Medical Electromyography System

Abstract

The surface electromyography system comprises a plurality of sensors for detecting electrical activity of muscles and an output unit connectable to the plurality of sensors, the output unit operable to provide an output representative of an output of each of the plurality of sensors, each sensor of the plurality of sensors including an electrode pair and operable to provide an output representative of a potential difference between the electrodes.

Description

[Technical field]

[0001] The technology described herein relates to medical electromyography systems, and in particular to surface electromyography systems. [Background technology]

[0002] Electromyography (EMG) is a diagnostic technique that measures muscle activity by detecting electrical activity in skeletal muscles. This electrical activity can be analyzed to detect medical abnormalities. There are two types of EMG: intramuscular EMG and surface EMG (sEMG). In intramuscular EMG, electrodes are inserted into the muscle to detect electrical activity in the muscle. In contrast, surface EMG detects muscle activity through the surface of the skin overlying the muscle.

[0003] Surface EMG is limited in that detection of electrical activity is restricted to superficial muscles and measurements are affected by the depth of the subcutaneous tissue at the recording site. Furthermore, surface EMG cannot reliably distinguish discharges from adjacent muscles.

[0004] Despite these limitations, surface EMG is less invasive than intramuscular EMG and can therefore be useful in rehabilitation and medical research. For example, previous studies have shown that measuring abdominal activity with surface EMG may be useful in detecting peritonitis. Summary of the Invention [Problem to be solved by the invention]

[0005] Accordingly, applicants have recognized that there is a need for improvements in the design and use of electromyography, and particularly surface electromyography, systems. [Means for solving the problem]

[0006] According to a first aspect of the technology described herein, there is provided a medical surface electromyography system, the system including a plurality of sensors for detecting electrical activity of muscles, and an output unit connected to the plurality of sensors. Each sensor has an electrode pair and is operable to provide an output indicative of a potential difference between the electrode pair, and the output unit is operable to provide an output indicative of an output value of each of the plurality of sensors.

[0007] The technology described herein also extends to performing a test using the system of the technology described herein to measure muscle electrical activity over an area on the surface of the skin of a subject.Accordingly, according to a second aspect of the technology described herein, there is provided a method of measuring muscle electrical activity over an area on the surface of the skin of a subject using the system of the technology described herein, the method comprising attaching a plurality of sensors to the skin of a subject such that the pairs of electrodes are in contact with the skin of the subject, detecting a potential difference between the pairs of electrodes, and providing an output indicative of the detected potential difference between the pairs of electrodes.

[0008] The technology described herein further extends to the use of a system or method of the technology described herein for measuring muscle electrical activity over an area on the surface of a subject's skin. Thus, a third aspect of the technology described herein includes the use of a surface electromyography system of the technology described herein for measuring muscle electrical activity over an area on the surface of a subject's skin. Effect of the Invention

[0009] The technology described herein provides methods and devices for detecting and analyzing electrical muscle signals that are medically useful and can be used as an aid to making medical diagnoses. For example, the devices can be used to detect electrical activity in abdominal muscles to aid in the diagnosis of peritonitis.

[0010] In contrast to existing EMG systems, the techniques described herein allow for the use of multiple sensors to simultaneously detect electrical activity in multiple different regions.

[0011] The present application has recognized that the use of multiple sensors simultaneously to detect muscle electrical activity provides several advantages over existing electromyography systems and methods. For example, many electromyography-based diagnostic procedures require measurements to be taken from multiple different sites. Existing systems require a single sensor to be repositioned several times during the course of each evaluation. This need for sensor repositioning can result in measurement errors, for example, because signal quality can be compromised by patient movement during the repositioning process. Additionally, by allowing measurements of electrical activity in each region to be taken simultaneously, the techniques described herein allow measurements in each region to be compared directly to one another in real time. This can be useful, for example, in detecting improper or suboptimal placement of one or more sensors. The use of multiple sensors simultaneously provides yet another advantage related to increased measurement accuracy. For example, the likelihood of false positive or false negative results is reduced by the use of additional sensors.

[0012] In one embodiment, the system includes four sensors. However, the system can include more than one sensor, including but not limited to 2, 3, 4, 5 or more sensors. The number of sensors can be selected based on the requirements of a particular electromyography test.

[0013] As described above, the system allows for the simultaneous detection of electrical activity in multiple different regions using multiple sensors, the sensors of which are physically spaced apart from one another such that the location of any sensor of the multiple sensors does not physically depend on (affect) the location of any other sensor of the multiple sensors. Thus, the multiple sensors can be independently (simultaneously) placed at different locations on the skin of a subject (patient).

[0014] In one embodiment, the multiple sensors can be positioned such that at least one sensor of the multiple sensors is positioned to measure electrical activity of the subject's external oblique muscle, and at least one (other) sensor of the multiple sensors is simultaneously positioned to measure electrical activity of the subject's internal oblique muscle.

[0015] In one embodiment, multiple sensors of the plurality of sensors can be positioned (simultaneously) at different locations on the subject's abdomen. In one embodiment, the plurality of sensors includes four sensors that can be positioned (simultaneously) on different quadrants of the subject's abdomen. In one embodiment, multiple sensors of the plurality of sensors can be positioned such that (different) sensors are positioned to simultaneously measure electrical activity in each of the subject's left external oblique, right external oblique, left internal oblique, and right internal oblique muscles.

[0016] Each of the plurality of sensors has an electrode pair configured to detect an electrical potential between the electrodes when placed on the skin of a subject. The electrode pair is arranged in a single differential (SD) configuration in one embodiment. The electrodes of the electrode pair are separated by an inter-electrode distance (IED), which is the distance between the centers of the two electrodes. In one embodiment, the IED of each of the plurality of electrode pairs is between 3 mm and 50 mm, and in one embodiment, between 3 mm and 40 mm, between 3 mm and 20 mm, or between 3 mm and 5 mm. Applicant has found that an IED in this range provides a sensor suitable for detecting signals related to surface electromyography. Alternatively, a separation distance greater than 50 mm can be used, or, for example, between 15 mm and 40 mm, 15 mm and 30 mm, or 15 mm and 25 mm. In one embodiment, an inter-electrode distance (IED) of 24 mm is used. For example, IEDs larger than 50 mm may be suitable for use in subjects with a large amount of subcutaneous tissue at the sensing location.

[0017] The applicant has recognized that the quality of the sEMG signal is highly dependent on the IED, since the larger the IED, the greater the degree of distortion of the sEMG signal. In general, an IED greater than 10 mm (or less than 1 / 4 of the total length of the muscle fibers of the muscle being evaluated) will cause distortion of the sEMG signal. However, as the muscle depth increases, the amplitude of the sEMG at the skin decreases. That is, the amplitude of the sEMG signal is affected, for example, by the depth of the subcutaneous tissue at the site where the sensor is placed. The depth of the subcutaneous tissue varies greatly depending on the patient's weight (or body mass index, "BMI"). For example, the higher the weight (or BMI), the weaker the signal may be. The applicant has recognized that the amplitude of the sEMG signal can be increased by increasing the IED, but at the cost of increased interference from adjacent muscles, increased risk of crosstalk, and potentially impaired spectral content of the sEMG signal.

[0018] The sensor may be configured to have a (permanently) unchanging IED. However, in one embodiment, the IED of the sensor may be changed. In one embodiment, the IED may be adjusted to any length between 3mm and 50mm, 3mm and 40mm, 3mm and 20mm, or 3mm and 5mm. For example, the sensor may have movable electrodes such that the IED of the electrode pair is variable. The electrode position may be fixed in one embodiment, allowing the electrodes to be securely positioned and thereby maintaining a fixed IED when the sensor is in use. Alternatively, the electrode position may be fixed (non-movable), but the electrodes may be removable and replaced with electrodes of different sizes (and therefore with different IEDs). Thus, in embodiments, the sensors are configured to accommodate electrodes of various (different) sizes (allowing the IED of the electrodes to be adjusted by attaching pairs of electrodes of different sizes to the sensor).

[0019] In some embodiments, the electrode pairs are removable from the sensor. In such embodiments, some sensors are configured to accommodate multiple electrode pairs. In such embodiments, electrode pairs of a desired size and / or having a desired IED can be attached to the sensor as needed (and, for sensors that allow the location of the electrodes to be moved, moved to a desired location).

[0020] Thus, in one embodiment, the surface electromyography system of the technology described herein is a complete device comprising: a plurality of sensors for detecting muscle electrical activity, each sensor of the plurality of sensors operable to accommodate an electrode pair, each sensor of the plurality of sensors operable to provide an output indicative of a potential difference between an electrode pair when attached to the sensor; and an output unit connectable to the plurality of sensors, the output unit operable to provide an output indicative of an output of each of the plurality of sensors; and The apparatus includes a plurality of electrodes configured for mounting within the plurality of sensors, optionally including a plurality of different sized electrodes.

[0021] Similarly, in one embodiment, a method for measuring electrical activity across an area of ​​a subject's skin surface using a system according to the technology described herein includes the following steps. providing an electrode pair within each sensor of the plurality of sensors; attaching the plurality of sensors to the subject's skin such that a plurality of the electrode pairs contact the subject's skin; Detecting a potential difference between a plurality of said electrode pairs. Providing an output indicative of the potential difference detected by each of a plurality of said electrode pairs.

[0022] The electrode pairs may be provided, for example, on (as part of) an electrode pad that is mountable within (and removable from) the sensor housing. Each electrode pair may be provided on (a single) electrode pad. Alternatively, each electrode may be provided on a respective electrode pad (such that each electrode pair is provided as a pair on one electrode pad). The electrode pad in one embodiment further comprises one or more connectors for forming a connection to the sensor. The connector(s) may (each) include electrical contacts (e.g., snap connectors, etc.), conductive adhesive, or any other suitable connector. The electrode pad may be a disposable, single-use pad. In one embodiment, the electrode pairs of the sensors are spaced apart by the same IED (when in use). In other embodiments, some or all of the sensors have different IEDs. For example, the system may include four sensors, two of which have 15 mm IEDs and two of which have 21 mm IEDs. In a second example, all of the sensors may have personalized (and therefore likely different) IEDs based on factors such as muscle depth at a particular site. It can be seen that the optimal IED for each sensor may vary from patient to patient, or from test to test for the same patient, or all sensors may have the same IED.

[0023] In one embodiment, the system automatically records the parameters used for each test. For example, the system can record the IED interval (or electrode pair selection) for each sensor. Alternatively, the system may include a means to manually record test parameters such as IED interval.

[0024] In one embodiment, the electrodes of the electrode pair have a maximum dimension between 1 mm and 20 mm, between 1 mm and 15 mm, between 1 mm and 10 mm, or between 1 mm and 5 mm. For example, the electrodes may be circular electrodes having a diameter between 1 mm and 20 mm, in one embodiment between 1 mm and 15 mm, or square electrodes with side lengths within this range. In one embodiment, circular electrodes with a diameter of 18 mm are used. The IEDs are large enough that there is a gap of at least 0.5 mm or 1 mm between the electrodes of the electrode pair in one embodiment. In some embodiments, there is a gap of at least 3 mm, or at least 4 mm, or at least 5 mm between the electrodes. In some embodiments, the ratio of the IED to the maximum dimension of the electrode ranges between 2:1 and 5:1, such as in embodiments of 3:1 or 4:1. Applicants recognize that the spectral characteristics of the sEMG signal are affected by the size of the electrodes. For example, the larger the diameter of the circular electrodes, the more attenuated the high frequency components of the sEMG signal. This is believed to be because the conductive area of ​​the electrode averages the voltage distribution underneath the electrode, producing a smoothed version of the actual spatial potential distribution. As a result, the electrode forms a low pass filter whose cutoff frequency decreases as the surface area increases. However, the tradeoff for decreasing surface area is increased skin surface impedance and increased noise. With the IEDs of each electrode pair falling within any of the ranges mentioned above, in one embodiment it has been found that a ratio of IED to maximum electrode dimension between 2:1 and 5:1 provides a good balance between these various considerations.

[0025] The electrodes are Ag / AgCl electrodes in one embodiment. Ag / AgCl electrodes provide an output with a relatively low level of noise due to their low electrode-skin impedance. However, other suitable electrode materials may be used. In embodiments where the electrode pairs are provided on (or as part of) an electrode pad, each electrode may also include (or be a layer within) the electrode pad (e.g., an Ag / AgCl layer). The sensor is in one embodiment suitable for use in a surface electromyography system, i.e., for detecting electrical potentials on the surface of the subject's skin. Thus, each sensor in one embodiment includes a means for fastening the sensor to the patient's skin, e.g., an adhesive pad or layer.

[0026] In embodiments in which multiple electrode pairs are provided on multiple electrode pads (e.g., as Ag / AgCl conductive layers on the electrode pads), each electrode pad may include an adhesive layer and / or a conductive gel layer that contacts the subject's skin during use and assists in adhering the sensor to the subject's skin.

[0027] In one embodiment, the sensor is adhered to the subject's skin (only) by a conductive gel or adhesive layer applied to and / or around the electrodes (e.g., as part of an electrode pad) (so as not to require a separate adhesive to connect the sensor body to the subject). Alternatively, other suitable and desirable means for securing the sensor to the patient's skin may be provided, such as an adhesive pad associated with the sensor.

[0028] When secured to the subject, the electrode pair of the sensor contacts the patient's skin.

[0029] In one embodiment, the sensor includes a conductive material to reduce the impedance of the contact between the electrodes and the skin (at least during use). For example, a conductive gel can be applied on and / or around the electrodes (e.g., as a conductive gel layer of an electrode pad). Alternatively or additionally, an adhesive applied on and / or around the electrodes (e.g., as an adhesive layer of an electrode pad) can be a conductive adhesive. In one embodiment, each sensor comprises an electrode pad with an adhesive pad / layer and an electrode pair, e.g., an electrode pair protruding from a surface of the adhesive pad / layer.

[0030] The sensors can be coupled to an output unit, which in one embodiment is a wired connection, i.e. by a connecting cable, but may alternatively be a wireless connection, such as Bluetooth. In one embodiment, each sensor can be individually coupled to the output unit, e.g. by a corresponding wired or wireless connection.

[0031] The (each) sensor in one embodiment includes a means for connecting the sensor to an output unit, such as a cableless tip or a plug for connecting a cable (such as a cable-to-board connector for connecting a cable to the sensor's Printed Circuit Board (PCB)). This connection means, in one embodiment, is on the opposite side to the electrodes on the sensor so that it remains accessible during use of the sensor. Cableless sensors may further include a power source, such as a battery, while wired sensors may receive power from the output unit.

[0032] In one embodiment, the system processes the sEMG signal detected by the electrodes of the sensor. For example, the system may amplify and / or filter the sEMG signal to reduce signal noise and / or reduce unwanted frequency components of the sEMG signal. Each processing step may be performed by hardware or software, or a combination of hardware and software. For example, the system may include hardware components configured to amplify and filter the sEMG signal, and may further include software configured to perform additional filtering steps. The processing may be performed between the sensor and the output unit, or in the sensor and the output unit. For example, some or all of the processing may be performed in the sensor, which outputs the processed sEMG signal to the output unit. In one embodiment, each sensor has processing circuit(s) and / or processing means (processor(s)) operable (configured) to perform processing of the sEMG signal detected by the electrodes. In one embodiment, the processing circuit(s) and / or processing means of the (each) sensor are integrated with the sensor's Printed Circuit Board (PCB). Alternatively (or additionally), some or all of the processing may be performed after the sEMG signal is output from the sensor, for example by components included in the output unit.

[0033] Thus, in one embodiment, the system includes one or more amplifiers for amplifying the sEMG signals detected by the electrode pairs of the sensor.

[0034] In one embodiment, the total gain of the sEMG signal from each sensor is at least 1000, but this gain can vary depending on the expected output amplitude from the sensors. The input range of a typical digitizer, such as an A / D converter, is approximately ±5V. Therefore, the total gain can be selected to amplify the expected signal strength (typically about 0.1 μV to 2 mV for EMG signals) to within this input range.

[0035] The one or more amplifiers in an embodiment include one or more front-end amplifiers for amplifying the sEMG signal, which in one embodiment are differential amplifiers having an input impedance of at least 100 MΩ.

[0036] In one embodiment, the front-end amplifier applies only a moderate gain (e.g., a gain of about 100). Advantageously, this small gain helps to avoid oversaturation. To obtain sufficient total gain, additional amplifiers can be added, as described above. In one embodiment, a first (front-end) amplifier amplifies the sEMG signal, and a second (additional) amplifier amplifies the output of the first amplifier after the signal has been filtered (as described below). In one example, the first amplifier can have a gain of 100 and the second amplifier can have a gain of 101, resulting in a total gain of 10100.

[0037] In one embodiment, the sEMG signals of the sensors are individually amplified. For example, the system may include separate first and second amplifiers for each of the sensors. Alternatively, one or more amplifiers may be configured to amplify the output of all or some of the sensors. For example, the system may include a single first amplifier and a single second amplifier configured to amplify the output from all of the sensors. Alternatively, the system may include a separate first amplifier for each sensor and a single second amplifier configured to amplify the output from all of the first amplifiers.

[0038] The detected sEMG signal is, in one embodiment, processed to remove unwanted frequencies and noise. This is particularly beneficial when examining muscles that typically produce small sEMG signals, since the system noise may be within the same order of magnitude as the sEMG signal. For example, in one embodiment of the technology described herein, measurements of abdominal muscles typically produce an average rectified signal of about 5 μV to about 10 μV during deep breathing movements, while the noise for these measurements may be between about 1 μV to about 3 μV.

[0039] Thus, in one embodiment, the system includes one or more filters configured to attenuate unwanted frequencies of the sEMG signals detected by the electrode pairs of the sensors. Again, in one embodiment, the sEMG signals of the sensors are individually filtered. For example, the system can have individual low-pass and high-pass frequency filters for each of the sensors. The one or more filters may alternatively or additionally include one or more filters configured to filter the output of all or some of the sensors. For example, the system may include a notch filter configured to filter the output signals from the sensors.

[0040] In one embodiment, the one or more filters comprise a low pass filter based on the frequency of the highest associated muscle harmonic, and in one embodiment, a low pass filter having a cutoff frequency at the frequency of the highest associated muscle harmonic, in one embodiment, the low pass filter has a cutoff frequency in the range of about 400 Hz to about 450 Hz.

[0041] In one embodiment, the one or more filters comprise a high-pass filter having a cutoff frequency between about 10 Hz and about 20 Hz. For example, the high-pass filter has a cutoff frequency of 16 Hz. For example, noise due to motion artifacts and electrode sliding is typically in the relatively low frequency range. Thus, in one embodiment, the high-pass filter removes or reduces low frequency signals to reduce the effects of these noise sources.

[0042] Both the low pass filter and the high pass filter are second order or higher filters in one embodiment.

[0043] In one embodiment, the one or more filters include one or more notch filters. At least one of the notch filters may be centered on the power line frequency (typically 50 Hz or 60 Hz, depending on the region) to reduce power line interference (PLI) in the detected signal. The system may also include a notch filter centered on the power line frequency and additional notch filters centered on harmonics of the power line frequency. For example, in one embodiment, the system is configured with notch filters centered at 50 Hz, 100 Hz, 150 Hz, 200 Hz, 250 Hz, 300 Hz, and 350 Hz. It will be appreciated that in regions with power line frequencies other than 50 Hz, different frequencies may apply.

[0044] Instead of or in addition to notch filters, other techniques can be used to reduce PLI, such as spectral interpolation or Driven-Right-Leg (DRL) circuits.

[0045] In one embodiment, the system includes a DRL circuit for inverting the common mode voltage of the system. In one embodiment, a reference electrode is used to feed back the inverted common mode voltage to the multiple sensors, e.g., the reference electrode is attached to the skin of the subject. In one embodiment, a single reference electrode may provide feedback to all sensors and be attached to the subject away from the area being tested. For example, if the sensors are detecting electrical activity of abdominal muscles, the reference electrode may be connected to the subject's arm. Beneficially, by inverting the common mode voltage of the system, the DRL circuit also inverts the common mode voltage injected from hardware components such as amplifiers and filters. For example, in a system that includes a front-end amplifier, the DRL circuit also reduces interference from the common mode voltage originating from the amplifier.

[0046] In one embodiment, the system further comprises an isolation device for isolating the sensor from devices powered from the power grid (eg, output devices), thereby protecting the circuitry, the user, and the subject.

[0047] In one embodiment, the sEMG signal is further processed to reduce artifacts and interference, for example from the ElectroCardioGram (ECG) signal, which in an embodiment is done using wavelet filtering techniques.

[0048] In one embodiment, the wavelet filtering utilizes Dauechies4 (DB4) wavelets and involves applying a threshold detail coefficient at levels 4, 5, 6 and 7 of the wavelet decomposition. The threshold is determined in one embodiment using the maximum amplitude of the relaxation signal from the muscles since the relaxation signal contains ECG artifacts without interference from the muscles. The relaxation signal is decomposed to determine separate thresholds for each of levels 4, 5, 6 and 7. In one embodiment, the threshold is set 10% above the maximum amplitude of the reference decomposition and all detail coefficients below the threshold at that particular level are zeroed out. In this way, ECG artifacts are reduced while large signal components in the same frequency band due to muscle activity, etc. are not significantly affected.

[0049] To further reduce noise in the sEMG signal, in one embodiment, the detail coefficients of levels 1 and 2 of the wavelet decomposition are zeroed out. These detail coefficients typically contain high frequency bandwidth components above about 450 Hz. Thus, wavelet filtering is beneficial as it also reduces undesired high frequency signals remaining above the cutoff frequency of the low pass filter.

[0050] As discussed above, each processing step may be performed via hardware components or software. For example, each of the one or more filters may be a hardware filter or a software filter. In one embodiment, the system includes both analog hardware filters and digital software filters with the same or nearly the same cutoff frequency to improve signal quality and reduce noise.

[0051] In one embodiment, the system includes both hardware and software processing steps. For example, the processing steps may include a set of hardware processing steps before digitization of the signal and a set of software processing steps after digitization of the signal. The hardware steps may include any one or more of a first amplification stage, low pass filtering, high pass filtering, a second amplification stage, and / or use of a DRL circuit to invert the common mode voltage. The software processing steps may include any one or more of a low pass filter, a high pass filter, a notch filter, and / or wavelet filtering.

[0052] In one embodiment, one or more of the sensors (in one embodiment, each sensor) are configured to perform analog processing (e.g., hardware processing) of the sEMG signal from the corresponding electrode pair, including one or more (in one embodiment, multiple, in one embodiment, all) of a first amplification stage, low-pass filtering, high-pass filtering, a second amplification stage, and / or using a DRL circuit to invert the common-mode voltage (e.g., as described above). In one embodiment, one or more of the sensors (in one embodiment, each sensor) are (also) configured to perform analog-to-digital conversion (ADC) of the (processed) sEMG signal to generate a corresponding digital (digitized) signal, and in one embodiment, configured to transmit the digital signal to an output unit. In such an embodiment, the output unit may be configured to receive the digital signal and perform further processing (e.g., software processing) of the digital signal, such as applying one or more (in one embodiment, multiple, in one embodiment, all) of a low-pass filter, a high-pass filter, a notch filter, and / or wavelet filtering, as described above.

[0053] As discussed above, because the sEMG signals resulting from abdominal muscle activity that are measured for purposes of detecting peritonitis may have small amplitudes, on the order of μV, Applicant recognizes that it is important to mitigate noise and other artifacts that may affect the sEMG signal. In this regard, Applicant recognizes that providing analog signal processing as part of the sensor and close to the patient helps to avoid introducing noise and artifacts into the sEMG signal.

[0054] Furthermore, by providing an analog-to-digital conversion function as part of the sensor, the digital signal can be transmitted to the output unit via a suitable connection, such as Wi-Fi, Bluetooth, or a wired connection. In one embodiment, the connection is a wired connection between each sensor and the output unit, through which the sensor also receives power. In one embodiment, the wired connection (cable) is unshielded. In this regard, the applicant recognizes that the transmission of digital signals can use relatively thin and flexible unshielded cables (compared to the transmission of analog signals, which require thick shielded cables to avoid noise and artifacts), making the sensor system less bulky and easier to use. In one embodiment, the system further comprises a digitizer for converting the voltage detected by each sensor into a digital signal. The potential detected by the electrodes of the sensor is generally an analog signal, and therefore it is beneficial to convert it into a digital signal, for example to aid in processing by software. The digitizer can be any suitable digitizer operable to digitize (convert) multiple analog signals received from multiple sensors into a single digital signal, such as an A / D converter. As mentioned above, each sensor may include a digitizer for digitizing the sEMG signal from its electrode pair. As mentioned above, a typical digitizer has an input range of approximately ±5V. Thus, the total gain from the amplification stages in the system (e.g., in the sensor) may be selected to amplify the expected signal strength (typically approximately 0.1 μV to 2 mV for sEMG signals) to within this input range.

[0055] In one embodiment, the system has a sampling frequency of at least 1000 Hz, and in one embodiment, 2048 Hz or thereabouts. To avoid aliasing, and in accordance with the Nyquist sampling theorem, the minimum sampling frequency of the digitizer should be greater than twice the maximum frequency of the signal. Thus, a digitizer sampling frequency of 1000 Hz is approximately sufficient for most sEMG applications.

[0056] The system comprises an output unit coupleable (connected) to a plurality of sensors. The output unit is operable to receive detected signals from the sensors and provide an output indicative of the detected sEMG signal. For example, the output may be a processed signal detected by the sensor. Alternatively, the output may be a numerical value representing the average or maximum amplitude of the sEMG signal, or any other suitable method of providing an indication of the amplitude of the sEMG signal.

[0057] The output unit can provide a superimposed or combined output of the signals received from each sensor, but in one embodiment provides an output for each sensor that can be displayed separately, e.g., side-by-side. In one embodiment, the output unit simultaneously outputs results indicative of the electrical potentials detected by each of the sensors, such that the detected sEMG signals can be directly compared to one another during testing. This comparison can be performed by software (e.g., mathematical analysis) or by a user (e.g., visual comparison).

[0058] In one embodiment, the signals from the sensors are synchronized such that sEMG signals detected by different sensors at the same time are aligned to the same (e.g., global) time. In one embodiment, a global time (global clock) is maintained (e.g., by the output unit) to which the sEMG signals from the sensors are synchronized. Applicant recognizes that such synchronization allows direct comparison of signals from different sensors and allows comparison of muscle responses (e.g., abdominal guarding in response to a trigger such as a cough or applied pressure) between different sensors at different abdominal locations on a patient. Applicant recognizes that such synchronization can be performed particularly reliably in an arrangement in which each sensor has its own circuitry for performing signal processing (thus forming a distributed processing system).

[0059] Thus, in embodiments where the sensors are configured to perform sEMG signal processing (as described above), each sensor in one embodiment has a local time (local clock). In such embodiments, the local time (local clock) of the sensor is synchronized to the global time (global clock) in one embodiment by periodically sending a synchronization signal (e.g., from the output unit) to each (all) of the sensors. In one embodiment, during each sEMG measurement, each sensor outputs (uses) its local clock, and the local clock is updated (in response to the synchronization signal) between sEMG measurements. In one embodiment, the sensor's local clock is updated between different measurements of the same patient and / or between measurements of different patients. That is, each sensor outputs its local clock during the sEMG signal measurement (acquisition of the sEMG signal).

[0060] The output unit in one embodiment has a display for displaying the output result, or the output unit may send the output result to an external display device, which can be any suitable display, such as a monitor, a television, a mobile device, or a dedicated display system.

[0061] In one embodiment, software for processing, for example, the sEMG signal is provided by the output unit.

[0062] In one embodiment, the output unit comprises means for controlling the sensors and / or the processing steps. For example, the output unit may comprise a touch screen, buttons, dials, or any other suitable control means. In this embodiment, the output unit or control unit may assist the user in activating / deactivating selected sensors, configuring the processing of the sEMG signal, and / or configuring the properties of the output results.

[0063] Some diagnostic techniques involve assessing muscle responses to applied pressure (or other stimuli, such as those elicited by coughing or other means of stimulation). For example, a patient with peritonitis may exhibit an involuntary muscle reaction (abdominal guarding) in the abdominal wall in response to stimulation of the abdominal wall. Abdominal guarding may be detected by a physician placing a hand on the patient's abdomen, but an experienced physician is required, as the muscle movements are very small and difficult to feel.

[0064] Thus, in one embodiment, the system is configured to detect stimulation of the subject (stimulus applied to the subject, in one embodiment, force (pressure) applied to the subject) during use of the system. In one embodiment, the system is configured to display (output indicative of) the amplitude (magnitude) and / or timing of the (applied) stimulation (e.g., force). In embodiments, the system is configured to indicate (detect) at least one (in one embodiment, more than one, in one embodiment, all) of the following: the time when the stimulation (e.g., force (pressure)) was applied (started) to the subject during use of the system, the time when the stimulation (e.g., force (pressure)) was released (removed) (stopped) from the subject during use of the system, and the amount (magnitude) of the stimulation (e.g., force (pressure)) applied to the subject during use of the system.

[0065] In one embodiment, the system comprises one or more force sensors (pressure sensors) for measuring the force (pressure) applied to the subject. In one embodiment, the one or more force sensors are coupleable to one or more of the multiple sensors, and thus capable of measuring the pressure applied to the sensor. In one embodiment, one or more of the sensors (in one embodiment, multiple sensors, in one embodiment, each sensor) are coupled to (include) the force sensor. In one embodiment, the force sensor is integrated into at least one of the multiple sensors (in one embodiment, multiple sensors, in one embodiment, all sensors) and measures the pressure applied to the (respective) sensor (and thus applied to the subject via the sensor). Thus, in one embodiment, each sensor of the multiple sensors has a respective (integrated) force sensor.

[0066] Any suitable and desired force sensor may be used. In one embodiment, the (each) force sensor comprises a load cell. Alternatively, the force sensor(s) may comprise any suitable and desired piezoresistive or piezoelectric sensor(s).

[0067] In this regard, Applicant has recognized that providing a (each) sensor with a force sensor has the advantage that the location, timing, and amplitude of the applied force can be more reliably identified (e.g., compared to applying a force to an arbitrary, unknown, location on the patient). Furthermore, providing multiple sensors with respective force sensors allows for the application of forces to multiple locations on a single patient (e.g., sequentially) without the need to move the sensors. This allows for comparison of muscle responses at different locations.

[0068] Thus, in one aspect of the technology described herein, there is provided a plurality of sensors for use in a surface electromyography system for detecting electrical activity of a muscle, each sensor of the plurality of sensors configured to house a respective electrode pair and configured to receive signals from the respective electrode pair when attached to the sensor; each sensor of the plurality of sensors having a respective force detector, each sensor being configured to receive a force signal from its respective force detector simultaneously with receiving a signal from its one electrode pair; Each sensor of the plurality of sensors is configured to output a signal indicative of the signal received from a respective one of the electrode pairs and the force sensor.

[0069] In some embodiments, the force sensor comprises a force sensitive button located on the top surface (when in use) of the sensor unit. In one embodiment, the force sensitive button comprises a button engageable with a force detector. In one embodiment, the force detector comprises a load cell. Applicants have recognized that such an arrangement of force sensors can provide a robust and reliable arrangement that responds relatively quickly to the application and removal of pressure. Alternatively, other types of force sensors can be used, for example other piezoresistive force sensors or piezoelectric sensors.

[0070] In some embodiments (such as those in which the force sensor is integrated into the system's sensor), the sensor (sensor unit) is configured to resist deformation in response to an applied force (regardless of the movement of the button in response to the applied force). In this regard, applicant recognizes that deformation or movement of the internal components of the sensor may adversely affect the quality of the sEMG signal. In some embodiments, the sensor (sensor unit) is rigid, and in one embodiment, has a hard housing (in which the force detector and other processing circuitry of the sensor are housed). In one embodiment, the housing of the sensor unit is constructed of a sturdy, non-conductive material, such as plastic.

[0071] In this regard, each sensor can be provided with a non-conductive housing to reduce electrical interference from a user touching the sensor to apply force. The sensor (or component, such as a PCB) can also be electrically shielded if desired.

[0072] In one embodiment (such as an embodiment where a force sensor is integrated into the system's sensor), the sensor (sensor unit) is configured (constructed) to mitigate the effect of pressure on the sEMG signal acquired by the electrodes. In this regard, the applicant recognizes that deformation of the electrodes (e.g., due to the application of pressure) may impair sEMG signal quality. Thus, in one embodiment, the sensor (sensor unit, e.g., the housing of the sensor unit) comprises one or more electrodes (electrode pad(s)) configured to accommodate at least a portion of the electrode pair (electrode pad(s)) such that the electrode pair (electrode pad(s)) is substantially flat (skin contact surface). The electrode may have a number of recesses, which may help reduce deformation forces on the electrode when pressure is applied to the sensor (sensor unit). In one embodiment, the one or more recesses are configured to contain at least a portion of an electrode (electrode pad) that forms an electrical connection with the sensor (sensor unit) (e.g., a protruding connector or a mating electrical connector, etc.).

[0073] In some embodiments, a single recess is provided in the sensor (sensor unit) to accommodate one electrode pair (e.g., as a single electrode pad or pair of electrode pads), or a pair of recesses (to accommodate each electrode (electrode pad)) or other configurations of recesses may be provided.

[0074] In some embodiments, the recess(es) of the (each) sensor are configured (dimensioned) such that an electrode pair fits (laterally) within the recess(es). In some embodiments, an electrode pair is substantially completely contained within the recess(es) such that the skin contacting surfaces of the electrodes are substantially flush with the sensor unit (do not protrude beyond the sensor unit). Thus, in some embodiments, the recess(es) of the sensor (sensor unit) substantially shields the electrodes from compressive forces applied to the sensor (sensor unit). In such embodiments, the electrodes can be in contact with the skin when the sensor unit is placed on the subject's skin without being compressed.

[0075] In embodiments where electrode pad(s) are used, the electrode pad(s) and the recess(es) can be dimensioned such that the electrode pad(s) extend (laterally) beyond the recess(es) and are supported (rest against) the bottom surface of the sensor (sensor unit) (but the electrodes in one embodiment can fit within the recess(es) because they are smaller than the overall size of the electrode pad). In one embodiment, the electrode pad(s) do not extend (laterally) beyond the bottom surface of the sensor (do not extend beyond the footprint of the sensor). This allows pressure to be applied uniformly across the electrode pad(s). Alternatively, the electrode pad(s) can extend (laterally) beyond the bottom surface of the sensor.

[0076] Thus, providing one or more recesses can help prevent pressure on the electrodes (electrode pads) that may affect the quality of the sEMG signal provided by the electrodes. In embodiments where an electrode pair (electrode pad(s)) includes (or is provided in combination with) a conductive gel, the one or more recesses can also help prevent uneven pressure on the conductive gel, which may otherwise cause gel to migrate or leak, which may affect the quality of the sEMG signal. In one embodiment, the one or more recesses are configured such that the conductive gel (and electrode) (both) is (both) laterally contained within the one or more recesses, and in one embodiment, the conductive gel (and electrode) (both) is (are) substantially completely contained within the one or more recesses. To (further) reduce the likelihood (extent) of gel migration or leakage, a relatively high viscosity conductive gel can be used, and in some embodiments, such a gel is used.

[0077] In an alternative embodiment, a flat electrical connection can be provided between the sensor (sensor unit) and one electrode pair (electrode pad(s)), in which case one or more recesses can be eliminated (the bottom surface of the sensor (sensor unit) that houses one electrode pair is substantially flat).

[0078] In one embodiment, a feedback system (as part of the force sensor or pressure sensor) is provided to indicate when an appropriate level of pressure has been applied. For example, the feedback system (force sensor) can monitor the applied pressure and compare it to a threshold pressure. When the applied pressure exceeds the threshold, the feedback system (force sensor) can provide feedback, e.g., one or more (or all) of visual feedback, audio feedback, and haptic feedback. In one embodiment, visual feedback, such as one or more lights, is provided to indicate that the correct pressure is being applied. The visual feedback (e.g., one or more lights) can be provided by a sensor unit that includes the force sensor as part of it. Alternatively, the visual feedback can be provided by the output unit, such as on a display of the output unit. Alternatively, the feedback system (force sensor) can compare the applied pressure to a desired pressure range and provide different indications depending on whether the applied pressure is below, above, or within this desired range.

[0079] In one embodiment, the results output by the output unit provide an indication of the time when pressure was applied and / or released. For example, if the output of the output unit includes a processed sEMG signal (e.g., with respect to time), the display may also include a dashed line for the time when pressure was applied and / or released. In another example, the signal line may change color based on the detected force, or the output may additionally include a graph of applied force versus time (wherein the graph of applied force may be displayed separately from one or more graphs of the sEMG signal, or may be overlaid on the graph for the sEMG signal).

[0080] The system of this embodiment is suitable for measuring potentials as low as 1 μV. The potential measured by the electrode pair is the sum of the action potentials generated during muscle contraction. The amplitude of the sEMG signal is typically in the range of 0.1 μV to 2 mV, depending on both the muscle and the contraction strength. For example, in one embodiment of the technology described herein, the average rectified value of a relaxed scalene muscle signal is typically in the range of 0.5 μV to 2 μV, while the signal during tension is in the range of 25 μV to 175 μV. It is therefore beneficial to provide a system with a sensitivity for potentials as low as 0.1 μV. However, measurement noise is typically expected to be in the range of 1 to 3 μV. As a result, in one embodiment, the system has a sensitivity of, for example, 1 μV, 3 μV, 5 μV or 10 μV, which helps distinguish the detected signal from noise.

[0081] The EMG system, in one embodiment, is a surface EMG system suitable for use in aiding in the diagnosis of muscle conditions. For example, the system may be used to aid in the detection of involuntary abdominal rigidity, which may indicate that a subject is suffering from peritonitis, etc. The system may also aid in the detection of any other condition that can be detected using EMG.

[0082] In one embodiment, a method of detecting muscle electrical activity using the system of the technology described herein includes attaching a plurality of sensors to the skin of a subject, in one embodiment, between the nerve area and the muscle tendon to reduce crosstalk and other signal distortions. If the system includes a reference electrode, in one embodiment, the reference electrode is also attached. The sensors are, in one embodiment, arranged such that the plurality of electrodes are spaced apart parallel to the direction of the muscle fibers.

[0083] Attaching the sensor to the subject may include applying a conductive gel to the subject or the sensor to improve contact between the electrodes and the skin, and / or applying an adhesive to secure the sensor in place and reduce unwanted movement of the sensor.

[0084] The electrode pair of the sensor then detects the electrical activity of the muscles across the subject's skin. The detected signal is processed as described above in one embodiment. In one embodiment, the processing includes amplifying the sEMG signal with a first amplifier, applying a low pass filter to attenuate signals above a first cutoff frequency (e.g., about 450 Hz), applying a high pass filter to attenuate signals below a second cutoff frequency (e.g., 16 Hz), amplifying the signal with a second amplifier such that the sum of the gains of the first and second amplifiers is at least 1000, and then digitizing the sEMG signal. After digitization, in one embodiment, the signal is further processed in software. The software processing in one embodiment includes applying a second low pass filter and a high pass filter with the same first and second cutoff frequencies, applying a notch filter to the signal centered around the power line frequency, e.g., 50 Hz, to reduce PLI, and finally applying a wavelet filtering technique. The output unit outputs the processed signal, and in one embodiment provides a separate output for each of the multiple sensors.

[0085] In one embodiment, the method includes a series of tests that may include, for example, detecting the potential of a relaxed muscle, detecting the potential of a tense muscle, detecting the residual potential after relaxation of a tense muscle, detecting the potential of a muscle during and after an involuntary movement (stimulus) (such as a cough), detecting the potential of a muscle while the subject consciously takes a deep breath, and / or detecting the potential of a muscle after applying pressure to a part of the subject's body.

[0086] In one embodiment, applying pressure to a portion of the subject's body includes applying pressure using or via one or more force sensors suitable for detecting the applied pressure. The force sensors may be directly attached to the subject's body or may be indirectly attached to the subject's body, for example by connecting the force sensor to one or more of the multiple sensors.

[0087] The detected signals may provide several means to aid in the detection of involuntary abdominal defenses: for example, in patients with peritonitis, abdominal muscle activity is expected to be high at rest, as well as increased residual activity following voluntary and involuntary muscle contractions (which may be stimulated (induced) by, for example, straining and / or coughing and / or applying pressure).

[0088] In one embodiment, a method of using the systems described herein includes determining one or more conditions indicative of a medical condition, such as peritonitis, based on an output indicative of a potential difference detected by any one or more (or all) of the electrode pairs of the one or more sensors.

[0089] In one embodiment, determining one or more conditions indicative of a medical condition (such as peritonitis) includes comparing the output (from one or more, or all, of the sensors) to an expected baseline activity (for a healthy patient), and in one embodiment, detecting a condition when the output significantly deviates from the expected baseline activity. In one embodiment, determining one or more conditions indicative of a medical condition (such as peritonitis) includes comparing the output (from one or more, or all, of the sensors) to one or more thresholds (in one embodiment, muscle activity indicated in the output(s) above a threshold level is indicative of a medical condition such as peritonitis).

[0090] In one embodiment, determining one or more conditions indicative of a medical condition (e.g., peritonitis) includes identifying residual muscle activity after inducing muscle stimulation (e.g., after applying pressure to the patient or inducing a cough from the patient). In one embodiment, residual muscle activity with an amplitude greater than a threshold amplitude and / or duration greater than a threshold duration is determined to be indicative of a medical condition such as peritonitis.

[0091] In one embodiment, the determination of the one or more conditions is made by a user by visually inspecting the output data (e.g., visually inspecting a graph showing the output data from one or more or all of the sensors displayed by the output unit), or alternatively, the determination of the one or more conditions may be performed (at least in part) by the output unit.

[0092] In this regard, the output unit may include a computer configured to perform decisions based on the output data (as described above). The processing performed by the output unit (computer) may be performed using a suitably configured processor.

[0093] The output unit (computer) may be implemented in accordance with a general-purpose or special-purpose computing system. Exemplary computing systems include, but are not limited to, software or other (e.g., hardware) components in personal computing devices, portable (e.g., handheld) or laptop devices, medical computing devices, microprocessor systems, and distributed computing systems (e.g., cloud-based computing systems, etc.). The output unit may include one or more processors and one or more machine-readable memories in communication with the one or more processors. The processor may assist in receiving data from one or more sensors, performing processing of the data, and displaying the data. The memory may store instructions for causing the output unit (and its processor) to perform the desired processing and display of the data. [Brief description of the drawings]

[0094] A number of embodiments of the technology described herein will now be described, by way of example only, and with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of an electromyography system according to one embodiment of the technology described herein. [Diagram 2] 1A and 1B are explanatory diagrams showing the configuration of a sensor electrode according to one embodiment of the technology described in this specification. [Diagram 3] 1A-1C show examples of voltage sensor placement in accordance with one embodiment of the technology described herein. [Figure 4] 4 is a flow chart illustrating example signal processing steps performed in one embodiment of the technology described herein. [Diagram 5] 1 is an example circuit diagram of an sEMG sensor according to one embodiment of the technology described herein. [Figure 6] 1 is a series of output results according to one embodiment of the technology described herein. [Figure 7]1 is a flow chart of a method for measuring electrical activity of a muscle according to one embodiment of the technology described herein. [Figure 8] 1 is an example output according to one embodiment of the technology described herein. [Figure 9] 1 is an example output according to one embodiment of the technology described herein. [Figure 10a] FIG. 1 is a diagram of a sensor according to one embodiment of the technology described herein. [Figure 10b] FIG. 1 is a diagram of a sensor according to one embodiment of the technology described herein. [Figure 10c] FIG. 1 is a diagram of a sensor according to one embodiment of the technology described herein. [Figure 10d] FIG. 1 is a diagram of a sensor according to one embodiment of the technology described herein. [Figure 10e] FIG. 1 is a diagram of a sensor according to one embodiment of the technology described herein. [Figure 10f] FIG. 1 is a diagram of a sensor according to one embodiment of the technology described herein. [Figure 11a] FIG. 1 is a diagram of a sensor according to another embodiment of the technology described herein. [Figure 11b] FIG. 1 is a diagram of a sensor according to another embodiment of the technology described herein. [Figure 11c] FIG. 1 is a diagram of a sensor according to another embodiment of the technology described herein. [Figure 11d] FIG. 1 is a diagram of a sensor according to another embodiment of the technology described herein. [Figure 11e] FIG. 1 is a diagram of a sensor according to another embodiment of the technology described herein. [Figure 12] 1 is an example of an electrode pad that may be used in embodiments of the sensor of the technology described herein. [Figure 13a] 1 is an example of output results according to one embodiment of the technology described herein, showing applied pressure; [Figure 13b] 1 is an example of output results according to one embodiment of the technology described herein, showing applied pressure; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0095] Where appropriate, like reference numerals are used throughout the drawings to refer to like elements.

[0096] One embodiment of the technology described herein will now be described. FIG. 1 shows a schematic diagram of an embodiment of an electromyography system according to an embodiment of the technology described herein. This embodiment of an electromyography system is intended for use primarily in measuring the electrical activity of abdominal muscles, particularly the external and internal oblique muscles. For example, the embodiment shown in this figure can be used to detect the electrical activity of abdominal muscles during a diagnostic test for peritonitis. However, it will be understood that the same or similar electromyography system designs can be used to detect the electrical activity of other skeletal muscles, particularly the superficial muscles.

[0097] The EMG system 100 has an output unit 102 connected to a set of sensors 104a-d. Although the EMG system 100 is shown with four sensors, it will be appreciated that more generally the system 100 can include any number of sensors suitable for the intended application.

[0098] Each sensor includes one electrode pair 106 arranged in a single differential (SD) configuration, as shown in FIG. 2. The electrodes may be any suitable electrodes, for example, in one embodiment, the electrodes have a maximum dimension between 1 mm and 15 mm, and in this embodiment, are Ag / AgCl electrodes. For example, the electrodes may be circular electrodes with a diameter of 10 mm. By comparing the potentials of two adjacent electrodes 106, the sensor measures the potential difference between two points on the subject's skin. Generally, the two points should be aligned with the direction of the muscle fibers under the skin at that point and on the same side of the nerve-sensitive area. By taking the voltage difference between the two points, the SD electrode configuration can reduce interference from common-mode signals. Compared to other electrode configurations, such as the mono-polar (MP) configuration, the SD configuration is less sensitive to noise, but can only detect surface and nearby sources. Therefore, the SD configuration is suitable for measuring electrical activity mainly in superficial muscles. Other electrode configurations, including MP and double differential (DD), can also be used.

[0099] In the SD configuration, the electrodes 106 are separated by an inter-electrode distance (IED) as shown in FIG. 2. An IED greater than 10 mm can distort the EMG signal due to the bandpass spatial filter introduced by the SD configuration. A smaller IED also reduces crosstalk between the sensors 104a-104d. As a result, smaller IEDs are generally preferred. However, smaller IEDs generally also reduce the amplitude of the EMG signal because the length of the muscle being tested is shorter. This can be particularly problematic for patients with more subcutaneous tissue (e.g., fat) at the sensing site, as the distance to the muscle is longer and the amplitude of the surface EMG signal can be smaller.

[0100] Thus, the IEDs may generally be in the range of 3 mm to 50 mm, and in one embodiment may be in the range of 3 mm to 40 mm, 3 mm to 20 mm, or 3 mm to 5 mm. In one embodiment, each sensor may have a fixed IED.

[0101] Alternatively, the sensors 104a-104d may include electrode pairs 106 with variable separation to allow for selection of an appropriate IED, in one embodiment, which may be fixed at an IED value range such that the IED may be fixed when the sensor is in use.

[0102] In yet another alternative, the sensor 104 can be configured to allow multiple electrode pairs 106 to be removable, and electrode pairs 106 with different IEDs can be attached to the sensor. For example, the electrode pairs 106 can be provided on electrode pads, and the sensor 104 can have a housing with a mount suitable for holding the electrode pads.

[0103] In use, each sensor 104 is attached to the patient's body using, for example, an adhesive pad that forms part of the sensor or other suitable means. Figure 3 shows an example sensor configuration during a test for peritonitis. Sensors 104a-104d are used to simultaneously detect electrical activity in the left and right external and internal oblique muscles. Each of sensors 104a-104d may be positioned in one of the abdominal quadrants shown in Figure 3, e.g., locations 304a-304d, while reference electrode 110 may be positioned away from the test region, e.g., location 310.

[0104] An output unit 102 is connected to the sensors 104a-104d, records measurements taken by each of the sensors 104, and provides an output indicative of these measurements. The output unit 102 may include software 102a suitable for processing the sEMG signals output from the sensors 104a-104d. The output unit may include a display 102b for displaying the output results, or may transmit the results to an external display device such as a monitor, mobile device, television, etc.

[0105] The system 100 may optionally include one or more hardware components 114 for processing the detected signals. Each of the hardware components 114 may be integrated into the sensors 104a-104d or the output unit 102, or may be provided separately from the sensors 104 and the output unit 102.

[0106] System 100 may optionally include a Drive Right Leg (DRL) circuit 112. DRL circuit 112 inverts the system common mode voltage and feeds back the inverted common mode voltage to electrodes 106 via a reference electrode 110 that is also connected to the subject's body as described above. The inverted common mode voltage may be fed back to all sensors 104 via a single reference electrode 110. As a result, in one embodiment, DRL circuit 112 inverts the common mode voltage based on a signal from only one of the sensors (e.g., sensor 104d as shown in FIG. 1). DRL circuit 112 is advantageous because it reduces power line interference (PLI) without attenuating the biopotential signal, thereby further reducing signal noise. Other components or techniques, such as notch filters or spectral interpolation, may be incorporated into system 100 in addition to or instead of DRL circuit 112 to reduce PLI.

[0107] The system 100 may optionally include one or more force or pressure sensors 108. The force sensors 108 may be any suitable sensor for measuring a force applied to a subject, such as a resistive sensor. In one embodiment, the sensors are operable to measure an applied force equivalent to a body weight of 0-100 Ib (0-45.5 kg). One non-limiting example of a suitable force sensor is the Flexiforce A201 resistive force sensor. The force sensors 108 may be used independent of the sensors 104 to measure the force applied to the subject, or the force sensors may be coupled to one or more of the sensors 104. For example, force sensors 104a-104d may be attached to sensor 104c to measure the force applied to sensor 104c.

[0108] In one embodiment, the force sensor 108 provides feedback to the user, such as a light, to indicate when the desired pressure has been applied to the subject.

[0109] The surface electromyography (sEMG) signals detected by the electrode pairs can be processed through a series of processing steps. These steps can include hardware and software processing steps. Flow diagram 400 of FIG. 4 illustrates an embodiment of processing steps that can be applied in a typical surface electromyography test using system 100. However, it will be understood that these steps may generally occur in any order and / or may be skipped while additional processing is performed.

[0110] In a first step 402, the sensor 104 detects electrical activity in the muscle being tested. This detection involves detecting the potential difference between the electrodes of an electrode pair, for example by determining the difference between the electrical signals from each electrode. This detected potential forms the sEMG signal and varies over time.

[0111] In step 404, the sEMG signals detected by the electrodes are amplified by a front-end amplifier, such as a differential amplifier. Such a differential amplifier may also be used to determine the difference between the electrical signals from each electrode, as described in step 402. The front-end amplifier may be any suitable amplifier operable to provide sufficient gain to the signal, such as an Analog Devices AD621 amplifier. Surface EMG signals are typically in the range of 0.1 μV to 2 mV, and therefore may be beneficially amplified to increase the peak-to-peak amplitude to fall within the input range of a typical digitizer. Since the input range of a digitizer is often on the order of ±5 V, in one embodiment a total gain of at least 1,000 is used. However, the preferred gain will vary depending on the expected signal amplitude, which in turn will vary depending on the muscle being tested. For example, abdominal muscles such as the oblique abdominal muscles typically generate surface EMG signals of about 5 μV to about 10 μV during expiration, and therefore a gain of 100,000 or more may be used in some tests.

[0112] Following initial amplification 406 of the signal, the signal is processed to remove unwanted frequencies and noise. Noise, for example due to motion artifacts and electrode sliding, is generally in the relatively low frequency range. Therefore, in step 406, a high pass filter is used to reduce, or ideally remove, the low frequency signal. The cutoff frequency of the high pass filter can be in the range of 10-20 Hz. In the present embodiment, the system 100 utilizes a high pass filter with a cutoff frequency of approximately 16 Hz.

[0113] In the second filtering step 408, a low pass filter is used to remove signals with frequencies above about 450 Hz. Generally, for abdominal muscles, the highest relevant muscle harmonics are in the range of 400-450 Hz. More generally, therefore, the cutoff frequency of the low pass filter may be between 400 Hz and 500 Hz, or in embodiments between 400 Hz and 450 Hz. It will be appreciated that these values ​​are merely exemplary and that the frequency of the highest relevant muscle harmonics will depend on the muscle being examined. In one embodiment, both the low pass filter and the high pass filter are at least second order filters. The filters may be any suitable low pass and high pass or band pass filters operable to cut off frequencies below 10-20 Hz and / or above 400-500 Hz. One non-limiting example of a suitable filter is a Sallen-Key filter, particularly a second order Sallen-Key filter.

[0114] Following frequency filtering steps 406 and 408, the sEMG signal is further amplified in a second amplification step 410. The second amplifier may be any amplifier operable to apply sufficient gain, such as a Texas Instruments TL072CP. Beneficially, the inclusion of the second amplification step 410 means that a lower gain may be applied in the first amplification step 404, thereby avoiding or reducing signal saturation. In this example, the first amplification step 404 applies a gain of 100 and the second amplification step 410 applies a gain of 101, for a total gain of 10,100 across steps 404 and 410.

[0115] In this example, the filtering steps 406 and 408 are shown as occurring between the amplification steps 404 and 410, but it will be appreciated that they may alternatively occur before or after the amplification of the signal. Similarly, the order of the filtering steps 406 and 408 may be reversed, with the low pass filtering step 408 occurring before the high pass filtering step 406.

[0116] In step 412, the sEMG signals are digitized using any suitable digitizer, e.g., an A / D converter. The detected sEMG signals are typically analog signals. Therefore, digitization of these sEMG signals aids subsequent signal processing by software, such as software 102a of output unit 102. To avoid aliasing, according to the Nyquist sampling theorem, the minimum sampling frequency must be greater than twice the maximum frequency of the signal. Therefore, in general, the digitizer may have a sampling frequency of 1000 Hz or higher. For example, the digitizer may have a sampling frequency of 2048 Hz. After digitization, further processing steps can be applied to the digitized sEMG signal.

[0117] In steps 414 and 416, the digitized signal is filtered by a digital filter to further reduce noise and unwanted artifacts. The high-pass and low-pass filters in one embodiment have approximately the same cutoff frequencies as the hardware analog high-pass and low-pass filters. Steps 414 and 416 can be performed by a single band-pass filter, in one embodiment by a second order band-pass filter, or by separate high-pass and low-pass filters.

[0118] In step 418, a notch filter is applied to remove the PLI. In one embodiment, step 418 includes multiple notch filters centered on the power line frequency and its harmonics. For example, in an area where the power line frequency is 50 Hz, step 418 can include a notch filter centered on 50 Hz and optionally one or more of its harmonics: 100 Hz, 150 Hz, 200 Hz, 250 Hz, 300 Hz, 350 Hz. Similarly, in an area where the power line frequency is 60 Hz, step 418 can include a notch filter centered on 60 Hz and optionally one or more of its harmonics: 120 Hz, 170 Hz, 240 Hz, 300 Hz, 360 Hz, 420 Hz. However, while many notch filters change the waveform of the EMG signal, this drawback can be discounted in the techniques described herein because the characteristic of interest in many applications is the amplitude of the signal rather than the waveform.

[0119] In step 420, the sEMG signal is further processed using wavelet filtering techniques to reduce artifacts and interference, for example from the electrocardiogram (ECG) signal (typically on the order of a few μV). In one example, the wavelet filtering utilizes the Dauechies 4 (DB4) wavelet, and the process includes applying zeroing of all detail coefficients of levels 4, 5, 6 and 7 that exceed a threshold set based on the maximum amplitude of the relaxation signal from the muscle. The threshold can be, for example, about 10% above this maximum amplitude.

[0120] To further reduce noise in the signal, in one embodiment, the detail coefficients of levels 1 and 2 of the wavelet decomposition are zeroed out. These detail coefficients typically contain high frequency bandwidth components above 450 Hz. Therefore, wavelet filtering is beneficial as it also reduces undesirable high frequency signals that remain above the cutoff frequency of the low pass filter.

[0121] After the processing, the output unit outputs the results at step 422. In one embodiment, the output unit provides a separate output for each of the sensors 104a-104d. For example, the output may include four graphs showing the processed sEMG signal from each sensor over time. Alternatively, the output may include, for example, a numerical value representing the average or maximum value of the sEMG signal detected by each of the sensors 104a-104d. As yet another option, the output unit may output the raw SEMG data detected by the sensors 104a-104d without additional processing.

[0122] Each of the processing steps 404-422 may be performed by hardware or software. In the exemplary system 100 of Figure 1, processing steps 404-410 (i.e. before digitization) are performed by hardware components of the system 100, and processing 414-420 (i.e. after digitization) are performed by software 102a of the output unit 102. However, any software processing may alternatively be performed by software provided, for example, in the sensors 104a-104d, which may output signals that have been processed to be suitable for display.

[0123] FIG. 5 is an example of a circuit diagram showing hardware components suitable for performing steps 404-422 described above. Each component may form part of the sensor 104 or the output unit 102, or may otherwise be located between the sensor 104 and the output unit 102. In one embodiment, a separate component for performing each of steps 404-410 is provided for each of the sensors 104a-104d. In one embodiment, a digitizer 412 is also provided (internally) for each of the sensors 104a-104d. Alternatively, a single digitizer 410 may be provided for digitizing the signals received from all the sensors 104a-104d. Optionally, the system 100 may further include an isolation stage for isolating the circuit from devices powered by the power grid, prior to digitization, thereby protecting the circuit, the user and the subject. The isolation stage may be any suitable device operable to isolate the circuit, for example a Texas Instruments ISO122.

[0124] In addition to amplifiers, filters, and isolators, an example DRL circuit 112 is shown in FIG. 5. Many components, such as amplifiers, in addition to PLIs, output a common mode voltage. Therefore, it is beneficial to have a DRL circuit 112 that inverts the common mode voltage from the system and feeds the inverted common mode voltage back to the electrodes 106 via the reference electrode 110. As discussed above, the inverted common mode voltage can be fed back to all of the sensors 104 via a single reference electrode. As a result, in one embodiment, only one of the sensors 104 needs to include a DRL circuit 112.

[0125] In this example system 100, the supply voltage Vs is provided by two 9 V batteries and has a range of ±9 V. A second supply voltage Vs2 is provided by the digitizer and provides ±15 V for the isolation stage, although other power sources such as a mains supply may alternatively be used.

[0126] An example output of the system 100 is shown in FIG. FIG. 6 shows example output results for the four abdominal quadrants during tension for two subjects. In this example, the output includes processed data collected during a 10 second test. It will be appreciated that the data may be processed in any manner known to those skilled in the art to provide a suitable output. For example, the output may include a numerical value representing the average or maximum amplitude of the signal. In one embodiment, the output includes individual results for each sensor 104, but may instead provide a single averaged result, or the results from each sensor 104 may be overlaid on a single graph.

[0127] By obtaining results from all sensors simultaneously, the techniques described herein are beneficial in providing a more accurate means of comparing signals. For example, the signal from the sensor in subject 2's left medial oblique is abnormally low compared to the signals from the other sensors. This could indicate a problem with the subject's left medial oblique, or, more likely, poor sensor positioning is the cause of the poor results. Without the ability to compare the raw signals of each sensor at the same time, as provided by the techniques described herein, it would typically be impossible to identify poor sensor placement, as the measured amplitudes vary from measurement to measurement and even with individual contractions of multiple muscles. Furthermore, because no sensor repositioning is required, signals can be acquired more quickly and without discomfort to the subject, and without inviting sources associated with sensor repositioning, such as subject movement, which can compromise signal quality. The sensitivity of the system means that as the subject moves, the signal becomes distorted, making it more difficult to interpret. Thus, sensor repositioning increases the risk of subject movement artifacts.

[0128] Furthermore, the use of multiple sensors facilitates signal processing and subsequent interpretation of the data, as any one or more of the sensors can be used as a reference signal for the subject. Thus, the system can compare sensing locations, aiding in the interpretation and visualization of differences between normal and pathological muscle responses, which can be shown live and in real-time, in contrast to conventional systems.

[0129] Furthermore, the use of multiple sensors allows the electrode diameter and IED to be optimized for each sensing location, aiding in detailed evaluation at each location. With multiple sensors, the IED can be as short as necessary to detect muscle activity in a well-defined area. In contrast, a single sensor system would require an electrode with a larger IED. The smaller IEDs enabled by the multiple sensors of the techniques described herein aid in the detection of smaller changes in the sensing area. This means that the sensors of the techniques described herein are sensitive enough for live comparison between sensors in a system that detects changes in muscle electrical activity resulting from involuntary activity. Furthermore, the smaller IEDs can reduce noise, such as from electrical activity in adjacent muscles.

[0130] Additionally, using multiple measurement points simultaneously assists in detecting anomalies such as outliers and signal errors. Thus, the use of multiple sensors can facilitate differentiation between voluntary and involuntary muscle activity, as well as between signal noise and other abnormalities, improving the ability to detect pathological activity due to disease.

[0131] 7 is a flow diagram 700 illustrating an example process for measuring electrical activity of abdominal muscles using an EMG system of the technology described herein. The following steps may be applied, for example, during an examination to aid in the diagnosis of peritonitis. However, the system is not limited to measuring electrical activity of abdominal muscles, and any one or more of the following steps may be applied to measure electrical activity of any muscle, particularly superficial muscles. At each stage of the method, the detected EMG signal is processed and the results are output as described above.

[0132] In step 702, multiple sensors and a reference electrode are attached to the subject, for example, using adhesive pads. To obtain accurate and stable measurements, it is important that the impedance between the electrodes and the skin is low. Therefore, in step 702, appropriate skin preparation can be performed, such as applying a conductive gel between the electrodes and the skin to further lower the impedance, scrubbing the skin with an abrasive paste to remove dead cells, and minimizing the thickness of the skin.

[0133] In step 704, measurements are taken with the muscles in a relaxed state (i.e., not tensed or contracted). Since there is no muscle activity in a healthy subject in this state, any activity is the result of residual noise, and therefore step 704 can provide a baseline for the test noise. For example, for abdominal muscles, the noise can be in the range of 0.5-2 μV during this step. However, the resting activity of a patient suffering from peritonitis is almost equal to 22% of the activity seen in a healthy subject during voluntary contraction. Thus, while the signal of a relaxed healthy subject is in the range of 0.5-2 μV, the range of the expected signal of peritonitis varies between about 30-70 μV. This difference can be easily identified with the sensitivity of the system of this embodiment.

[0134] In step 706, measurements are taken during voluntary muscle contraction. For abdominal muscles, the detected amplitude is typically in the range of 25-175 μV. However, it should be noted that the measured voluntary contraction strength will vary depending on the subject, the contraction site, the measurement duration, and the electrode position.

[0135] In step 708, interval measurements can be performed by having the subject alternate between contracting and relaxing the abdominal muscles. For a subject suffering from peritonitis, the detected signal may exhibit higher levels of residual activity (e.g., amplitude) and / or a longer period of decay of the amplitude of the detected activity when moving from a state of tension to a state of relaxation. Thus, the pattern of decay of the amplitude of the signal may provide a useful indication in some tests.

[0136] In step 710, measurements can be taken during a period of conscious deep breathing by the subject. In a healthy patient, a deep breath can generate an action potential of approximately 10 μV, which is visible above the 0.5-2 μV system noise as described above. In contrast, in a patient suffering from peritonitis, respiratory activity is difficult to see due to high baseline relaxation activity of the abdominal muscles.

[0137] In step 712, measurements are recorded during the cough. Cough activity typically lasts 200-300 ms and has an amplitude between 100-500 μV. The duration of the cough can be visually identified from the output results. A patient with peritonitis may have residual electrical activity for 200 ms after the initial cough activity.

[0138] In step 714, a force or pressure is applied to one or more sensors and a corresponding signal is observed at the opposing sensor. For example, when pressure is applied to the subject's right hand, electrical activity associated with muscle tension may be observed at the detector on the left hand upon release. The application of pressure may be assisted by the use of a force sensor 108 configured to detect when adequate pressure has been applied. The force sensor 108 may provide a time, duration and / or magnitude reading of the pressure applied to the subject to an output unit, which may include the reading in the output result. Optionally, the force sensor 108 may be attached to one or more sensors 104.

[0139] As discussed above, the various tests 704, 706, 708, 710, 712, 714 may provoke a muscular response indicative of peritonitis, as various actions (such as relaxing breathing, abdominal tension, deep breathing, coughing, and applying pressure) can each irritate the peritoneal surface and cause involuntary muscle contractions in a patient suffering from peritonitis. Although the process of Figure 7 sets out a number of tests 706, 708, 710, 712, 714, all of which may be performed, or alternatively, only one or more of the tests set out in Figure 7 may be performed, or other tests that stimulate the peritoneal surface may be performed.

[0140] Figures 8 and 9 show examples of how the output signal can be used to aid in the diagnosis of a condition such as peritonitis. In Figure 8, a virtual signal of peritonitis from measurements of the internal and external oblique muscles (IO and EO) is compared to a healthy respiratory signal from measurements of the same muscles. As mentioned above, sEMG signals from healthy subjects are expected to be on the same order as the system noise (approximately 0.5-2 μV), and even during deep respiratory movements, signals from a virtual healthy patient are unlikely to exceed 10 μV. In contrast, a virtual sEMG signal from a patient suffering from peritonitis is expected to be in the range of 20-50 μV. As a result, an sEMG signal that exceeds a threshold of, for example, 30-40 μV during relaxation periods may be indicative of peritonitis. Similarly, a prolonged period of exceeding 20 μV during relaxation periods provides another sign that can be used to diagnose peritonitis.

[0141] In contrast, Figure 9 shows measurements of a cough signal starting at approximately 0.2 seconds and ending at approximately 0.4 seconds. In a healthy patient, the measured cough signal ends almost immediately with little residual activity. However, in a hypothetical sEMG signal from a patient with peritonitis, the sEMG signal is expected to show residual activity for approximately 200 ms after the end of the cough. Thus, residual activity after involuntary muscle contractions (e.g., coughing) or voluntary muscle contractions (e.g., straining) may be yet another indicator of peritonitis.

[0142] FIG. 13a shows an example of an sEMG output signal 1200 from the sensor in a healthy patient and a graph of the force signal 1201 output from a force sensor integrated within the sensor unit (force applied during sEMG measurement) versus time.

[0143] From the graph one can see the time that pressure is applied 1202 and the time that it is released 1204. One can also see the magnitude of the applied pressure 1206. The force is applied for 1 second, but if necessary the force can be applied for a longer period of time.

[0144] Alternatively, instead of displaying the overall force sensor output versus time on a graph, an indication of the time that the force is applied and / or released may be provided, as well as other indications of the timing and magnitude of the force applied.

[0145] The example shown in FIG. 13a is an sEMG signal measured on a healthy patient 1200, where the application of pressure does not result in residual muscle activity above the baseline muscle activity. FIG. 13b similarly shows the sEMG signal 1200 of a healthy patient and the applied force 1201. FIG. 13b further shows a hypothetical sEMG signal 1203 of a patient with peritonitis. As shown in FIG. 13b, in a patient with peritonitis, muscle activity is present during pressure application and there may be residual muscle activity after pressure application (similar to the residual activity seen after coughing in FIG. 9). However, the advantage of applying pressure compared to the cough test is that the specific time when pressure was applied (and released) can be determined, making it easier to interpret when the abdominal muscles were elicited (whereas it is difficult to determine the time when the coughing ended).

[0146] In the data shown in Figures 13a and 13b, pressure is applied to a sensor that is detecting an sEMG signal by an integrated pressure sensor as discussed herein. As described herein, the sensor can be configured to reduce interference (e.g., noise or other artifacts) in the sEMG signal that may result from applying pressure to the sensor. As a result, in such a configuration, as shown for example in Figure 13a, the application of pressure may have little effect on the quality of the sEMG signal. As shown in Figure 13b, in an embodiment (as disclosed herein), the release of pressure is (significantly) faster than the expected duration of residual muscle activity. If the sEMG signal is affected by the application of pressure, the rapid release of pressure helps to avoid (continuous) failure. It will be appreciated that these indications are merely examples for a single muscle condition, and that the techniques described herein can instead be used to aid in the diagnosis of numerous other conditions, each of which may exhibit different or the same sEMG signal characteristics.

[0147] Figures 10a-10e show various views of a single sensor unit 1000. Figure 10a is a side view of the sensor unit 1000 having an upper surface 1006 and a lower surface 1004. The sensor unit 1000 is connected to an output unit via a cable 1002. The cable 1002 provides power from the output unit to the sensor 1000 and also carries the measured sEMG signal from the sensor unit 1000 to the output unit.

[0148] 10b is a top view of the sensor unit 1000. The sensor unit 1000 includes an integrated force sensor 1008. The force sensor 1008 may be, for example, a button type that can provide an indication of the applied force when pressed.

[0149] 10c is a bottom view of the sensor unit 1000. The sensor unit 1000 includes a removable electrode pad 1012 having one electrode pair 1010. In use, the sensor unit 1000 is positioned such that the electrode pair 1010 is in electrical contact with the skin of a subject. The electrode pad 1012, in one embodiment, may include an adhesive layer to secure the sensor 1000 to the subject and / or a conductive layer on the electrode pair 1010 to reduce electrode-skin contact impedance in use.

[0150] 10d is a bottom view of the sensor unit 1000 with the electrode pads 1012 removed. The sensor unit 1000 includes slots 1014 for inserting the contacts 1016 of the electrode pads.

[0151] 10e shows an example of an electrode pad 1012. The electrode pad includes two electrodes 1010 spaced apart by an inter-electrode distance (IED) measured between the centers of each of the electrodes 1010, and contacts 1016 for insertion into slots 1014 when the electrode pad 1012 is attached to the sensor unit 1004. The contacts 1016 secure the electrode pad 1012 to the sensor unit 1000 while providing a means for transmitting sEMG signals detected by the electrodes 1010 to the sensor unit 1000 for further processing and / or display by the output unit.

[0152] FIG. 10 f is a top view of the electrode pad 1012 , which includes electrodes 1010 and contacts 1016 for insertion into slots 1014 when the electrode pad 1012 is attached to the sensor unit 1004 .

[0153] 11a-11e show various views of a single sensor unit 2000 according to another embodiment of the technology described herein. Fig. 11a shows a top perspective view of the sensor unit 2000 having an upper surface 2006 and a lower surface 2004, with the lower surface 2004 placed against the skin of a subject in use. The sensor unit 2000 is connected to an output unit via a cable 2002. The cable 2002 provides electricity from the output unit to the sensor 2000 and also transmits electricity from the sensor unit 2000 to the output unit.

[0154] The sensor unit 2000 has an integrated force sensor 2008 with a button 2017 on the top surface 2006 of the sensor unit 2000 through which a force is applied, and which transmits the applied force to the patient in use when the sensor unit is placed on the patient's skin. As mentioned above, the force sensor provides an indication of the applied force when pressed. As mentioned above, the force sensor may provide visual feedback, such as one or more lights on the sensor unit to indicate that the correct pressure is being applied. Alternatively, visual feedback may be provided via a display, for example coupled to the output unit. Alternatively (or additionally), other types of feedback may be provided, such as audio and / or tactile feedback.

[0155] Figure 11b is a bottom view of the sensor unit 2000. Figures 11c and 11d are exploded perspective views of the sensor unit 2000. Figure 11e is a cross-sectional view of the sensor unit.

[0156] 11b, the bottom surface 2004 of the sensor unit 2000 has a pair of connectors 2014 for making electrical connections with an electrode pair, for example in the form of an electrode pair pad (by connecting to a corresponding mating connector of each of the electrode pads). Alternatively, a single pad (having two electrical connections) can be attached to the pair of connectors 2014. The electrode pad(s) may be single use and disposable.

[0157] The electrode pad(s) configured to be received by the sensor unit 2000 may be of the type described above and may, for example, include an adhesive layer for securing the electrode pad to the subject's skin and / or a conductive (e.g., gel) layer for reducing electrode-skin contact impedance during use.

[0158] 12 shows an example of an electrode pad 3000 that can be used in accordance with the techniques described herein, for example in combination with the sensor unit 2000. The electrode pad has one electrode pair 3001, each including a connector 3004 for forming an electrical connection with the sensor. The connectors can be protruding mating connectors. The electrodes have a defined center-to-center distance (inter-electrode distance, IED).

[0159] The electrode pad 3000 of FIG. 12 also includes a pair of conductive gel layers 3002, each of which is in contact with a respective (underlying) electrode 3001. In the illustrated example, each conductive gel layer 3002 is the same size as the respective electrode 3001. Thus, the spacing between the electrodes corresponds to the "gel spacing." Alternatively, the conductive gel layers may be of different sizes compared to the electrodes. The electrode pad 3000 of FIG. 12 also includes a substrate layer (in this example, an adhesive foam) 3003 that extends laterally beyond the electrodes 3001 and gel layers 3002, and defines the overall size (pad length and pad width) of the electrode pad.

[0160] The example shown in Figure 12 is an electrode pad with one electrode pair. As described herein, one electrode pair pad, each with a single electrode, can alternatively be used.

[0161] Returning to Figs. 11a-11e, the connector 2014 of the sensor unit 2000 provides a means for transmitting the sEMG signals detected by the electrodes to the sensor unit 2000 for further processing and / or display by the output unit. The connector 2014 shown is a mating / "snap-fit" connector type. However, other types of connectors or other types of electrical connections between the sensor unit and the electrodes may be used as desired. For example, instead of providing a mating connector, a conductive adhesive may be used to provide a secure electrical connection to the electrodes or electrode pad(s). In this case, the connector on the electrode (electrode pad) may be flat.

[0162] 11a-11e, the connector 2014 is fixed in position. However, the connector can be made movable if necessary, for example, to help accommodate different electrode spacing and electrode (or electrode pad) sizes.

[0163] The bottom surface 2004 of the sensor unit 2000 defines a recess 2015 for receiving at least a portion of one electrode pair (electrode pad(s)). In the illustrated embodiment, the connector 2014 is provided in the recess 2015.

[0164] The recess 2015 is configured (e.g., has a depth dimension D) such that (at least) the electrical connection (interface) to the electrode (electrode pad) is substantially contained within the recess (e.g., the connector 3004 shown in FIG. 12 is contained within the recess). In this regard, the recess allows the electrode (electrode pad(s)) to lie substantially flat, despite the protruding or mating portions of the electrode that form the electrical connection to the sensor unit 2000. The electrode (e.g., electrode 3001 in FIG. 12) may fit laterally within the recess 2015 and can generally fit within the depth D of the recess such that the electrode is generally flush with the bottom surface 2018 of the sensor unit. Gel (e.g., gel layer 3002) provided with the electrode can also fit laterally within the recess 2015 and can generally fit within the recess 2015.

[0165] The electrode pad(s) in one embodiment (e.g., electrode pad substrate layer 3003) have a size (area) larger than the recess such that the electrode pad extends (laterally) beyond the recess and rests against the bottom surface 2018 of the sensor unit. In this regard, the electrode pad(s) may be supported substantially entirely by the bottom surface 2018 of the sensor unit 2000 (such that the electrode pad(s) do not extend beyond the bottom surface 2018 of the sensor unit 2000). This helps to apply pressure evenly when the button 2017 is pressed. Alternatively, larger electrode pad(s) may be provided that extend beyond the footprint of the sensor (bottom surface 2018).

[0166] Alternatively, the electrode pad(s) may fit completely within the recess 2015, for example, allowing the electrode pad(s) to lie approximately flush with the bottom surface 2018 of the sensor unit and therefore maintain contact with the patient's skin.

[0167] Providing the recess 2015 can help prevent uneven pressure on the electrode (electrode pad) that may affect the quality of the sEMG signal obtained by the electrode. If the electrode pad includes (or is provided in combination with) a conductive gel, the recess also helps prevent uneven pressure on the conductive gel that may otherwise cause gel migration or leakage that may affect the quality of the sEMG signal. A relatively thick conductive gel may also be used to (further) reduce the likelihood (degree) of gel migration or leakage.

[0168] Alternatively, a flat electrical connection can be provided between the sensor unit and the electrodes (electrode pads), in which case the recess can be omitted.

[0169] 11c-e, in this embodiment, the force sensor 2008 has a button 2017 that communicates with (is in contact with) a sensor 2009 located below the button 2017. The button 2017 may include an engagement member 2011 that engages with the sensor 2009 and transmits pressure applied to the button to the sensor. The sensor 2009 generates an electrical signal in response to (and proportional to) the applied pressure. The electrical signal may be processed by the sensor unit 2000 and / or transmitted to an output unit via cable 2002.

[0170] The illustrated sensor 2009 is a load cell, which generates an electrical signal in response to an applied load (as a result of pressure applied to the button 2017 being transmitted to the sensor 2009). The load cell is configured to deform in response to an applied load (pressure) and return to its original shape when the load (pressure) is removed. In one embodiment, the load cell has a metallic body with one or more integrated strain gauges that generate an electrical signal in response to deformation of the load cell. Alternatively, the load cell can be made of other suitable and desired materials. Other types of force (pressure) sensors can also be used.

[0171] Applicants have discovered that the use of a button 2017 in contact with a load cell provides a relatively robust and reliable mechanism for measuring the pressure applied to the patient via the sensor unit 2000. This arrangement is also sensitive to and capable of measuring pressure release. It is also relatively robust during use and has few moving parts, making it easy to assemble during manufacture of the sensor unit 2000. Alternatively, other force sensors may be used, such as piezoresistive or piezoelectric force sensors.

[0172] To ensure intimate contact between the button 2017 and the sensor 2009, the button 2017 and the sensor 2009 may be coupled by a non-conductive connection (e.g., a plastic screw), or other coupling means or no coupling means may be provided (e.g., where the button simply rests on and / or engages the sensor).

[0173] The sensor unit 2000 has circuitry for processing the sEMG signals received from the electrodes (when worn) and circuitry (integrated or separate) for processing the signals from the force sensor 2009. As shown in Figs. 11c-11e, the sensor unit 2000 comprises a printed circuit board (PCB) 2005 containing (mounted) various processing elements (circuitry) 2007 for processing the signals from the electrodes and the force sensor 2009. The electrodes are mounted to the PCB 2005 via connectors 2014, and the force sensor 2009 is also mounted to the PCB. In one embodiment, the sensor unit 2000 is configured to perform the necessary analog processing of the sEMG signals received from the electrodes (e.g., amplification, application of high-pass and / or low-pass filters, etc.) and to perform digitization (analog-to-digital conversion) of the processed sEMG signals. The sensor unit 2000 also digitizes the signals received from the force sensor 2008. The sensor unit 2000 is configured to transmit the digitized sEMG signal and the force sensor signal to the output unit via a cable 2002 .

[0174] By mounting the force sensor 2008 and electrodes on the PCB, and providing the processing circuitry on the PCB, no (or minimal) wiring is required within the sensor unit 2000 (apart from the cable 2002 which transfers data to the output unit). This reduces the number of moving parts within the sensor unit 2000, resulting in a robust and easy to assemble configuration. Furthermore, avoiding the use of cables and reducing the moving parts within the sensor unit 2000 helps to avoid interference with the sEMG signal from the electrodes, and therefore can only help to enable small signals on the order of μV (which need to be detected to measure abdominal muscle activity indicative of peritonitis).

[0175] Additionally, by performing the analog signal processing in the sensor unit 2009 (using circuitry provided on PCB 2005), the signal processing is close to the patient and the analog signal is only transmitted short distances within the sensor unit 2009 and not transmitted to an external processor outside the sensor unit, helping to improve signal quality and avoid artifacts / interference.

[0176] Additionally, because cable 2002 is only required for the transmission of digitized signals (since the circuitry in the sensor unit performs analog-to-digital conversion of the EMG and force sensor signals), a cable configured to transmit digitized signals can be used, which means that a relatively thin, flexible cable that is unshielded can be used (compared to a thicker, electromagnetically shielded cable that may be required to transmit analog signals externally from the sensor unit). The point where cable 2002 enters sensor unit 2000 may be provided with strain relief components or materials, such as adhesives.

[0177] In an embodiment where multiple (e.g., four) sensors are provided to measure sEMG signals simultaneously at multiple (e.g., four different quadrants of a patient's abdomen), each sensor can be of the type shown and described above. In this way, each sensor can perform its own respective processing of the sEMG signals and pressure sensor signals (e.g., by processing circuitry provided on the PCB of the sensor unit). Thus, a system including multiple sensors can be configured to perform distributed processing. Each sensor (sensor unit 1000, 2000) can adjust its timing (have its own clock). The sensor's clock can be synchronized to a global clock (e.g., maintained by the output unit). This is done by periodically sending a synchronization signal to the sensor unit (from the output unit via the respective cable 1002, 2002 connecting the sensor unit to the output unit). The sensor clocks are synchronized (by sending a synchronization signal) before the sensors start recording the patient's sEMG signals, and can then continue to use their respective clocks while performing measurements on that patient. The sensor clock can be synchronized (by sending a synchronization signal) between uses on different patients and / or between different measurements on the same patient.

[0178] As described herein, synchronizing the sensors to the same global clock has the advantage that data collected simultaneously from different sensors can be compared (e.g., by displaying the output from multiple sensors simultaneously on an appropriate display), which can aid in comparing sEMG activity measured at different locations on a patient to identify sEMG activity that may be indicative of a health problem such as peritonitis, and can assist in synchronizing data across all sensor locations from any of the interval tests, breathing tests, cough tests, or pressure tests described herein. Synchronization can also identify the times of pressure application and release in relation to all sEMG signals detected by the sensors, which can aid in identifying sEMG activity responsive to pressure application at any sensor location (not just the sensor unit where pressure was applied).

[0179] In the above embodiments, transmission of data (e.g., synchronization signals) to the sensor units 1000, 2000 and reception of signals (e.g., digitized sEMG and force sensor signals) from the sensor units 1000, 2000 is performed using cables 1002, 2002, but in alternative embodiments, data can be transmitted to (and received from) the sensor units by wireless communication means (e.g., Wi-Fi, Bluetooth, or other wireless communication means).

[0180] 11a-11e, the sensor unit 2000 has a rigid housing including an upper housing part 2001 and a lower housing part 2003 that together enclose at least a force sensor 2009 and a PCB 2005. The housing parts 2001, 2003 of the sensor unit may comprise one or more rigid non-conductive materials, such as, for example, plastic.

[0181] The sensor unit may have one or more features to reduce (help avoid) mechanical shock ("jamming") and / or resistance (such as friction) between moving parts that may affect the sEMG signal. For example, the sensor unit may include a gap (spacing) between the mechanical moving parts and / or a damping feature for the mechanical moving parts. For example, in the embodiment shown in FIG. 11e, the sensor unit has a gap between the upper and lower housing components 2001, 2003, and in one embodiment, this gap is maintained when pressure is applied to the sensor unit (button 2017).

[0182] In embodiments of the technology described herein (such as those illustrated and described with reference to Figs. 10a-10f and 11a-11e), the force sensor is incorporated into a sensor unit configured to also detect sEMG signals. In one embodiment, the force sensor is incorporated into each of a plurality of sensor units configured to detect sEMG signals. Incorporating the force sensor into the sensor unit has the advantage that a single unit is required to both apply force to the patient and measure sEMG signals from the patient, thus allowing for easy deployment and use of the system. Furthermore, this means that pressure can be applied to the same site on the patient's body and sEMG signals can be measured (compared to, for example, a user applying pressure to an unspecified site on the subject, since the location where pressure is applied for sEMG signal measurement is known).

[0183] Additionally, the user can apply pressure to the subject by pressing the button 2017, eliminating the need for the user to directly touch the patient. This is advantageous as direct contact with the patient can result in electrical interference with the patient and affect the sEMG signal. In one embodiment, the housing of the sensor is a non-conductive material, thus providing an electrically insulating barrier and helping to reduce electrical interference caused by the user touching the button 2017. As mentioned above, in one embodiment, the technology described herein provides a medical surface electromyography system, comprising a plurality of sensors for detecting electrical activity of muscles, and an output unit operable to couple to the plurality of sensors and provide an output representative of the output of each of the plurality of sensors.

[0184] In one embodiment, when using the system, the user may be prompted by the system to input details of the patient from whom electrical muscle activity is detected. The patient details may include, for example, one or more (in some embodiments, more than one, in one embodiment, all) of the patient's weight (or BMI), the patient's height, and the patient's gender. In one embodiment, the system may output an indication (suggestion) of the size and / or electrode spacing of the electrodes (or electrode pads) to be used for the patient. The suggested size and / or spacing may be the same for all sensors of the multiple sensors, or may be different for different sensors of the multiple sensors.

[0185] The user may attach electrodes (electrode pads) to each sensor of the plurality of sensors in response to the suggestions (e.g., of the suggested size and / or at the suggested spacing). The system may have storage for a plurality of electrodes (electrode pads) of different sizes from which the user may select a desired electrode. In one embodiment, in response to the user attaching an electrode, the system may prompt the user to confirm which electrode size was used. The system may be configured to detect whether electrodes (and which electrodes) have been attached to each sensor of the plurality of sensors.

[0186] In one embodiment, the sensors (once the electrodes are attached to each sensor of the plurality of sensors) can be attached to the patient's skin by an adhesive. In one embodiment, the electrodes (electrode pads) have a protective film that can be removed to expose a layer of adhesive.

[0187] In some embodiments, the system is configured to guide the user to one or more (in some embodiments, multiple) locations where the sensors should be (simultaneously). In one embodiment, the locations include locations on the user's four abdominal quadrants. In one embodiment, the system can indicate to the user which sensor is assigned to which location (quadrant), for example by displaying it on a display.

[0188] After guiding the user to place the sensors (in an embodiment, after the user confirms via the system that the sensors are placed), the system may prompt the user to begin a measurement session. The system may then be configured to begin the measurement session in response to input from the user and to begin displaying an output indicative of muscle activity from the multiple sensors. In one embodiment, the output includes a graph of the detected sEMG signal from each sensor versus time, in one embodiment displayed simultaneously for each sensor. The user may ask the patient to cough and observe the effect this has on muscle activity by viewing the system display. If the display (e.g., a graph) does not appear correct, the user may remove and replace the electrodes to confirm correct electrode placement.

[0189] In embodiments where each sensor has its own force sensor, the system may (once a measurement session is started) prompt the user to press the sensors in sequence, and the system may be configured to indicate to the user (e.g., via a signal of the sensor being pressed and / or via a signal on a display of the output unit) when sufficient pressure has been applied to each sensor.

[0190] In one embodiment, the system is configured to graph an indication of the force applied to each sensor, in one embodiment simultaneously with the sEMG signal from the sensor, and in one embodiment both the sEMG signal and the applied force, over time, and a user can refer to the graphed responses to identify signals indicative of peritonitis.

Claims

1. A surface electromyogram system for medical use, a plurality of sensors for detecting the electrical activity of muscles, each of the plurality of sensors including one electrode pair and being operable to provide an output indicating the potential difference between the one electrode pair, and an output unit connectable to the plurality of sensors, the output unit being operable to provide an output representing the respective outputs of the plurality of sensors, characterized in that it comprises a surface electromyogram system.

2. The electrodes of each of the electrode pairs of the plurality of sensors are spaced apart by a distance within the range of 3 mm to 50 mm, and optionally, the distance is within any of the ranges of (i) 3 mm to 40 mm, 3 mm to 20 mm, or 3 mm to 5 mm, or (ii) 15 mm to 40 mm, 15 mm to 30 mm, or 15 mm to 25 mm, and / or at least one of the electrode pairs has circular electrodes with a diameter between 1 mm and 5 mm characterized in that it is the surface electromyogram system according to Claim 1.

3. Among the plurality of sensors, at least one sensor is arranged to measure the electrical activity of the external oblique muscle of a subject, and at the same time, at least one other sensor among the plurality of sensors is arranged to measure the electrical activity of the internal oblique muscle of the subject characterized in that it is the surface electromyogram system according to Claim 1.

4. The plurality of sensors includes at least four sensors characterized in that it is the surface electromyogram system according to Claim 1.

5. The electrode pair of the sensor can be removed characterized in that it is the surface electromyogram system according to Claim 1.

6. The electrode pairs of the plurality of sensors include electrode pads, the electrode pads being removably attached to the plurality of sensors, and / or each of the sensors includes means for fixing the sensor to the skin of a subject, the means having an adhesive pad or an adhesive layer, and / or each of the sensors has a conductive substance for reducing the skin contact impedance of the electrode pair characterized in that it is the surface electromyogram system according to Claim 1.

7. configured to detect a stimulus applied to a subject during use of the surface electromyogram system characterized in that it is the surface electromyogram system according to Claim 1.

8. The surface electromyogram system is configured to indicate at least one of the amplitude and timing of the stimulation The surface electromyogram system according to claim 7, characterized in that

9. The stimulation applied by the surface electromyogram system to the subject to be examined includes the force applied to the subject during the use of the surface electromyogram system The surface electromyogram system according to claim 7, characterized in that

10. Having one or more force sensors connectable to one or more of the plurality of sensors, and the one or more force sensors are operative to measure the force applied to the one or more of the plurality of sensors The surface electromyogram system according to claim 9, characterized in that

11. Each of the plurality of sensors is provided with a force sensor having a force-sensitive button respectively The surface electromyogram system according to claim 10, characterized in that

12. Each of the plurality of sensors has one or more recesses configured to accommodate at least a portion of the electrode pair of each sensor The surface electromyogram system according to claim 1, characterized in that

13. Each of the plurality of sensors is configured to perform analog-to-digital conversion of the signal detected by the respective electrode pair and transmit the digital signal to the output unit The surface electromyogram system according to claim 1, characterized in that

14. Each sensor is configured to perform analog processing of the signal detected by the respective electrode pair before performing the analog-to-digital conversion, and the analog processing includes at least one of first amplification, low-pass filtering, high-pass filtering, second amplification, and inversion of the common-mode voltage The surface electromyogram system according to claim 13, characterized in that

15. Each sensor maintains its own local clock, and the local clocks of the respective sensors are synchronized The surface electromyogram system according to claim 1, characterized in that

16. Having one or more amplifiers for amplifying the output of one or more of the plurality of sensors, and configured to amplify the output of each of the sensors to at least a total gain of 1000 The surface electromyogram system according to claim 1, characterized in that

17. The one or more amplifiers include a first amplifier operable to amplify the output of one or more of the plurality of sensors, and a second amplifier operable to amplify the output of the first amplifier. The surface electromyogram system according to claim 16, characterized in that.

18. An electric circuit operable to output a signal including the common-mode rejection ratio voltage of the surface electromyogram system, and A reference electrode operable to feedback the output of the electric circuit to the plurality of sensors, further comprising. The surface electromyogram system according to claim 16, characterized in that.

19. The output unit includes a display for displaying an output representing each of the outputs of the plurality of sensors, and preferably, the output unit provides each of the outputs of the sensors that are separately and simultaneously displayed on the display. The surface electromyogram system according to claim 1, characterized in that.

20. Comprising one or more high-pass filters, the one or more high-pass filters can operate to attenuate at least one of the outputs of the plurality of sensors having a cut-off frequency below between 10 Hz and 20 Hz, and / or Comprising one or more low-pass filters, the one or more low-pass filters can operate to attenuate at least one of the outputs of the plurality of sensors having a cut-off frequency exceeding between 400 Hz and 500 Hz, and / or Having one or more notch filters for removing power line interference, The surface electromyogram system according to claim 1, characterized in that it can operate to apply a wavelet filter to the output of the plurality of sensors. The surface electromyogram system according to claim 1, characterized in that.

21. The surface electromyogram system can operate to detect a potential difference between each of the electrode pairs of less than 10 μV, less than 5 μV, less than 3 μV, or less than 1 μV. The surface electromyogram system according to claim 1, characterized in that.

22. A surface electromyogram system for use in measuring the electrical activity of muscles across one area of the surface of a subject's skin, the surface electromyogram system according to any one of claims 1 to 21. A surface electromyogram system, characterized in that.

23. A plurality of sensors for use in a surface electromyogram system for detecting the electrical activity of muscles, each sensor among the plurality of sensors being configured to accommodate respective electrode pairs and being configured to receive signals from each of the electrode pairs when attached to the sensor, each sensor of the plurality of sensors having respective force sensors and being configured to receive force signals from each of the force sensors simultaneously with receiving signals from each of the electrode pairs, each sensor of the plurality of sensors being configured to output a signal indicative of the signals received from each of the electrode pairs and the force sensors characterized by the sensor.

24. A method of measuring the electrical activity of muscles over an area of the surface of a subject's skin using the surface electromyogram system according to any one of claims 1 to 21 or the sensor according to claim 23, comprising: attaching the plurality of sensors to the skin of the subject such that a plurality of the electrode pairs are in contact with the skin of the subject; detecting a potential difference between the electrode pairs; providing an output indicative of the potential difference detected by each of the plurality of electrode pairs characterized by the method.

25. further comprising comparing an amplitude of the potential difference detected by the plurality of electrode pairs with a threshold amplitude characterized by the method according to claim 24.

26. applying a force to the subject; the surface electromyogram system further providing an output indicative of at least one of an amplitude and a timing of the applied force further comprising characterized by the method according to claim 24.

27. further comprising determining one or more states indicative of peritonitis based on an output indicative of the potential difference detected by one or more of the plurality of electrode pairs characterized by the method according to claim 24.

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