Long-term changes in dynamic cerebral autoregulation: a 10 years follow up study

This study takes a novel approach to describing time-related changes in dynamic cerebral autoregulation (dCA). It is well-recognized that dCA exhibits both intra- and inter- subject variability, and this study seeks to characterize the extent to which intra-subject variability occurs after a significant period of time by studying the same subjects 10 years apart, thus eliminating inter-subject variability as a source of error. Ten healthy subjects were identified in 1998 and followed up in 2008. On each visit they underwent simultaneous recordings of right middle cerebral artery cerebral blood flow velocity (RMCA CBFV), blood pressure and heart rate. Data were analysed in the frequency domain using transfer function analysis and in the time domain using CBFV step response, from which the autoregulatory index (ARI) was calculated. Ten subjects of mean age 35.5 (range 24-51) years in 1998 (seven male) were studied. There was a significant fall in ARI from 1998-2008 (DeltaARI = 1.1, P = 0.021), along with a significant rise in coherence in 2008 (at 0.05 Hz, P = 0.018). Difference in mean step response between 1998 and 2008 was also significant (P = 0.045). This is the first study to assess dCA in the same subjects 10 years apart, providing a novel opportunity to assess intra-subject variation in dCA after a long time period has elapsed. A fall in frequency and time domain parameters was observed. This is important, and needs to be considered in future studies assessing long-term changes in dCA, particularly given the body evidence which suggests that dCA is unaffected by ageing.