WO2022099338A1

WO2022099338A1 - Method and measuring system for continuously non-invasively determining the arterial blood pressure

Info

Publication number: WO2022099338A1
Application number: PCT/AT2021/060421
Authority: WO
Inventors: Jürgen FORTIN
Original assignee: Cnsystems Medizintechnik Gmbh
Priority date: 2020-11-12
Filing date: 2021-11-09
Publication date: 2022-05-19
Also published as: AT524039A4; AT524039B1

Abstract

The invention relates to a method and a measuring system for continuously non-invasively determining the arterial blood pressure at an extremity containing an artery, the measuring system comprising a housing (300) or housing piece that can be attached to the extremity and is suited to at least partly surround the extremity, and comprising a flexible bubble (309) which is supported on the housing (300), acts on the extremity and is filled with a fluid. According to the invention, the flexible bubble (309) is filled with an incompressible fluid, e.g. a liquid or gel, and an actuator which comes in contact with the incompressible fluid or the flexible bubble (309) and is suited to vary the pressure in the incompressible fluid is placed in or on the housing (300). Furthermore, the flexible bubble (309) includes a pressure sensor (310) which is is fluidic contact with the incompressible fluid and which is suited to continuously measure the pressure applied to the incompressible fluid by the actuator and to generate a pressure signal pc and additionally capture a pulsatile signal that is coupled from the artery into the incompressible fluid.

Description

Method and measuring system for the continuous, non-invasive determination of arterial blood pressure

The invention relates to a method and a measuring system for the continuous, non-invasive determination of the arterial blood pressure on an extremity that contains an artery, with a housing or housing part that can be attached to the extremity and is suitable for at least partially enclosing the extremity, as well as with a housing supporting, limb-acting, flexible bladder filled with a fluid.

The continuous, non-invasive measurement of blood pressure still poses a major challenge for measurement technology. The simplest method for continuously recording blood pressure is what is known as tonometry. In this case, a pressure sensor is brought into contact with an area containing an artery, the pressure measured thereby only inadequately corresponding to the pressure in the artery. The method of coupling the pressure sensor to the artery is essential. A small pressure sensor is usually attached directly to the skin over a superficial artery (e.g. radial artery in the wrist or temporal artery in the temple) and then pressed against the underlying bone.

In the so-called "Vascular Unloading Technique", which goes back to a publication by Pe äz (Digest of the 10th International Conference on Medical and Biological Engineering 1973 Dresden), a finger is X-rayed and the registered flow kept constant.

The Vascular Unloading Technique requires a pressure generation system that can fully follow the continuous blood pressure. This means that pressure changes of more than 1500 mmHg/sec must be achieved with an upper frequency limit of around 40 Hz. EP 1 179 991 B1 shows such a pressure generation system with the help of separate inlet and outlet valves. In addition to these inlet and outlet valves, an air pressure pump, an air reservoir and numerous electronic components are required for the pressure generation system.

EP 2 493 370 describes a form of the vascular unloading technique in which a digital volume signal is generated using a so-called "light-to-frequency converter". The information about the current blood volume in the finger is contained in the output frequency of the converter. “Light-to-frequency converters” can be implemented as integrated circuits, with a photodiode already on the chip acting as the light signal detector. EP 2 854 626 B1 now describes a new method and a device that only applies a very slowly changing contact pressure to the extremity (usually fingers) in order to follow the mean arterial blood pressure. WO 2016/110781 A1 describes various measurement modes and additional elements that are also advantageous for use as a portable device.

It is known from clinical studies that have already been carried out that the methods and devices described, for example, in EP 2 854 626 B1 or WO 2016/110781 A1 cause an average change in the contact pressure of 1.4 mmHg per heartbeat or 1.3 mmHg/sec need, the maximum values are 24.4 mmHg per heartbeat or 25 mmHg/sec. However, no actuators or devices for applying/generating pressure are described. Both EP 2 854 626 and WO 2016/110781 A1 use complex photoplethysmographic systems for measuring the blood volume in the artery, which have at least one light source (LED) and one light detector (photodiode).

A measuring system for the continuous determination of blood pressure has become known from EP 3 419 515 B1, which has the external shape of a computer mouse, on the surface of which a double-finger sensor is designed to record two fingers of one hand. The finger sensors have inflatable cuffs, the pressure of which tracks the intra-arterial blood pressure in the finger with the help of a photoplethysmographic system. This requires real-time controlled valves at the entrance to the cuffs that supply pressure from a compressed air source. According to one embodiment variant, the pressure generation system together with the pump and an air reservoir can be arranged in the body of the computer mouse.

Finally, WO 2020/176214 A1 describes a finger sensor for measuring blood pressure, which has a bladder that can be pressed against the finger with constant pressure and is filled with an incompressible fluid. A pressure sensor is arranged in the bladder, with which the arterial blood pressure can be measured in the finger.

The aim of the invention is to develop a measuring system and a method for the continuous, non-invasive determination of the arterial blood pressure in an extremity in such a way that a compact system consisting of few individual parts and inexpensive to produce is realized, which can also be made into a portable unit can be integrated. This object is achieved by a measuring system according to claim 1 and a measuring method according to claim 9. Advantageous embodiment variants are disclosed in the dependent claims.

The present application discloses various design variants of a measuring system that can operate simultaneously as an actuator and as a volume signal pickup, with the components of a photoplethysmographic system mentioned at the outset, such as light sources (LEDs) and light detectors (photodiodes), being omitted.

The invention uses an incompressible fluid-filled (e.g., liquid-filled), flexible bladder that is directly coupled to the limb (e.g., the finger). An actuator acts on this bladder (for example a piston, a ram, a clamp, etc., with a corresponding drive device), which can increase and decrease the pressure in the bladder. This pressure in turn acts on the extremity and thus on the artery. Furthermore, a pressure sensor is provided which, in addition to the absolute pressure generated by the actuator, can also record pressure pulsations and thus the volume signal, which are caused by the movement of blood in the artery. The pressure signal consisting of the absolute pressure and the pressure pulsations is fed to a controller that controls the actuator for pressurizing the flexible bladder.

With the help of this measuring system, the blood pressure acting in the artery can be continuously measured. The present invention also describes a new "Vascular Control Technique" method (VCT method) for continuous blood pressure measurement.

In contrast to the classic vascular unloading technique described at the outset, no light elements such as LEDs or photodiodes are required in photoplethysmography to record the volume signal.

In addition, the blood pressure can also be determined intermittently using the known oscillometric method.

The invention is explained in more detail below using schematic representations and diagrams:

1a shows a non-invasive blood pressure measuring system (“wearable”);

FIG. 1b shows an enlarged view of the wearable according to FIG. 1a; FIG. 2 shows the front view, side view, top view and bottom view of the wearable according to FIG. 1b;

3 shows a section according to line A-A in FIG. 2 through the wearable with a first position of the actuator for generating pressure;

FIG. 4 shows the wearable according to FIG. 3 with a second position of the actuator for generating pressure;

5 shows a schematic representation of the mode of operation of the measuring system according to the invention together with the regulator (controller);

FIG. 6 shows a second embodiment variant of the measuring system in a sectional illustration according to FIG. 3;

7 shows a detailed representation of the oscillometric signals; such as

Fig. 8 Diagrams of oscillometric signals in the search phase.

The present application describes different embodiment variants of a measuring system, as well as a method of how these measuring systems can measure the arterial blood pressure. The blood pressure can be measured both discontinuously and continuously - i.e. for each heartbeat. The measuring system consists of at least one actuator (device for generating pressure) and a flexible bladder filled with an incompressible fluid. The e.g. fluid-filled bladder acts on an extremity in which at least one artery is located. In the described embodiment variants, the finger of one hand is used, but applications on other parts of the body are also possible, such as the wrist, the temple and also the tail of an animal in veterinary applications.

In FIG. 1a and in detail according to FIG. 1b, a portable measuring system 301 (wearable) is shown in the form of a finger ring including a ring attachment for use on a finger of one hand. The corresponding device for generating pressure (or actuator) is integrated into the wearable in order to exert a predeterminable, variable pressure on the finger.

2 also shows the finger ring in front view, side view, top view and bottom view.

FIG. 3 shows a section through the measurement system or wearable 301, in whose housing 300 the elements of the actuator are located. The actuator is driven by a motor whose stator 302 is mounted on a printed circuit board under the flat surface. surface of the ring attachment is attached. Below is the rotor 303 which is rotatably attached to the stator 302 by a spring 304 . A possible variant of this motor is a low-energy, piezoelectric motor for use on electronic printed circuit boards (see eg www.pcbmotor.com).

In principle, an actuator is present in the measuring system 301, which consists, for example, of a piston 307, a plunger or another element and its drive unit 302, 303. The piston or plunger is moved in one direction (see arrow 313) and thus generates pressure in a fluid-filled bladder 309. The actuator and thus the piston 307 could also be driven differently than shown in FIG are also located outside of the blood pressure monitor shown.

In FIG. 3 the rotor 303 drives a transmission element 305 which in turn drives a rotatable piston 307 via a gear element 306 . The transmission element 305 is fixed directly to the rotor 303, while the piston 307 can move in the direction of the finger. This movement of the piston 307 is made possible by the gear element 306 shown schematically.

The piston 307 is guided in a cylinder 308 in the housing 300 . Together they form the gear element 306. For example, the gear element 306 can be realized by a simple thread, with the piston 307 being equipped with an external thread and the cylinder 308 with an internal thread. The illustrated thread 306 is only one possible embodiment. It is important that the friction losses are kept as low as possible. Other mechanical or hydraulic transmission elements are also possible.

The movement of the rotor 303 now pushes the piston 307 in the direction of the finger. The piston 307 then presses on a bladder 309 filled with an incompressible fluid, for example a liquid or a gel. The pressure in the liquid is thereby increased and now acts on the finger (not shown in FIG is in the measuring system 301.

The fluid-filled bladder 309 has a rigid outer wall and a largely flexible inner wall that abuts the extremity (e.g., fingers).

In particular, the liquid should be incompressible or sufficiently incompressible. This will require all gases to be removed prior to application. Furthermore, the liquid must be biocompatible for use in medical products. Of course, gels or creams are also considered liquids in this context. When coupling the piston 307 to the liquid-filled bladder 309, there are two different variants. In the first variant, the piston 307 presses directly onto the liquid. In this case, the transmission element 306 must also function as a seal at the same time. The advantage of this is that the liquid can also serve as a lubricant for the gear element 306, which reduces friction overall.

In a second variant, the piston 307 presses on the outer wall of the liquid-filled bladder 309, which then has to be made flexible at this point. This has the advantage that the tightness of the bladder can be more easily ensured. In certain implementations, the bladder 309 can be designed to be replaced after a few uses, making it disposable.

Figure 4 shows the situation when the piston 307 has moved towards the finger. For this purpose, the transmission element 305 has rotated and thus displaced the piston 307 . The pressure in the liquid-filled bladder 309 was thereby increased.

The pressure in the liquid-filled bladder 309 is measured by means of a pressure sensor 310, small piezoelectric pressure sensors being preferably suitable. This pressure sensor 310 is also used at the same time as a sensor for the arterial pulses or pulsatile pressure fluctuations. These pulsatile pressure fluctuations are caused by the blood movements that occur in the arteries depending on the heartbeat. For this purpose, the pressure sensor 310 must have sufficient resolution and be able to detect pressure changes of at least 0.01 mmHg (0.013 mbar) at an upper limit frequency of at least 40 Hz.

The pressure sensor 310 thus measures, on the one hand, the absolute pressure that occurs in the liquid-filled bladder 309 and thus acts on the finger. On the other hand, this pressure sensor also measures the pressure pulsations and thus a so-called “plethysmographic” volume signal, without a light sensor system consisting of a light source and a light sensor being present for this purpose (“photoplethysmography”).

FIG. 5 shows how the pressure signal is fed to a controller 315 which in turn controls the actuator of the measuring system 301 . In FIG. 5 the actuator consists of a motor, which in turn consists of a stator 302 and a rotor 303 . The rotor 303 can adjust a piston 307 as a result of its rotational movement, so that the pressure in the liquid-filled bladder 309 is changed and the pressure signal is generated with the aid of a pressure sensor 310 . Preferably, the controller operates in real time to adjust the pressure in the flexible, fluid-filled bladder 309 as precisely as necessary to subsequently determine blood pressure. FIG. 5 schematically shows the mode of operation of the controller 315 in question and is described in detail below.

This controller 315 is preferably constructed as an electronic circuit. As shown in FIG. 6, the electronic components 320 of the controller are preferably located on the same electronic circuit board as the stator 302 of the motor. This embodiment variant of the measuring system 301 subsequently shows batteries 321 for the power supply and optionally a display 322 which is located on the upper side of the ring attachment of the finger ring shown here.

Furthermore, the controller 315 can also be implemented as a digital electronic circuit. The following elements are preferably required for this: microcomputer, memory for the program code, main memory, analog-to-digital converter, digital-to-analog converter, components for voltage generation, etc. For example, a microcontroller can be used that already provides most of the functions integrated in one component . However, the controller can also be built using other methods, such as using analog circuits.

The controller 315 is initially able to measure and process the absolute pressure pc(t) in the liquid-filled bladder 309 . Furthermore, the controller 315 is able to measure and process the arterial pulsations and thus the volume signal. Seen electronically, the absolute values correspond to the direct component (DC component) and the pulsations to the alternating component (AC component) of the pressure signal pc(t), as shown in FIG.

Controller 315 may have multiple control loops that have different functions. On the one hand, a control loop that controls the absolute pressure p _c (t) can prove to be advantageous. The actuator of the measuring system is adjusted until the measured absolute pressure p _c (t) corresponds to a target value pr(t).

The target value pr(t) can be specified by another control loop - the so-called "Vascular Control Technique" control loop (VCT controller). The desired value (target value) pr(t) can be the mean arterial blood pressure (mBP). This is reached when the amplitudes of the pulsations have reached a maximum value. A typical amplitude profile is shown in FIG. 7, the mean arterial blood pressure occurring here at a pc(t) of 115 mmHg. The pulse amplitude is at its maximum. Nota bene: the absolute values of the pulsations are unimportant here, the relative maximum is important. This is not the case with a tonometric method - the measured pulses would also correspond to the continuous blood pressure signal. Since this absolute pulse signal depends on many disturbing factors (such as the coupling factor, vascular stiffness, etc.), the clinical accuracy and thus the suitability of these tonometric methods suffer.

If the mean arterial blood pressure now changes, then the condition of the maximum pulse amplitude is no longer met. However, the VCT controller cannot tell from the pulse amplitude alone whether the mBP has become smaller or larger. As can be seen in FIG. 7, the pulse amplitudes become smaller both when the pressure is too low and when the pressure is too high.

The VCT controller can recognize from the pulse waveform whether the pressure pc(t) in the liquid-filled bladder 309 is too small or too large. If the pressure is too low, the pulse is wide or "thick" (see Fig. 7, B: pulse at 103 mmHg") compared to the "normal" pulse (see Fig. 7, A: pulse at 115 mmHg"), the pulse at too high a pressure is "spike" (see Fig. 7, C: pulse at 141 mmHg"). The VCT controller is now set to follow the pulse waveform of the optimal pulse with maximum amplitude. If due to a If the actual mean arterial blood pressure mBP changes, the pulse is "thick", then the target value p-r(t) and subsequently pc(t) in the liquid-filled bladder 309 are increased until the curve shape becomes "normal" again. Conversely, that p-r(t) and subsequently pc(t) is reduced when the pulse becomes "spiky".

This VCT mechanism now adjusts the setpoint p-r(t) and subsequently pc(t) in the liquid-filled bladder 309 such that pc(t) follows the actual mBP occurring in the artery of the limb. Studies in patients fitted with an intra-arterial catheter for blood pressure measurement during surgical procedures have shown that pc(t) tracks the true intra-arterial pressure mBP with reasonable clinical accuracy. For this it is advantageous if the VCT controller receives a starting value for mBP and a template for the "normal" pulse waveform.

For this purpose, according to the invention, a search phase can be carried out before the start of the measurement. For example, Figure 8 shows how this search phase works. The setpoint pr(t) and then pc(t) are increased continuously and the pulsations are registered. These so-called "Oscillometric Waves" (OMW) are filtered and an envelope of the OMW is generated. This envelope corresponds to the amplitudes of the pulsations. The absolute value of the pc(t) at which the maximum amplitude was registered corresponds to the starting value for mBP, the pulse registered is the template for the "normal" pulse waveform. This search phase works according to the oscillometric principle and also allows the determination of the systolic and diastolic blood pressure. The present measuring system can thus also determine the blood pressure intermittently.

After this search phase at the beginning of each measurement, the actual measurement of the continuous blood pressure can begin. This search phase can be repeated automatically at any time in order to increase the accuracy of the measurement - this option is not so easily possible with a pure tonometric measurement.

In the search phase, the systolic and diastolic blood pressure and thus the pulse pressure can be determined from the oscillometric envelope. This can be helpful when determining an amplification factor for a so-called transfer function. A simple transfer function for determining the continuous blood pressure can look like this: bp(t) = p _DC (t) + /c * PAc(t) where bp(t) is the continuous blood pressure signal, poc(t) is the absolute value of the pressure in the liquid-filled bladder 309, PAc(t) are the pulsations of the pressure in the liquid-filled bladder 309, and k is the gain factor calculated from the pulse pressure in the search phase.

Claims

PATENT CLAIMS Measuring system for the continuous, non-invasive determination of arterial blood pressure on a limb containing an artery, with a housing (300) or housing part that can be attached to the limb and is suitable for at least partially enclosing the limb, with a a flexible limb-acting bladder (309) supported on the housing (300) and filled with a fluid, characterized in that the flexible bladder (309) is filled with an incompressible fluid, for example a liquid or a gel is that an actuator is arranged in or on the housing (300), which contacts the incompressible fluid or the flexible bladder (309) and is suitable for varying the pressure in the incompressible fluid that the flexible bladder (309) one Pressure sensor (310) having in fluid contact with the incompressible fluid, wherein the pressure sensor (310) is adapted to the pressure applied by the actuator to the incompressible fluid to measure continuously and to generate a pressure signal p _c (t), and that the pressure sensor (310) is suitable for additionally measuring a pulsatile signal coupled from the artery into the incompressible fluid. Measuring system according to Claim 1, characterized in that the measuring system has a controller (315), at the input of which the pressure signal p _c (t) of the pressure sensor (310) is present, the output of the controller (315) being connected to a drive device (302, 303 ) of the actuator is connected. Measuring system according to Claim 2, characterized in that the controller (315) has at least a first control loop which is suitable for setting the pressure Pc(t) in the flexible bladder (309) based on a setpoint value pr(t). Measuring system according to Claim 2 or 3, characterized in that the controller (315) is constructed analogously from electronic components (320). Measuring system according to Claim 2 or 3, characterized in that the controller (315) is constructed digitally and has at least one computer unit including program code. Measuring system according to one of Claims 1 to 5, characterized in that the actuator is designed as an electric motor with a stator (302) arranged in the housing (300) and a rotor (303) acting on a tappet or piston (307). Measuring system according to Claim 6, characterized in that the piston (307) is guided in a cylinder (308), with gear elements (305, 306) being provided between the rotor (303) and the piston (307) which are suitable for the rotary Convert movement of the rotor (303) into an up and down movement of the piston (307). Measuring system according to one of Claims 1 to 7, characterized in that the housing (300) is designed in shape and dimensions as a finger ring including a ring attachment, the flexible bladder (309) being arranged on the inside of the finger ring and the ring attachment being a control circuit board with a Controller (315) having the actuator for changing the pressure and means for supplying energy (321). A method for the continuous, non-invasive determination of arterial blood pressure in a limb containing an artery, the limb being at least partially surrounded by a flexible bladder (309) filled with an incompressible fluid and arranged in a housing (300) or housing part is, and wherein a pressure sensor (310) in the bladder (309) is arranged, which generates a pressure signal p _c (t), characterized in that the pressure in the flexible bladder (309) with the aid of the incompressible fluid or the flexible bladder (309) acting, in or on the housing (300) arranged actuator is changed. Method according to Claim 9, characterized in that the pressure signal p _c (t) from the pressure sensor (310) is fed to a controller (315), the control signal of which is fed to the actuator and controls the pressure in the flexible bladder (309). Method according to claim 10, characterized in that the controller (315) has at least one control loop which adjusts the pressure pc(t) in the flexible bladder (309) based on a setpoint pr(t), the setpoint value pr(t) is calculated from the pulsatile component of the pressure signal p _c (t) of the pressure sensor (310).

12. The method as claimed in claim 11, characterized in that the pulse waveform of the pulsatile component of the pressure signal p _c (t) of the pressure sensor (310) is used to determine the desired value pr(t).

13. The method according to claim 11 or 12, characterized in that the initial value of the target value p-r(t) of the regulation is determined in a search phase.

14. The method according to claim 13, characterized in that the amplitudes of the pulsatile component of the pressure signal p _c (t) of the pressure sensor (310) are determined and that the mean, systolic and diastolic blood pressure is determined therefrom.

15. The method according to claim 12, characterized in that the pulse waveforms are registered at different pressures pc(t) in the liquid-filled bladder (309).

2021 11 09

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