  Cerebral autoregulation refers to regulation mechanisms that aim to maintain
cerebral blood flow approximately constant. It is often assessed by
autoregulation index (ARI), which uses arterial blood pressure and cerebral
blood flow velocity time series to produce a ten-scale index of autoregulation
performance (0 denoting the absence of and 9 the strongest autoregulation).
Unfortunately, data are rarely free from various artefacts. Here, we consider
four of the most common non-physiological blood pressure artefacts (saturation,
square wave, reduced pulse pressure and impulse) and study their effects on ARI
for a range of different artefact sizes. We show that a sufficiently large
saturation and square wave always result in ARI reaching the maximum value of
9. The pulse pressure reduction and impulse artefact lead to a more diverse
behaviour. Finally, we characterised the critical size of artefacts, defined as
the minimum artefact size that, on average, leads to a 10\% deviation of ARI
