Normal basilar artery structure and biaxial mechanical behaviour

Much is known about cerebral vasospasm, a devastating sequela to ruptured intracranial aneurysms, yet underlying mechanisms remain unclear and clinical treatments have proven unsatisfactory. We have hypothesised that biochemical stimuli associated with the formation of extravascular blood clots dominate early maladaptive responses, leading to marked structural and functional changes in affected cerebral arteries. Before a precise picture of vasospasm can be obtained, however, we must understand better the structure and mechanical behaviour of normal cerebral arteries. Basilar arteries from rabbits were tested mechanically under biaxial loading conditions with and without active tone, segments were imaged using intravital nonlinear optical microscopy to quantify transmural orientations of fibrillar collagen, and passive mechanical data were fit with a four-fiber family stress–stretch relation. This constitutive model predicted well the overall mechanical behaviour and mean collagen fiber distributions, and thereby has promise to contribute to analyses of the biochemomechanics of cerebral vasospasm and similar cerebral pathologies. It is now time, therefore, to focus on mechanisms of vasospasm via mathematical models that incorporate growth and remodelling in terms of changes in the cross-linking and distributions of adventitial and medial collagen, primary contributors to the structural integrity of the arterial wall.