AT524038B1 - PORTABLE DEVICE FOR GENERATION OF VARIABLE PRESSURE ON A LIMB - Google Patents

Abstract

The invention relates to a portable device for generating a variable pressure on an extremity containing an artery, with a housing (300, 600) or housing part that can be attached to the extremity and is suitable for at least partially enclosing the extremity, and with a a flexible limb engaging bladder (309, 609) supported on the housing (300, 600) and filled with a fluid. According to the invention, the flexible bladder (309, 609) is filled with an incompressible fluid, for example a liquid or a gel, with an actuator being arranged in or on the housing (300, 600) which moves the incompressible fluid or the flexible bladder (309 , 609) and is suitable to vary the pressure in the incompressible fluid.

Description

description

The invention relates to a portable device, suitable for generating a variable pressure on a limb containing an artery, with a housing or housing part which is attachable to the limb and is suitable to include the limb at least partially, and with a limb-acting flexible bladder supported on the housing and filled with a fluid. The main application of the device is to measure blood pressure on the finger of one hand.

[0002] It is possible to record all relevant cardiovascular parameters including blood pressure, cardiac output, vascular resistance and medical variables for assessing the autonomic nervous system with the help of stationary measurement systems. A medically approved, portable sensor - a so-called "wearable" - for these cardiovascular values would be desirable. The basis for calculating these parameters is continuous recording of the blood pressure signal.

The continuous, non-invasive measurement of blood pressure is still a major challenge for measurement technology. The so-called "Vascular Unloading Technique" is beginning to assert itself on the market, which is based on a publication by Pehäz (Digest of the 10th International Conference on Medical and Biological Engineering 1973 Dresden), in which a finger is X-rayed and the registered flow is kept constant by servo control and the resulting pressure on the finger.

[0004] The vascular unloading technique requires a pressure generating 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 1179 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, which make use in a portable system difficult or impossible. The average power consumption of such a blood pressure module is 2.5W with peak power in the start-up phase of up to 5W. This high energy consumption also makes the use of the Vascular Unloading Technique in a "wearable" at least difficult.

[0005] 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 supplementary elements that are 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, the maximum values are 24.4 mmHg per heartbeat or 25 mmHg/sec. However, no actuators or devices for pressure application/pressure generation that would be suitable for a “wearable” are described.

[0007] 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 for recording two fingers of one hand is formed. 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

described, which has a bladder that can be pressed against the finger with constant pressure and that 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 device or an actuator for generating a variable pressure on an extremity containing an artery in such a way that a portable application, in particular as part of a blood pressure measuring device, is possible easily and inexpensively will.

This object is achieved by a device according to claim 1. Advantageous variants are disclosed in claims 2-10.

The actuator according to the invention is, for example, part of a sphygmomanometer that is attached to an extremity in which there is at least one artery. A finger of the hand is preferably used for this purpose, but the wrist, the temple and, in veterinary applications, the tail of an animal could also be used as a measurement site.

So that the actuator according to the invention - which consists essentially of a drive device and an actuating element (eg piston, plunger, clamp, etc.) for changing the pressure in the flexible bladder - is suitable for installation in a portable sphygmomanometer, must the device for generating pressure can be miniaturized. This means that it can be assembled from just a few small parts. The aim is to integrate the actuator into a finger ring, for example.

[0013] In addition, the energy requirement of the drive for the actuator must be kept small. The goal for the energy requirement is that the "wearable" can measure continuously for 24 hours if possible. The battery required for this must therefore be so small that it can also be integrated into the "wearable".

The actuator serves to generate only small changes in the contact pressure so that the mean arterial blood pressure can be followed. According to the study above, only maximum changes of 30 mmHg/sec are necessary, on average it is only 1.3 mmHg/sec. The maximum contact pressure is 150mmHg (200 mbar).

If the actuator is part of a sphygmomanometer, elements are required with which one can detect pulsations, ie changes in the volume of the extremity for each heartbeat, while the contact pressure on the extremity can be changed by the actuator.

The actuator as part of a blood pressure measuring device must generate a homogeneous contact pressure for the precise detection of the pulsations. This is achieved by suitable geometry of the system. This is essential because it is the only way to ensure high clinical accuracy. If, for example, the transmission or coupling factor for detecting the pulsations over the pressure range were to change, the pressure-related pulsations would have different amplitudes in different contact pressure ranges. However, the detection of the pulsations and their amplitude is essential for an accurate detection of the blood pressure.

The actuators and sensor systems described in this application meet these requirements.

The invention is explained in more detail below with the aid of schematic representations and diagrams. Show it:

[0019] FIG. 1a shows a non-invasive blood pressure measuring device (“wearable”) that can be worn on the finger of one hand, into which the device according to the invention for generating pressure (“actuator”) is integrated;

[0020] FIG. 1b shows an enlarged view of the wearable according to FIG. 1a;

[0021] FIG. 2 shows the front view, the side view, the top view and the bottom view of the wearable according to FIG. 1b;

[0022] FIG. 3 shows a section according to line A-A in FIG. 2 through the wearable with a first embodiment variant of the device for generating pressure;

4 diagrams of oscillometric signals during blood pressure measurement; 5 shows a detailed representation of the oscillometric signals; as

[0025] FIG. 6 shows a second embodiment variant of the device for generating pressure in a sectional view according to FIG.

The present invention describes different embodiment variants of an actuator, as well as a method of how these actuators pass on the pressure to an extremity. These actuators can be used, for example, for portable sphygmomanometers—so-called “wearables”. The actuator generates a pressure that is transmitted to a limb that contains at least one artery. In the embodiment variants described, 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 or in detail according to FIG. 1b, the portable blood pressure measuring device 301 is shown in the form of a finger ring including a ring attachment for use on a finger. The corresponding device for generating pressure (or actuator) is integrated into the wearable in order to exert a predeterminable, variable pressure on the finger.

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

shows a section through the wearable 301, in the housing 300 are the elements of the actuator. The actuator is driven by a motor whose stator 302 is mounted on a printed circuit board under the flat surface of the ring cap. 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 e.g. www.pcbmotor.com).

Basically, the selected motor should have a high holding torque. This means that rotor 303 of the motor will stop at the desired location without the application of rest energy, even if some back pressure is applied. In the present variant, this high holding torque is generated by the spring 304, which to a certain extent latches the rotor 303 when it is to stop because no more energy is being applied in the stator 302.

Basically, the rotor 303 is intended to move a piston 307 in order to apply pressure to the extremity. A gear mechanism is installed to convert the rotational movement of the rotor 303 into a linear movement of the piston 307 .

For this purpose, the rotor 303 drives a transmission element 305 which in turn drives the rotatable piston 307 via a transmission element 306 . The transmission element 305 is fixed directly to the rotor 303, while the piston 307 can move up and down in the direction of the finger. This movement of the piston 307 is made possible by the present gear element 306 .

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.

By the movement of the rotor 303, the piston 307 is now pressed 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. 3), the in

Wearable 301 is located.

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

The liquid should in particular be incompressible or sufficiently incompressible. This will require all gases to be removed before use. 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.

The pressure in the liquid-filled bladder 309 is preferably measured using the pressure sensor 310 . In some embodiment variants, this pressure sensor 310 can also be used 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.

[0040] A further possibility is the detection of the arterial pulsatile signals via photoplethysmography (PPG). This requires light sensors or PPG sensors 311 or 611, which can detect the arterial pulse in the finger in a known manner.

Figure 4 shows how the present actuator works in a blood pressure measurement system. On the one hand, the actuator can be used for the so-called “oscillometric detection of blood pressure” (oscillometry), as is the state of the art on the basis of inflatable cuffs in almost all automated sphygmomanometers on the upper arm or wrist.

Another blood pressure measurement method for which the present actuator is suitable is the Vascular Control Technique (VCT) described in EP 2 854 626 and EP 3 242 591. The pressure on the finger generated by the actuator is continuously adjusted to the mean arterial blood pressure. This method is again based on principles known from oscillometry. Therefore, the correct acquisition of the oscillometric signals with the present actuator is essential.

In oscillometry, the contact pressure of a cuff or also of the flexible bladder on an extremity is continuously increased (see top image of FIG. 4 "Pressure") or reduced in some other applications. The pulsations (middle image of FIG. 4 "Oscillometric Waves OMW") are recorded which are caused by the blood movements in the artery. The pulsations in the pressure system are usually recorded using a pressure sensor, but other sensors such as PPG sensors, Doppler, radar, etc. can also be used. The envelope of the pulsation signal is then generated from these pulsations by suitable filters and other signal analysis methods (see lower image of FIG. 4 "Envelope of the OMW"').

Figure 5 shows the details of an "oscillometric envelope" (Osecillometric Wave OMW envelope). The maximum of these bell curves occurs when the contact pressure generated by the actuator corresponds exactly to the mean arterial blood pressure. The associated pulsation A (pulse at 115 mmHg) has the highest amplitude and corresponds to

Waveform similar to that found in true arterial blood pressure. However, the inverted representation in FIG. 5 is correct because this pulse was recorded using the PPG method. In systole, there is more arterial blood in the finger and the light or PPG signal becomes smaller, while in diastole and therefore less blood in the measuring section, more light energy can radiate through the finger.

The pulsations that occur when the contact pressure is above or below the mean blood pressure naturally have a lower amplitude. However, the curve shapes are fundamentally different. If the contact pressure generated by the actuator is less than the average blood pressure, then a broad ("fat") pulse B occurs - (see pulse at 103 mmHg). If, on the other hand, the contact pressure is greater than the average blood pressure, a so-called "sharp pulse" C - (see pulse at 141 mmHg) occurs.

The system shown in Figure 3 includes a flexible, fluid-filled bladder 309 that completely encloses the finger. The PPG system must be mounted on the flexible inner wall of the bladder 309 here.

In Fig. 6, a further embodiment of the wearables 601 is now shown, in which a liquid-filled bladder 609 applies the pressure only on the top of the finger. The PPG sensors 611 are built into fixed contact points 612 on the underside of the finger that do not move. All other elements (stator 302, rotor 303, spring 304, U-transmission element 305, gear element 306, piston 307, cylinder 308, pressure sensor 310) are identical to the embodiment variant that was shown in FIG.

The application of pressure by the actuators described here produces oscillometric signals of sufficiently high quality. This was determined in comparison measurements with commercially available sensors for stationary measuring systems (CNAP, CNSystems Graz, Austria), which work with air pressure and therefore with pumps, valves and hoses.

Claims (10)

patent claims 1. Portable device suitable for generating variable pressure on a limb containing an artery, with a housing (300, 600) or housing part that can be attached to the extremity and is suitable for at least partially enclosing the extremity, with a flexible bladder (309, 609) which is supported on the housing (300, 600) and acts on the extremity and which is filled with a fluid, characterized, that the flexible bladder (309, 609) is filled with an incompressible fluid, for example a liquid or a gel, wherein an actuator is arranged in or on the housing (300, 600) which contacts the incompressible fluid or the flexible bladder (309, 609) and is suitable for varying the pressure in the incompressible fluid. 2. Device according to claim 1, characterized in that the actuator is designed as an electric motor with a stator (302) arranged in the housing and a rotor (303) acting on a plunger or piston (307). 3. Device according to claim 2, characterized in that the piston (307) is guided in a cylinder (308), wherein between the rotor (303) and the piston (307) gear elements (305, 306) are provided which are suitable to convert the rotational movement of the rotor (303) into an up and down movement of the piston (307). 4. The device according to claim 1, characterized in that the actuator is designed as a piezoelectric drive element acting on a tappet or piston (307). 5. Device according to one of claims 1 to 4, characterized in that the flexible bladder (309, 609) has at least one pressure sensor (310) in fluid contact with the incompressible fluid, the pressure sensor (310) being suitable for use by a plunger or piston (307) to measure pressure applied to the incompressible fluid. 6. Device according to claim 5, characterized in that the pressure sensor (310) is suitable for additionally measuring a pulsatile signal coupled from the artery into the incompressible fluid. 7. Device according to one of claims 1 to 6, characterized in that the device has sensors directed towards the extremity (311, 611) of a photoplethysmographic (PPG) system, which are suitable for a pulsatile coupled from the artery into the incompressible fluid measure signal. 8. Device according to claim 7, characterized in that the flexible bladder (609) only partially encloses the extremity and that the sensors (611) of the photoplethysmographic (PPG) system directed towards the extremity are arranged in the free area (612). 9. Device according to one of claims 1 to 8, characterized in that the device for generating a variable pressure on an extremity is designed as part of a non-invasive blood pressure measuring device. 10. Device according to one of Claims 1 to 9, characterized in that the housing (300, 600) is designed in shape and dimensions as a finger ring including a ring attachment, the flexible bladder (309, 609) being arranged on the inside of the finger ring and the ring attachment has a control circuit board, the actuator for changing the pressure and means for supplying energy. 6 sheets of drawings