Are there differences in cerebral autoregulation between small increases or decreases of blood pressure? (1184.7)

Abstract

Cerebral blood flow velocity (CBFV) in the middle cerebral and arterial blood pressure (ABP) were recorded while a pseudorandom sequence of lower body negative pressure (LBNP) steps was applied for approximately 5 minutes in 31 healthy adult volunteers (53 recodings). The LBNP provoked ABP changes of 4.5 ± 4.1 mmHg (mean ± standard deviation). Cerebral autoregulation (CA) was quantified from phase at 0.1 Hz, calculated over the whole recording (Pwhole) and then only over segments with increasing or decreasing LBNP (Plbnp2, Plbnp1), respectively. Phase was also estimated over all signal segments with only increasing (or only decreasing) ABP (Pabp1, Pabp2) ‐ whether spontaneous or provoked. The results showed small, but significant differences between the estimates (Friedman, p<0.0001), with the largest mean values for Pabp1 and Pabp2. There was no significant difference (Wilcoxon) between Pabp1 and Pabp2, or between Plbnp1 and Plbnp2, but all were significantly different to Pwhole. There was no significant difference in dispersion from the mean, between phase estimates from different signal segments. The results thus indicate that the response to small increases or decreases in LBNP and ABP are similar. The data also provides further evidence that some signal segments within a recording are more suitable for CA analysis than others. Selection of only the segments with increasing or decreasing LBNP was not beneficial.Grant Funding Source: Supported by EPSRC (UK)