Jakobsen et evaluated the effect of vasospasm secondary to subarachnoid hemorrhage on cerebral perfusion. They calculated a Spasm Index (SI) and correlated it with the change in the radius for the affected cerebral artery. The authors are from Odense University Hospital in Denmark.
Measurements:
(1) flow velocity by transcranial Doppler signals (normally 55 +/- 12 cm in the middle cerebral artery)
(2) cerebral blood flow by 133-Xe inhalation and the Initial Slope Index (ISI)
flow velocity =
= (cerebral blood flow) / (PI() * ((radius)^2))
spasm index =
= (flow velocity in cm/s) / (cerebral blood flow in mL/s)
The normal spasm index is in the range of 0.74 to 1.48. With vasospasm the spasm index increases as the radius of the affected artery decreases.
