Transcranial doppler flow velocity vs. cerebral blood flow in pigs - A validation study using the radioactive microspheres method

Introduction: Validity of determination of transcranial doppler flow veloci ty in the middle cerebral artery as a measure for cerebral blood flow is di scussed controversely. We have investigated the correlation between transcr anial doppler flow velocity in the middle cerebral artery and the regional cerebral blood flow measured with the radioactive microspheres method in pi gs. Materials and methods: The animals were randomly divided into xenon group ( n=5), which received anaesthesia with 70% xenon inhaled in 30% oxygen in ad dition to buprenorphine 15 mu gkg(-1)h(-1). The TIVA group (n=5) was anaest hetized with a continuous infusion of pentobarbital at a rate of 15 mgkg(-1 )h(-1) and buprenorphine at a rate of 15 mu gkg(-1)h(-1). Under normoventil ation heart rate, mean arterial pressure, arterial oxygen saturation, arter ial pH, arterial pCO(2) and temperature were determined. Then hyper- and hy poventilation was carried out and controlled by measuring expiratory CO, le vels and arterial blood gases. Transcranial doppler flow velocity was measu red in normo-(target p(a)CO(2)=40 mmHg), hyper- (target p(a)CO(2)=30mmHg) a nd hypoventilation (target p(a)CO(2)=50mmHg). Simultaneously radiolabelled microspheres with three different radioactive markers (Niobium 95, Rutenium 103, Cereum 141) were injected into the left ventricle. Three tissue aliqu ots were taken from several parts of the brain (cortex, brainstem, medulla oblongata and cerbellum) to calculate the regional cerebral flow by measuri ng radioactivity. A total number of 252 microsphere samples were studied. Results: We found a good correlation between transcranial doppler flow velo city and cerebral blood flow measured with the microspheres method in pigs. The regional changes of CBF in cortex, brainstem, medulla and cerebellum w ere parallel, revealing a nearly equal change on cerebral blood flow in the different regions of the brain due to ventilatory manipulations under xeno n or total intravenous anaesthesia. Discussion: We conclude, that the transcranial doppler flow velocity measur ement in the middle cerebral artery is a reliable and useful non-invasive m ethod to estimate cerebral blood flow.