Study of noninvasive estimation the lower limit of cerebral autoregulation in human.

Objective To study the method of noinvasive estimation the lower limit of cerebral autoregulation (LLCA) in human. Methods TCD velocities in the middle cerebral artery and noninvasive blood pressure in the radial artery were continuous recorded in 32 healthy young volunteers. Critical closing pressure (CCP) and LLCA were calculated by two different methods: 1) linear extrapolation from normal heartbeat data; 2)first harmonic Fourier filtering of normal heartbeat data. Results Although 4 negative CCP values were elicited by the method of linear extrapolation from normal heartbeat data, 4 positive values were produced when the data of the same 4 volunteers were estimated with the use of a Fourier filter. LLCA calculated by the firet method(66.76 ± 9.14) mm Hg was higher than the LLCA estimated by the second method (60.79 ± 10.12) mm Hg. Conclusions Fourier transform method is recommended in the future studies of noninvasive estimation of the LLCA in human.