Received November 24, 2004
Revised January 5, 2005
Accepted after revision January 5, 2005

¹ Rigshospitalet
² University of Copenhagen

^* To whom correspondence should be addressed. E-mail: gitte{at}nru.dk.

	Abstract

Aim: Laser Doppler flowmetry is a more recent technique that is increasingly used to monitor relative changes in cerebral blood flow whereas the intra-arterial 133Xenon injection technique is a well-established method for repeated absolute measurements of cerebral blood flow. This study validates laser Doppler flowmetry for assessment of cerebral autoregulation and CO2- reactivity with the 133Xenon injection technique as the gold standard. Methods: Simultaneous measurements of cerebral blood flow were collected by laser Doppler flowmetry (CBFLDF) and the 133Xenon method (CBFXe) while 1) cerebral autoregulation was challenged by controlled systemic haemorrhage, or 2) cerebral blood flow was varied by manipulating PaCO2. Results: Laser Doppler flowmetry slightly overestimated CBF under conditions of haemorrhagic shock and hemodilution caused by controlled haemorrhage (paired t-test, p<0.05). For pooled data, the autoregulation lower limit was, however, similar determined with the 133Xenon and the LDF technique, 65±3.9 (standard error) and 60±5.6 mmHg, respectively. Linear regression analysis yielded CBFXe= (1.02*CBFLDF) + 9.1 and r=0.90. Even at substantial PaCO2-changes, the two methods resulted in similar results. Conclusion: Even though laser Doppler flowmetry overestimated cerebral blood flow during haemorrhagic shock caused by controlled haemorrhage, the lower limit autoregulation was correctly identified. The Doppler technique provides a reliable method for detection of a wide range of cerebral blood flow changes under CO2-challenge. Hemodilution influences the two methods differently causing relative overestimation of blood flow by the laser Doppler technique compared to the xenon method.

Key Words: Blood pressure, Brain, Microcirculation