Measurement of the hemodynamic reserve in emission computed tomography. Applications to the cerebral vascular pathology

The concept of haemodynamic reserve (H.R.) understands two steps: the increase of the cerebral blood volume (C.B.V.) in compensation to the decrease of the brain central blood pressure, and then after, the increase of the oxygen extraction rate (OER), that insures the steady state of the consumption metabolic rate of O2 (CMRO2). The main methods of H.R. measurement are presented and discussed. The most often used is the acetazolamide challenge, but without overall technical consensus. The main indications of the coupled C.B.F. - H.R. measurements are presented: in transient ischemic attacks (TIAs), in assistance with the surgical decision (endarterectomy, extra-intracranial By-pass). It appears that CBF-HR measurement is useful to depicts abnormalities in TIAs (when CT or MRI are normals), to help the surgical decision when the carotid stenosis is lower than 70%, or even to manage the operative methodology (extra-corporal shunting) when the stenosis is higher than 70% with alterations of abolition of the H.R. values. (author)