 Blood velocity in the middle cerebral artery MCAV will be determined using transcranial Doppler sonography. A 2 MHz Doppler probe was positioned over the right middle cerebral artery using previously described search techniques Aaslid et al. 1982 and will be secured with an adjustable headset DiaMon, Compumedics DWL. The mean depth for Doppler signals was 51 3 mm. Arterial blood pressure will be recorded with a transducer located at heart level TruWave, Edwards Lifesciences, Nyon, Switzerland. 