RU210873U1 - DEVICE FOR HIGH-ACCURACY MEASUREMENT OF INTRACRANIAL PRESSURE - Google Patents

Abstract

The utility model relates to experimental medicine and medical technology, namely to devices for measuring the intracranial pressure of laboratory animals by an invasive method. The technical problem is the creation of a device for measuring the physiologically normal intracranial pressure of laboratory animals (rats, mice) for a long time. The technical result of the utility model is to increase the duration of measurements without carrying out preventive maintenance by eliminating the overgrowth of the hole for connecting the sensor to the subarachnoid space while maintaining measurement accuracy. The technical result is achieved by the fact that in the device for measuring the intracranial pressure of a laboratory animal, containing a platform intended for installation on the animal's skull, with a removable measuring pressure sensor located on it, provided with an output for connecting to a data processing unit, the platform has an opening for connecting the sensor to the subarochnoid space, according to the solution, the platform is equipped with a branch pipe located in its lower part coaxially with the hole, the measuring sensor is installed on the platform with the possibility of multiple hermetic connection. 1 w.p. f-ly, 5 ill.

Description

The utility model relates to experimental medicine and medical technology, namely to devices for measuring the intracranial pressure of laboratory animals by an invasive method.

A device for invasive measurement of intracranial pressure (ICP) is known (see US patent 4846191, IPC A61B 5/00; A61B 5/02), containing a catheter that includes a hollow flexible tube filled with a low viscosity liquid and having a plug of gel-like material at the distal end that transmits the pressure signal to a solid state transducer, which is typically connected to amplifying electronics and an implantable radio transmitter capable of transmitting pressure information from within the body to a radio receiver located outside the body. The principle of operation of the device is based on the transfer of the measured pressure of the cerebrospinal fluid to the pressure sensor using a flexible catheter filled with an incompressible liquid with low viscosity. To prevent mixing of fluid inside the catheter and cerebrospinal fluid, the distal end of the catheter is sealed with a biocompatible gel.

The disadvantage of the device is the limited sensitivity and significant errors associated with the deformation of the catheter and the change in the position contained in the liquid column when moving the animal under study. In addition, with long-term measurements, a significant decrease in accuracy as a result of the reaction of the surrounding tissues to the inserted catheter and, in particular, in the change in the properties of the gel sealing the catheter.

A system for transcutaneous monitoring of intracranial pressure is known (see US patent 10045697, IPC A61B 5/00; A61B 5/03), which includes a sensor module implanted in the patient and an external processing module optically connected to the sensor module through an external connection module. A sensor in the sensor module converts the measured pressure, and a near-infrared emitter transmits telemetry when requested by an external communication module. The computer in the processing module calculates the physiological parameter from the telemetry signal and presents this data in numerical, graphical or analog format.

The disadvantage of the system is the significant volume of the implantable sensor module, which makes it impossible to implant it under the scalp of a laboratory animal. Implantation of the sensor module eliminates the possibility of revision of the catheter, since this requires its removal from the brain. Measuring intracranial pressure inside the ventricle is much more traumatic for the animal's brain than accessing the subarachnoid space through the dura mater.

A device for measuring intracranial pressure in mice is known (Nusbaum, Derek M., Samuel M. Wu, and Benjamin J. Frankfort. "Elevated intracranial pressure causes optic nerve and retinal ganglion cell degeneration in mice". Experimental eye research 136 (2015): 38-44), containing a module for placing a pressure sensor in the form of a radio wave probe. The module is a cannula in the form of a nylon screw with a hole in the center to accommodate the sensor. The cannula is screwed in and fixed with dental cement to the skull bone. The cannula is intended for introduction into the subarachnoid space of the animal's brain. The radio wave probe is connected to the receiver. The tip of the pressure control probe is inserted through the hole in the center of the cannula. The device is based on shallow insertion of a pressure sensor catheter into the subarachnoid space of the animal's brain.

The disadvantage of the device is the inability to accurately measure the physiologically normal ICP of the animal. The system provides reproducible measurements only in the case of a significant (up to 30 mm Hg) increase in intracranial pressure, since the systematic measurement error is about 3 mm Hg, while the physiologically normal ICP of the animal is 6-7 mm Hg. Art.

The closest solution is a device for measuring the intracranial pressure of a laboratory animal, containing a platform designed for installation on the animal's skull, with a removable measuring pressure sensor located on it, provided with an output for connecting to a data processing unit, the platform has an opening for connecting the sensor with the subarachnoid space (see Mamedova A.T., Blokhina I.A., Ageev V.B. "Perspective technology for studying the drainage function of the brain" // Collection of materials of the All-Russian scientific and practical conference of students, undergraduates, graduate students "Modern achievements of young scientists in biology and medicine ". - Astrakhan University: Astrakhan, June 15-16, 2021, pp. 56-58).

The disadvantage is the need for frequent preventive maintenance to eliminate the consequences of overgrowth of the hole for connecting the sensor with the subarachnoid space.

The technical problem is the creation of a device for measuring the physiologically normal intracranial pressure of laboratory animals (rats, mice) for a long time.

The technical result of the utility model is to increase the duration of measurements without carrying out preventive maintenance by eliminating the overgrowth of the hole for connecting the sensor to the subarachnoid space while maintaining measurement accuracy.

The technical result is achieved by the fact that in the device for measuring the intracranial pressure of a laboratory animal, containing a platform designed to be installed on the animal's skull, with a removable measuring pressure sensor located on it, provided with an output for connecting to a data processing unit, the platform has an opening for connecting the sensor to the subarochnoid space, according to the solution, the platform is equipped with a branch pipe located in its lower part coaxially with the hole, the measuring sensor is installed on the platform with the possibility of multiple hermetic connection.

An integral digital pressure sensor was chosen as a measuring sensor.

The device contains a tap for connecting a catheter.

The utility model is illustrated by drawings, where figure 1 shows a General view of the proposed device; figure 2 - device in transverse and longitudinal sections; figure 3 - the location of the sensor on the head of an awake rat; figure 4 is a graph of measured ICP versus time (a) and an enlarged fragment of the graph (b); figure 5 is a graph of the average ICP value from time to time.

Positions in the drawings indicate:

1. Platform;

2. Measuring pressure sensor;

3. Screw;

4. Hole in the platform;

5. Branch pipe;

6. Conductors for power supply and signal transmission of the pressure sensor;

7. PCB;

8. Gasket;

9. Skull bone;

10. Dura mater;

11. Subarachnoid space;

12. Brain;

13. Tap for placement of the catheter.

The device contains a platform 1 for placement on the surface of the animal's skull. Platform 1 is attached to the surface of the skull with an adhesive such as dental acrylic. A removable pressure sensor 2 is installed on platform 1. Integrated digital pressure sensors are used to measure pressure.

The pressure sensor is fixed on the platform with a screw 3. The pressure sensor is hydraulically connected to the subarachnoid space of the animal's brain through hole 4 and a short pipe 5 built into platform 1 coaxially with hole 4.

The conductors 6, through which the sensor is powered and the pressure measurement results are transmitted, are connected to the printed circuit board 7, fixed by means of screws 3 on the platform 1. The pressure sensor 2 is pressed against the platform 1 through the gasket 8. The overall dimensions of the platform 1 in the plan do not exceed 4 × 10 mm, which allows you to fix it on the head of a laboratory animal.

To measure intracranial pressure, a surgical intervention is performed on an anesthetized animal, which consists in making a hole in the skull bone 9 and dura mater 10 in the scalped area. subarachnoid space 11 of the brain 12. The procedure is controlled by the appearance of cerebrospinal fluid in the canal of the branch pipe 5. With the help of the compound, the tightness of the connection between the platform and the skull bone is achieved. After the polymerization of the compound, the board with sensor 2 is fixed to the body with screws 3. The wire lines of the sensor are connected to an external data acquisition device that provides chronic measurements of the animal's intracranial pressure. The animal is placed in the arena. Figure 2 shows an awake animal with an installed intracranial pressure sensor. The device is equipped with a tap 13 for connecting the catheter to the canal of the nozzle 5, through which the animal's intracranial pressure can be modulated. The catheter is filled with liquid (isotonic solution) and communicates with the container, the level of the free surface of the liquid is at a given height. The change in intracranial pressure in this case is determined by the difference in the height of the free surface of the liquid in the external vessel and the height of the installation of pressure sensor 2 on platform 1. Modulation of intracranial pressure in the described way allows you to check the state of the hole and test the pressure sensor without disconnecting it from the platform. In addition, the catheter can be used to treat the burr hole with antiseptic agents when performing long-term measurements, as well as to carry out physiological experiments associated with an artificial increase in intracranial pressure.

The data collection device contains a microcontroller that controls pressure sensors, collects and transmits measurement results in real time to a personal computer via USB. A reference pressure sensor is placed in the data collection device, similar to the measuring sensor installed on the animal's head. The reference sensor communicates with the atmosphere and serves to measure the atmospheric pressure in the room where the animal is kept.

The collapsible sensor mount allows revision of the tube channel and its periodic cleaning during chronic ICP measurements for extended periods of time. The mounting scheme of the pressure sensor ensures minimal intervention in the brain tissue.

Before taking measurements, the sensors are calibrated to ensure that the excess pressure in the subarachnoid space is measured with the required accuracy. When performing measurements and calibration, the sensors are installed in the same position (inlet down). Intracranial pressure is defined as the difference between the readings of two sensors.

The use of two pressure sensors will compensate for the effect of changes in atmospheric pressure in the room on the measurement result. When performing high-precision measurements of ICP, it should be taken into account that the change in atmospheric pressure associated with atmospheric processes can reach several mmHg. at one o'clock. In addition, the results are affected by changes in atmospheric pressure in the room, due to the mode of operation of ventilation, drafts, opening and closing doors, wind, etc. The use of the second sensor makes it possible to completely exclude the influence of these factors on the measurement results.

The software installed in a personal computer provides calibration and zeroing of pressure sensors, as well as calculation of the difference in sensor readings corresponding to the excess of intracranial pressure over atmospheric pressure. The measurement results are displayed in real time in the form of a graph and are recorded on the computer's hard disk.

Measurements of intracranial pressure were made four times per second. The measurement results are shown in Fig.3. Figure 3(a) shows a pressure measurement record for 3.5 hours after installation. Figure 3(b) shows an enlarged fragment of the recording with a duration of 30 seconds, starting from the 20th minute of the recording. Figure 3(b) distinguishable fluctuations in intracranial pressure associated with the breathing of the animal (44 breaths per minute). The amplitude of these fluctuations is less than 1 mm Hg, however, they are reliably recorded and the resolution of the proposed method is not worse than 0.1 mm Hg. The device provides high accuracy of measurement of intracranial pressure of a laboratory animal in comparison with known analogues.

Figure 4 shows the change in the average intracranial pressure of the animal over time. The moving average was calculated from 80 readings recorded over 20 s. Pressure registration began before the moment the sensor was attached to the head. Both sensors communicate with the atmosphere, the pressure difference between them is set to 0 mmHg. A pressure jump of up to 5 minutes corresponds to fixing the board 2 with the pressure sensor on the case 4 and tightening the fixing screws.

When the rat was turned over on its back at 11 minutes, the pressure rose to 9 mm Hg. There was also a good increase in pressure when lifting the back of the body and a decrease in lifting the head (jump up and down immediately after the surge at the 11th minute). At rest, the pressure was restored. Sensor sensitivity 0.05 mmHg

Under anesthesia, ICP was about 3.5 mm Hg. (sensor on top of the skull) and remained unchanged for about an hour. At the 75th minute there was a sharp jump - the animal was picked up and placed in an EEG arena.

Before awakening, from 140 to 160 minutes, pressure surges were recorded in a resting animal, and the pressure rose to 6 mm Hg. The rat was placed in a transparent EEG arena. The interval from 160 to 190 minutes corresponds to the active movements of the awake animal. At 190 minutes, the rat lay motionless with its eyes open. The pressure dropped to 4 mm Hg. and remained constant for 4 minutes. Then, from 195 to 200 minutes, the animal raised its head three times. The mechanical impact on the wire and the body does not lead to noticeable changes in the sensor readings, the recorded bursts are associated precisely with the change in ICP, and not with the vibrations of the wires and the sensor.

At 212 minutes the rat was taken out of the arena. She immediately came to her senses and began to actively move around the table (this moment is shown in figure 2). At 216 minutes, the rat was picked up to remove the sensor. In the process of removing the sensor, bursts began, associated with pressure fluctuations when the screws were unscrewed. After removing the sensors, the recording was stopped.

Claims (2)

1. A device for measuring intracranial pressure of a laboratory animal, containing a platform designed to be installed on the skull of an animal, with a removable measuring pressure sensor located on it, provided with an output for connecting to a data processing unit, the platform has an opening for connecting the sensor to the subarachnoid space, characterized in that that the platform is provided with a branch pipe placed in its lower part coaxially with the hole, the measuring sensor is fixed on the platform by means of a screw with the possibility of multiple tight connection with the subarachnoid space by connecting the platform to the skull bone using a compound, and the device is equipped with a tap for connecting a catheter. 2. The device according to claim 1, characterized in that an integrated digital pressure sensor is selected as a measuring sensor.

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