Abstract
Since the investigations by Brawley and coworkers it has been known that cerebral vasospasm is a biphasic phenomenon: the acute phase occurs within minutes after the subarachnoid hemorrhage and lasts less than one hour. The chronic phase occurs 3 to 24 hours after the hemorrhage. Numerous workers so far have carried out studies on the vasospasm based on the assumption that the vasospasm is due to functional constriction of the smooth muscles of the cerebral arterial wall. However, it has not been demonstrated whether the vasospasm, not only in the acute phase but also in the chronic phase, is actually a functional spasm of the arterial smooth muscles or not. To investigate such basic problems related to the cerebral vasospasm, we attempted to record and evaluate the electrical activity from the smooth muscles of the arterial wall in vivo which underwent experimentally induced vasospasm. The results thus obtained were as follows.
1. No spontaneous electrical activity was recorded from the intact basilar arteries of normal dogs. From the basilar arteries of the denervated dogs, however, electrical activities, spikes with 100 to 200 msec. duration and less than 1 mV amplitude, were induced by intravenous injection of epinephrine.
2. Similar electrical activities were reocrded during the entire course of the acute phase of vasospasm. The onset of the electrical activity coincided with the onset of vasospasm and they lasted less than 120 minutes.
3. In the chronic phase of vasospasm no electrical activity was recorded from the arteries which definitely showed the phenomenon of so-called vasospasm. Even when epinephrine was administrated to the denervated dogs with the chronic phase of vasospasm, no electrical activity of the arterial wall could be induced.
From these experimental results, we concluded that the acute phase of vasospasm is due to functional constriction of the arterial smooth muscles, and that it is not due to functional constriction in the chronic phase but is due to some organic changes of the arterial wall.
