Assessment of cerebral haemodynamics in comatose patients by laser Doppler flowmetry--preliminary observations.

Preliminary observations of laser Doppler flowmetry (LDF) signal changes in comatose patients with severe head injury or higher grade subarachnoid haemorrhage are presented. The data demonstrate that LDF measurements by no means lend themselves to a straightforward and unequivocal interpretation. Three main sources of LDF signal "bias" are tentatively distinguished: (1) properties inherent to the LDF measurement system and (2) spatial as well as (3) temporal heterogeneity of functional responses of the cerebral microvascular bed lead to unexpected, unpredictable and seemingly "paradox" patterns of the LDF signals. Despite the exploratory character of our data, we are convinced that they strongly suggest a more critical and cautious appraisal of the present possibilities of LDF in monitoring comatose patients than suggested by several other recent reports on this topic.