Intracranial Hypertension and Ocular Circulation in the Dog

A New Method of Intracranial Pressure Measurement

Abstract

It has not been established yet how to estimate intracranial pressure (ICP) by a simple, practical and non-surgical method at the early stage of intracranial hypertension in case of head injury and cerebral vascular accident. The author payed attention to the ocular findings under the condition of intracranial hypertension, and designed an experimental study for understanding the correlation between the ocular circulation and intracranial pressure.
Intracranial hypertension was made by means of inflation of epidural balloon (0.05 ml/min)placed on the right frontal region. Epidural pressure was measured on the left frontal region and EEG was recorded on both frontal areas. Ocular circulation was recorded by fluorescein angiography on the left eye.0.15 ml of 0.05% fluorescein sodium was injected through the catheter canulated into the lingual artery under the condition of external carotid artery ligation. Vital signs were checked and fluorescein angiography was done at the following stages in each dog; Control: before inflation of the balloon, Stage A: no increase in ICP, (spacial compensation), Stage B: EEG change, Stage C: midriasis on the right eye, Stage D: Cushing phenomenon.
The experiment was carried out under two different conditions; Group 1: und er controlled respiration, Group 2: under spontaneous respiration. The results obtained are as follows:
A: Group 1
1) The order of the appearance of the retinal arteries is not affected by the increase in ICP.
2) Refilling phenomenon, that is, reincrease of fluorescence in the retinal arteries once after the decrease in its intensity, was observed in 10 dogs out of 14. This phenomenon bec a me remarkable as ICP increases up to Stage C. At Stage D, it became more prominent in 4dogs and obscure in 6 dogs.
3) Retinal circulation time was not prolonged at Stage A. Nine dogs at stage B and all dogs at Stage C showed prolonged circulation time which became prominent in proportion to the increase of ICP. At Stage D, circulation time was prolonged in.4 dogs and shortened in 8 dogs.
4) Retinal circulation time had relationship with cerebral perfusion pressure in linear fashion.
5) Washout curves of fluorescence in the eye ground and optic disc were comparatively resembling. At Stage A, no difference from the control was observed. At Stage B in som e dogs and at Stage C and D, fluorescence was observed till late in all dogs and two-peak pat t e rn and prolonged washout curve were observed in accordance with the degree of the r e filling phenomenon.
6) Neither hemorrhage nor leakage of fluorescence was found in any dogs.
B: Group 2
No critical difference from the results of Group 1 was obtained in the retinal circulation time and appearance curve of fluorescence, respectively. Hemorrhage and leakage of fluorescence were not remarked at all.