Cerebral blood flow and evoked potentials during Cushing response in sheep

Embolic occlusion of internal carotid artery in conscious rats: Immediate effects of cerebral ischemia

In most preclinical models of focal ischemic stroke, vascular occlusion is performed under general anesthesia. However, anesthetic agents exert confounding effects on mean arterial blood pressure (MABP), cerebrovascular tone, oxygen demand, and neurotransmitter receptor transduction. Moreover, the majority of studies do not use a blood clot, which more fully models embolic stroke. Here, we developed a blood clot injection model to produce large cerebral artery ischemia in unanesthetized rats. Under isoflurane anesthesia, an indwelling catheter was implanted in the internal carotid artery via a common carotid arteriotomy and preloaded with a 0.38-mm-diameter clot of 1.5, 3, or 6 cm length. After discontinuing anesthesia, the rat was returned to a home cage where it regained normal mobility, grooming, eating activity, and a stable recovery of MABP. One hour later, the clot was injected over a 10-s period and the rats were observed for 24 h. Clot injection produced a brief period of irritability, then 15-20 min of complete inactivity, followed by lethargic activity at 20-40 min, ipsilateral deviation of the head and neck at 1-2 h, and limb weakness and circling at 2-4 h. Neurologic deficits, elevated MABP, infarct volume, and increased hemisphere water content varied directly with clot size. Mortality after 6-cm clot injection (53%) was greater than that after 1.5-cm (10%) or 3-cm (20%) injection. Combined non-survivor groups had the greatest MABP, infarct volume, and water content. Among all groups, the pressor response correlated with infarct volume. The coefficient of variation of infarct volume with the 3-cm clot was less than that in published studies with the filament or standard clot models, and therefore may provide stronger statistical power for stroke translational studies. The more severe outcomes from the 6-cm clot model may be useful for the study of malignant stroke.

Transcranial Doppler sonography in experimental Cushing response

Searching for the early warning symptoms of brain ischaemia, transcranial Doppler sonography (TCD) was used in cats during the Cushing response. The study was performed on seven cats. The intracranial pressure was increased by means of different rate lumbar infusions. The TCD changes of middle cerebral artery (MCA) and basilar artery (BA) flows were analyzed at the stage of the slightest but significant systemic blood pressure increase. The first symptoms of Cushing phenomenon were accompanied by BA flow pattern alternations while the MCA flow remained unchanged. The study suggests the necessity of BA TCD monitoring in cases at risk from brain stem ischaemia. It was shown also that in such cases the MCA TCD study can be misleading.