WO2016035041A1 - Appareil et procédé de mesure non invasive de la pression d'un fluide confiné dans un contenant à parois souples ou rigides dotées d'une fenêtre souple - Google Patents

Appareil et procédé de mesure non invasive de la pression d'un fluide confiné dans un contenant à parois souples ou rigides dotées d'une fenêtre souple Download PDF

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Publication number
WO2016035041A1
WO2016035041A1 PCT/IB2015/056750 IB2015056750W WO2016035041A1 WO 2016035041 A1 WO2016035041 A1 WO 2016035041A1 IB 2015056750 W IB2015056750 W IB 2015056750W WO 2016035041 A1 WO2016035041 A1 WO 2016035041A1
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WIPO (PCT)
Prior art keywords
pressure
vibrator
accelerometer
vessel
vessel wall
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PCT/IB2015/056750
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English (en)
Inventor
Helena Catarina DE BASTOS MARQUES PEREIRA
Carlos Manuel Bolota Alexandre Correia
João Manuel RENDEIRO CARDOSO
Miguel DA GAMA FALCÃO CORREIA
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Universidade De Coimbra
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Publication of WO2016035041A1 publication Critical patent/WO2016035041A1/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/02133—Measuring pressure in heart or blood vessels by using induced vibration of the blood vessel
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0048—Detecting, measuring or recording by applying mechanical forces or stimuli
    • A61B5/0051—Detecting, measuring or recording by applying mechanical forces or stimuli by applying vibrations
    • 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
    • A61B5/7228—Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2560/00—Constructional details of operational features of apparatus; Accessories for medical measuring apparatus
    • A61B2560/02—Operational features
    • A61B2560/0223—Operational features of calibration, e.g. protocols for calibrating sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0219—Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches

Definitions

  • the present application discloses a non-invasive pressure sensing method and apparatus for continuously measuring the internal pressure of a fluid, confined in a vessel with elastic or rigid walls or fitted with an elastic window.
  • the pressure of a fluid confined in an elastic vessel can be measured in a number of different ways.
  • the standard method relies on the insertion of a pressure gauge through the vessel wall to provide a direct coupling from the enclosed fluid to the transducer's sensing surface.
  • This method provides a direct, accurate and continuous measurement of fluid pressure; however in some systems, such as the biological ones, it is not always reasonable to apply such an invasive approach.
  • the measurement of arterial blood pressure (ABP) in a living subject is perhaps the most significant case where the use of non ⁇ invasive methods has several advantages: ease of use, convenience, speed, low-cost, lower risk to the patient and ability to be applied to large number of subjects.
  • the most well-known non-invasive method of clinical measurement of ABP is based on a Riva-Rocci sphygmomanometer that is composed by an arm-encircling elastic cuff to occlude the blood vessel, a rubber bulb to inflate the cuff and an aneroid manometer to measure the blood pressure.
  • a stethoscope is required, in order to auscultate the sounds generated, as the cuff is slowly deflated.
  • These (Koroktoff) sounds - a complex series of audible frequencies produced by turbulent flow as the cuff is deflated - are clinically important for measuring systolic and diastolic blood pressures.
  • NIBP automated non-invasive blood pressure devices
  • NIBP NIBP-based on the technique called oscillometry that measures the amplitude of oscillations which show up in the inner cuff pressure signal during cuff deflation, using a pressure transducer inside the monitor. Peak amplitude of arterial pulsations corresponds to the mean arterial pressure. Values for systolic and diastolic pressures are derived using specific and often proprietary algorithms that evaluate the rate of change of the pressure pulsations.
  • Other techniques have been described for automated NIBP measurement, e.g.: employing a microphone in the place of the stethoscope or employing a transcutaneous Doppler sensor to detect the motion of the blood vessel walls in the different occlusion states, none have yet succeeded the standard oscillometric technique.
  • the Penaz method is based on unloading the arterial wall to measure a calibrated waveform in a finger.
  • a cuff is placed around the middle of a finger and blood pressure is determined by registering the cuff pressure needed to maintain a constant arterial volume, measured by light diodes or photoplethysmography .
  • Applanation tonometry consists in flattening a superficial artery supported by a bone structure, e.g. radial artery, using a pressure transducer called tonometer.
  • EP0681168B1 A method and apparatus for determining the internal pressure of a sealed container is disclosed in EP0681168B1. This approach uses a striker to excite, at least, the container' s fundamental radial circumferential mode of vibration and its first harmonic and an accelerometer to detect the vibration resulting from the striking of that container.
  • this approach differs from the present invention in significant aspects, such as : 1) the referred method is based on a vibratory mode analysis while the present one is based on the attenuation's analysis of a permanent oscillation induced by the vibrator and sensed by the accelerometer; 2) the referred apparatus is applied to a sealed substantially cylindrical container while the present apparatus must only be used in a vessel with an elastic wall or window; and 3) the present apparatus presents an unique configuration, based on the combination of one or several exciters/detectors. Other documents were analysed, namely 1) an exciter- detector unit for measuring physiological parameters
  • accelerometers for the non-invasive assessment of arterial blood pressure is also common in the literature, but usually as an auxiliary element that minimizes the error of a measurement, through the elimination of movement artifacts or positioning adjustment (US20070142730, US20110054329) .
  • the use of accelerometers as the main element of the measurement is in fact the most distinguishable feature of the present invention .
  • the present application discloses an apparatus and method for the non-invasive and continuous measurement of the internal pressure of a fluid confined in a vessel with elastic or rigid walls fitted with an elastic window.
  • the apparatus is based on a vibrator-accelerometer unit that is mounted on a common support containing at least one vibrator, as exciter, and at least one acceleration sensor, as detector.
  • the vibrator can be a mechanical or electro ⁇ mechanical device such as any type of motor or actuator, an electromagnetic loudspeaker of any type or a piezoelectric transducer.
  • the acceleration sensor is an electric, magnetic, optic or electronic device that delivers at least one electrical voltage proportional to the acceleration that is transmitted to him.
  • the method for pressure measurement relies on the amplitude modulation effect that occurs when the fluid pressure transmitted through the vessel wall or window attenuates the vibrator oscillations sensed by the accelerometer .
  • the vessel can be of any shape, including tubular, and of any nature, including the vessels of the vascular system of animals and humans, such as arteries and veins.
  • This technology further comprises a method of simultaneously estimating the morphology of the pressure wave and other related parameters such as vessel wall compliance, distension and distension dynamics and a method of calibrating the estimated pressure waveform based on the re-establishment of the attenuation to a predefined reference amplitude value whatever the force exerted on the vessel wall may be.
  • a method of simultaneously estimating the morphology of the pressure wave and other related parameters such as vessel wall compliance, distension and distension dynamics and a method of calibrating the estimated pressure waveform based on the re-establishment of the attenuation to a predefined reference amplitude value whatever the force exerted on the vessel wall may be.
  • the present technology is expected to have a particular impact in the fields of physiology and medicine, since it can be used for the non-invasive monitoring of ABP and other hemodynamic parameters.
  • the technology now disclosed aims at fulfilling all the foregoing needs providing an improved instrument and method for the non-invasive measurement of a fluid pressure confined in a vessel with elastic or rigid walls fitted with an elastic window, by means of a combined vibrator- accelerometer unit.
  • the accelerometer is mounted alongside the vibrator in a common platform and the measurement relies on the amplitude modulation effect that occurs when the fluid pressure, transmitted through the vessel wall or window, attenuates the vibrator oscillations sensed by the accelerometer .
  • Figure 1 is a block diagram of the present technology.
  • Figure 2a to 2d are cross-sectional views of a possible general configuration of the apparatus with its main elements, referring some of the preferred embodiments.
  • Figures 2e to 2f are cross-sectional views of an alternative configuration of the apparatus, referring some of the preferred embodiments.
  • Figure 3 is a 3-D top view of a possible external configuration of the present apparatus.
  • Figure 4 depicts the main recording sites for arterial pressure assessment in a living subject and the preferred attachment mechanisms for signal acquisition with the present technology.
  • Figure 5a is a schematic flowchart explaining the general stages of the first preferred method for fluid pressure and other related parameters estimation.
  • Figure 5b is a schematic flowchart explaining the general steps of the second preferred method for fluid pressure and other related parameters estimation.
  • Figure 6 is a graphic representation of the typical signals acquired in a test bench system with the present technology, based on a 3-axis accelerometer, right before the probe is in contact with the vessel wall and when it progressively gets in touch with the vessel wall.
  • Figures 7a to 7c are graphical representations of the signals obtained in a test bench system, with a 3-axis accelerometer based probe and with a manometer that is inserted through the vessel wall.
  • Figure 7d is a graphical representation of the manometer reference signal and the upper and lower profiles computed from the signals presented in figures 7a to 7c, using the envelope detector approach.
  • Figure 7e is a graphical representation of the filtered frequency spectra of the product between the modulated carriers and the original carrier wave, when the product detector approach is used.
  • Figure If is a graphical representation of the manometer reference signal and the time profiles computed from the signals presented in figures 7a to 7c, using the product detector approach.
  • Figure 7g is a graphical representation comparing the waveform obtained, invasively, with the manometer and the waveform obtained, non-invasively, using the difference between the lower and the upper profiles of the accelerometric signal that is aligned with the direction of the vessel wall movement.
  • Figure 7h is a graphical representation comparing the waveform obtained, invasively, with the manometer and the waveform obtained, non-invasively, using the total profile of the profiles presented in figure 7d.
  • Figure 7i is a graphical representation comparing the waveform obtained, invasively, with the manometer and the waveform obtained, non-invasively, using the upper and lower profiles of the accelerometric signal that is aligned with the direction of the vessel wall movement.
  • Figure 7j is a graphical representation comparing the waveform obtained, invasively, with the manometer and the waveform obtained, non-invasively, using the recovered time profile of the accelerometric signal that is aligned with the direction of the vessel wall movement presented in figure 7f.
  • Figure 71 is a graphical representation comparing the waveform obtained, invasively, with the manometer and the waveform obtained, non-invasively, using the total profile of the profiles presented in figure 7f.
  • Figure 7m is a graphical representation of calibrated pressure waveforms resultant from the computation of the lower profile presented in figure 7i and the calibration equation .
  • Figure 8 is an example of a calibration curve, obtained experimentally, for use in arterial blood pressure assessment .
  • Figures 9a to 9c are graphical representations of raw (unprocessed) signals acquired in a human subject with a 3- axis accelerometer based probe, when the sensing apparatus is placed on the carotid artery.
  • Figure 9d is a graphical representation of the upper and lower profiles computed from the signals presented in figures 9a to 9c, using the envelope detector approach.
  • Figure 9e is a graphical representation of the profiles that result from the four preferred approaches: lower and upper profiles of the accelerometric signal that is aligned with the direction of the vessel wall movement, difference between the previous profiles and total profile of the signals presented in figure 9d.
  • Figure 9f is a graphical representation showing the sum of the upper and lower profiles of the accelerometric signal that is aligned with the direction of the vessel wall movement .
  • Figure 9g is a graphical representation of calibrated arterial pressure waveforms resultant from the computation of the difference between the lower and the upper profiles presented in figure 9e and the adequate calibration equation .
  • Figure 9h is a graphical representation of calibrated arterial pressure waveforms resultant from the computation of the total profile presented in figure 9e and the adequate calibration equation.
  • Figure 9i is a graphical representation of calibrated arterial pressure waveforms resultant from the computation of the lower profile presented in figure 9e and the adequate calibration equation.
  • Figure 9j is a graphical representation of calibrated arterial pressure waveforms resultant from the computation of the upper profile presented in figure 9e and the adequate calibration equation.
  • Figure 91 is a graphical representation of one calibrated arterial pressure waveform presented in figure 9g and its main prominent points.
  • Figure 10a is an example of a calibration curve, obtained experimentally, for pressure measurement of a fluid confined in an elastic vessel.
  • Figure 10b is a graphical representation comparing the waveform obtained, invasively, with the manometer and the calibrated waveform obtained, non-invasively, with the apparatus through the computation of the difference between the lower and the upper profiles and the adequate calibration curve (figure 10a) .
  • the technology is a probe 2 and a system for non-invasive and automatic measurement of the internal pressure of a fluid confined in a vessel with elastic or rigid walls or fitted with an elastic window in the wall.
  • the technology is a set of methods for assessing internal pressure of the fluid and other related parameters that are independent of the operator's action, that is to say, on the force that he exerts on the vessel wall.
  • the probe 2, system and the set of methods are used to assess physiological function, e.g. arterial blood pressure, of a human subject in order to provide baseline information about his cardiovascular status.
  • physiological function e.g. arterial blood pressure
  • the technology may also conceivably be adapted to monitor physiological function on other warmblooded species.
  • FIG. 1 illustrates the components and general process of the preferred embodiment.
  • a probe 2 is placed in mechanical contact with one wall or window of the vessel that contains the confined fluid 1.
  • the probe 2 includes a vibrator 4 and an accelerometer 3, mounted on a common platform, and it is connected to an acquisition system 5 and to a signal generator 9 which is responsible for delivering an oscillating electrical signal to the vibrator.
  • the vibrator generates an equivalent oscillating perturbation that is transmitted to the mechanical unit and is sensed by the accelerometer.
  • the fluid pressure that is transmitted through the vessel wall or window is also sensed by the accelerometer in such a way that its permanent oscillatory signal derived from vibrator' s excitation is attenuated and modulated in amplitude.
  • the output of the probe 2 is fed to a conditioning circuit 6 that amplifies the accelerometer signals and monitors the instantaneous current and power of the vibrator 4 using a sensing resistor.
  • the signals are then deliver to a digitizer 7 that converts the analog signals to a digital representation.
  • the digitized signals are supplied to an electronic control device 8 that performs the various steps that constitute the methodology of the technology, including: peak detection 12, profiles extraction 13, artifact removal 14, calibration 11 and estimation of fluid pressure and other related variables 15.
  • the electronic control device 8 output signal is then converted to a useful form for the user by means of a digital or analog display device that contains numerical and graphical information.
  • the electronic control device 8 can also be responsible for controlling and generating the signals that excite the vibrator, by means, for instance, of a direct digital synthesizer (DDS) .
  • DDS direct digital synthesizer
  • Figures 2a to 2e show preferred embodiments of the probe 2 that constitutes the present technology.
  • the main elements that constitute the probe 2 are: 1) at least one accelerometer 3 ; 2) at least one vibrator 4; 3) a printed circuit board (PCB) or other support board with the respective electrical connections 16; 4) a mechanical interface 17 that is in contact with the vessel wall 18; 5) a semi-rigid bed such as foam, plastic or some type of metalloid 19 that accommodates the main structure and 6) a frame 20 that encloses the assembly and is adapted to be held against the vessel wall 18 by a fixation device or an operator.
  • PCB printed circuit board
  • the vibrator 4 can be a mechanical or electro- mechanical device such as any type of off-axis motor or actuator, an electromagnetic loudspeaker of any type or a piezoelectric.
  • the acceleration sensor is an electric, magnetic or electronic device that delivers one or more electrical voltages proportional to the acceleration that is transmitted to it.
  • the mechanical interface 17 consists in a flattened-shaped-piece or another element with an ergonomic configuration, such as a polymeric material, that allows the transmission of the moving wall distension to the sensing unit. The centre of the mechanical interface 17 is aligned with the centre of the vibrator.
  • the accelerometer 3, mounted on the same board than the other two elements is positioned anywhere either alongside the vibrator 4 or alongside the mechanical interface 17 as illustrated in figures 2a to 2d. In another embodiment, illustrated in figures 2e to 2f, the accelerometer 3 is placed on the opposite side of the board where the vibrator 4 stands and is aligned with the centre of the latter one.
  • the sensing probe there are several possible implementations of the sensing probe in what concerns its arrangement, elements positioning and encasement.
  • an accelerometer 3 of the Microelectromechanical System (MEMS) type and one vibrator, contained and connected by a PCB.
  • the accelerometer 3 is of the MEMS type, and there is at least two vibrators 4, contained and connected by a PCB.
  • this embodiment is suitable for using either two different frequencies of vibration or very similar frequencies, in order to create beats.
  • Both accelerometers 3 are equally oriented and well aligned and the output of both signals can be electronically subtracted, in order to remove all common acceleration components.
  • This configuration is suitable mainly for eliminating artifacts or parasitic mechanical interferences that are introduced, for instance, by an operator.
  • This configuration is also adequate in circumstances in which 2-axis MEMS accelerometers are used to obtain 3-axis acceleration information .
  • the accelerometer 3 of the MEMS type and the vibrator 4 are contained and connected by a PCB that enhances the vibrations of the assembly.
  • the PCB presents a distinctive structure where the rear part is fixed to the case with screws 21 and the front part is free and can vibrate with more amplitude due to the middle beam-shaped structure that joins them.
  • the interface piece is aligned with the centre of the vibrator 4 that is mounted on the opposite side of the PCB and is pressed against a semi-rigid material.
  • the interface piece is directly coupled to a non-flexible bridge 22 that is placed in the middle of the vibrator 4.
  • the interface is a polymeric material that covers and/or encapsulates the vibrator 4 in such a way that the whole vibrator's surface may be used to touch the vessel wall 18. In what concerns the vibrator' s support, two different arrangements can be identified.
  • the vibrator 4 is in contact with the PCB by means of a foot holder 23 that supports it in the centre.
  • a foot holder 23 that supports it in the centre.
  • an equilateral configuration in which three equidistant foot holders 23 sustain the vibrator 4 at its periphery is used. In both cases, the foot holders 23 serve as spacers between the vibrator 4 and the PCB.
  • the sensing probe is contained in a sensing frame, such as plastic or metal housing 24, and is in contact with the vessel by means of an interface piece 25 that locally compresses the elastic wall.
  • the sensing probe can be framed on a patch that includes the vibrator-accelerometer unit and is coupled directly to the vessel wall 18, using an attachment mechanism such as an adhesive layer, a band or belt that holds the patch.
  • the preferred probe 2 implementation is applied to measure the arterial blood pressure of a human subject, using two different approaches.
  • the encased probe 2 is held by an operator 26, while in the second it is attached to the subject by means of a Velcro® collar 27, a rubber band or any other fixation device known to one skilled in the art.
  • the sensor frame that is being held is adjacent to an anatomical position of the subject, and the mechanical interface is overlying, with a certain pressure, a superficial artery where the pulse is palpable, such as: carotid A, braquial B, radial C or femoral D arteries.
  • FIG 5a the method for measuring fluid pressure according to the present technology is schematically described in a block diagram.
  • the first step to start of the process consists in setting the parameters of excitation of the vibrator 28.
  • the excitation waveform that drives the vibrator 4 can be sinusoidal, square, triangular or of any suitable shape and its frequency can be comprised of a wide range of frequencies and applied either in a continuous or burst mode.
  • Experiments conducted to determine the range of satisfactory frequencies found that a range superior to 150Hz works well with human tissues. Nevertheless, it was verified that the optimal frequency to be used, though conditioned by the accelerometer bandwidth, should correspond to the frequency where the maximum amplitude of the acceleration oscillations is achieved.
  • the first stage of the method involves the determination of this optimal frequency of vibration, which will allow getting the maximum system' s gain .
  • the acquisition process starts immediately before the probe 2 is positioned and pressed against the vessel wall 18, in order to establish an acceleration carrier amplitude
  • the (constrained) amplitude-modulated oscillations sensed by the accelerometer are recorded 32.
  • the data may be acquired over a short period of time, for example 5s, 30s or 60 seconds. Other data acquisitions times can also be considered by the present technology.
  • data can be acquired continuously over a long period of time, such as 24-48h.
  • recordings should be made over the period of time during which it is interesting to cover fluid pressure variability.
  • Figure 6 illustrates the typical signals acquired in a test bench system with the present technology, based on a 3-axis accelerometer, in this initial acquisition process.
  • the axis c is aligned with the direction of the vessel wall movement and the other two axis a, b are orthogonally lined up with the axis c, from now on, a, b and c refer to the x, y and z directions depicted in figure 2..
  • region Rl shows the oscillations sensed by the accelerometer, right before the probe is in contact with the vessel wall; region R2 coincides with the positioning of the probe when it progressively gets in touch with the vessel wall and R3 represents the accelerometer oscillations, when the probe is placed on the vessel wall, with a certain pressure.
  • the difference between the amplitude of the oscillations from regions Rl and R3 corresponds to the attenuation At c that is proportional to the force that is exerted on the tube.
  • the principle of operation of the sensing apparatus is based on the amplitude modulation of the accelerometric signals that takes place when the probe 2 is set on the vessel wall 18 and the fluid pressure, transmitted through it, attenuates the vibrator 4 oscillations sensed by the accelerometer 3.
  • the probe 2 is submitted to a sinusoidal displacement x(t) induced by the vibrator then:
  • L is the amplitude of the oscillation
  • w is the angular frequency of the oscillation
  • 6(t) is the phase of the oscillation.
  • the sinusoidal waveform x(t) is sensed by the accelerometer as:
  • This waveform is known as the carrier wave or carrier and corresponds to an unconstrained and therefore unmodulated oscillation .
  • the amplitude L suffers an immediate attenuation At c (0 ⁇ At c ⁇ 100%) that is proportional to the force that is applied on the vessel wall F and also to the resistance that is offered by the vessel wall 18 to the deformation (stiffness k) .
  • the fluctuations in fluid pressure P are also transmitted through the vessel wall 18, modulating the oscillations sensed by the accelerometer 3 through attenuation.
  • the fluid pressure variation is defined as the modulating signal and the accelerometer signal corresponds to the amplitude-modulated carrier.
  • the attenuation At c of the modulated data can be measured up to 100% in the total amount of amplitude L.
  • i (t) and p(t) are the current and power signals of the vibrator 4.
  • v(t) is the voltage delivered to the vibrator 4 by a signal generator 9, matching the carrier wave x(t) and bi, b 2 , b 3 are calibration constants.
  • a reverse process of demodulation 45 is initiated on the electronic control device 8, with peak detection of the respective modulated amplitude oscillations 34.
  • the local maxima and minima are calculated using a threshold based approach and then interpolated, where in the upper and lower envelopes of the modulated carrier are extracted 35. These envelopes, corresponding to the modulating signal, undergo a filtering stage to remove the high frequency noise 36 that is typically present in this type of measurements.
  • the extracted lower and upper profiles ( lp, up ) are the main sources of information of fluid pressure fluctuations, allowing a direct estimation of the fluid pressure waveform or even the extraction of operator handling artifacts.
  • Different methods based on the use of at least one profile 38, can be used to assess the pressure wave morphology 40.
  • the simplest method uses either the upper or the lower profiles extracted from the accelerometer 3 signal that matches the direction of the vessel wall 18 movement ( ⁇ ⁇ ⁇ ⁇ , ⁇ ⁇ ⁇ ) ⁇
  • Another method requires the determination of the difference between the lower and the upper profiles 37, extracted also from the accelerometer 3 signal that matches the direction of the vessel wall 18 movement ( lp mov - up mov ) .
  • a third method, applied when the technology is based on a 3- axis accelerometer involves the computation of the total profile 39, ( total _ profile _a ) extracted from the various orthogonal accelerometer signals, where:
  • aux_ mov lp mov - up mov (Eq. 10)
  • aux _ orth l lp ol -up ol (Eq. 11)
  • lp 0 ⁇ -up oX , lp o2 -upo2 are the differences between the lower and the upper profiles, extracted from the accelerometer 3 signals that match the orthogonal directions to the vessel wall 18 movement.
  • this method allows the recovery of the modulating signal through the following steps: a) computation of the product of the modulated carrier (s) and the original carrier wave, i.e. excitation waveform that drives the vibrator 47; b) computation of the frequency spectra using the fast Fourier transform algorithm 48; c) low pass filtering of the frequency spectra 49 and d) computation of the time profiles by means of the inverse Fast Fourier Transform algorithm 50.
  • the recovered time profiles, corresponding to the modulating signal then undergo a smoothing stage to remove the high frequency noise 51.
  • the morphology of the pressure wave can also be assessed using one or several profiles 52.
  • the simplest method uses the profile extracted from the accelerometer/current/power signal that matches the direction of the vessel wall 18 movement ( p mov ) .
  • the calibration method is focused on the use of calibration curves (acceleration-pressure type), who's determination and application demand the conservation of the acceleration sensed by the apparatus.
  • the acceleration carrier amplitude measured when the sensing probe is freely vibrating must be the same as that measured when it is pressed against the vessel wall.
  • the electronic control device 8 manually or automatically chooses the adequate calibration curve from the database of curves to be used, according to the acceleration carrier amplitude established as reference.
  • the implementation of an automatic acceleration-voltage control loop is crucial for the efficiency of the calibration process.
  • the loop constantly measures the attenuation of the acceleration carrier when the sensing tip is placed on the elastic wall, re-establishing the reference amplitude value through the adjustment of the vibrator's input voltage. As such, whatever the force exerted on the vessel wall 18 may be during the acquisition process, it does not interfere with the calibration process.
  • the distension of vessel wall 18, for example, can be inferred when the sensing unit is not being excited, and the accelerometer 3 only senses the displacement changes associated with the pressure wave propagation. It is also possible to assess vessel wall 18 distension, when the sensing unit is being excited, by means of the sum of the upper and lower profiles, extracted from the modulated accelerometer 3 signals (Ip + up) . Independently of the method that is used, it's necessary to end the process with a double integration of the obtained acceleration signal, to quantify the total displacement of the vessel wall 18.
  • ⁇ is another parameter that can be easily estimated.
  • ⁇ is obtained directly from the calibrated pressure waveform while AV is calculated based on the geometry and distension of the vessel.
  • This embodiment aimed at non-invasively measuring the morphology of a pressure wave that propagates through a fluid confined in an elastic tube.
  • a special purpose test bench was developed, capable of originating arbitrarily shaped pressure waveforms through a latex tube with diameter and wall thickness of the same order of magnitude as that of a large artery.
  • the pressure waves were generated manually by a piston mechanism placed at one of the extremities and launched in a 70cm long tube (12.7mm inner diameter, 0.8mm wall thickness), filled with water.
  • a manometer placed longitudinally to the tube monitored the DC pressure level and the pressure fluctuations. Measurements were performed over a short period of time and close to the pressure sensor, using the apparatus and the method according to the present technology.
  • the sensing probe based on a 3-axis accelerometer, was excited by a continuous 700Hz sinusoidal waveform and held by a fixation device that allowed maintaining a constant force, while the probe 2 was against tube's wall sensing pressure variations.
  • Data acquisition was performed through a dedicated acquisition system 5, based on a 16-bit digitizer. All the signals were sampled at 12.5 kHz and stored for offline analysis. The accelerometric data were then compared with the data taken by the manometer, used as the reference device in pressure assessment .
  • the acquired data are presented in figures 7a to 7c, where a, b, c are modulated carriers and d is the manometer reference signal, c is the modulated carrier sensed by the accelerometric axis aligned with the direction of the vessel wall 18 movement and the other two modulated carriers (a, b) are sensed by the accelerometric axes orthogonally lined up with the first one.
  • the upper and lower profiles of the modulated carriers were extracted, as illustrated in figure 7d, and then slightly smoothed, where: al, bl, cl are the lower profiles and a2, b2, c2 are the upper profiles of the previous described modulated carriers.
  • FIGS 7g to 71 graphical representations comparing the waveform obtained, invasively, with the manometer and the waveforms obtained, non-invasively, using the different methods of the present invention are illustrated.
  • the root mean square errors (RMSE) between the reference waveform and the waveforms obtained using different methods were determined and are summarized in table 1.
  • the cl, c2 and c3 profile is obtained through the accelerometric axis that is aligned with the direction of the vessel's wall 18 movement.
  • the present study shows that the different methods used by the present technology have the capability of precisely rendering the original pressure waveform, evidencing a better performance when the lower profile method or the profiles difference approach are used.
  • Figure 7m exemplifies a calibrated pressure waveform resultant from the computation of the best method (lower profile cl) and the calibration equation, obtained experimentally, in this study, as illustrated in figure 8.
  • the presented range of values covers the range of the typical normal values of a healthy human artery.
  • APW calibrated arterial pressure waveform
  • the sensing probe 2 based on a 3-axis accelerometer, was excited by a continuous 700Hz sinusoidal waveform and held by an operator that attempted to maintain a constant pressure on the carotid artery. Data acquisition was performed through a dedicated acquisition system 5, based on a 16-bit digitizer. All the signals were sampled at 12.5 kHz and stored for offline analysis.
  • e corresponds to the upper and lower profiles difference method, f to the total profile method, cl to the lower and c2 to the upper profiles3 approach.
  • An additional method, based on the sum of the upper and lower profiles3 was also applied, in order to obtain the mean baseline fluctuations of the accelerometric data, illustrated in figure 9f.
  • the obtained pattern represents not only the wall acceleration waveform, but also some artifacts that could be induced by the operator, during acquisition.
  • the profile is obtained through the accelerometric axis that is aligned with the direction of the vessel's wall 18 movement .
  • DP ventricular ejection time
  • LVET LVET
  • Buckberg index tension time index
  • diastolic time index or other related parameters known to one skilled in the art .
  • This study aimed at non-invasively measuring the water pressure confined in a latex tube for different applanation positions .
  • Measurements were performed in the test bench system described in embodiment 1, using the apparatus and the method according to the present technology.
  • the sensing probe rigidly attached to a tri-axial position monitoring system, was placed at the end of the latex tube, close to the manometer and was excited by a continuous sinusoidal waveform whose frequency matched its mechanical resonance value.
  • Ten distinct measurements with successively higher applanation positions were performed over a short period of time, aiming to acquire the pressure wave generated by a piston that was manually maneuvered by an operator.
  • the linear positioner system travelled to positions ranging from 80500 to 113500 microsteps, guarantying that the PZ's central part was in direct contact and flattening the latex tube.
  • the several acquisitions were carried out following the conservation of the acceleration carrier amplitude, more precisely the value pre-established in the calibration curve to be used, illustrated in figure 10a.
  • the input voltage of the excitation signal that drives the vibrator was adjusted in order to restore the reference calibration value.
  • the pressure wave was generated and acquired by the apparatus. Data acquisition was performed through a dedicated acquisition system, based on a 16-bit digitizer. All the signals were sampled at 12.5 kHz and stored for offline analysis.
  • the calibration curve was applied to the acceleration modulating profile recovered using the envelope detector algorithm and the difference between the lower and the upper profiles method.
  • the main characteristic pressure values (maximum, minimum, mean and difference) obtained with the technology after calibration were compared with the reference pressure values obtained with the manometer.

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Abstract

La présente invention concerne un appareil et un procédé pour la mesure non-invasive et continue de la pression interne d'un fluide confiné dans un contenant ayant des parois souples ou rigides ou équipé d'une fenêtre souple dans la paroi. L'appareil est basé sur une combinaison vibreur-accéléromètre montée sur un support commun, qui permet à l'accéléromètre de détecter les vibrations produites. Le procédé de mesure de pression repose sur l'effet de modulation d'amplitude qui survient lorsque la pression de fluide transmise à travers la paroi du contenant ou de la fenêtre atténue les oscillations du vibreur détectées par l'accéléromètre. Cette technologie comprend en outre : 1) un procédé d'estimation simultanée de la morphologie de l'onde de pression et d'autres paramètres associés tels que l'élasticité, la distension et la distension dynamique, et 2) un procédé d'étalonnage de la forme d'onde de pression estimée sur la base du rétablissement de l'atténuation à une valeur d'amplitude de référence prédéfinie, quelle que soit la force exercée sur la paroi du contenant. Bien qu'ayant d'autres applications possibles, l'invention a pour but principal l'évaluation non invasive de la pression artérielle et de la forme d'onde de la pression artérielle chez l'humain.
PCT/IB2015/056750 2014-09-04 2015-09-04 Appareil et procédé de mesure non invasive de la pression d'un fluide confiné dans un contenant à parois souples ou rigides dotées d'une fenêtre souple WO2016035041A1 (fr)

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Cited By (2)

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WO2019155390A1 (fr) * 2018-02-06 2019-08-15 Tarilian Laser Technologies Limited Surveillance continue non invasive de la pression artérielle
US20210161503A1 (en) * 2018-06-07 2021-06-03 Healthcare Technology Innovation Centre Multi-modal ultrasound probe for calibration-free cuff-less evaluation of blood pressure

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US5904654A (en) 1995-10-20 1999-05-18 Vital Insite, Inc. Exciter-detector unit for measuring physiological parameters
EP0681168B1 (fr) 1994-05-04 1999-11-10 The BOC Group plc Procédé et appareil pour déterminer la pression interne d'un récipient fermé
US6471655B1 (en) 1999-06-29 2002-10-29 Vitalwave Corporation Method and apparatus for the noninvasive determination of arterial blood pressure
EP1743572A1 (fr) * 1996-06-26 2007-01-17 Masimo Corporation Appareil de mesure rapide et non-invasive de la tension arterielle
US20070142730A1 (en) 2005-12-13 2007-06-21 Franz Laermer Apparatus for noninvasive blood pressure measurement
US20110054329A1 (en) 2009-08-27 2011-03-03 Memsic, Inc. Devices, systems, and methods for accurate blood pressure measurement
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Publication number Priority date Publication date Assignee Title
US5590649A (en) 1994-04-15 1997-01-07 Vital Insite, Inc. Apparatus and method for measuring an induced perturbation to determine blood pressure
EP0681168B1 (fr) 1994-05-04 1999-11-10 The BOC Group plc Procédé et appareil pour déterminer la pression interne d'un récipient fermé
US5904654A (en) 1995-10-20 1999-05-18 Vital Insite, Inc. Exciter-detector unit for measuring physiological parameters
EP1743572A1 (fr) * 1996-06-26 2007-01-17 Masimo Corporation Appareil de mesure rapide et non-invasive de la tension arterielle
US6471655B1 (en) 1999-06-29 2002-10-29 Vitalwave Corporation Method and apparatus for the noninvasive determination of arterial blood pressure
US20070142730A1 (en) 2005-12-13 2007-06-21 Franz Laermer Apparatus for noninvasive blood pressure measurement
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GB2493850A (en) * 2011-08-17 2013-02-20 Cercacor Lab Inc Modulated physiological sensor

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019155390A1 (fr) * 2018-02-06 2019-08-15 Tarilian Laser Technologies Limited Surveillance continue non invasive de la pression artérielle
CN111989033A (zh) * 2018-02-06 2020-11-24 胡马疗法有限公司 非侵入式连续血压监测
US20210161503A1 (en) * 2018-06-07 2021-06-03 Healthcare Technology Innovation Centre Multi-modal ultrasound probe for calibration-free cuff-less evaluation of blood pressure

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