Cardiovascular Engineering

, Volume 8, Issue 1, pp 60–71 | Cite as

Nonlinear Assessment of Cerebral Autoregulation from Spontaneous Blood Pressure and Cerebral Blood Flow Fluctuations

Original Paper

Abstract

Cerebral autoregulation (CA) is an most important mechanism responsible for the relatively constant blood flow supply to brain when cerebral perfusion pressure varies. Its assessment in nonacute cases has been relied on the quantification of the relationship between noninvasive beat-to-beat blood pressure (BP) and blood flow velocity (BFV). To overcome the nonstationary nature of physiological signals such as BP and BFV, a computational method called multimodal pressure-flow (MMPF) analysis was recently developed to study the nonlinear BP–BFV relationship during the Valsalva maneuver (VM). The present study aimed to determine (i) whether this method can estimate autoregulation from spontaneous BP and BFV fluctuations during baseline rest conditions; (ii) whether there is any difference between the MMPF measures of autoregulation based on intra-arterial BP (ABP) and based on cerebral perfusion pressure (CPP); and (iii) whether the MMPF method provides reproducible and reliable measure for noninvasive assessment of autoregulation. To achieve these aims, we analyzed data from existing databases including: (i) ABP and BFV of 12 healthy control, 10 hypertensive, and 10 stroke subjects during baseline resting conditions and during the Valsalva maneuver, and (ii) ABP, CPP, and BFV of 30 patients with traumatic brain injury (TBI) who were being paralyzed, sedated, and ventilated. We showed that autoregulation in healthy control subjects can be characterized by specific phase shifts between BP and BFV oscillations during the Valsalva maneuver, and the BP–BFV phase shifts were reduced in hypertensive and stroke subjects (P < 0.01), indicating impaired autoregulation. Similar results were found during baseline condition from spontaneous BP and BFV oscillations. The BP–BFV phase shifts obtained during baseline and during VM were highly correlated (R > 0.8, P < 0.0001), showing no statistical difference (paired-t test P > 0.47). In TBI patients there were strong correlations between phases of ABP and CPP oscillations (R = 0.99, P < 0.0001) and, thus, between ABP–BFV and CPP–BFV phase shifts (P < 0.0001, R = 0.76). By repeating the MMPF 4 times on data of TBI subjects, each time on a selected cycle of spontaneous BP and BFV oscillations, we showed that MMPF had better reproducibility than traditional autoregulation index. These results indicate that the MMPF method, based on instantaneous phase relationships between cerebral blood flow velocity and peripheral blood pressure, has better performance than the traditional standard method, and can reliably assess cerebral autoregulation dynamics from ambulatory blood pressure and cerebral blood flow during supine rest conditions.

Keywords

Spontaneous oscillations Instantaneous phase shift Valsalva maneuver Baseline resting condition Stroke Hypertension Traumatic brain injury 

Abbreviations

BP

Blood pressure

ABP

Intra-arterial blood pressure

CPP

Cerebral perfusion pressure

ICP

Intracranial pressure

BFV

Blood flow velocity

BI

Brain injury

ARI

Autoregulation index

MMPF

Multimodal pressure-flow

EMD

Empirical mode decomposition

EEMD

Ensemble empirical mode decomposition

VM

Valsalva maneuver

HTN

Hypertensive

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  1. 1.Division of GerontologyBeth Israel Deaconess Medical Center, Harvard Medical SchoolBostonUSA
  2. 2.Division of Interdisciplinary Medicine & Biotechnology and Margret and H.A. Rey Institute for Nonlinear Dynamics in MedicineBeth Israel Deaconess Medical Center/Harvard Medical SchoolBostonUSA
  3. 3.Academic Neurosurgical UnitAddenbrooke’s HospitalCambridgeUK
  4. 4.Division of GerontologyBeth Israel Deaconess Medical Center, Harvard Medical SchoolBostonUSA

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