System and method for filtering interference generated by an electrosurgical unit from an ECG signal

Abstract

A system and method for filtering interference generated by an interference signal, such as an electrosurgical instrument (ESU), from a biopotential signal, such as an electrocardiogram (ECG) signal displayed on a patient display. The system includes acquisition circuitry to acquire incoming electrical signals from a patient including biopotential signals and interference signals. The system includes an attenuation circuit to attenuate the voltage to a level below a predetermined clipping threshold of the front-end protection circuit. A filter is provided to remove interference generated by the interfering signal from the attenuated incoming electrical signal to obtain a filtered biopotential signal with reduced interference. A gain circuit is provided to amplify the filtered biopotential signal to obtain an output biopotential signal suitable for display on a patient display monitor.

Description

Technical Field

[0001] The present disclosure generally relates to methods and systems for removing unwanted noise or interference from electrocardiogram signals. Background Art

[0002] Patients in an intensive care unit (ICU) or critical care unit (CCU) may require continuous monitoring of electrocardiogram (ECG) signals and other biopotential signals such as electroencephalogram ("EEG") signals and electromyogram ("EMG") signals. The ECG waveform on the patient monitor may be viewed and interpreted by qualified medical personnel or automatically processed by algorithms in the patient monitor to identify or detect specific features or characteristics of the waveform.

[0003] Patient monitors are used to provide feedback to clinicians regarding real-time patient health. Patient monitors are configured to display outputs related to real-time physiological parameters or vital signs of the patient. Clinical professionals monitor the display outputs to determine the current state of patient health and diagnose the current patient condition. In addition to the visual display, if the particular physiological parameter or vital sign being monitored falls outside of a threshold range, the patient monitor may also be configured to generate an audible output (e.g., an alarm) to alert the clinical professional of an unsafe condition that may require medical assistance or attention.

[0004] An example of a biopotential signal that is typically monitored and displayed on a patient monitor is an ECG waveform that indicates electrical activity in the heart. A clinical professional can monitor the ECG waveform to determine if any deviation or anomaly occurs that may indicate an unsafe and potentially life-threatening condition (e.g., atrial fibrillation, ventricular tachycardia, heart disease, cardiac arrest) that may require immediate medical attention or therapy. The ECG waveform can be used to assess heart rate, rhythm, and other cardiac anomalies and make a diagnosis. Therefore, it is desirable that the ECG waveform displayed on the patient monitor is clean and uncorrupted so as not to generate false alarms or prompt unwarranted medical treatment and may cause harm to the patient.

[0005] During the detection of the biopotential signal, it is not uncommon for the biopotential sensor to pick up other electrical signals. Therefore, for the purpose of making the biopotential signal easier to read and interpret, it is known to provide filtering. If the amplitude of the interfering signal is significantly greater than the amplitude of the biopotential signal, filtering the noise from the biopotential signal is particularly challenging because the interfering signal will be limited by the front-end protective circuitry present in most devices (such as patient monitors) used to collect the biopotential signal. Once the interfering signal is limited, it is extremely difficult to filter.

[0006] For example, electrosurgical units (ESUs) are routinely used in operating rooms and are known to interfere with the monitoring of a patient's biopotential signals. Unfortunately, the presence of electromagnetic energy generated by the operation of the ESU may cause unwanted interference to the biopotential signals. The terms ESU signal, ESU interference, and ESU noise are used interchangeably herein and are all intended to refer to the noise in the biopotential signals generated by the ESU used on a patient. For example, noise from the use of an ESU on a patient may cause an ECG waveform to be difficult or impossible to read, decipher, or interpret. Therefore, attempts have been made to filter the ECG signal in an attempt to reduce the noise generated by the use of the ESU.

[0007] Filtering the ECG signal to remove interference from the ESU can be challenging due to the difference between the amplitude of the ECG signal (typically no more than 1 mV) and the amplitude of the signal applied to the patient's body when the ESU is used (often between 10V and 100V). A typical patient monitoring system ECG sensor interface (or "front end") is designed to receive ECG signals, and therefore often has a maximum signal amplitude of approximately ±2V. Therefore, when the ESU signal is applied to the patient, the signal received by the ECG interface may exceed the capacity of the ECG sensor interface, which will cause the signal to be limited by the front end protection circuit, meaning that portions of the signal above the maximum amplitude of the ECG sensor interface are removed from the signal. Because the limited signal is non-linear, it is very difficult to filter the limited signal using known filtering techniques.

[0008] The present invention utilizes a novel technique to filter interference from the ESU to present a clean and uncorrupted ECG waveform, so that the surgeon can continue to use the ESU in the operating room while monitoring the patient's ECG. Summary of the invention

[0009] In the embodiments described herein, the input biopotential signal including the interfering signal is attenuated to a level sufficient to avoid clipping of the input biopotential signal by the front-end protection circuit. The signal is then filtered and amplified to its original level before being displayed on the graphical user interface of the patient monitor.

[0010] The following are additional aspects of the invention.

[0011] Aspect 1: A method of operating a patient monitor, the method comprising:

[0012] (a) receiving an input biopotential signal from at least one biopotential electrode electrically coupled to a patient, the input biopotential signal having an input voltage;

[0013] (b) attenuating the input biopotential signal to generate an attenuated biopotential signal having an attenuated voltage, the attenuated voltage being less than the input voltage;

[0014] (c) filtering the attenuated biopotential signal to reduce any interference generated by an electrosurgical unit (ESU), thereby producing a filtered biopotential signal;

[0015] (d) amplifying the filtered biopotential signal to obtain an output biopotential signal having an amplified voltage; and

[0016] (e) Displays the output biopotential signal.

[0017] Aspect 2: The method according to aspect 1, wherein step (b) comprises attenuating the input biopotential signal at a predetermined voltage attenuation ratio.

[0018] Aspect 3: The method according to aspect 2, wherein the predetermined voltage decay ratio is at least 20.

[0019] Aspect 4: The method according to any one of aspects 2 to 3, wherein step (d) comprises amplifying the filtered biopotential signal at a voltage amplification ratio equal to the voltage attenuation ratio.

[0020] Aspect 5: The method according to any one of aspects 1 to 4, wherein the input biopotential signal is an electrocardiogram (ECG).

[0021] Aspect 6: The method according to any one of aspects 1 to 5, further comprising:

[0022] (f) Detect the presence of ESU signal.

[0023] Aspect 7: The method according to aspect 6, wherein step (c) is performed only when step (f) is performed and an ESU signal is detected.

[0024] Aspect 8: The method according to aspect 6, wherein steps (b) to (d) are performed only when step (f) is performed and an ESU signal is detected.

[0025] Aspect 9: A method according to any one of Aspects 6 to 8, wherein step (f) is performed in response to at least one selected from the following group: (a) a user-selectable switch is activated, and (b) a position device determines that the patient monitor is located in the operating room.

[0026] Aspect 10: The method of any one of aspects 6 to 8, wherein step (f) is performed in response to the location device determining that the patient monitor is docked with a monitor base located in the operating room.

[0027] Aspect 11: The method according to any one of aspects 1 to 10 further comprises performing step (b) before feeding the attenuated biopotential signal to a front-end protection circuit of a physiological monitoring device, the front-end protection circuit having a limiting voltage.

[0028] Aspect 12: The method of aspect 11, wherein when the ESU is used on a patient, the input voltage exceeds the clipping voltage.

[0029] Aspect 13: The method according to any one of aspects 1 to 12, further comprising:

[0030] (g) processing the output biopotential signal before performing step (e).

[0031] Aspect 14: The method according to any one of aspects 1 to 12, wherein the input biopotential signal further includes noise generated by using the ESU on the patient.

[0032] Aspect 15: The method according to any one of aspects 1 to 12 further comprises:

[0033] (h) measuring the impedance of each of the at least one biopotential electrode;

[0034] (i) adjusting the attenuator circuit based on the impedance measured in step (h) to maintain a predetermined voltage attenuation ratio.

[0035] Aspect 16: The method according to aspect 15 further comprises:

[0036] (j) Repeating steps (h) and (i) at predetermined time intervals.

[0037] Aspect 17: The method according to any one of aspects 15 to 16, further comprising performing the impedance measurement of step (h) using AC impedance measurement when the ESU signal is detected.

[0038] Aspect 18: A system comprising:

[0039] a sensor interface adapted to receive an input biopotential signal from at least one biopotential electrode electrically coupled to a patient, the input biopotential signal having an input voltage;

[0040] an attenuator electrically coupled to the output of the sensor interface, the attenuator adapted to receive the input biopotential signal and generate an attenuated biopotential signal having an attenuated voltage reduced from the input voltage at a voltage attenuation ratio;

[0041] an analog-to-digital converter electrically coupled to the output of the attenuator, the analog-to-digital converter adapted to convert the attenuated biopotential signal into a digital attenuated biopotential signal;

[0042] a protection circuit electrically coupled to the output of the analog-to-digital converter, the protection circuit being adapted to remove any portion of the digital attenuated biopotential signal that exceeds a clipping voltage and produce a clipped biopotential signal;

[0043] at least one filter electrically coupled to the output of the protection circuit, the at least one filter adapted to reduce any ESU signal noise in the clipped biopotential signal generated by using an electrosurgical unit (ESU) on a patient when receiving the input biopotential signal, and to produce a filtered biopotential signal;

[0044] an amplifier electrically coupled to an output of the at least one filter, the amplifier being adapted to receive the filtered biopotential signal and generate an amplified biopotential signal having an amplified voltage increased from an attenuated voltage at a voltage amplification ratio; and

[0045] A display is electrically coupled to the amplifier, the display being adapted to provide a visual representation of the amplified biopotential signal or a biopotential signal derived from the amplified biopotential signal.

[0046] Aspect 19: The system of aspect 18, wherein the attenuator is adapted to attenuate the input biopotential signal with a voltage attenuation ratio of at least 20.

[0047] Aspect 20: The system according to aspect 19, wherein the amplifier is adapted to amplify the filtered biopotential signal at a voltage amplification ratio equal to a voltage attenuation ratio.

[0048] Aspect 21: The system of any one of Aspects 18 to 19, wherein the sensor interface comprises an electrocardiogram (ECG) sensor interface.

[0049] Aspect 22: The system of aspect 21, wherein the at least one biopotential electrode comprises a plurality of ECG electrodes.

[0050] Aspect 23: The system according to any one of aspects 18 to 22, further comprising an ESU detection unit having an active state and an inactive state, wherein the ESU detection unit is adapted to detect the presence of the ESU signal in the input biopotential signal only in the active state.

[0051] Aspect 24: The system according to aspect 23, wherein the ESU detection unit is further adapted to cause the input biopotential signal to bypass the attenuator, the at least one filter and the amplifier when the ESU detection unit is in an active state and detects the ESU signal.

[0052] Aspect 25: The system according to Aspect 24 further includes a position detection unit, which is adapted to place the ESU detection unit in an active state in response to at least one selected from the following group: (a) the user-selectable switch is activated, and (b) the position detection unit determines that the patient monitor is located in the operating room.

[0053] Aspect 26: The system of any one of Aspects 18 to 25, wherein the attenuator comprises a variable resistor.

[0054] Aspect 27: The system according to any one of aspects 18 to 26, further comprising an AC impedance detection circuit adapted to measure the impedance of each of the at least one biopotential electrode.

[0055] Aspect 28: A method comprising:

[0056] (a) receiving an input biopotential signal from at least one biopotential electrode electrically coupled to a patient and a physiological monitoring device, the input biopotential signal having an input voltage;

[0057] (b) detecting the presence of interference signals in the input biopotential signal;

[0058] (c) attenuating the input biopotential signal at a predetermined voltage attenuation ratio to produce an attenuated biopotential signal having an attenuated voltage that is less than the input voltage and less than a clipping threshold of a protection circuit of the physiological monitoring device;

[0059] (d) filtering the attenuated biopotential signal to remove at least one component of the interfering signal, thereby producing a filtered biopotential signal;

[0060] (e) amplifying the filtered biopotential signal to obtain an output biopotential signal having an amplified voltage; and

[0061] (f) Displays the output biopotential signal.

[0062] Aspect 29: The method according to Aspect 28 further comprises:

[0063] (g) Steps (c) to (e) are performed only when an interference signal is detected in step (b).

[0064] Aspect 30: The method of aspect 29, wherein step (b) is performed in response to at least one selected from the group consisting of: a user-selectable switch being activated, and a location device determining that the patient monitor is located in an operating room.

[0065] Aspect 31: The method of aspect 29, wherein step (b) is performed in response to the location device determining that the patient monitor is docked with a monitor base located in the operating room.

[0066] Aspect 32: The method according to any one of aspects 28 to 31, further comprising:

[0067] (h) measuring electrode impedance of each of the at least one biopotential electrode; and

[0068] (i) Adjusting the attenuator resistance based on the measured electrode impedance so as to achieve a predetermined voltage attenuation ratio.

[0069] Aspect 33: The method according to Aspect 32 further comprises:

[0070] (j) Repeating steps (h) and (i) at predetermined time intervals.

[0071] Aspect 34: The method according to any one of aspects 32 to 33, further comprising

[0072] When the ESU signal is detected, the impedance measurement of step (h) is performed using AC impedance measurement.

[0073] Aspect 35: According to the method described in any one of Aspects 28 to 34, step (c) further includes attenuating the input biopotential signal at a predetermined voltage attenuation ratio to produce an attenuated biopotential signal having an attenuated voltage, wherein the attenuated voltage is less than the input voltage and less than the limiting threshold of the protection circuit of the physiological monitoring device.

[0074] Aspect 36: The method according to any one of aspects 28 to 34, wherein the at least one biopotential electrode is an ECG electrode.

[0075] Aspect 37: The method according to any one of aspects 28 to 34, wherein step (c) comprises attenuating the input biopotential signal at a predetermined voltage attenuation ratio of at least 20.

[0076] Aspect 38: The method according to Aspect 37, wherein step (e) includes amplifying the filtered biopotential signal at a voltage amplification ratio equal to the voltage attenuation ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The present invention will be described with reference to the following drawings, in which like reference numerals designate like elements, and in which:

[0078] Figure 1 is a schematic diagram showing an exemplary physiological monitoring system illustrating major components of a signal processing system of the present disclosure;

[0079] Figure 2 is a diagram illustrating signal processing components of a signal processing system of the present disclosure;

[0080] Figure 3 is a graph showing amplitude (mV) versus time (seconds) of an exemplary signal generated by an electrocardiogram;

[0081] Figure 4 is a graph showing amplitude (V) versus time (seconds) of an exemplary signal including an ECG signal component and an interfering ESU signal component;

[0082] Figure 5 is a graph showing amplitude (V) versus time (μs) of an exemplary ESU signal after being clipped at ±2V;

[0083] Figure 6 is a graph showing the magnitude spectrum (relative) versus frequency (Hz) of frequency components generated by clamping an ESU signal;

[0084] Figure 7 yes Figure 4 The amplitude (mV) of the signal after filtering is shown in the figure compared with the time (seconds);

[0085] Figure 8 is a schematic diagram showing an exemplary attenuator circuit having a variable resistor; and

[0086] Fig. 9 is a flow chart illustrating an exemplary method of operating a physiological monitoring system to filter an ESU signal from an ECG signal. DETAILED DESCRIPTION

[0087] The following disclosure is presented to provide an illustration of the general principles of the invention and is not meant to limit the inventive concepts contained herein in any way. In addition, the specific features described in this section can be used in combination with other described features in each of the multiple possible permutations and combinations contained herein.

[0088] All terms defined herein should be given their broadest possible interpretation, including any implied meaning as dictated by a reading of the specification, and any words to which a person skilled in the art and / or a dictionary, treatise, or similar authority would assign a specific meaning. Further, it should be noted that, as described in the specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless otherwise stated. Additionally, the terms "include" and "comprise" when used herein specify that certain features are present in the embodiment, but should not be interpreted as excluding the presence or addition of additional features, components, operations, and / or combinations thereof.

[0089] As used herein, the term "interference signal" means an electrical signal detected by a biopotential sensor connected to a patient that (a) is not a non-biopotential signal, (b) has a frequency of 40 Hz or greater, and (c) has an amplitude that exceeds the dynamic range of the instrument to which the biopotential sensor is connected. Examples of interference signals include ESU noise, power line interference (PLI) noise, Gaussian white noise (often generated by wireless transmission of ECG signals), and EMG noise.

[0090] As used herein, the term "biopotential signal" means an electrical signal (voltage) generated directly or indirectly by a physiological process occurring within the human body. Examples of biopotential signals include, but are not limited to, electroencephalogram ("EEG") signals, electromyogram ("EMG") signals, electrocardiogram (ECG) signals, neuromuscular transmission (NMT) signals, and pulse oximetry (SpO2) signals.

[0091] Figure 1 1 is a schematic diagram of an exemplary physiological monitoring system 19 (also referred to as a patient monitor) having a plurality of sensors 17 connected to a patient 1, and an exemplary ESU 20. For example, the plurality of sensors may include an ECG sensor having a plurality of surface ECG leads (electrodes) for detecting and analyzing ECG waveforms. As illustrated, the system includes a physiological monitoring device 7 capable of receiving physiological data from the sensors 17, and a monitor base 10 to which the physiological monitoring device 7 may be mounted or docked.

[0092] The physiological monitoring device 7 is, for example, a patient monitor implemented to monitor various physiological parameters of the patient 1 via sensors 17. The physiological monitoring device 7 includes a sensor interface 2, one or more processors 3, a display / GUI 4, a communication interface 6, a memory 8, and a power supply 9. The sensor interface 2 can be implemented in software or hardware, and is used to connect to one or more physiological sensors and / or medical devices 17 via wired and / or wireless connections for collecting physiological data from the patient 1. The data signals from the sensors 17 include, for example, data related to electrocardiogram (ECG), non-invasive peripheral blood oxygen saturation (SpO2), non-invasive blood pressure (NIBP), temperature and / or end-tidal carbon dioxide (etCO2), apnea detection, neuromuscular transmission ("NMT"), electroencephalogram ("EEG"), and external brain monitoring ("BISx"), as well as other similar physiological data.

[0093] The communication interface 6 allows the physiological monitoring device 7 to communicate directly or indirectly (e.g., via the monitor base 10) with one or more computing networks and devices (not shown). The communication interface 6 may include various network cards, interfaces, or circuits to enable wired and wireless communications with such computing networks and devices. The communication interface 6 may also be used to implement, for example, a Bluetooth connection, a cellular network connection, and / or a WiFi connection. Other wireless communication connections implemented using the communication interface 6 include wireless connections operating according to, but not limited to, the IEEE 802.11 protocol, the Radio Frequency for Consumer Electronics (RF4CE) protocol, the ZigBee protocol, and / or the IEEE 802.15.4 protocol.

[0094] Additionally, the communication interface 6 may enable direct (i.e., device-to-device) communication (e.g., messaging, signaling, etc.), such as from the monitor base 10 to the physiological monitoring device 7 using, for example, a USB connection. The communication interface 6 may also enable direct device-to-device connection, such as to other devices such as a tablet, PC, or similar electronic device, or to an external storage device or memory.

[0095] The power source 9 may include a self-contained power source such as a battery pack, and / or include an interface for powering via a power outlet (either directly or by way of the monitor base 10). The power source 9 may also be a rechargeable battery that can be removed to allow replacement. In the case of a rechargeable battery, a small built-in backup battery (or supercapacitor) may be provided to provide continuous power to the physiological monitoring device 7 during battery replacement. Communications between the components (e.g., 2, 3, 4, 6, 8, and 9) of the physiological monitoring device 7 are established using an internal bus 5.

[0096] like Figure 1As shown in FIG. 1 , the physiological monitoring device 7 is connected to the monitor base 10 via a connection 18, which establishes a communication connection between, for example, the corresponding communication interfaces 6, 14 of the devices 7, 10. The connection 18 enables the monitor base 10 to removably secure the physiological monitoring device 7 to the monitor base 10. In this regard, "removably secure" means that the monitor base 10 can secure the physiological monitoring device 7, but the physiological monitoring device 7 can be removed or detached from the monitor base 10 by the user when desired. The connection 18 can include, but is not limited to, a universal serial bus (USB) connection, a parallel connection, a serial connection, a coaxial connection, a high-definition multimedia interface (HDMI) connection, or other similar connections known in the art for connecting to electronic devices.

[0097] The monitor base 10 includes one or more processors 12, a memory 13, a communication interface 14, an I / O interface 15, and a power supply 16. The one or more processors 12 are used to control the general operation of the monitor base 10. The memory 13 may be used to store any type of instructions associated with algorithms, processes, or operations for controlling the general functions and operations of the monitor base 10.

[0098] The communication interface 14 allows the monitor base 10 to communicate with one or more computing networks and devices (e.g., physiological monitoring device 7). The communication interface 14 may include various network cards, interfaces, or circuits to enable wired and wireless communications with such computing networks and devices. The communication interface 14 may also be used to implement, for example, Bluetooth connections, cellular network connections, and WiFi connections. Other wireless communication connections implemented using the communication interface 14 include wireless connections operating according to, but not limited to, the IEEE 802.11 protocol, the Radio Frequency for Consumer Electronics (RF4CE) protocol, the ZigBee protocol, and / or the IEEE 802.15.4 protocol.

[0099] The communication interface 14 may also enable direct (i.e., device-to-device) communication (e.g., messaging, signaling, etc.), such as from the monitor base 10 to the physiological monitoring device 7, using, for example, a USB connection, a coaxial connection, or other similar electrical connection. The communication interface 14 may enable direct connection (i.e., device-to-device) to other devices, such as a tablet, PC, or similar electronic device, or to an external storage device or memory.

[0100] The I / O interface 15 may be an interface for enabling information to be transferred between the monitor base 10, one or more physiological monitoring devices 7, and external devices (such as peripheral devices connected to the monitor base 10) that require a special communication link for interfacing with the one or more processors 12. The I / O interface 15 may be implemented to accommodate a variety of connections to the monitor base 10, including but not limited to a universal serial bus (USB) connection, a parallel connection, a serial connection, a coaxial connection, a high-definition multimedia interface (HDMI) connection, or other known connections in the art to connect to external devices.

[0101] The power source 16 may include a self-contained power source such as a battery pack, and / or include an interface to be powered by an electrical outlet (either directly or by way of the physiological monitoring device 7). The power source 16 may also be a rechargeable battery that can be removed to allow replacement. Communications between the components (e.g., 12, 13, 14, 15, and 16) of the monitor base 10 are established using the internal bus 11.

[0102] The ESU 20 includes a signal generator 26 that supplies an electrical signal to a handpiece 22 that is used to perform various surgical functions on the tissue of the patient 1, such as cutting, coagulation, ablation, and contraction, depending on the nature of the electrical signal supplied by the signal generator 26. The handpiece 22 is an active electrode for applying the electrical signal. In this embodiment, a return electrode 21 is applied to the surface of the patient's skin, in close proximity to the site at which the handpiece 22 is used. The surgical function applied by the handpiece 22 can be changed by changing the voltage and / or frequency of the signal. This is done using one or more mode switches 25. The ESU 20 also preferably includes a graphical user interface 24 that displays various information about the operating status of the ESU 20, such as which surgical function is active. A power supply 23 provides power to the other components of the ESU. The power supply is preferably an interface powered by a power outlet. Communication between the ESU components is established using an internal bus 26.

[0103] Figure 2 is an exemplary embodiment of a portion of a physiological monitoring device 107 adapted to receive, process and display ECG signals from a patient and reduce interference generated by ESU signals. It should be noted that Figure 2 Many of the functional elements schematically shown in the figure may be implemented using hardware and / or software. Additionally, additional functional elements may be present in the physiological monitoring device 107. The embodiments described are intended to be exemplary and may be advantageously applied to filter other interfering signals from other types of biopotential signals.

[0104] In this embodiment, sensor interface 102 includes a 12-lead ECG interface 128. ECG leads 117 are represented by arrows pointing to interface 128. From ECG interface 128, input biopotential signals 129 (in this embodiment, ECG signals) are received. Figure 3 An example of a "clean" ECG input biopotential signal is shown, ie, without any significant interference from the ESU or other sources. Figure 4 The input biopotential signal with both ECG signal and ESU noise / interference is shown. Figure 5 As can be seen in , the relatively high amplitude and frequency of the ESU signal "swamps" the ECG and renders the signal unusable for purposes of observing the ECG component of the signal.

[0105] As noted above, the ESU is most often employed during surgical procedures in an operating room. During use, the ESU will generate significant electromagnetic interference, which will be detected by the ECG leads 117 and will therefore become part of the input biopotential signal 129. As is common in the industry, the physiological monitoring device 107 includes a protection circuit (front-end protection circuit 132) that is intended to protect other circuits from damage from high voltage signals or surges. Therefore, the input biopotential signal 129 will have a voltage much greater than the voltage of the protection circuit, and the signal will be clipped (surge-limited) by the protection circuit. Figure 3 and Figure 4 for comparison). Figure 5 Shows Figure 4 The ESU component of the biopotential signal after being limited by the front-end protection circuit 132. Figure 5 As can be seen in , the peaks 270 and valleys 272 of the ESU signal (which is typically a sine wave) are flattened (amplified) at ±2V. Additionally, Figure 4 Amplitude limiting of a biopotential signal will often generate additional high frequency components. An example of this is shown in Figure 6 In. Figure 6 , the clamping of the 500 Hz ESU signal 280 generates several high frequency components 282a to 282f ranging from 1500 Hz to 6500 Hz. Currently, no technology exists that can be used to effectively recover the clipped signal and then filter the ECG signal from the ESU interference.

[0106] To avoid such clipping, the input biopotential signal 129 is passed to an attenuator 130, which attenuates the input biopotential signal 129 to produce an attenuated biopotential signal 131. In this embodiment, the attenuator 130 preferably reduces the voltage amplitude of the input biopotential signal 129 at a voltage attenuation ratio of 20. The voltage attenuation ratio of 20 is a compromise because some clipping of the input biopotential signal 129 will still occur, but a higher voltage attenuation ratio will result in an unacceptably low signal-to-noise ratio in the output signal. In other embodiments, the attenuator 130 preferably reduces the voltage amplitude of the input biopotential signal 129 at a voltage attenuation ratio of at least 20, more preferably at least 50, and most preferably at least 80. The attenuator 130 may include any suitable attenuator circuit, such as a resistor divider.

[0107] The attenuated biopotential signal 131 is then passed through the front end protection circuit 132, which removes ("clips") any portion of the attenuated biopotential signal 131 having a voltage greater than the (positive or negative) maximum voltage (also referred to as the "voltage limit") of the circuit 132, thereby producing a clipped biopotential signal 133. The voltage limits of the front end protection circuit 132 of the physiological monitoring device 107 are typically between ±2.0V and 2.7V. As noted above, the purpose of attenuating the input biopotential signal 129 before passing through the front end protection circuit 132 is to reduce the clipping of the ESU signal noise in the input biopotential signal 129 by the front end protection circuit 132, because it is much more difficult to filter the ESU signal noise from the biopotential signal once it has been clipped.

[0108] The limited biopotential signal 133 is then converted to a digital biopotential signal 139 by an analog-to-digital converter 136. Any suitable analog-to-digital converter 136 may be used, such as a Texas Instruments ADS1298 24-bit analog-to-digital converter. The digital biopotential signal 139 is then filtered by (one or more) filters 138 to reduce ESU signal noise and produce a filtered biopotential signal 139. The filtering of the biopotential signal 139 may be performed using any suitable means, including hardware and / or software based filtering. Examples of suitable filtering techniques may be found in U.S. Patent No. 6,246,902, entitled “Lead Set Filter for a Patient Monitor,” which is incorporated herein by reference as if fully set forth. Preferably, the filtering includes a high pass filter that will remove any DC component of the biopotential signal 139. Figure 7 An example of a filtered biopotential signal 139 is shown in FIG.

[0109] The filtered biopotential signal 139 is then amplified using the amplifier 140 to generate an amplified biopotential signal 141. Preferably, the amplified biopotential signal 141 has substantially the same signal level as the input biopotential signal 129. In other words, preferably, the voltage attenuation ratio applied by the attenuator 130 is substantially the same as the voltage amplification ratio applied by the amplifier 140.

[0110] The amplified biopotential signal 141 is then further processed by one or more processors 142 and optionally other circuits before being displayed on the graphical user interface 104. As is known in the art, the amplified biopotential signal 141 may be processed in multiple parallel signal paths for different purposes, such as analog output, QRS synchronization markers, to provide adaptive filtering, and ECG waveform display.

[0111] It is also desirable that the circuitry providing the ESU filtering functionality, i.e., the attenuator 130, the ESU signal filter 138, and the amplifier 140 (hereinafter referred to as the "ESU filtering circuitry"), is only active when the ESU device is actively used on the patient. In this embodiment, this is accomplished by activating the ESU filtering circuitry only when the ESU detection unit 144 detects an ESU signal, and activating the ESU detection unit 144 only when the patient is in the operating room.

[0112] Examples of suitable circuits for the ESU detection unit 144 are disclosed in US10568678, entitled "Neutral Drive Feedback Loop Compensation for Detected Electrosurgical Unit Signal," and in US11103190, entitled "Circuits and Methods for Electrosurgical Unit Signal Detection," which are incorporated by reference as if fully set forth. Figure 2 An exemplary ESU detection unit 144 is schematically shown in FIG. 1 . Lead 152 is electrically connected to the input biopotential signal 129 to detect ESU interference. If ESU interference is detected, the ESU filter circuit is activated or engaged. The bypass of the ESU filter circuit is Figure 2 144 is schematically shown by bypass circuits 146 and 147. Switches 148 and 150, controlled by leads 154 and 156, respectively, send signals through bypass circuits 146 and 147 when no ESU interference is detected or if ESU detection circuit 144 is inactive.

[0113] Preferably, the ESU detection unit 144 is active only when the patient is located in a room (such as an operating room) where the ESU unit is likely to be used. In this embodiment, a position detection unit 158 ​​is provided. The position detection unit 158 ​​is electrically connected to the ESU detection unit 144 and places the ESU detection unit 144 in an active or inactive mode. There are many inputs that can be used by the position detection unit 158 ​​alone or in combination to determine that the ESU detection unit 144 should be active. The input can be as simple as an on-off switch activated by the user in the graphical user interface 104. Other possible inputs include a sensor 162 that detects when a patient monitor is docked to a monitor base 110 located in an operating room, or a GPS-enabled sensor (not shown) that can detect when a patient monitor is in an operating room.

[0114] In some applications, it may be desirable to adjust attenuator 130 to maintain a desired voltage attenuation ratio even if the impedance of the ECG electrodes generating input biopotential signal 129 changes. The impedance of the ECG electrodes may change significantly (in some cases by an order of magnitude) during the period in which the patient is being monitored. Changes in electrode impedance may occur due to a number of factors, including patient sweating, patient movement, electrodes being pulled away from the skin, or simply losing adhesion to the skin over time.

[0115] Figure 8 An exemplary circuit that enables such adjustment is shown. In this embodiment, the input biopotential signal is received from one of the ECG electrodes 360 ( Figure 8 The attenuated signal is then passed to the next circuit in the physiological monitoring device 307, such as a passband filter or an A / D converter (see FIG. 1 ). Figure 2 and the accompanying description above). When ESU filtering is not active, attenuator switch 363 is opened, which disconnects attenuator resistor 364 from the circuit. In this embodiment, attenuator resistor 364 is a variable resistor. As will be described below, this enables physiological monitoring device 307 to maintain a desired voltage attenuation ratio of the input biopotential signal by compensating for changes in the impedance of each of ECG electrodes 360. In other examples, alternative methods can be used to compensate for changes in the impedance of ECG electrodes 360, such as using an amplifier to buffer the signal.

[0116] Fig. 94 is a flow chart showing an exemplary method for monitoring ECG signals. It should be understood that the method can be applied to other types of biopotential signals. Throughout the process, the impedance of each ECG electrode is monitored. When ESU detection is inactive, DC impedance monitoring is used. As will be described herein, due to the higher accuracy of AC impedance monitoring, AC impedance monitoring is preferably used when ESU filtering is active. Monitor the ECG signal (step 410) until ESU detection is activated (step 412). As explained above, ESU detection can be activated in multiple ways, including manual user activation (e.g., via an icon on the display / GUI) and automatic activation when it is determined that the patient is in the operating room. If ESU detection is active, the system monitors the input biopotential signal to determine whether the ESU signal exists. When an ESU signal is detected, ECG monitoring, impedance respiration, and PACE detection are suspended (step 416). ECG monitoring is temporarily suspended until a more accurate impedance is measured. Impedance respiration and PACE detection interfere with AC impedance monitoring. Therefore, these parameters are suspended until ECG electrode impedance monitoring is switched back to DC mode. The ECG lead impedance measurement is switched to AC mode (step 418), and the impedance of each ECG electrode is measured. At the end of the impedance measurement step 418, the attenuation circuit is adjusted (step 420) to provide the desired voltage attenuation ratio based on the measured impedance, and ECG monitoring is resumed (step 422). Figure 8 For a circuit of the attenuation circuit, the adjustment of the attenuation circuit is accomplished by adjusting the resistance of the attenuation resistor 364.

[0117] Then, attenuation of the input biopotential signal and filtering of the ESU signal are activated (step 424). Figure 8 If the circuit is switched to an active state, attenuation is activated by closing the attenuator switch 363. The system then periodically checks to determine if the ESU signal is still detected (step 426).

[0118] If the ESU signal is still detected, it is determined whether the ECG impedance has changed (step 428). In this example, re-measurement is triggered by a predetermined time interval (e.g., with step 424 active, the ECG impedance is re-measured every 5 minutes). In other examples, re-checking of the ECG impedance may be triggered by an event that is likely to cause a change in electrode impedance, such as movement of the patient, or an event that is likely to indicate a change in impedance, such as a significant change in the filtered ECG signal. If a change in ECG impedance is detected, the attenuation circuit is adjusted (step 430) to compensate for the change.

[0119] If the ESU signal is no longer detected, the attenuator circuit and ESU filter circuit are bypassed (step 432), and the ECG electrode impedance measurement is switched to DC mode. Impedance respiration and PACE detection are then restarted (step 438), and the process returns to step 410.

[0120] Although various embodiments have been disclosed, it will be apparent to those skilled in the art that various changes and modifications that will realize some of the advantages of the concepts disclosed herein may be made without departing from the spirit and scope of the present disclosure. It will be apparent to those skilled in the art that other components that perform the same function may be appropriately replaced. It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. It should be mentioned that the features explained with reference to a particular figure may be combined with the features of other figures, even in those figures that are not explicitly mentioned. Such modifications to the overall inventive concept are intended to be covered by the appended claims and their legal equivalents.

[0121] Furthermore, the following claims are hereby incorporated into the detailed description, wherein each claim can be independent of the others as a separate exemplary embodiment. Although each claim can be independent of the others as a separate exemplary embodiment, it should be noted that - although a dependent claim may refer to a specific combination with one or more other claims in a claim - other exemplary embodiments may also include a combination of a dependent claim with the subject matter of each other dependent or independent claim. Such combinations are proposed herein unless it is stated that a specific combination is not intended. Furthermore, it is intended to also include features of a claim to any other independent claim, even if the claim is not directly dependent on the independent claim.

[0122] It should be further noted that the methods disclosed in the specification or claims may be implemented by a device having components for performing each of the corresponding actions of these methods. For example, the techniques described in this disclosure may be implemented at least in part in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, including one or more microprocessors, DSPs, ASICs, or any other equivalent integrated or discrete logic circuits, as well as any combination of such components.

[0123] Further, it should be understood that the disclosure of multiple actions or functions disclosed in the specification or claims may not be interpreted as being in a particular order. Therefore, the disclosure of multiple actions or functions will not limit these actions or functions to a particular order, unless such actions or functions are not interchangeable for technical reasons. Further, in some embodiments, a single action may include or may be divided into multiple sub-actions. Unless explicitly excluded, such sub-actions may be included and are part of the disclosure of the single action.

Claims

1. A method of operating a patient monitor, the method comprising: (k) receiving an input biopotential signal from at least one biopotential electrode electrically coupled to the patient, the input biopotential signal having an input voltage; (1) attenuating an input biopotential signal to generate an attenuated biopotential signal having an attenuated voltage, wherein the attenuated voltage is less than the input voltage; (m) filtering the attenuated biopotential signal to reduce any interference generated by an electrosurgical unit (ESU), thereby producing a filtered biopotential signal; (n) amplifying the filtered biopotential signal to obtain an output biopotential signal having an amplified voltage; and (o) Displays the output biopotential signal.

2. The method of claim 1, wherein step (b) comprises attenuating the input biopotential signal at a predetermined voltage attenuation ratio. The method of claim 2 , wherein the predetermined voltage decay ratio is at least 20.

4. The method of claim 2, wherein step (d) comprises amplifying the filtered biopotential signal at a voltage amplification ratio equal to the voltage attenuation ratio. The method of claim 1 , wherein the input biopotential signal is an electrocardiogram (ECG).

6. The method according to claim 1, further comprising: (p) Detect the presence of ESU signal.

7. The method of claim 6, wherein step (c) is performed only when step (f) is performed and an ESU signal is detected.

8. The method of claim 6, wherein steps (b) to (d) are performed only when step (f) is performed and an ESU signal is detected.

9. The method of claim 6, wherein step (f) is performed in response to at least one selected from the group consisting of: (a) a user-selectable switch being activated, and (b) a location device determining that the patient monitor is located in an operating room.

10. The method of claim 8, wherein step (f) is performed in response to the location device determining that the patient monitor is docked with a monitor base located in an operating room.

11. The method of claim 1, further comprising performing step (b) before feeding the attenuated biopotential signal into a front-end protection circuit of a physiological monitoring device, the front-end protection circuit having a limiting voltage.

12. The method of claim 11, wherein the input voltage exceeds the clipping voltage when the ESU is used on the patient.

13. The method according to claim 1, further comprising: (q) processing the output biopotential signal before performing step (e).

14. The method of claim 1, wherein the input biopotential signal further comprises noise generated by applying an ESU to the patient.

15. The method according to claim 1, further comprising: (r) measuring the impedance of each of the at least one biopotential electrode; (s) adjusting the attenuator circuit based on the impedance measured in step (h) to maintain a predetermined voltage attenuation ratio.

16. The method according to claim 15, further comprising: (t) Repeating steps (h) and (i) at predetermined time intervals.

17. The method of claim 15, further comprising performing the impedance measurement of step (h) using an AC impedance measurement when the ESU signal is detected.

18. A system comprising: a sensor interface adapted to receive an input biopotential signal from at least one biopotential electrode electrically coupled to the patient, the input biopotential signal having an input voltage; an attenuator electrically coupled to the output of the sensor interface, the attenuator adapted to receive the input biopotential signal and generate an attenuated biopotential signal having an attenuated voltage reduced from the input voltage at a voltage attenuation ratio; an analog-to-digital converter electrically coupled to the output of the attenuator, the analog-to-digital converter adapted to convert the attenuated biopotential signal into a digital attenuated biopotential signal; a protection circuit electrically coupled to the output of the analog-to-digital converter, the protection circuit being adapted to remove any portion of the digital attenuated biopotential signal that exceeds a clipping voltage and produce a clipped biopotential signal; at least one filter electrically coupled to the output of the protection circuit, the at least one filter adapted to reduce any ESU signal noise in the limited biopotential signal, the ESU signal noise being generated by using an electrosurgical unit (ESU) on a patient when receiving the input biopotential signal, and to produce a filtered biopotential signal; an amplifier electrically coupled to an output of the at least one filter, the amplifier being adapted to receive the filtered biopotential signal and generate an amplified biopotential signal having an amplified voltage increased from an attenuated voltage at a voltage amplification ratio; as well as A display is electrically coupled to the amplifier, the display being adapted to provide a visual representation of the amplified biopotential signal or a biopotential signal derived from the amplified biopotential signal.

19. The system of claim 18, wherein the attenuator is adapted to attenuate the input biopotential signal with a voltage attenuation ratio of at least 20.

20. The system of claim 19, wherein the amplifier is adapted to amplify the filtered biopotential signal at a voltage amplification ratio equal to a voltage attenuation ratio.

21. The system of claim 18, wherein the sensor interface comprises an electrocardiogram (ECG) sensor interface.

22. The system of claim 21, wherein the at least one biopotential electrode comprises a plurality of ECG electrodes.

23. The system of claim 18, further comprising an ESU detection unit having an active state and an inactive state, the ESU detection unit being adapted to detect the presence of the ESU signal in the input biopotential signal only in the active state.

24. The system of claim 23, wherein when the ESU detection unit is in an active state and detects an ESU signal, the ESU detection unit is further adapted to enable the input biopotential signal to bypass the attenuator, the at least one filter, and the amplifier.

25. The system of claim 24, further comprising a position detection unit adapted to place the ESU detection unit in an active state in response to at least one selected from the following group: (a) a user-selectable switch is activated, and (b) the position detection unit determines that the patient monitor is located in the operating room.

26. The system of claim 18, wherein the attenuator comprises a variable resistor.

27. The system of claim 18, further comprising an AC impedance detection circuit adapted to measure impedance of each of the at least one biopotential electrode.

28. A method comprising: (k) receiving an input biopotential signal from at least one biopotential electrode electrically coupled to the patient and to a physiological monitoring device, the input biopotential signal having an input voltage; (l) detecting the presence of interference signals in the input biopotential signal; (m) attenuating the input biopotential signal at a predetermined voltage attenuation ratio to produce an attenuated biopotential signal having an attenuated voltage that is less than the input voltage and less than a clipping threshold of a protection circuit of the physiological monitoring device; (n) filtering the attenuated biopotential signal to remove at least one component of the interfering signal, thereby producing a filtered biopotential signal; (o) amplifying the filtered biopotential signal to obtain an output biopotential signal having an amplified voltage; as well as (p) Displays the output biopotential signal.

29. The method according to claim 28, further comprising: (q) Only when an interference signal is detected in step (b), perform steps (c) to (e).

30. The method of claim 29, wherein step (b) is performed in response to at least one selected from the group consisting of: a user-selectable switch being activated, and a location device determining that the patient monitor is located in an operating room.

31. The method of claim 29, wherein step (b) is performed in response to the location device determining that the patient monitor is docked with a monitor base located in an operating room.

32. The method of claim 28, further comprising: (r) measuring electrode impedance of each of the at least one biopotential electrode; as well as (s) adjusting the attenuator resistance based on the measured electrode impedance to achieve a predetermined voltage attenuation ratio.

33. The method of claim 32, further comprising: (t) Repeating steps (h) and (i) at predetermined time intervals.

34. The method of claim 32, further comprising performing the impedance measurement of step (h) using an AC impedance measurement when the ESU signal is detected.

35. According to the method according to claim 28, step (c) further includes attenuating the input biopotential signal at a predetermined voltage attenuation ratio to produce an attenuated biopotential signal having an attenuated voltage, wherein the attenuated voltage is less than the input voltage and less than the limiting threshold of the protection circuit of the physiological monitoring device.

36. The method of claim 28, wherein the at least one biopotential electrode is an ECG electrode.

37. The method of claim 28, wherein step (c) comprises attenuating the input biopotential signal at a predetermined voltage attenuation ratio of at least 20.

38. The method of claim 37, wherein step (e) comprises amplifying the filtered biopotential signal at a voltage amplification ratio equal to the voltage attenuation ratio.

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