Diagnosis of hemodynamic compromise in patients with chronic cerebral ischemia; the detection of impaired vasodilatory capacity with ¹³³Xe SPECT and acetazolamide (Diamox) test

To evaluate the efficacy of ¹³³Xe SPECT and Diamox test, for selecting patients with hemodynamic compromise, tests using ¹³³Xe inhalation method and single photon emission computed tomography (SPECT) with acetazolamide (Diamox) were performed in twenty-three patients with chronic cerebral ischemia, before and after extracranial-intracranial bypass surgery or carotid-endarterectomy. All patients complained of TIA, RIND, or minor completed stroke, and cerebral angiography of all patients demonstrated severe stenosis or occlusion in the ipsilateral internal carotid artery or middle cerebral artery. Cerebral blood flow (CBF) was measured in each patient with ¹³³Xe SPECT, and was also measured 15 minutes after intravenous administration of 10 - 12 mg/kg Diamox, which is known as a cerebral vasodilatory agent (Diamox test). Our results revealed that all patients could be divided into four types according to the findings of their resting rCBF and Diamox reactivity. The patients who had normal resting rCBF and normal Diamox reactivity (type 1) were considered to have well-developed collateral circulation and normal cerebral perfusion pressure (CPP) in spite of severe occlusive lesions in the carotid system. Moderate vasodilation due to reduced CPP was considered to occur in patients who had normal resting rCBF and decreased Diamox reactivity (type 2). The resting rCBF remained unchanged, but Diamox reactivity improved to the normal range after surgery in the patients of type 2 (p<0.01), which indicated the improvement of CPP and the resolution of the autoregulatory vasodilation. Maximum vasodilatation or dysautoregulation was considered to occur due to the inadequate collateral flow and the severely reduced CPP in patients whose findings revealed decrease in the resting rCBF and impaired Diamox reactivity (type 3). Remarkable improvement was seen in both resting rCBF and Daimox reactivity after surgery in the patients of type 3 (p<0.01). In the patients who had decreased resting rCBF and normal Diamox reactivity (type 4), the decreased resting rCBF was considered to result from the reduction in the metabolic demand because of irreversible ischemic neuronal damage. In conclusion, our results suggest that ¹³³Xe SPECT and Diamox test are very useful to diagnose the cerebral perfusion reserve and hemodynamic compromise in patients with chronic cerebral ischemia.