Chronic cerebral vasospasm: effect of volume and timing of hemorrhage in a canine model.

The effect of altering the volume and timing of hemorrhage on the severity of spasm was studied in a canine model. All animals received three cisterna magna injections of fresh unheparinized autologous arterial blood. Selective left vertebral arteriograms were obtained during the week before and exactly 7 days after the initial subarachnoid injection. Increasing volumes of hemorrhage (from 9 to 15 ml of blood) delivered over 24 hours produced increasingly more severe arterial spasm, with reductions in basilar artery diameter of 37% +/- 14 (SD) and 58% +/- 15, respectively. Delay of the final injection of blood to 96 hours in the 15-ml hemorrhage group resulted in even more intense spasm, with an average 71% +/- 12 reduction in basilar artery diameter. Serial angiographic evaluation demonstrated the resolution of spasm in this group over approximately 3 weeks. Finally, small, late rebleeding episodes resulted in the rapid onset of intense spasm. Our results support the clinical impression of previous studies that the severity of spasm is related to the volume of hemorrhage and, in addition, suggest that the time course of hemorrhage may play a significant role in determining the overall severity of chronic cerebral vasospasm.