| Acute cerebral blood circulation disorders, such as acute cerebral hypoxia, ischemia and hemorrhage, is the third deadly disease after cancer and heart diseases in the world. It is the second most deadly disease following cancer in China, which cause more than 2 million cases of morbidity one year and the disability up to 75%. It is crucial for prognosis that acute cerebral blood circulation disorders can be discovered and diagnosed in time.Cerebral oxygen and nutrients are supplied by the blood. Cerebral tissue is very sensitive for cerebral acute hypoxic and ischemic, which will cause permanent neurons impairment in 10 minutes and only can be diagnosed after 6 hours later by CT. Intracerebral hemorrhage can be diagnosed by CT examination after hematoma formation, but it is unfavorable to prognosis because of the time differences. Therefore, it would be extremely beneficial to the patient's recovery that diagnosis and treatment can be acted immediately when acute cerebral blood circulation disorders occur.Many scholars pay attention to bioelectrical impedance measurement because of the advantage of function testing and non-invasion. It is important and promising to research the detection of cerebrovascular disease using bioelectrical impedance technique, which performed with fixed-frequency. The brain is composed by different organizations, which have different frequency characteristics of impedance, therefore, we monitor and analyse the impedance changes with the frequency of 100Hz-180kHz to study the impedance real part, imaginary part, modulus and its rate of change of frequency characteristics and to find the best range of frequency to monitor the acute cerebral blood circulation disorders. At the same time, after studying the frequency characteristics of impedance changes with cerebral hypoxia, ischemia and hemorrhage, we could discover the method to diagnose and discriminate cerebral hypoxia, ischemia and hemorrhage.Since it is difficult to conduct experiments of monitoring cerebral impedance for acute cerebral hypoxia, ischemia and hemorrhage in clinic practice, we established the rebbit model to monitor impedance changes of acute cerebral hypoxia,ischemia and hemorrhage.Before and after acute cerebral blood circulation disorder, the cerebral impedance will be measured by electrical impedance monitor with four-electrode mode, which was developed by Faculty of Medical Electronic Engineering, Department of Biomedical Engineering, Fourth Military Medical University. The driving current was set to 1000uA at the frequency of 100Hz, 200Hz, 400Hz, 600Hz, 800Hz, 1kHz, 2kHz, 4kHz, 6kHz, 8kHz, 10kHz, 20kHz, 40kHz, 60kHZ, 80kHz, 100kHz, 180kHz, respectively.1) Monitoring of cerebral hypoxiaAfter establishing the rabbit model of cerebral hypoxia with asphyxia in 15 rabbits, the monitoring results show that the absolute real and absolute imaginary parts of rabbit cerebral impedance distinctly rose during short-term hypoxia(150s) and recovered after oxygen supplied. At the frequency of 8kHz, the rate of change of impedance was most obvious(real part1.92%, modulus1.94%) and the two means are significantly different at the 0.001 level with paired t test.2) Monitoring of cerebral ischemia After establishing the rabbit model of cerebral ischemia with bilateral carotid artery occlusion in 9 rabbits,the monitoring results indicate that absolute real and absolute imaginary parts of impedance increased significantly and two means are significantly different at the 0.001 level with paired t test after cerebral ischemia. 150s after cerebral ischemia, the rate of change of impedance was most obvious at the frequency of 8kHz (where the maximum rate of impedance change, the real part of 1.36%, 1.38% modulus) and 900s after cerebral ischemia, the rate of change of impedance was most obvious at the frequency of 6kHz (where the maximum rate of impedance change, the real part of 15.5% , modulus 15.4%). The frequency where the rate of change of impedance was most obvious shifted from 8kHz to 6kHz over time.3) Monitoring of cerebral hemorrhageAfter establishing the rabbit model of cerebral hemorrhage with autologous blood injection in 7 rabbits, the monitoring results show that the real part of impedance decreased and the imaginary part did not change significantly at the initial time; two real means are significantly different at the 0.001 level with paired t test. The real and absolute imaginary part of impedance rose over time. The frequency of impedance is proportional to the rate of impedance change at the time of 150s. At the time of 900s, the rate of change of impedance was most obvious at the frequency of 20kHz (where the maximum rate of impedance change, modulus|-3.12 % |). The frequency where the rate of change of impedance was most obvious shifted to lower frequency over time.The results showed that the cerebral impedance changes of acute cerebral blood circulation disorders (hypoxia, ischemia, hemorrhage) could be monitored in rabbits. The correlation analysis of cerebral impedance real part, imaginary part and the modulus indicated that the cerebral impedance of hypoxia, ischemia, and hemorrhage had different expression in impedance trends, impedance change rate and the frequency where the rate of change of impedance was most obvious. The results of animal experiments indicated that electrical impedance technique can be used as a method of early diagnosis of cerebral blood circulation disorders (hypoxia, ischemia, hemorrhage). Acute cerebral blood circulation disorders (hypoxia, ischemia, hemorrhage) can be identified according to the trend, rate of cerebral impedance change and the frequency where the rate of change of impedance was most obvious, which will greatly improve the chances of the patient's rehabilitation.With acute cerebral hypoxia, ischemia and hemorrhage, the real part, imaginary part and modulus spectrum of impedance changes over time, which means it can't fully reflect the impedance changes of acute cerebral hypoxia, ischemia and hemorrhage with fixed-frequency, therefor, it should be performed to monitor and analyse frequency characteristics of the real part, imaginary part and modulus with frequency sweep and it should can be used as a method to identify the extent and stage ( acute, subacute, chronic phase) of acute cerebral hypoxia, ischemia and hemorrhage.
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