WO2005051201A1

WO2005051201A1 - Monitoring of neuromuscular blockade using phonomyography

Info

Publication number: WO2005051201A1
Application number: PCT/CA2004/002047
Authority: WO
Inventors: Thomas Hemmerling; Guillaume Trager; Stéphane DESCHAMPS; Pierre Mathieu; Robert Guardo; Chang Bou-Phon
Original assignee: Thomas Hemmerling; Guillaume Trager; Deschamps Stephane; Pierre Mathieu; Robert Guardo; Chang Bou-Phon
Priority date: 2003-11-26
Filing date: 2004-11-26
Publication date: 2005-06-09

Abstract

In a method and device using phonomyography for monitoring the function of at least one muscle of a patient, a stimulator applies muscle-activating stimulation signals to the patient's muscle via at least one electrode, and a microphone detects phonomyographic signals produced by the patient's muscle in response to the muscle-activating stimulation signals. The microphone has a frequency characteristic adjusted to frequency requirements of the muscle. Also, a signal processor supplies processed muscle function representative data in response to the sensed phonomyographic signals, and a display illustrates the processed muscle function representative data from the signal processor.

Description

MONITORING OF NEUROMUSCULAR BLOCKADE USING PHONOMYOGRAPHY

FIELD OF THE INVENTION

The present invention relates to a method and device using phonomyography to monitor a patient's muscle function. More specifically, but not exclusively, the present invention is concerned with a method and device for monitoring the function of any patient's muscle at any state of contraction, for example for monitoring in real time the muscle relaxation of a patient undergoing surgery under general anesthesia.

BACKGROUND OF THE INVENTION

Monitoring of neuromuscular blockade, more specifically the monitoring of muscle relaxation is as essential as controlling blood pressure or heart rate during surgery. A patient who is extubated when still partially relaxed is at great risk of respiratory complications. Also, a patient incompletely relaxed during surgery can endanger the success of surgery.

Ideally, (a) neuromuscular blockade should be easily monitored for all physiologically important muscles in a non-invasive and reliable way, (b) easy- to-use neuromuscular monitoring method and device should be available to provide precise and reliable information about the state of neuromuscular blockade at any given time during surgery, and finally (c) reliable data should be acquired for any given muscle relaxant on onset, offset and peak effect for different muscles. Since muscle contraction creates acoustic signals, monitoring of neuromuscular blockade, for example monitoring of muscle relaxation can be performed by detecting the function of a patient's muscle using phonomyography. More specifically, the function of a patient's muscle can be detected through, in particular but not exclusively, a sensitive low frequency microphone. SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a method using phonomyography for monitoring the function of at least one muscle of a patient, comprising: applying muscle-activating stimulation signals to the patient's muscle via at least one electrode; sensing phonomyographic signals produced by the patient's muscle in response to the muscle-activating stimulation signals, via a microphone having a frequency characteristic adjusted to frequency requirements of the muscle; and processing the sensed phonomyographic signals to produce processed muscle function representative data; and displaying the processed muscle function representative data. The present invention is also concerned with a device using phonomyography for monitoring the function of at least one muscle of a patient, comprising a stimulator for applying muscle-activating stimulation signals to the patient's muscle via at least one electrode, and a microphone for sensing phonomyographic signals produced by the patient's muscle in response to the muscle-activating stimulation signals. The microphone has a frequency characteristic adjusted to frequency requirements of the muscle. A signal processor supplies processed muscle function representative data in response to the sensed phonomyographic signals, and a display shows the processed muscle function representative data from the signal processor.

In accordance with non-restrictive illustrative embodiments, the function of a plurality of different muscles of the patient is monitored. For that purpose, a plurality of stimulators apply muscle-activating stimulation signals to the plurality of patient's muscles, respectively, via respective electrodes, and a plurality of microphones sense phonomyographic signals produced by the plurality of patient's muscles, respectively, wherein each microphone has a frequency characteristic adjusted to frequency requirements of the corresponding patient's muscle.

In accordance with another non-restrictive illustrative embodiment, the stimulators are microprocessor-controlled neurostimulators and are integrated to the muscle function monitoring device to enable separate control of a plurality of channels of stimulation through which the muscle-activating stimulation signals are applied to the plurality of patient's muscles, respectively. The above and other objects, advantages and features of the present invention will become more apparent upon reading of the following non- restrictive description of an illustrative embodiment thereof, given by way of example only with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

Figure 1 illustrates a set-up according to the non-restrictive illustrative embodiment of the present invention, for monitoring simultaneously the function of two muscles;

Figure 2a is a schematic flow chart illustrating the operation of the muscle function monitoring method implemented by the set-up of Figure 1 ;

Figure 2b is a schematic block diagram illustrating the structure of the set-up of Figure 1 ; Figure 3 is an example of display interface for the set-up of Figure 1 , showing different windows of that display; and Figure 4 are examples of curves showing the evolution of the amplitude of a muscle relaxation trend with time for two different muscles;

Figure 5 illustrates an advanced set-up of the muscle function monitoring device according to the illustrative embodiment of the present invention, with two integrated neurostimulators and with an option for two- channel stimulation and recording;

Figure 6 shows the display interface for two channels of the advanced set-up of Figure 5, this display interface using JAVA programming language;

Figure 7 shows a display interface of the advanced set-up of Figure 5 for controlling the stimulation pattern; and

Figure 8 shows a display interface of the advanced set-up for controlling features of signal sampling.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

The muscle function monitoring method and device according to the non-restrictive illustrative embodiment of the present invention was designed with the following objectives:

1. Acquiring easy-to-use and very detailed information on relaxation and muscle function of the human body with or without anaesthesia;

2. Monitoring the function of more than one muscle simultaneously; and 3. Displaying and storing a trend of the monitored muscle function during any given period of time and retrospectively.

According to the non-restrictive illustrative embodiment, phonomyographic data of more than one muscle can be acquired. The phonomyographic data of each muscle can be displayed separately, and analysed in real time and retrospectively after individual storing.

The type of display used by the illustrative embodiment to present the phonomyographic data is a graphical trend of the muscle function, for example muscle relaxation. For example, at least one trend of the muscle function or relaxation is displayed for each monitored muscle. This graphical trend is designed to clearly show the evolution, in time, of the patient's muscular function or relaxation.

The monitoring method and device according to the illustrative embodiment of the present invention, using phonomyography, constitute a unique way of monitoring muscle function to determine neuromuscular blockade, i.e. muscle relaxation; they can be used in applications such as anesthesia, sports medicine or physiology. As indicated in the foregoing description, phonomyography is based on the recording of sound created by muscle contraction.

The software that has been used for implementing the set-up of Figure 1 is LabVIEW, because this programming language allows the creation of a user-friendly and easy-to-use user interface. For other applications and advanced set-ups such as the one illustrated in Figure 5, JAVA was used as the programming language. The non-restrictive illustrative embodiment of the muscle function monitoring method and device according to the present invention will now be described with reference to Figures 1-8 of the appended drawings. Microphones 210 (Figure 2b)

As indicated in the foregoing description, muscle contraction creates acoustic signals or sounds which can be detected, in particular but not exclusively, through a sensitive low frequency microphone. According to phonomyography, these acoustic signals can be used to determine a patient's muscle function. For proper phonomyographic analysis, for example in the frequency domain, of the detected acoustic signals or sounds, microphones capable of detecting very low frequencies and the full range of these acoustic signals or sounds are used. The non-restrictive illustrative embodiment of the muscle function monitoring method and device uses small piezoelectric microphones which can easily be attached to the surface of a patient's skin over the muscle to be monitored.

More specifically, the non-restrictive illustrative embodiment of the muscle function monitoring device according to the present invention comprises two piezoelectric microphones 210, such as microphone 11 of Figure 1 , for sampling phonomyographic signals from two different muscles, for example the corrugator supercilii and adductor pollicis muscles (Operation 21 of Figure 2a).

Of course, microphone other than piezoelectric could potentially be used.

The sampled phonomyographic signals are analysed to display online data related to the muscle function, for example muscle relaxation (Operations 23-26 of Figure 2a); this is a real time application. Real-time graphical display 220 (Figure 2b) The real-time graphical display 220 comprises two interface windows (not shown) respectively dedicated to the real-time graphical display of the two phonomyographic signals respectively sampled through the two piezoelectric microphones 201 (Operation 22 of Figure 2a).

Prior to display, each phonomyographic signal can be filtered through a low-pass filter (not shown) with a cut-off frequency lower than 60 Hz. Power spectrum analysis of the phonomyographic signals show that such filtering is not only possible but will improve the signal-to-noise ratio of the phonomyographic signals.

Stimulators 230 and 250 (Figure 2b)

In the non-restrictive illustrative embodiment of the muscle function monitoring device, two types of stimulations are used.

More specifically, stimulator 230 produces a single stimulation (Operation 23 of Figure 2a), for example a single electric twitch applied to the patient through electrodes such as 12 (Figure 1) adhered to the patient's skin in the region of the muscle to be investigated.

Stimulator 250 produces a train-of-four stimulation (Operation 25 of

Figure 2a) applied to the patient through electrodes such as 12 (Figure 1) adhered to the patient's skin in the region of the muscle to be investigated. Those of ordinary skill in the art will appreciate that a train-of-four stimulation corresponds to a series of four electric twitches.

Processor 240 (Figure 2b) When a single stimulation (single electric twitch) is applied by the stimulator 230 to the patient's body in the area of the muscle under investigation (Operation 23 of Figure 2s), the analysis (Operation 24 of Figure 2a) conducted by the processor 240 can consist of determining a graphical trend calculated by means of a ratio A/A_ref. As illustrated in Figure 1 , the processor 240 comprises, in the non-restrictive illustrative embodiment, a laptop computer 13 including a display screen 14.

The term "A" represents a peak-to-peak amplitude of the phonomyographic signal produced by the muscle in response to a single stimulation from the stimulator 230, this phonomyographic signal being sampled through one of the piezoelectric microphones 201 associated to the muscle of concern.

The term "A_ref" represents the peak-to-peak amplitude of the phonomyographic signal produced by the same patient's muscle in response to a single stimulation from the stimulator 230 before injection of relaxant to the patient. More specifically, the term "A_ref" constitutes a reference amplitude measured with the piezoelectric microphone 201 when no relaxant has been administered to the patient.

Windows 31 and 32 of the display screen 14 of the lap-top computer 13 (Figure 3) are examples of displays of the evolution of the graphical trend A/Ar_ef with time for two different muscles.

Processor 260 (Figure 2b) When a train-of-four stimulation (a series of four electric twitches) is applied to the patient by the stimulator 250 in the area of the muscle under investigation (Operation 25 of Figure 2a), the analysis (Operation 26 of Figure 2a) conducted by the processor 260 can consist of determining a graphical trend calculated through a ratio T4/T1. As illustrated in Figure 1 , the processor 260 comprises, in the non-restrictive illustrative embodiment, the lap-top computer 13 including the display screen 14. T4 represents a peak-to-peak amplitude of the phonomyographic signal produced by the muscle in response to the last stimulation of the trains-of-four as sampled through one of the piezoelectric microphones 201. T1 represents a peak-to-peak amplitude of the phonomyographic signal produced by the muscle in response to the first stimulation of the trains-of-four as sampled through the same piezoelectric microphone 201.

Windows 33 and 34 of the display screen 14 of the lap-top computer 13 (Figure 3) are examples of displays of the evolution of the graphical trend (ratio T4/T1 ) with time for two different muscles.

Curves 41 and 42 of Figure 4 are other examples of curves showing the evolution of the amplitude of a graphical muscle relaxation trend with time for two different muscles.

The muscle relaxation trend can be the above described ratio A/A_ref, the above described ratio T4/T1 , or any other suitable value.

An alternative consist of using dedicated stimulators to control separately, for example four channels of stimulation in view of choosing the most suitable type of stimulation, for example single stimulation, train-of-four stimulation, tetanus, etc.

An important advantage of the non-restrictive illustrative embodiment of the present invention is that the reaction of a plurality of different muscles can be visualized. This additional information is valuable since different muscles have different patterns of relaxation; for example, the corrugator supercilii does not behave like the adductor pollicis. By appropriately positioning the piezoelectric microphones, one can obtain a full image of relaxation of the patient's body. Of course, more than two microphones and corresponding display and stimulation and analysis chains can be used to monitor the function of more than two muscles. Set-up of Figures 5-8

The set-up of the muscle function monitoring device according to the illustrative embodiment of the present invention as illustrated in Figures 5-8 comprise disposable, single-use microphones 52 equipped with a self- adhesive surface which can easily be attached to a patient's skin. The material can be chosen to be hypoallergic. The microphones 52 can also be equipped with an isolation shield satisfying conventional medical regulations. The connections between the microphones 52 and the set-up of Figure 5 can either be via wireless connections or standard cables. These cables can be of different colours according to their specific muscle correlation.

Based on a frequency-domain analysis of the acoustic propensities of all muscles of interest, the frequency characteristic of each microphone 52 can be adjusted to the frequency requirements of every muscle of interest. This can be done by configuring the size and shaped of each microphone to adjust the frequency characteristic of this microphone to the frequency requirements of the muscle. For example, several sizes and shapes of microphones can be made available to satisfy the requirements of the different muscles.

Another characteristic of the non-restrictive illustrative set-up of Figure 5 is that the stimulators 230 and 250 are microprocessor-controlled neurostimulators integrated to the muscle function monitoring device, for example to the casing 56 of Figure 5, to enable separate control of at least two channels of stimulation such as 57 (Figure 5), through which the muscle- activating stimulation signals, for example the electric twitches, are applied to a plurality of patient's muscles, respectively, via the respective electrodes 52. The set-up of Figure 5 comprises, for example: - two stimulation channels 57 with respective electrodes 52 that can be adhered to the patient's skin in the region of the muscles of which the function is to be monitored;

- two microphone channels to receive phonomyographic signals from microphones such as 51 ;

- a simple button 53 to start monitoring;

- a battery indicator 54; and

- a pulse indicator 55 indicating the stimulations.

Referring to Figure 6, the display screen 14 of the lap-top computer 13 (Figure 3) displays:

- graphical trends of the function of two muscles (for example 61 and 62);

- the original, raw phonomyographic acoustic signals 63 and 64 related to the two muscles; and

- a general information window 65.

The lap-top computer 13 produces a window 70 (Figure 7) to allow the user to choose the type of stimulation. More specifically, the window 70 includes display items for selecting a type of stimulation selected from the group consisting of a single electric twitch and train-of-four electric twitches.

The lap-top computer 13 also produces a window 72 (Figure 7) to allow the user select a programmable programmable twitch stimulation patterns for example from 0 to 80 mA for optimal nerve location during anaesthesia for example in increments of 1 mA. The lap-top computer 13 produces a window 71 (Figure 7) to allow the user to select a frequency of repetition of the electric twitches, for example from 0 to 33 s whenever needed, for example in increments of 1 s.

The lap-top computer 13 is also programmed to produce windows for selecting or adjusting at least one of the following parameters:

- a window (Figure 8) for selecting a frequency of sampling of the phonomyographic signals;

- a window (not shown) for selecting best results for 100 Hz or 200 Hz;

- a window (not shown) for selecting a cut-off frequency of a low-pass filter for low-pass filtering the phonomyographic signals;

- a window 73 (Figure 7) for selecting a gain of pre-amplification of the phonomyographic signals for example in the range of 1 to 800; and

- a window (not shown) for selecting a measurement window in which the whole signal is analysed.

The lap-top computer can also be programmed to synchronize application of the muscle-activating stimulation signals (electric twitches) with processing of the phonomyographic signals to obtain better results. Noise sources can further be processed to improve signal quality and avoid artefacts.

The lap-top computer 13 will obviously control the microprocessor- controlled neurostimulator and processing of the sensed phonomyographic signals on the basis of the parameters selected as described hereinabove in connection with Figures 5-8 of the appended drawings. Although the present invention has been described in the foregoing description by means of a non-restrictive illustrative embodiment thereof, this embodiment can be modified within the scope of the appended claims without departing from spirit and nature of the present invention. For example, a number of microphones larger than two can be used. In the same manner, microphones of a type other than "piezoelectric" could be used. Finally, other types of stimulations could be used and other types of trends could be calculated and displayed.

Claims

WHAT IS CLAIMED IS:

1. A device using phonomyography for monitoring the function of at least one muscle of a patient, comprising: a stimulator for. applying muscle-activating stimulation signals to the patient's muscle via at least one electrode; a microphone for sensing phonomyographic signals produced by the patient's muscle in response to the muscle-activating stimulation signals, wherein the microphone has a frequency characteristic adjusted to frequency requirements of the muscle; and a signal processor supplying processed muscle function representative data in response to the sensed phonomyographic signals; and a display for the processed muscle function representative data from the signal processor.

2. A muscle function monitoring device as defined in claim 1 , wherein the device monitors the function of a plurality of different muscles of the patient, and wherein said device comprises: a plurality of stimulators for applying muscle-activating stimulation signals to the plurality of patient's muscles, respectively, via respective electrodes; and a plurality of microphones for sensing phonomyographic signals produced by the plurality of patient's muscles, respectively, wherein each microphone has a frequency characteristic adjusted to frequency requirements of the corresponding patient's muscle.

3. A muscle function monitoring device as defined in claim 1 , wherein the microphone has a size and shape configured to adjust the frequency characteristic of said microphone to the frequency requirements of the muscle.

4. A muscle function monitoring device as defined in claim 1 , wherein the microphone is a disposable, single-use microphone equipped with a self- adhesive surface which can easily be attached to the patient's skin.

5. A muscle function monitoring device as defined in claim 2, wherein the stimulators are integrated to said muscle function monitoring device to enable separate control of a plurality of channels of stimulation through which the muscle-activating stimulation signals are applied to the plurality of patient's muscles, respectively, via the respective electrodes.

6. A muscle function monitoring device as defined in claim 1 , wherein the stimulator is a microprocessor-controlled neurostimulator.

7. A muscle function monitoring device as defined in claim 5, wherein the stimulators are microprocessor-controlled neurostimulators.

8. A muscle function monitoring device as defined in claim 1 , wherein the signal processor comprises a computer for selecting a type of stimulation.

9. A muscle function monitoring device as defined in claim 8, wherein the computer is programmed to display a window for selecting the type of stimulation.

10. A muscle function monitoring device as defined in claim 9, wherein the window includes display items for selecting a type of stimulation selected from the group consisting of a single electric twitch and train-of-four electric twitches.

11. A muscle function monitoring device as defined in claim 1 , wherein: the muscle-activating stimulation signals comprises electric twitches; and the signal processor comprises a computer for selecting at least one of the following parameters: a programmable twitch stimulation pattern and a frequency of repetition of the electric twitches.

12. A muscle function monitoring device as defined in claim 11 , wherein the computer is programmed to display a window for selecting said at least one parameter.

13. A muscle function monitoring device as defined in claim 12, wherein the window comprises display items for selecting the programmable twitch stimulation pattern for optimal nerve location during anaesthesia.

14. A muscle function monitoring device as defined in claim 12, wherein the window comprises display items for selecting the frequency of repetition of the electric twitches.

15. A muscle function monitoring device as defined in claim 1 , wherein the signal processor comprises a computer for selecting at least one of the following parameters: a frequency of sampling of the phonomyographic signals, a cut-off frequency of a low-pass filter for low-pass filtering the phonomyographic signals, a gain of pre-amplification of the phonomyographic signals.

16. A muscle function monitoring device as defined in claim 1 , wherein the signal processor comprises a computer that synchronizes application of the muscle-activating stimulation signals with processing of the phonomyographic signals.

17. A method using phonomyography for monitoring the function of at least one muscle of a patient, comprising: applying muscle-activating stimulation signals to the patient's muscle via at least one electrode; sensing phonomyographic signals produced by the patient's muscle in response to the muscle-activating stimulation signals, via a microphone having a frequency characteristic adjusted to frequency requirements of the muscle; and processing the sensed phonomyographic signals to produce processed muscle function representative data; and displaying the processed muscle function representative data.

18. A muscle function monitoring method as defined in claim 17, wherein the method monitors the function of a plurality of different muscles of the patient, and wherein said method comprises: applying muscle-activating stimulation signals to the plurality of patient's muscles via respective electrodes; and sensing phonomyographic signals produced by the plurality of patient's muscles though a plurality of microphones each having a frequency characteristic adjusted to frequency requirements of the corresponding patient's muscle.

19. A muscle function monitoring method as defined in claim 17, comprising configuring a size and shape of the microphone to adjust the frequency characteristic of said microphone to the frequency requirements of the muscle.

20. A muscle function monitoring method as defined in claim 18, comprising integrating stimulators to a muscle function monitoring device to produce the muscle-activating stimulation signals applied to the plurality of patient's muscles via respective electrodes.

21. A muscle function monitoring method as defined in claim 17, comprising selecting a type of stimulation.

22. A muscle function monitoring method as defined in claim 17, wherein selecting a type of stimulation comprises displaying a window including display items for selecting the type of stimulation from the group consisting of a single electric twitch and train-of-four electric twitches.

23. A muscle function monitoring method as defined in claim 17, wherein: the muscle-activating stimulation signals comprises electric twitches; and processing the sensed phonomyographic signals comprises selecting at least one of the following parameters: a programmable twitch stimulation pattern and a frequency of repetition of the electric twitches.

24. A muscle function monitoring method as defined in claim 23, wherein selecting at least one parameter comprises displaying a window comprising display items for selecting the programmable twitch stimulation pattern for optimal nerve location during anaesthesia.

25. A muscle function monitoring method as defined in claim 24, wherein selecting at least one parameter comprises displaying a window comprising display items for selecting the frequency of repetition of the electric twitches.

26. A muscle function monitoring method as defined in claim 17, wherein processing the sensed phonomyographic signals comprises selecting at least one of the following parameters: a frequency of sampling of the phonomyographic signals, a cut-off frequency of a low-pass filter for low-pass filtering the phonomyographic signals, a gain of pre-amplification of the phonomyographic signals.

27. A muscle function monitoring method as defined in claim 17, wherein processing the sensed phonomyographic signals comprises synchronizing application of the muscle-activating stimulation signals with processing of the phonomyographic signals.