gms | German Medical Science

Objective: Cerebral arteries of the rat can be visualized ultrasonographically through an extended craniectomy. Direct measurements of blood flow velocities and estimations of vessel diameter are obtained using triplex mode, combining B-mode, color-coding and Doppler examination. The present study was performed to examine the feasibility of the model for detection of changes in blood flow velocities.

Methods: In a first set of experiments, normal values for blood flow velocities were obtained by 395 measurements in 52 female Wistar rats and for vessel diameter by 298 measurements in 39 animals. Anesthesia was performed with intraperitoneal injection of a mixture of ketamine with xylazine, the basal cerebral arteries were examined following a standardized scheme. Measurements from one animal were averaged to obtain individual values and then all 52 individual values were averaged to determine normal values.

In a second set of experiments, the time course of heart rate during anesthesia was determined in 25 animals. Blood flow velocities of the anterior cerebral trunk, the left carotid artery and the basilar artery were obtained in one to two minute intervalls and correlated to the heart rate at the same time point. Blood flow velocities of the anterior trunk and of the basilar artery were plotted against the flow in the left carotid artery and the data was analyzed by linear regression curves.

Results: Normal values of median blood flow velocities and for vessel diameter were as follows: anterior cerebral trunk: 8.57 cm/s, 0.73 mm, left carotid artery: 9.03 cm/s, 0.82 mm, basilar artery: 5.9 cm/s, 0.58 mm.

Analysis of the regression curves revealed that the basilar blood flow velocity was not or inversely related to the carotid flow in more than 80% of animals, whereas the flow in the anterior trunk remained proportional to the carotid flow in over 75% of rats.

Conclusions: Blood flow velocity in the basilar artery shows less variation than flow velocities in the anterior parts of cerebral circulation and in most cases is independent of the carotid flow. Since blood flow velocity in the anterior trunk mostly correlates to changes in the carotid artery, we postulate an independent flow regulation in the posterior part of cerebral circulation. Thus, in addition to the evaluation of experimental models of stroke or cerebral vasospasm, the ultrasonographic model may offer new insights into cerebral autoregulation.