RU2051614C1 - Catheter for hydrodynamic measurements of blood stream in cardiovascular system - Google Patents

Abstract

FIELD: medical engineering. SUBSTANCE: catheter comprises a flexible tube ending in a converter which consists of a cylindrical housing accommodating a revolving impeller and two Hall's sensors. The impeller is made of a nonmagnetic material with magnetic inserts installed on the edges of its blades, the magnetic poles of said inserts being directed radially so that the polarity of the end of one blade is opposite to that of the other blade ends. Installed on the internal surface of the housing are an electromagnet and Hall's sensors coated with a layer of sealant. EFFECT: improved design. 2 cl, 7 dwg

Description

 The invention relates to medicine and medical equipment and is intended to determine the hydrodynamic parameters of the blood flow in the cardiovascular system (CVS) of a living organism.

 Replacing incapable of functioning of the heart valves with prostheses, as well as operations on the heart and heart vessels, require accurate data on some parameters of the blood flow circulating in the CVS of a living organism. These parameters include speed, direction and swirl angle, tangential component and degree of flow turbulization.

 A device for determining the parameters of the blood flow, which makes it possible to set the temperature and pressure in various sections of the CCC [1] But this device does not determine the hydrodynamic parameters of the flow.

 The closest known technical solutions for the technical nature and the achieved result is a catheter for hydrodynamic measurements in the heart [2] adopted as a prototype.

 The specified device is a catheter with a transducer at the working end. The converter contains a base, a four-blade impeller made of magnetic material, two Hall sensors and a cylindrical casing, on the walls of which an odd number of longitudinal slots are made.

The casing is fixed on the base, on which two Hall sensors are also fixed through an angle of 90 ^about . The passage of the blades near the sensors is accompanied by an amplification of the recorded signals. The impeller rotation speed is determined by the number of signals per revolution, and the flow velocity and the swirl angle are determined by the known rotation speed.

 The disadvantages of the known device are the low accuracy and reliability of determining the hydrodynamic parameters of the measured flow, due to its deformation when passing through the longitudinal slots of the casing, and the complexity of implementation. The latter is explained by the fact that the determination of two unknown flow velocities and the swirl direction is based on the measurement of only one impeller rotation speed parameter. Therefore, in measurements it is necessary to use an equivalent, which makes it possible by comparison to exclude one of the values from the solution of the problem. The use of the equivalent is associated with the need to change the calibration of measurements when changing the flow conditions of the transducer.

 The technical result of the invention is to increase the accuracy of measuring the hydrodynamic parameters of the blood flow and the reliability of the results, while simplifying the measurement procedure.

+ B

+CΦ=X
(1) где Х суммарный момент сил, действующих на вращающуюся систему;
I момент инерции вращающейся системы;
Φ- угол закрутки потока;
В постоянная демпфирования;
С сила пружины, создающей вращающий момент системы.The technical result is achieved by creating a device whose action is based on the processes described by differential control from the theory of oscillations for a rotating system placed in a fluid flow [3]
J

+ B

+ CΦ = X
(1) where X is the total moment of forces acting on the rotating system;
I moment of inertia of the rotating system;
Φ - flow swirl angle;
In constant damping;
With the force of the spring creating the system's torque.

 Since there are no laminar flows in the body, tangential forces caused by swirling of blood flow will act on the rotating system. Having determined the total moment of forces indicated in equation (1) by X, we can find the swirl angle Φ.

v²ρkS
(2) где v скорость измеряемого потока;
ρ- плотность жидкости;
k гидродинамический коэффициент вращающейся системы;
S площадь, на которую действует набегающий поток.Then, it is easy to find the blood flow rate from relation (2), known from the source [4]
C

v ² ρkS
(2) where v is the velocity of the measured flow;
ρ is the fluid density;
k hydrodynamic coefficient of a rotating system;
S is the area over which the incident flow acts.

 Such a device does not need additional calibration and the use of an equivalent when changing flow conditions and makes it possible to measure flow parameters directly.

 The essence of the invention lies in the fact that in the catheter containing a flexible tube with a transducer at the end, consisting of a cylindrical casing, mounted in it with the possibility of rotation of the impeller and two Hall sensors, an electromagnet is installed, installed, like Hall sensors, on the inner wall of the casing, covered with a layer of sealing substance, the impeller is made of non-magnetic material, and along the edges of the blades are magnetic liners with a radial direction of the magnetic poles so that the end face of one blade has polarity opposite to the polarity of the other ends.

 The axial transverse electromagnet and Hall sensors are in the same plane of the cross section of the casing, and the angles between the radii connecting the center of the circumference of the casing section with the geometric centers of these elements differ from the angles between the impeller blades to reduce their mutual influence. The inner diameter of the cylindrical casing, taking into account the thickness of the layer of sealing material covering the inner machines of the casing, is larger than the outer diameter of the impeller and the flexible tube through which the electrical leads pass through to connect the electromagnet and Hall sensors to the measuring circuit, which creates favorable conditions for the free flow of the stream through the catheter transducer without noticeable violation of its structure.

 In FIG. 1 shows a device, a General view; figure 2 is a cross section of the device in the plane of the axial section of the sensors and the electromagnet; figure 3 plots of stresses removed from the sensors when the impeller rotates clockwise (figure 2); figure 4 plots of stresses removed from the sensors when the impeller rotates counterclockwise (figure 2); figure 5 plots of stresses taken from the turbulent flow sensors; Fig.6 is a structural diagram of a measuring device; Fig.7 layout of the catheter when measuring flow in the aorta.

 The device contains a cylindrical casing 1 (see figure 1) of a non-magnetic material, for example, titanium, with jumpers in the open ends. The impeller 3 of non-magnetic material is pivotally mounted in the casing 1 with the possibility of rotation around the axles 4, supported by jumpers 2. Along the edge of each blade of the impeller 3 is fixed (for example, glued) a magnetic insert 5 with a radial direction of the magnetic field so that the ends of the three blades have the same polarity opposite the polarity of the fourth end.

 An electromagnet 6 and two Hall sensors 7 and 8 are located on the inner wall of the casing 1 (see Fig. 2). The conclusions 9 from the electromagnet 6 and the sensors 7 and 8 are conducted to the axis and then to the flexible tube 10 to the external connections.

 The structural diagram of the measuring device shown in Fig.6, contains Hall sensors 7 and 8, which constantly receives the voltage of the sinusoidal voltage generator 12. Sensors 7 and 8 are connected to the detectors 13, which, in turn, are connected to amplifiers 14. Amplifiers 14 connected to matching devices 15 having an output to a recording device 16. Standard devices, for example, an amplifier of type U4-12 and generator G3-36, can be used as amplifiers and a generator. The data recorded by the recording device 16, for example, a recorder, after decryption, can be submitted to the computer.

 The device operates as follows.

 Through the incision (see Fig. 7), the proposed device is introduced into a vessel, for example, by an aorta (i.e., a cylindrical casing 1 with an impeller 3) towards the measured flow. The Converter is fixed by ligatures 17, and the incision is closed with a continuous seam. The blood flow passes through the aorta through the cavity of the cylindrical casing 1, affecting the impeller blades 3. Since the studied flow has a tangential component, the impeller blades 3 experience pressure directed normal to the plane of the blade, and the impeller 3 begins to rotate. The direction of rotation coincides with the direction of flow swirl.

To determine the twist angle, a constant voltage is applied to the coil of the electromagnet 6, while the electromagnetic field of the coil interacts with the magnetic field of the liners 5. By changing the voltage, you can slow down the rotation of the impeller 3 until it stops at the position when the blade with the magnetic liner 5 is located strictly under the electromagnet 6, which means the equality of the efforts of the electromagnetic field of the coil and the pressure of the measured flow, acting normal to the blade. Having the dependence of the voltage on the coil of the electromagnet 6 and the moment on the impeller 3, it is possible to determine the magnitude of the moment X (see equation 1). In the case under consideration in equation (1), the moment of inertia of the rotating system I is the moment of inertia of the impeller 3, which can be neglected, since it manifests itself only at the time of starting the device, and the damping constant At the moment of friction in the bearings of rotation of the axles 4 of the impeller 3, which can also be neglected , since before installation the impeller is subjected to static balancing on the basis that the friction moment should be an order of magnitude less than the expected moment of rotation of the impeller 3. The value C in the case under consideration is the tangential pressure force of the flow component normal to the impeller blade 3 can be found by the speed of rotation of the impeller 3, which, in turn, is determined by the number of signals taken from the Hall sensors when inserts 5 pass by them. Thus, solving equation (1), we can find flow swirl angle, and then from relation (2) the flow velocity v. The area S on which the incident flow acts, in this case the projection area of the blade. It is determined from the relation S = S _о · sinΦ, where S _{о is the} geometric area of the blade.

The direction of the swirling flow is determined using Hall sensors, from which under the influence of a constant magnetic field of the liners 5 are removed, respectively, the electrical signals U ₂ and U ₁ . Signals of a different level are supplied to each sensor and signals of a different level are also taken. When approaching the Hall sensors 7 and 8 of the insert 5, the amplitude of the sinusoidal voltage supplied to them from the generator 12 (see figure 6) increases. As a result, signals having the form of rounded peak-like pulses are recorded from the sensors. Further, the signals are detected by detectors 13, amplified by amplifiers 14, and fed to matching devices 15, which separate them in time. After that, the signals are fed to the recording device 16, most often a recorder, which gives a visual representation of the relative position of the pulses. When the impeller 3 rotates clockwise (in FIG. 2), the diagrams of the removed stresses correspond to those depicted in FIG. 3, i.e. if the insert 5 first passes by the sensor 8, and then by the sensor 7, then the recording device 16 detects the advance signal U _{1 of the} signal U ₂ . When the impeller rotates counterclockwise (FIG. 2), the stress plots correspond to those depicted in FIG. 4, where it can be seen that the signal U _{2 is} ahead of the signal U ₁ . In order to avoid malfunctions in the display, for example, the appearance of false signals when the impeller 3 is inhibited, one of the magnetic inserts 5 is fixed so that it creates a signal of reverse polarity, which can also serve as a reference for determining the speed of rotation of the impeller 3.

 The sensitivity of the impeller 3 makes it possible to note the turbulization of the measured flow. When there is turbulence in the flow, pressure asymmetry appears on the blades, which is noted by the uneven rotation of the impeller 3. The voltage plots taken from the sensors 7 and 8, in this case, have the form shown in Fig. 5. By the magnitude of the amplitude and frequency of oscillations, one can judge the magnitude of the turbulization of the measured flow. In most cases, such measurements are sufficient to gain an idea of the degree of turbulence.

 Thus, the catheter can improve the accuracy of determining the flow parameters and the reliability of the measurement results due to the passage of the stream through the end opening of the casing, which increases the sensitivity of the impeller, and the absence of deformation of the stream when it passes through the inner cavity of the casing.

 The location of one of the magnetic liners so that its polarity is opposite to the polarity of the others increases the reliability of determining the direction of rotation of the stream.

 The device does not need additional calibration and the use of an equivalent when changing the flow conditions around the converter and makes it possible to simplify the measurement procedure.

 The catheter can be used to measure blood flow parameters and its in vivo structure as a new tool for diagnosis and examination in the field of cardiopulmonary bypass and cardiovascular surgery.

Claims (2)

 1. A CATHETER FOR HYDRODYNAMIC MEASUREMENTS OF BLOOD FLOW IN A CARDIOVASCULAR SYSTEM, comprising a flexible tube with a transducer at the end, consisting of a cylindrical casing installed in it with the possibility of rotation of the impeller and two Hall sensors, characterized in that the impeller is made of non-magnetic material, on the edges of its blades have magnetic inserts with the radial orientation of the magnetic poles so that the end face of one blade has a polarity opposite to that of the other ends, and on the inside ozhuha mounted electromagnet and the Hall sensors.  2. The catheter according to claim 1, characterized in that the inner surface of the casing, the electromagnet and the Hall sensors are coated with a layer of a sealing substance.

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