Autoregulation and CO2 responses of cerebral blood flow in patients with acute severe head injury

Amantadine for Traumatic Brain Injury-Supporting Evidence and Mode of Action

Traumatic brain injury (TBI) is an important global clinical issue, requiring not only prevention but also effective treatment. Following TBI, diverse parallel and intertwined pathological mechanisms affecting biochemical, neurochemical, and inflammatory pathways can have a severe impact on the patient's quality of life. The current review summarizes the evidence for the utility of amantadine in TBI in connection to its mechanism of action. Amantadine, the drug combining multiple mechanisms of action, may offer both neuroprotective and neuroactivating effects in TBI patients. Indeed, the use of amantadine in TBI has been encouraged by several clinical practice guidelines/recommendations. Amantadine is also available as an infusion, which may be of particular benefit in unconscious patients with TBI due to immediate delivery to the central nervous system and the possibility of precise dosing. In other situations, orally administered amantadine may be used. There are several questions that remain to be addressed: can amantadine be effective in disorders of consciousness requiring long-term treatment and in combination with drugs approved for the treatment of TBI? Do the observed beneficial effects of amantadine extend to disorders of consciousness due to factors other than TBI? Well-controlled clinical studies are warranted to ultimately confirm its utility in the TBI and provide answers to these questions.

Circadian and Diurnal Regulation of Cerebral Blood Flow

Circadian and diurnal variation in cerebral blood flow directly contributes to the diurnal variation in the risk of stroke, either through factors that trigger stroke or due to impaired compensatory mechanisms. Cerebral blood flow results from the integration of systemic hemodynamics, including heart rate, cardiac output, and blood pressure, with cerebrovascular regulatory mechanisms, including cerebrovascular reactivity, autoregulation, and neurovascular coupling. We review the evidence for the circadian and diurnal variation in each of these mechanisms and their integration, from the detailed evidence for mechanisms underlying the nocturnal nadir and morning surge in blood pressure to identifying limited available evidence for circadian and diurnal variation in cerebrovascular compensatory mechanisms. We, thus, identify key systemic hemodynamic factors related to the diurnal variation in the risk of stroke but particularly identify the need for further research focused on cerebrovascular regulatory mechanisms.

A Systematic Review on Traumatic Brain Injury Pathophysiology and Role of Herbal Medicines in its Management

BACKGROUND

Traumatic brain injury (TBI) is a worldwide problem. Almost about sixtynine million people sustain TBI each year all over the world. Repetitive TBI linked with increased risk of neurodegenerative disorder such as Parkinson, Alzheimer, traumatic encephalopathy. TBI is characterized by primary and secondary injury and exerts a severe impact on cognitive, behavioral, psychological and other health problem. There were various proposed mechanism to understand complex pathophysiology of TBI but still there is a need to explore more about TBI pathophysiology. There are drugs present for the treatment of TBI in the market but there is still need of more drugs to develop for better and effective treatment of TBI, because no single drug is available which reduces the further progression of this injury.

OBJECTIVE

The main aim and objective of structuring this manuscript is to design, develop and gather detailed data regarding about the pathophysiology of TBI and role of medicinal plants in its treatment.

METHOD

This study is a systematic review conducted between January 1995 to June 2021 in which a consultation of scientific articles from indexed periodicals was carried out in Science Direct, United States National Library of Medicine (Pubmed), Google Scholar, Elsvier, Springer and Bentham.

RESULTS

A total of 54 studies were analyzed, on the basis of literature survey in the research area of TBI.

CONCLUSION

Recent studies have shown the potential of medicinal plants and their chemical constituents against TBI therefore, this review targets the detailed information about the pathophysiology of TBI and role of medicinal plants in its treatment.

Transcranial Doppler ultrasound: Clinical applications from neurological to cardiological setting

Transcranial Doppler (TCD) ultrasonography is a rapid, noninvasive, real-time, and low-cost imaging technique. It is performed with a low-frequency (2 MHz) probe in order to evaluate the cerebral blood flow (CBF) and its pathological alterations, through specific acoustic windows. In the recent years, TCD use has been expanded across many clinical settings. Actually, the most widespread indication for TCD exam is represented by the diagnosis of paradoxical embolism, due to patent foramen ovale, in young patients with cryptogenic stroke. In addition, TCD has also found useful applications in neurological care setting, including the following: cerebral vasospasm following acute subarachnoid hemorrhage, brain trauma, cerebrovascular atherosclerosis, and evaluation of CBF and cerebral autoregulation after an ischemic stroke event. The present review aimed to describe the most recent evidences of TCD utilization from neurological to cardiological setting.

Impaired capillary-to-arteriolar electrical signaling after traumatic brain injury

Traumatic brain injury (TBI) acutely impairs dynamic regulation of local cerebral blood flow, but long-term (>72 h) effects on functional hyperemia are unknown. Functional hyperemia depends on capillary endothelial cell inward rectifier potassium channels (Kir2.1) responding to potassium (K+) released during neuronal activity to produce a regenerative, hyperpolarizing electrical signal that propagates from capillaries to dilate upstream penetrating arterioles. We hypothesized that TBI causes widespread disruption of electrical signaling from capillaries-to-arterioles through impairment of Kir2.1 channel function. We randomized mice to TBI or control groups and allowed them to recover for 4 to 7 days post-injury. We measured in vivo cerebral hemodynamics and arteriolar responses to local stimulation of capillaries with 10 mM K+ using multiphoton laser scanning microscopy through a cranial window under urethane and α-chloralose anesthesia. Capillary angio-architecture was not significantly affected following injury. However, K+-induced hyperemia was significantly impaired. Electrophysiology recordings in freshly isolated capillary endothelial cells revealed diminished Ba2+-sensitive Kir2.1 currents, consistent with a reduction in channel function. In pressurized cerebral arteries isolated from TBI mice, K+ failed to elicit the vasodilation seen in controls. We conclude that disruption of endothelial Kir2.1 channel function impairs capillary-to-arteriole electrical signaling, contributing to altered cerebral hemodynamics after TBI.

Cardiac Output and Cerebral Blood Flow: A Systematic Review of Cardio-Cerebral Coupling

Control of cerebral blood flow (CBF) is crucial to the management of neurocritically ill patients. Small studies which have examined the role of cardiac output (CO) as a determinant of CBF have inconsistently demonstrated evidence of cardio-cerebral coupling. Putative physiological mechanisms underpinning such coupling include changes in arterial blood pressure pulsatility, which would produce vasodilation through increased oscillatory wall-shear-stress and baroreceptor mediated reflex sympatholysis, and changes in venous backpressure which may improve cerebral perfusion pressure. We sought to summarize and contextualize the literature on the relationship between CO and CBF and discuss the implications of cardio-cerebral coupling for neurocritical care. A systematic review of the literature yielded 41 studies; all were of low-quality and at high-risk of bias. Results were heterogenous, with evidence for both corroboration and confutation of a relationship between CO and CBF in both normal and abnormal cerebrovascular states. Common limitations of studies were lack of instantaneous CBF measures with reliance on transcranial Doppler-derived blood flow velocity as a surrogate, inability to control for fluctuations in established determinants of CBF (eg, PaCO2), and direct effects on CBF by the interventions used to alter CO. Currently, the literature is insufficiently robust to confirm an independent relationship between CO and CBF. Hypothetically, the presence of cardio-cerebral coupling would have important implications for clinical practice. Manipulation of CBF could occur without the risks associated with extremes of arterial pressure, potentially improving therapy for those with cerebral ischemia of various etiologies. However, current literature is insufficiently robust to confirm an independent relationship between CO and CBF, and further studies with improved methodology are required before therapeutic interventions can be based on cardio-cerebral coupling.

Review: pathophysiology of intracranial hypertension and noninvasive intracranial pressure monitoring

Measurement of intracranial pressure (ICP) is crucial in the management of many neurological conditions. However, due to the invasiveness, high cost, and required expertise of available ICP monitoring techniques, many patients who could benefit from ICP monitoring do not receive it. As a result, there has been a substantial effort to explore and develop novel noninvasive ICP monitoring techniques to improve the overall clinical care of patients who may be suffering from ICP disorders. This review attempts to summarize the general pathophysiology of ICP, discuss the importance and current state of ICP monitoring, and describe the many methods that have been proposed for noninvasive ICP monitoring. These noninvasive methods can be broken down into four major categories: fluid dynamic, otic, ophthalmic, and electrophysiologic. Each category is discussed in detail along with its associated techniques and their advantages, disadvantages, and reported accuracy. A particular emphasis in this review will be dedicated to methods based on the use of transcranial Doppler ultrasound. At present, it appears that the available noninvasive methods are either not sufficiently accurate, reliable, or robust enough for widespread clinical adoption or require additional independent validation. However, several methods appear promising and through additional study and clinical validation, could eventually make their way into clinical practice.

Assessment of Dynamic Intracranial Compliance in Children with Severe Traumatic Brain Injury: Proof-of-Concept

Background and Aims

Intracranial compliance refers to the relationship between a change in intracranial volume and the resultant change in intracranial pressure (ICP). Measurement of compliance is useful in managing cardiovascular and respiratory failure; however, there are no contemporary means to assess intracranial compliance. Knowledge of intracranial compliance could complement ICP and cerebral perfusion pressure (CPP) monitoring in patients with severe traumatic brain injury (TBI) and may enable a proactive approach to ICP management. In this proof-of-concept study, we aimed to capitalize on the physiologic principles of intracranial compliance and vascular reactivity to CO₂, and standard-of-care neurocritical care monitoring, to develop a method to assess dynamic intracranial compliance.

Methods

Continuous ICP and end-tidal CO₂ (ETCO₂) data from children with severe TBI were collected after obtaining informed consent in this Institutional Review Board-approved study. An intracranial pressure-PCO₂ Compliance Index (PCI) was derived by calculating the moment-to-moment correlation between change in ICP and change in ETCO₂. As such, “good” compliance may be reflected by a lack of correlation between time-synched changes in ICP in response to changes in ETCO₂, and “poor” compliance may be reflected by a positive correlation between changes in ICP in response to changes in ETCO₂.

Results

A total of 978 h of ICP and ETCO₂ data were collected and analyzed from eight patients with severe TBI. Demographic and clinical characteristics included patient age 7.1 ± 5.8 years (mean ± SD); 6/8 male; initial Glasgow Coma Scale score 3 [3–7] (median [IQR]); 6/8 had decompressive surgery; 7.1 ± 1.4 ICP monitor days; ICU length of stay (LOS) 16.1 ± 6.8 days; hospital LOS 25.9 ± 8.4 days; and survival 100%. The mean PCI for all patients throughout the monitoring period was 0.18 ± 0.04, where mean ICP was 13.7 ± 2.1 mmHg. In this cohort, PCI was observed to be consistently above 0.18 by 12 h after monitor placement. Percent time spent with PCI thresholds > 0.1, 0.2, and 0.3 were 62% [24], 38% [14], and 23% [15], respectively. The percentage of time spent with an ICP threshold > 20 mmHg was 5.1% [14.6].

Conclusions

Indirect assessment of dynamic intracranial compliance in TBI patients using standard-of-care monitoring appears feasible and suggests a prolonged period of derangement out to 5 days post-injury. Further study is ongoing to determine if the PCI—a new physiologic index, complements utility of ICP and/or CPP in guiding management of patients with severe TBI.

Electronic supplementary material

The online version of this article (10.1007/s12028-020-01004-3) contains supplementary material, which is available to authorized users.

Anodal Transcranial Direct Current Stimulation Improves Impaired Cerebrovascular Reactivity in Traumatized Mouse Brain

Cerebrovascular reactivity (CVR) is a compensatory mechanism where blood vessels dilate in response to a vasodilatory stimulus, and is a biomarker of vascular reserve and microvascular health. Impaired CVR indicates microvascular hemodynamic dysfunction, which is implicated in traumatic brain injury (TBI) and associated with long-term neurological deficiency. Recently we have shown that anodal transcranial direct current stimulation (tDCS) caused prolonged dilatation of cerebral arterioles that increased brain microvascular flow and tissue oxygenation in traumatized mouse brain and was associated with neurologic improvement. Here we evaluate the effects of tDCS on impaired CVR and microvascular cerebral blood flow (mCBF) regulation after TBI. TBI was induced in mice by controlled cortical impact (CCI). Cortical microvascular tone, mCBF, and tissue oxygen supply (by nicotinamide adenine dinucleotide, NADH) were measured by two-photon laser scanning microscopy before and after anodal tDCS (0.1 mA/15 min). CVR and mCBF regulation were evaluated by measuring changes in arteriolar diameters and NADH during hypercapnia test before and after tDCS. Transient hypercapnia was induced by 60-s increase of CO₂ concentration in the inhalation mixture to 10%. As previously, anodal tDCS dilated arterioles which increased arteriolar blood flow volume that led to an increase in capillary flow velocity and the number of functioning capillaries, thereby improving tissue oxygenation in both traumatized and sham animals. In sham mice, transient hypercapnia caused transient dilatation of cerebral arterioles with constant NADH, reflecting intact CVR and mCBF regulation. In TBI animals, arteriolar dilatation response to hypercapnia was diminished while the NADH level increased (tissue oxygen supply decreased), reflecting impaired CVR and mCBF regulation. Anodal tDCS enhanced reactivity in parenchymal arterioles in both groups (especially in TBI mice) and restored CVR thereby prevented the reduction in tissue oxygen supply during hypercapnia. CVR has been shown to be related to nitric oxide elevation due to nitric oxide synthases activation, which can be sensitive to the electrical field induced by tDCS.

Pioglitazone Therapy and Fractures: Systematic Review and Meta- Analysis

INTRODUCTION

Thiazolidinediones are a group of synthetic medications used in type 2 diabetes treatment. Among available thiazolidinediones, pioglitazone is gaining increased attention due to its lower cardiovascular risk in type 2 diabetes mellitus sufferers and seems a promising future therapy. Accumulating evidence suggests that diabetic patients may exert bone fractures due to such treatments. Simultaneously, the female population is thought to be at greater risk. Still, the safety outcomes of pioglitazone treatment especially in terms of fractures are questionable and need to be clarified.

METHODS

We searched MEDLINE, Scopus, PsyInfo, eLIBRARY.ru electronic databases and clinical trial registries for studies reporting an association between pioglitazone and bone fractures in type 2 diabetes mellitus patients published before Feb 15, 2016. Among 1536 sources that were initially identified, six studies including 3172 patients proved relevant for further analysis.

RESULT

Pooled analysis of the included studies demonstrated that after treatment with pioglitazone patients with type 2 diabetes mellitus had no significant increase in fracture risk [odds ratio (OR): 1.18, 95% confidence interval (CI): 0.82 to 1.71, p=0.38] compared to other antidiabetic drugs or placebo. Additionally, no association was found between the risk of fractures and pioglitazone therapy duration. The gender of the patients involved was not relevant to the risk of fractures, too.

CONCLUSION

Pioglitazone treatment in diabetic patients does not increase the incidence of bone fractures. Moreover, there is no significant association between patients' fractures, their gender and the period of exposure to pioglitazone. Additional longitudinal studies need to be undertaken to obtain more detailed information on bone fragility and pioglitazone therapy.

Traumatic Brain Injury Impairs Myogenic Constriction of Cerebral Arteries: Role of Mitochondria-Derived H2O2 and TRPV4-Dependent Activation of BKca Channels

Traumatic brain injury (TBI) impairs autoregulation of cerebral blood flow, which contributes to the development of secondary brain injury, increasing mortality of patients. Impairment of pressure-induced myogenic constriction of cerebral arteries plays a critical role in autoregulatory dysfunction; however, the underlying cellular and molecular mechanisms are not well understood. To determine the role of mitochondria-derived H₂O₂ and large-conductance calcium-activated potassium channels (BK_Ca) in myogenic autoregulatory dysfunction, middle cerebral arteries (MCAs) were isolated from rats with severe weight drop-impact acceleration brain injury. We found that 24 h post-TBI MCAs exhibited impaired myogenic constriction, which was restored by treatment with a mitochondria-targeted antioxidant (mitoTEMPO), by scavenging of H₂O₂ (polyethylene glycol [PEG]-catalase) and by blocking both BK_Ca channels (paxilline) and transient receptor potential cation channel subfamily V member 4 (TRPV4) channels (HC 067047). Further, exogenous administration of H₂O₂ elicited significant dilation of MCAs, which was inhibited by blocking either BK_Ca or TRPV4 channels. Vasodilation induced by the TRPV4 agonist GSK1016790A was inhibited by paxilline. In cultured vascular smooth muscle cells H₂O₂ activated BK_Ca currents, which were inhibited by blockade of TRPV4 channels. Collectively, our results suggest that after TBI, excessive mitochondria-derived H₂O₂ activates BK_Ca channels via a TRPV4-dependent pathway in the vascular smooth muscle cells, which impairs pressure-induced constriction of cerebral arteries. Future studies should elucidate the therapeutic potential of pharmacological targeting of this pathway in TBI, to restore autoregulatory function in order to prevent secondary brain damage and decrease mortality.

Cerebral hemodynamic and metabolic changes in fulminant hepatic failure

ABSTRACT Intracranial hypertension and brain swelling are a major cause of morbidity and mortality of patients suffering from fulminant hepatic failure (FHF). The pathogenesis of these complications has been investigated in man, in experimental models and in isolated cell systems. Currently, the mechanism underlying cerebral edema and intracranial hypertension in the presence of FHF is multi-factorial in etiology and only partially understood. The aim of this paper is to review the pathophysiology of cerebral hemodynamic and metabolism changes in FHF in order to improve understanding of intracranial dynamics complication in FHF.

Cerebral Autoregulation-oriented Therapy at the Bedside

This comprehensive review summarizes the evidence regarding use of cerebral autoregulation-directed therapy at the bedside and provides an evaluation of its impact on optimizing cerebral perfusion and associated functional outcomes. Multiple studies in adults and several in children have shown the feasibility of individualizing mean arterial blood pressure and cerebral perfusion pressure goals by using cerebral autoregulation monitoring to calculate optimal levels. Nine of these studies examined the association between cerebral perfusion pressure or mean arterial blood pressure being above or below their optimal levels and functional outcomes. Six of these nine studies (66%) showed that patients for whom median cerebral perfusion pressure or mean arterial blood pressure differed significantly from the optimum, defined by cerebral autoregulation monitoring, were more likely to have an unfavorable outcome. The evidence indicates that monitoring of continuous cerebral autoregulation at the bedside is feasible and has the potential to be used to direct blood pressure management in acutely ill patients.

Hypertension-Induced Enhanced Myogenic Constriction of Cerebral Arteries Is Preserved after Traumatic Brain Injury

Traumatic brain injury (TBI) was shown to impair pressure-induced myogenic response of cerebral arteries, which is associated with vascular and neural dysfunction and increased mortality of TBI patients. Hypertension was shown to enhance myogenic tone of cerebral arteries via increased vascular production of 20-hydroxyeicosatrienoic acid (HETE). This adaptive mechanism protects brain tissue from pressure/volume overload; however, it can also lead to increased susceptibility to cerebral ischemia. Although both effects may potentiate the detrimental vascular consequences of TBI, it is not known how hypertension modulates the effect of TBI on myogenic responses of cerebral vessels. We hypothesized that in hypertensive rats, the enhanced myogenic cerebrovascular response is preserved after TBI. Therefore, we investigated the myogenic responses of isolated middle cerebral arteries (MCA) of normotensive and spontaneously hypertensive rats (SHR) after severe impact acceleration diffuse brain injury. TBI diminished myogenic constriction of MCAs isolated from normotensive rats, whereas the 20-HETE-mediated enhanced myogenic response of MCAs isolated from SHRs was not affected by TBI. These results suggest that the optimal cerebral perfusion pressure values and vascular signaling pathways can be different and, therefore, should be targeted differently in normotensive and hypertensive patients following TBI.

Rheological effects of drag-reducing polymers improve cerebral blood flow and oxygenation after traumatic brain injury in rats

Cerebral ischemia has been clearly demonstrated after traumatic brain injury (TBI); however, neuroprotective therapies have not focused on improvement of the cerebral microcirculation. Blood soluble drag-reducing polymers (DRP), prepared from high molecular weight polyethylene oxide, target impaired microvascular perfusion by altering the rheological properties of blood and, until our recent reports, has not been applied to the brain. We hypothesized that DRP improve cerebral microcirculation and oxygenation after TBI. DRP were studied in healthy and traumatized rat brains and compared to saline controls. Using in-vivo two-photon laser scanning microscopy over the parietal cortex, we showed that after TBI, nanomolar concentrations of intravascular DRP significantly enhanced microvascular perfusion and tissue oxygenation in peri-contusional areas, preserved blood-brain barrier integrity and protected neurons. The mechanisms of DRP effects were attributable to reduction of the near-vessel wall cell-free layer which increased near-wall blood flow velocity, microcirculatory volume flow, and number of erythrocytes entering capillaries, thereby reducing capillary stasis and tissue hypoxia as reflected by a reduction in NADH. Our results indicate that early reduction in CBF after TBI is mainly due to ischemia; however, metabolic depression of contused tissue could be also involved.

Traumatic brain injury-induced autoregulatory dysfunction and spreading depression-related neurovascular uncoupling: Pathomechanisms, perspectives, and therapeutic implications

Traumatic brain injury (TBI) is a major health problem worldwide. In addition to its high mortality (35-40%), survivors are left with cognitive, behavioral, and communicative disabilities. While little can be done to reverse initial primary brain damage caused by trauma, the secondary injury of cerebral tissue due to cerebromicrovascular alterations and dysregulation of cerebral blood flow (CBF) is potentially preventable. This review focuses on functional, cellular, and molecular changes of autoregulatory function of CBF (with special focus on cerebrovascular myogenic response) that occur in cerebral circulation after TBI and explores the links between autoregulatory dysfunction, impaired myogenic response, microvascular impairment, and the development of secondary brain damage. We further provide a synthesized translational view of molecular and cellular mechanisms involved in cortical spreading depolarization-related neurovascular dysfunction, which could be targeted for the prevention or amelioration of TBI-induced secondary brain damage.

Chronic cerebrovascular dysfunction after traumatic brain injury

Traumatic brain injuries (TBI) often involve vascular dysfunction that leads to long-term alterations in physiological and cognitive functions of the brain. Indeed, all the cells that form blood vessels and that are involved in maintaining their proper function can be altered by TBI. This Review focuses on the different types of cerebrovascular dysfunction that occur after TBI, including cerebral blood flow alterations, autoregulation impairments, subarachnoid hemorrhage, vasospasms, blood-brain barrier disruption, and edema formation. We also discuss the mechanisms that mediate these dysfunctions, focusing on the cellular components of cerebral blood vessels (endothelial cells, smooth muscle cells, astrocytes, pericytes, perivascular nerves) and their known and potential roles in the secondary injury cascade. © 2016 Wiley Periodicals, Inc.

Brain monitoring in severe head injury: a practical guide

There is, as yet, no specific therapy available for post-traumatic brain damage; the treatment of head injury is therefore aimed at limitation of secondary damage at the cellular, whole organ and systemic level.

The purpose of monitoring the injured brain is twofold:

1. to obtain a better understanding of the mechanisms by which pathophysiological processes further damage the injured brain

2. to continuously detect potentially harmful influences and allow them to be reversed before damage is done.

In this review, we provide a general overview of mechanisms of brain damage due to high intracranial pressure (ICP) and discuss the following ‘brain specific’ haemodynamic monitoring techniques:

• ICP/CPP (cerebral perfusion pressure) monitoring;

• jugular vein saturation (SjO2) monitoring;

• cerebral oxygen monitoring (PtiO2) and near infra-red spectroscopy (NIRS);

• brain temperature monitoring;

• cerebral blood flow (CBF) monitoring; and

• transcranial Doppler.

We also discuss the role of functional techniques such as electroencephalogram (EEG) and evoked potential monitoring. This article gives an overview of the techniques currently available in a rapidly expanding field within neuro-intensive care, mainly for the interest of trauma surgeons, intensivists, and others with a practical need to understand the monitoring of the injured brain.

Autoregulation monitoring and outcome prediction in neurocritical care patients: Does one index fit all?

Indexes PRx and Mx have been formerly introduced to assess cerebral autoregulation and have been shown to be associated with 3-month clinical outcome. In a mixed cohort of neurocritical care patients, we retrospectively investigated the impact of selected clinical characteristics on this association. Forty-one patients (18-77 years) with severe traumatic (TBI, N = 20) and non-traumatic (N = 21) brain injuries were studied. Cerebral blood flow velocity, arterial blood pressure and intracranial pressure were repeatedly recorded during 1-h periods. Calculated PRx and Mx were correlated with 3-month clinical outcome score of modified Rankin Scale (mRS) in different subgroups with specific clinical characteristics. Both PRx and Mx correlated significantly with outcome (PRx: r = 0.38, p < 0.05; AUC = 0.64, n.s./Mx: r = 0.48, p < 0.005; AUC = 0.80, p < 0.005) in the overall group, and in patients with hemicraniectomy (N = 17; PRx: r = 0.73, p < 0.001; AUC = 0.89, p < 0.01/Mx: r = 0.69, p < 0.005; AUC = 0.87, p < 0.05). Mx, not PRx, correlated significantly with mRS in patients with heart failure (N = 17; r = 0.69, p < 0.005; AUC = 0.92, p < 0.005), and in non-traumatic patients (r = 0.49, p < 0.05; AUC = 0.79, p < 0.05). PRx, not Mx, correlated significantly with mRS in TBI patients (r = 0.63, p < 0.01; AUC = 0.89, p < 0.01). Both indexes did not correlate with mRS in diabetes patients (N = 15), PRx failed in hypocapnic patients (N = 26). Both PRx and Mx were significantly associated with 3-month clinical outcome, even in patients with hemicraniectomy. PRx was more appropriate for TBI patients, while Mx was better suited for non-traumatic patients and patients with heart failure. Prognostic values of indexes were affected by diabetes (both Mx and PRx) and hypocapnia (PRx only).

Radial primary percutaneous coronary intervention is independently associated with decreased long-term mortality in high-risk ST-elevation myocardial infarction patients

AIM

To compare long-term clinical outcomes in patients with ST-elevation myocardial infarction (STEMI) treated by primary percutaneous coronary intervention (PPCI) using radial and femoral arterial access.

METHODS AND RESULTS

The present study was an observational cohort study of patients with STEMI treated consecutively with PPCI between 2004 and 2011 at a single centre. The primary end point was all-cause mortality at a median follow-up of 3 years.Among 2727 patients, 1600 (58.7%) underwent PPCI via the femoral route. The femoral group was older (64.7 vs. 61.7 years; P < 0.0001), and had higher rates of diabetes (18.6% vs. 16.0%; P < 0.0001), previous PCI (11.2 vs. 7.8%; P = 0.004), previous myocardial infarction (15.3 vs. 8.3%; P < 0.0001) and cardiogenic shock (9.8 vs. 1.3%; P < 0.0001). Bleeding complications were more frequent in the femoral group (4.7 vs. 1.2%; P < 0.0001). The 5-year death rate was significantly higher in the femoral group than in the radial group (10.4 vs. 3.0%; P < 0.0001). After adjustment for confounding variables, bleeding complications [heart rate 2.07 (95% confidence interval 1.05-4.08)] and femoral access [heart rate 1.60 (95% confidence interval 1.02-2.53)] were independent predictors of all-cause mortality. After stratification using the propensity score, excess long-term mortality in patients treated via the femoral approach was predominantly in patients with a high baseline risk of death.

CONCLUSION

Patients undergoing PPCI via the femoral route are at a higher risk of adverse short-term and long-term outcomes than patients undergoing PPCI via the radial route. Patients with a high baseline risk may benefit most from radial access, and future outcome studies should focus on the most at-risk patients.

Is Impaired Autoregulation Associated with Mortality in Patients with Severe Cerebral Diseases?

BACKGROUND

Cerebral autoregulation (CA) is a mechanism that compensates for variations in cerebral perfusion pressure (CPP) by changes in cerebral blood flow resistance to keep the cerebral blood flow constant. In this study, the relationship between lethal outcome during hospitalisation and the autoregulation-related indices PRx and Mx was investigated.

MATERIALS AND METHODS

Thirty patients (aged 18-77 years, mean 53 ± 16 years) with severe cerebral diseases were studied. Cerebral blood flow velocity (CBFV), arterial blood pressure (ABP) and intracranial pressure (ICP) were repeatedly recorded. CA indices were calculated as the averaged correlation between CBFV and CPP (Mx) and between ABP and ICP (PRx). Positive index values indicated impairment of CA.

RESULTS

Six patients died in hospital. In this group both PRx and Mx were significantly higher than in the group of survivors (PRx: 0.41 ± 0.33 vs 0.09 ± 0.25; Mx: 0.28 ± 0.40 vs 0.03 ± 0.21; p = 0.01 and 0.04, respectively). PRx and Mx correlated significantly with Glasgow Outcome Scale (GOS) score (PRx: R = -0.40, p < 0.05; Mx: R = -0.54, p < 0.005). PRx was the only significant risk factor for mortality (p < 0.05, logistic regression).

CONCLUSION

Increased PRx and Mx were associated with risk of death in patients with severe cerebral diseases. The relationship with mortality was more pronounced in PRx, whereas Mx showed a better correlation with GOS score.

Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature

Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

Continuous optical monitoring of cerebral hemodynamics during head-of-bed manipulation in brain-injured adults

INTRODUCTION

Head-of-bed manipulation is commonly performed in the neurocritical care unit to optimize cerebral blood flow (CBF), but its effects on CBF are rarely measured. This pilot study employs a novel, non-invasive instrument combining two techniques, diffuse correlation spectroscopy (DCS) for measurement of CBF and near-infrared spectroscopy (NIRS) for measurement of cerebral oxy- and deoxy-hemoglobin concentrations, to monitor patients during head-of-bed lowering.

METHODS

Ten brain-injured patients and ten control subjects were monitored continuously with DCS and NIRS while the head-of-bed was positioned first at 30° and then at 0°. Relative CBF (rCBF) and concurrent changes in oxy- (ΔHbO2), deoxy- (ΔHb), and total-hemoglobin concentrations (ΔTHC) from left/right frontal cortices were monitored for 5 min at each position. Patient and control response differences were assessed.

RESULTS

rCBF, ΔHbO2, and ΔTHC responses to head lowering differed significantly between brain-injured patients and healthy controls (P < 0.02). For patients, rCBF changes were heterogeneous, with no net change observed in the group average (0.3 ± 28.2 %, P = 0.938). rCBF increased in controls (18.6 ± 9.4 %, P < 0.001). ΔHbO2, ΔHb, and ΔTHC increased with head lowering in both groups, but to a larger degree in brain-injured patients. rCBF correlated moderately with changes in cerebral perfusion pressure (R = 0.40, P < 0.001), but not intracranial pressure.

CONCLUSION

DCS/NIRS detected differences in CBF and oxygenation responses of brain-injured patients versus controls during head-of-bed manipulation. This pilot study supports the feasibility of continuous bedside measurement of cerebrovascular hemodynamics with DCS/NIRS and provides the rationale for further investigation in larger cohorts.

Cerebrovascular regulation, exercise, and mild traumatic brain injury

A substantial number of people who sustain a mild traumatic brain injury report persistent symptoms. Most common among these symptoms are headache, dizziness, and cognitive difficulties. One possible contributor to sustained symptoms may be compromised cerebrovascular regulation. In addition to injury-related cerebrovascular dysfunction, it is possible that prolonged rest after mild traumatic brain injury leads to deconditioning that may induce physiologic changes in cerebral blood flow control that contributes to persistent symptoms in some people. There is some evidence that exercise training may reduce symptoms perhaps because it engages an array of cerebrovascular regulatory mechanisms. Unfortunately, there is very little work on the degree of impairment in cerebrovascular control that may exist in patients with mild traumatic brain injury, and there are no published studies on the subacute phase of recovery from this injury. This review aims to integrate the current knowledge of cerebrovascular mechanisms that might underlie persistent symptoms and seeks to synthesize these data in the context of exploring aerobic exercise as a feasible intervention to treat the underlying pathophysiology.

Capillary transit time heterogeneity and flow-metabolism coupling after traumatic brain injury

Most patients who die after traumatic brain injury (TBI) show evidence of ischemic brain damage. Nevertheless, it has proven difficult to demonstrate cerebral ischemia in TBI patients. After TBI, both global and localized changes in cerebral blood flow (CBF) are observed, depending on the extent of diffuse brain swelling and the size and location of contusions and hematoma. These changes vary considerably over time, with most TBI patients showing reduced CBF during the first 12 hours after injury, then hyperperfusion, and in some patients vasospasms before CBF eventually normalizes. This apparent neurovascular uncoupling has been ascribed to mitochondrial dysfunction, hindered oxygen diffusion into tissue, or microthrombosis. Capillary compression by astrocytic endfeet swelling is observed in biopsies acquired from TBI patients. In animal models, elevated intracranial pressure compresses capillaries, causing redistribution of capillary flows into patterns argued to cause functional shunting of oxygenated blood through the capillary bed. We used a biophysical model of oxygen transport in tissue to examine how capillary flow disturbances may contribute to the profound changes in CBF after TBI. The analysis suggests that elevated capillary transit time heterogeneity can cause critical reductions in oxygen availability in the absence of 'classic' ischemia. We discuss diagnostic and therapeutic consequences of these predictions.

Adherence to guidelines for management of cerebral perfusion pressure and outcome in patients who have severe traumatic brain injury

PURPOSE

The aims of this study are to assess adherence to the Brain Trauma Foundation (BTF) cerebral perfusion pressure (CPP) guidelines and to determine if adherence is associated with mortality in patients who have a severe traumatic brain injury.

MATERIALS AND METHODS

Retrospective cohort study of 127 patients admitted to one intensive care unit between 2006 and 2012. Adherence to BTF guidelines was measured as the time that the CPP was within 50 to 70 mm Hg divided by the total time of CPP monitoring (CPP time index).

RESULTS

The percentage of time that the CPP was within the recommended range was 31.6% (SD, 22.2); CPP was greater than 70 mm Hg for 63.9% (SD, 26.2) of the time and less than 50 mm Hg for 4.5% of the time (SD, 16.3). After adjustment for covariates, CPP time index (between 50 and 70 mm Hg) was not associated with hospital mortality (odds ratio [OR], 1.2; 95% confidence interval [CI], 0.98-1.6; P= .079). The time indices for CPP ≥70 and <50 mm Hg were associated with decreased (OR, 0.66; 95%CI, 0.52-0.82; P< .0001) and increased (OR, 9.9; 95% CI, 1.4-69.6; P= .021) mortality, respectively.

CONCLUSION

Cerebral perfusion pressure was greater than 70 mm Hg for most of the time. This level of CPP was associated with decreased hospital mortality.

Bolus arrival time and cerebral blood flow responses to hypercarbia

The purpose of this study was to evaluate how cerebral blood flow and bolus arrival time (BAT) measures derived from arterial spin labeling (ASL) MRI data change for different hypercarbic gas stimuli. Pseudocontinuous ASL (pCASL) was applied (3.0T; spatial resolution=4 × 4 × 7 mm(3); repetition time/echo time (TR/TE)=3,600/11 ms) sequentially in healthy volunteers (n=12; age=30±4 years) for separate experiments in which (i) normocarbic normoxia (i.e., room air), hypercarbic normoxia (i.e., 5% CO₂/21% O₂/74% N2), and hypercarbic hyperoxia (i.e., carbogen: 5% CO₂/95% O₂) gas was administered (12 L/minute). Cerebral blood flow and BAT changes were quantified using models that account for macrovascular signal and partial volume effects in all gray matter and regionally in cerebellar, temporal, occipital, frontal, and parietal lobes. Regional reductions in BAT of 4.6% to 7.7% and 3.3% to 6.6% were found in response to hypercarbic normoxia and hypercarbic hyperoxia, respectively. Cerebral blood flow increased by 8.2% to 27.8% and 3.5% to 19.8% for hypercarbic normoxia and hypercarbic hyperoxia, respectively. These findings indicate that changes in BAT values may bias functional ASL data and thus should be considered when choosing appropriate experimental parameters in calibrated functional magnetic resonance imaging or ASL cerebrovascular reactivity experiments that use hypercarbic gas stimuli.

Injury timing alters metabolic, inflammatory and functional outcomes following repeated mild traumatic brain injury

Repeated head injuries are a major public health concern both for athletes, and members of the police and armed forces. There is ample experimental and clinical evidence that there is a period of enhanced vulnerability to subsequent injury following head trauma. Injuries that occur close together in time produce greater cognitive, histological, and behavioral impairments than do injuries separated by a longer period. Traumatic brain injuries alter cerebral glucose metabolism and the resolution of altered glucose metabolism may signal the end of the period of greater vulnerability. Here, we injured mice either once or twice separated by three or 20days. Repeated injuries that were separated by three days were associated with greater axonal degeneration, enhanced inflammatory responses, and poorer performance in a spatial learning and memory task. A single injury induced a transient but marked increase in local cerebral glucose utilization in the injured hippocampus and sensorimotor cortex, whereas a second injury, three days after the first, failed to induce an increase in glucose utilization at the same time point. In contrast, when the second injury occurred substantially later (20days after the first injury), an increase in glucose utilization occurred that paralleled the increase observed following a single injury. The increased glucose utilization observed after a single injury appears to be an adaptive component of recovery, while mice with 2 injuries separated by three days were not able to mount this response, thus this second injury may have produced a significant energetic crisis such that energetic demands outstripped the ability of the damaged cells to utilize energy. These data strongly reinforce the idea that too rapid return to activity after a traumatic brain injury can induce permanent damage and disability, and that monitoring cerebral energy utilization may be a tool to determine when it is safe to return to the activity that caused the initial injury.

Neurotraumatology

Neurotraumatology has its roots in ancient history, but its modern foundations are the physical examination, imaging to localize the pathology, and thoughtful medical and surgical decision making. The neurobiology of cranial and spinal injury is similar, with the main goal of therapies being to limit secondary injury. Brain injury treatment focuses on minimizing parenchymal swelling within the confined cranial vault. Spine injury treatment has the additional consideration of spinal coumn stability. Current guidelines for non-operative and operative management are reviewed in this chapter.

BOLD MRI and early impairment of cerebrovascular reserve after aneurysmal subarachnoid hemorrhage

Currently no biological or radiological marker is available to identify patients at risk of delayed ischemic deficit (DIND) after aneurysmal subarachnoid hemorrhage (aSAH). We hypothesized whether MR-based quantitative assessment of cerebrovascular reserve (CVR) would detect early radiological markers of vasospasm and DIND. This manuscript describes our initial experience with this population. Five patients with aSAH underwent blood-oxygen level dependent-MRI (BOLD-MRI) with CO2 challenge for assessment of whole brain CVR. Patients were examined as soon as possible after aneurysm treatment. We obtained good quality anatomical and functional images without complications. Initial anatomical cerebrovascular imaging showed no vasospasm in all patients. Two patients had abnormal CVR-MRI tests and both developed DIND. Of the 3 others with normal CVR-MRI, one developed posterior circulation DIND. One patient with a normal CVR-MRI developed angiographic vasospasm but no DIND. Changes in CVR maps as early as 36 h after hemorrhage had good spatial correlation with delayed ischemia during short-term follow-up. Our series shows that MRI with CO2 challenge is feasible in this difficult population. Further developments might allow BOLD-MRI with CO2 challenge to identify patients at risk and provide anatomical correlation with future DIND, opening a new venue for prophylactic treatments. Further study is warranted in a larger patient cohort.

Time-varying modeling of cerebral hemodynamics

The scientific and clinical importance of cerebral hemodynamics has generated considerable interest in their quantitative understanding via computational modeling. In particular, two aspects of cerebral hemodynamics, cerebral flow autoregulation (CFA) and CO2 vasomotor reactivity (CVR), have attracted much attention because they are implicated in many important clinical conditions and pathologies (orthostatic intolerance, syncope, hypertension, stroke, vascular dementia, mild cognitive impairment, Alzheimer's disease, and other neurodegenerative diseases with cerebrovascular components). Both CFA and CVR are dynamic physiological processes by which cerebral blood flow is regulated in response to fluctuations in cerebral perfusion pressure and blood CO2 tension. Several modeling studies to date have analyzed beat-to-beat hemodynamic data in order to advance our quantitative understanding of CFA-CVR dynamics. A confounding factor in these studies is the fact that the dynamics of the CFA-CVR processes appear to vary with time (i.e., changes in cerebrovascular characteristics) due to neural, endocrine, and metabolic effects. This paper seeks to address this issue by tracking the changes in linear time-invariant models obtained from short successive segments of data from ten healthy human subjects. The results suggest that systemic variations exist but have stationary statistics and, therefore, the use of time-invariant modeling yields "time-averaged models" of physiological and clinical utility.

Linear and Nonlinear Modeling of Cerebral Flow Autoregulation Using Principal Dynamic Modes

Cerebral Flow Autoregulation (CFA) is the dynamic process by which cerebral blood flow is maintained within physiologically acceptable bounds during fluctuations of cerebral perfusion pressure. The distinction is made with “static” flow autoregulation under steady-state conditions of perfusion pressure, described by the celebrated “autoregulatory curve” with a homeostatic plateau. This paper studies the dynamic CFA during changes in perfusion pressure, which attains critical clinical importance in patients with stroke, traumatic brain injury and neurodegenerative disease with a cerebrovascular component. Mathematical and computational models have been used to advance our quantitative understanding of dynamic CFA and to elucidate the underlying physiological mechanisms by analyzing the relation between beat-to-beat data of mean arterial blood pressure (viewed as input) and mean cerebral blood flow velocity(viewed as output) of a putative CFA system. Although previous studies have shown that the dynamic CFA process is nonlinear, most modeling studies to date have been linear. It has also been shown that blood CO2 tension affects the CFA process. This paper presents a nonlinear modeling methodology that includes the dynamic effects of CO2 tension (or its surrogate, end-tidal CO2) as a second input and quantifies CFA from short data-records of healthy human subjects by use of the modeling concept of Principal Dynamic Modes (PDMs). The PDMs improve the robustness of the obtained nonlinear models and facilitate their physiological interpretation. The results demonstrate the importance of including the CO2 input in the dynamic CFA study and the utility of nonlinear models under hypercapnic or hypocapnic conditions.

Linear and nonlinear modeling of cerebral flow autoregulation using principal dynamic modes

Cerebral Flow Autoregulation (CFA) is the dynamic process by which cerebral blood flow is maintained within physiologically acceptable bounds during fluctuations of cerebral perfusion pressure. The distinction is made with “static” flow autoregulation under steady-state conditions of perfusion pressure, described by the celebrated “autoregulatory curve” with a homeostatic plateau. This paper studies the dynamic CFA during changes in perfusion pressure, which attains critical clinical importance in patients with stroke, traumatic brain injury and neurodegenerative disease with a cerebrovascular component. Mathematical and computational models have been used to advance our quantitative understanding of dynamic CFA and to elucidate the underlying physiological mechanisms by analyzing the relation between beat-to-beat data of mean arterial blood pressure (viewed as input) and mean cerebral blood flow velocity(viewed as output) of a putative CFA system. Although previous studies have shown that the dynamic CFA process is nonlinear, most modeling studies to date have been linear. It has also been shown that blood CO2 tension affects the CFA process. This paper presents a nonlinear modeling methodology that includes the dynamic effects of CO2 tension (or its surrogate, end-tidal CO2) as a second input and quantifies CFA from short data-records of healthy human subjects by use of the modeling concept of Principal Dynamic Modes (PDMs). The PDMs improve the robustness of the obtained nonlinear models and facilitate their physiological interpretation. The results demonstrate the importance of including the CO2 input in the dynamic CFA study and the utility of nonlinear models under hypercapnic or hypocapnic conditions.

Rehabilitation of Concussion and Post-concussion Syndrome

CONTEXT

Prolonged symptoms after concussion are called post-concussion syndrome (PCS), which is a controversial disorder with a wide differential diagnosis.

EVIDENCE ACQUISITION

MEDLINE and PubMed searches were conducted for the years 1966 to 2011 using the search terms brain concussion/complications OR brain concussion/diagnosis OR brain concussion/therapy AND sports OR athletic injuries. Secondary search terms included post-concussion syndrome, trauma, symptoms, metabolic, sports medicine, cognitive behavioral therapy, treatment and rehabilitation. Additional articles were identified from the bibliographies of recent reviews.

RESULTS

Of 564 studies that fulfilled preliminary search criteria, 119 focused on the diagnosis, pathophysiology, and treatment/rehabilitation of concussion and PCS and formed the basis of this review. Rest is the primary treatment for the acute symptoms of concussion. Ongoing symptoms are either a prolonged version of the concussion pathophysiology or a manifestation of other processes, such as cervical injury, migraine headaches, depression, chronic pain, vestibular dysfunction, visual dysfunction, or some combination of conditions. The pathophysiology of ongoing symptoms from the original concussion injury may reflect multiple causes: anatomic, neurometabolic, and physiologic.

CONCLUSIONS

Treatment approaches depend on the clinician's ability to differentiate among the various conditions associated with PCS. Early education, cognitive behavioral therapy, and aerobic exercise therapy have shown efficacy in certain patients but have limitations of study design. An algorithm is presented to aid clinicians in the evaluation and treatment of concussion and PCS and in the return-to-activity decision.

Cerebrovascular response in children following severe traumatic brain injury

OBJECTIVE

To describe the pathophysiologic response in cerebral blood flow (CBF) and autoregulation after severe traumatic brain injury (TBI), Glasgow Coma Score (GCS) ≤8 on admission, in children, defining a baseline for future studies.

METHODS

Retrospective chart review of 95 patients following TBI, ages 0.1-18.4 years (<5 years (n = 44), <2 years (n = 17)) for CBF using Xenon Computerized Tomography (XeCT) over a 10-year period and 6-month Glasgow Outcome Scores (GOS). A total of 140 CBF studies were performed variably from admission up to post injury day (PID) 9; 27 patients underwent repeat CBF study after PaCO(2) was manipulated to determine CO(2) vasoreactivity (CO(2)VR).

RESULTS

Mean CBF on admission (PID 0, n = 26) was 32.05 ± 21.45 ml/100 g/min (mean ± SEM) and was ≤20 ml/100 g/min in eight patients. At PID 1-2, mean CBF increased to 55.36 ± 23.11 ml/100 g/min. There was significant differences in mean CBF of "favorable" outcomes (GOS ≥ 4) versus "unfavorable" outcome (GOS ≤ 3) (61.74 ± 18.27 vs. 46.54 ± 26.26, respectively (P = 0.01)). "Unfavorable" outcomes were seen in all patients with CBF ≤20 ml/100 mg/min during PID 0-2 and in 76.5% of children <2 years. CO(2)VR <2%/Torr PaCO(2) within PID 0-2 was significantly associated with "unfavorable" outcome (P = 0.029).

CONCLUSION

Younger age, early or later low CBF, and CO(2)VR <2%/Torr PaCO(2) were correlated with poorer outcomes in children. This represents the largest experience with XeCT CBF in children and confirms our preliminary report of low early CBF after TBI in children, disturbed CO(2)VR, and relationship of low CBF and unfavorable outcome.

Critical thresholds for transcranial Doppler indices of cerebral autoregulation in traumatic brain injury

BACKGROUND

Transcranial Doppler-derived indices of cerebral autoregulation are related to outcome after TBI. We analyzed our retrospective material to identify thresholds discriminative of outcome for these indices.

METHODS

248 sedated and ventilated patients after head injury were eligible for the study. The indices of autoregulation derived from transcranial Doppler were calculated as correlation coefficients of blood flow velocity with cerebral perfusion pressure (index Mx) or arterial blood pressure (index Mxa). 2 × 2 tables were created grouping patients according to survival-death or favorable-unfavorable outcomes and varying thresholds for Mx and Mxa. Pearson's chi-square was calculated. Thresholds returning the highest chi-square value were assumed to have the best discriminative value between survival-death and favorable-unfavorable outcomes.

RESULTS

Mx and Mxa demonstrated that worse autoregulation is associated with poorer outcome and greater mortality (P = 0.0033 for Mx and P = 0.047 for Mxa). Both indices were more effective for prediction of favorable outcome than mortality. Chi-square for Mx showed a double peak with thresholds at 0.05 and 0.3. Mxa had only one peak at 0.3. Peak chi-square for Mx (11.3) was greater than for Mxa (8.7), indicating that Mx was a better discriminant of outcome than Mxa.

CONCLUSIONS

We propose that Mx greater than 0.3 indicates definitely disturbed autoregulation and lower than 0.05 good autoregulation. For values between 0.05 and 0.3 the state of autoregulation is uncertain.

Effects of ageing on cerebral haemodynamics assessed during respiratory manoeuvres

BACKGROUND

cerebral autoregulation (CA) is the ability to control cerebral blood flow during fluctuations in arterial blood pressure (ABP). It is impaired in a number of conditions including acute stroke, though studies so far have not found a decline in CA with age. CA is very sensitive to changes in pCO₂.

OBJECTIVE

this study investigates the effect of ageing on CA using a moving-window autoregressive moving average (MW-ARMA) to calculate CA as autoregulatory index (ARMA-ARI) during hypercapnia and hypocapnia, to ascertain whether this method would detect age-related differences in CA due to change in pCO₂.

METHOD

ECG was used to measure R-R interval, Finapres to measure ABP and capnography to measure end-tidal CO₂. Transcranial Doppler ultrasonography was used to measure left and right middle cerebral artery cerebral blood flow velocity (CBFV). Hypercapnia was induced by a breath-hold, hypocapnia by hyperventilation.

RESULTS

thirty volunteers of mean age 25 ± 6 years and 30 volunteers of mean age 64 ± 4 years were recruited. CBFV was higher and change in CBFV due to respiratory manoeuvre was significantly greater in the younger group compared with the older group. However, no difference in ARMA-ARI was found between the groups.

CONCLUSION

these findings suggest that CA is not affected by healthy ageing.

Transcranial Doppler pulsatility index: not an accurate method to assess intracranial pressure

BACKGROUND

Transcranial Doppler sonography (TCD) assessment of intracranial blood flow velocity has been suggested to accurately determine intracranial pressure (ICP).

OBJECTIVE

We attempted to validate this method in patients with communicating cerebrospinal fluid systems using predetermined pressure levels.

METHODS

Ten patients underwent a lumbar infusion test, applying 4 to 5 preset ICP levels. On each level, the pulsatility index (PI) in the middle cerebral artery was determined by measuring the blood flow velocity using TCD. ICP was simultaneously measured with an intraparenchymal sensor. ICP and PI were compared using correlation analysis. For further understanding of the ICP-PI relationship, a mathematical model of the intracranial dynamics was simulated using a computer.

RESULTS

The ICP-PI regression equation was based on data from 8 patients. For 2 patients, no audible Doppler signal was obtained. The equation was ICP = 23*PI + 14 (R = 0.22, P < .01, N = 35). The 95% confidence interval for a mean ICP of 20 mm Hg was -3.8 to 43.8 mm Hg. Individually, the regression coefficients varied from 42 to 90 and the offsets from -32 to +3. The mathematical simulations suggest that variations in vessel compliance, autoregulation, and arterial pressure have a serious effect on the ICP-PI relationship.

CONCLUSIONS

The in vivo results show that PI is not a reliable predictor of ICP. Mathematical simulations indicate that this is caused by variations in physiological parameters.

Cerebrovascular pathophysiology following mild traumatic brain injury

Mild traumatic brain injury (mTBI) or sport-induced concussion has recently become a prominent concern not only in the athletic setting (i.e. sports venue) but also in the general population. The majority of research to date has aimed at understanding the neurological and neuropsychological outcomes of injury as well as return-to-play guidelines. Remaining relatively unexamined has been the pathophysiological aspect of mTBI. Recent technological advances including transcranial Doppler ultrasound and near infrared spectroscopy have allowed researchers to examine the systemic effects of mTBI from rest to exercise, and during both asymptomatic and symptomatic conditions. In this review, we focus on the current research available from both human and experimental (animal) studies surrounding the pathophysiology of mTBI. First, the quest for a unified definition of mTBI, its historical development and implications for future research is discussed. Finally, the impact of mTBI on the control and regulation of cerebral blood flow, cerebrovascular reactivity, cerebral oxygenation and neuroautonomic cardiovascular regulation, all of which may be compromised with mTBI, is discussed.

A comparison study of cerebral autoregulation assessed with transcranial Doppler and cortical laser Doppler flowmetry

OBJECTIVES

We compared autoregulation monitored with cortical laser Doppler flowmetry (LDF) and autoregulation monitored with transcranial Doppler (TCD) in the middle cerebral artery (MCA) to verify the hypothesis that, following brain trauma, cortical vessel autoregulation to intracranial hypertension is different than assessed in the MCA.

METHODS

Data collected from 29 head injured patients were analysed retrospectively. Arterial blood pressure (ABP), intracranial pressure (ICP), flow velocity (FV) of the MCA and cortical flux (LDF) were monitored. Indices of cortical autoregulation (Lx) and autoregulation of cerebral blood flow in the MCA (Mx) were calculated as a moving correlation coefficient between slow waves of LDF and cerebral perfusion pressure (CPP) (Lx) or FV and CPP (Mx), respectively. Intact autoregulation was indicated by negative values for Lx and Mx; disturbed autoregulation was reflected by positive values.

RESULTS

FV and LDF showed a high coherence in the slow wave spectrum of 1-4 cycles/min (mean: 0.79 +/- 0.12), indicating that similar information regarding autoregulation is carried by both signals. Mx and Lx correlated in all patients (R=0.43, p=0.02). On average, Lx was significantly higher than Mx; the mean difference was 0.13 +/- 0.38 (p=0.032), potentially due to severe intracranial hypertension above 40 mmHg, driving CPP values below 60 mmHg.

CONCLUSION

After traumatic brain injury, cortical autoregulation appears to be worse than autoregulation assessed in the MCA during rising ICP and falling CPP. When CPP is above 60 mmHg, cortical assessed autoregulation is similar to autoregulation assessed in the MCA.

Intraaortic Balloon Pump Counterpulsation and Cerebral Autoregulation: an observational study

Background

The use of Intra-aortic counterpulsation is a well established supportive therapy for patients in cardiac failure or after cardiac surgery. Blood pressure variations induced by counterpulsation are transmitted to the cerebral arteries, challenging cerebral autoregulatory mechanisms in order to maintain a stable cerebral blood flow. This study aims to assess the effects on cerebral autoregulation and variability of cerebral blood flow due to intra-aortic balloon pump and inflation ratio weaning.

Methods

Cerebral blood flow was measured using transcranial Doppler, in a convenience sample of twenty patients requiring balloon counterpulsation for refractory cardiogenic shock (N = 7) or a single inotrope to maintain mean arterial pressure following an elective placement of an intra-aortic balloon pump for cardiac surgery (N = 13). Simultaneous blood pressure at the aortic root was recorded via the intra-aortic balloon pump. Cerebral blood flow velocities were recorded for six minute intervals at a 1:1 balloon inflation-ratio (augmentation of all cardiac beats) and during progressive reductions of the inflation-ratio to 1:3 (augmentation of one every third cardiac beat). Real time comparisons of peak cerebral blood flow velocities with systolic blood pressure were performed using cross-correlation analysis. The primary endpoint was assessment of cerebral autoregulation using the time delay between the peak signals for cerebral blood flow velocity and systolic blood pressure, according to established criteria. The variability of cerebral blood flow was also assessed using non-linear statistics.

Results

During the 1:1 inflation-ratio, the mean time delay between aortic blood pressure and cerebral blood flow was -0.016 seconds (95% CI: -0.023,-0.011); during 1:3 inflation-ratio mean time delay was significantly longer at -0.010 seconds (95% CI: -0.016, -0.004, P < 0.0001). Finally, upon return to a 1:1 inflation-ratio, time delays recovered to those measured at baseline. During inflation-ratio reduction, cerebral blood flow irregularities reduced over time, whilst cerebral blood flow variability at end-diastole decreased in patients with cardiogenic shock.

Conclusions

Weaning counterpulsation from 1:1 to 1:3 inflation ratio leads to a progressive reduction in time delays between systolic blood pressure and peak cerebral blood flow velocities suggesting that although preserved, there is a significant delay in the establishment of cerebral autoregulatory mechanisms. In addition, cerebral blood flow irregularities (i.e. surrogate of flow adaptability) decrease and a loss of cerebral blood flow chaotic pattern occurs during the end-diastolic phase of each beat in patients with cardiogenic shock.

Intracranial pressure pulse amplitude during changes in head elevation: a new parameter for determining optimum cerebral perfusion pressure?

OBJECTIVE

During short-term postural changes, the factors determining the amplitude of intracranial pulse pressure (ICPPA) remain constant, except for cerebrovascular resistance (CVR). Therefore, it may be possible to draw conclusions from the ICPPA onto the cerebrovascular resistance (CVR) and thus the relative change in cerebral perfusion pressure (CPP).

METHODS

Age, sex, disease, Glasgow Coma Scale score, placement of ventricular drain, blood gas analysis, and parameters of airway management were prospectively recorded in 40 patients. The changes in intracranial pressure (ICP), CPP, mean arterial pressure (MAP), and ICPPA at head elevations of 0 degrees, 30 degrees, and 60 degrees were measured and analyzed online. Status of cerebrovascular autoregulation was checked using the pressure-reactivity index (PRx).

RESULTS

Altogether 36 subjects fulfilled the study conditions. Three patients had positive PRx indicating disturbed autoregulation and were excluded. Thus, 33 were left for analysis (18 females and 15 males). All of them were sedated and mechanically ventilated with Glasgow Coma scores ranging from 3-8. During change in head elevation from 0 degrees to 60 degrees, we found a significant (p < 0.05) improvement of the ICP, an increase of the ICCPA, a reduction of the MAP, and a decrease in the CPP. Increasing ICPPA was linked to decreasing CPP (0 degrees to 60 degrees, r = -0.42, p < 0.05).

CONCLUSIONS

Head elevation is an important part of the ICP and CPP therapy in neurointensive care. When searching for the patient-specific optimum upper body position, ICPPA may provide additional information. Providing that the cerebral autoregulation is intact, the lowest ICPPA of a patient corresponds to the individual upper body position with the highest CPP.