WO2020113024A1

WO2020113024A1 - Methods and systems for detecting loose electrodes

Info

Publication number: WO2020113024A1
Application number: PCT/US2019/063636
Authority: WO
Inventors: Michael R. Girouard; Michael D. Halleck; Michael E. Halleck
Original assignee: Brain Sentinel, Inc.
Priority date: 2018-11-29
Filing date: 2019-11-27
Publication date: 2020-06-04

Abstract

Systems and methods are described for monitoring a group of electrodes for skin contact integrity using a test signal and to use one or more of the electrodes to collect a signal from a person. For example, the signal may be an EMG signal and a person may further be monitored in order to detect seizure activity.

Description

METHODS AND SYSTEMS FOR DETECTING LOOSE ELECTRODES

CROSS REFERENCE AND RELATED APPLICATIONS

[0001] This application claims priority to US Provisional Application No. 62/773,059, filed November 29, 2018, and titled“Methods and Systems for Detecting Loose Electrodes,” the disclosure of which is herein fully incorporated by reference.

FIELD

[0002] The present application relates to systems and methods for monitoring the quality of a skin electrode interface. The application further relates to mobile sensor systems which include capability for loose electrode detection.

BACKGROUND

[0003] Physiological signals may be sensed using one or more electrodes disposed on a patient’s skin. Signal quality typically depend on one or more upon a number of factors, including, for example, the quality of contact between the skin and electrodes. For example, when an electrode becomes loose, signals may become erratic or change in ways that may be difficult to predict. Accordingly, a number of systems have been developed to check the quality of a skin-electrode interface. For example, systems may sometimes apply a test signal at one electrode and collect the test signal at another electrode in order to measure an impedance of a person’s skin. A measured impedance may then be compared to an expected impedance in order to characterize the quality of skin contact. Systems for measuring the impedance of skin and/or for otherwise checking the quality of an electrode-skin interface are, for example, sometimes used with existing electrocardiography (EKG), electromyography (EMG), and electroencephalography (EEG) systems.

[0004] Some of those systems may comprise complicated electrical systems. While configured for measurement of impedance or otherwise testing for skin/contact integrity, such systems may include a number of components raising sensor cost. Moreover, in order to measure a qualify of skin-electrode contact, such systems may consume a significant amount of useable energy.

[0005] In some systems designed for testing for skin-contact integrity, detection of skin-electrode integrity may include application of a test signal intermittently, and during test signal application detection of other signals may be significantly compromised or simply not be possible. For example, systems may switch between states for impedance detection and other states where additional sensor data may be collected. Thus, such systems may not be ideally suited for some applications where sensor signals may be collected continuously or where it may be desirable to initiate responses based on detection of sensor signals with minimal latency.

[0006] Accordingly, for various reasons, existing systems for measuring skin- contract integrity may be inappropriate or limited for use in some applications, such as where cost and energy consumption criteria are demanding or where minimal latency between physiological event occurrence and event detection may be important. Particularly, many systems for establishing the quality of skin-electrode contact may be inappropriate for use in some mobile biosensor applications, where signals may need to be collected continuously or semi-continuously while also operating with minimal power consumption.

[0007] There remains a need for improved systems and methods for monitoring an electrode system for skin-contact integrity, such as in mobile sensor applications. Methods and systems herein may be directed to technologies for measuring contact integrity between electrodes and a patient’s skin and for collecting and/or processing a sensor signal in systems with low power consumption, latency for event detection, or both, meeting the above and other needs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. l is a diagram of a system for monitoring a group of electrodes for skin contact integrity.

[0009] Fig. 2A is a graph of a segmented test signal.

[0010] Fig. 2B is a detailed view of a portion of the graph shown in Fig. 2A showing a deviation between the segmented test signal and a corresponding signal shaped as a periodic function approximated by the segmented test signal at a point A.

[0011] Fig. 2C is a graph of another segmented test signal.

[0012] Fig. 3 is a flowchart showing a method of monitoring a group of electrodes for skin contact integrity.

[0013] Fig. 4A is a diagram of a part of the system shown in Fig. 1.

[0014] Fig. 4B is a graph of collected signals from different detection electrodes at the inputs of a detection amplifier. [0015] Fig. 4C is a graph showing the form of signals at the inputs of a detection amplifier and at the output of the detection amplifier.

[0016] Fig. 5 shows a graph of peaks in an amplified collected signal.

[0017] Fig. 6 is a flowchart showing a method of monitoring a group of electrodes for skin contact integrity and analysis of an EMG signal.

[0018] Fig. 7 is a flowchart showing a method of calibrating a system for detection of an applied signal.

[0019] Fig. 8 is an alternative embodiment of a system for monitoring a group of electrodes for skin contact integrity.

[0020] Fig. 9 is another alternative embodiment of a system for monitoring a group of electrodes for skin contact integrity.

DETAILED DESCRIPTION

[0021] The following terms as used herein should be understood to have the indicated meanings.

[0022] When an item is introduced by“a” or“an,” it should be understood to mean one or more of that item.

[0023] “Comprises” means includes but is not limited to.

[0024] “Comprising” means including but not limited to.

[0025] “Computer” means any programmable machine capable of executing machine-readable instructions. A computer may include but is not limited to a general-purpose computer, microprocessor, computer server, digital signal processor, or a combination thereof. A computer may comprise one or more processors, which may comprise part of a single machine or multiple machines.

[0026] The term“computer program” means a list of instructions that may be executed by a computer to cause the computer to operate in a desired manner.

[0027] The term“computer readable medium” means an article of manufacture having a capacity for storing one or more computer programs, one or more pieces of data, or a combination thereof. A computer readable medium may include but is not limited to a computer memory, hard disk, memory stick, magnetic tape, floppy disk, optical disk (such as a CD or DVD), zip drive, or combination thereof. [0028] The term“electrode assembly” as used herein means a group of at least two electrodes structured or configured to be structured in a desired orientation. For example, a group of electrodes may be mounted on an adhesive pad or an electrode patch for holding or orienting a group of electrodes in a desired orientation. And, an electrode assembly may refer to the adhesive pad and associated electrodes, including electrodes which may be mounted or mountable to the adhesive pad.

[0029] The term“electrode support” refers to a mount, housing, patch, or other structure which may be used for holding or orientating one or more electrodes in a desired orientation.

[0030] “Having” means including but not limited to.

[0031] The term“seizure-detection routine” refers to a method or part of a method that may be used to process signal collected from a person and detect seizure activity or indicate increased risk that a seizure may occur, be occurring, or may have occurred. A seizure- detection routine may be run individually or may be run in combination with other seizure- detection routines or methods. One or more seizure-detection routines may sometimes be used to monitor a patient in real-time, such as may be used to initiate one or more alarms based on detection of seizure activity or activity that may indicate increased risk that a seizure may occur, be occurring, or may have occurred.

[0032] The term“seizure-related event” as used herein refers to physiological events wherein a patient has suffered a seizure or exhibited physiological activity resembling the presence of a seizure, even if a true seizure may not have occurred.

[0033] Where a range of values is described, it should be understood that intervening values, unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in other stated ranges, may be used within embodiments herein.

[0034] The systems and methods described herein may be used for monitoring the contact integrity between one or more electrodes and a person’s skin. Systems may further be configured for initiating a fault or warning condition when one or more of the electrodes becomes loose or loses contact with the skin. For example, if a collected test signal designed for measuring skin contact integrity is determined to be less than some threshold, a fault may be provided. Alternatively, if a collected test signal designed for measuring skin contact integrity drifts or varies in intensity, skin contact integrity may be deemed to have been compromised.

[0035] In some embodiments, the one or more electrodes may be part of a sensor unit. A sensor unit, may, for example, comprise an electrode assembly, such as may include a group of electrodes and a housing, mount, patch, pad, or other structure for holding, rigidly holding, or positioning a group of electrodes in a desired orientation. Alternatively, a sensor unit may include an electrode support and associated electrodes which may be reversibly attachable to the electrode support. In one example, a sensor unit may include a plurality of stud ports configured to receive studs of an electrode patch. Thus, when the electrode patch and associated electrodes are mounted to the sensor unit the electrodes may be reproducibly oriented. Electrode supports and/or assemblies may sometimes be integrally or reversibly connected to other parts of a sensor unit, such as one or more associated processor, amplifier, transceiver or other electronic components of a sensor unit.

[0036] In some embodiments, a sensor unit may comprise a simple sensor, such as may include an assembly of electrodes for collecting a signal and a transmitter or transceiver to send collected signals to a base station or other remote device for processing. In some embodiments, a sensor unit may include a processor having capability for processing a collected sensor signal and for storing or recording information. For example, a sensor unit may comprise a“smart” sensor having data processing and storage capability. A sensor unit may also comprise a housing for receiving one or more electrodes or an electrode assembly. For example, electrodes or an electrode assembly may be inserted or placed into either of a smart sensor or simple sensor in order to configure a sensor unit for operation.

[0037] A sensor unit may be a biosensor unit configured or configurable for collecting bioelectric signals or other physiological signals from a person’s body. In some embodiments, a sensor unit may be configured for collecting an applied signal (which may be the same signal or a different signal than a test signal applied for monitoring contact integrity) and processing the test signal in order to measure one or more properties of a person’s tissues, such as a skin or tissue conductance as may be measured in electrodermal analysis (EDA). In some embodiments, sensor units may be configured for collection of muscle-related electrical signals originating from one or more of a person’s muscles, such as may be used to perform EMG. For example, an EMG sensor unit may be placed on or near one or more muscles of a person’s body, such as the biceps, triceps, hamstrings, quadriceps, frontalis, temporalis, or other suitable muscles of a person’s body and any combinations thereof. Collected muscle- related electrical signals may then be processed to determine one or more conditions related to muscle activity, including a seizure condition, for example.

[0038] The systems and methods herein have particular technological benefits when applied in use with mobile sensor units, such as may be in wireless contact with a remote reference device and attached to an ambulatory person or patient. For example, systems and methods herein may be used in mobile sensor applications and/or in other applications where minimizing power consumption, affected skin surface area, and/or weight may be desirable. In some embodiments, systems herein are designed to operate with low power consumption and low latency for detection of a patient condition, such as a patient seizure. For example, a test signal used for measuring contact integrity and another signal used for monitoring a signal collected from a patient, such as an EMG signal, may each be measured continuously or semi- continuously and without having to switch between states suitable for detecting a particular signal. In some embodiments, systems herein are configured for detection of both an applied test signal and another signal using a common detection pathway, such as may involve a minimum number of detection amplifiers and/or a minimum number of other electronic components. Accordingly, concomitant energy use or dissipation of energy associated with additional circuit elements may be lessened. In addition, such systems may be more readily miniaturized than other systems that may include a greater number of electrical components. Thus, in some embodiments, electrodes herein are part of a mobile biosensor of reduced size and including loose electrode detection capability, the mobile biosensor further configured for placement on or near the skin of a patient and for collection and processing of one or more physiological signals while minimizing power consumption.

[0039] In some embodiments, a sensor includes or is configured to receive and hold a pair of detection electrodes and a reference or common electrode, such as may be used to execute bipolar detection of a collected signal. A group of electrodes may be mounted or may be configured for mounting in a structure or housing in order to form an electrode assembly. For example, a group of electrodes may be part of an electrode assembly including a number of surface electrodes arranged at strategic positions on the surface of a person’s skin and arranged in or near an outer surface of a housing which is configured to lie against the surface of the skin, such as alongside or near one or more of a person’s muscles.

[0040] An embodiment of a system 10 for collecting a signal using a group of electrodes and for monitoring electrodes therein for skin-contact integrity is shown in Figure 1. This embodiment of system 10 includes a test signal module 12 (which includes system components within a first dashed line in Fig. 1), the module 12 configured for generating and/or conditioning a test signal 14. The system 10 further includes a signal detection module 16 (which may include system components within a second dashed line in Fig. 1) and a group of electrodes. For example, a group of electrodes may include a common electrode 18 and a pair of detection electrodes 20, 22.

[0041] In some embodiments, a group of electrodes is part of an electrode assembly. Alternatively, system 10 may comprise a sensor unit including a housing for insertion and positioning of electrodes. Electrodes may then be inserted and attached to the sensor as needed. Electrodes may, for example, comprise Ag/AgCl electrodes, such as reusable sintered or disposable electrodes, or other suitable electrodes may be used.

[0042] In some embodiments, system 10 includes a clock or oscillator 24. Clock or oscillator 24 may, for example, be operatively connected to either or both of test signal module 12 and/or detection module 16. Alternatively, in some embodiments wherein system 10 may be a sensor unit, the sensor 10 is configured to receive an external trigger signal, such as may be fed into the system 10 from one or more external clocks or oscillators.

[0043] In some embodiments, system 10 includes a processor 49, such as may be included in a mobile sensor unit. Alternatively, system 10 may be configured to provide one or more signals (e.g., an amplified collected signal) to a physically separate processor, which may or may not be part of the system 10.

[0044] Test signal 14 is a time-varying signal constructed so as to include one or more amplitude steps. For example, test signal 14 may be constructed using a direct current voltage source 26 (e.g., a stable voltage source or suitably referenced battery) and a digital -to- analog converter 28. At discrete time intervals, an adjustable portion of the output voltage of source 26 may be selectively passed by digital-to-analog converter 28. Therefore, the output of the voltage source 26 may be made in discrete segments. Accordingly, the test signal 14 may be referred to as a segmented test signal. Some exemplary segmented test signals 14 are further described in relation to Figures 2A-2C below. In some embodiments, an amplifier 30 is used to condition or adjust the magnitude of the test signal 14. For example, in some embodiments, the gain of amplifier 30 may be adjusted to control the strength or amplitude of the applied test signal 14.

[0045] In some embodiments, segmented test signal 14 includes a stepped profile and may be shaped to approximate another periodic function. For example, as shown in Figure 2A, the test signal 14 is a segmented sine wave or stepped sine wave which may also be referred to herein as a modified or approximate sine wave. In Fig. 2A a smooth sine wave 32 is shown superimposed with segmented or approximate sine wave 34. As shown therein, a segmented test signal comprises a stepped profile or shape and may approximate a smooth periodic function. Alternatively, the test signal 14 may have a profile that approximates another periodically varying test signal profile. For example, as shown in Figure 2C, the test signal 14 may comprise a wave with a generally triangular shape. In Fig. 2C, a triangular shape 36 is shown superimposed with segmented triangular wave 38. In this disclosure, sine waves may sometimes be used to illustrate the systems and methods herein. However, unless the context implies otherwise, where reference herein is made to a sine wave, or to a segmented or approximate sine wave, other periodic waves or approximations thereof may also be used.

[0046] Segmented or approximate sine waves (or other segmented waves) may sometimes be generated in other electronic systems. However, such systems may commonly incorporate one or more elements to try and smooth or reduce the steps so that an approximate sine waves may more accurately reflect a true sine wave. For example, other systems may commonly incorporate a resistance/capacitance (RC) filter to try and minimize differences between a segmented or approximate sine wave pattern and a pure sine wave pattern. Alternatively, an approximate sine wave may simply be tolerated in some electronic systems. Systems herein may not only be configured to generate a test signal that comprises a segmented or approximate sine wave (or other periodic wave) but may also use the steps to detect a collected signal in order to verify contact integrity. For example, in some embodiments, a test signal may include a plurality of steps. And, as further described below, a delay element may be used to unbalance the collected signals at inputs of a detection amplifier. Amplification of the imbalanced collected signals may then produce a characteristic pattern that may be detected to verify contact integrity of a skin-electrode interface.

[0047] For example, referring back to Figure 1, test signal modulel2 is connected to the common electrode 18 so as to configure the test signal module for applying the test signal 14 to the common electrode 18. Upon application of the test signal 14, a portion of the test signal 14 is collected at the detection electrodes 20, 22. Signal collected at the detection electrodes 20, 22 is directed to the inputs 42, 44 of a detection amplifier 46, and the output of the detection amplifier 46 is processed for signal detection. For example, detection amplifier 46 may be connected to an analog-to-digital converter 48 for digital processing and then fed into a processor 49 for analysis and/or visualization.

[0048] In some embodiments, a delay element 50 is disposed between one or more of the detection electrodes 20, 22 and the inputs 42, 44. For example, as arranged in Fig. 1, the delay element 50 is disposed along a pathway or connection 45 between the detection electrode 22 and the input 44. A second pathway or connection 47 may route collected signals from the detection electrode 20 to the input 42. As further described in relation to Figs. 4A-4C, delay element 50 functions to unbalance the two signals collected at each of the detection electrodes 20, 22. The delay element 50 may, for example, comprise a resistance capacitance (RC) circuit, or other suitable electronic delays or elements may be used to unbalance collected signals. In some embodiments wherein system 10 is or comprises a mobile sensor unit, delay element 50 may comprise a passive RC circuit or other electronic element which may operate without significant power consumption. In some embodiments, delay element 50 may comprise a delay-locked loop or a phase-locked loop. However, residual power consumption in some otherwise suitable elements may limit their applicability for some applications herein.

[0049] In some embodiments including delay element 50, collected signal directed along a pathway from detection electrode 22 to input 44 may be slightly phase shifted with respect to collected signal directed to the input 42. And, amplification may transform a segmented test wave pattern (e.g., segmented sine wave) to a series of detectable spikes. Detection of those spikes (e.g., a threshold number of spikes over a certain time period) may then be used for establishing contact integrity. In some embodiments, detection of spikes includes using one or more analysis time windows for spike detection, and then comparing a detected spike number to an expected spike detection value, such as may be based on the frequency and/or shape of the applied test signal 14. To further increase confidence that spikes are related to the test signal, an average shift (e.g., an average time or phase shift between spikes and a clock driven trigger signal) may also be determined. For example, one or more analysis windows may be generated synchronously with test signal segmentation by using clock or oscillator 24 as a common trigger. Accordingly, shifts between a clock driven trigger signal and detectable spikes may be relatively constant when system 10 is working properly and contact integrity is maintained.

[0050] In some embodiments, clock or oscillator 24 is connected to either of analog-to-digital converter 48 or an associated processor connected therein. Clock or oscillator 24 may also be used in generation of the test signal 14. For example, as shown in Fig. 1, clock or oscillator 24 may be linked to digital-to-analog converter 28, and intervals of time for segmentation of the voltage source 26 are set or triggered using the clock or oscillator 24. Therefore, the test signal 14 and system components used for analysis of detected test signal in some embodiments operate in a synchronized manner. For example, as described above, clock or oscillator 24 may be used to trigger one or more analysis time windows for spike detection.

[0051] Additional details of the systems herein are described in relation to the following methods. For example, as shown in Figure 3, system 10 (as well as some embodiments of systems 200, 300) may be configured to execute method 60 for monitoring a group of electrodes for skin contact integrity. As shown in step 62, a group of electrodes is positioned on the skin of a person. For example, in some embodiments wherein the electrodes are part of an EMG sensor, the electrodes are positioned on or near one or more of a person’s muscles, such as the biceps or other suitable muscle for collecting an EMG signal. To facilitate positioning, a group of electrodes may be part of an electrode assembly, such as may include a housing to orient the electrodes in a desired orientation. As shown in the systems 10, 200, 300, a group of electrodes may include common electrode 18 and a pair of detection electrodes 20, 22.

[0052] In some embodiments, the common electrode 18, is arranged symmetrically with respect to the detection electrodes 20, 22. For example, the relative distance between common electrode 18 and detection electrode 20 may be about the same as the distance between common electrode 18 and detection electrode 22. In other embodiments, the common electrode 18 may be arranged asymmetrically with respect to the detection electrodes 20, 22. Asymmetric position of electrodes 18, 20, 22 may, for example, encourage a difference in potential drop between common electrode 18 and each of the detection electrode 20, 22. Such may, for example, be used to unbalance collected signals at each of electrodes 20, 22 and to provide an imbalance potential between the inputs 42, 44 of detection amplifier 46.

[0053] As shown in step 64, a segmented test signal 14 may be generated, the test signal including one or more amplitude steps. For example, in some embodiments, the test signal may be shaped or segmented to provide a signal shape that approximates the shape of a periodic function, such as a sine (or cosine) function, triangular function, saw-tooth function, or other periodic function. As also described in reference to test signal module 12, generation of test signal 14 may include selectively passing various amounts or portions of direct current voltage source 26. For example, the digital-to-analog converter 28 may function as a time varying filter, selectively adjusting voltage passed to segment the constant amplitude output of source 26, the amplitude of individual segments being selected, for example, using an appropriate look-up table. Timing for switching between values of the look-up table may be controlled using clock or oscillator 24. In some embodiments, a signal produced at the output of digital -to-analog converter 28 may be routed through test signal module 12 with only minimal or no smoothing which may otherwise disrupt one or more steps in the shape of test signal 14. For example, if test signal module 12 includes an amplifier 30, the amplifier may preferably operate so as to induce only minimal test signal 14 distortion. Other elements commonly used to smooth a segmented function, such as RC filter elements may likewise not be included in test signal module 12. Or, if used, RC filters elements may be configured to only minimally disrupt the stepped profile of test signal 14.

[0054] In step 66, the test signal 14 is applied to the common electrode 18. For example, test signal 14 may be applied directly from test signal module 12 to the common electrode 18 with minimal or no smoothing which may otherwise disrupt the segmented profile of the test signal 14. The shape of the test signal 14 may be conveniently described as it is injected or applied to the common electrode. For example, referring back to the embodiment of Figs. 2A-2C, the test signal is segmented and configured to include a stepped profile or shape approximating a smooth periodic function. The stepped profile of a segmented test signal may be characterized by an average amplitude deviation or percentage average deviation. An “average amplitude deviation” herein refers to the average of the absolute value of the difference in amplitude between a test signal with a stepped profile and the best-fit smooth periodic function which it approximates. For example, Fig. 2B shows the amplitude deviation (D) of the test signal 32 at a point A along the test signal profile. An amplitude deviation of a test signal may be compared to the corresponding amplitude of the periodic function to which the test signal approximates. For example, the amplitude of a sine wave refers to the maximum amplitude of the sine wave from its average value. Comparison between these amplitudes may be expressed as a percentage average deviation (or a corresponding ratio or other relative metric may be used), as defined in Equation 1.

[0055] % Average Dev. = [(Deviation (D)) / (Amp. Periodic Fxn.)] x 100% EQN. 1

[0056] In some embodiments, a percentage average deviation for a segmented test function with a stepped profile ranges from about 0.1% to about 25%. In some embodiments, within that range, a lower boundary may be about 0.1%, about 0.5%, about 1% or about 2%. In some embodiments, within that range, an upper boundary may be about 25%, about 15%, or about 5%. Steps in a segmented test function with a stepped profile may also be characterized by a step amplitude. For example, in some embodiments, steps in a stepped periodic wave may range from about 0.1 mV to about 500 mV. In some embodiments, within that range, an upper boundary may range from about 500 mV to about 1 mV, or other suitable ranges may be selected.

[0057] As shown in step 68, test signal 14 may be sensed or collected at each of the detection electrodes 20, 22. For example, test signal 14 may be applied at the common electrode 18. If electrodes are properly in contact with the skin, application of test signal 14 may initiate a corresponding or related collection of signal (e.g., a related flow of current) at the surface of the detection electrodes 20, 22. Current flow or injection of signal across or at the surface of one or more skin electrode interfaces (such as the interfaces associated with skin and the electrodes 20, 22) may herein be referred to as collection of signal. The collected signals (or sensed signals) may then be further processed.

[0058] As shown in step 70, collected signals are routed to a detection amplifier and amplified in order to provide an amplified collected signal. For example, as shown in Fig. 1, collected signals produced by current flow into or at the surface of each of the detection electrodes 20, 22 may be routed to the detection amplifier 46.

[0059] In some embodiments, the relative position of the detection electrodes 20, 22 with respect to the common electrode 18 and/or relative impedance values of electrodes 20, 22 may be different. Accordingly, in such embodiments, signals collected at the each of the two electrodes 20, 22 are out of balance or imbalanced. The term“imbalanced” as used herein in reference to two signals, refers to a condition where the two signals have different amplitude, phase, or both. The term“unbalance” as used herein refers to the verb meaning to cause loss of balance or to produce an imbalance. For example, decreasing the relative impedance for one of the electrodes 20 or 22 decreases the magnitude of potential drop during collection of signal at the electrode of reduced impedance. Accordingly, the collected signals at each of the two detection electrodes 20, 22 are imbalanced. For example, in some embodiments, a first detection electrode among the pair of detection electrodes 20, 22 has an input impedance of about 2 KW to about 20 KW and wherein the other of said pair of detection electrodes 20, 22 has an input impedance that is about 1% to about 10% lower in magnitude than the first detection electrode. Accordingly, in some embodiments, positioning of electrodes and/or collection of signal (as described above in steps 62 and 68) provides an imbalance potential at the inputs 42, 44. And, in some of those embodiments, signals may be routed to each of the inputs 42, 44 of detection amplifier 46 without any significant additional processing in step 70, such as without any component to modify the timing or phase relationship between collected signals in each of the two signal paths (i.e., signal paths from each of the pair of detection electrodes 20, 22 to an associated input 42, 44). [0060] In some embodiments, collected signals produced by current injection into or at the surface of the detection electrodes 20, 22 are unbalanced during routing of the collected signals from the detection electrodes 20, 22 to the inputs 42, 44 of detection amplifier 46. For example, collected signal may be routed along one signal path (e.g., one of the detection electrodes 20, 22 and an associated input 42, 44) in a manner that is different from how collected signal is routed along the other signal path (e.g., the other of the detection electrodes 20, 22 and an associated input 42, 44). For example, in some embodiments, a phase imbalance between the two signals paths may arise from a delay element 50 disposed between one of the detection electrodes 20, 22 and a corresponding input (42 or 44) of the detection amplifier 46.

[0061] In some embodiments, unbalancing of collected signals is achieved by a combination of a differential impedance between the detection electrodes 20, 22, asymmetric positioning of the detection electrodes 20, 22, use of one or more imbalance-inducing element (e.g., delay element 50) or any combinations thereof.

[0062] Some of the effects of unbalancing collected signals, including, for example, use of imbalanced signals to generate peaks in an amplified collected signal, are further described in relation to Figures 4A-4C. Figure 4A shows a part 80 of an embodiment of system 10 (e.g., an embodiment wherein delay element 50 is disposed between detection electrode 22 and an input 44), and further including details about signals therein. As shown in Fig. 4A, a test signal 14 is injected at the common electrode 18. In response to signal injection, signals 82, 84 are collected at each of the detection electrodes 20, 22. Collected signals 82, 84 are further routed to the inputs 42, 44 of detection amplifier 46. For example, as shown by arrow 86, collected signal 82 is routed to input 42. Likewise, as shown by arrow 88, collected signal 84 is routed to input 44. As shown in Fig. 4B, delay element 50 initiates a delay (f) in the collected signal 84.

[0063] Amplifier 46 provides an amplified output signal 90. For example, in some embodiments, amplifier 46 may be a differential amplifier, and output signal 90 may be proportional to the difference in amplitude between signals at the inputs 42, 44. Thus, it should be understood that output signal 90 is related to the signals collected at the detection electrodes 20, 22 and may be referred to as output signal 90 or as an amplified collected signal. In this disclosure, the output signal 90 may be referred to when specifically discussing signal in its form at the output of the detection amplifier. However, amplified collected signal may be referred to when more generally describing signals downstream of amplification using amplifier 46, such as signals routed to and from analog-to-digital converter 48 (shown in Fig.

1)^.

[0064] Figure 4C shows the amplitude of signals at the inputs 42, 44 and the corresponding amplitude of output signal 90. As shown therein, a relative delay between the collected signals 82, 84 may shift the signals in order to offset steps in the two collected signals (e.g., the signals at 86, 88). This shift or unbalancing may provide a difference in signal amplitude between the signals at 86, 88, the difference in signal amplitude manifested as a characteristic spike in the amplified output signal 90 at times and frequencies related to the stepped pattern in the test signal 14. In some embodiments, the shift (f) may be suitable in magnitude so that a transient difference in signal amplitude is manifested between the two collected signals at 86, 88. For example, a transient difference in amplitude may be present during a time period between a first time point A and a second time point B as shown in Figs. 4B and 4C. However, at other times near the time points A, B, (such as time points C and D) the two signals 86, 88 may each be associated with the same segment of segmented test signal 14. For example, at times C, D (immediately adjacent time points A, B but not between the time points A, B), the signals 86, 88 may be at the same step level and about the same in amplitude. Thus, those portions adjacent time points A, B may generally be canceled and not amplified by amplifier 46, and spikes in the amplified output signal 90 may be clearly differentiated from adjacent signal thereby facilitating high sensitivity spike detection. In some embodiments, to facilitate high sensitivity spike detection, the shift (f) may be suitable in magnitude so that collected signals (i.e., signals collected at each of the detection electrodes 20, 22) are not unbalanced in phase during routing to the detection amplifier by an amount greater than the phase subtended by each segment of the segmented test signal 14. For example, if test signal 14 is segmented into 10 segments for each period of the test signal, each of those segments may subtend a phase of about 36 ° (i.e., 360 ° / 10 segments). In some embodiments, a phase shift (f) may be less than about 99%, less than about 50% or less than about 5% of a phase subtended by each segment of segmented test signal 14.

[0065] The width and/or amplitude of the spikes may be dependent various factors, including, for example, properties of the delay element 50, amplitude of steps of the test signal 14, and any additional unbalancing such as may be manifested through differences in impedance between detection electrodes 20, 22 or asymmetric positioning of detection electrodes 20, 22, and any combinations thereof. Notably, at least some of those factors may be readily adjusted. For example, in some embodiments, the magnitude of spikes may be readily adjusted by changing the inputs of a programmable look-up table operatively coupled to digital-to-analog converter 28 or by changing one or more adjustable properties of delay element 50.

[0066] An shown in step 72, the amplified collected signal (e.g., output signal 90 of detection amplifier 46) may then be further processed for detection of test signal 14. For example, amplified collected signal may be routed to analog-to-digital converter 48 and further routed, such as to a processor 49, for digital signal processing. In one example, output signal 90 may be directly routed from amplifier 46 to analog-to-digital converter 48, such as may be executed to minimize distortion of spikes included in output signal 90 and to ensure that the spikes, which may be short duration spikes, are not substantially degraded and/or lost during digitization.

[0067] In some embodiments, detection of test signal 14 may include analyzing the amplified collected signal to determine one or more property values of the amplified collected signal. Property values may, for example, include an average phase of spikes, frequency of spikes, amplitude, number of spikes, slope between adjacent spikes, or other property value of the amplified collected signal and combinations thereof. Property values may then be compared to expected or threshold property values based on properties of the test signal 14. In some embodiments, processing to detect the test signal 14 may include defining one or more analysis time windows (referred to herein as analysis windows) and determining one or more property values of amplified collected signal within the one or more analysis windows. In some embodiments, analysis windows may be synchronized with test signal generation. An analysis window used to detect test signal 14 may, for example, be accomplished by synchronizing operation of analog-to-digital converter 48 or processor 49 and digital-to-analog converter 28.

[0068] Additional description of synchronization between analysis windows and spikes of the amplified collected signal is provided in Figure 5. As shown in Fig. 5, an amplified collected signal 92 may include spikes 94, 96, and clock or oscillator 24 may trigger the start of the analysis windows 98, 100. For example, clock or oscillator 24 may feed a trigger signal into the processor 49 (not shown in Fig. 5) which may then initiate the start of an analysis window. As shown therein, a shift (Q) (which may be expressed as either a phase or time delay) may be measured between a detected spike and the start of an analysis window 99. An average shift may then be tracked over some number of detected spikes, and a running average value for the shift may be determined. Because the same trigger signal may be supplied to test signal module 12, the shift may remain substantially constant if contact integrity is maintained. And, changes in shift (Q) may be indicative of a system fault and loss of contact integrity.

[0069] In some embodiments, a property value of the amplified collected signal may comprise an integrated amplitude. Because the timing of steps in test signal 14 is related to the peaks 94, 96 (and the phase shift Q is nearly constant in a well-functioning system), the analysis windows 98, 100 may be closely positioned in relation to peaks 98, 100 improving signal-to-noise for detection of test signal. At some regular interval, such as after some number of peaks or cycles of periodic test signal 14, the integrated amplitude of collected signal (or some other property value) may be examined, and if the amplitude is within an expected range (e.g., above some threshold amplitude or between a minimum threshold amplitude and a maximum threshold amplitude) the test signal 14 may be deemed detected, and contact integrity may be verified. Alternatively, if an integrated amplitude is outside of an expected range, a short or loose electrode condition may be determined. As shown in step 74, one or more responses may be initiated based on detection of test signal. For example, an alarm or fault condition may be initiated if the test signal fails to be detected, such as may occur if skin- contact integrity is lost and the test signal 14 fails to be collected at the detection electrodes 20, 22

[0070] Figure 6 shows method 110, which describes an embodiment of a method for monitoring a sensor signal for skin-electrode contact integrity and for collecting an EMG signal. Any of various appropriate systems may be configured for executing the embodiment of method 110. For example, at least in some embodiments, each of systems 10, 200, 300 may be configured for executing the method 110. As shown in step 112, an EMG sensor unit is positioned on the skin of a person. The EMG sensor unit may include an electrode assembly for orienting a common electrode and a pair of detection electrodes in a desired orientation on a person’ s skin near one or more of the person’ s muscles. The pair of detection electrodes may be configured for collecting test signal and also for collecting signals from muscle-related electrical activity associated with activation of muscle.

[0071] In step 114, a test signal 14 is generated and applied to the common electrode 18. As described in relation to steps 64 and 66 of method 60, the test signal 14 may be a segmented test function with a stepped profile that approximating a smooth periodic function. For example, the test signal 14 may be a repetitive waveform with a frequency of about 1 KHz to about 10 KHz or about 2.8 KHz to about 3.2 KHz. In some embodiments, a segmented test function may be generated using a voltage source 26 and digital-to-analog converter 28. For example, the digital-to-analog converter 28 may function as a time varying filter, selectively adjusting voltage passed to segment the constant amplitude output of source 26, the amplitude of individual segments being selected, for example, using an appropriate look-up table. In some embodiments, the test signal 14 may be a sine wave with a frequency of about 2.8 KHz to about 3.2 KHz produced in segments of varying amplitude using a look up table with some number of points, such as about 8 to about 64 points. For example, an 8- point table may segment a sine wave into 8 discrete segments. In some embodiments, the test signal 14 may be continuously or substantially continuously applied to the common electrode 18.

[0072] In step 116, signals may be collected form the pair of detection electrodes 20, 22. For example, as further described in relation to step 68 of the method 60, application of the test signal 14 to common electrode 18 may initiate a corresponding injection of current into each of the detection electrodes 20, 22. In addition, muscle-related electrical activity, if present, may also be collected using the pair of detection electrodes 20, 22.

[0073] In step 118, collected signals may then be routed to the inputs 42, 44 of detection amplifier 46 and amplified to provide an amplified collected signal. In some embodiments, routing of collected signal may include routing collected signals at each of the detection electrodes 20, 22 through asymmetric paths and creating an imbalance between the signals. For example, in some embodiments, at least one of the pathways or connections from the detection electrodes 20, 22 to respective inputs 42, 44 of detection amplifier 46 may include delay element 50. Accordingly, as describe more fully in relation to Figs. 4A-4C, the delay element 50 may unbalance collected signals collected in response to test signal application, and a series of repetitive output spikes may be generated upon amplification of the imbalanced collected signals. In addition, collected signals related to muscle-related electrical activity may likewise be collected using detection electrodes 20, 22 and routed to detection amplifier 46. Thus, the amplified collected signal may include both signal components related to the test signal and signal components related to muscle-related electrical activity.

[0074] In step 120, amplified collected signal may be processed for detection of both test signal and muscle-related electrical activity associated with one or more seizure- related events. For example, detection of test signal may include analyzing the amplified collected signal to determine one or more property values of the amplified collected signal, including, for example, an average phase between clock 24 and detected spikes, a frequency of detected spikes, an amplitude of the amplified collected signal, a number of spikes, a slope between adjacent detected spikes, or other property value of the amplified collected signal and combinations thereof. Property values of the amplified collected signal may then be compared to expected or threshold property values based on properties of the test signal 14. In some embodiments, analysis windows 98, 100 used for measurement of property values may operate synchronously with clock or oscillator 24. Accordingly, analysis windows 98, 100 may be narrowly focused on spikes in the amplified collected signal, such as may be used to provide for high signal-to-noise detection of spikes. For example, signal associated with amplitude spikes may be fully collected if the duration width of an analysis window is aligned with and about the duration width of spikes. However, signal noise may be minimized by minimizing the duration width of the analysis window. Signal to noise may further be minimized by controlling the magnitude of an imbalance phase shift (f) and configuring the system so that times immediately adjacent spikes are associated with the same step of a segmented or stepped test signal 14. For example, such a condition may be achieved by configuring the detection system so that the phase shift (f) is less than a phase subtended by individual segments of the test signal 14.

[0075] In some embodiments, spikes in the amplified collected signal may be measured during one or more calibration protocols and analysis windows for spike detection may be set or adjusted therein. For example, analysis windows may be set during calibration and applied during general system operation to facilitate high sensitivity detection of test signal. For example, as further discussed in relation to calibration method 130, one or more parameters of delay element 50 or of analysis windows 98, 100 may be set during calibration. In some embodiments, calibration may be executed at regular intervals, executed based on a detected change in property values of the amplified collected signal or executed during initial setup of a sensor, or executed based on any combinations thereof. Accordingly, in some embodiments of method 110, analysis windows used for detection of test signal 14 may be calibrated during sensor operation. In some embodiments of method 110, timing or placement of analysis windows and/or duration width may be predetermined values.

[0076] Further in step 120, amplified collected signal may be analyzed for detection of muscle-related electrical activity associated with one or more seizure-related events. In some embodiments, the detection electrodes 20, 22 may be connected to a differential detection amplifier, and any signal that is common between the electrodes, such as may be part of environmental or noise components generated at a distance from the detection region and unrelated to signal from muscle activation intended for detection, may be rejected. For example, as understood in the art, the detection amplifier 46 may be a differential amplifier having a capability for common-mode rejection of signal components that may be present at each of the detection electrodes 20, 22. Accordingly, it should be understood that phase shifting of collected signals in paths from different detection electrodes 20, 22 may generally have a deleterious effect on the common mode rejection. However, in some embodiments, one or more seizure-detection routines may be applied for seizure detection, the seizure detection routines configured for high sensitivity detection of seizure activity. Accordingly, method 110 may still detect seizures with high sensitivity even with the common mode rejection compromised, at least to some degree. And, as may be advantageous for some remote sensor applications, method 110 may involve a common detection pathway (e.g., a path including common detection amplifier 46) for detection of both muscle-related electrical activity and test signal.

[0077] In some embodiments, seizure detection routines applied herein in step 120 may be configured for detection of seizure-related events based on analysis of amplified collected signal using an integration or frequency transform. For example, processing amplified collected signal to generate a seizure-related event signal may include applying an integration algorithm or a frequency transformation algorithm to the amplified collected signals and determining whether the integrated or frequency transformed signals are above a predetermined power content within one or more time windows.

[0078] In some embodiments, sensitivity for detection of seizure-related events may be enhanced by executing a frequency transform and determining the variance/covariance of power amplitudes for selected frequency bands. For example, the variance/covariance data may be further used to calculate one or more of a T-squared statistical value or principal component value (PCA) for the amplified collected signal. Data value may then be compared to a threshold T-squared value or threshold principal component value to identify seizure- related events.

[0079] In some embodiments, seizure detection routines herein may be configured for processing amplified collected signal to generate a seizure-related event signal, the processing including counting a number of crossings between a filtered amplified collected signal and a predetermined hysteresis value defining a positive and a negative threshold value within each of a number of time windows. [0080] In some embodiments, a processor 49 may be configured to execute one or more seizure-detection routines for analysis of the collected signals from muscle-related electrical activity. Processor 49 may, for example, be part of the EMG sensor (e.g., in embodiments where the EMG sensor is a“smart sensor”) or may be physically separate from the EMG sensor. For example, in some embodiments, processor 49 may comprise a remote base station or remote caregiver device capable of receiving collected signals and processing the signals for seizure detection.

[0081] In step 122, one or more responses may be initiated based on the processing of the amplified collected signal. For example, if test signal 14 is not detected during some period, a loose electrode fault warning or alarm may be initiated. In some embodiments, if test signal is not detected during some period, one or more calibration routines may be executed to improve sensitivity for test signal detection. Also, in step 122, one or more alerts may further be initiated if one or more seizure-related events is detected or another appropriate response may be initiated.

[0082] A method 130 of calibrating a system for test signal detection is shown in Figure 7. In step 132, one or more calibration routines may be initiated. For example, in some embodiments, calibration may be executed when a use initially turns on a sensor device or positions a group of electrodes on the skin. During calibration a patient may maintain relatively motionless. Accordingly, muscle related activity may be relatively low during calibration. As shown in step 134, test signal may be applied to the common electrode and signal may be collected and analyzed for test signal detection. And, as shown in step 136, one or more parameter related to test signal detection may be adjusted, such as the duration of an analysis window used for test signal detection.

[0083] In some embodiments, a test signal may be applied at a predetermined amplitude. Alternatively, the test signal may be applied over a range of amplitude gradations. For example, based on a strength of test signal detection for different applied amplitudes, an acceptable amplitude of test signal may be selected for use in monitoring. In some embodiments, a relative phase delay between the clock 24 and the detected test signal may be established during calibration. For example, analysis windows may be aligned with spikes generated in response to test signal collection. For example, an analysis window may be centered or otherwise appropriately aligned with detected spikes. In some embodiments, a duration width of the test signal may also be adjusted to improve sensitivity for test signal detection. For example, a duration width of an analysis window may be defined based on a duration width 140 of a spike (as shown in Fig. 5). A duration width may, for example, be defined as a duration width that includes about 90% or some other percentage of the integrated amplitude of a spike. A duration width of an analysis window may then be selected as being some percentage of the duration width of a spike. For example, in some embodiments, a duration width of an analysis window may be about 100% to about 1,000% of the duration width of a spike. In some embodiments, delay element 50 may be adjustable. And, as part of calibration, a duration width of spikes may be tuned or adjusted to a desired value during system calibration.

[0084] An alternative embodiment of a system 200 for loose electrode detection is shown in Figure 8. System 200 may include more than one detection pathway. For example, the detection electrodes 20, 22 may be connected to amplifier 46 and to at least one additional detection pathway. As similarly described above, test signal 14 may be applied to the common electrode 18. Collected signal related to the test signal 14 may be routed to amplifier 46 and amplified collected signal 206 analyzed for detection of test signal. For example, in some embodiments wherein delay element 50 is used to unbalance the collected signals (e.g., to produce spikes in the amplified collected signal 206), detection of test signal may be based on one or more property values of detected spikes. For example, detection of test signal may be based on one or more of an average phase shift between a trigger signal from clock 24 and detected spikes, a frequency of detected spikes, an amplitude of the amplified collected signal, a number of detected spikes, a slope between adjacent detected spikes, and combinations thereof. Property values may then be compared to threshold property values in order to detect the test signal 14.

[0085] The detection electrodes 20, 22 may also be connected to the second detection amplifier 202. A processor 49 may be configured for receiving amplified collected signals 204, 206 from each of the detection amplifiers 46, 202. Alternatively, separate processors may be used for analysis of the two amplified collected signals 204, 206. In some embodiments of method 200, detection amplifier 202 may be a differential amplifier configured for high sensitivity detection of signal collected at the detection electrodes 20, 22. For example, in some embodiments, system 200 may comprise an EMG sensor, and the detection electrodes 20, 22 may route signals from muscle-related electrical activity to the differential amplifier 202 for detection. Notably, collected signals collected in response to application of the test signal 14 to the common electrode may be substantially balanced at the inputs of differential amplifier 202. Accordingly, the test signal 14 may make only a negligible contribution to amplified collected signal 204, encouraging high sensitivity detection of signals from muscle-related electrical activity. In some embodiments, one or more of the detection pathways in system 200 may further include one or more filters. For example, a low-pass filter or notch filter (not shown) may be added, for example between amplifier 202 and analog-to-digital converter 206 to enhance sensitivity for detection of a collected signal. Also, by way of example, a bandpass or high pass filter (not shown) may be added in the path between the detection amplifier 46 and analog-to-digital converter 48, and the filter may be selected in order to improve sensitivity for detecting the test signal 14.

[0086] An alternative embodiment of a system 300 for loose electrode detection is shown in Figure 9. In the system 300, collected signals associated with the test signal 14 may again be processed using the amplifier 46. For example, amplified collected signal 314 may be routed to analog-to-digital converter 48 and further routed to processor 49 for detection of test signal 14. A first detection electrode 22 may be connected to amplifier 302. Signal collected by the first detection electrode 22 may be amplified using amplifier 302 in order to provide amplified collected signal 310, which may be processed using analog-to-digital converter 304 and routed to processor 49. Likewise, second detection electrode 20 may be connected to amplifier 306. Signal collected by the second detection electrode 20 may be amplified using amplifier 304 in order to provide amplified collected signal 312, which may be processed using analog-to-digital converter 308 and routed to processor 49. Alternatively, the signals 310, 312, 314 may be processed by physically distinct processors.

[0087] Amplifiers 302, 306 may be differential amplifiers, but may also be cheaper and/or more energy efficient summing amplifiers. In some embodiments, one or more of the detection pathways in system 300 may further include one or more filters. For example, a low- pass filter or notch filter (not shown) may be added, for example, between amplifier 302 and analog-to-digital converter 304 to enhance sensitivity for detection of a collected signal. Similarly, a low-pass filter or notch filter (not shown) may be added, for example, between amplifier 306 and analog-to-digital converter 308 to enhance sensitivity for detection of a collected signal. Also, by way of example, a bandpass or high pass filter (not shown) may be added in the path between the detection amplifier 46 and analog-to-digital converter 48, and the filter may be selected in order to improve sensitivity for detecting the test signal 14.

[0088] It is an object of some embodiments of the systems and methods described herein to monitor a group of electrodes for skin contact integrity and to detect one or more signals using a limited or minimum number of electrical components, such as may be applied for use in systems designed for low power consumption and/or weight.

[0089] It is an object of some embodiments of the systems and methods described herein to detect a test signal and one or more other sensor signals using a common detection amplifier and using a minimal number of additional electronic components.

[0090] It is an object of some embodiments of the systems and methods described herein to monitor an electrode assembly for skin contact integrity by applying and detecting a test signal and to detect one or more additional signals, wherein the signals may be detected in a continuous or semi-continuous manner. For example, a test signal and one or more other sensor signals may be detected concurrently without having to switch or toggle a system between states suitable for detection of the individual signals.

[0091] It is an object of some embodiments of the systems and methods described herein to monitor a group of electrodes for skin contact integrity using a test signal and to use one or more of the electrodes to collect an electromyography (EMG) signal. It is a further object of some of those embodiments to record or process a collected EMG signal to monitor a person for signs of abnormal muscle activity such as may be associated with an impaired ability to control or activate muscles. For example, an EMG signal may be collected and used to monitor a patient for conditions such as epilepsy, conditions that may present as psychogenic nonepileptic seizures, cerebral palsy, dystonia, multiple sclerosis, Parkinson’s disease, essential tremor disorder, strokes, injuries to the central nervous system, and other conditions that may permanently or temporarily result in abnormal control or activation of muscles.

[0092] It is an object of some embodiments of the systems and methods described herein to monitor a group of electrodes for skin contact integrity using a test signal and to use one or more of the electrodes to collect an EMG signal from a person. The person may further be monitored in order to detect seizure activity in real-time and with minimal latency between the start of a seizure and its detection. For example, in some embodiments, seizure detection may include analysis of collected signals using one or more seizure-detection routine configured for sensitive detection of EMG signals. In some embodiments, seizure detection may be accomplished using one or more seizure-detection routine configured for sensitive detection of EMG signals and using a system designed for continuous detection of an applied test signal to provide continuous monitoring of the quality of an electrode-skin contact.

[0093] Various embodiments are described in the following clauses.

[0094] Clause 1. A method of monitoring a group of electrodes for skin contact integrity, the method including positioning a group of electrodes on the skin of a person, the group of electrodes including a common electrode and a pair of detection electrodes; generating a test signal, the test signal including one or more amplitude steps and shaped to approximate a periodic function; applying said test signal to said common electrode; collecting signals in response to the application of said test signal in order to provide collected signals, the collected signals including a first collected signal at a first detection electrode of said pair of detection electrodes and a second collected signal at a second detection electrode of said pair of detection electrodes; routing each of said first collected signal and said second collected signal to the inputs of a detection amplifier, said routing unbalancing the first collected signal and the second collected signal in order to provide imbalanced signals at said inputs of said detection amplifier; amplification of a difference between said imbalanced signals in order to provide an amplified collected signal including one or more spikes; and processing the amplified collected signal to detect said one or more spikes, the detection of said one or more spikes used to establish whether skin contact integrity is maintained for said group of electrodes.

[0095] Clause 2. The method of clause 1, said pair of detection electrodes having different impedance values, the impedance difference suitable to maintain an imbalance potential at the inputs of said detection amplifier when contact integrity is maintained between the patient's skin and said group of electrodes.

[0096] Clause 3. The method of clause 2, a first detection electrode among said pair of detection electrodes having an input impedance of about 2 KW to about 20 KW, the other of said pair of detection electrodes having an input impedance that is about 1% to about 10% lower in magnitude than the first detection electrode.

[0097] Clause 4. The method of clause 1, said group of electrodes being part of an electrode assembly, the electrode assembly configured for asymmetric placement of said common electrode with respect to said pair of detection electrodes.

[0098] Clause 5. The method of clause 1, said test signal shaped to approximate one or more of a sine function, cosine function, triangular function, saw-tooth function, square function, and combinations thereof.

[0099] Clause 6. The method of clause 1, said one or more amplitude steps ranging from about 0.1 mV to about 500 mV.

[0100] Clause 7. The method of clause 1, said unbalancing of said first collected signal and said second collected signal comprising a phase imbalance. [0101] Clause 8. The method of clause 7, the test signal comprising a segmented test signal, said phase imbalance being less than a phase subtended by individual segments of the segmented test signal.

[0102] Clause 9. A system for monitoring a group of electrodes for skin contact integrity, the system comprising a group of electrodes including a common electrode and a pair of detection electrodes, the group of electrodes positionable on the skin of a person; a test signal module, the test signal module configured for generating a test signal with a profile that includes one or more amplitude steps, the test signal module further connected to said common electrode for applying said test signal to said common electrode when said group of electrodes is positioned on the skin of said person; said pair of detection electrodes configured for collecting signals generated in response to an application of said test signal to said common electrode; and a pair of connections routing each of said pair of detection electrodes to a detection amplifier, at least one of the pair of connections including one or more delay elements for unbalancing the collected signals in order to provide imbalanced signals at the inputs to said detection amplifier; said detection amplifier configured for amplifying a difference between said imbalanced signals in order to provide an amplified collected signal; and a processor for receiving said amplified collected signal and processing the amplified collected signal to establish whether skin contact integrity is maintained for said group of electrodes.

[0103] Clause 10. The system of clause 9, further comprising an electrode patch including said group of electrodes, the electrode patch mountable to an EMG sensor unit; said EMG sensor unit housing said test signal module and said detection amplifier.

[0104] Clause 11. The system of clause 9, said pair of detection electrodes further configured for collecting muscle-related electrical signals from one or more patient muscles when said group of electrodes is positioned on the skin of said person; said processor further configured for processing said muscle-related electrical signals using one or more seizure detection routines configured for detecting seizure-related events.

[0105] Clause 12. The system of clause 11 further comprising a transceiver, the transceiver configured for transmitting one or more alarms based on a detected seizure-related event.

[0106] Clause 13. The system of clause 9, said detection amplifier being the only amplifier in said system.

[0107] Clause 14. The system of clause 9, said test signal module including a direct current voltage source and a digital -to-analog converter, the digital -to-analog converter capable of receiving a trigger signal from a clock or oscillator;

[0108] Clause 15. The system of clause 14 further comprising said clock or oscillator.

[0109] Clause 16. The system of clause 14, said trigger signal being a common trigger applied to each of said processor and said test signal module, the processor configured for generating one or more analysis windows synchronously in time with generation of said one or more amplitude steps of said test signal.

[0110] Clause 17. The system of clause 9, the test signal comprising a segmented test signal shaped to approximate any of a sine function, cosine function, triangular function, or saw-tooth function.

[0111] Clause 18. The system of clause 9, said one or more delay elements comprising at least one resistor and at least one capacitor.

[0112] Clause 19. The system of clause 9, said pair of detection electrodes having different impedance values, the impedance difference suitable to maintain an imbalance potential at the inputs of said detection amplifier when contact integrity is maintained between the patient's skin and said group of electrodes.

[0113] Clause 20. The system of clause 19, a first detection electrode among said pair of detection electrodes having an input impedance of about 2 KW to about 20 KW, the other of said pair of detection electrodes having an input impedance that is about 1% to about 10% lower in magnitude than the first detection electrode.

[0114] Clause 21. The system of clause 9, said group of electrodes being part of an electrode assembly, the electrode assembly configured for asymmetric placement of said common electrode with respect to said pair of detection electrodes.

[0115] Clause 22. The system of clause 9, said group of electrodes being part of an electrode assembly, the electrode assembly configured for symmetric placement of said common electrode with respect to said pair of detection electrodes.

[0116] Clause 23. The system of clause 9, said imbalanced signals comprising signals with a phase imbalance.

[0117] Clause 24. The system of clause 23, the test signal comprising a segmented test signal, said phase imbalance being less than a phase subtended by individual segments of the segmented test signal.

[0118] Clause 25. A system for monitoring a group of electrodes for skin contact integrity, the system comprising a group of electrodes including a common electrode and a pair of detection electrodes, the group of electrodes positionable on the skin of a person; a test signal module, the test signal module configured for generating a test signal with a profile that includes one or more amplitude steps, the test signal module further connected to said common electrode for applying said test signal to said common electrode when said group of electrodes is positioned on the skin of said person; said pair of detection electrodes configured for collecting signals generated in response to an application of said test signal to said common electrode; and a signal detection module, the signal detection module configured for processing of the collected signals to provide imbalanced collected signals at the inputs of a detection amplifier when contact integrity is maintained between the person’s skin and said group of electrodes and for amplifying the imbalanced collected signals to generate an amplified collected signal including one or more spikes; said signal detection module including said detection amplifier and a processor, the processor configured for analysis of said one or more spikes in order to detect said test signal and to establish whether skin contact integrity is maintained between the group of electrodes and said person’s skin.

[0119] Clause 26. The system of clause 25, further comprising an electrode patch including said group of electrodes, the electrode patch mountable to an EMG sensor unit; said EMG sensor unit housing said test signal module and said signal detection module.

[0120] Clause 27. The system of clause 25, said pair of detection electrodes further configured for collecting muscle-related electrical signals from one or more patient muscles; said signal detection module further configured for processing said muscle-related electrical signals using one or more seizure detection routines configured for detecting seizure-related events.

[0121] Clause 28. The system of clause 27 further comprising a transceiver, the transceiver configured for transmitting one or more alarms based on a detected seizure-related event.

[0122] Clause 29. The system of clause 25, said detection amplifier being the only amplifier in said signal detection module.

[0123] Clause 30. The system of clause 25, said test signal module including a direct current voltage source and a digital-to-analog converter, the digital-to-analog converter capable of receiving a trigger signal from a clock or oscillator;

[0124] Clause 31. The system of clause 25 further comprising said clock or oscillator.

[0125] Clause 32. The system of clause 30, said trigger signal being a common trigger applied to each of said processor and said test signal module, the processor configured for generating one or more analysis windows synchronously in time with generation of said one or more amplitude steps of said test signal.

[0126] Clause 33. The system of clause 25, the test signal comprising a segmented test signal shaped to approximate any of a sine function, cosine function, triangular function, or saw-tooth function.

[0127] Clause 34. The system of clause 25, said signal detection module including one or more delay elements.

[0128] Clause 35. The system of clause 25, said signal detection module including at least one resistor and at least one capacitor.

[0129] Clause 36. The system of clause 25, said signal detection module including a delay element, the delay element configured for initiating at least a portion of said imbalance between said collected signals at the inputs of said detection amplifier.

[0130] Clause 37. The system of clause 36, said delay element comprising at least one resistor and at least one capacitor.

[0131] Clause 38. The system of clause 25, said pair of detection electrodes having different impedance values, the impedance difference suitable to maintain an imbalance potential at the inputs of said detection amplifier when contact integrity is maintained between a patient's skin and said group of electrodes.

[0132] Clause 39. The system of clause 38, a first detection electrode among said pair of detection electrodes having an input impedance of about 2 KW to about 20 KW, the other of said pair of detection electrodes having an input impedance that is about 1% to about 10% lower in magnitude than the first detection electrode.

[0133] Clause 40. The system of clause 25, said group of electrodes being part of an electrode assembly, the electrode assembly configured for asymmetric placement of said common electrode with respect to said pair of detection electrodes. [0134] Clause 41. The system of clause 25, said group of electrodes being part of an electrode assembly, the electrode assembly configured for symmetric placement of said common electrode with respect to said pair of detection electrodes.

[0135] Although the disclosed subject matter and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the claimed subject matter is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition, or matter, means, methods and steps described in the specification. Among other things, any feature described for one embodiment may be used in any other embodiment, and methods described and shown in the figures may be combined. In addition, the order of steps shown in the figures and described above may be changed in different embodiments. Use of the word“include,” for example, should be interpreted as the word“comprising” would be, i.e., as open-ended. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods or steps.

Claims

CLAIMS What is claimed is:

1. A method of monitoring a group of electrodes for skin contact integrity, the method including:

positioning a group of electrodes on the skin of a person, the group of

electrodes including a common electrode and a pair of detection electrodes;

generating a test signal, the test signal including one or more amplitude steps and shaped to approximate a periodic function;

applying said test signal to said common electrode;

collecting signals in response to the application of said test signal in order to provide collected signals, the collected signals including a first collected signal at a first detection electrode of said pair of detection electrodes and a second collected signal at a second detection electrode of said pair of detection electrodes;

routing each of said first collected signal and said second collected signal to the inputs of a detection amplifier, said routing unbalancing the first collected signal and the second collected signal in order to provide imbalanced signals at said inputs of said detection amplifier;

amplification of a difference between said imbalanced signals in order to

provide an amplified collected signal including one or more spikes; and processing the amplified collected signal to detect said one or more spikes, the detection of said one or more spikes used to establish whether skin contact integrity is maintained for said group of electrodes.

2. The method of claim 1, said pair of detection electrodes having different impedance values, the impedance difference suitable to maintain an imbalance potential at the inputs of said detection amplifier when contact integrity is maintained between the patient's skin and said group of electrodes.

3. The method of claim 2, a first detection electrode among said pair of detection

electrodes having an input impedance of about 2 KW to about 20 KW, the other of said pair of detection electrodes having an input impedance that is about 1% to about 10% lower in magnitude than the first detection electrode.

4. The method of claim 1, said group of electrodes being part of an electrode assembly, the electrode assembly configured for asymmetric placement of said common electrode with respect to said pair of detection electrodes.

5. The method of claim 1, said test signal shaped to approximate one or more of a sine function, cosine function, triangular function, saw-tooth function, square function, and combinations thereof.

6. The method of claim 1, said one or more amplitude steps ranging from about 0.1 mV to about 500 mV.

7. The method of claim 1, said unbalancing of said first collected signal and said second collected signal comprising a phase imbalance.

8. The method of claim 7, the test signal comprising a segmented test signal, said phase imbalance being less than a phase subtended by individual segments of the segmented test signal.

9. A system for monitoring a group of electrodes for skin contact integrity, the system comprising:

a group of electrodes including a common electrode and a pair of detection electrodes, the group of electrodes positionable on the skin of a person; a test signal module, the test signal module configured for generating a test signal with a profile that includes one or more amplitude steps, the test signal module further connected to said common electrode for applying said test signal to said common electrode when said group of electrodes is positioned on the skin of said person;

said pair of detection electrodes configured for collecting signals generated in response to an application of said test signal to said common electrode; and a pair of connections routing each of said pair of detection electrodes to a detection amplifier, at least one of the pair of connections including one or more delay elements for unbalancing the collected signals in order to provide imbalanced signals at the inputs to said detection amplifier;

said detection amplifier configured for amplifying a difference between said imbalanced signals in order to provide an amplified collected signal; and a processor for receiving said amplified collected signal and processing the

amplified collected signal to establish whether skin contact integrity is maintained for said group of electrodes.

10. The system of claim 9, further comprising:

an electrode patch including said group of electrodes, the electrode patch mountable to an EMG sensor unit;

said EMG sensor unit housing said test signal module and said detection

amplifier.

11. The system of claim 9, said pair of detection electrodes further configured for

collecting muscle-related electrical signals from one or more patient muscles when said group of electrodes is positioned on the skin of said person;

said processor further configured for processing said muscle-related electrical signals using one or more seizure detection routines configured for detecting seizure-related events.

12. The system of claim 11 further comprising a transceiver, the transceiver configured for transmitting one or more alarms based on a detected seizure-related event.

13. The system of claim 9, said detection amplifier being the only amplifier in said

system.

14. The system of claim 9, said test signal module including a direct current voltage

source and a digital-to-analog converter, the digital-to-analog converter capable of receiving a trigger signal from a clock or oscillator;

15. The system of claim 14 further comprising said clock or oscillator.

16. The system of claim 14, said trigger signal being a common trigger applied to each of said processor and said test signal module, the processor configured for generating one or more analysis windows synchronously in time with generation of said one or more amplitude steps of said test signal.

17. The system of claim 9, the test signal comprising a segmented test signal shaped to approximate any of a sine function, cosine function, triangular function, or saw-tooth function.

18. The system of claim 9, said one or more delay elements comprising at least one

resistor and at least one capacitor.

19. The system of claim 9, said pair of detection electrodes having different impedance values, the impedance difference suitable to maintain an imbalance potential at the inputs of said detection amplifier when contact integrity is maintained between the patient's skin and said group of electrodes.

20. The system of claim 19, a first detection electrode among said pair of detection

21. The system of claim 9, said group of electrodes being part of an electrode assembly, the electrode assembly configured for asymmetric placement of said common electrode with respect to said pair of detection electrodes.

22. The system of claim 9, said group of electrodes being part of an electrode assembly, the electrode assembly configured for symmetric placement of said common electrode with respect to said pair of detection electrodes.

23. The system of claim 9, said imbalanced signals comprising signals with a phase

imbalance.

24. The system of claim 23, the test signal comprising a segmented test signal, said phase imbalance being less than a phase subtended by individual segments of the segmented test signal.

25. A system for monitoring a group of electrodes for skin contact integrity, the system comprising:

said pair of detection electrodes configured for collecting signals generated in response to an application of said test signal to said common electrode; and a signal detection module, the signal detection module configured for

processing of the collected signals to provide imbalanced collected signals at the inputs of a detection amplifier when contact integrity is maintained between the person’s skin and said group of electrodes and for amplifying the imbalanced collected signals to generate an amplified collected signal including one or more spikes;

said signal detection module including said detection amplifier and a

processor, the processor configured for analysis of said one or more spikes in order to detect said test signal and to establish whether skin contact integrity is maintained between the group of electrodes and said person’s skin.

26. The system of claim 25, further comprising: an electrode patch including said group of electrodes, the electrode patch

mountable to an EMG sensor unit;

said EMG sensor unit housing said test signal module and said signal detection module.

27. The system of claim 25, said pair of detection electrodes further configured for

collecting muscle-related electrical signals from one or more patient muscles;

said signal detection module further configured for processing said muscle- related electrical signals using one or more seizure detection routines configured for detecting seizure-related events.

28. The system of claim 27 further comprising a transceiver, the transceiver configured for transmitting one or more alarms based on a detected seizure-related event.

29. The system of claim 25, said detection amplifier being the only amplifier in said

signal detection module.

30. The system of claim 25, said test signal module including a direct current voltage source and a digital-to-analog converter, the digital-to-analog converter capable of receiving a trigger signal from a clock or oscillator;

31. The system of claim 25 further comprising said clock or oscillator.

32. The system of claim 30, said trigger signal being a common trigger applied to each of said processor and said test signal module, the processor configured for generating one or more analysis windows synchronously in time with generation of said one or more amplitude steps of said test signal.

33. The system of claim 25, the test signal comprising a segmented test signal shaped to approximate any of a sine function, cosine function, triangular function, or saw-tooth function.

34. The system of claim 25, said signal detection module including one or more delay elements.

35. The system of claim 25, said signal detection module including at least one resistor and at least one capacitor.

36. The system of claim 25, said signal detection module including a delay element, the delay element configured for initiating at least a portion of said imbalance between said collected signals at the inputs of said detection amplifier.

37. The system of claim 36, said delay element comprising at least one resistor and at least one capacitor.

38. The system of claim 25, said pair of detection electrodes having different impedance values, the impedance difference suitable to maintain an imbalance potential at the inputs of said detection amplifier when contact integrity is maintained between a patient's skin and said group of electrodes.

39. The system of claim 38, a first detection electrode among said pair of detection

40. The system of claim 25, said group of electrodes being part of an electrode assembly, the electrode assembly configured for asymmetric placement of said common electrode with respect to said pair of detection electrodes.

41. The system of claim 25, said group of electrodes being part of an electrode assembly, the electrode assembly configured for symmetric placement of said common electrode with respect to said pair of detection electrodes.