A Study of Regional Autoregulation in the Cerebral Circulation to Increased Perfusion Pressure in Normocapnia and Hypercapnia

Symon, Lindsay; Held, Klaus; Dorsch, Nicholas W.C.

doi:10.1161/01.str.4.2.139

Cited by 143 publications

(79 citation statements)

References 31 publications

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“…A study in apes, using sharp induced upward ABP stimuli, also found such very strong and rapid autoregulatory responses. 1 The dynamic cerebral autoregulation seems to prioritize protection against the imminent danger of cerebral hemorrhage that may accompany upward spike ABP. Ischemia and infarctions, which are the primary dangers of hypoperfusion, would develop over a longer time scale, and more time would be available for compensatory action.…”

Section: Discussionmentioning

confidence: 99%

“…This physiological control system is remarkably effective, any deviations are rapidly compensated for, 1,2 and the steady-state cerebral blood flow is kept remarkably constant. 3 In patients recovering from head injuries, the cerebral autoregulation mechanism may become impaired, leaving the brain exposed to the vagaries of blood pressure fluctuations, possibly adding to the damage caused by the initial trauma.…”

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confidence: 99%

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Asymmetric Dynamic Cerebral Autoregulatory Response to Cyclic Stimuli

Aaslid

Bláha

Sviri

et al. 2007

Stroke

100

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Background and Purpose-Dynamic cerebral autoregulation has been shown to be fast and effective, but it is not well known if the mechanism is symmetric, that is to say, it acts with equal compensatory action to upward as compared with downward abrupt changes in arterial blood pressure (ABP). Methods-Fourteen patients with head injuries and 10 normal subjects had bilateral transcranial Doppler and continuous ABP recording. Cyclic ABP stimuli were generated by large thigh cuffs, which were rapidly inflated above systolic pressure for 15 seconds alternating with 15 seconds of deflation. At least 8 such cycles were ensemble-averaged and the dynamic autoregulatory gain (AG up and AG dn ) was estimated separately for upward and downward changes in ABP. The results were compared with the autoregulation index using conventional leg cuff releases. Results-In normal subjects, AG dn was 0.74Ϯ0.18 and AG up was 0.77Ϯ0.17 (meanϮSD); the difference was insignificant.The correlation between AG dn and AG up , however, was weak (rϭ0.24). In the patients with head injury, AG dn was 0.30Ϯ0.21 and AG up was 1.27Ϯ0.76, the difference being highly significant (PϽ0.001). There was a negative relationship between AG dn and AG up (rϭϪ0.33). Autoregulation index correlated well with AG dn (rϭ0.79) and weakly negatively with AG up (rϭϪ0.47). Conclusions-A strongly asymmetric dynamic response of the cerebral autoregulation was seen the majority of patients with head injury. It might also have been present, albeit to a lesser degree, in the normal subjects. The findings suggest that nonlinear effects may be present in the operation of the cerebral autoregulation mechanism.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Asymmetric Dynamic Cerebral Autoregulatory Response to Cyclic Stimuli

Aaslid

Bláha

Sviri

et al. 2007

Stroke

100

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“…34 A fast dynamic response to changes in pressure pulsations is followed by a slow static response that restores cerebral blood flow after the initial dynamic response has settled 35 by myogenic (mechanogenic) and metabolic (chemogenic) mechanisms. 36 With decreasing BP, there is vasodilation of arterioles until maximal vasodilation occurs, and subsequently, there is reduction of blood flow. With increasing BP, there is progressive vasoconstriction of arterioles until the BP exceeds the upper limit of autoregulation, followed by breakthrough vasodilation, increase in cerebral blood flow, 36 blood-brain barrier dysfunction, and cerebral edema.…”

Section: Cerebrovascular Physiology and Implications For Treatmentmentioning

confidence: 99%

Acute Hypertensive Response in Patients With Stroke

2008

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A cute hypertensive response is the elevation of blood pressure (BP) above normal and premorbid values that initially occurs within the first 24 hours of symptom onset in patients with stroke. This phenomenon was reported in Ͼ60% of patients presenting with stroke in a nationally representative study from the United States. 1 With Ϸ980 000 patients 2 admitted with stroke each year in the United States, the estimated annual prevalence of acute hypertensive response is more than half a million patients. With Ϸ15 million patients experiencing stroke worldwide each year, 3 the acute hypertensive response may be expected in Ϸ10 million patients per year. The acute hypertensive response in stroke patients is managed by a diverse group of physicians, including emergency physicians, intensivists, internists, primary care physicians, neurologists, neurosurgeons, and cardiologists. Previous audits suggest that antihypertensive agents and management strategies vary considerably and are not always consistent with recommended guidelines. 4 Data from 1181 acute ischemic stroke patients enrolled in the Project for Improvement of Stroke Care Management suggested that administration of antihypertensive medication within 24 hours in 56% of the patients was inconsistent with guidelines provided by the American Stroke Association (ASA). 5 The present review article summarizes the current concepts pertaining to treatment of the acute hypertensive response derived from recent guidelines provided by professional organizations and "best available" evidence derived from experimental and clinical studies and discusses incorporation of these concepts into clinical practice. Randomized trials, nonrandomized controlled studies, and selected observational studies were identified with multiple searches on Medline from 1980 to 2007 by cross-referencing the key words of stroke, acute hypertension, antihypertensive agents, acute stroke, and hypertension. Pertinent articles identified from bibliographies of selected articles were also reviewed. Treatment targets and strategies were identified by review of existing guidelines from professional organizations. Definition of Acute Hypertensive ResponseThe 2003 World Health Organization (WHO)/International Society of Hypertension (ISH) statement 6 and the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) 7 define hypertension on the basis of the presence of consistent BP Ն140/90 mm Hg (multiple readings on separate days). This definition of hypertension is a threshold for the use of long-term antihypertensive treatment that is supported by evidence derived from randomized trials and clinicor population-based data that demonstrate reduction in cardiovascular events with this threshold for treatment. The same definition cannot be applied in the case of acute hypertensive response, because the above-mentioned ascertainment criteria and rationale are not valid. The executive summary of the ISH statement 8 on management of BP i...

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“…Although that many studies selected ~0.1Hz as an upper frequency boundary in the transfer function analysis, such choice of frequency range for the estimation of cerebral autoregulation is somewhat arbitrary. Previous studies showed that after a sudden blood flow decline, baseline levels can be restored within 3-6 seconds (corresponding to 0.16-0.33Hz in frequency domain) [53,54], and therefore there is no reason to refute the notion that cerebral autoregulation can operate at frequencies >0.1Hz. Studies of using phase synchronization technique and transfer function analysis also indicated that the relationship between BP and BFV oscillations at frequency >0.1 is altered in patients with strokes and, thus, may also provide useful information on cerebral autoregulation [48,55].…”

Section: B Active Frequency Range Of Cerebral Autoregulationmentioning

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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A Study of Regional Autoregulation in the Cerebral Circulation to Increased Perfusion Pressure in Normocapnia and Hypercapnia

Cited by 143 publications

References 31 publications

Asymmetric Dynamic Cerebral Autoregulatory Response to Cyclic Stimuli

Asymmetric Dynamic Cerebral Autoregulatory Response to Cyclic Stimuli

Acute Hypertensive Response in Patients With Stroke

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

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