Abstract

Cerebral metabolism is critically dependent on the regulation of cerebral blood flow (CBF), so it would be expected that vascular mechanisms that play a critical role in CBF regulation would be tightly conserved across individuals. However, the relationships between blood pressure (BP) and cerebral blood velocity fluctuations exhibit inter-individual variations consistent with heterogeneity in the integrity of CBF regulating systems. Here we sought to determine the nature and consistency of dynamic cerebral autoregulation (dCA) during the application of oscillatory lower body negative pressure (OLBNP). In 18 volunteers we recorded BP and middle cerebral artery blood flow velocity (MCAv) and examined the relationships between BP and MCAv fluctuations during 0.03, 0.05 and 0.07Hz OLBNP. dCA was characterised using project pursuit regression (PPR) and locally weighted scatterplot smoother (LOWESS) plots. Additionally, we proposed a piecewise regression method to statistically determine the presence of a dCA curve, which was defined as the presence of a restricted autoregulatory plateau shouldered by pressure-passive regions. Results show that LOWESS has similar explanatory power to that of PPR. However, we observed heterogeneous patterns of dynamic BP-MCAv relations with few individuals demonstrating clear evidence of a dCA central plateau. Thus, although BP explains a significant proportion of variance, dCA does not manifest as any single characteristic BP-MCAv function.

Highlights

  • The human brain is a highly metabolically active organ that comprises only 1–2% of total body weight, but accounts for 20% of resting total body O2 consumption [1]

  • We found that the coherence between blood pressure (BP) and middle cerebral artery blood flow velocity (MCAv) fluctuations increased with increase in oscillatory lower body negative pressure (OLBNP) frequency (P < 0.05; one-way repeated measures ANOVA)

  • Similar to the results based on 5-Hz data, we found that BP-MCAv relationships characterised using locally weighted scatterplot smoother (LOWESS) were similar to those with project pursuit regression (PPR) with comparable MCAv variance explained (47.5 ±5.28% by PPR vs. 52±4.5% by LOWESS; see S1 Fig and S2 File for details)

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Summary

Introduction

The human brain is a highly metabolically active organ that comprises only 1–2% of total body weight, but accounts for 20% of resting total body O2 consumption [1]. Because of this high demand for energy, stringent regulation of cerebral blood flow (CBF) is paramount for normal brain function and several mechanisms have been identified as key regulators of CBF homeostasis [2,3,4]. PLOS ONE | DOI:10.1371/journal.pone.0139470 September 30, 2015

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