Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
  • A61B5/316—Modalities, i.e. specific diagnostic methods
  • A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
  • A61B5/346—Analysis of electrocardiograms
  • A61B5/349—Detecting specific parameters of the electrocardiograph cycle
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
  • A61B5/316—Modalities, i.e. specific diagnostic methods
  • A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
  • A61B5/346—Analysis of electrocardiograms
  • A61B5/349—Detecting specific parameters of the electrocardiograph cycle
  • A61B5/352—Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/48—Other medical applications
  • A61B5/4821—Determining level or depth of anaesthesia
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/48—Other medical applications
  • A61B5/4824—Touch or pain perception evaluation
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
  • A61B5/7235—Details of waveform analysis
  • A61B5/7253—Details of waveform analysis characterised by using transforms
  • A61B5/726—Details of waveform analysis characterised by using transforms using Wavelet transforms

Definitions

• the present invention generally relates to the analysis of the variability of heart rhythm in a living being, and its applications to the evaluation of pain in a living being, including a conscious living under local anesthesia of the epidural type, or an unconscious living being under general anesthesia, and the evaluation of the stress felt by a living being.
• the heart of a living being automatically contracts itself very regularly like a metronome, under the action of the sinus node which generates an independent nerve impulse, and thus - even causes a spontaneous contraction of the heart muscle.
• the heart is not isolated, however, but is connected to the Autonomic Nervous System (ANS) through the parasympathetic and sympathetic systems.
• ANS Autonomic Nervous System
• This autonomic nervous system influences the activity of the heart: the sympathetic system accelerates the heart rate, while the parasympathetic system slows it down.
• the heart undergoes influences of the autonomic nervous system, which allows the body of a living being to adapt the heart rate according to its needs, within reasonable limits. It is therefore understood that the analysis of the evolution over time of the cardiac rhythm, and in particular of the variations of the cardiac rhythm (variation of the interval of time between two heart beats) makes it possible to obtain an important information on the heart rhythm. activity of the cardiac system, and more particularly on the activity of the autonomic nervous system.
• knowledge of ANS activity can be of great help in developing a diagnosis of many clinical situations.
• the main methods of analysis of heart rhythm variability known to date consist in: - acquiring a cardiac signal, by any invasive or non-invasive means [for example, and non-exhaustively, acquisition of an electrocardiographic signal (ECG ) by means of an electrocardiograph, or use of a blood pressure sensor connected to a catheter introduced into an artery, or use of an infrared pulse sensor],
• RR which consists of a plurality of samples (RRi) representing the time intervals that separate two successive heart beats
• the spectral analysis of a RR series derived from a cardiac signal is usually performed in two main steps.
• the spectral density curve of the RR series is calculated, for example between 0 and 2 Hz, using various known methods.
• the most commonly used method is to compute the fast discrete Fourier transform of the RR series, in predefined time windows, weighted by means of a weighting window. predefined. H may be according to the envisaged embodiment of a rectangular weighting window, or for example a weighting window of Kaiser, Hamming, Hanning or Bartlett.
• the calculation time windows can be predefined and fixed, or it can be a calculation time window, of predetermined size, which is dragged over time.
• the Fourier transform is performed in a sliding 256 second time window, applied to the RR series, and subjected to Kaiser weighting to limit edge effects due to windowing.
• the spectral power (areas under the spectral density curve) are automatically calculated between predetermined frequency terminals, and possibly adjustable by a user.
• the fast Fourier transform must be computed in relatively wide time slots (for example 256s), which corresponds to a large number of samples from the RR series. It follows that this spectral analysis method is accompanied by a memory effect which delays the taking into account of a change in the RR series.
• the main object of the present invention is to propose a new method of automatic processing of a series RR, which overcomes the aforementioned drawbacks inherent to the prior art methods based on a spectral analysis, and which allows the calculation a quantitative information (parameter) characterized with a very good sensitivity the activity of the SNA. Summary of the invention
• the method of treatment of a series RR of the invention is based on a temporal analysis method of the samples (RRj) representing the time intervals ( ⁇ ti) which separate two successive heart beats or the inverse (1 / ⁇ ti) of these time intervals.
• a temporal analysis method of the samples (RRj) representing the time intervals ( ⁇ ti) which separate two successive heart beats or the inverse (1 / ⁇ ti) of these time intervals.
• the subject of the invention is a system for analyzing the variability of the heart rate, said apparatus comprising means for acquiring an analog cardiac signal, means for sampling this cardiac signal, and means for processing the cardiac rhythm.
• sampled signal which are adapted to construct a series RR consisting of a plurality of samples (RRj) representing the time intervals ( ⁇ ti) which separate two successive heart beats or the inverse (1 / ⁇ ti) of these time intervals, and automatically calculating from the series (RR) at least one parameter according to the aforesaid method of processing an RR series.
• the third object of the invention is a method for analyzing the variability of the heart rhythm of a living being. This process comprises the following main steps:
• cardiac signal denotes any physical signal characteristic of the instantaneous rhythm (or frequency) of the living being.
• various invasive or non-invasive techniques may be used to acquire this cardiac signal.
• a known invasive technique is for example to use a blood pressure sensor connected to a catheter introduced into an artery.
• non-invasive methods known there may be mentioned for example the use of an infrared pulse sensor, the use of an ultrasonic sensor for the detection of cardiac cycles, of the type the sensor implemented in a cardiotocograph, or the acquisition of an electrocardiographic signal (ECG).
• ECG electrocardiographic signal
• an electrocardiographic signal (ECG) is in practice the most commonly used method, because in addition to its non-invasive nature, it makes it possible to obtain a more accurate cardiac signal than that obtained, for example, by means of a pulse sensor. infrared pulse.
• RR series generally denotes a series of several successive samples (RRj), obtained after sampling an analog cardiac signal characteristic of the cardiac rhythm of the living being, each sample (RRi) generally characterizing a time interval ( ⁇ ti) between two successive heart beats or the inverse (1 / ⁇ ti) of this time interval.
• this series RR is more particularly constructed from the R waves of an ECG signal.
• the so-called "RR" series can be constructed by using the other depolarization waves (P, Q, S or T) of the ECG signal to construct the RR series, although the accuracy is less good than using the R-waves of the ECG signal .
• the samples of the RR series are not calculated by determining the time interval separating two successive R waves of the ECG signal, but are more generally determined by detecting in the heart signal the time interval between two successive heart beats.
• the final parameter calculated by the method or system of the invention generally permits characterization of any stimulus having an effect on SNA activity, and resulting in a change in cardiac rhythm (or frequency).
• a first important application of the invention is in the medical or surgical field, to assess the level of pain in a living being.
• it is indeed important to be able to know the level of pain felt by a patient, in particular to be able to take into account and treat this pain optimally.
• the most common pain assessment method to date is a subjective method, based on the use of a ruler allowing the patient to indicate by means of a slider or equivalent the level of pain he feels on a pre-established pain scale.
• This method has the disadvantage on the one hand to be purely subjective, and is therefore not really reliable, and secondly can be considered with conscious patients.
• the present invention thus has for other objects the use of the above-mentioned analysis system as well as the application of the aforementioned method for analyzing the variability of the cardiac rhythm, for the evaluation of the pain felt by a living being, the parameter final calculated characterizing the level of pain.
• the evaluation of the pain can be carried out on a conscious living being and not mechanically ventilated (that is to say a living being whose respiratory rate is any and variable) , and is not imposed by a contrast-controlled ventilation device, in particular with a patient under general anesthesia) or on an unconscious living being, and in particular a living being under general anesthesia.
• a conscious living being and not mechanically ventilated that is to say a living being whose respiratory rate is any and variable
• a contrast-controlled ventilation device in particular with a patient under general anesthesia
• an unconscious living being and in particular a living being under general anesthesia
• a second important application of the invention is in the paramedical field, to evaluate the level of stress in a living being.
• FIG. 1 schematically represents the main elements of an example of an analysis system of the invention
• FIG. 2 represents the set of waves (PQRST) characteristic of a heart beat in an ECG signal
• FIG. 3 represents an example of an ECG digital signal obtained after sampling an analog ECG signal
• FIG. 4 represents an exemplary series RR (still designated RR signal) constructed from the signal of FIG. 3
• FIG. 5 represents an exemplary RR series after filtering and normalization.
• FIG. 1 shows an example of a system for analyzing the variability of the cardiac rhythm which enables acquisition and treatment of the cardiac signal of a living being (hereinafter referred to as "patient") according to the invention .
• This system comprises:
• ECG electrocardiographic
• means 3 for processing the ECG signal output by the ECG monitor 2.
• the processing means 3 of the ECG signal comprise an analog / digital converter 4, and a programmed processing unit 5.
• the input of the converter 4 is connected to the output of the ECG2 monitor, and the output of the converter 4 is connected to a port
• the processing unit 5 is constituted by a microcomputer, the converter 4 being connected to a communication port of FIG. this microcomputer (eg RS232 serial port or USB port).
• the electrodes 1 are applied to the body of a patient, and the ECG monitor usually outputs an analog electrical signal, referred to as the ECG signal, which for each heartbeat, for example, has the shape of the signal shown in FIG. FIG. 2.
• this electrocardiographic signal (ECG) consists of a set of electric waves:
• the P wave which corresponds to the depolarization of the atria, and which has a small amplitude and a dome shape; the PQ space which reflects the atrioventricular conduction time;
• the R wave considered in practice as a marker of ventricular systole, or heartbeat, the QRS complex reflecting ventricular contraction, and - the T wave which reflects ventricular repolarization.
• This analog ECG signal is digitized by the converter 4, with a predetermined sampling frequency (fc), for example equal to 256 Hz.
• the sampled signal delivered at the output of the converter 4 (signal represented in FIG. 3) is processed by the processing unit 5 by means of a specific processing software (pain evaluation software) which is described in FIG. detail later.
• This pain evaluation software is stored in memory of the processing unit 5, and allows, when it is executed, to automatically calculate, from the digital signal delivered by the analog / digital converter 4, two distinct parameters. (AUCmax and AUCmoy) measuring the patient's pain level.
• the main successive steps of the pain assessment software algorithm are:
• the system can be programmed to be used in real time or in deferred time.
• step 1 is carried out in real time in real time so as to acquire all the RRi samples over the desired analysis period; all of these successive RRi samples are stored in an acquisition file in memory of the processing unit.
• steps 2 to 8 are performed in loop, deferred, on the interval values RRi stored in the acquisition file.
• Step 1 Acquisition of the RRi samples and resampling at a predefined f frequency
• the acquisition of the RRi samples is performed by a first software sub-module which is fed with the successive digital data constituting the digitized ECG signal (signal of the FIG. 3) delivered by the digital analog converter 4.
• the first sample acquisition sub-module RRj is designed to automatically detect each successive peak Ri in the digital signal delivered by the converter 4, and to automatically build a series RR (FIG. 4) consisting of a succession of samples RRJ.
• Each sample RRj is defined by the pair of coordinates: ti [a sampling instant (or number)]; time interval ⁇ ti (expressed for example as a multiple of the sampling period fc) separating a peak R 1 from the next peak R i + i (in another variant it could be the previous peak R n).
• the R wave being most often the thinnest and the widest part of the QRS, it is preferably used to detect the heartbeat with a very good accuracy, the corresponding time interval ⁇ ti in practice at the time separating two successive heartbeats.
• other waves for example Q wave or S wave
• the RR series (FIG. 4) delivered by the aforementioned first submodule is resampled automatically by a second sub-module software at a preset frequency f. This frequency of re-sampling must be greater than twice the maximum physiological heart rate of the patient.
• the resampling frequency f is preferably set at a value greater than 6 Hz.
• the objective of this resampling is to obtain at the output a series RR whose RRj samples are equidistant from a temporal point of view, that is to say in other words a series RR whose instants d Sampling is regular.
• This resampling is performed in a manner known per se by interpolation, and for example by linear interpolation.
• Step 2 Selection of RRi samples included in a main time window of n seconds (n> 1 / f)
• Step 3 filtering / [f 1; f2]
• This step consists in applying a band-pass filter on the samples of the series RR included in the main window so as to preserve only the frequencies included in a predefined frequency band [f1; f2].
• the frequency band [f1; f2] is equal to or within the frequency band [0.05Hz; 5Hz].
• the frequency band [f1; f2] is equal to [0.1Hz; 1Hz].
• a high-pass digital filter having a cut-off frequency at frequency f1 in series with a low-pass digital filter having a cutoff frequency at frequency f2. It is also possible to use a recursive selective filter with infinite impulse response (RII filter) centered on the frequency band [f1; f2].
• RII filter infinite impulse response
• the high pass filter (cutoff frequency fi) is intended to filter low frequencies below 0.1 Hz, and incidentally to remove many artifacts in the signal.
• the cut-off frequency est is therefore greater than or equal to 0.1 Hz, and preferably between 0.1 Hz and 0.15 Hz. It also advantageously makes it possible to suppress the average value of the signal. It is conceivable not to make a high-pass filter. In this case, it is preferable, before calculating the intermediate parameters (Aj) to refocus the signal on its mean.
• the low-pass filter (cut-off frequency f2) has the objective of filtering high frequencies, typically greater than 1 Hz, because in practice they do not contain any interesting information.
• This step is performed by means of a software sub-module which initially calculates the S standard of the signal resulting from step 3 according to the usual formula below:
• p will be chosen equal to 2.
• the software sub-module performs a normalization of the signal by dividing each value Sj of the signal by the norm S previously calculated.
• This step 4 makes it possible to obtain a better sensitivity on the final result (sensitivity of the parameters AUCmoy and AUCmax measuring the level of pain).
• Step 5 Detecting the minima in the main window
• FIG. 5 shows an exemplary signal RR (after filtering and normalization) coming from the above-mentioned step 4.
• the abscissa axis corresponds to the null value of the filtered and normalized signal.
• Step 5 is carried out by means of a software sub-module which detects the minimums (points Pj in FIG. 5) of this signal, for example by means of an algorithm detecting an inversion of the slope (or in an equivalent manner a change in the sign of the derivative of the signal).
• Step 6 Cutting of the main time window in m [m> 2] sub-windows (F j ) and calculation for each sub-window (Fj) of the area (Aj) delimited by the lower envelope (C j ) , connecting the minimums detected in the previous step.
• the software sub-module corresponding to step 6 automatically calculates, for each sub-window (F j ), a lower envelope
• step 6 calculates, for each sub-window (Fj), the area (A j ) delimited by the envelope lower (C j ) and the abscissa (zero value of the signal)
• the area (A j ) corresponds to the shaded area in Figure 5.
• this area calculation (A j ) amounts to calculating the sum of the areas of the trapezoids delimited by two successive minimum points (Pi) and the abscissa axis. .
• the area (Aj) could be delimited by the lower envelope (Cj) and a horizontal line different from the abscissa axis, and preferably (but not necessarily) positioned under the axis of the abscissa, such as for example the line D in dashed lines in FIG. 5.
• this straight line D for the calculation of the area (Aj) could be located above the abscissa axis, and in particular go through the point Mi of greater ordinate (point M 10 in the particular example of Figure 5).
• Step 7 Calculation of the parameters: AUCmoy and AUCmax The two parameters AUCmoy and AUCmax make it possible to measure
• AUCmoy is equal (or more generally proportional) to the average of the areas Aj of (m) sub-windows Fj.
• AUCmax is equal (or more generally proportional) to the value of the largest area Aj calculated for the (m) sub-windows F j .
• Step 8 Offset, of a time step worth p seconds (p ⁇ n), of the time window of n seconds, and reiteration of the calculation from step 2.
• step (p) for the sliding of the main calculation window and reiteration of steps 2 to 8 affects the sensitivity of the parameters AUCmoy and AUCmax, and thus depends on the desired sensitivity. As indicative, and in practice, very satisfactory results were obtained by choosing a step (p) worth 2s.
• the aforementioned filtering step (Step 3) could be carried out before the selection step 2, for example continuously as the samples RRi are acquired. Also, in another variant embodiment, this filtering step could be performed after the normalization step (step 4 above).
• AUCmoy and AUCmax values were compared with pain level indications provided by parturients using a visual analogue pain scale (VAS), prior to epidural placement, and after epidural placement. .
• VAS visual analogue pain scale
• the AUCmax parameter is the most reliable parameter, and is therefore preferential.
• AUCmax and AUCmoy have been tested on conscious patients, and it has been found that, advantageously according to the invention, these parameters are independent of the respiratory frequency proper to the living being. Both AUCmax and AUCmoy parameters were also successfully tested for pain assessment in non-conscious patients under general anesthetic whose respiratory rate was imposed by a controlled ventilation mechanism. Knowledge in general anesthesia of these parameters allows indirectly to measure the analgesic component of general anesthesia.
• the invention is however not limited to the two particular parameters mentioned above AUCmax and AUCmoy, which have been given only as preferred examples. More generally, it has been found that an essential element of the invention affecting the desired result (evaluation of pain) is the calculation of a final parameter from intermediate parameters calculated on RRi samples included in sub-samples. temporal window, in contrast with a solution (not covered by the invention) in which the final parameter would be calculated directly on all RRi samples of the main window.
• the method of the invention can therefore be implemented with any RRi sample processing method for calculating an intermediate parameter Aj in temporal sub-windows, the final parameter correlated with the intensity of the painful stimulus, depending on these intermediate parameters.
• the pain stimulus very significantly influenced the respiratory peaks (minimum points Pi); the greater the intensity of the pain, and the greater the amplitude of the peaks in the signal corresponding to the minimums (Pi) is small, and can in some cases be almost zero.
• the maxima (Mi) of the curve are not significantly affected by the pain stimulus. Consequently, any method for processing the RRi samples in each sub-window (Fj) making it possible to take into account the amplitude variations of these peaks (Pi) will be appropriate for calculating the intermediate parameters in each sub-window, and the invention is therefore not limited to the calculation of area previously described and given by way of example only.
• the calculation of the areas (Aj) could be replaced by the calculation of an intermediate parameter according to the amplitudes of the peaks corresponding to the minimum points (Pi).
• the calculation algorithms are applied to a series RR whose samples (RRi) characterize the time intervals ( ⁇ ti) which separate two successive heart beats.
• the invention can be implemented from a series RR whose samples (RRi) characterize the inverse (1 / ⁇ ti) of the time intervals ( ⁇ ti) between two successive heart beats.
• RRi samples characterize the inverse (1 / ⁇ ti) of the time intervals ( ⁇ ti) between two successive heart beats.
• the algorithm of calculation which has just been described in detail, as well as the parameters which result from it, in particular the parameters AUCmoy and AUCmax, are not limited in terms of application to the evaluation of the pain in a living being, but may more generally be used to measure the variability of the heart rhythm in a living being (conscious or unconscious), and thus to study the effects on the ANS (Autonomic Nervous System) of any stimulus likely to modify the ANS activity.
• the aforementioned teaching applied to the evaluation of the pain can also be used and transposed as such in other fields. applications, and especially in the paramedical field, to assess the level of stress felt by a living being (conscious or unconscious).

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• 2004
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