Effect of intracranial hypertension on cerebral hemorrhage induced autonomic nerve imbalance

BACKGROUND： Cerebral hemorrhage can cause the imbalance of nerve function, whereas its mechanism and main impact factors are still not quite clear. OBJECTIVE： To explore the rules about the changes of intracranial pressure in brainstem hemorrhage and internal capsule hemorrhage, and analyze the role of intracranial hypertension in the changes of nerve function caused by cerebral hemorrhage. DESIGN： A self-controlled trial. SETTING： Department of Physiology, Tianjin Medical University. MATERIALS： Sixty-five healthy male Japanese white rabbits with long ears （1.5-1.8 kg） were supplied and fed by the Department of Animal Experiment of Tianjin Medical University. The RM6240B biological signal collecting and processing system was used. METHODS： The experiments were conducted in the Department of Physiology, Tianjin Medical University from August 2001 to May 2006. ① The rabbits were anesthetized, then fixed onto the brain stereotaxic apparatus, and afterwards fenestration on skull and intubation to lateral ventricle were performed.The dynamic changes of intracranial pressure were monitored continuously. Rabbits were infused with autologous arterial blood （0.3 mL） into midbrain corpora quadrigemina inferior colliculus to induce model of acute brainstem hemorrhage; models of internal capsule hemorrhage were established by infusing autologous arterial blood into internal capsule. ② The dynamic intracranial pressures under the above conditions were recorded continuously with the RM6240B biological signal collecting and processing system. ③ An animal model of persistent intracranial hypertension was established by infusion of physiologic saline into lateral ventricle. ④ The changes of the intensity of autonomic nerve discharge were analyzed, using the biological signal collecting and processing system before and after hemorrhage and under persistent intracranial hypertension.⑤ Ten animal models of internal capsule hemorrhage and 10 of bminstem hemorrhage were selected respectively, then gross pathological samples were cut open, and the accuracy of hemorrhage models was affirmed. Histological sections in hemorrhage point and around this point were prepared for with hernatoxylin and eosin staining, and the pathological changes were observed under light microscope. MAIN OUTCOME MEASURES： ① Changes of intracranial pressures before and after internal capsule hemorrhage and brainstem hemorrhage; ②Changes of the discharge intensity of cervical vagus nerve trunk in animal models of internal capsule hemorrhage, brainstem hemorrhage and persistent intracranial hypertension without hemorrhage; ③ Accuracy of location of internal capsule hemorrhage and brainstem hemorrhage confirmed by gross pathological samples and sections. RESULTS： Totally 65 rabbits were involved in the analysis of results. ① Dynamic state of intracranial pressure： Intracranial pressure increased obviously at 45 minutes after internal capsule hemorrhage and brainstem hemorrhage, the intracranial pressures were （1.31 ±0.30）, （1.82±0.45） kPa, which were obviously higher than those before hemorrhage [（1,04±0.18）, （1.05±0.19） kPa, P 〈 0.01]. ② Discharge of vagus nerve： Under intracranial hypertension, the discharge of cervical vagus nerve trunk was enhanced, and the discharge intensity of vagus nerve trunk was significantly different before and after persistent intracranial hypertension [（364.28±78.55）, （1252.19±151.75）μ V·s, P 〈 0.01]. The discharges of cervical vagus nerve trunk were significantly enhanced after internal capsule hemorrhage and brainstem hemorrhage （P 〈 0.01）. ③ Validation of hemorrhage sites： The hemorrhage sites were internal capsule and brainstem on histopathological sections. CONCLUSION： Intracranial pressure may play an important role in the pathophysiological process of vagus nerve imbalance caused by cerebral hemorrhage.