PT2016035041B - Apparatus and method for non-invasive pressure measurement of a fluid confined in a vessel with elastic or rigid walls fitted with an elastic window - Google Patents

Description

DESCRIPTION apparatus and method for non-invasive blood pressure measurement

A FLUID CONFINED IN A WALL OF ELASTIC WALLS OR

RIGID WALLS GATED FROM AN ELASTIC WINDOW

Technical Area of the Invention

This invention relates to a non-invasive detection method and apparatus for continuously measuring the internal pressure of a fluid confined in an elastic wall vessel or provided with an elastic window.

Background Art / Background of the Invention

The pressure of a confined fluid in an elastic vessel can be assessed in various ways. The standard method is to insert a pressure gauge through the vessel wall to provide direct coupling from the fluid to the transducer detection surface. This method provides a direct, accurate and continuous measurement of fluid pressure; however, in some systems (such as biological), it is not always appropriate to apply such an invasive approach. Measuring blood pressure (BP) or blood pressure in a living individual is possibly the most significant case where the use of noninvasive methods has several advantages: ease of use, convenience, speed, low cost, lower patient risk, and ability to be applied to a large number of subjects.

The present invention is expected to have particular impact in the fields of physiology and medicine as it can be used for noninvasive monitoring of BP and other hemodynamic parameters. The most well-known noninvasive method of clinical BP measurement is based on a Riva-Rocci sphygmomanometer which consists of an elastic cuff surrounding the arm to occlude the blood vessel, a rubber bulb to inflate the cuff and an aneroid manometer. to measure blood pressure. When BP measurement is obtained manually, a stethoscope is required to hear the sounds generated as the cuff is slowly deflated. These sounds (Koroktoff) - a complex series of audible frequencies produced by turbulent flow while the cuff is emptied - are clinically important for measuring systolic and diastolic blood pressure. When BP measurement is obtained by non-invasive automatic BP measurement devices (NIPA), a stethoscope is not required.

Most NIPA automatic systems are based on the oscillometry technique that measures the amplitude of oscillations that appear on the cuff internal pressure signal during cuff emptying using a pressure transducer inside the monitor. The maximum amplitude of arterial pulsations corresponds to the mean arterial pressure. Values for systolic and diastolic pressures are obtained using specific and often proprietary algorithms that evaluate the rate of change of pressure pulsations. Although other techniques have been described for automatic BP measurement (eg using a microphone instead of a stethoscope or a transcutaneous Doppler sensor to detect the movement of blood vessel walls in different occlusion states), none of them still prevailed the oscillometric technique.

The non-invasive methods previously described (standard auscultatory method and oscillometry) are widely used in clinical practice, however, they only allow discrete and slow BP measurements. Both methods typically require 20-45 seconds to obtain a valid measurement and a long period (> 1 minute) is required to start a new measurement to avoid damage to the wall vessels. These methods also have other drawbacks such as: peripheral BP measurement, dependence on appropriate cuff size, operator sensitivity dependence (auscultatory method), absence of a standardized algorithm for identifying systolic and diastolic pressures, and inconsistent measurements. due to lack of system validation (oscillometric method).

In order to address the need for continuous and noninvasive BP analysis, several systems have been suggested. Gues that are well accepted among the medical community are based on either the Poor method or the applanation arterial tonometry. Penaz's method is based on the measurement of a calibrated arterial waveform on a finger. A cuff is placed around the middle of the finger and blood pressure is determined by recording the cuff pressure required to maintain a constant arterial volume (measured by light-emitting diodes or photoplethysmography). Arterial applanation tonometry is the applanation of a superficial artery supported by a bony structure (radial artery, for example) using a pressure transducer (tonometer). Both methods allow continuous BP wave recording and pulse-to-pulse BP measurement. However, these two methods only allow distal measurement, particularly vulnerable to motion artifacts. In tonometric measurements a highly specialized operator is required since the positioning of the tonometer tip as well as the compression level on the vessel wall has to be very precise and repeatedly adjusted and recalibrated. In addition, and in order to obtain a calibrated pressure waveform, applanation arterial tonometry requires an external device, usually based on a cuff technique, to achieve the minimum (diastolic) and maximum (systolic) values. blood pressure.

In measurements based on the Penaz method, there is a high risk of venous occlusion due to permanent cuff inflation. This method also has other disadvantages such as high cost, inconvenience to the patient and relative inaccuracy in measuring absolute BP levels.

Based on the foregoing, it is clear that a new method and system for continuous and non-invasive BP measurement and related parameters needs to be developed in a simple, convenient, clamp-free manner with reduced susceptibility to noise and movement. subject / operator and insensitivity to the positioning of the device on the subject. The present invention aims to fill in all of the foregoing gaps by providing an improved instrument and method for noninvasive measurement of fluid pressure confined in an elastic wall or rigid wall vessel provided with an elastic window by means of a combined unit. accelerometer-vibrator. The accelerometer is mounted next to the vibrator on a common platform and the measurement is based on the amplitude modulation effect that occurs when fluid pressure transmitted through the vessel wall or window attenuates vibrator oscillations detected by the accelerometer.

Description of Related Art

Existing literature reveals several attempts to measure the internal pressure of a fluid in a non-invasive manner using exciter-detector units.

EP0681168B1 discloses a method and apparatus for determining the internal pressure of a sealed container. This approach uses a beater to excite at least the container radial circumferential fundamental mode of vibration and its first harmonic, and an accelerometer to detect the vibration resulting from beating in that container. However, this approach differs from the present invention in significant respects such as: 1) said method is based on a vibration mode analysis while the present method is based on the vibration-induced permanent oscillation attenuation analysis detected by the accelerometer; 2) said apparatus is applied to a sealed, substantially cylindrical container, whereas the present apparatus is to be used only in a vessel with an elastic wall or window; and 3) the present apparatus has a unique configuration based on the combination of one or more exciter / detectors.

Other patents have been further analyzed, namely 1) an exciter-detector unit for measuring physiological parameters (US5904654), 2) an apparatus and method for measuring an induced disorder to determine blood pressure (US55590649) and 3) a method and device for noninvasive determination of BP (US6471655). In the first and second patents, the principle of obtaining hemodynamic parameters is based on the induction of a disturbance in the body, followed by the detection and study of the disturbance after it has traveled a certain distance along the body. In the third patent, an ultrasound-based apparatus transmits an acoustic wave into the vessel during compression, receives its echo, and estimates the pressure within the vessel using an echo time-frequency distribution. All of these inventions differ from the present invention, where a permanent disturbance is mainly used to excite the accelerometer rather than the vessel wall and is not reintroduced into the system.

It should also be mentioned that the use of accelerometers for noninvasive BP assessment is also common in the literature, but generally as an auxiliary element that minimizes measurement error by eliminating motion artifacts or positioning adjustment ( US20070142730, US20110054329). The use of accelerometers as the main element of measurement is in fact the most distinguishable feature of the present invention.

As a final note, it is also important to note that the idea of using acceleration sensors to assess other aspects of cardiovascular condition was first disclosed in 2007 in the project report entitled Cardioacelerometry - The assessment of pulse wave velocity using accelerometers. Different acceleration sensor-based devices for assessing pulse wave velocity were presented in this report, and the results obtained on test benches or various subjects suggested the enormous potential of these sensors to evaluate a significant number of hemodynamic parameters. However, the present invention uses a totally different approach, both in terms of device architecture and its main application (internal fluid pressure measurement).

Summary of the Invention

The present invention relates to an apparatus and method for noninvasive and continuous measurement of the internal pressure of a fluid confined in an elastic wall or rigid walled vessel provided with an elastic window.

The apparatus is based on a vibrometer-accelerometer unit which is mounted on a common support containing one or more vibrators as exchangers and one or more acceleration sensors as detectors. The vibrator may be a mechanical or electromechanical device, such as any type of motor or actuator, an electromagnetic loudspeaker of any kind, or a piezoelectric transducer. An acceleration sensor is an electrical, magnetic or electronic device that supplies one or more electrical voltages proportional to the acceleration transmitted to it. The method for pressure measurement is based on the amplitude modulation effect that occurs when the pressure of fluid transmitted through the vessel wall or window attenuates the vibrator oscillations detected by the accelerometer. This comprises electronic processing and computation of accelerometer information and vibration parameters when the device is placed in mechanical contact with the elastic wall or vessel window. The vessel may be of any shape, including tubular, and of any nature, including vascular vessels of animals and humans, such as arteries and veins.

This invention further contemplates: 1) a method for simultaneously estimating pressure wave morphology and other associated parameters such as vessel wall compliance, distension and distension dynamics, and an estimated pressure waveform calibration method , based on restoring attenuation to a preset reference amplitude value, regardless of the force exerted on the vessel wall. Although some other possible applications can be found for this invention, its main focus is the noninvasive blood pressure and blood pressure waveform assessment in humans.

Brief Description of the Figures

The following descriptions are based on the accompanying drawings in which, without any limiting intention, the most important features and advantages of the present invention are graphically represented.

Figure 1 is a block diagram of the present invention.

Figures 2a to 2d are cross-sectional views of a possible general configuration of the apparatus with its main elements, referring to some of the preferred embodiments.

Figures 2e to 2f are cross-sectional views of a possible alternative embodiment of the apparatus referring to 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 the assessment of blood pressure in a living subject and preferred binding mechanisms for signal acquisition with the present invention.

Figure 5a is a schematic flowchart clarifying the general phases of the first preferred method for estimating fluid pressure and other related parameters.

Figure 5b is a schematic flow chart showing the general phases of the second preferred method for estimating fluid pressure and other related parameters.

Figure 6 is a graphical representation of typical signals drawn on a test bench of the present invention based on a 3-axis accelerometer just before the probe contacts the vessel wall and progressively contacts the vessel wall. vase.

Figures 7a to 7c are graphical representations of signals obtained on a test bench, with a probe based on a 3-axis accelerometer and with a pressure gauge which is inserted through the vessel wall.

Figure 7d is a graphical representation of the reference signal obtained by the pressure gauge and the upper and lower profiles, calculated from the signals shown in figures 7a to 7c, using the envelope detector approach.

Figure 7e is a graphical representation of the filtered product frequency spectra between the modulated carriers and the original carrier wave using the product detector approach.

Figure 7f is a graphical representation of the reference signal from the pressure gauge and the time profiles calculated from the signals shown in figures 7a to 7c using the product detector approach.

Figure 7g is a graphical representation comparing the invasively obtained waveform with the pressure gauge and the non-invasively obtained waveform using the difference between the upper and lower profiles of the accelerometric signal that is aligned with the direction. of vessel wall movement.

Figure 7h is a graphical representation comparing the invasively obtained waveform with the manometer and the noninvasively obtained waveform using the total profile of the profiles shown in Figure 7d.

Figure 7i is a graphical representation comparing the invasively obtained waveform with the pressure gauge and the non-invasively obtained waveform using the upper and lower profiles of the accelerometric signal that is aligned with the direction of motion of the toilet wall.

Figure 7j is a graphical representation comparing the invasively obtained waveform with the pressure gauge and the non-invasively obtained waveform using the recovered time profile of the accelerometric signal that is aligned with the direction of wall movement. of the vessel shown in figure 7f.

Figure 71 is a graphical representation comparing the invasively obtained waveform with the pressure gauge and the noninvasively obtained waveform using the total profile of the profiles shown in Figure 7f.

Figure 7m is a graphical representation of calibrated pressure waveforms resulting from the calculation of the lower profile shown in Figure 7i and the calibration equation.

Figure 8 is an example of an experimentally obtained calibration curve for use in 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 detector is placed over the carotid artery.

Figure 9d is a graphical representation of the upper and lower profiles, calculated from the signals shown in figures 9a to 9c, using the envelope detector method.

Figure 9e is a graphical representation of the profiles resulting from the four preferred approaches (methods): lower and upper profiles of the accelerometric signal that are aligned with the direction of vessel wall movement, difference between the previous profiles and the total signal profile. shown 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 vessel wall movement.

Figure 9g is a graphical representation of the calibrated blood pressure waveforms resulting from the computation of the difference between the upper and lower profiles shown in Figure 9e, and the appropriate calibration equation.

Figure 9h is a graphical representation of the calibrated blood pressure waveforms resulting from the computation of the total profile shown in Figure 9e and the appropriate calibration equation.

Figure 9i is a graphical representation of the calibrated blood pressure waveforms resulting from the computation of the lower profile shown in Figure 9e and the appropriate calibration equation.

Figure 9j is a graphical representation of calibrated blood pressure waveforms resulting from the computation of the upper profile shown in Figure 9e and the appropriate calibration equation.

Figure 91 is a graphical representation of a calibrated blood pressure waveform shown in Figure 9g and its major notable points.

Figure 10a is an example of an experimentally obtained calibration curve for pressure measurement of a fluid confined in an elastic vessel.

Figure 10b is a graphical representation comparing the invasively obtained waveform with the pressure gauge and the non-invasively calibrated waveform obtained with the apparatus by computing the difference between the lower and upper profiles and the curve. of proper calibration (figure 10a).

Subtitle

Acceleration Sensor 1

2.7 - Structure

2.2 - Vibrator

Sensor

Acceleration 2

2.3 - Vibrator

Screw

Fixation

Board of

Printed Circuit

2.10

Bridge No Other Support Plate

Flexible

2.5

2.11

Support foot

2.12

Vase wall

2.6 - Mechanical Interface

Detailed Description of the Invention

For illustrative purposes, and without limitation, the present invention will be described in detail with reference to the figures given in section 4. Specific details are specified throughout the following description to provide a more complete understanding to those skilled in the art. This invention is by no means limited in its application to the construction details and component arrangement illustrated herein. Similarly, the results presented in some figures are not limited to what is set forth herein. In addition, the use of syntax and technical writing should not be construed as limiting. Use of included, containing, existing, compound, wrapping, and variations thereof is made to include the above and its equivalent.

In one perspective, the invention is a probe and a system for noninvasively and automatically measuring the internal pressure of a fluid confined in an elastic wall vessel or having an elastic window in its wall. From another perspective, the invention is a set of methods for assessing the internal pressure of the fluid and other associated parameters that are independent of the action of the operator, that is, the force exerted on the vessel wall. In a preferred application, the probe, system, and set of methods are used to assess the physiological function (e.g., blood pressure) of a human subject to provide background information on its cardiovascular state. The invention may also be designed to be adapted to monitor the physiological function of other warm-blooded species.

Figure 1 illustrates the components and general process of the preferred embodiment. A probe 1.2 is placed in mechanical contact with a vessel wall or window containing the confined fluid 1.1. The probe includes a vibrator

1.4 and an accelerometer 1.3, mounted on a common platform, and is connected to a 1.5 acquisition system and a 1.9 signal generator which is responsible for delivering an oscillatory electrical signal to the vibrator. The vibrator generates an equivalent oscillatory disturbance that is transmitted to the mechanical unit and is detected by the accelerometer. At the same time, the pressure of the fluid that is transmitted through the vessel wall or window is also detected by the accelerometer, such that its permanent oscillatory signal (resulting from vibrator excitation) is attenuated and amplitude modulated.

The probe output is fed into a conditioning circuit 1.6 which amplifies the accelerometer signals and monitors the instantaneous current and vibrator power using a sensing resistor. The signals are then delivered to a digitizer 1.7 which converts the analog signals into a digital representation. The digitized signals are provided to an electronic control device 1.8 which performs the various steps constituting the methodology of the invention including: peak detection 1.12, profile extraction 1.13, artifact removal 1.14, calibration 1.11 and estimation of fluid pressure and other related variables 1.15. The output signal of the electronic control device is then converted into a form useful for the user by means of a digital or analog display device containing numerical and graphic information. The electronic control device may also be responsible for controlling and generating the vibrating excitation signals 1.9, for example by means of a direct digital synthesizer (SDD).

Figures 2a to 2e show preferred embodiments of the probe constituting the present invention. In general, the main elements that make up the probe are:

1) one or more accelerometers 2.1, 2.8 (in the case of Figure 2c);

2) one or more vibrators 2.2, 2.3; 3) a printed circuit board (PCB) or other support plate with its electrical connections 2.4; 4) a mechanical interface 2.6 which is in contact with the vessel wall 2.12 5) a semi-rigid base such as foam, plastic or certain type of metalloid 2.5 that accommodates the main structure and 6) a structure 2.7 that surrounds the assembly and is adapted to be held against the vessel wall by a fastener or an operator. The vibrator may be a mechanical or electromechanical device such as any type of off-axis motor or actuator, an electromagnetic loudspeaker of any kind or a piezoelectric. An acceleration sensor is an electrical, magnetic or electronic device that generates one or more electrical voltages proportional to the acceleration transmitted to it. The mechanical interface consists of a flattened part or other ergonomically shaped element, such as a polymeric material, which allows transmission of the movable wall strain to the sensing unit. The center of the mechanical interface is aligned with the center of the vibrator. In one embodiment, the accelerometer, mounted on the same plate as the other two elements, is positioned anywhere either beside the vibrator or beside the mechanical interface (Figures 2a to 2d). In another embodiment (Figures 2e to 2f), the accelerometer is placed on the opposite side of the plate, where the vibrator is and is aligned with the center of the latter.

There are several possible implementations of the sensing probe with regard to its arrangement, positioning elements and encapsulation. In a direct and preferred embodiment (Figures 2a and 2e) there is a MEMS-type accelerometer (Microelectromechanical System) and a vibrator, contained and connected by a PCB. In another embodiment (Figure 2b), the accelerometer is of the MEMS type, and there are two or more vibrators contained and connected by a PCB. In particular, this embodiment is suitable for using either two distinct vibration frequencies or very similar frequencies to create beats.

In another embodiment (Figure 2c) there is a vibrator and two MEMS-type accelerometers contained and connected by a PCB. Both accelerometers are equally oriented and well aligned and the output of both signals can be electronically subtracted to remove all common acceleration components. This configuration is especially suitable for eliminating parasitic artifacts or mechanical interference that is introduced, for example, by an operator. This setting is also suitable in circumstances where 2-axis MEMS accelerometers are used to obtain 3-axis acceleration information.

In a further embodiment (FIGS. 2d), the MEMS-type accelerometer and vibrator are contained and connected by a PCB that increases the vibrations of the assembly. The PCB has a distinct structure where the rear is fixed to the housing with screws 2.9 and the front is free and can vibrate more widely due to the average beam-like structure joining them together.

Regarding the mechanical interface of the detection probe, it is possible to identify several preferred configurations. In one embodiment (Figures 2a-2d), the interface piece is aligned with the center of the vibrator which is situated on the opposite side of the PCB and is pressed against a semi-rigid material. In a further embodiment (Figure 2f), the interface piece is directly coupled to a non-flexible bridge 2.10 which is disposed in the middle of the vibrator. In another possible embodiment, the interface is a polymeric material that covers and / or encapsulates the vibrator such that the entire surface of the vibrator may be used to touch the vessel wall.

With respect to the vibrator holder, two distinct arrangements can be identified. In one embodiment (Figures 2a to 2d), the vibrator is in contact with the PCB by means of a support foot 2.11 which supports it in the center. In another embodiment (Figures 2e to 2f), an equilateral configuration is used in which three equidistant base supports 2.11 support the vibrator at its periphery. In either case, the support feet serve as spacers between the vibrator and the PCB.

In Figure 3, a workable 3-D configuration of the top view of the probe outer structure is shown. In a preferred embodiment, the sensing probe is contained in a sensing structure, such as a plastic or metal housing 3.1, and is in contact with the vessel by means of an interface piece 3.2 that locally compresses the elastic wall. In another arrangement, the sensing probe may be framed in a piece of material that includes the vibrator-accelerometer unit and is coupled directly to the vessel wall using a clamping mechanism such as an adhesive layer, band or strip that supports it. . In Figure 4, the preferred probe implementation is applied to measure the blood pressure of a human subject using two different approaches. In the first, the enclosed probe is supported by an operator 4.1, while in the second approach the probe is attached to the subject by means of a Velcro® 4.2 collar, rubber strap or any other fixation device known to the person skilled in the art. In both cases, the sensor structure being supported is adjacent to an anatomical position of the subject and the mechanical interface is superimposed with some pressure on a superficial artery where the pulse is palpable, such as: carotid arteries A , brachial B, radial C or femoral D.

In Figure 5a, the method for measuring fluid pressure according to the present invention is described schematically in a block diagram. The first step to start the process is to set the vibrator 5.01 excitation parameters. The excitation waveform driving the vibrator may be sinusoidal, square, triangular or any other suitable shape and its frequency may be comprised of a wide range of frequencies and applied either in a continuous or burst mode. Experiments conducted to ascertain the satisfactory frequency range determined that a range greater than 150Hz works well with human tissues. However, it has been found that the optimal frequency to be used, although conditioned by the accelerometer bandwidth, must correspond to the frequency at which the maximum amplitude of acceleration oscillations is reached. As such, in a preferred implementation, the first phase of the method involves determining this optimum vibration frequency, which will yield the maximum system gain.

The acquisition process begins immediately before the probe is positioned and pressed against the vessel wall to establish an acceleration carrier amplitude (reference value for calibration) and to record unrestricted vibrator oscillations detected by the probe itself. accelerometer 5.02. As a result of positioning the probe on the vessel wall 5.03, the oscillations detected by the accelerometer are attenuated in amplitude. As such, and for calibration purposes, the initially preset reference amplitude value is restored by adjusting the excitation signal that drives the vibrator 5.04. Then the new amplitude modulated (conditioned) oscillations detected by the accelerometer are recorded 5.05. In a particular embodiment of the invention, data may be acquired for a short period of time, for example 5s, 30s or 60 seconds. Other data acquisition times may also be considered by the present invention. In fact, data can be acquired continuously over a long period of time, such as 2448h. In a preferred embodiment, recordings should be made during the time period during which it is interesting to cover the variability of fluid pressure.

Figure 6 illustrates typical signals acquired on a test bench of the present invention based on a 3-axis accelerometer in this initial acquisition process. Axis c is aligned with the direction of movement of the vessel wall and the other two axes a, b are orthogonally aligned with axis c ¹ . In these signals, three different regions can be highlighted: the region R1 shows the oscillations detected by the accelerometer just before the probe is in contact with the vessel wall; the R2 region coincides with the positioning of the probe when it progressively comes into contact with the vessel wall and the R3 region represents the accelerometer oscillations when the probe is placed on the vessel wall at a certain pressure. A ^{2 2} From now on, a, b and c refer to the x, y, and z directions shown in figure 2.

The difference between the amplitude of the oscillations of the regions R1 and R3 corresponds to the attenuation Ate which is proportional to the force exerted on the tube.

The principle of operation of the detection apparatus is based on the amplitude modulation of the accelerometric signals, which occurs when the probe is placed on the vessel wall and the fluid pressure transmitted through it attenuates the vibrator oscillations detected by the accelerometer.

In a direct model, and considering that the probe is subjected to a vibrator-induced sinusoidal shift x (t), then:

x (t) = L.sin (w.t + Θ (t)), where L is the amplitude of oscillation, w is the angular frequency of oscillation and 6 (t) is the phase of oscillation.

When the probe is unrestricted, the sinusoidal waveform x (t)) is detected by the accelerometer as:

a (t) = - Lw ² .sin (wt + Θ (t)) = -Lx (t) ²

This waveform is referred to as a carrier or carrier wave and corresponds to an unrestricted and therefore unmodulated wobble.

When the probe is placed against the vessel wall, the amplitude L is immediately attenuated At _c (Od At _{c Is} 100%) which is proportional to the force that is applied to the vessel wall F and also to the resistance that is provided by the vessel wall. vessel to deformation (stiffness k). Fluctuations in fluid pressure P are also transmitted through the vessel wall, modulating the oscillations detected by the accelerometer through attenuation. At this stage, the change in fluid pressure is defined as the modulation signal and the accelerometer signal corresponds to the amplitude modulated carrier. Like this:

a (t) = -Atc.x (t) ²

At _c α ai.F

At _c α a ₂ .k

Atc α a ₂ .P where ai, a2, as are calibration constants. Attenuation At _c of modulated data can be measured up to 100% over the total amount of amplitude L.

In addition to the accelerometer signals, the amplitude modulation process is further verified when the vibrator electrical parameters are measured. Therefore:

p (t) = Atc.i (t) .v (t)

Atc α bi.F

Atc α b ₂ .k

Atc α b ₂ .P where i (t) and p (t) are the vibrator current and electric power signals. v (t) is the electrical voltage supplied to the vibrator by a signal generator corresponding to the carrier wave x (t) and bi, b2, b ₂ are calibration constants.

Referring again to Figure 5a, and after modulation process 5.06, an inverse demodulation process 5.18 is initiated on the electronic control device 1.8, with peak detection of the respective amplitude modulated oscillations 5.07. Local maxima and minima are calculated using a threshold based approach and then interpolated, with upper and lower envelopes extracted from the modulated carrier. These envelopes, corresponding to the modulation signal, undergo a filtering phase to remove the high frequency noise 5.09 that is typically present in such measurements.

The extracted lower and upper profiles (pi, ps) are the main sources of information on fluid pressure fluctuations, allowing direct estimation of the fluid pressure waveform or even extraction of operator manipulation artifacts. Different methods, based on the use of several or only one profile 5.11, can be used to evaluate pressure wave morphology 5.13. The simplest method uses the upper or lower profiles extracted from the accelerometer signal that coincide with the direction of vessel wall motion (pi _{IIK) V} , ps ^) · Another method requires determining the difference between the lower and upper profiles 5.10 , also extracted from the accelerometer signal that coincides with the direction of vessel wall motion (pi ^ ^_ P ^s n 'v) · A third method, applied when the invention is based on a 3-axis accelerometer, involves the calculation of the profile total 5.12, (total_profile_a) extracted from the various orthogonal accelerometric signals, where:

aux_mov = pi _ra , _v -ps _{nK) V} aux-ortog, = pi _ol - ps _ol aux_ortog ₂ = pi _o2 - ps _o2 / 7 2 2 total_a profile = Jaux_mov + aux_ortog ₁ + aux_ortog ₂

And, pi _ol - ps _ol , pi _o2 - ps _o2 are the differences between the lower and upper profiles, extracted from the signs that coincide with the orthogonal directions to the vessel wall movement.

Relevant information can also be extracted when the upper or lower profiles extracted from the accelerometer signals are summed (pi + ps) 5.16. With this approach, it is possible to remove the average baseline fluctuations of each of the accelerometer signals. These baseline fluctuations reproduce the artifacts that are especially present in this type of measurement, as well as the movement induced by the probe by distending the vessel wall 5.17.

In the case of modulated current or power signals detected by the vibrator, the approaches to assess pressure wave morphology are the same. The only difference is that the method applied when the probe is based on a 3-axis accelerometer (total_profile_a) 5.12 is not used, since vector quantities are not present. As a consequence, only methods using the upper or lower profiles extracted from the current and power signals, as well as the methods involving the determination of their difference or sum, can be applied.

With respect to demodulation process 5.18, it is also feasible to apply another method of signal processing based on a product detector approximation to modulated acceleration, current and / or power signals. This method, illustrated in Figure 5b, allows the modulation signal to be recovered by the following steps: a) calculating the product of the modulated carrier (s) and the original carrier wave (ie the waveform of excitation that drives the vibrator) 5.20; b) computation of frequency spectra using the Fast Fourier Transform algorithm 5.21; C) low pass filtering of frequency spectra 5.22 and d) calculation of time profiles using the Inverse Fourier Fast Transform algorithm 5.23. The recovered time profiles corresponding to the modulation signal then undergo a smoothing phase to remove high frequency noise 5.24.

Similar to the previous signal processing method (envelope detector approach - figure 5a), with this method (product detector approach figure 5b), pressure wave morphology can also be evaluated using one or more profiles. 5.25 . The simplest method uses the profile extracted from the acceleration / current / power signal that coincides with the direction of vessel wall movement (p _mO v). The other method, applied when the invention is based on a 3-axis accelerometer, involves the calculation of the total profile (total_profile__b) 5.26, taken from the various orthogonal accelerometer signals (p _mov Poi P ₀ 2) r where: aux_mov = p _mov aux_ortg ₁ = p ₀₁ aux_ortg ₂ = p _o2 total _ profile_b = Jaux_ mov ² + aux_ ortgx ² + aux_ ortg2 ² _E P _o j Po2 are the profiles that correspond to the orthogonal directions of vessel wall movement.

After phase 5.18 and to quantify the pressure waveform and other related parameters, it is necessary to proceed to the parameter calibration and evaluation step 5.19. The calibration method is focused on the use of calibration curves (acceleration-pressure type) whose determination and application require the conservation of acceleration detected by the device. In other words, the amplitude of the acceleration carrier measured when the sensing probe vibrates freely should be equal to the measurement when it is pressed against the vessel wall.

In a preferred embodiment, the electronic control device 1.8 manually or automatically selects the appropriate calibration curve from the curve database to be used, and according to the acceleration carrier amplitude set as a reference. Following this step, the implementation of an automatic acceleration-voltage control loop is crucial for the efficiency of the calibration process. The circuit constantly measures the attenuation of the acceleration carrier when the sensing tip is placed on the elastic wall, restoring the reference amplitude value by adjusting the vibrator input voltage. As such, whatever force exerted on the vessel wall during the acquisition process does not interfere with the calibration process.

In addition to fluid pressure and wave morphology, there are other associated parameters that can be calculated by the present invention.

Vessel wall distension, for example, can be inferred when the sensory unit is not being excited, and the accelerometer only detects the displacement changes associated with pressure wave propagation. It is also possible to assess the distension of the vessel wall when the sensory unit is being excited by summing the upper and lower profiles extracted from the modulated accelerometric signals (pi + ps). Regardless of the method used, it is necessary to terminate the process with a double integration of the acceleration signal obtained to quantify the total displacement of the vessel wall.

Vessel compliance ( _c _ ^AV ) defined as the AP volume change (AV) per unit pressure change (ΔΡ) is another parameter that can be easily estimated. ΔΡ is obtained directly from the calibrated pressure waveform, while AV is calculated based on vessel geometry and distension.

Since other important parameters can also be determined, three different applications of the probe, system and detection methods will be presented, taking advantage of the usefulness of the present invention in various fields.

APPLICATION 1

Application of the apparatus and method for measuring the dynamics of

WATER IN A TEST BENCH ACCORDING TO THE INVENTION

This study was designed to noninvasively measure pressure wave morphology that propagates through a fluid confined in an elastic tube. A dedicated test bench has been developed, capable of arbitrarily generating pressure waveforms through a latex tube with a diameter and wall thickness of the same order as a large artery. The pressure waves were generated manually by a piston mechanism placed at one end and released into a water-filled 70 cm (12.7 mm internal diameter, 0.8 mm wall thickness) tube. At the other end, a manometer placed longitudinally to the tube monitored the DC pressure level and pressure fluctuations. Measurements were performed for a short time and near the pressure sensor using the apparatus and method according to the present invention. The detection probe, based on a 3-axis accelerometer, was excited by a 700Hz continuous sine waveform and held by a clamping device that maintained a constant force while the probe was against the pipe wall to detect variations. pressure Data acquisition was performed using a dedicated acquisition system based on a 16-bit digitizer. All signals were sampled at 12.5 kHz and stored for offline analysis. The accelerometric data were then compared with the data obtained by the pressure gauge, used as a reference in the pressure assessment.

The acquired data are shown in figures 7a to 7c, where a, b, c are the modulated carriers and d is the gauge reference signal, and c is the modulated carrier detected by the accelerometric axis aligned with the direction of vessel wall movement. and the other two modulated carriers (a, b) are detected by the accelerometric axes orthogonally aligned with the first one. The upper and lower profiles of the modulated carriers were extracted (Figure 7d) and then slightly smoothed, where: al, bl, cl are the lower profiles and a2, b2, c2 are the upper profiles of the modulated carriers described above. At the same time, and based on the product detector approach, it was also possible to retrieve the time profiles of modulated carriers (a, b, c), identified in figure 7f, respectively as a3, b3 and c3. After calculating and filtering the product frequency spectra between the modulated carriers and the original carrier wave (Figure 7e), the Inverse Fourier Fast Transform algorithm was applied to obtain these time profiles.

7g to 71 are graphical representations comparing the invasively obtained waveform with the manometer and the non-invasively obtained waveforms using the different methods of the present invention. The square roots of the mean square error (RMSE) between the reference waveform and the waveforms obtained using different methods were determined and are summarized in Table 1.

Table 1 RMSE measurements between the reference waveform (manometer) and the waveforms obtained using the different methods of the present invention.

Process of Demodulation Method RMSE (%) Detector Envelope Difference between upper and lower profiles ² (e) 2.62 Total Profile (f) 3.64 Upper Profile (c2) ² 3.41 Lower Profile (cl) ² 1.94 Detector Product Time Profile (c3) ² 3.88 Total Profile (f3) 4.55

This study shows that the different methods used by the present invention have the ability to accurately restore the original pressure waveform, showing better performance when using the lower profile method or the profile difference approach.

In addition to the pressure waveform evaluation, it was also possible to calibrate the pressure waveform obtained for the different methods and validate the general relationship between fluid pressure and the detected acceleration. Figure ² Profile obtained through the accelerometric axis that is aligned with the direction of movement of the vessel wall.

7m exemplifies a calibrated pressure waveform resulting from the calculation of the best method (lower profile cl) and the calibration equation obtained experimentally in this study (Figure 8). The range of values presented covers the range of normal values typical of a healthy human artery.

APPLICATION 2

Application of the apparatus and method for measuring blood pressure and other hemodynamic parameters according to the invention

This study aimed to noninvasively evaluate the calibrated blood pressure (OPA) waveform in the ascending aorta of a human subject. OPA was analyzed at a central level, where the true load imposed on the left ventricle and the walls of the great central artery is represented. Measurements were performed for a short time and on the common carotid artery of a healthy individual using the apparatus and method according to the present invention.

The detection probe, based on a 3-axis accelerometer, was excited by a continuous 700Hz sine waveform and held by an operator who tried to maintain a constant pressure on the carotid artery. Data acquisition was performed using a dedicated acquisition system based on a 16-bit digitizer. All signals were sampled at 12.5 kHz and stored for offline analysis.

The acquired data are presented in Figures 9a to 9c, where c is the modulated carrier detected by the accelerometric axis aligned with the direction of vessel wall movement and a, b are the modulated carriers detected by the accelerometric axes orthogonally aligned with the first. In order to demodulate, the envelope method was used, where the upper and lower profiles of the modulated carriers were extracted (Figure 7d) and filtered by a low pass, al, bl, cl are the lower profiles and a2, b2, c2 are the upper profiles of the modulated carriers described above.

Figure 9e illustrates the non-invasively obtained waveforms using the different methods of the present invention: and corresponds to the upper and lower profile difference method, f to the total profile method, cl and c2 to the methods of the lower and upper ³ profiles, respectively. An additional method, based on the sum of the upper and lower profiles ³ , was also applied to obtain the mean baseline fluctuations of the accelerometric data (Figure 9f). The pattern obtained represents not only the acceleration waveform of the wall, but also some artifacts that could be induced by the operator during acquisition.

In order to calibrate the pulsed OPA, a reference amplitude of the acceleration carrier was established for the axis aligned with the direction of vessel wall movement, and then the ³ PerfiI curve obtained through the accelerometric axis was chosen. aligned with the direction of movement of the vessel wall.

calibration of the set of curves that correspond to the same reference value. Figures 9g to 9f show the resulting calibrated PAHO for each method, showing very similar values for diastolic (PDias) and systolic (PSist) pressures. The values obtained for the Day, PSist and pulse pressure are within the normal range of a healthy individual.

In the present application, another data analysis can also be done in order to evaluate other types of hemodynamic parameters. In fact, with this information it is possible, for example, to determine mean blood pressure, heart rate or to identify prominent OPA points (Figure 91) such as: wave foot (PO), systolic peak (PS), the reflection point (PR), the dicrotic node (ND) or the dicrotic peak (PD). These fiduciary points can thus be employed for studies of determining other important indices, such as: enlargement index (Aix), left ventricular ejection time (LVET), buckberg index, tension, diastolic time index or other related parameters known to one skilled in the art.

The results of this study demonstrate that this invention has the potential to be an important tool for cardiovascular risk assessment, providing meaningful information on central arterial pressure assessment, OPA descriptive analysis and the assessment of relevant hemodynamic parameters.

APPLICATION 3

Application of the apparatus and method for the evaluation of water pressure inside a latex pipe for different application positions

This study aimed to noninvasively measure the pressure of water confined in a latex tube to different applanation positions.

Measurements were performed on the test bench described in application 1 using the apparatus and method according to the present invention. The sensing probe, rigidly connected to a tri-axial position monitoring system, was placed at the end of the latex tube near the pressure gauge and was excited by a continuous sinusoidal waveform whose frequency corresponded to its resonance value. mechanical. Ten distinct measurements, with successively higher applanation positions, were performed over a short period of time with the objective of acquiring the pressure wave generated by a piston manually moved by an operator. In the planing process, the linear positioner system shifted to positions ranging from 80500 to 113500 microspheres, ensuring that the central part of the piezoelectric was in direct contact and flattening the latex tube. The various acquisitions were performed after conserving the acceleration carrier amplitude, more precisely the value pre-established in the calibration curve to be used (figure 10a). As such, for each planing position, the input voltage of the excitation signal driving the vibrator has been adjusted to reset the reference calibration value. Subsequently, the pressure wave was generated and acquired by the apparatus. Data acquisition was performed using a dedicated acquisition system based on a 16-bit digitizer. All signals were sampled at 12.5 kHz and stored for offline analysis.

For each acquisition, the calibration curve was applied to the recovered acceleration modulation profile using the envelope detector algorithm and the difference between the lower and upper profiles. The main pressure values (maximum, minimum, mean and difference) obtained with the invention after calibration were compared with the reference pressure values obtained with the pressure gauge.

The results obtained are summarized in Table 2, and in Figure 10b a graphical representation can be observed comparing the invasively obtained waveform with the pressure gauge and the non-invasively calibrated waveform obtained with the device in Al series.

Successive changes in pipe flattening do not impair the accurate estimation of the main pressure values using the present invention. Estimates of maximum, minimum, mean and differential pressure values are, on average, 1.53 mmHg, 0.41 mmHg, 0.78 mmHg and 1.33 mmHg higher than the pressure gauge respectively. The achievement of this precision criterion in test bench experiments appears to be a very good indicator of the feasibility of this invention in the assessment of blood pressure, particularly when the pressure values generated within the latex tube are mostly within the range found. in a healthy population or with cardiovascular disease.

It is evident from the results obtained that the most important force of the present invention, namely the calibration method, is its validity for different planing positions and therefore its independence inherent to an operator action. Whatever the force exerted on the vessel wall, the procedure provides for the restoration of attenuation to the calibration reference value.

Various embodiments have already been described. However, various modifications may be made without departing from the scope of the invention as defined by the following claims.

Claims (20)

1. Apparatus for non-invasive pressure measurement of a fluid confined in an elastic wall vessel or provided with an elastic window in its wall, comprising the following components in position and geometric configuration and functionality described: (a) a vibrator and an accelerometer (sensing unit / probe) mounted on a common support plate, where the accelerometer and vibrator are placed on opposite sides of the plate; and, the vibrator is supported and maintained in contact with the plate by at least one support foot supporting it at the center or periphery; (b) a mechanical interface whose center is aligned with the center of the vibrator, allowing the distention of the movable vessel wall to be transmitted to the detection unit; (c) an electronic control device configured to receive the modulated accelerometer signal and adapted to apply calibration and signal processing methods to obtain parameters corresponding to fluid pressure, pressure wave morphology and other related parameters. Apparatus according to claim 1, wherein the electronic control device by means of an automatic voltage-acceleration control circuit constantly measures the attenuation of the acceleration carrier when the vibrator-accelerometer unit is placed on the elastic wall by means of mechanical interface, restoring the reference amplitude value by adjusting the vibrator input voltage. Apparatus according to claim 1, wherein the electronic control device manually or automatically selects the appropriate calibration curve from the curve database to be used, and according to the acceleration carrier amplitude set as a reference. Apparatus according to claim 1, comprising an acquisition system including a conditioning circuit that amplifies the accelerometer signals and measures the instantaneous electric current and the vibrator power using a sensing resistor; and a digitizer that converts the analog signal into a digital representation. Apparatus according to claim 1, wherein the vibrator is a mechanical or electromechanical device, such as any type of off-axis motor or actuator, an electromagnetic loudspeaker of any kind, or a piezoelectric. Apparatus according to claim 1, wherein the accelerometer is an electrical, magnetic or electronic device that generates one or more electrical voltages proportional to the acceleration transmitted to it. A method for noninvasively measuring the pressure of a fluid confined by an elastic wall vessel or provided with an elastic window in its wall, comprising some or all of the following steps: • adjusting the vibrator sweep parameters, including determining its optimum vibration frequency; • start of the acquisition process immediately before the probe is positioned on the vessel wall to establish the acceleration carrier amplitude (reference value for calibration) and to record the unrestricted vibrator oscillations detected by the accelerometer itself; • positioning of the probe on the vessel wall by means of a clamping device or an operator; • restoring the amplitude of the reference acceleration carrier (initially preset) by adjusting the excitation signal that drives the vibrator; • Acquisition of new (restricted) amplitude oscillations, detected by the accelerometer and modulated by pressure fluid fluctuations - modulated carrier; • application of signal processing methods that extract the modulation signal, calibrate it and thus obtain parameters that correspond to fluid pressure, pressure wave morphology and other related parameters; • Display of calculated parameters. A method according to claim 7, wherein the optimum vibration frequency corresponds to its mechanical resonance value and, therefore, to the frequency at which the maximum amplitude of acceleration oscillations is reached. The method of claim 7, wherein the processing methods may be applied to the current and power amplitude modulated carriers detected by the vibrator. The method of claim 7, wherein the pressure waveform step utilizes the upper profile, the lower profile, or other time profiles extracted from the accelerometric signal that coincides with the direction of vessel wall movement. A method according to claims 7 and 9, wherein the pressure waveform determination step utilizes the upper profile, the lower profile or other time profiles extracted from the electrical signals (current or power) of the vibrator. Method according to Claim 7, characterized in that the pressure waveform determination step uses the difference between the lower and upper profiles, extracted from the accelerometric signal that coincides with the direction of movement of the vessel wall. A method according to claims 7 and 9, wherein the pressure waveform determination step utilizes the difference between the lower and upper profiles extracted from the electrical signals (current or power) of the vibrator. The method of claim 7, wherein the pressure waveform step involves computing the total profile extracted from the various orthogonal accelerometric signals when the invention is based on a 3-axis accelerometer. The method according to claim 7, wherein the step of removing the average baseline fluctuations uses the sum of the upper and lower profiles of each of the accelerometer signals or the vibrator electrical signals (current or power). 16, wherein an automatic acceleration voltage control circuit constantly measures the acceleration carrier attenuation when the sensing tip is placed on the elastic wall, restoring the reference amplitude value by adjusting the vibrator input voltage. The method of claim 7, wherein the pressure waveform calibration step depends on calibration curves, the determination and application of which require the conservation of the acceleration carrier amplitude, that is, the amplitude measured when The sensor that is vibrating freely is the same as that measured when it compresses the vessel wall. A method according to claims 7 and 7. The method of claim 7, wherein the extracted parameters are at least internal fluid pressure, fluid pressure waveform, vessel distension and vessel compliance. 19 Method as described in claim 7, in whereas that vase is an artery. 20 Method according the claim 19, in that the registration site is located in a superficial artery where the pulse is palpable. Method according to claims 16 and 20, where the extracted parameters are, among others, the heart rate, the blood pressure waveform (OPA), the systolic blood pressure, the diastolic blood pressure, the mean arterial pressure, the pulse pressure, the augmentation and other hemodynamic parameters extracted from the prominent points of the calibrated pressure waveform.