Altered cerebral vasoregulation in hypertension and stroke

Novak, Vera; Chowdhary, Abhineet; Farrar, Bertha B.; Haleagrahara, Nagaraja; Braun, Johann; Kanard, Roly; Novák, Péter; Slivka, Andrew

doi:10.1212/01.wnl.0000068023.14587.06

Cited by 83 publications

(82 citation statements)

References 24 publications

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“…Cerebral autoregulation dynamics are usually evaluated by the changes in BFV and BP during the interventions that induce rapid BP reductions or increases such as the Valsalva maneuver, thigh cuff deflation and the head-up tilt [2,9,50,[60][61][62][63]. The conventional approach is valuable, because it allows assessments of the autoregulation responses during rapid variations in systemic pressure under the stressed conditions.…”

Section: Ivc Assessment Of Cerebral Autoregulation From Spontaneousmentioning

confidence: 99%

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

Peng

Huang

et al. 2008

Physica A: Statistical Mechanics and its Applications

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Cerebral autoregulation (CA) is an important mechanism that involves dilation and constriction in arterioles to maintain relatively s cerebral blood flow in response to changes of systemic blood pressure. Traditional assessments of CA focus on the changes of cerebral blood flow velocity in response to large blood pressure fluctuations induced by interventions. This approach is not feasible for patients with impaired autoregulation or cardiovascular regulation. Here we propose a newly developed technique-the multimodal pressure-flow (MMPF) analysis, which assesses CA by quantifying nonlinear phase interactions between spontaneous oscillations in blood pressure and flow velocity during resting conditions. We show that CA in healthy subjects can be characterized by specific phase shifts between spontaneous blood pressure and flow velocity oscillations, and the phase shifts are significantly reduced in diabetic subjects. Smaller phase shifts between oscillations in the two variables indicate more passive dependence of blood flow velocity on blood pressure, thus suggesting impaired cerebral autoregulation. Moreover, the reduction of the phase shifts in diabetes is observed not only in previously-recognized effective region of CA (<0.1Hz), but also over the higher frequency range from ~0.1 to 0.4Hz. These findings indicate that Type 2 diabetes alters cerebral blood flow regulation over a wide frequency range and that this alteration can be reliably assessed from spontaneous oscillations in blood pressure and blood flow velocity during resting conditions. We also show that the MMPF method has better performance than traditional approaches based on Fourier transform, and is more sui for the quantification of nonlinear phase interactions between nonstationary biological signals such as blood pressure and blood flow.

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Section: Ivc Assessment Of Cerebral Autoregulation From Spontaneousmentioning

confidence: 99%

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

Peng

Huang

et al. 2008

Physica A: Statistical Mechanics and its Applications

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“…An FDA exemption for use of an investigational device was obtained. Stroke patients participating in this 8-T MRI study were selected from a larger cohort evaluating the effects of a minor chronic ischemic stroke on cerebral vasoregulation [15]. All subjects were screened using a detailed protocol including medical history, routine laboratory examinations, transcranial Doppler evaluations and 24-h ambulatory blood pressure monitoring.…”

Section: Subjectsmentioning

confidence: 99%

High-resolution ultrahigh-field MRI of stroke

Novak

Abduljalil

Novák

et al. 2005

Magnetic Resonance Imaging

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Background: Ultrahigh-field MRI at 8 T offers unprecedented resolution for imaging brain structures and microvasculature.Objective: The aim of this study is to apply high-resolution MRI for stroke imaging and to characterize findings at 1.5 and 8 T.Methods: Seventeen subjects with minor ischemic infarcts were studied using T2-weighted gradient echo (GE) and rapid acquisition with relaxation enhancement (RARE) images at 8 T with resolution up to 200 μm. In 10 subjects, T1-and T2-weighted fast spin echo (FSE) and fluid-attenuated inversion recovery (FLAIR) images were also acquired at 1.5-T MRI.Results: The 8-T images showed infarcts as sharply demarcated areas of high-signal intensity (n=21) and revealed more infarctions than 1.5-T images (n=14) (P <.003). The low-signal intensity areas that surrounded infarctions were suggestive of hemosiderin deposits. The 8-T characteristics of microvessels terminating within the infractions were distinct from normal vasculature. The 8-T images revealed an angioma at the site of a second stroke, not apparent on 1.5-T images.Conclusions: Ultrahigh-field MRI at 8 T is feasible for stroke imaging. The 8-T MRI visualized infarcts and microvasculature with high resolution, revealing infarcts and vascular pathologies that were not apparent at 1.5 T.

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“…Hypertension and diabetes, that are the leading causes of stroke and dementia of elderly people, are associated with microvascular disease that compromises capacity to regulate perfusion in cerebrovascular bed (Lipsitz et al 2000;Novak et al 2003). Cerebral autoregulation compensating fluctuations of systemic BP is lost post-stroke (Eames et al 2002;Novak et al 2004;Immink et al 2005) and after traumatic brain injury (TBI) (Czosnyka et al 1997;Schmidt et al 2003), rendering blood flow dependent on perfusion pressure.…”

Section: Introductionmentioning

confidence: 99%

“…Traditional approaches assess autoregulatory responses by challenging cerebrovascular systems using interventions such as the Valsalva maneuver, thigh cuff deflation and the head-up tilt (Carey et al 2003;Panerai 1998;Novak et al 1998;Tiecks et al 1999;Dawson et al 1999;Panerai et al 2001;Novak et al 2003). These intervention procedures induce large intracranial pressure fluctuations and require patients' cooperation and, therefore, such procedures are limited for clinical evaluation of autoregulation.…”

mentioning

confidence: 99%

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

Peng

Czosnyka

et al. 2007

Cardiovasc Eng

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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 (pairedt 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.

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Altered cerebral vasoregulation in hypertension and stroke

Abstract: Cerebral vasoregulation is impaired with minor stroke, and cerebral blood flow depends on blood pressure. Decline of blood flow velocities during orthostatic stress may pose a risk of silent hypoperfusion.

Cited by 83 publications

References 24 publications

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

High-resolution ultrahigh-field MRI of stroke

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

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