Effects of induced hypertension on intracranial pressure and flow velocities of the middle cerebral arteries in patients with large hemispheric stroke

Lassen's Cerebral Autoregulation Plot Revisited and Validated 65 Years Later: Impacts of Vasoactive Drug Treatment on Cerebral Blood Flow

Niels Lassen's seminal 1959 cerebral autoregulation plot, a cornerstone in understanding the relationship between mean arterial pressure (MAP) and cerebral blood flow (CBF), was based on preexisting literature. However, this work has faced criticism for selective data presentation, leading to inaccurate interpretation. This review revisits and validates Lassen's original plot using contemporary data published since 2000. Additionally, we aim to understand the impact of vasoactive drug treatments on CBF, as Lassen's referenced studies used various drugs for blood pressure manipulation. Our findings confirm Lassen's concept of a plateau where CBF remains relatively stable across a specific MAP range in awake humans with normal brains. However, significant variations in cerebral autoregulation among different populations are evident. In critically ill patients and those with traumatic brain injury, the autoregulatory plateau dissipates, necessitating tight blood pressure control to avoid inadequate or excessive cerebral perfusion. A plateau is observed in patients anesthetized with intravenous agents but not with volatile agents. Vasopressor treatments have population-dependent effects, with contemporary data showing increased CBF in critically ill patients but not in awake humans with normal brains. Vasopressor treatment results in a greater increase in CBF during volatile than intravenous anesthesia. Modern antihypertensives do not significantly impact CBF based on contemporary data, exerting a smaller impact on CBF compared to historical data. These insights underscore the importance of individualized blood pressure management guided by modern data in the context of cerebral autoregulation across varied patient populations.

Rescue therapy of early neurological deterioration in lacunar stroke

BACKGROUND

Early neurological deterioration (END) occurs in many patients with acute ischemic stroke due to a variety of causes. Although pharmacologically induced hypertension (PIH) and anticoagulants have been investigated in several clinical trials for the treatment of END, the efficacy and safety of these treatments remain unclear. Here, we investigated whether PIH or anticoagulation is better as a rescue therapy for the progression of END in patients with lacunar stroke.

METHODS

This study included patients with lacunar stroke who received rescue therapy with END within 3 days of symptom onset between April 2014 and August 2021. In the PIH group, phenylephrine was administered intravenously for 24 h and slowly tapered when symptoms improved or after 5 days of PIH. In the anticoagulation group, argatroban was administered continuously intravenously for 2 days and twice daily for next 5 days. We compared END recovery, defined as improvement in NIHSS from baseline, excellent outcomes (0 or 1 mRS at 3 months), and safety profile.

RESULTS

Among the 4818 patients with the lacunar stroke, END occurred in 147 patients. Seventy-nine patients with END received PIH (46.9%) and 68 patients (46.3%) received anticoagulation therapy. There was no significant difference in age (P = 0.82) and sex (P = 0.87) between the two groups. Compared to the anticoagulation group, the PIH group had a higher incidence of END recovery (77.2% vs. 51.5%, P < 0.01) and excellent outcomes (34.2% vs. 16.2%, P = 0.04). PIH was associated with END (HR 2.49; 95% CI 1.06-5.81, P = 0.04). PIH remained associated with END recovery (adjusted HR 3.91; 95% CI 1.19-12.90, P = 0.02). Safety outcomes, like hemorrhagic conversion and mortality, were not significantly different between the two groups.

CONCLUSIONS

As a rescue therapy for the progression of END in lacunar stroke patients, PIH with phenylephrine was more effective with similar safety compared to anticoagulation with argatroban.

Noradrenaline-induced changes in cerebral blood flow in health, traumatic brain injury and critical illness: a systematic review with meta-analysis

BACKGROUND

Noradrenaline is a standard treatment for hypotension in acute care. The precise effects of noradrenaline on cerebral blood flow in health and disease remain unclear.

METHODS

We systematically reviewed and synthesised data from studies examining changes in cerebral blood flow in healthy participants and patients with traumatic brain injury and critical illness.

RESULTS

Twenty-eight eligible studies were included. In healthy subjects and patients without critical illness or traumatic brain injury, noradrenaline did not significantly change cerebral blood flow velocity (-1.7%, 95%CI -4.7-1.3%) despite a 24.1% (95%CI 19.4-28.7%) increase in mean arterial pressure. In patients with traumatic brain injury, noradrenaline significantly increased cerebral blood flow velocity (21.5%, 95%CI 11.0-32.0%), along with a 33.8% (95%CI 14.7-52.9%) increase in mean arterial pressure. In patients who were critically ill, noradrenaline significantly increased cerebral blood flow velocity (20.0%, 95%CI 9.7-30.3%), along with a 32.4% (95%CI 25.0-39.9%) increase in mean arterial pressure. Our analyses suggest intact cerebral autoregulation in healthy subjects and patients without critical illness or traumatic brain injury., and impaired cerebral autoregulation in patients with traumatic brain injury and who were critically ill. The extent of mean arterial pressure changes and the pre-treatment blood pressure levels may affect the magnitude of cerebral blood flow changes. Studies assessing cerebral blood flow using non-transcranial Doppler methods were inadequate and heterogeneous in enabling meaningful meta-analysis.

CONCLUSIONS

Noradrenaline significantly increases cerebral blood flow in humans with impaired, not intact, cerebral autoregulation, with the extent of changes related to the severity of functional impairment, the extent of mean arterial pressure changes and pre-treatment blood pressure levels.

Time Window for Induced Hypertension in Acute Small Vessel Occlusive Stroke With Early Neurological Deterioration

BACKGROUND

Therapeutic-induced hypertension treatment (iHTN) is helpful for alleviating early neurological deterioration (END) in acute small vessel occlusive stroke. We examined the time parameters related to iHTN effectiveness in these patients.

METHODS

We retrospectively reviewed patients with acute small vessel occlusive stroke who underwent iHTN for END, defined as an increase of ≥2 points in total National Institutes of Health Stroke Scale (NIHSS) score or ≥1 point in motor items of NIHSS. The primary outcome was an early neurological improvement (ENI; a decrease of ≥2 points in total NIHSS score or ≥1 point in motor items of NIHSS), and the secondary outcome was any neurological improvement (a decrease of ≥1 point in the total NIHSS score). We conducted a multivariable logistic regression analysis, adjusting for demographics, risk factors, baseline clinical status, and intervention-related variables. We also generated a restricted cubic spline curve for the END-to-iHTN time cutoff.

RESULTS

Among the 1062 patients with small vessel occlusive stroke screened between 2017 and 2021, 136 patients who received iHTN within 24 hours from END were included. The mean age was 65.1 (±12.0) years, and 61.0% were male. Sixty-five (47.8%) patients showed ENI and 77 (56.6%) patients showed any neurological improvement. END-to-iHTN time was significantly shorter in patients with ENI (150 [49-322] versus 290 [97-545] minutes; P=0.018) or any neurological improvement (150 [50-315] versus 300 [130-573] minutes; P=0.002). A 10-minute increase in the time between END and iHTN decreased the odds of achieving ENI (odds ratio, 0.984 [95% CI, 0.970-0.997]; P=0.019) or any neurological improvement (odds ratio, 0.978 [95% CI, 0.964-0.992]; P=0.002). The restricted cubic spline curve showed that the odds ratio of ENI reached its minimum at ≈3 hours.

CONCLUSIONS

Among patients with small vessel occlusive stroke with END, a shorter interval between END and the initiation of iHTN was associated with increased odds of achieving neurological improvement. The efficacy of iHTN may be limited to induction within the first 3 hours of END.

Evolving Clinical-Translational Investigations of Cerebroprotection in Ischemic Stroke

Ischemic stroke is a highly morbid disease, with over 50% of large vessel stroke (middle cerebral artery or internal carotid artery terminus occlusion) patients suffering disability despite maximal acute reperfusion therapy with thrombolysis and thrombectomy. The discovery of the ischemic penumbra in the 1980s laid the foundation for a salvageable territory in ischemic stroke. Since then, the concept of neuroprotection has been a focus of post-stroke care to (1) minimize the conversion from penumbra to core irreversible infarct, (2) limit secondary damage from ischemia-reperfusion injury, inflammation, and excitotoxicity and (3) to encourage tissue repair. However, despite multiple studies, the preclinical-clinical research enterprise has not yet created an agent that mitigates post-stroke outcomes beyond thrombolysis and mechanical clot retrieval. These translational gaps have not deterred the scientific community as agents are under continuous investigation. The NIH has recently promoted the concept of cerebroprotection to consider the whole brain post-stroke rather than just the neurons. This review will briefly outline the translational science of past, current, and emerging breakthroughs in cerebroprotection and use of these foundational ideas to develop a novel paradigm for optimizing stroke outcomes.

The role of the autonomic nervous system in cerebral blood flow regulation in stroke: A review

Stroke is a pathophysiological condition which results in alterations in cerebral blood flow (CBF). The mechanism by which the brain maintains adequate CBF in presence of fluctuating cerebral perfusion pressure (CPP) is known as cerebral autoregulation (CA). Disturbances in CA may be influenced by a number of physiological pathways including the autonomic nervous system (ANS). The cerebrovascular system is innervated by adrenergic and cholinergic nerve fibers. The role of the ANS in regulating CBF is widely disputed owing to several factors including the complexity of the ANS and cerebrovascular interactions, limitations to measurements, variation in methods to assess the ANS in relation to CBF as well as experimental approaches that can or cannot provide insight into the sympathetic control of CBF. CA is known to be impaired in stroke however the number of studies investigating the mechanisms by which this occurs are limited. This literature review will focus on highlighting the assessment of the ANS and CBF via indices derived from the analyses of heart rate variability (HRV), and baroreflex sensitivity (BRS), and providing a summary of both clinical and animal model studies investigating the role of the ANS in influencing CA in stroke. Understanding the mechanisms by which the ANS influences CBF in stroke patients may provide the foundation for novel therapeutic approaches to improve functional outcomes in stroke patients.

Timing of Revascularization in Ischemic Moyamoya Disease: Association of Early Versus Delayed Surgery with Perioperative and Long-Term Outcomes

OBJECTIVE

Patients with nmoyamoya disease (MMD) who present primarily with ischemic stroke are known to have greater rates of perioperative strokes as compared with those who present with nonstroke symptoms. The optimal timing for revascularization for these patients remains unclear.

METHODS

From 1994 to 2015, 91 patients with MMD presented with signs and symptoms of an acute ischemic stroke with diffusion restriction correlate on magnetic resonance imaging, and these patients were subdivided into those who underwent early revascularization (<90 days from last stroke), versus those who underwent delayed revascularization (≥90 days after last stroke), based on evidence that most neurological recovery after stroke occurs during the first three months. Perioperative and long-term outcomes were compared between the 2 surgical cohorts.

RESULTS

In total, 27 patients underwent early revascularization, and 64 patients underwent delayed revascularization. Patients who underwent early revascularization had a statistically greater rate of perioperative stroke (P = 0.04) and perioperative mortality (P = 0.03), and overall complication rate (P = 0.049). At last follow-up of 5.2 ± 4.3 years, patients who underwent delayed revascularization had a lower mortality rate (P = 0.01) and a lower overall postoperative stroke incidence (P = 0.002). As a function of time, patients with MMD undergoing delayed revascularization had a statistically higher length of stroke-free survival (P = 0.005).

CONCLUSIONS

Patients with MMD who present with ischemic stroke are more likely to have perioperative strokes, overall perioperative complications, worse long-term mortality rates, and lower rates of stroke-free survival if revascularization surgery occurred within 90 days of last stroke.

Effect of head-down tilt on clinical outcome and cerebral perfusion in ischemic stroke patients: A case series

Background

The effect of head position on stroke is not clear. The current study aimed to observe the effect of head-down tilt on acute ischemic stroke (AIS) patients with large vessel occlusion.

Methods

We observed the influence of head-down tilt position on clinical outcomes, myocardial enzymogram and N-terminal pro b-type Natriuretic Peptide in 4 AIS patients who suffered early neurological deterioration (END). Cerebral perfusion imaging was performed in 3 patients using arterial spin labeling.

Results

In series of AIS patients with END, head down tilt (-20°) prevented further neurological deterioration and improved clinical outcomes. An increase in cerebral blood flow was observed by arterial spin labeling after head down tilt treatment. No obvious adverse events occurred.

Conclusion

The case series suggest that head-down tilt may improve clinical outcome in AIS patients through increasing the cerebral perfusion with no obvious adverse events. The finding needs to be confirmed in future clinical trials.

Cerebral Augmentation Effect Induced by External Counterpulsation Is Not Related to Impaired Dynamic Cerebral Autoregulation in Ischemic Stroke

Background and Purpose

Dynamic cerebral autoregulation is impaired after ischemic stroke. External counterpulsation (ECP) augments the cerebral blood flow of patients with ischemic stroke by elevation of blood pressure (BP). We aimed to investigate if cerebral augmentation effects during ECP were associated with impaired dynamic cerebral autoregulation in patients after acute ischemic stroke.

Methods

Forty patients with unilateral ischemic stroke and large artery atherosclerosis in the anterior circulation territory within 7 days from symptom onset and eighteen healthy controls were recruited. We monitored changes in mean flow velocity over both middle cerebral arteries (MCA) by transcranial Doppler (TCD) before, during, and immediately after ECP. Cerebral augmentation index was MCA mean flow velocity increase in percentage during ECP compared with baseline to evaluate the augmentation effects of ECP. Spontaneous arterial BP and cerebral blood flow velocity in both bilateral MCAs were recorded using a servo-controlled plethysmograph and TCD, respectively. Transfer function analysis was used to derive the autoregulatory parameters, including phase difference (PD), and gain.

Results

The cerebral augmentation index in patients with stroke was significantly higher on both the ipsilateral and contralateral sides than that in controls, while the PD in patients with stroke was significantly lower on both sides than those in controls (all P < 0.05). The cerebral augmentation index did not correlate with PD and gain on either the ipsilateral or contralateral side of patients with stroke or in controls (all P > 0.05). The cerebral augmentation index of patients with stroke was significantly related to mean BP change on the ipsilateral side (R² = 0.108, P = 0.038).

Conclusion

The degree of ECP-induced cerebral augmentation effects as measured by the cerebral augmentation index did not correlate with the magnitude of impaired dynamic cerebral autoregulation.

Pressor therapy in acute ischaemic stroke: an updated systematic review

Background

Low blood pressure (BP) in acute ischaemic stroke (AIS) is associated with poor functional outcome, death, or severe disability. Increasing BP might benefit patients with post-stroke hypotension including those with potentially salvageable ischaemic penumbra. This updated systematic review considers the present evidence regarding the use of vasopressors in AIS.

Methods

We searched the Cochrane Database of Systematic Reviews, MEDLINE, EMBASE and trial databases using a structured search strategy. We examined reference lists of relevant publications for additional studies examining BP elevation in AIS.

Results

We included 27 studies involving 1886 patients. Nine studies assessed increasing BP during acute reperfusion therapy (intravenous thrombolysis, mechanical thrombectomy, intra-arterial thrombolysis or combined). Eighteen studies tested BP elevation alone. Phenylephrine was the most commonly used agent to increase BP (n = 16 studies), followed by norepinephrine (n = 6), epinephrine (n = 3) and dopamine (n = 2). Because of small patient numbers and study heterogeneity, a meta-analysis was not possible. Overall, BP elevation was feasible in patients with fluctuating or worsening neurological symptoms, large vessel occlusion with labile BP, sustained post-stroke hypotension and ineligible for intravenous thrombolysis or after acute reperfusion therapy. The effects on functional outcomes were largely unknown and close monitoring is advised if such intervention is undertaken.

Conclusion

Although theoretical arguments support increasing BP to improve cerebral blood flow and sustain the ischaemic penumbra in selected AIS patients, the data are limited and results largely inconclusive. Large, randomised controlled trials are needed to identify the optimal BP target, agent, duration of treatment and effects on clinical outcomes.

Blood Pressure Management Before, During, and After Endovascular Thrombectomy for Acute Ischemic Stroke

There is an absence of specific evidence or guideline recommendations on blood pressure management for large vessel occlusion stroke patients. Until randomized data are available, the periprocedural blood pressure management of patients undergoing endovascular thrombectomy can be viewed in two phases relative to the achievement of recanalization. In the hyperacute phase, prior to recanalization, hypotension should be avoided to maintain adequate penumbral perfusion. The American Heart Association guidelines should be followed for the upper end of prethrombectomy blood pressure: ≤185/110 mm Hg, unless post-tissue plasminogen activator administration when the goal is <180/105 mm Hg. After successful recanalization (thrombolysis in cerebral infarction [TICI]: 2b-3), we recommend a target of a maximum systolic blood pressure of < 160 mm Hg, while the persistently occluded patients (TICI < 2b) may require more permissive goals up to <180/105 mm Hg. Future research should focus on generating randomized data on optimal blood pressure management both before and after endovascular thrombectomy, to optimize patient outcomes for these divergent clinical scenarios.

The cerebrovascular response to norepinephrine: A scoping systematic review of the animal and human literature

Intravenous norepinephrine (NE) is utilized commonly in critical care for cardiovascular support. NE's impact on cerebrovasculature is unclear and may carry important implications during states of critical neurological illness. The aim of the study was to perform a scoping review of the literature on the cerebrovascular/cerebral blood flow (CBF) effects of NE. A search of MEDLINE, BIOSIS, EMBASE, Global Health, SCOPUS, and Cochrane Library from inception to December 2019 was performed. All manuscripts pertaining to the administration of NE, in which the impact on CBF/cerebral vasculature was recorded, were included. We identified 62 animal studies and 26 human studies. Overall, there was a trend to a direct vasoconstriction effect of NE on the cerebral vasculature, with conflicting studies having demonstrated both increases and decreases in regional CBF (rCBF) or global CBF. Healthy animals and those undergoing cardiopulmonary resuscitation demonstrated a dose-dependent increase in CBF with NE administration. However, animal models and human patients with acquired brain injury had varied responses in CBF to NE administration. The animal models indicate an increase in cerebral vasoconstriction with NE administration through the alpha receptors in vessels. Global and rCBF during the injection of NE displays a wide variation depending on treatment and model/patient.

Trans-ocular brain impedance index for assessment of cerebral autoregulation in a porcine model of cerebral hemodynamic perturbation

Cerebrovascular autoregulation (CA) is often impaired following traumatic brain injury. Established technologies and metrics used to assess CA are invasive and conducive for measurement, but not for continuous monitoring. We developed a trans-ocular brain impedance (TOBI) method that may provide non-invasive and continuous indices to assess CA. In this study, we monitored impedance metrics such as respiratory-induced impedance amplitude changes (dz) as well as a novel impedance index (DZx), which is a moving Pearson correlation between mean arterial pressure (MAP) and dz. Yorkshire swine were instrumented to continuously record ICP, MAP, and cerebral blood flow (CBF). TOBI was recorded by placement of standard ECG electrodes on closed eyelids and connected to a data acquisition system. MAP, ICP and CBF were manipulated utilizing an intravenous vasopressor challenge. TOBI indices (dz and DZx) were compared to the hemodynamic indicators as well as pressure reactivity index (PRx). During the vasopressor challenge, dz was highly correlated with ICP, CPP, and CBF (r =  < - 0.49, p < 0.0001). ICP, CPP, and CBF had a mean percent increase (standard deviation) from baseline of 29(23.2)%, 70(25)%, and 37(72.6)% respectively while dz decreased by 31(15.6)%. Receiver operator curve test showed high predictive performance of DZx when compared to PRx with area under the curve above 0.86, with high sensitivity and specificity. Impedance indices appear to track changes in PRx and hemodynamics that affect cerebral autoregulation. TOBI may be a suitable less invasive surrogate to PRx and capable of tracking cerebral autoregulation.

Steady-state cerebral autoregulation in older adults with amnestic mild cognitive impairment: linear mixed model analysis

We examined whether the efficacy of steady-state cerebral autoregulation (CA) is reduced in older adults with amnestic mild cognitive impairment (aMCI), a prodromal stage of clinical Alzheimer disease (AD). Forty-two patients with aMCI and 24 cognitively normal older adults (NC) of similar age, sex, and education underwent stepwise decreases and increases in mean arterial pressure (MAP) induced by intravenous infusion of sodium nitroprusside and phenylephrine, respectively. Changes in cerebral blood flow (CBF) were measured repeatedly in the internal carotid and vertebral artery. Linear mixed modeling, including random effects of both individual intercept and regression slope, was used to quantify the MAP-CBF relationship accounting for nonindependent, repeated CBF measures. Changes in end-tidal CO₂ (EtCO₂) associated with changes in MAP were also included in the model to account for their effects on CBF. Marginal mean values of MAP were reduced by 13-14 mmHg during sodium nitroprusside and increased by 20-24 mmHg during phenylephrine infusion in both groups with similar doses of drug infusion. A steeper slope of changes in CBF in response to changes in MAP was observed in aMCI relative to NC, indicating reduced efficacy of CA (MAP × Group, P = 0.040). These findings suggest that cerebrovascular dysfunction may occur early in the development of AD.NEW & NOTEWORTHY Cerebral autoregulation is a fundamental regulatory mechanism to protect brain perfusion against changes in blood pressure that, if impaired, may contribute to the development of Alzheimer's disease. Using a linear mixed model, we demonstrated that the efficacy of cerebral autoregulation, assessed during stepwise changes in arterial pressure, was reduced in individuals with amnestic mild cognitive impairment, a prodromal stage of Alzheimer's disease. These findings support the hypothesis that cerebrovascular dysfunction may be an important underlying pathophysiological mechanism for the development of clinical Alzheimer's disease.

Intercellular Conduction Optimizes Arterial Network Function and Conserves Blood Flow Homeostasis During Cerebrovascular Challenges

OBJECTIVE

Cerebral arterial networks match blood flow delivery with neural activity. Neurovascular response begins with a stimulus and a focal change in vessel diameter, which by themselves is inconsequential to blood flow magnitude, until they spread and alter the contractile status of neighboring arterial segments. We sought to define the mechanisms underlying integrated vascular behavior and considered the role of intercellular electrical signaling in this phenomenon. Approach and Results: Electron microscopic and histochemical analysis revealed the structural coupling of cerebrovascular cells and the expression of gap junctional subunits at the cell interfaces, enabling intercellular signaling among vascular cells. Indeed, robust vasomotor conduction was detected in human and mice cerebral arteries after focal vessel stimulation: a response attributed to endothelial gap junctional communication, as its genetic alteration attenuated this behavior. Conducted responses were observed to ascend from the penetrating arterioles, influencing the contractile status of cortical surface vessels, in a simulated model of cerebral arterial network. Ascending responses recognized in vivo after whisker stimulation were significantly attenuated in mice with altered endothelial gap junctional signaling confirming that gap junctional communication drives integrated vessel responses. The diminishment in vascular communication also impaired the critical ability of the cerebral vasculature to maintain blood flow homeostasis and hence tissue viability after stroke.

CONCLUSIONS

Our findings highlight the integral role of intercellular electrical signaling in transcribing focal stimuli into coordinated changes in cerebrovascular contractile activity and expose, a hitherto unknown mechanism for flow regulation after stroke.

Therapeutic-induced hypertension in patients with noncardioembolic acute stroke

OBJECTIVE

To evaluate the safety and efficacy of induced hypertension in patients with acute ischemic stroke.

METHODS

In this multicenter randomized clinical trial, patients with acute noncardioembolic ischemic stroke within 24 hours of onset who were ineligible for revascularization therapy and those with progressive stroke during hospitalization were randomly assigned (1:1) to the control and intervention groups. In the intervention group, phenylephrine was administered intravenously to increase systolic blood pressure (SBP) up to 200 mm Hg. The primary efficacy endpoint was early neurologic improvement (reduction in NIH Stroke Scale [NIHSS] score of ≥2 points during the first 7 days). The secondary efficacy endpoint was a modified Rankin Scale score of 0 to 2 at 90 days. Safety outcomes included symptomatic intracranial hemorrhage/edema, myocardial infarction, and death.

RESULTS

In the modified intention-to-treat analyses, 76 and 77 patients were included in the intervention and control groups, respectively. After adjustment for age and initial stroke severity, induced hypertension increased the occurrence of the primary (odds ratio 2.49, 95% confidence interval [CI] 1.25-4.96, p = 0.010) and secondary (odds ratio 2.97, 95% CI 1.32-6.68, p = 0.009) efficacy endpoints. Sixty-seven (88.2%) patients of the intervention group exhibited improvements in NIHSS scores of ≥2 points during induced hypertension (mean SBP 179·7 ± 19.1 mm Hg). Safety outcomes did not significantly differ between groups.

CONCLUSION

Among patients with noncardioembolic stroke who were ineligible for revascularization therapy and those with progressive stroke, phenylephrine-induced hypertension was safe and resulted in early neurologic improvement and long-term functional independence.

CLINICALTRIALSGOV IDENTIFIER

NCT01600235.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that for patients with acute ischemic stroke, therapeutic-induced hypertension increases the probability of early neurologic improvement.

Hypertensive Response to Ischemic Stroke in the Normotensive Wistar Rat

Background and Purpose—

Over 80% of ischemic stroke patients show an abrupt increase in arterial blood pressure in the hours and days following ischemic stroke. Whether this poststroke hypertension is beneficial or harmful remains controversial and the underlying physiological basis is unclear.

Methods—

To investigate the dynamic cardiovascular response to stroke, adult Wistar rats (n=5–8 per group, 393±34 g) were instrumented with telemeters to blood pressure, intracranial pressure, renal sympathetic nerve activity, and brain tissue oxygen in the predicted penumbra (P o 2 ). After 2 weeks of recovery, cardiovascular signals were recorded for a 3-day baseline period, then ischemic stroke was induced via transient middle cerebral artery occlusion, or sham surgery. Cardiovascular signals were then recorded for a further 10 days, and the functional sensorimotor recovery assessed using the cylinder and sticky dot tests.

Results—

Baseline values of all variables were similar between groups. Compared to sham, in the 2 days following stroke middle cerebral artery occlusion produced an immediate, transient rise above baseline in mean blood pressure (21±3 versus 2±4 mm Hg; P <0.001), renal sympathetic nerve activity (54±11% versus 7±4%; P =0.006), and cerebral perfusion pressure (12±5 versus 1±4; P ≤0.001). Intracranial pressure increased more slowly, peaking 3 days after middle cerebral artery occlusion (14±6 versus −1±1 mm Hg; P <0.001). Treating with the antihypertensive agent nifedipine after stroke (1.5–0.75 mg/kg per hour SC) ameliorated poststroke hypertension (12±3 mm Hg on day 1; P =0.041), abolished the intracranial pressure increase (3±1; P <0.001) and reduced cerebral perfusion pressure (10±3 mm Hg; P =0.017). Preventing poststroke hypertension affected neither the recovery of sensorimotor function nor infarct size.

Conclusions—

These findings suggest that poststroke hypertension is immediate, temporally matched to an increase in sympathetic outflow, and elevates cerebral perfusion pressure for several days after stroke, which may enhance cerebral perfusion. Preventing poststroke hypertension does not appear to worsen prognosis after stroke in young, normotensive, and otherwise healthy rats.

Visual Overview—

An online visual overview is available for this article.

Cerebral Blood Flow Response During Bolus Normal Saline Infusion After Ischemic Stroke

GOALS

We quantified cerebral blood flow response to a 500 cc bolus of 0.9%% normal saline (NS) within 96 hours of acute ischemic stroke (AIS) using diffuse correlation spectroscopy (DCS).

MATERIALS AND METHODS

Subjects with AIS in the anterior, middle, or posterior cerebral artery territory were enrolled within 96 hours of symptom onset. DCS measured relative cerebral blood flow (rCBF) in the bilateral frontal lobes for 15 minutes at rest (baseline), during a 30-minute infusion of 500 cc NS (bolus), and for 15 minutes after completion (post-bolus). Mean rCBF for each time period was calculated for individual subjects and median rCBF for the population was compared between time periods. Linear regression was used to evaluate for associations between rCBF and clinical features.

RESULTS

Among 57 subjects, median rCBF (IQR) increased relative to baseline in the ipsilesional hemisphere by 17% (-2.0%, 43.1%), P< 0.001, and in the contralesional hemisphere by 13.3% (-4.3%, 36.0%), P < .004. No significant associations were found between ipsilesional changes in rCBF and age, race, infarct size, infarct location, presence of large vessel stenosis, NIH stroke scale, or symptom duration.

CONCLUSION

A 500 cc bolus of .9% NS produced a measurable increase in rCBF in both the affected and nonaffected hemispheres. Clinical features did not predict rCBF response.

Central Noradrenergic Agonists in the Treatment of Ischemic Stroke-an Overview

Ischemic stroke is the leading cause of morbidity and mortality with a significant health burden worldwide and few treatment options. Among the short- and long-term effects of ischemic stroke is the cardiovascular sympathetic autonomic dysfunction, presented in part as the by-product of the ischemic damage to the noradrenergic centers of the brain. Unlike high levels in the plasma, the brain may face suboptimal levels of norepinephrine (NE), with adverse effects on the clinical and functional outcomes of ischemic stroke. The intravenous administration of NE and other sympathomimetic agents, in an attempt to increase cerebral perfusion pressure, often aggravates the ischemia-induced rise in blood pressure (BP) with life-threatening consequences for stroke patients, the majority of whom present with hypertension at the time of admission. Unlike the systemic administration, the central administration of NE reduces BP while exerting anti-inflammatory and neuroprotective effects. These characteristics of centrally administered NE, combined with the short latency of response, make it an ideal candidate for use in the acute phase of stroke, followed by the use of centrally acting noradrenergic agonists, such as NE reuptake inhibitors and B2-adrenergic receptor agonists for stroke rehabilitation. In addition, a number of nonpharmacological strategies, such as transcutaneous vagus nerve stimulation (tVNS) and trigeminal nerve stimulation (TNS), have the potential to enhance the central noradrenergic functional activities and improve stroke clinical outcomes. Many factors could influence the efficacy of the noradrenergic treatment in stroke patients. These factors include the type of the noradrenergic agent; the dose, frequency, and duration of administration; the timing of administration in relation to the acute event; and the site and characteristics of the ischemic lesions. Having this knowledge, combined with the better understanding of the regulation of noradrenergic receptors in different parts of the brain, would pave the path for the successful use of the centrally acting noradrenergic agents in the management of ischemic stroke.

Alterations in the coupling functions between cerebral oxyhaemoglobin and arterial blood pressure signals in post-stroke subjects

Cerebral autoregulation (CA) is the complex homeostatic regulatory relationship between blood pressure (BP) and cerebral blood flow (CBF). This study aimed to analyze the frequency-specific coupling function between cerebral oxyhemoglobin concentrations (delta [HbO₂]) and mean arterial pressure (MAP) signals based on a model of coupled phase oscillators and dynamical Bayesian inference. Delta [HbO₂] was measured by 24-channel near-infrared spectroscopy (NIRS) and arterial BP signals were obtained by simultaneous resting-state measurements in patients with stroke, that is, 9 with left hemiparesis (L–H group), 8 with right hemiparesis (R–H group), and 17 age-matched healthy individuals as control (healthy group). The coupling functions from MAP to delta [HbO₂] oscillators were identified and analyzed in four frequency intervals (I, 0.6–2 Hz; II, 0.145–0.6 Hz; III, 0.052–0.145 Hz; and IV, 0.021–0.052 Hz). In L–H group, the CS from MAP to delta [HbO₂] in interval III in channel 8 was significantly higher than that in healthy group (p = 0.003). Compared with the healthy controls, the coupling in MAP→delta [HbO₂] showed higher amplitude in interval I and IV in patients with stroke. The increased CS and coupling amplitude may be an evidence of impairment in CA, thereby confirming the presence of impaired CA in patients with stroke. In interval III, the CS in L–H group from MAP to delta [HbO₂] in channel 16 (p = 0.001) was significantly lower than that in healthy controls, which might indicate the compensatory mechanism in CA of the unaffected side in patients with stroke. No significant difference in region-wise CS between affected and unaffected sides was observed in stroke groups, indicating an evidence of globally impaired CA. These findings provide a method for the assessment of CA and will contribute to the development of therapeutic interventions in stroke patients.

Blood Pressure and Penumbral Sustenance in Stroke from Large Vessel Occlusion

The global burden of stroke remains high, and of the various subtypes of stroke, large vessel occlusions (LVOs) account for the largest proportion of stroke-related death and disability. Several randomized controlled trials in 2015 changed the landscape of stroke care worldwide, with endovascular thrombectomy (ET) now the standard of care for all eligible patients. With the proven success of this therapy, there is a renewed focus on penumbral sustenance. In this review, we describe the ischemic penumbra, collateral circulation, autoregulation, and imaging assessment of the penumbra. Blood pressure goals in acute stroke remain controversial, and we review the current data and suggest an approach for induced hypertension in the acute treatment of patients with LVOs. Finally, in addition to reperfusion and enhanced perfusion, efforts focused on developing therapeutic targets that afford neuroprotection and augment neural repair will gain increasing importance. ET has revolutionized stroke care, and future emphasis will be placed on promoting penumbral sustenance, which will increase patient eligibility for this highly effective therapy and reduce overall stroke-related death and disability.

Enhancing cerebral perfusion with external counterpulsation after ischaemic stroke: how long does it last?

OBJECTIVE

External counterpulsation (ECP) is a non-invasive method used to augment cerebral perfusion in ischaemic stroke. We aimed to investigate time-course effects on blood pressure elevation and cerebral blood flow augmentation induced by ECP in ischaemic stroke.

METHODS

Patients with acute unilateral ischaemic stroke and large artery occlusive disease were recruited to receive 35 daily 1 h ECP treatment sessions. Serial transcranial Doppler monitoring of bilateral middle cerebral arteries was performed on days 3, 5, 7, 10, 14, 21, 28 and 35 after stroke onset. Flow velocity changes before, during and after ECP and continuous beat-to-beat blood pressure data were recorded. The cerebral augmentation index (CAI) is the increase in the percentage of the middle cerebral artery mean flow velocity during ECP compared with baseline.

RESULTS

The CAI in patients with stroke was significantly higher on the ipsilateral side and on the contralateral side on day 3 (ipsilateral CAI, 9.3%; contralateral CAI, 7.2%), day 5 (7.0%; 6.7%), day 7 (6.8%; 6.0%), day 10 (6.0%; 5.1%), day 14 (4.7%; 2.6%) and day 21 (4.1%; 2.2%) after stroke onset than that in controls (-2.0%) (all p<0.05). There was a significant trend of decreasing CAI on the ipsilateral and contralateral sides over time after a stroke. Differences in the percentage increase in the mean blood pressure did not change significantly over time in patients with stroke.

CONCLUSIONS

Blood pressure elevation persists throughout ECP treatment, which consists of 35 sessions. However, cerebral blood flow augmentation may last at least 3 weeks and then appears to return to baseline 1 month after acute stroke onset.

Evidence-based guidelines for the management of large hemispheric infarction : a statement for health care professionals from the Neurocritical Care Society and the German Society for Neuro-intensive Care and Emergency Medicine

Large hemispheric infarction (LHI), also known as malignant middle cerebral infarction, is a devastating disease associated with significant disability and mortality. Clinicians and family members are often faced with a paucity of high quality clinical data as they attempt to determine the most appropriate course of treatment for patients with LHI, and current stroke guidelines do not provide a detailed approach regarding the day-to-day management of these complicated patients. To address this need, the Neurocritical Care Society organized an international multidisciplinary consensus conference on the critical care management of LHI. Experts from neurocritical care, neurosurgery, neurology, interventional neuroradiology, and neuroanesthesiology from Europe and North America were recruited based on their publications and expertise. The panel devised a series of clinical questions related to LHI, and assessed the quality of data related to these questions using the Grading of Recommendation Assessment, Development and Evaluation guideline system. They then developed recommendations (denoted as strong or weak) based on the quality of the evidence, as well as the balance of benefits and harms of the studied interventions, the values and preferences of patients, and resource considerations.

Cerebral collaterals and collateral therapeutics for acute ischemic stroke

Cerebral collaterals are vascular redundancies in the cerebral circulation that can partially maintain blood flow to ischemic tissue when primary conduits are blocked. After occlusion of a cerebral artery, anastomoses connecting the distal segments of the MCA with distal branches of the ACA and PCA (known as leptomeningeal or pial collaterals) allow for partially maintained blood flow in the ischemic penumbra and delay or prevent cell death. However, collateral circulation varies dramatically between individuals, and collateral extent is significant predictor of stroke severity and recanalization rate. Collateral therapeutics attempt to harness these vascular redundancies by enhancing blood flow through pial collaterals to reduce ischemia and brain damage after cerebral arterial occlusion. While therapies to enhance collateral flow remain relatively nascent neuroprotective strategies, experimental therapies including inhaled NO, transient suprarenal aortic occlusion, and electrical stimulation of the parasympathetic sphenopalatine ganglion show promise as collateral therapeutics with the potential to improve treatment of acute ischemic stroke.

Intracranial pressure elevation after ischemic stroke in rats: cerebral edema is not the only cause, and short-duration mild hypothermia is a highly effective preventive therapy

In both the human and animal literature, it has largely been assumed that edema is the primary cause of intracranial pressure (ICP) elevation after stroke and that more edema equates to higher ICP. We recently demonstrated a dramatic ICP elevation 24 hours after small ischemic strokes in rats, with minimal edema. This ICP elevation was completely prevented by short-duration moderate hypothermia soon after stroke. Here, our aims were to determine the importance of edema in ICP elevation after stroke and whether mild hypothermia could prevent the ICP rise. Experimental stroke was performed in rats. ICP was monitored and short-duration mild (35 °C) or moderate (32.5 °C) hypothermia, or normothermia (37 °C) was induced after stroke onset. Edema was measured in three studies, using wet-dry weight calculations, T2-weighted magnetic resonance imaging, or histology. ICP increased 24 hours after stroke onset in all normothermic animals. Short-duration mild or moderate hypothermia prevented this rise. No correlation was seen between ΔICP and edema or infarct volumes. Calculated rates of edema growth were orders of magnitude less than normal cerebrospinal fluid production rates. These data challenge current concepts and suggest that factors other than cerebral edema are the primary cause of the ICP elevation 24 hours after stroke onset.

Medical Management of Patients with an Acute Stroke: Treatment and Prevention

Stroke is a common and serious disorder and will probably occur with increasing frequency due to an aging of the population. Acute therapies aimed at reversing the effects of acute ischemic stroke are limited to recombinant tissue plasminogen activator administered intravenously within 3 hours of stroke onset. Neuroprotective agents and acute anticoagulation with agents such as heparinoids and heparin are not effective in most cases. Poststroke medical complications such as infection and venous thromboembolism are common but are largely preventable. A variety of medical therapies such as antiplatelet agents, warfarin, statins, and ACE inhibitors can reduce the risk of a recurrent stroke. A key aspect of management for stroke is selection of the proper treatment regimen for each patient.

Optical bedside monitoring of cerebral blood flow in acute ischemic stroke patients during head-of-bed manipulation

BACKGROUND AND PURPOSE

A primary goal of acute ischemic stroke (AIS) management is to maximize perfusion in the affected region and surrounding ischemic penumbra. However, interventions to maximize perfusion, such as flat head-of-bed (HOB) positioning, are currently prescribed empirically. Bedside monitoring of cerebral blood flow (CBF) allows the effects of interventions such as flat HOB to be monitored and may ultimately be used to guide clinical management.

METHODS

Cerebral perfusion was measured during HOB manipulations in 17 patients with unilateral AIS affecting large cortical territories in the anterior circulation. Simultaneous measurements of frontal CBF and arterial flow velocity were performed with diffuse correlation spectroscopy and transcranial Doppler ultrasound, respectively. Results were analyzed in the context of available clinical data and a previous study.

RESULTS

Frontal CBF, averaged over the patient cohort, decreased by 17% (P=0.034) and 15% (P=0.011) in the ipsilesional and contralesional hemispheres, respectively, when HOB was changed from flat to 30°. Significant (cohort-averaged) changes in blood velocity were not observed. Individually, varying responses to HOB manipulation were observed, including paradoxical increases in CBF with increasing HOB angle. Clinical features, stroke volume, and distance to the optical probe could not explain this paradoxical response.

CONCLUSIONS

A lower HOB angle results in an increase in cortical CBF without a significant change in arterial flow velocity in AIS, but there is variability across patients in this response. Bedside CBF monitoring with diffuse correlation spectroscopy provides a potential means to individualize interventions designed to optimize CBF in AIS.

Chinese consensus statement on the evaluation and intervention of collateral circulation for ischemic stroke

Background

Collateral circulation is becoming more significant in the individual management strategy of ischemic stroke, there are more data updated recently.

Aim

To make the further acknowledgment of the evaluation and how to improving collateral flow, for better treatment selection.

Method

A panel of experts on stroke providing related statement based on review the results from most up‐to‐date clinical research.

Results

DSA is the gold standard in evaluating all levels of collaterals. CTA can be used for evaluating leptomeningeal collaterals, MRA for CoW, TCD or TCCS can be used as screening tool for primary evaluation. The treatment modalities include direct interventions, such as Extracranial–Intracranial bypass, and indirect interventions, as External counterpulsation and pressor therapy. The consideration of methodology to augment and improve can be considered on an individual basis.

Discussion

In this consensus, we interpret the definition, neuroimaging evaluation, intervention and potential strategy on collaterals in the future.

Conclusion

Assessment of collateral circulation is crucial for selecting therapeutic options, predicting infarction volume and making prognosis after ischemic stroke. Data is still needed to provide therapeutic evidence for many new developed technologies. Until more evidence is available, the clinical significance of applying the new technologies is unclear and perhaps limited.

Augmenting collateral blood flow during ischemic stroke via transient aortic occlusion

Collateral circulation provides an alternative route for blood flow to reach ischemic tissue during a stroke. Blood flow through the cerebral collaterals is a critical predictor of clinical prognosis after stroke and response to recanalization, but data on collateral dynamics and collateral therapeutics are lacking. Here, we investigate the efficacy of a novel approach to collateral blood flow augmentation to increase collateral circulation by optically recording blood flow in leptomeningeal collaterals in a clinically relevant model of ischemic stroke. Using high-resolution laser speckle contrast imaging (LSCI) during thromboembolic middle cerebral artery occlusion (MCAo), we demonstrate that transiently diverting blood flow from peripheral circulation towards the brain via intra-aortic catheter and balloon induces persistent increases in blood flow through anastomoses between the anterior and middle cerebral arteries. Increased collateral flow restores blood flow in the distal middle cerebral artery segments to baseline levels during aortic occlusion and persists for over 1 hour after removal of the aortic balloon. Given the importance of collateral circulation in predicting stroke outcome and response to treatment, and the potential of collateral flow augmentation as an adjuvant or stand-alone therapy for acute ischemic stroke, this data provide support for further development and translation of collateral therapeutics including transient aortic occlusion.

Vascular remodeling after ischemic stroke: mechanisms and therapeutic potentials

The brain vasculature has been increasingly recognized as a key player that directs brain development, regulates homeostasis, and contributes to pathological processes. Following ischemic stroke, the reduction of blood flow elicits a cascade of changes and leads to vascular remodeling. However, the temporal profile of vascular changes after stroke is not well understood. Growing evidence suggests that the early phase of cerebral blood volume (CBV) increase is likely due to the improvement in collateral flow, also known as arteriogenesis, whereas the late phase of CBV increase is attributed to the surge of angiogenesis. Arteriogenesis is triggered by shear fluid stress followed by activation of endothelium and inflammatory processes, while angiogenesis induces a number of pro-angiogenic factors and circulating endothelial progenitor cells (EPCs). The status of collaterals in acute stroke has been shown to have several prognostic implications, while the causal relationship between angiogenesis and improved functional recovery has yet to be established in patients. A number of interventions aimed at enhancing cerebral blood flow including increasing collateral recruitment are under clinical investigation. Transplantation of EPCs to improve angiogenesis is also underway. Knowledge in the underlying physiological mechanisms for improved arteriogenesis and angiogenesis shall lead to more effective therapies for ischemic stroke.

Transcranial ultrasound analysis of cerebral blood flow during induced hypertension in acute ischemic stroke - a case series

Background

Current recommendations of stroke treatment favour a moderately elevated blood pressure in the acute phase, based on the concept of an improved cerebral perfusion. Here, cerebral blood flow was assessed in a case series of patients with acute hemodynamic stroke by means of transcranial colour-coded sonography (TCCS) to study the effects of pharmacologically induced hypertension.

Findings

We investigated six patients with acute hemodynamic stroke and blood pressure-dependent clinical fluctuation of neurological symptoms. TCCS was performed during the initiation phase of catecholamine-induced controlled hypertension. A blood pressure-dependent increase of flow velocity in the ipsilesional middle and the posterior cerebral artery was found in all patients (mean increase 0.80% and 0.65% per mmHg, respectively).

Conclusions

Catecholamine-induced hypertension in severe hemodynamic stroke leads to an ultrasound-detectable rise of cerebral blood flow. This finding gives ‘proof-of-principle’ evidence, supporting active blood pressure management in this selected group of stroke patients. Outcome-related questions of target blood pressure, treatment duration or applicability to other forms of stroke, however, remain to be studied. In this, transcranial ultrasound may be a valuable tool for patient selection and subsequent bedside monitoring.

External counterpulsation augments blood pressure and cerebral flow velocities in ischemic stroke patients with cerebral intracranial large artery occlusive disease

BACKGROUND AND PURPOSE

External counterpulsation (ECP) is a novel noninvasive method used to improve the perfusion of vital organs, which may benefit ischemic stroke patients. We hypothesized that ECP may augment cerebral blood flow of ischemic stroke patients via induced hypertension.

METHODS

We recruited ischemic stroke patients with cerebral intracranial large artery occlusive disease and healthy elderly controls into this study. Bilateral middle cerebral arteries of subjects were monitored using transcranial Doppler. Flow velocity changes before, during, and after ECP were, respectively, recorded for 3 minutes while continuous beat-to-beat blood pressure data were recorded. Cerebral augmentation index was the increase in percentage of middle cerebral artery mean flow velocity during ECP compared with baseline. Transcranial Doppler data were analyzed based on ipsilateral or contralateral to the infarct side.

RESULTS

ECP significantly increased mean blood pressure of stroke patients and controls. During ECP, middle cerebral artery mean flow velocities of stroke patients increased on both ipsilateral and contralateral sides when compared with baseline (ipsilateral cerebral augmentation index, 9.64%; contralateral cerebral augmentation index, 9%; both P<0.001), but there was no increase in difference between the 2 sides when compared with each other. Mean flow velocities of controls did not change under ECP. After ECP, blood pressure and flow velocity of stroke patients returned to baseline level.

CONCLUSIONS

ECP provides a new method of cerebral blood flow augmentation in ischemic stroke by elevation of blood pressure. Flow augmentation induced by ECP suggests the improvement of cerebral perfusion and collateral supply from infarct ipsilateral and contralateral sides.

Sulcal effacement on fluid attenuation inversion recovery magnetic resonance imaging in hyperacute stroke: association with collateral flow and clinical outcomes

BACKGROUND AND PURPOSE

The clinical significance of sulcal effacement has been widely investigated in CT studies, but the results are controversial. In this study, we evaluated the presence of perisylvian sulcal effacement (PSE) on fluid attenuation inversion recovery MRI and hypothesized that PSE may be related to collateral flow status together with hyperintense vessels on fluid attenuation inversion recovery in hyperacute stroke. In addition, we investigated whether an association between PSE and clinical outcome could be found in these patients.

METHODS

Consecutive patients with acute middle cerebral artery infarcts within 6 hours of symptom onset were included. All patients had internal carotid artery or middle cerebral artery occlusion and underwent MRI including FLAIR. The presence of PSE and hyperintense vessels on fluid attenuation inversion recovery and the collateral status and occurrence of early recanalization (ER) on conventional angiography were evaluated.

RESULTS

Of 139 patients, 79 (56.8%) had PSE. Multivariate testing revealed PSE was independently associated with collateral status. The association between hyperintense vessels and collaterals was different depending on PSE. Compared to PSE-positive and ER-negative patients, PSE-negative and ER-negative patients (odds ratio, 4.11; 95% confidence interval, 1.12-15.17) and PSE-negative and ER-positive patients (odds ratio, 34.62; 95% confidence interval, 5.75-208.60), but not PSE-positive and ER-positive patients, were more likely to experience favorable clinical outcomes (modified Rankin Scale score ≤ 2 at 3 months).

CONCLUSIONS

PSE is independently associated with collateral status in patients with acute middle cerebral artery stroke. Moreover, PSE in conjunction with recanalization status can predict clinical outcomes in these patients.

Cerebral autoregulation in stroke: a review of transcranial Doppler studies

BACKGROUND AND PURPOSE

Cerebral autoregulation may become impaired after stroke. To provide a review of the nature and extent of any autoregulation impairment after stroke and its course over time, a technique allowing repeated bedside measurements with good temporal resolution is required. Transcranial Doppler (TCD) in combination with continuous blood pressure measurements allows noninvasive continuous bedside investigation with high temporal resolution of the dynamic and the steady-state components of cerebral autoregulation. Therefore, this review focuses on all TCD studies on cerebral autoregulation in the setting of documented ischemic stroke.

METHODS

PubMed and EMBASE were searched for studies of stroke, autoregulation, and TCD. Studies were either acute phase (<96 hours after index stroke) or chronic phase (>96 hours after index stroke) autoregulation studies. Quality of studies was studied in a standardized fashion.

RESULTS

Twenty-three studies met the inclusion criteria. General agreement existed on cerebral autoregulation being impaired, even after minor stroke. Bilateral impairment of autoregulation was documented, particularly after lacunar stroke. Studies showed progressive deterioration of cerebral autoregulation in the first 5 days after stroke and recovery over the next 3 months. Impaired cerebral autoregulation as assessed by TCD was related to neurological deterioration, the necessity for decompressive surgery, and poor outcome. Synthesis of the data of various studies was, however, limited by studies not meeting key methodological criteria for observational studies.

CONCLUSIONS

TCD in combination with continuous blood pressure measurement offers a method with a high temporal resolution feasible for bedside evaluation of cerebral autoregulation in the stroke unit. TCD studies have shown impairment of cerebral autoregulation in various subtypes of ischemic stroke. To improve the synthesis of data from various research groups, there is urgent need for standardization of methodology of TCD studies in cerebral autoregulation.

Hyperacute ischemic stroke management: reperfusion and evolving therapies

Management of acute ischemic stroke patients is organized around several priorities aimed at ensuring optimal patient outcomes, the first of which is reperfusion therapy, followed by determination of pathogenic mechanism by provision of a comprehensive workup to determine probable cause of the ischemic stroke or transient ischemic attack, for the purpose of providing appropriate prophylaxis for subsequent events. Provision of secondary prevention measures along with therapies that prevent complications associated with neurologic disability, and evaluation for the most appropriate level of rehabilitation services are the final priorities during acute hospitalization. This article provides an overview of reperfusion therapies and emerging hemodynamic treatments for hyperacute ischemic strokes. Gaps in the scientific evidence that are driving current blood flow augmentation research are identified.

Influence of changes in blood pressure on cerebral perfusion and oxygenation

Cerebral autoregulation (CA) is a critical process for the maintenance of cerebral blood flow and oxygenation. Assessment of CA is frequently used for experimental research and in the diagnosis, monitoring, or prognosis of cerebrovascular disease; however, despite the extensive use and reference to static CA, a valid quantification of "normal" CA has not been clearly identified. While controlling for the influence of arterial Pco(2), we provide the first clear examination of static CA in healthy humans over a wide range of blood pressure. In 11 healthy humans, beat-to-beat blood pressure (radial arterial), middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), end-tidal Pco(2), and cerebral oxygenation (near infrared spectroscopy) were recorded continuously during pharmacological-induced changes in mean blood pressure. In a randomized order, steady-state decreases and increases in mean blood pressure (8 to 14 levels; range: approximately 40 to approximately 125 mm Hg) were achieved using intravenous infusions of sodium nitroprusside or phenylephrine, respectively. MCAv(mean) was altered by 0.82+/-0.35% per millimeter of mercury change in mean blood pressure (R(2)=0.82). Changes in cortical oxygenation index were inversely related to changes in mean blood pressure (slope=-0.18%/mm Hg; R(2)=0.60) and MCAv(mean) (slope=-0.26%/cm . s(-1); R(2)=0.54). There was a progressive increase in MCAv pulsatility with hypotension. These findings indicate that cerebral blood flow closely follows pharmacological-induced changes in blood pressure in otherwise healthy humans. Thus, a finite slope of the plateau region does not necessarily imply a defective CA. Moreover, with progressive hypotension and hypertension there are differential changes in cerebral oxygenation and MCAv(mean).

Cerebral flow velocities during daily activities depend on blood pressure in patients with chronic ischemic infarctions

BACKGROUND AND PURPOSE

Target blood pressure (BP) values for optimal cerebral perfusion after an ischemic stroke are still debated. We sought to examine the relationship between BP and cerebral blood flow velocities (BFVs) during daily activities.

METHODS

We studied 43 patients with chronic large vessel ischemic infarctions in the middle cerebral artery territory (aged 64.2+/-8.94 years; at 6.1+/-4.9 years after stroke) and 67 age-matched control subjects. BFVs in middle cerebral arteries were measured during supine baseline, sitting, standing, and tilt. A regression analysis and a dynamic phase analysis were used to quantify the BP-BFV relationship.

RESULTS

The mean arterial pressure was similar between the groups (89+/-15 mm Hg). Baseline BFVs were lower by approximately 30% in the patients with stroke compared with the control subjects (P=0.0001). BFV declined further with postural changes and remained lower in the stroke group during sitting (P=0.003), standing (P=0.003), and tilt (P=0.002) as compared with the control group. Average BFVs on the stroke side were positively correlated with BP during baseline (R=0.54, P=0.0022, the slope 0.46 cm/s/mm Hg) and tilt (R=0.52, P=0.0028, the slope 0.40 cm/s/mm Hg). Regression analysis suggested that BFV may increase approximately 30% to 50% at mean BP >100 mm Hg. Orthostatic hypotension during the first minute of tilt or standing was independently associated with lower BFV on the stroke side (P=0.0008). Baseline BP-BFV phase shift derived from the phase analysis was smaller on the stroke side (P=0.0006).

CONCLUSIONS

We found that BFVs are lower in patients with stroke and daily activities such as standing could induce hypoperfusion. BFVs increase with mean arterial pressure >100 mm Hg. Dependency of BFV on arterial pressure may have implications for BP management after stroke. Further prospective investigations are needed to determine the impact of these findings on functional recovery and strategies to improve perfusion pressure during daily activities after ischemic stroke.

Role of vasopressor administration in patients with acute neurologic injury

INTRODUCTION

Pharmacologic blood pressure elevation is often utilized to prevent or treat ischemia in patients with acute neurologic injury, and routinely requires administration of vasopressor agents. Depending on the indication, vasopressor agents may be administered to treat hypotension or to induce hypertension.

METHODS

Although numerous guideline statements exist regarding the management of blood pressure in these patients, most recommendations are based largely on Class III evidence. Further, there are few randomized controlled trials comparing vasopressor agents in these patients and selection is often guided by expert consensus.

RESULTS

We discuss the clinical evidence regarding vasopressor administration for blood pressure management in patients with acute neurologic injury. The effect of various vasopressors on cerebral hemodynamics is also discussed.

CONCLUSION

Although high-quality clinical data are scarce, the available evidence suggests that norepinephrine should be considered as the vasopressor of choice when blood pressure elevation is indicated in patients with acute neurologic injury.

Mild induced hypertension improves blood flow and oxygen metabolism in transient focal cerebral ischemia

BACKGROUND AND PURPOSE

In focal ischemic cortex, cerebral blood flow autoregulation is impaired, and perfusion passively follows blood pressure variations. Although it is generally agreed that profound hypotension is harmful in acute stroke, the hemodynamic and metabolic impact of increased blood pressure on the ischemic core and penumbra are less well understood. We, therefore, tested whether pharmacologically induced hypertension improves cerebral blood flow and metabolism and tissue outcome in acute stroke using optical imaging with high spatiotemporal resolution.

METHODS

Cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen were measured noninvasively using simultaneous multispectral reflectance imaging and laser speckle flowmetry during distal middle cerebral artery occlusion in mice. Hypertension was induced by phenylephrine infusion starting 10 or 60 minutes after ischemia to raise blood pressure by 30% for the duration of ischemia; control groups received saline infusion.

RESULTS

Mild induced hypertension rapidly increased cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen in both the core and penumbra and prevented the expansion of cerebral blood flow deficit during 1 hour distal middle cerebral artery occlusion. Induced hypertension also diminished the deleterious effects of periinfarct depolarizations on cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen without altering their frequency. Consistent with this, mild induced hypertension reduced infarct volume by 48% without exacerbating tissue swelling when measured 2 days after 1 hour transient distal middle cerebral artery occlusion.

CONCLUSIONS

Our data suggest that mild induced hypertension increases collateral cerebral blood flow and oxygenation and improves cerebral metabolic rate of oxygen in the core and penumbra, supporting its use as bridging therapy in acute ischemic stroke until arterial recanalization is achieved.

Blood pressure augmentation in acute ischemic stroke

Although control of hypertension is established as an important factor in the primary and secondary prevention of stroke, management of blood pressure in the setting of acute ischemic stroke remains controversial. Given limited data, the general consensus is that there is no proven benefit to lowering blood pressure in the first hours to days after acute ischemic stroke. Instead, there is concern that relative hypotension may lead to worsening of cerebral ischemia. For many years, the use of blood pressure augmentation ("induced hypertension") has been studied in animal models and in humans as a means of maintaining or improving perfusion to ischemic brain tissue. This approach is now widely used in neurocritical care units to treat delayed neurological deficits after subarachnoid hemorrhage, but its use in ischemic stroke patients remains anecdotal. This article reviews the cerebral physiology, animal models and human studies of induced hypertension as a treatment for acute ischemic stroke. Although there has not been a large, randomized clinical trial of this treatment, the available clinical data suggests that induced hypertension can result in at least short-term neurological improvement, with an acceptable degree of safety.