动物实验,出血性中风,缺血性中风 z-bo 2020-09-09 425

　　Background: Stroke can be divided into hemorrhagic stroke and ischemic stroke. With the aging of the global population and increasing social pressure, the incidence of this disease is increasing. Early thrombolytic therapy for ischemic stroke is an established procedure today, but it can be catastrophic when thrombolytic therapy is given to patients with hemorrhagic stroke. Currently, computed tomography (CT) and magnetic resonance imaging (MRI) are used to distinguish hemorrhagic stroke from ischemic stroke. Thrombolytic therapy immediately after the onset of ischemic symptoms can produce satisfactory results. However, it is not recommended to use this treatment 4.5 hours after the onset of symptoms, because its potential benefits do not exceed the risk of bleeding complications, which increase with time. Most of the time after the onset of ischemic symptoms is wasted on commuting diagnostic equipment and imaging examinations. Therefore, only 1-8% of the entire stroke population receive this treatment. This clinical challenge has prompted the development of new and simple prehospital methods that can distinguish between ischemic and hemorrhagic strokes. Over the years, several techniques have been developed to distinguish between ischemic and hemorrhagic strokes. Doppler ultrasound can accurately identify the state of cerebral arteries (for example, stenosis, obstruction, convulsions, or ischemia), but it cannot rule out the ischemic area from the hemorrhagic transition. Electrical impedance tomography (EIT) has been proposed as a possible technique for detecting cerebral hemorrhage (ICH) in animal models, and impedance spectroscopy is suggested as a method for detecting stroke-related brain asymmetry in men. However, EIT needs to inject current through the electrode-cranial contact, which may reduce the detection accuracy. In addition, it is difficult for current to pass through the skull with ultra-high resistivity, which may severely degrade image quality. Near-infrared spectroscopy (NIRS) detects hemorrhagic strokes because hemoglobin absorbs more near-infrared light than other tissues. However, this method can only detect hematomas with a volume less than 2.5 cm below the scalp and greater than 3.5 ml. The same type of instrument identified 28 cases of childhood bleeding with a sensitivity of 100% and a specificity of 80%, but it failed to detect deep or early bleeding. Microwave technology relies on a significant dielectric contrast between blood and other tissues. The microwave method can distinguish hemorrhage and ischemic stroke, as well as hemorrhage and health status. However, this technique is very sensitive to the displacement between the antenna and the bleeding site. In addition, the attenuation of microwaves in the brain is much greater than that of magnetic fields. Therefore, microwaves are not sensitive to deep bleeding. MIPS technology is based on the principle of electromagnetic induction, which measures the phase perturbation of the induced magnetic field (IMF) to the excitation magnetic field (EMF). The phase disturbance is proportional to the conductivity of the measurement object. The change in conductivity can be detected by MIPS technology. Both hemorrhage and ischemia are accompanied by changes in intracranial tissue volume and composition. Considering that these changes will subsequently cause changes in the electrical conductivity of the entire brain, MIPS technology can identify pathological conditions in the brain. Bleeding and ischemia are opposite pathological states. Bleeding is caused by the rupture of parenchymal blood vessels. In the early stages, bleeding reduces cerebrospinal fluid (CSF). When the cerebrospinal fluid compensation mechanism ends, the increased amount of bleeding will significantly increase intracranial pressure (ICP). Cerebral ischemia refers to diseases such as hypoxia and ischemia in a certain area. ? Ischemic stroke can be a thrombotic type, in which the diseased or damaged cerebral artery is blocked or embolized, and the thrombus (embolism) is formed outside the brain itself. Ischemia causes a large number of neuron necrosis, leading to infarction. After prolonged ischemia, the necrotic tissue cannot be recovered. Conductivity varies with the type of brain tissue, from cerebrospinal fluid and blood to gray matter and white matter. In addition, when the cells are in different pathological states, such as necrosis and edema, the conductivity will change. In this case, MIPS technology can reflect the status of the organization. Foreign research on MIPS encephalopathy detection methods is still at the level of physical models and simulation experiments. Our group has been engaged in MIPS detection research for cerebral hemorrhage, cerebral ischemia, and cerebral edema for a long time, and has carried out a large number of animal experiments. Experimental results show that as the amount of bleeding increases, MIPS gradually decreases. In this experiment, a new type of coil structure was designed and used to measure the changes of MIPS after hemorrhage or ischemia in rabbits. In MIPS technology, the object to be measured is always placed between the transmitting coil and the receiving coil, and the current flow in the transmitting coil will cause the primary magnetic field. This primary magnetic field then causes eddy currents in the object, thereby creating a secondary magnetic field. Both the primary field and the secondary field are detected by the receiving coil.

　　Detection coil: Two square coils of the same size (a transmitting coil and a receiving coil) were used in the experiment. Both coils are made of 25 turns of copper wire, rolled on a square plastic with side length r=100mm. The coil diameter d=180mm. The transmitting coil generates EMF (solid line) passing through the test object (red ball), which in turn generates IMF (dashed line). The receiving coil receives part of EMF and IMF. The distance between the receiving coils is large, and only a small part of electromagnetic waves can be received. The square coil can produce a uniform sensitivity area between the two coils. The experiment confirmed that the resonant frequency of the coil group under no-load conditions is 14.8MHz. When the rabbit head is placed in the coil structure, the resonance frequency shifts to 16.4MHz. When working at this frequency, both the magnetic field strength and MIPS sensitivity reach the maximum. Therefore, a frequency of 16.4MHz was chosen for all experiments.

　　Experimental device: use AFG3252 arbitrary waveform generator as the signal source. The generator outputs two signal channels with the same frequency and phase. A signal with an amplitude of 200mVPP is input to the RF instrument power amplifier. The bandwidth of this amplifier ranges from 0.5MHz to 1000MHz, the output power is +35dBm, and the typical high gain is 38dB. The output signal from the receiving coil is connected to the other input port of PCI5124. The rabbit is placed on a polyvinyl chloride flat platform that can go up and down, left and right, and back. Before measurement, readjust the height and horizontal position of the platform, and place the rabbit brain precisely between the two coils. Using LabVIEW software, a phase difference measurement program based on FFT algorithm is compiled. This program is used to measure the phase difference between the two input signals of the PCI5124 acquisition card. The sampling rate is set at 100M/S, and the number of sampling points is 1 million. According to ischemia time or injection volume, the changes in this stage were recorded.

　　Experimental animals: 20 New Zealand rabbits (weight 2.0～2.5kg) were randomly selected and divided into two groups, bleeding and ischemia groups (n=10 in each group). To reduce killing and maintain consistency, the two groups measured 4 animals 2 hours before blood transfusion or ligation. Data before blood transfusion or ligation served as a control group.

　　Hemorrhage surgery: Considering that intracranial hemorrhage mainly occurs in the internal capsule, we used autologous blood to be injected into the hind limb of the right capsule to establish an internal capsule hemorrhage model. The operating procedures of this study are similar to previous studies. Rabbit ears were anesthetized by intravenous injection of carbamate (25%, 5ml/kg). The experimental group did not add anesthetics after the first anesthesia, because the measurement time did not exceed 2h. In the control group, 3ml carbamate (25%) was added 2h after surgery. As a result, a longitudinal incision was made in the middle of the rabbit's head, exposing the bregma and coronal suture. . Drill a hole 1mm in front of the coronal suture and 6mm from the midline (d=1mm). A total of 2 ml of fresh autologous blood was extracted from the subcutaneous vein of the hind limb using a heparinized syringe. Introduce the plastic tube (d=0.7mm) into the appropriate depth (H=13mm). After the operation, the rabbit was fixed on the platform. The position of the rabbit is adjusted so that its brain is accurately located between the two coils. Then connect the measurement system. Using a syringe pump, 1ml of autologous blood was injected into the inner capsule at a constant speed (1ml/h). The experimental device also measured MIPS. The data before blood transfusion was used as the baseline data. After the determination, 1.5 mol/l KCL solution was injected into the ear vein of the rabbit to kill the rabbit.

　　Ischemia surgery: permanent ligation of bilateral carotid arteries is used to establish an ischemic model. Rabbit ears were anesthetized by intravenous injection of carbamate (25%, 5ml/kg). Under anesthesia, the rabbit’s neck was depilated and disinfected. Subsequently, the middle neck skin was incised and bluntly dissected to expose and separate the bilateral common carotid arteries, which were knotted with two 1mm thick nylon sutures, but not ligated. After the operation, the rabbit head is fixed on the platform and placed between the two coils. Once the system is stable, the bilateral carotid arteries are tightly ligated, and then MIPS is measured simultaneously for 2 hours. 1ml of 1.5mol/l KCL solution was injected into the ear vein of the rabbits to be killed.

　　Result: Use wavelet decomposition to filter the breathing and heartbeat signals in each group of animal data. For the results of each animal in the ischemia group and the control group, the MIPS data of ischemia 2-h was divided into 42 consecutive parts. Then determine the average value of each part. This processing method is essentially equivalent to obtaining one MIPS data every 2.85 minutes. Then the animal data of all groups were averaged and the standard deviation (SD) was determined. For the results of each animal in the hemorrhage group, the MIPS data of 1 hour of injection was divided into 21 consecutive parts. Then determine the average value of each part. This treatment is basically equivalent to obtaining MIPS data every 2.85 minutes or every 0.047 ml injection. Then the animal data of all groups are averaged. Figure 5 shows that the X-axis represents the results of the measurement time, and the Y-axis represents the MIPS data. Each group of data is the average of all related groups of animals. Each animal data from the bleeding group is not injected relative to the baseline data. The data of the ischemic group were baseline data before ligation. The data of the control group were also normalized relative to the initial data. After statistical processing, there are significant differences between the two groups.

　　Conclusion: Cerebral ischemia is an important clinical problem. When used as a treatment for bleeding, it can cause serious consequences. This study uses a new coil structure based on MIPS technology to distinguish ischemic stroke from hemorrhagic stroke. Using two animal models of stroke, the measurement showed that MIPS gradually decreased with the increase of bleeding, but increased with the extension of ischemic time. The change trends of MIPS caused by the two types of strokes were completely opposite. The absolute value of MIPS changes in the hemorrhage group and the ischemic group was significantly greater than that of the normal control group. The mechanisms of these two types of strokes causing MIPS changes are different. The analysis in the previous chapters shows that the decrease of MIPS during early bleeding is caused by the regulation of cerebrospinal fluid, while the change of MIPS is mainly caused by the change of tissue volume during early bleeding. The increase in MIPS caused by ischemia is the result of changes in tissue composition. At high frequencies, the increase in MIPS is mainly caused by changes in the total ion content in the tissue. With the prolongation of ischemia time, the accumulation of metabolites in the tissue increases, resulting in a decrease in impedance and an increase in MIPS. The consistency of the results of each group of animals is low, mainly because it cannot guarantee that the placement of the rabbit head between the two coils is completely consistent. Individual differences (e.g., weight) between the samples used may be another reason for the low consistency. Generally speaking, this is just a preliminary study to verify the feasibility of this method to distinguish between the two types of stroke. According to the experimental results, the measurement sensitivity of the two strokes is low, and the coil system needs to be improved. Second, the experimental device needs to be improved to improve accuracy. An animal positioning device should be made to maintain the consistency of all animals in the experiment. In addition, efforts should be made to establish models of cerebral hemorrhage and ischemia that are more clinically consistent.