Methods and devices for establishing analgesia in mammals

Abstract

Methods and devices for establishing analgesia in humans or other mammals have been disclosed. The method includes the following steps: providing a skin conductance signal measured at a region of the skin of a mammal over a time interval; detecting a peak of the skin conductance signal within the time interval; determining the rate of the peak within the time interval; comparing the determined rate of the peak with a predetermined reference value; and providing an output signal indicating a state of analgesia in the mammal if the measured rate of the peak is lower than the predetermined reference value.

Description

Technical Field

[0001] The present invention generally relates to methods and devices for establishing analgesia in mammals. Background Art

[0002] In this technical field, there are methods and devices for monitoring the nervous system of humans and other mammals, particularly for detecting pain in unconscious, non-verbal patients (e.g., patients anesthetized during surgery or patients on artificial ventilation). Some of these methods and devices are used to determine whether a patient requires medication due to the pain state of the determined patient.

[0003] There is a need for methods and devices for establishing analgesia in mammals in all populations from conscious and presumably healthy humans or other mammals to hospitalized humans or other mammals.

[0004] WO-00 / 72751 relates to devices and methods for monitoring the autonomic nervous system of an individual by utilizing spontaneous changes in skin conductance, particularly for detecting pain. The device includes: measuring equipment for measuring the conductance of the skin; and storage and processing means for deriving secondary characteristics of the conductance signal. The pain of a patient can be indicated based on the amplitude and frequency of the fluctuations of the skin conductance signal. Summary of the Invention

[0005] The object of the present invention is to provide methods and devices for establishing analgesia in mammals.

[0006] According to the present invention, the above object is achieved by the methods and devices defined in the appended independent claims.

[0007] Further advantages and features of the present invention are indicated in the dependent claims. Brief Description of the Drawings

[0008] The present invention will be described by way of example with reference to the accompanying drawings, in which

[0009] Figure 1 is a schematic block diagram showing the principle of a device for establishing analgesia in mammals;

[0010] Figure 2 is a perspective view showing a device for establishing analgesia in mammals during use; and

[0011] Figure 3 is a flowchart showing a method for establishing analgesia in mammals. Detailed Description of the Invention

[0012] Figure 1It is a schematic block diagram showing the principle of a device for establishing analgesia in a human or other mammal in all groups from a specifically conscious and presumably healthy human or other mammal to a hospitalized human or other mammal.

[0013] A sensor device 3 for measuring the conductance of the skin is placed on a region 2 of the skin of a body part 1 of a human or other mammal. In the case of a human, the body part 1 is preferably a hand or a foot, and the region 2 of the skin on the body part 1 is preferably the palmar side of the hand (in the palm of the hand) or the plantar side of the foot (under the sole of the foot). In the case of a non-human mammal (specifically, a mammal with claws), the region of the body part can be the palmar side of the claw. The sensor device 3 includes contact electrodes, and at least one electrode (measurement electrode) is placed on the skin region 2. In a preferred embodiment, the sensor device 3 is composed of three electrodes: a signal electrode, a measurement electrode, and a reference voltage electrode, and the reference voltage electrode ensures a constant voltage is applied to the stratum corneum (the epidermal layer of the skin) under the measurement electrode. Preferably, the measurement electrode and the signal electrode are placed on the skin region 2. The reference voltage electrode can also be placed on the skin region 2, but preferably, the reference voltage electrode is placed in a nearby position suitable for the measurement arrangement involved.

[0014] In a preferred embodiment, an alternating current is used to measure the conductance of the skin. Advantageously, corresponding to the region approximately linear with the conductance of the skin, the alternating current has a frequency in the range up to 1000 Hz. The frequency should be selected to ensure that interference from, for example, the mains frequency affects the measurement signal to the minimum possible extent. In a preferred embodiment, the frequency is 88 Hz. A signal generator operating at the specified frequency applies a signal current to the signal electrode.

[0015] In the case of an alternating current, the conductance is the same as the real part of the complex admittance, and thus, it does not have to be the same as the inverse value of the resistance. The advantage of using an alternating current instead of a direct current in conductance measurement is that by this means, the adverse effects on the measurement of the polarization characteristics of the skin are avoided.

[0016] The current generated through the measurement electrode is transmitted to a measurement converter 4. This includes a current-to-voltage converter, and in a preferred embodiment, the current-to-voltage converter is a transimpedance amplifier, but in its simplest form, it can be a resistor that converts the current from the measurement electrode into a voltage.

[0017] The measuring transducer further includes a decomposition circuit, preferably in the form of a synchronous rectifier, which decomposes the complex admittance into a real part (conductance) and an imaginary part (susceptance). However, it suffices if the decomposition circuit only includes means for deriving the conductance. The synchronous rectifier multiplies the measured voltage by the voltage from the signal generator. The two signals are in phase. After multiplication, the result conforms to the cosine(2μ) equation, where the result is a DC component and a component at the 2μ frequency. In a preferred embodiment, this becomes 176 Hz. In a preferred embodiment, the synchronous rectifier is implemented as an analog circuit with the required accuracy.

[0018] The measuring transducer 4 may further include an amplifier and a filter circuit. In a preferred embodiment, the measuring transducer includes low-pass filters at both the input and output ends. The purpose of the input low-pass filter is to attenuate high-frequency noise, for example, from other medical equipment, and the input low-pass filter also serves as an anti-aliasing filter to prevent high-frequency components from being received by subsequent circuits for time discretization. The output low-pass filter should attenuate the 2μ component generated by the multiplication operation in the synchronous rectifier so that only the signal near DC is used for further processing.

[0019] Furthermore, through the selection of components and design details, the measuring transducer is designed to achieve high sensitivity and a low noise level.

[0020] Although the measuring transducer 4 has been shown by way of example as being external to the control unit 5, it should be understood that the measuring transducer may be included in the control unit 5.

[0021] The control unit 5 includes a time discretization unit 51 for time-discretizing the signal from the measuring transducer. The time discretization advantageously occurs at a sampling rate on the order of 20 to 200 samples per second. The control unit further includes an analog-to-digital converter 52 for converting the measurement data into digital form. The selection of the circuits for time discretization and analog-to-digital conversion represents a technical decision suitable for a person skilled in the art. In a preferred embodiment, the time discretization is accomplished in an integrated circuit that combines oversampling, filtering, and discretization.

[0022] In addition to the input from the measuring transducer 4, the control unit may advantageously include additional analog inputs and possibly digital inputs (not shown). In this case, the control unit 5 may be equipped with a plurality of analog-to-digital converters 52 or may employ various multiplexing techniques known to those skilled in the art in order to increase the number of analog inputs. For example, these additional analog inputs may be arranged for additional electrodermal measurements, or for other physiological measurements that may advantageously be performed simultaneously or in parallel with the electrodermal measurements, such as body temperature, pulse, ECG, respiration measurement, oxygen saturation measurement in the blood, or EEG (bispectral index).

[0023] The control unit 5 further includes: a processing unit 53 for processing digital measurement data; storage means in the form of at least one memory for storing data and programs, the storage means being shown as a non-volatile memory 54 and a random access memory 55. The control unit 5 further includes an interface circuit 61 that provides a first output signal 71 and optionally a second output signal 72. Optionally, the control unit 5 further includes another interface circuit 81 that is further connected to the display unit 8. The control unit 5 may also optionally include a wireless communication adapter or communication port 56 for digital communication with an external unit 10 such as a personal computer, tablet, mobile terminal, or smart phone. Such communication is well-suited for loading or changing programs held in the memories 54, 55 of the control unit, or for adding or changing other data held in the memories 54, 55 of the control unit. Such communication is also well-suited for reading out data from the memories 54, 55 of the device, thereby enabling the transfer of this data to the external unit 10 for further subsequent analysis or storage.

[0024] In a preferred embodiment, the non-volatile memory 54 includes a read-only memory in the form of a programmable ROM circuit, containing at least program code and permanent data, and the random access memory 55 includes a read and write memory in the form of a RAM circuit for storing measurement data and other temporary data.

[0025] The control unit 5 further includes an oscillator (not shown) that transmits a clock signal for controlling the processing unit 53. The processing unit 53 also includes timing means (not shown) in order to provide a representation of the current time for the analysis of the measurements. Such timing means are known to those skilled in the art and are typically included in microcontrollers or processor systems that those skilled in the art find suitable for use with the present invention.

[0026] The control unit 5 can be implemented as a microprocessor-based unit with connected inputs, outputs, memory, and other peripheral circuits, or can be implemented as a microcontroller unit integrating some or all of the connected circuits. The time discretization unit 51 and / or the analog-to-digital converter 52 can also be included in such a unit. The choice of the appropriate form of the control unit 5 involves a decision suitable for a person skilled in the art.

[0027] An alternative solution is to implement the control unit 5 as a digital signal processor (DSP).

[0028] The control unit 5 is arranged to preferably read the time-discretized and quantized measurements of the skin conductance from the measurement converter 4 by means of an executable program code stored in the non-volatile memory 54 and executed by the processing unit 53. The control unit 5 is further arranged to be able to store the measurements in the read and write memory 55. By means of the program code, the control unit 5 is further arranged to perform a real-time analysis of the measurements, i.e., to analyze simultaneously or in parallel with the execution of the measurements. In this context, simultaneously or in parallel should be understood to mean simultaneously or in parallel for practical purposes, observed in conjunction with the time constant of the nature of the measurements. This means that the input, storage, and analysis can be carried out in separate time intervals, but in this case, these time intervals, and the time between these time intervals, are so short that the individual actions appear to occur simultaneously.

[0029] The control unit 5 is further arranged to detect the peak fluctuations in the time-discretized, quantized measurement signal by means of a part of the program code stored in the non-volatile memory 54 and executed by the processing unit 53.

[0030] The control unit 5 is further arranged to determine the rate of the peak fluctuations in the time-discretized, quantized measurement signal within a time interval by means of a part of the program code stored in the non-volatile memory 54 and executed by the processing unit 53.

[0031] The control unit 5 is further arranged to compare the determined rate of the peaks with a predetermined reference value by means of a part of the program code stored in the non-volatile memory 54 and executed by the processing unit 53.

[0032] If the rate of the measured peaks is lower than the predetermined reference value, the control unit 5 is further arranged to provide a first output signal 71 of the interface circuit 61 by means of a part of the program code stored in the non-volatile memory 54 and executed by the processing unit 53 to indicate the state of loss of pain sensation in a human or other mammal.

[0033] The control unit 5 can be further arranged to perform, by means of a part of the program code stored in the non-volatile memory 54 and executed by the processing unit 53, what is disclosed herein (specifically, with reference to the followingFigure 3 ) steps and combinations of steps of the method.

[0034] The processing unit 53, memories 54, 55, analog / digital converter 52, communication port 56, interface circuit 81, and interface circuit 61 are all connected to the bus unit 59. The detailed construction of this bus architecture for the design of a microprocessor-based instrument is considered well-known to those skilled in the art.

[0035] The interface circuit 61 is a digital port circuit. When the interface circuit 61 is addressed by program code executed by the processing unit 53, the interface circuit 61 transmits at least a first digital output signal 71 from the processing unit 53 via the bus unit 59.

[0036] The first digital output signal 71 indicates that the analysis of the skin conductance measurement has established a state of analgesia in a human or other mammal.

[0037] The interface circuit 61 can also provide an additional output signal schematically shown as the second output signal 72.

[0038] In a preferred embodiment, the display device 8 consists of a screen for graphical visualization of the conductance signal and a digital display for displaying the frequency and amplitude of the measured signal fluctuations. Preferably, the display unit is of a low-power consumption type, such as an LCD screen and an LCD display. The display device can be separate or integrated into the same unit.

[0039] The device further includes a power supply unit 9 for supplying operating power to the various components of the device. The power supply can include a battery, preferably a rechargeable battery, or alternatively be connected to an external power source such as a mains power supply.

[0040] Figure 2 is a perspective view showing a device for establishing analgesia in a mammal during use.

[0041] The electrodes, generally referring to the three electrodes described in the disclosure above with reference to Figure 1 are placed on the palm side of the human hand 21, and thus, in Figure 2 the electrodes are not visible. In the case of a mammal with claws, the electrodes are placed on the palm side of the claws. The electrodes are interconnected with the device 23 for establishing analgesia in a mammal by means of a cable 22. The device 23 includes those covering the above reference Figure 2A housing that encapsulates the electronics of the described measuring transducer 4 and control unit 5. The housing of the device is strapped to the wrist of a human or other mammal by a suitable wristband 24, preferably made of an elastic material. The device 23 includes a simple operating interface that includes an operable element 25, which can be a touch button for turning the device on and off. The device 23 also includes an indicator, which can be an optical indicator or an auditory indicator, or both an optical indicator and an auditory indicator, that provides an optical or auditory indication corresponding to a first output signal 71 indicating the state of loss of pain sensation in the mammal. Further operation of the device can be provided by an external terminal, such as a smart phone, corresponding to the external unit 10 and capable of supporting communication with the control unit 5 in the device 23 described above with reference to Figure 1 The device 23 described above.

[0042] Figure 3 is a flowchart showing a method for establishing loss of pain sensation in a human or other mammal.

[0043] The method starts at reference 31.

[0044] In a measurement step 32, a skin conductance signal measured at a region of the skin of a human or mammal over a time interval is provided. For this purpose, as already explained above with reference to Figure 1 and Figure 2 The skin conductance signal or EDR (electrodermal response) signal is measured by a sensor device 3, such as a contact electrode, disposed on a body part 1 of a human or other mammal (preferably, the palmar side of the hand or paw).

[0045] The skin conductance (preferably in units of conductivity (μS)) is time-quantified and converted to digital form, for example, by using the equipment described above with reference to Figure 1 The device described above. A time series of a specific duration containing skin conductance data is acquired during step 32, typically between 5 seconds and 60 seconds, and more preferably between 15 seconds and 45 seconds, and even more preferably between 25 seconds and 35 seconds. For example, at 15 seconds, at a sampling rate of 20 to 200 samples per second, the time series can contain 300 to 3000 samples.

[0046] In a subsequent peak rate determination step 33, the peaks of the skin conductance signal within the time interval are detected, and the rate of the peaks within the time interval is determined.

[0047] In a peak detection sub-step of step 33, a test can be performed to detect the presence of valid peaks in the acquired time series of the skin conductance signal. If one or more peaks are detected, the rate of the peaks is then determined. If no peaks are detected, the rate of the peaks is considered zero.

[0048] If the derivative of the signal changes sign within a smaller period of the interval, the presence of a valid peak can be established. The derivative of the signal can be calculated as the difference between two subsequent sample values. Additionally, a simple digital filter that looks at two or more subsequent sign changes can be used before accepting a sign change.

[0049] In the test step of establishing a valid peak, additional criteria need to be established for when a peak is considered valid. In its simplest form, such a criterion can be based on the fact that the signal amplitude must exceed an absolute limit in order to be considered a valid fluctuation. As suggested, this reference value of conductance is between 0.005 μS and 0.03 μS, preferably 0.015 μS.

[0050] Optionally or additionally, it can be advantageous to base the criterion on the fact that the signal has actually formed a peak that has persisted for a specific time. The criterion can also be based on the fact that if the maximum value is considered valid, the skin conductance signal value must remain below a specific limit as it increases over time, typically 20 μS / s.

[0051] Another possible condition for establishing a valid peak is that the absolute value of the change in the conductance signal from a local peak to the following local valley exceeds a predetermined value, such as between 0.01 μS and 0.02 μS, preferably 0.015 μS.

[0052] Furthermore, a maximum value that occurs at the boundary of the interval, i.e., the starting point or the ending point of the interval, should not preferably be considered a valid peak.

[0053] The purpose achieved thereby is that artifacts that may occur in error situations (such as, for example, loose electrodes being operated on the skin, or other noise or interference sources) do not lead to the false detection of peaks.

[0054] In comparison step 34, the rate of the determined peak is compared with a predetermined reference value.

[0055] The predetermined reference value is in the range of 0.00 to 0.12 peaks per second. Advantageously, the predetermined reference value can be in the range of 0.00 to 0.06 peaks per second. Even more advantageously, the predetermined reference value can be in the range of 0.00 to 0.03 peaks per second.

[0056] Advantageously, if it has additionally been determined that the average rate of the peak has persisted for a specific time period within the time interval, an output signal indicating the state of analgesia of the mammal is provided, and this time period is in the range of 2 minutes to 10 minutes, or in the range of 3 minutes to 6 minutes, or in the range of 4 minutes to 5 minutes.

[0057] If the rate of the determined peak is lower than a predetermined reference value, the establishment step 35 is performed. In the establishment step 35, a first output signal 71 indicating a state of analgesia of a mammal is provided.

[0058] Additionally, in the comparison step 34, if the rate of the determined peak is equal to or greater than the predetermined reference value, the process continues at another iteration of the measurement step 32.

[0059] After the analgesia signal is established in step 35, the process can end at the termination step 36 or, optionally, the process can be repeated by continuing at the measurement step 32.

[0060] The process can be interrupted or terminated at any time by operating a device (not shown) or by a command input from the communication port 56.

[0061] The disclosed method and device result in reliably establishing analgesia in a human or other mammal, specifically, a conscious human or mammal and an in-hospital human or mammal. In the case of a human, the human does not have to be a patient. On the one hand, the method and device can be a non-medical method and non-medical device. On the one hand, the method and device can be specifically used to provide confirmation of a hypothesized analgesia for a human who is assumed to be generally healthy or has a minor illness to be treated especially at home. On the one hand, the method and device may not be specifically intended for the purpose of administering drugs to a human or mammal.

Claims

1. A method for establishing analgesia in a mammal, comprising the following steps: - Providing a skin conductance signal measured at a region of the skin of the mammal over a time interval; - Detecting a peak of the skin conductance signal within the time interval; - Determining a rate of the peak within the time interval; - Comparing the determined rate of the peak with a predetermined reference value; - If the determined rate of the peak is lower than the predetermined reference value, providing an output signal indicating a state of analgesia in the mammal; And wherein the predetermined reference value ranges from 0.00 to 0.03 peaks per second.

2. The method according to claim 1, Among them, wherein the time interval ranges from 5 seconds to 60 seconds.

3. The method according to claim 1, Among them, wherein the time interval ranges from 15 seconds to 45 seconds.

4. The method according to claim 1, Among them, wherein the time interval ranges from 25 seconds to 35 seconds.

5. The method according to claim 1, Among them, If it is further determined that the average rate of the peak persists for a specific time period within the time interval, providing the output signal indicating a state of analgesia in the mammal, the time period ranging from 2 minutes to 10 minutes.

6. The method according to claim 1, Among them, If it is further determined that the average rate of the peak persists for a specific time period within the time interval, providing the output signal indicating a state of analgesia in the mammal, the time period ranging from 3 minutes to 6 minutes.

7. The method according to claim 1, Among them, If it is further determined that the average rate of the peak persists for a specific time period within the time interval, providing the output signal indicating a state of analgesia in the mammal, the time period ranging from 4 minutes to 5 minutes.

8. The method according to claim 1, Among them, The step of detecting a peak of the skin conductance signal within the time interval includes: establishing the presence of a valid peak if the derivative of the skin conductance signal changes sign within a smaller period within the time interval.

9. The method according to claim 8, Among them, The derivative is calculated as the difference between two subsequent sample values.

10. The method according to claim 8, Among them, Establishing additional criteria for when a peak is considered valid, including ensuring that the signal amplitude of the skin conductance signal exceeds an absolute limit value selected from the range [0.005 µS, 0.03 µS].

11. The method according to claim 8, Among them, Establishing additional criteria for when a peak is considered valid, including ensuring that the skin conductance signal remains below 20 µS / s as time increases.

12. The method according to claim 8, Among them, Establishing additional criteria for when a peak is considered valid, including ensuring that the absolute value of the change of the skin conductance signal from a local peak to a subsequent local minimum exceeds a predetermined value selected from the range [0.005 µS, 0.03 µS].

13. The method according to claim 8, Among them, Establish additional criteria for when a peak is considered valid, including ensuring that the start or end point of the time interval is not considered a valid peak.

14. A device for establishing analgesia in a mammal, comprising: - Measuring means for providing a skin conductance signal measured at a region of the skin of the mammal; and - A control unit configured to perform the method according to one of claims 1 to 13.

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