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Static pressure–volume curves were done on seven intracranial saccular aneurysms and 16 major cerebral arteries from human autopsies. The aneurysms were much less distensible than the arteries. The major change was in the initial or elastin part of the curve (elastance of 6 ± 5 S.D. × 10 5 dynes/cm per 100% elongation in the artery compared to 13.5 ± 5 × 10 5 dynes/cm per 100% elongation for the aneurysm; p < 0.005). This agrees well with histological studies which show that elastin is decreased and fragmented in aneurysms.As the aneurysm enlarges, its wall must become thinner. This change, coupled with the loss of distensibility, makes it more prone to rupture. Obviously the larger the aneurysm, the thinner the wall (if the volume of tissue remains constant), and the greater the risk of rupture.The distensibility of major cerebral arteries could be dramatically decreased by two or three runs to pressures of 200 mm Hg. The elastance of the initial part of the curve changed from 2 ± 1 × 10 5 dynes/cm per 100%; elongation to 8 ± 1 × 10 5 dynes/cm per 100% elongation (different at p < 0.001). The final elastance was altered less significantly (42 ± 6 × 10 5 dynes/cm per 100% elongation to 82 ± 28 × 10 5 dynes/cm per 100% elongation; p < 0.01). This shift in distensibility was accompanied by a significant increase in diameter of the artery. High pressures appear able to break the single elastin layer of cerebral arteries.
Scott et al. (Sat,) studied this question.