Capillary flow disturbances after experimental subarachnoid hemorrhage: A contributor to delayed cerebral ischemia?

BACKGROUND: The high mortality and morbidity after subarachnoid hemorrhage (SAH) is partly due to delayed cerebral ischemia, which is traditionally ascribed to development of angiographic vasospasms. This relation has been challenged, and capillary flow disturbances are proposed as another mechanism contributing to brain damage after SAH.OBJECTIVE: To investigate capillary flow changes four days following experimental SAH.METHODS: SAH was induced by endovascular perforation of circle of Willis. We used two-photon microscopy (TPM) to evaluate blood flow characteristics. Cortical capillary diameters were investigated by both TPM and histology.RESULTS: We found elevated capillary transit-time heterogeneity and mean transit time of blood in SAH mice compared to sham animals. We observed capillaries with stagnant red blood cells, and capillaries with increased red blood cell linear density in the SAH group, suggesting severe blood maldistribution among cortical capillaries. Favoring that these capillary flow changes were primary to upstream vasoconstrictions, TPM showed no significant differences in arteriolar diameter between groups, while histological examination showed reduced capillary diameter in SAH group.CONCLUSION: Our study shows profound subacute hypoperfusion and capillary flow disturbances in a mouse SAH model and suggests that these changes are the result of changes in capillary function, rather than upstream vasospasm. This article is protected by copyright. All rights reserved.