An update to the Monro-Kellie doctrine to reflect tissue compliance after severe ischemic and hemorrhagic stroke

Noninvasive Method Using Mechanical Extensometer for the Estimation of Intracranial Compliance by Repeated Measures Agreement Analysis

BACKGROUND

Intracranial compliance refers to the relationship between changes in volume and the resultant changes in intracranial pressure (ICP). This study aimed to assess the agreement of a noninvasive ICP waveform device for the estimation of compliance compared with invasive ICP monitoring employing three distinct methods.

METHODS

We conducted a retrospective analysis of ICP waveform morphology recorded through both invasive (external ventricular drain) and noninvasive (mechanical extensometer) methods in adult patients with acute brain injury admitted to a neurointensive care unit between August 2021 and August 2022. Compliance was calculated as the amplitude of the fundamental component of cerebral arterial blood volume (estimated with concurrent Transcranial Doppler [TCD] recordings), divided by the amplitude of the fundamental component of the invasive and noninvasive ICP waveforms. Subsequently, we assessed the agreement between invasive and noninvasive intracranial compliance by repeated measures correlation coefficient analysis using three methods: TCD-derived, P2/P1 ratio, and time-to-peak (TTP). A linear mixed-effects model was used to compute the concordance correlation coefficient, total deviation index, and coefficient of individual agreement. Coverage probability plot was calculated to estimate the percent of observations within different cut points for each of the three methods.

RESULTS

A total of 21 patients were identified for this study. Repeated measures correlation analysis showed a strong correlation (R = 0.982, 95% confidence interval [0.980-0.984], p < 0.0001) between log-transformed noninvasive and invasive compliance. Agreement statistics for TCD, P2/P1 ratio, and TTP indicated that although the concordance correlation coefficient was highest for log(TCD) values, TTP and P2:P1 ratio measures had better agreement with total deviation index and coverage probability plot analyses.

CONCLUSIONS

Repeated measures correlations suggest that ICP waveform analyses may offer a more accurate estimate of compliance than TCD-derived methods for noninvasive ICP monitoring. Further validations studies are warranted to confidently establish this method as an indicator of intracranial compliance.

A retrospective case-control study evaluating systemic blood pressure and heart rate in dogs with brain herniation under general anesthesia

OBJECTIVE

To examine whether increased systemic arterial blood pressure (ABP) and decreased heart rate (HR) under inhalant anesthesia were suggestive of the Cushing reflex (CR) in dogs with neurological diseases based on magnetic resonance imaging (MRI) findings.

STUDY DESIGN

Retrospective case-control study.

ANIMALS

A sample of 137 client-owned dogs admitted to two veterinary teaching hospitals for diagnosis and patient care owing to suspected intracranial disease from 2005 to 2020. All dogs underwent general anesthesia for MRI of the brain.

METHODS

Based on MRI study reports, dogs were divided into three study groups: group A, dogs with suspected brain herniation; group B, dogs with an abnormal MRI finding but without suspicion of herniation; and group C, dogs with structurally unremarkable brains (control). Initial evaluation by an anesthesiologist resulted in 58 cases selected for further review based on suspicion of having intracranial hypertension, as indicated by ABP and HR changes under anesthesia. Anesthetic records were randomized and independently reviewed by three board-certified anesthesiologists blinded to MRI diagnosis who allocated each dog into one of three groups: 1) likely to have CR; 2) unlikely to have CR; or 3) insufficient data for determination.

RESULTS

Of the 58 cases evaluated, nine were considered likely to have CR and 48 were considered unlikely to have CR. In one case, the anesthesiologists were unable to determine whether CR occurred. Of the nine dogs with likely CR, three had an MRI diagnosis of intracranial herniation. The remaining six dogs suspected of CR belonged to the normal brain group.

CONCLUSIONS AND CLINICAL RELEVANCE

The ABP and HR changes associated with CR are not reliably associated with brain herniation in dogs undergoing general anesthesia.

Review of the Brain's Behaviour after Injury and Disease for Its Application in an Agent-Based Model (ABM)

The brain is the most complex organ in the human body and, as such, its study entails great challenges (methodological, theoretical, etc.). Nonetheless, there is a remarkable amount of studies about the consequences of pathological conditions on its development and functioning. This bibliographic review aims to cover mostly findings related to changes in the physical distribution of neurons and their connections-the connectome-both structural and functional, as well as their modelling approaches. It does not intend to offer an extensive description of all conditions affecting the brain; rather, it presents the most common ones. Thus, here, we highlight the need for accurate brain modelling that can subsequently be used to understand brain function and be applied to diagnose, track, and simulate treatments for the most prevalent pathologies affecting the brain.

Hemorrhage Volume Drives Early Brain Injury and Outcome in Poor-Grade Aneurysmal SAH

BACKGROUND AND PURPOSE

Early brain injury is a major determinant of clinical outcome in poor-grade (World Federation of Neurosurgical Societies [WFNS] IV-V) aneurysmal SAH and is radiologically defined by global cerebral edema. Little is known, though, about the effect of global intracranial hemorrhage volume on early brain injury development and clinical outcome.

MATERIALS AND METHODS

Data from the multicentric prospective Poor-Grade Aneurysmal Subarachnoid Hemorrhage (POGASH) Registry of consecutive patients with poor-grade aneurysmal SAH admitted from January 1, 2015, to August 31, 2022, was retrospectively evaluated. Poor grade was defined according to the worst-pretreatment WFNS grade. Global intracranial hemorrhage volume as well as the volumes of intracerebral hemorrhage, intraventricular hemorrhage, and SAH were calculated by means of analytic software in a semiautomated setting. Outcomes included severe global cerebral edema (defined by Subarachnoid Hemorrhage Early Brain Edema Score grades 3-4), in-hospital mortality (mRS 6), and functional independence (mRS 0-2) at follow-up.

RESULTS

Among 400 patients (median global intracranial hemorrhage volume of 91 mL; interquartile range, 59-128), severe global cerebral edema was detected in 218/400 (54.5%) patients. One hundred twenty-three (30.8%) patients died during the acute phase of hospitalization. One hundred fifty-five (38.8%) patients achieved mRS 0-2 at a median of 13 (interquartile range, 3-26) months of follow-up. Multivariable analyses showed global intracranial hemorrhage volume as independently associated with severe global cerebral edema (adjusted OR, 1.009; 95% CI, 1.004-1.014; P < .001), mortality (adjusted OR, 1.006; 95% CI, 1.001-1.01; P = .018) and worse clinical outcome (adjusted OR, 0.992; 95% CI, 0.98-0.996; P < .010). The effect of global intracranial hemorrhage volume on clinical-radiologic outcomes changed significantly according to different age groups (younger than 50, 50-70, older than 70 year of age). Volumes of intracerebral hemorrhage, intraventricular hemorrhage, and SAH affected the 3 predefined outcomes differently. Intracerebral hemorrhage volume independently predicted global cerebral edema and long-term outcome, intraventricular hemorrhage volume predicted mortality and long-term outcome, and SAH volume predicted long-term clinical outcome.

CONCLUSIONS

Global intracranial hemorrhage volume plays a pivotal role in global cerebral edema development and emerged as an independent predictor of both mortality and long-term clinical outcome. Aging emerged as a reducing predictor in the relationship between global intracranial hemorrhage volume and global cerebral edema.

Intraorbital pressure-volume characteristics in a piglet model: In vivo pilot study

Intracranial pressure measurement is frequently used for diagnosis in neurocritical care but cannot always accurately predict neurological deterioration. Intracranial compliance plays a significant role in maintaining cerebral blood flow, cerebral perfusion pressure, and intracranial pressure. This study's objective was to investigate the feasibility of transferring external pressure into the eye orbit in a large-animal model while maintaining a clinically acceptable pressure gradient between intraorbital and external pressures. The experimental system comprised a specifically designed pressure applicator that can be placed and tightly fastened onto the eye. A pressure chamber made from thin, elastic, non-allergenic film was attached to the lower part of the applicator and placed in contact with the eyelid and surrounding tissues of piglets' eyeballs. External pressure was increased from 0 to 20 mmHg with steps of 1 mmHg, from 20 to 30 mmHg with steps of 2 mmHg, and from 30 to 50 mmHg with steps of 5 mmHg. An invasive pressure sensor was used to measure intraorbital pressure directly. An equation was derived from measured intraorbital and external pressures (intraorbital pressure = 0.82 × external pressure + 3.12) and demonstrated that external pressure can be linearly transferred to orbit tissues with a bias (systematic error) of 3.12 mmHg. This is close to the initial intraorbital pressure within the range of pressures tested. We determined the relationship between intraorbital compliance and externally applied pressure. Our findings indicate that intraorbital compliance can be controlled across a wide range of 1.55 to 0.15 ml/mmHg. We observed that external pressure transfer into the orbit can be achieved while maintaining a clinically acceptable pressure gradient between intraorbital and external pressures.

Tissue Compliance and Intracranial Pressure Responses to Large Intracerebral Hemorrhage in Young and Aged Spontaneously Hypertensive Rats

BACKGROUND

After a large intracerebral hemorrhage (ICH), the hematoma and swelling cause intracranial pressure (ICP) to increase, sometimes causing brain herniation and death. This is partly countered by widespread tissue compliance, an acute decrease in tissue volume distal to the stroke, at least in young healthy animals. Intracranial compensation dynamics seem to vary with age, but there is no data on old animals or those with hypertension, major factors influencing ICH risk and outcome.

METHODS

We assessed hematoma volume, edema, ICP, and functional deficits in young and aged spontaneously hypertensive rats (SHRs) and young normotensive control strains after collagenase-induced ICH. Macroscopic and microscopic brain volume fractions, such as contralateral hemisphere volume, cortical thickness, and neuronal morphology, were assessed via histological and stereological techniques.

RESULTS

Hematoma volume was 52% larger in young versus aged SHRs; surprisingly, aged SHRs still experienced proportionally worse outcomes following ICH, with 2× greater elevations in edema and ICP relative to bleed volume and 3× the degree of tissue compliance. Aged SHRs also experienced equivalent neurological deficits following ICH compared with their younger counterparts, despite the lack of significant age-related behavioral effects. Importantly, tissue compliance occurred across strains and age groups and was not impaired by hypertension or old age.

CONCLUSIONS

Aged SHRs show considerable capacity for tissue compliance following ICH and seem to rely on such mechanisms more heavily in settings of elevated ICP. Therefore, the ICP compensation response to ICH mass effect varies across the lifespan according to risk factors such as chronic hypertension.

The Role of ICP Monitoring in Minimally Invasive Surgery for the Management of Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is the second major stroke type, with high incidence, high disability rate, and high mortality. At present, there is no effective and reliable treatment for ICH. As a result, most patients have a poor prognosis. Minimally invasive surgery (MIS) is the fastest treatment method to remove hematoma, which is characterized by less trauma and easy operation. Some studies have confirmed the safety of MIS, but there are still no reports showing that it can significantly improve the functional outcome of ICH patients. Intracranial pressure (ICP) monitoring is considered to be an important part of successful treatment in traumatic brain diseases. By monitoring ICP in real time, keeping stable ICP could help patients with craniocerebral injury get a good prognosis. In the course of MIS treatment of ICH patients, keeping ICP stable may also promote patient recovery. In this review, we will take ICP monitoring as the starting point for an in-depth discussion.

Intracranial Pressure Dysfunction Following Severe Intracerebral Hemorrhage in Middle-Aged Rats

Rising intracranial pressure (ICP) aggravates secondary injury and heightens risk of death following intracerebral hemorrhage (ICH). Long-recognized compensatory mechanisms that lower ICP include reduced cerebrospinal fluid and venous blood volumes. Recently, we identified another compensatory mechanism in severe stroke, a decrease in cerebral parenchymal volume via widespread reductions in cell volume and extracellular space (tissue compliance). Here, we examined how age affects tissue compliance and ICP dynamics after severe ICH in rats (collagenase model). A planned comparison to historical young animal data revealed that aged SHAMs (no stroke) had significant cerebral atrophy (9% reduction, p ≤ 0.05), ventricular enlargement (9% increase, p ≤ 0.05), and smaller CA1 neuron volumes (21%, p ≤ 0.05). After ICH in aged animals, contralateral striatal neuron density and CA1 astrocyte density significantly increased (12% for neurons, 7% for astrocytes, p ≤ 0.05 vs. aged SHAMs). Unlike young animals, other regions in aged animals did not display significantly reduced cell soma volume despite a few trends. Nonetheless, overall contralateral hemisphere volume was 10% smaller in aged ICH animals compared to aged SHAMs (p ≤ 0.05). This age-dependent pattern of tissue compliance is not due to absent ICH-associated mass effect (83.2 mm3 avg. bleed volume) as aged ICH animals had significantly elevated mean and peak ICP (p ≤ 0.01), occurrence of ICP spiking events, as well as bilateral evidence of edema (e.g., 3% in injured brain, p ≤ 0.05 vs. aged SHAMs). Therefore, intracranial compliance reserve changes with age; after ICH, these and other age-related changes may cause greater fluctuation from baseline, increasing the chance of adverse outcomes like mortality.

Intracranial pressure for clinicians: it is not just a number

BACKGROUND

Invasive intracranial pressure (ICP) monitoring is a standard practice in severe brain injury cases, where it allows to derive cerebral perfusion pressure (CPP); ICP-tracing can also provide additional information about intracranial dynamics, forecast episodes of intracranial hypertension and set targets for a tailored therapy to prevent secondary brain injury. Nevertheless, controversies about the advantages of an ICP clinical management are still debated.

FINDINGS

This article reviews recent research on ICP to improve the understanding of the topic and uncover the hidden information in this signal that may be useful in clinical practice. Parameters derived from time-domain as well as frequency domain analysis include compensatory reserve, autoregulation estimation, pulse waveform analysis, and behavior of ICP in time. The possibility to predict the outcome and apply a tailored therapy using a personalised perfusion pressure target is also described.

CONCLUSIONS

ICP is a crucial signal to monitor in severely brain injured patients; a bedside computer can empower standard monitoring giving new metrics that may aid in clinical management, establish a personalized therapy, and help to predict the outcome. Continuous collaboration between engineers and clinicians and application of new technologies to healthcare, is vital to improve the accuracy of current metrics and progress towards better care with individualized dynamic targets.

Contribution of intracranial pressure to human dynamic cerebral autoregulation after acute brain injury

Cerebral perfusion pressure (CPP) is normally expressed by the difference between mean arterial blood pressure (MAP) and intracranial pressure (ICP) but comparison of the separate contributions of MAP and ICP to human cerebral blood flow autoregulation has not been reported. In patients with acute brain injury (ABI), internal jugular vein compression (IJVC) was performed for 60 s. Dynamic cerebral autoregulation (dCA) was assessed in recordings of middle cerebral artery blood velocity (MCAv, transcranial Doppler), and invasive measurements of MAP and ICP. Patients were separated according to injury severity as having whole/undamaged skull, large fractures, or craniotomies, or following decompressive craniectomy. Glasgow coma score was not different for the three groups. IJVC induced changes in MCAv, MAP, ICP, and CPP in all three groups. The MCAv response to step changes in MAP and ICP expressed the dCA response to these two inputs and was quantified with the autoregulation index (ARI). In 85 patients, ARI was lower for the ICP input as compared with the MAP input (2.25 ± 2.46 vs. 3.39 ± 2.28; P < 0.0001), and particularly depressed in the decompressive craniectomy (DC) group (n = 24, 0.35 ± 0.62 vs. 2.21 ± 1.96; P < 0.0005). In patients with ABI, the dCA response to changes in ICP is less efficient than corresponding responses to MAP changes. These results should be taken into consideration in studies aimed to optimize dCA by manipulation of CPP in neurocritical patients.

The Monro-Kellie Doctrine: A Review and Call for Revision

The Monro-Kellie doctrine is a well-accepted principle of intracranial hemodynamics. It has undergone few consequential revisions since it was established. Its principle is straightforward: The combined volume of neuronal tissue, blood, and CSF is constant. To maintain homeostatic intracranial pressure, any increase or decrease in one of these elements leads to a reciprocal and opposite change in the others. The Monro-Kellie doctrine assumes a rigid, unadaptable calvaria. Recent studies have disproven this assumption. The skull expands and grows in response to pathologic changes in intracranial pressure. In this review, we outline what is known about calvarial changes in the setting of pressure dysregulation and suggest a revision to the Monro-Kellie doctrine that includes an adaptable skull as a fourth component.

Early, Intense Rehabilitation Fails to Improve Outcome After Intra-Striatal Hemorrhage in Rats

BACKGROUND

The formation and degradation of an intracerebral hemorrhage causes protracted cell death, and an extended window for intervention. Experimental studies find that rehabilitation mitigates late cell death, with accelerated hematoma clearance as a potential mechanism.

OBJECTIVE

We assessed whether early, intense, enriched rehabilitation (ER, environmental enrichment and massed skills training) enhances functional benefit, reduces brain injury, and augments hematoma clearance.

METHODS

In experiment 1, rats (n = 56) were randomized to intervention in the light (-L) or dark phase (-D) of their housing cycle, then to 10 days of ER or control (CON) treatment after collagenase-induced striatal intracerebral hemorrhage (ICH). ER rats were treated from 5 to 14 days after ICH. Behavior and residual hematoma volume was assessed on day 14. In experiment 2, rats (n = 72) were randomized to ER-D10, ER-D20, or CON-D. ER rats completed 10 or 20 days of training in the dark. Rats were euthanized on day 60 for histology. In both experiments, behavioral assessment was completed pre-ICH, pre-ER (day 4 post-ICH), and post-ER (experiment 1: days 13-14; experiment 2: days 16-17 and 30-31).

RESULTS

Reaching intensity was high but similar between ER-D10 and ER-L10. Unlike previous work, rehabilitation did not alter skilled reaching or hematoma resolution. Varying ER duration also did not affect reaching success or lesion volume.

CONCLUSIONS

In contrast to others, and under these conditions, our findings show that striatal ICH was generally unresponsive to rehabilitation. This highlights the difficulty of replicating and extending published work, perhaps owing to small inter-study differences.

Molecular, Pathological, Clinical, and Therapeutic Aspects of Perihematomal Edema in Different Stages of Intracerebral Hemorrhage

Acute intracerebral hemorrhage (ICH) is a devastating type of stroke worldwide. Neuronal destruction involved in the brain damage process caused by ICH includes a primary injury formed by the mass effect of the hematoma and a secondary injury induced by the degradation products of a blood clot. Additionally, factors in the coagulation cascade and complement activation process also contribute to secondary brain injury by promoting the disruption of the blood-brain barrier and neuronal cell degeneration by enhancing the inflammatory response, oxidative stress, etc. Although treatment options for direct damage are limited, various strategies have been proposed to treat secondary injury post-ICH. Perihematomal edema (PHE) is a potential surrogate marker for secondary injury and may contribute to poor outcomes after ICH. Therefore, it is essential to investigate the underlying pathological mechanism, evolution, and potential therapeutic strategies to treat PHE. Here, we review the pathophysiology and imaging characteristics of PHE at different stages after acute ICH. As illustrated in preclinical and clinical studies, we discussed the merits and limitations of varying PHE quantification protocols, including absolute PHE volume, relative PHE volume, and extension distance calculated with images and other techniques. Importantly, this review summarizes the factors that affect PHE by focusing on traditional variables, the cerebral venous drainage system, and the brain lymphatic drainage system. Finally, to facilitate translational research, we analyze why the relationship between PHE and the functional outcome of ICH is currently controversial. We also emphasize promising therapeutic approaches that modulate multiple targets to alleviate PHE and promote neurologic recovery after acute ICH.

Correlation Between Computed Tomography-Based Tissue Net Water Uptake and Volumetric Measures of Cerebral Edema After Reperfusion Therapy

BACKGROUND

Cerebral edema after large hemispheric infarction is associated with poor functional outcome and mortality. Net water uptake (NWU) quantifies the degree of hypoattenuation on unenhanced-computed tomography (CT) and is increasingly used to measure cerebral edema in stroke research. Hemorrhagic transformation and parenchymal contrast staining after thrombectomy may confound NWU measurements. We investigated the correlation of NWU measured postthrombectomy with volumetric markers of cerebral edema and association with functional outcomes.

METHODS

In a pooled individual patient level analysis of patients presenting with anterior circulation large hemispheric infarction (core 80-300 mL or Alberta Stroke Program Early CT Score ≤5) in the HERMES (Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke trials) data set, cerebral edema was defined as the volumetric expansion of the ischemic hemisphere expressed as a ratio to the contralateral hemisphere(rHV). NWU and midline-shift were compared with rHV as the reference standard on 24-hour follow-up CT, adjusted for hemorrhagic transformation and the use of thrombectomy. Association between edema markers and day 90 functional outcomes (modified Rankin Scale) was assessed using ordinal logistic regression.

RESULTS

Overall (n=144), there was no correlation between NWU and rHV (r_s=0.055, P=0.51). In sub-group analyses, a weak correlation between NWU with rHV was observed after excluding patients with any degree of hemorrhagic transformation (r_s=0.211, P=0.015), which further improved after excluding thrombectomy patients (r_s=0.453, P=0.001). Midline-shift correlated strongly with rHV in all sub-group analyses (r_s>0.753, P=0.001). Functional outcome at 90 days was negatively associated with rHV (adjusted common odds ratio, 0.46 [95% CI, 0.32-0.65]; P<0.001) and midline-shift (adjusted common odds ratio, 0.85 [95% CI, 0.78-0.92]; P<0.001) but not NWU (adjusted common odds ratio, 1.00 [95% CI, 0.97-1.03]; P=0.84), adjusted for age, baseline National Institutes of Health Stroke Scale, and thrombectomy. Prognostic performance of NWU improved after excluding patients with hemorrhagic transformation and thrombectomy (adjusted odds ratio, 0.90 [95% CI, 0.80-1.02]; P=0.10).

CONCLUSIONS

NWU correlated poorly with conventional markers of cerebral edema and was not associated with clinical outcome in the presence of hemorrhagic transformation and thrombectomy. Measuring NWU postthrombectomy requires validation before implementation into clinical research. At present, the use of NWU should be limited to baseline CT, or follow-up CT only in patients without hemorrhagic transformation or treatment with thrombectomy.

Headache and neuroimaging findings in conditions of cerebrospinal fluid (CSF) circulation disorders: in hydrocephalus, pseudotumor cerebri, and CSF hypotension syndrome

The authors wish in this narrative minireview show and comment on some neuroimaging findings encountered in patients with conditions of cerebrospinal fluid circulation disorders, such as in the hydrocephalus, pseudotumor cerebri, and CSF hypotension syndrome. The MRI of a young woman with a clinical diagnosis of post-dural puncture headache, performed on the fourth postpartum day after cesarean delivery, evolving with headache and diplopia, is shown. Non-contrast-enhanced sagittal T1 magnetic resonance imaging shows that the cerebellar tonsils are at the level of the foramen magnum, therefore still within normal limits, but, despite that, the opening of the cerebral aqueduct in the third ventricle is below the imaginary line connecting the anterior clinoid to the vein of Galen, therefore considered abnormally lower than the expected anatomical position. The axial T1-weighted images with post-contrast fat suppression also show impregnation and thickening of the dura mater. There is also mild engorgement of the cerebral venous sinuses, best demonstrated on T1 with post-contrast fat suppression, which is also identified on post-contrast magnetic resonance angiography, with no signs of venous thrombosis. We conclude that the diagnosis of a patient with intracranial hypotension syndrome can be suspected or confirmed with typical neuroimaging findings.

Decreased Intracranial Pressure Elevation and Cerebrospinal Fluid Outflow Resistance: A Potential Mechanism of Hypothermia Cerebroprotection Following Experimental Stroke

Background: Elevated intracranial pressure (ICP) occurs 18–24 h after ischaemic stroke and is implicated as a potential cause of early neurological deterioration. Increased resistance to cerebrospinal fluid (CSF) outflow after ischaemic stroke is a proposed mechanism for ICP elevation. Ultra-short duration hypothermia prevents ICP elevation 24 h post-stroke in rats. We aimed to determine whether hypothermia would reduce CSF outflow resistance post-stroke. Methods: Transient middle cerebral artery occlusion was performed, followed by gradual cooling to 33 °C. At 18 h post-stroke, CSF outflow resistance was measured using a steady-state infusion method. Results: Hypothermia to 33 °C prevented ICP elevation 18 h post-stroke (hypothermia ∆ICP = 0.8 ± 3.6 mmHg vs. normothermia ∆ICP = 4.4 ± 2.0 mmHg, p = 0.04) and reduced infarct volume 24 h post-stroke (hypothermia = 78.6 ± 21.3 mm³ vs. normothermia = 108.1 ± 17.8 mm³; p = 0.01). Hypothermia to 33 °C did not result in a significant reduction in CSF outflow resistance compared with normothermia controls (0.32 ± 0.36 mmHg/µL/min vs. 1.07 ± 0.99 mmHg/µL/min, p = 0.06). Conclusions: Hypothermia treatment was protective in terms of ICP rise prevention, infarct volume reduction, and may be implicated in CSF outflow resistance post-stroke. Further investigations are warranted to elucidate the mechanisms of ICP elevation and hypothermia treatment.

Targeting focal ischemic and hemorrhagic stroke neuroprotection: Current prospects for local hypothermia

Therapeutic hypothermia (TH) has applications dating back millennia. In modern history, however, TH saw its importation into medical practice where investigations have demonstrated that TH is efficacious in ischemic insults, notably cardiac arrest and hypoxic-ischemic encephalopathy. As well, studies have been undertaken to investigate whether TH can provide benefit in focal stroke (i.e., focal ischemia and intracerebral hemorrhage). However, clinical studies have encountered various challenges with induction and maintenance of post-stroke TH. Most clinical studies have attempted to use body-wide cooling protocols, commonly hindered by side effects that can worsen post-stroke outcomes. Some of the complications and difficulties with systemic TH can be circumvented by using local hypothermia (LH) methods. Additional advantages include the potential for lower target temperatures to be achieved and faster TH induction rates with LH. This systematic review summarizes the body of clinical and preclinical LH focal stroke studies and raises key points to consider for future LH research. We conclude with an overview of LH neuroprotective mechanisms and a comparison of LH mechanisms with those observed with systemic TH. Overall, whereas many LH studies have been conducted preclinically in the context of focal ischemia, insufficient work has been done in intracerebral hemorrhage. Furthermore, key translational studies have yet to be done in either stroke subtype (e.g., varied models and time-to-treat, studies considering aged animals or animals with co-morbidities). Few clinical LH investigations have been performed and the optimal LH parameters to achieve neuroprotection are unknown.

Losing the dogmatic view of cerebral autoregulation

In 1959, Niels Lassen illustrated the cerebral autoregulation curve in the classic review article entitled Cerebral Blood Flow and Oxygen Consumption in Man. This concept suggested a relatively broad mean arterial pressure range (~60-150 mmHg) wherein cerebral blood flow remains constant. However, the assumption that this wide cerebral autoregulation plateau could be applied on a within-individual basis is incorrect and greatly variable between individuals. Indeed, each data point on the autoregulatory curve originated from independent samples of participants and patients and represented interindividual relationships between cerebral blood flow and mean arterial pressure. Nonetheless, this influential concept remains commonly cited and illustrated in various high-impact publications and medical textbooks, and is frequently taught in medical and science education without appropriate nuances and caveats. Herein, we provide the rationale and additional experimental data supporting the notion we need to lose this dogmatic view of cerebral autoregulation.

Understanding breast cancer heterogeneity through non-genetic heterogeneity

Intricacy in treatment and diagnosis of breast cancer has been an obstacle due to genotype and phenotype heterogeneity. Understanding of non-genetic heterogeneity mechanisms along with considering role of genetic heterogeneity may fill the gaps in landscape painting of heterogeneity. The main factors contribute to non-genetic heterogeneity including: transcriptional pulsing/bursting or discontinuous transcriptions, stochastic partitioning of components at cell division and various signal transduction from tumor ecosystem. Throughout this review, we desired to provide a conceptual framework focused on non-genetic heterogeneity, which has been intended to offer insight into prediction, diagnosis and treatment of breast cancer.