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    • 专利摘要:
    Method and apparatus to detect mechanical systolic events from the balistocardiogram. We propose a method and apparatus to detect mechanical systolic events from the balistocardiogram (BCG). A transfer function is applied to BCG that compensates for the mechanical response of the subject's body so that the global transfer function is flat and zero phase in the frequency range of interest. In this way, a signal corresponding to the mechanical activity occurring in the heart and the aortic root is obtained in which mechanical systolic events can be reliably detected. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2656765A1
    申请号:ES201631026
    申请日:2016-07-27
    公开日:2018-02-28
    发明作者:Ramon Pallàs Areny；Ramon Casanella Alonso；Joan GÓMEZ CLAPERS
    申请人:Universitat Politecnica de Catalunya UPC；
    IPC主号:
    专利说明:

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    METHOD AND APPARATUS FOR DETECTING MECHANICAL SYSTOLIC EVENTS A
    FROM THE BALISTOCARDIOGRAMA
    DESCRIPTION
    SECTOR OF THE TECHNIQUE
    The present invention relates in general to physiological parameter measurement systems by physical methods and, in particular, to a method and apparatus for detecting mechanical systolic events from the balistocardiogram (BCG).
    STATE OF THE TECHNIQUE
    The detection of systolic events is of great interest to assess the health status of the heart in a non-invasive way. The intervals between systolic events provide information on electrodynamic and mechanical parameters involved in systolic activity, so its use as a diagnostic tool is widely recognized among the medical community. The systolic intervals (Systolic Time Intervals or STI) with greater interest are the pre-ejection period (PEP), corresponding to the delay between the electrical activation of the ventricles and the beginning of the ejection of blood to the aorta , and the left ventricular ejection time (LVET), corresponding to the time during which the aortic valve remains open. From a clinical point of view, a prolongation of the PEP is usually attributed to a reduction in the contractile capacity of the myocardium or a reduction in vascular elasticity. On the contrary, a shortening of the LVET indicates vascular deterioration and myocardial weakening. Therefore, the PEP / LVET ratio is used, together with STIs, as an indicator of heart health status, as described for example in the document by SS Ahmed, GE Levinson, CJ Schwartz, and PO Ettinger, "Systolic Time Intervals as Measures of the Contractile State of the Left Ventricular Myocardium in Man, ”Circulation, DOI 10.1161 / 01.CIR.46.3.559.
    The measurement of intervals between systolic events and vascular events can also provide information about the state of the circulatory system, since the opening
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    The aortic valve can be used as a proximal point to measure the transit time of the pressure pulse (Pulse Transit Time or PTT) to a distal point. PTT in the aorta depends on its elasticity and is a direct predictor of the risk of cardiovascular disease. Arterial elasticity has been associated with the presence of cardiovascular risk factors and arteriosclerotic diseases, and its ability to predict the risk of future cardiovascular events such as myocardial infarction, stroke, revascularization or aortic syndromes, among others, has been widely corroborated. , as described in the document by C. Vlachopoulos, K. Aznaouridis, and C. Stefanadis, "Prediction of Cardiovascular Events and All-cause Mortality With Arterial Stiffness: a Systematic Review and Meta-analysis," Journal American College Cardiology, DOI 10.1016 / j.jacc.2009.10.061 Additionally, PTT is used to estimate changes in blood pressure and measure absolute pressure values by means of different calibration methods, as described for example in the document of D. Buxi, JM Redouté, and MR Yuce, "A Survey on Signals and Systems in Ambulatory Blood Pressure Monitoring Using Pulse Transit Time," Physiological Measurements, DOI 10.1088 / 0967-3334 / 36/3 / R1.
    Systolic events are measured non-invasively in clinical settings from the electrocardiogram (ECG), whose Q wave marks the beginning of the electrical activation of the ventricles, and the Doppler echocardiogram, which allows the opening and closing of the valve to be identified. aortic Although the ECG can be obtained relatively easily using surface electrodes, the measurement of systolic events
    Mechanical using the Doppler echocardiograph requires the exposure of the thoracic area and its preparation using an aqueous gel, in addition to an operator trained to handle the device, which leads to slow measurement and discomfort for the subject.
    An alternative to avoid using the Doppler echocardiograph is to detect the closure of the aortic valve from the sound S2 of the phonocardiogram (PCG) and calculate the LVET from a pulse sensor placed on the left carotid artery. The PEP is then calculated as the difference between S2 and the LVET, as described for example in the document of A. M. Weissler, W. S. Harris, and C. D. Schoenfeld, "Systolic Time Intervals in Heart Failure in Man," Circulation, DOI
    10.1161 / 01.CIR.37.2.149. Although this method prevents exposure and preparation of
    thorax, the correct placement of the sensors is complicated, especially the
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    Pressure sensor placement on the carotid artery, and is a common cause of measurement inaccuracies, so this method is rarely used.
    An alternative method to measure mechanical systolic events is by means of the impedance cardiogram (ICG), which consists of the recording of thoracic impedance changes detected between two pairs of electrodes normally located around the base of the neck and around the chest at the height of the xifoesternal line, as described for example in the document by L. Jensen, J. Yakimets, and KK Teo, "A Review of Impedance Cardiography," Hear. Lung J. Acute Crit. Care, DOI 10.1016 / S0147-9563 (05) 80036-6. Although this procedure to obtain the ICG is relatively simple, it requires the exposure of the subject's torso and the placement of adhesive electrodes, which entails slowness and discomfort.
    Another alternative to obtain mechanical information derived from systolic activity that requires less preparation of the subject is from fiducial points of the seismocardiogram (SCG), obtained from an accelerometer placed in the thorax, as detailed in the OT document Inan, PF Migeotte, K.-S. Park, M. Etemadi, K. Tavakolian, et al., "Ballistocardiography and Seismocardiography: a Review of Recent Advances," IEEE Journal of Biomedical Health and Informatics, DOI 10.1109 / JBHI.2014.2361732. Although the placement of accelerometers on the body is simpler than that of the electrodes and can be performed on the clothing, the position of the sensor significantly affects the shape and amplitude of the signal, and its orientation can cause crossings between axes, which leads to inaccuracies in the measurement.
    An additional alternative to record mechanical information derived from systolic activity that does not require the placement of sensors on the subject and that is less susceptible to crossings between axes is from fiducial points of the balistocardiogram (BCG), which reflects the variations experienced by the center of gravity of the human body as a result of the ejection of blood in each beat and the subsequent spread of the pressure pulse through the arterial network. The BCG can be obtained in multiple ways, some of which can be implemented with sensors incorporated in everyday objects, for example scales weighing people, chairs, seats or beds, as detailed in the same document of OT Inan, PF Migeotte, K.-S. Park, M. Etemadi, K. Tavakolian, et al. These solutions allow to obtain the BCG quickly and conveniently, and in some cases for periods of time
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    long, because sensors are not placed on the body but it is the body that comes into contact naturally with an element (platform, scale, chair, seat, bed, or an accessory used in conjunction with them, such as a mat, cover, pillow, etc.) where BCG sensors are incorporated. Although the I and J waves of the BCG have been used in some cases to indirectly detect variations in the moment of opening of the aortic valve and estimate the PEP, these waves are subsequent to the opening of the aortic valve, so their use for that purpose it requires a calibration that corrects its delay. In addition, until now no fiducial point of the BCG has been identified as a possible faithful indicator of aortic valve closure.
    Faithful detection of mechanical systolic events from the BCG would allow to assess the health status of the heart more quickly and comfortably even for long periods of time, which would be very useful for monitoring. It would also serve to calculate other indicators where mechanical systolic events intervene along with other cardiovascular parameters, for example in the determination of PTT to assess arterial elasticity or blood pressure.
    BRIEF DESCRIPTION OF THE INVENTION
    The invention consists of a method and an apparatus for detecting mechanical systolic events from the balistocardiogram (BCG). The innovative solution proposed by the present invention is the application of a transfer function to the BCG that compensates for the mechanical response of the subject's body so that the signal corresponding to the mechanical activity occurred in the heart and the aortic root can be reconstructed. and detect in said signal fiducial points that allow identifying the moments of opening and closing of the aortic valve. As the BCG is usually obtained by sensors integrated in a single element in contact with the body of the subject, the use of the BCG avoids the discomfort of having to place several sensors on its body.
    This innovative solution is based on the fact that BCG waves generated as a result of the ejection of blood at each beat are transmitted through the subject's body, which makes the recorded signal include the effect of the subject's own mechanical response of the body , which prevents the reliable observation of events
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    mechanical systolic actually occurred in the heart and aortic root. In order to reliably detect mechanical systolic events, a method is proposed to reconstruct the signal corresponding to the mechanical activity that occurred in the heart and the aortic root, which consists in applying a transfer function to the BCG that compensates for the effect of the mechanical response of the body of the subject, so that the global transfer function is flat and zero phase in the frequency range of interest, usually between 0.5 Hz and 50 Hz, and thus reflects only mechanical events occurring in the heart and the aortic root .
    A mechanical response of the body of the usual subject in BCG systems integrated in weigh-person scales is equivalent to a second-order low pass filter, whose resonance frequency fr and damping coefficient kd depend on the subject itself and have an approximate average value of 5 Hz and 0.2, respectively. A possible transfer function that compensates for the effect of said mechanical response could be, for example, one that consists of two zeros on
    the mechanical response poles, located in (2nfrkd, ± j'2nfrJl - kd2) in the
    diagram of zeros and poles, and two poles in the upper cutoff frequency fc, located at (2nfc, 0). To obtain the exact values of fr and kd that characterize the mechanical response of a subject's body, different methods can be used. For example, average values can be calculated from the subject's biometric data compared to statistical data obtained from a reference group, or a more personalized estimate can be made from the signal recorded in response to a maneuver performed by the own subject. From the application of said transfer function to the BCG a signal corresponding to the mechanical activity occurred in the heart and the aortic root is obtained where two groups of waves B1 and B2 are identified, whose waves can be used as fiducial points with which Identifies the opening and closing of the aortic valve.
    Although the proposed method could be implemented by an expert who reconstructs the signal corresponding to the mechanical activity that occurred in the heart and the aortic root from the BCG and an estimate of the mechanical response of the subject's body, and that visually identifies the fiducial points corresponding to mechanical systolic events, an optimal implementation is by means of an apparatus that contains the necessary signal processing systems
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    to apply to a BCG a transfer function that compensates for the mechanical response of the body of a subject and automatically locate fiducial points in the signal obtained, and that contains a communication system that is responsible for its representation in a display element or of the communication of the value to another device.
    The invention described herein has the main advantage that it allows to detect mechanical systolic events using only the BCG, that is, without the Doppler echocardiograph or the PCG, which facilitates its detection more easily, quickly and comfortably even for long periods of time. compared to other commonly used systems.
    DESCRIPTION OF THE DRAWINGS
    To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, a set of drawings is attached as an integral part of this description, where the following is illustrated and not limited to the following. :
    Figure 1 - Shows a diagram of a weigh-people scale capable of obtaining the BCG and constituting the element with which the subject comes into contact in one of the embodiments of the present invention.
    Figure 2 - Shows, from top to bottom, a record of the ECG, the BCG obtained with a weight scale-people, the signal corresponding to the mechanical activity occurred in the heart and the aortic root and the PCG, all measured simultaneously in the same subject .
    Figure 3 - Shows a trace obtained from a weigh-people scale during a maneuver to estimate the mechanical response of the subject's body, from which the resonance frequency and the damping coefficient can be estimated.
    Figure 4 - Shows an example of the mechanical response of a subject's body, the transfer function applied to compensate for it and the total transfer function.
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    EMBODIMENTS OF THE INVENTION
    In a preferred embodiment of the invention, a system integrated in a weight scale (1) detects a longitudinal BCG (along the body) indicative of the mechanical activity associated with cardiac ejection, from a sensor (2) formed by the strain gauges themselves used by the scale to measure body weight and an analog signal processing circuit (3), as shown in figure 1.
    From the BCG obtained at the output of the described system, a digital signal processing system (4) applies a transfer function that compensates the mechanical response of the subject's body so that the global transfer function is flat and zero phase in the range of frequencies of interest, between 0.5 Hz and 50 Hz, and a signal is obtained that corresponds only to the mechanical activity that occurred in the heart and the aortic root. In this preferred embodiment, the mechanical response of the body is modeled as a second order low pass mechanical filter with fixed resonance frequency values fr = 5 Hz and damping coefficient kd = 0.2, so that the transfer function that it is applied to compensate for said mechanical response consisting of two zeros on the poles of the low pass filter and a double pole at the upper cutoff frequency fc = 50 Hz. Next, the digital processing system (4) detects fiducial points in the signal obtained that allows to identify the opening and closing of the aortic valve, and that in this embodiment correspond to the beginnings of the wave groups B1 and B2, respectively. Finally, the communication module (5) is responsible for communicating the measured values through an LCD monitor.
    Figure 2 simultaneously shows an example of the ECG, the BCG and the signal corresponding to the mechanical activity that occurred in the heart and the aortic root of the same subject obtained in this embodiment, where the two groups of waves generated by the opening (B1) and the closure (B2) of the aortic valve, whose respective beginnings are used as fiducial points for the detection of the opening and closing of the aortic valve, and the PCG. The figure illustrates how group B1 is before wave I of the BCG and in the middle of group S1 of the PCG, as corresponds to the opening of the aortic valve, and that the start of group B2 coincides with the start of the S2 wave of the PCG, indicative of the closure of the aortic valve.
    To improve the accuracy in estimating the mechanical response of the subject's body, a second way of determining it is proposed in which it is obtained by a maneuver performed by the subject, consisting of tapping the 5 person-weight scale with the heel of a foot. Figure 3 shows an example of the signal obtained during this maneuver, from which the resonance frequency fr is determined by the equation
    N
    fr = t —t ’
    l2 l1
    where and t2 are the temporal positions of two peaks and N is the number of cycles
    which separates them, while the damping coefficient kd is measured from 10 the equation
    log (V1 - V2) d 2nN ’
    where V1 and V2 are the peak value in two cycles.
    Figure 4 shows the frequency response of the mechanical response of the subject's body calculated from fr and kd, and the frequency response of the function of
    15 transfer applied to the BCG to compensate for it and achieve a function of
    total flat and zero phase transfer in the frequency range of interest.
    Once the invention is sufficiently described, as well as two preferred embodiments, it should only be added that modifications to its constitution are possible,
    20 materials used, in the choice of the elements and sensors used to
    detect the BCG and in the methods to identify the fiducial points of the signal corresponding to the mechanical activity occurred in the heart and the aortic root, without departing from the scope of the invention, defined in the following claims.
    权利要求:
    Claims (1)
    [1]
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    1 - A method to detect mechanical systolic events from the balistocardiogram (BCG) of a subject characterized by:
    a) a transfer function that compensates the mechanical response of the subject's body is applied to the subject's BCG so that the total transfer function is flat in the bandwidth of interest
    b) mechanical systolic events are detected from fiducial points of the signal obtained by the previous process.
    2 - The method according to claim 1, characterized in that the mechanical response of the human body is modeled as a second-order low pass mechanical filter.
    3 - The method according to claim 2, characterized in that the resonance frequency is modeled as a fixed value between 4 Hz and 8 Hz and the damping coefficient is modeled as a fixed value between 0.5 and 0.005.
    4 - The method according to claims 1-2, characterized in that the parameters of the mechanical response of the subject's body are calculated from its biometric data compared to statistical data obtained from a group of reference subjects.
    5 - The method according to claims 1-2, characterized in that the parameters of the mechanical response of the subject's body are calculated from a maneuver performed by the subject.
    6 - The method according to claims 1-2 and 3,4 or 5, characterized in that the opening of the aortic valve is detected from fiducial points of the signal obtained.
    7 - The method according to claim 6, characterized in that the opening of the aortic valve is detected in the signal obtained from the start of the B1 wave group.
    8 - The method according to claims 1-2 and 3,4 or 5, characterized in that
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    detects the closure of the aortic valve from fiducial points of the signal obtained.
    9 - The method according to claim 6, characterized in that the closure of the aortic valve is detected in the signal obtained from the start of the B2 wave group.
    10 - An apparatus for automatically detecting mechanical systolic events from the balistocardiogram (BCG), comprising:
    a) a signal processing system capable of applying a transfer function to a BCG that compensates for the mechanical response of a subject's body so that the global transfer function is flat and zero phase in the frequency range of interest;
    b) a signal processing system capable of detecting fiducial points in the signal obtained from applying said transfer function to the BCG and identifying the opening and closing of the aortic valve from said fiducial points;
    c) a communication system capable of communicating the result obtained to a user or to another device.
    DRAWINGS
    image 1
    Communication
    Indicted
    digital
    Indicted
    analogical
    Sensor
    Figure 1
    image2
    Figure 2
    Magnitude (dB)
    image3
    Time (s) Figure 3
    -------- Mechanical body response
    .......... Correction
    --------- Total response
    image4
    Figure 4
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