Temporal stability of hemodynamic stage in patients with carotid artery occlusion

We assessed cerebral hemodynamic status longitudinally with serial positron emission tomography (PET) studies in patients with carotid occlusion and no interval stroke. Regional measurements of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral rate of oxygen metabolism (CMRO₂), oxygen extraction fraction (OEF), and mean transit time (MTT) were obtained using PET in 21 patients with unilateral carotid artery occlusion and were repeated 12 to 59 months later. Hemodynamic stage was assigned based on left to right hemispheric ratios of mean quantitative values as: Stage 0, normal hemodynamics; Stage 1, increased MTT (autoregulatory vasodilatation); and Stage 2, increased OEF. Eight patients (9 paired studies) were initially categorized as Stage 0. Repeat mean hemispheric ratios remained within the range of normal value (95% confidence limits). Three patients (4 paired studies) were categorized as Stage 1. Repeat MTT ratios remained elevated while other ratios remained normal. Ten patients (11 paired studies) were categorized as Stage 2. A statistically significant increase in the CBF ratios (p = 0.26) and decrease in OEF ratios was found (p = 0.23). A statistically significant increase in mean quantitative CMRO₂ between initial and follow up examinations was observed bilaterally in patients with normal hemodynamics but not in Stage 1 or 2 patients. In selected patients with carotid occlusion and no interval stroke, the degree of hemodynamic compromise does not progress. In the subset of patients with increased OEF, both OEF and CBF improve over time.