Neurovascular coupling and cerebral autoregulation can be described in terms of a control system

Neurovascular coupling and cerebral autoregulation are important and fast m echanisms for maintaining an adequate blood supply to the brain. It was sug gested that both mechanisms follow a common control system. The aim of our study was to describe neurovascular coupling and cerebral autoregulation in mathematical terms of a control system and to test the aforementioned hypo thesis. We analyzed the input-output dynamics of neurovascular coupling (fl icker light test) and cerebral autoregulation (leg cuff test) in terms of a control system, and compared both systems. A transcranial Doppler device w as used to measure continuously the blood flow velocity changes in young he althy volunteers who lacked vascular risk factors. For both tests, a contro l system model with only four parameters was sufficient to allow the vascul ar reaction to be described in all (rate time, undamped natural angular fre quency, attenuation, gain). All parameters were identical for both control systems, except for gain, which is not directly comparable because, in the flicker light test, input function was not measured but assumed as a unit s tep function in each volunteer. This new method permits description of the regulation of cerebral blood Bow using a control loop with four parameters. For the first time, these parameters allowed a demonstration that cerebral autoregulation and neurovascular coupling could be governed by the same co ntrol system. (C) 2001 World Federation for Ultrasound in Medicine & Biolog y.