second received photon signal.

[0126] Example 28. An apparatus according to Example 27, wherein, in order to determine the first intensity of the first received photon signal, the circuit system is configured to drive the first light-emitting diode to output the first output photon signal to the tissue of the subject and to receive the first received photon signal from a first detector after the first output photon signal is transmitted through the tissue of the subject; and wherein, in order to determine the second intensity of the second received photon signal, the circuit system is configured to drive the second light-emitting diode to output the second output photon signal to the tissue of the subject and to receive the second received photon signal from a second detector after the second output photon signal is transmitted through the tissue of the subject.

[0127] Embodiment 29. An apparatus according to any combination of embodiments 27 to 28, wherein the memory is further configured to store calibration information, and wherein, to determine the oxygen saturation level, the circuit system is configured to determine the oxygen saturation level based on the first intensity of the first received photon signal and the second intensity of the second received photon signal and also based on the calibration information.

[0128] Example 30. An apparatus according to Example 29, wherein, to determine the oxygen saturation level, the circuit system is configured to: estimate a first wavelength of the first output photon signal based on the calibration information; estimate a second wavelength of the output second output photon signal based on the calibration information; and wherein, to determine the oxygen saturation level, the circuit system is configured to determine the oxygen saturation level based on the first intensity of the first received photon signal and the second intensity of the second received photon signal and also based on the first wavelength of the first output photon signal and the second wavelength of the second output photon signal.

[0129] Embodiment 31. The apparatus of any combination of Embodiments 29 to 30, wherein the circuitry is configured to decrypt the calibration information based on a difference in the measured forward voltages.

[0130] Embodiment 32. The device of any combination of Embodiments 21 to 31, wherein the first light emitting diode is configured to emit red light; and wherein the second light emitting diode is configured to emit infrared light.

[0131] Embodiment 33. An apparatus according to any combination of Embodiments 31 to 32, wherein the circuit system is configured to estimate the temperature at one or more of the first light emitting diode or the second light emitting diode based on the difference in the measured forward voltage.

[0132] Embodiment 34. A method for measuring oxygen saturation, the method comprising: determining, by circuitry, a difference in measured forward voltages based on a first forward voltage at a first light-emitting diode and a second forward voltage at a second light-emitting diode; determining, by the circuitry, that the first light-emitting diode and the second light-emitting diode are valid based on the difference in calibrated forward voltages and the difference in measured forward voltages; and in response to determining that the first light-emitting diode and the second light-emitting diode are valid, determining, by the circuitry, an oxygen saturation level using the first light-emitting diode and the second light-emitting diode and outputting, by the circuitry, an indication of the oxygen saturation level.

[0133] Example 35. The method according to Example 34 further includes: applying a first current with a positive polarity by the circuit system with a current amplitude so that the first current flows from the anode of the first light-emitting diode to the cathode of the first light-emitting diode; when applying the first current, measuring the first forward voltage across the anode of the first light-emitting diode and the cathode of the first light-emitting diode by the circuit system; applying a second current with a negative polarity by the circuit system with the current amplitude so that the second current flows from the anode of the second light-emitting diode to the cathode of the second light-emitting diode; and measuring the second forward voltage across the anode of the second light-emitting diode and the cathode of the second light-emitting diode by the circuit system when applying the second current.

[0134] Embodiment 36. A method according to any combination of embodiments 34 to 35, wherein determining that the first light-emitting diode and the second light-emitting diode are valid includes determining that the difference between the calibrated forward voltage difference and the measured forward voltage difference is less than a threshold.

[0135] Embodiment 37. The method of any combination of Embodiments 34 to 36, wherein the anode of the second light-emitting diode is coupled to the cathode of the first light-emitting diode, and the cathode of the second light-emitting diode is coupled to the anode of the first light-emitting diode.

[0136] Embodiment 38. The method according to any combination of Embodiments 34 to 37, further comprising: applying, by the circuit system, a first current from a first terminal to an anode of the first light-emitting diode through a first cable, from the anode of the first light-emitting diode to the cathode of the first light-emitting diode, and from the cathode of the first light-emitting diode to a second terminal through a second cable; and measuring, by the circuit system, the first forward voltage, wherein measuring the first forward voltage includes measuring a voltage across the first terminal and the second terminal when the first current is applied.

[0137] Embodiment 39. According to the method of embodiment 38, the circuit system applies a second current from the second terminal to the anode of the second light-emitting diode through the second cable, from the anode of the second light-emitting diode to the cathode of the second light-emitting diode, and from the cathode of the second light-emitting diode to the first terminal through the first cable; and the circuit system measures the second forward voltage, wherein measuring the second forward voltage includes measuring the voltage across the first terminal and the second terminal when the second current is applied.

[0138] Embodiment 40. A system for measuring oxygen saturation, the system comprising: a sensor device comprising a first light emitting diode and a second light emitting diode; and an oximetry device comprising: a memory configured to store a calibrated forward voltage difference; and a circuit system configured to: determine a measured forward voltage difference based on a first forward voltage at the first light emitting diode and a second forward voltage at the second light emitting diode; determine that the first light emitting diode and the second light emitting diode are valid based on the calibrated forward voltage difference and the measured forward voltage difference; and in response to the determination that the first light emitting diode and the second light emitting diode are valid, determine an oxygen saturation level using the first light emitting diode and the second light emitting diode and output an indication of the oxygen saturation level.

[0139] The present disclosure contemplates a computer-readable storage medium comprising instructions that cause a processor to perform any of the functions and techniques described herein. The computer-readable storage medium can take the form of any volatile, non-volatile, magnetic, optical, or electrical medium, such as RAM, ROM, NVRAM, EEPROM, or flash memory. The computer-readable storage medium can be referred to as non-transient. Programmers such as patient programmers or clinician programmers, or other computing devices can also contain more portable removable memory types to enable easy data transfer or offline data analysis.

[0140] The techniques described in this disclosure (including those attributed to devices 100 and 200, processing circuitry 110, 210, 214, and 216, memory 120 and 220, displays 132 and 232, sensing circuitry 140 to 142, circuitry 240 and 245, sensing devices 150, 151, 152, and 250, and various constituent components) may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the techniques may be implemented within one or more processors embodied in a patient monitor (such as a multi-parameter patient monitor (MPM) or other device), a remote server, or other device, the one or more processors comprising one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combination of such components. The term "processor" or "processing circuitry" may generally refer to any of the foregoing logic circuitry, or any other equivalent circuitry, alone or in combination with other logic circuitry.

[0141] As used herein, the term "circuitry" refers to an ASIC, electronic circuit, processor (shared, dedicated, or group) and memory, combinational logic, and / or other suitable components that execute one or more software or firmware programs, and provide the described functionality. The term "processing circuitry" refers to one or more processors distributed across one or more devices. For example, a "processing circuitry" may include a single processor or multiple processors on a device. A "processing circuitry" may also include processors on multiple devices, where the operations described herein may be distributed across the processors and devices.

[0142] Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. For example, any of the techniques or processes described herein may be performed within a device or at least partially distributed between two or more devices, such as between devices 100 and 200, processing circuit systems 110, 210, 214, and 216, memories 120 and 220, sensing circuit systems 140 to 142, and / or circuit systems 240 and 245. In addition, any of the units, modules, or components may be implemented together or individually as discrete but interoperable logic devices. Describing different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be implemented by separate hardware or software components. On the contrary, the functions associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0143] The techniques described in this disclosure may also be embodied or encoded in an article of manufacture comprising a non-transitory computer-readable storage medium encoded with instructions. The instructions embedded or encoded in the article of manufacture comprising the encoded non-transitory computer-readable storage medium may cause one or more programmable processors or other processors to implement one or more techniques described herein, for example when the instructions included or encoded in the non-transitory computer-readable storage medium are executed by one or more processors. Exemplary non-transitory computer-readable storage media may include RAM, ROM, programmable ROM (PROM), erasable programmable ROM (EPROM), electronically erasable programmable ROM (EEPROM), flash memory, hard disk, compact disk ROM (CD-ROM), floppy disk, cassette tape, magnetic media, optical media, or any other computer-readable storage device or tangible computer-readable medium.

[0144] In some instances, computer-readable storage media include non-transitory media. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or propagating signal. In some examples, non-transitory storage media may store data that may change over time (e.g., in RAM or cache). The elements of the devices and circuit systems described herein (including but not limited to devices 100 and 200, processing circuit systems 110, 210, 214, and 216, memories 120 and 220, displays 132 and 232, sensing circuit systems 140 to 142, circuit systems 240 and 245, and sensing devices 150 to 152 and 250) may be programmed with various forms of software. For example, one or more processors may be at least partially implemented as or include one or more executable applications, application modules, libraries, classes, methods, objects, routines, subroutines, firmware, and / or embedded code.

[0145] Various embodiments of the present disclosure have been described. Any combination of the described systems, operations, or functions is contemplated. These and other examples are within the scope of the following claims.

Claims

1. A device for measuring oxygen saturation, the device comprising: a memory configured to store a calibrated forward voltage difference; A circuit system configured to: applying a first current from an anode of a first light emitting diode to a cathode of the first light emitting diode; measuring a first forward voltage across the anode of the first light emitting diode and the cathode of the first light emitting diode while applying the first current; applying a second current from the anode of the second light emitting diode to the cathode of the second light emitting diode; measuring a second forward voltage across the anode of the second light emitting diode and the cathode of the second light emitting diode while applying the second current; determining a difference in measured forward voltages based on a comparison of the first forward voltage and the second forward voltage; determining that the first light emitting diode and the second light emitting diode are valid based on a difference in the calibrated forward voltages and a difference in the measured forward voltages; as well as In response to the determination that the first and second light emitting diodes are valid, an oxygen saturation level is determined using the first and second light emitting diodes and an indication of the oxygen saturation level is output.

2. The device according to claim 1, in, To apply the first current, the circuit system is configured to apply the first current with a current magnitude and with a positive polarity such that the first current flows from the anode of the first light emitting diode to the cathode of the first light emitting diode; and To apply the second current, the circuit system is configured to apply the second current with the current amplitude and negative polarity so that the second current flows from the anode of the second light-emitting diode to the cathode of the second light-emitting diode.

3. The device according to any one of claims 1 to 2, wherein: To determine that the first and second light emitting diodes are valid, the circuitry is configured to determine that a difference between the calibrated forward voltage difference and the measured forward voltage difference is less than a threshold. 4 . The device of claim 1 , wherein the anode of the second light emitting diode is coupled to the cathode of the first light emitting diode, and the cathode of the second light emitting diode is coupled to the anode of the first light emitting diode.

5. The device according to any one of claims 1 to 2, in, To apply the first current, the circuit system is configured to apply the first current from a first terminal to the anode of the first light-emitting diode through a first cable, from the anode of the first light-emitting diode to the cathode of the first light-emitting diode, and from the cathode of the first light-emitting diode to a second terminal through a second cable; and Wherein, to measure the first forward voltage, the circuit system is configured to measure a voltage across the first terminal and the second terminal when the first current is applied.

6. The device according to claim 5, in, To apply the second current, the circuit system is configured to apply the second current from the second terminal through the second cable to the anode of the second light-emitting diode, from the anode of the second light-emitting diode to the cathode of the second light-emitting diode, and from the cathode of the second light-emitting diode through the first cable to the first terminal; and Wherein, to measure the second forward voltage, the circuit system is configured to measure a voltage across the first terminal and the second terminal when the second current is applied.

7. The apparatus of claim 1 , wherein to determine the oxygen saturation level, the circuitry is configured to: determining a first intensity of a first received photon signal corresponding to a first output photon signal output using the first light emitting diode; determining a second intensity of a second received photon signal corresponding to a second output photon signal output using the second light emitting diode; and The oxygen saturation level is determined based on the first intensity of the first received photon signal and the second intensity of the second received photon signal.

8. The device according to claim 7, in, To determine the first intensity of the first received photon signal, the circuit system is configured to drive the first light emitting diode to output the first output photon signal toward tissue of the subject and to receive the first received photon signal from a first detector after the first output photon signal is transmitted through the tissue of the subject; and In order to determine the second intensity of the second received photon signal, the circuit system is configured to drive the second light-emitting diode to output the second output photon signal to the tissue of the subject and receive the second received photon signal from the second detector after the second output photon signal is transmitted through the tissue of the subject.

9. The apparatus according to any one of claims 7 to 8, wherein the memory is further configured to store calibration information, and wherein the determination of the oxygen saturation level is also based on the calibration information.

10. The device according to claim 9, wherein To determine the oxygen saturation level, the circuitry is configured to: estimating a first wavelength of the first output photon signal based on the calibration information; estimating a second wavelength of the output second output photon signal based on the calibration information; and Wherein said determination of said oxygen saturation level is further based on said first wavelength of said first output photon signal and said second wavelength of said second output photon signal.

11. The apparatus of claim 9, wherein the circuitry is configured to decrypt the calibration information based on a difference in the measured forward voltages.

12. The device according to any one of claims 1 to 2, wherein the first light emitting diode is configured to emit red light; and The second light emitting diode is configured to emit infrared light.

13. The apparatus of any one of claims 1 to 2, wherein the circuitry is configured to estimate a temperature at one or more of the first light emitting diode or the second light emitting diode based on a difference in the measured forward voltages.

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