Rheoencephalogram reflects cerebral blood flow autoregulation in pigs

Abstract

Cerebral blood flow autoregulation (CBF AR) is the phenomenon that makes blood flow constant within a physiological range regardless of blood pressure variations. When systemic arterial pressure (SAP) increases, vasoconstriction is taking place in the brain. The objective of the present study was to compare SAP, rheoencephalogram (REG), and carotid flow (CF) measured by Doppler ultrasound. Twen-tyeight anesthetized Yorkshire pigs were measured to evaluate CBF AR during several CBF manipulations: haemorrhage, positive end-expiratory pressure (PEEP), and transitory SAP decrease and increase. Data were sampled with 200 Hz and processed off-line. 1) Haemorrhage elicited a decrease in SAP and transitory increases in REG and CF amplitude; 2) PEEP resulted in a decrease in SAP and increases in REG and CF amplitude; 3) PEEP after haemorrhage caused decreases in SAP, REG and CF amplitudes. When CBF AR was present, it was detected by both REG and carotid flow. Following haemorrhage, CBF AR was lost; CF and REG passively followed SAP. The clinical importance of these findings is that REG can be measured more conveniently and continuously in humans than can Doppler ultrasound. Therefore, measurement of CBF autoregulation by REG has potential for use as a life sign monitoring modality. © Springer-Verlag 2007.