Maintaining the permanence principle of death during normothermic regional perfusion in controlled donation after the circulatory determination of death: Results of a prospective clinical study.

One concern about the use of normothermic regional perfusion (NRP) in controlled donation after the circulatory determination of death (cDCD) is that the brain may be perfused. We aimed to demonstrate that certain technical maneuvers preclude such brain perfusion. A nonrandomized trial was performed on cDCD donors. In abdominal normothermic regional perfusion (A-NRP), the thoracic aorta was blocked with an intra-aortic occlusion balloon. In thoracoabdominal normothermic regional perfusion (TA-NRP), the arch vessels were clamped and the cephalad ends vented to the atmosphere. The mean intracranial arterial blood pressure (ICBP) was invasively measured at the circle of Willis. Ten cDCD donors subject to A-NRP or TA-NRP were included. Mean ICBP and mean blood pressure at the thoracic and the abdominal aorta during the circulatory arrest were 17 (standard deviation [SD], 3), 17 (SD, 3), and 18 (SD, 4) mmHg, respectively. When A-NRP started, pressure at the abdominal aorta increased to 50 (SD, 13) mmHg, while the ICBP remained unchanged. When TA-NRP was initiated, thoracic aorta pressure increased to 71 (SD, 18) mmHg, but the ICBP remained unmodified. Recorded values of ICBP during NRP were 10 mmHg. In conclusion, appropriate technical measures applied during NRP preclude perfusion of the brain in cDCD. This study might help to expand NRP and increase the number of organs available for transplantation.

The Pathophysiology of Collateral Circulation in Acute Ischemic Stroke.

Cerebral collateral circulation is a network of blood vessels which stabilizes blood flow and maintains cerebral perfusion whenever the main arteries fail to provide an adequate blood supply, as happens in ischemic stroke. These arterial networks are able to divert blood flow to hypoperfused cerebral areas. The extent of the collateral circulation determines the volume of the salvageable tissue, the so-called "penumbra". Clinically, this is associated with greater efficacy of reperfusion therapies (thrombolysis and thrombectomy) in terms of better short- and long-term functional outcomes, lower incidence of hemorrhagic transformation and of malignant oedema, and smaller cerebral infarctions. Recent advancements in brain imaging techniques (CT and MRI) allow us to study these anastomotic networks in detail and increase the likelihood of making effective therapeutic choices. In this narrative review we will investigate the pathophysiology, the clinical aspects, and the possible diagnostic and therapeutic role of collateral circulation in acute ischemic stroke.

An anatomically detailed arterial-venous network model. Cerebral and coronary circulation.

In recent years, several works have addressed the problem of modeling blood flow phenomena in veins, as a response to increasing interest in modeling pathological conditions occurring in the venous network and their connection with the rest of the circulatory system. In this context, one-dimensional models have proven to be extremely efficient in delivering predictions in agreement with in-vivo observations. Pursuing the increase of anatomical accuracy and its connection to physiological principles in haemodynamics simulations, the main aim of this work is to describe a novel closed-loop Anatomically-Detailed Arterial-Venous Network (ADAVN) model. An extremely refined description of the arterial network consisting of 2,185 arterial vessels is coupled to a novel venous network featuring high level of anatomical detail in cerebral and coronary vascular territories. The entire venous network comprises 189 venous vessels, 79 of which drain the brain and 14 are coronary veins. Fundamental physiological mechanisms accounting for the interaction of brain blood flow with the cerebro-spinal fluid and of the coronary circulation with the cardiac mechanics are considered. Several issues related to the coupling of arterial and venous vessels at the microcirculation level are discussed in detail. Numerical simulations are compared to patient records published in the literature to show the descriptive capabilities of the model. Furthermore, a local sensitivity analysis is performed, evidencing the high impact of the venous circulation on main cardiovascular variables.

Developing a Digital Technology System to Address COVID-19 Health Needs in Guatemala: A Scientific Diaspora Case Study.

Scientific diasporas are organized groups of professionals who work together to contribute to their country of origin. Since the start of the COVID-19 pandemic in 2020, scientific diasporas around the world have focused their efforts to support the public health response in their countries of origin. As the first cases of COVID-19 were reported in Guatemala in March of 2020, a team of four Guatemalan nationals, residing abroad and in-country, started collaborating to tackle COVID-19 misinformation and issues with healthcare services navigation. Their collaboration was facilitated by FUNDEGUA, a Guatemalan nonprofit, which provided a legal framework to establish partnerships and fundraise. The team created a digital technological system called ALMA (Asistente de Logística Médica Automatizada in Spanish). A female character named ALMA was created to personify the digital information services, through social media profiles, an interactive website, a free national multilingual call center, and an artificial intelligence-based chatbot. More members joined the nascent interdisciplinary diaspora through professional/personal references or social media. ALMA provided a platform for Guatemalan nationals to contribute with their skillset to their country during a global crisis through flexible schedules and short- or long-term involvement. As the team grew, the services for query resolution and information dissemination expanded as well. The ALMA initiative shows that scientific diasporas can provide an avenue for professionals to contribute to Guatemala, regardless of their residence and job commitments.

Recognize and Alleviate a Resource Management Conundrum Facing Science Diaspora Networks.

Increasingly, science diaspora networks are managed by formal organizations such as embassies or non-profit organizations. Researchers have studied these networks to understand how they influence international collaborations and science diplomacy, and to determine which network activities foster those outcomes and which do not. In this perspective, we suggest that many of these network organizations confront an underappreciated conundrum for managing resources: organizations with few resources must learn how to obtain more resources despite lacking means to do so. To substantiate our suggestion, we do the following. We review exploratory results from a study of network organizations that indicate that these organizations generally lack resources, learn too little from each other, and struggle to overcome the resource conundrum. We also show that this conundrum is expected from organizational theory based on bounded rationality. To help organizations confront the issue, we do the following. First we provide a new database of operating science diaspora networks. We encourage managers of network organizations to use it as a resource to identify peers with whom to regularly exchange knowledge about securing resources. We also suggest that other scientific organizations should infuse network organizations with fresh resources. Ultimately, we urge all relevant stakeholders to recognize that the conundrum results not from the shortcomings of individual managers, but rather is a legitimate organizational phenomena that must be addressed by organizational design.

Connecting Scientists Residing Abroad: A Review of Converciencia as a Practice to Engage the Guatemalan Scientific Diaspora From 2005-2020.

In 2005, the Guatemala National Secretariat of Science and Technology (Senacyt) introduced Converciencia, a program designed to connect Guatemalan scientists residing abroad with their country of origin. Converciencia has been a flagship practice for over 15 years. This program involves three main groups of participants: (i) science and technology (S&T) policy agents, (ii) the scientific community (including parts of the Guatemala scientific diaspora, GSD), and (iii) host institutions (local co-organizers, mainly universities, and research institutes). This article presents a comprehensive and balanced overview of the Converciencia program applying an in-depth analysis of its creation, evolution, leading trends, and legacies. Using a qualitative methodology and conducting a four-level analysis (descriptive, explanatory, normative, and prescriptive) allowed for the identification of nuances of this S&T practice in the context of a scientifically lagging country such as Guatemala. The detailed data collected through documentary and desk review, gray literature, focus group discussions, and semi-structured interviews resulted in a framework to highlight the strengths, weaknesses, opportunities, and threats (SWOTs) in the planning, organization, implementation, monitoring, and perception of the results achieved by Converciencia. Findings portray the contrasting views and perceptions from a single S&T practice, depending on the participating parties' roles and responsibilities. Direct participants examined how Converciencia has achieved its objectives while questioning the effectiveness and impact that the resources allocated to the initiative have yielded over time. Evidence indicates that despite the design, coordination, and evaluation limits of Converciencia, the GSD, the scientific community in Guatemala, and the host institutions are interested in the continuity of the practice. Indeed, the main recommendation involves restructuring and turning Converciencia into a robust S&T policy. Converciencia as a policy engaging the GSD could produce greater results and impacts by involving all the key actors in co-designing activities, clearly determining roles and responsibilities, and establishing performance and impact indicators for evaluation.

Engaging the Guatemala Scientific Diaspora: The Power of Networking and Shared Learning.

The underdevelopment of the higher education system in Guatemala and the fragility of its science and technology (S&T) contexts have compelled a significant number of talented Guatemalan scientists to be trained, educated, and employed abroad. The relocation of such skilled human power to different countries and regions has resulted in a growing Guatemalan Scientific Diaspora (GSD). Until recently, the emigration of scientists from the Global South to scientifically advanced countries in the North was studied as it negatively impacted the countries of origin. However, technological upgrades and globalization have progressively shifted the paradigm in which such scientific diasporas interact and connect, thus enabling them to influence their home countries positively. Due to the lack of knowledge-based evidence and functioning connecting platforms, the value and potential of the GSD in their involvement in proposing solutions to complex socio-economic, environmental, and other challenges faced by Guatemalan society remain unknown. Moreover, the lack of interaction of relevant stakeholders (S&T policy agents, international partners, higher education institutions and research centers, industry, and relevant not governmental organizations) represents a pervasive obstacle to the untapped impact of the GSD in the country. This study outlines the Guatemalan scientific diasporas' networking as a mechanism for building research excellence and intellectual capital. This force could respond to the need to strengthen the national science capacities and meet the demands for knowledge production and access to broader sectors of society. This research applied qualitative methodology that, through the conduction of focus group discussions and semi-structured interviews with members of the Guatemalan scientific community and relevant key stakeholders, delved into the existence and articulation of the GSD and potential stages for their engagement with their country of origin. Findings highlight the importance of digital and technological pathways that might leverage the GSD's knowledge and experience, channeling skills, and international connections for better interaction with the Guatemalan society. Furthermore, the discussion addresses how technology might turn brain drain into brain circulation, enabling the articulation of the GSD as a viable opportunity to generate collaboration between scientists abroad and local actors, ultimately impacting the building and development of Guatemalan science and national research capacities.

Intracranial Venous Alteration in Patients With Aneurysmal Subarachnoid Hemorrhage: Protocol for the Prospective and Observational SAH Multicenter Study (SMS).

Background: Arterial vasospasm has been ascribed as the responsible etiology of delayed cerebral infarction in patients with aneurysmal subarachnoid hemorrhage (aSAH), but other neurovascular structures may be involved. We present the protocol for a multicenter, prospective, observational study focused on analyzing morphological changes in cerebral veins of patients with aSAH. Methods and Analysis: In a retrospective arm, we will collect head arterial and venous CT angiograms (CTA) of 50 patients with aSAH and 50 matching healthy controls at days 0-2 and 7-10, comparing morphological venous changes. A multicenter prospective observational study will follow. Patients aged ≥18 years of any gender with aSAH will be enrolled at 9 participating centers based on the predetermined eligibility criteria. A sample size of 52 aSAH patients is expected, and 52 healthy controls matched per age, gender, and comorbidities will be identified. For each patient, sequential CTA will be conducted upon admission (day 0-2), at 7-10 days, and at 14-21 days after aSAH, evaluating volumes and morphology of the cerebral deep veins and main cortical veins. One specialized image collecting center will analyze all anonymized CTA scans, performing volumetric calculation of targeted veins. Morphological venous changes over time will be evaluated using the Dice coefficient and the Jaccard index and scored using the Boeckh-Behrens system. Morphological venous changes will be correlated to clinical outcomes and compared between patients with aSAH and healthy-controls, and among groups based on surgical/endovascular treatments for aSAH. Ethics and Dissemination: This protocol has been approved by the ethics committee and institutional review board of Ethikkommission, SALK, Salzburg, Austria, and will be approved at all participating sites. The study will comply with the Declaration of Helsinki. Written informed consent will be obtained from all enrolled patients or their legal tutors. We will present our findings at academic conferences and peer-reviewed journals. Approved Protocol Version and Registration: Version 2, 09 June 2021.

Determining Clinically-Viable Biomarkers for Ischaemic Stroke Through a Mechanistic and Machine Learning Approach.

Assessment of distal cerebral perfusion after ischaemic stroke is currently only possible through expensive and time-consuming imaging procedures which require the injection of a contrast medium. Alternative approaches that could indicate earlier the impact of blood flow occlusion on distal cerebral perfusion are currently lacking. The aim of this study was to identify novel biomarkers suitable for clinical implementation using less invasive diagnostic techniques such as Transcranial Doppler (TCD). We used 1D modelling to simulate pre- and post-stroke velocity and flow wave propagation in a typical arterial network, and Sobol's sensitivity analysis, supported by the use of Gaussian process emulators, to identify biomarkers linked to cerebral perfusion. We showed that values of pulsatility index of the right anterior cerebral artery > 1.6 are associated with poor perfusion and may require immediate intervention. Three additional biomarkers with similar behaviour, all related to pulsatility indices, were identified. These results suggest that flow pulsatility measured at specific locations could be used to effectively estimate distal cerebral perfusion rates, and ultimately improve clinical diagnosis and management of ischaemic stroke.

Brain Circulation: The Educational Profile of Return Migrants.

Countries increasingly compete to attract and retain human capital. However, empirical studies, particularly those of migrants moving back to developing countries, have been limited due to the lack of education-specific migration flow data. Drawing on census microdata from IPUMS, we derive flow data by level of education and age group to quantify the level of return migration and examine the educational and age profile of return migrants for a global sample of 60 countries representing 70% of the world population. We show that return migrants account for a significant share of in-migration flows, particularly in Africa and Latin America, and, in all countries but six, return migrants are more educated than the population in the migrants' country of birth. Our age decomposition reveals that young adults contribute the most to the positive educational selectivity of return migrants, particularly in Africa and Asia. While this paper does not quantify the net effect of return migration on education levels, it underlines the importance of the human capital contributions of young adult returnees. Supplementary Information: The online version contains supplementary material available at 10.1007/s11113-021-09655-6.

Talent Migration in Knowledge Economy: The Case of China's Silicon Valley, Shenzhen.

Talent is a key resource in a knowledge economy. It plays a critical role in national economic growth and technological innovation. China's technological power is rising, and its ambitious push for talent is supported by central and local government. Through the lens of Shenzhen, China's Silicon Valley, this article examines the Shenzhen Talent Policy and its effectiveness in attracting both domestic talent and overseas returnees. Document analysis is combined with in-depth interviews with returnee entrepreneurs, university professors, and Shenzhen local government officials to examine talent migration and the effectiveness of talent policy. This study findings reveal that the welcoming and tolerant culture of Shenzhen is key to the city's attractiveness to its existing and potential talent. Entrepreneurial scientists and engineers are likely to return to Shenzhen from abroad for business opportunities in applied innovation and technology commercialization. Academics report an average or dissatisfying attitude towards the scientific environment and professional development. State-led talent policy puts emphasis on technical human capital to meet its urgent developmental needs. The reform of higher education system in Shenzhen is needed to fully realize its technological ambition. In addition, this study shows that younger generation Chinese cares about their personal wellbeing, individual happiness, and career opportunities compared to older generation's emphasis on economic benefits. This article concludes with policy implications on worldwide talent attraction and talent migration in a new geopolitical era.

[The Activities of the Resources Innovation Center in Relation to Brain Drain-Drain Circulation]. / Die Aktivitäten des Resources Innovation Center im Spannungsfeld Brain Drain ­ Brain Circulation.

The Resources Innovation Center Leoben at the Montanuniversität Leoben has been organizing a conference series called East and South East Europe Dialogue Conferences since 2014. At the end of 2020, the online version of the conference was used to allow various stakeholders in the raw materials sector, as well as experts on the topic of brain drain, to have their say. The article outlines the tension between brain drain and brain circulation and shows possibilities and future steps to initiate cooperation with East and South East Europe and thus contribute to Brain Circulation, the multidirectional flow of manpower and knowledge.

Internal Jugular Vein Thrombosis: Etiology, Symptomatology, Diagnosis and Current Treatment.

(1) Background: internal jugular vein thrombosis (IJVthr) is a potentially life-threating disease but no comprehensive reviews on etiology, symptomatology, diagnosis and current treatment guidelines are yet available; (2) Methods: we prospectively developed a protocol that defined objectives, search strategy for study identification, criteria for study selection, data extraction, study outcomes, and statistical methodology, according to the PRISMA standard. We performed a computerized search of English-language publications listed in the various electronic databases. We also retrieved relevant reports from other sources, especially by the means of hand search in the Glauco Bassi Library of the University of Ferrara; (3) Results: using the predefined search strategy, we retrieved and screened 1490 titles. Data from randomized control trials were few and limited to the central vein catheterization and to the IJVthr anticoagulation treatment. Systematic reviews were found just for Lemierre syndrome, the risk of pulmonary embolism, and the IJVthr following catheterization. The majority of the information required in our pre-defined objectives comes from perspectives observational studies and case reports. The methodological quality of the included studies was from moderate to good. After title and abstract evaluation, 1251 papers were excluded, leaving 239 manuscripts available. Finally, just 123 studies were eligible for inclusion. We found out the description of 30 different signs, symptoms, and blood biomarkers related to this condition, as well as 24 different reported causes of IJVthr. (4) Conclusions: IJVthr is often an underestimated clinical problem despite being one of the major sources of pulmonary embolism as well as a potential cause of stroke in the case of the upward propagation of the thrombus. More common symptoms are neck pain and headache, whereas swelling, erythema and the palpable cord sign beneath the sternocleidomastoid muscle, frequently associated with fever, are the most reported clinical signs. An ultrasound of the neck, even limited to the simple and rapid assessment of the compression maneuver, is a quick, economic, cost-effective, noninvasive tool. High quality studies are currently lacking.

Talent goes to global cities: The world network of scientists' mobility.

Global cities boast higher rates of innovation as measured through patent and scientific production. However, the source of the location advantage of innovation hubs is still debated in the literature, with arguments ranging from localized knowledge spillovers to network effects. Thanks to an extensive data set of individual scientist career paths, we shed new light on the role of scientist location choices in determining the superior innovative performance of global cities. We analyze the career paths of around two million researchers over a decade across more than two thousand cities around the globe. First, we show that scientists active in global cities are more productive in terms of citation weighted publications. We then show that this superior performance is in part driven by highly prolific scientists moving and remaining preferentially in global cities, i.e., central cities in the international scientist mobility network. The overall picture that emerges is that global cities are better positioned to attract and retain prolific scientists than more peripheral cities.

The intracranial vasculature of canines represents a model for neurovascular ischemia and training residents and fellows in endovascular neurosurgery.

BACKGROUND: We describe use of a canine model to evaluate physiological effects and neuroprotective strategies in the setting of cerebral ischemia and endovascular neurosurgery training. METHODS: We performed transfemoral digital subtraction cerebral and cervical angiography on eight anesthetized dogs. Angiographic images of cerebral arteries were obtained following cannulation of the femoral artery. Cerebral ischemia models were made after angiography. RESULTS: The canine cerebral vasculature exhibited extensive tortuosity of the carotid and vertebral arteries. Conversely, the bilateral anterior spinal arteries were easily catheterized using microcatheters and microguidewires. The basilar artery and its branches were facilely cannulable. Circle of Willis continuity sans hypoplasia or aplasia of its constitutive segments was appreciated in all animals. The middle cerebral arteries could be easily accessed via the posterior communicating arteries. We generated an empirically evaluable therapeutically interventional experimental animal model of cerebral ischemia by occluding the middle cerebral artery using small coils for a duration between 15 and 60 min. CONCLUSION: Unique amenability of the canine intracranial vasculature to selective and microcatheter cannulation renders experimentally induced cerebral, cerebellar, and brainstem via occlusion of the supratentorial and infratentorial arteries a simple matter. The neural vasculature irrigating the canine cerebrum, brainstem, and cerebellum may consequently prove useful in helping young and nascent endovascular neurosurgeons in developing and refining their skills of microcatheter navigation and manipulation and deployment of therapeutic devices to achieve effective occlusion of aneurysms, arteriovenous malformations, arteriovenous fistulas, and neoplasms of the intracranial cavity.

Persistent Trigeminal Artery: Neuroanatomic and Clinical Relevance.

INTRODUCTION: Persistent trigeminal artery (PTA) is the most common remnant of primitive circulation communicating the developing carotid and vertebrobasilar junction. Although discovered incidentally, an altered hemodynamic may lead to an increased association of aneurysms, vascular malformations, and stroke. Neurosurgeons should be aware of the presence and significance of PTA when interpreting imaging and planning interventions. METHODS: We retrospectively reviewed all magnetic resonance angiography and cerebral digital subtraction angiography performed between 2012 and 2017 for the presence of PTA. The radiologic and anatomic details were noted and analyzed along with the clinical profiles. We categorized the radiologic findings with respect to the available classification systems. A review of the available literature was done comparing our results. RESULTS: We found 33 cases of incidentally detected PTA. The average age of the patients was 45.42 years. The lateral surface of the proximal cavernous internal carotid artery was the most common origin (n = 23). Only 3 cases had a medial/transsellar course. Most cases were Saltzman/Weon type I (19/33). Intracranial aneurysms were associated with 6 patients (18.18%). Trigeminal neuralgia (TN) was a presenting feature in 5 patients. None had a direct neurovascular conflict at the root entry zone. CONCLUSIONS: Our study is one of the largest to describe the incidence of PTA. We emphasized the importance of PTA to the neurosurgeons; increased association of aneurysms, as a route for intervention in occlusive disease of the posterior fossa; risk of injury and bleeding during transsphenoidal surgery; and the association with TN. However, we found that only PTA variants are likely to be associated with TN because of their cisternal course causing NV conflict.

Thrombectomy in posterior circulation stroke: differences in procedures and outcome compared to anterior circulation stroke in the prospective multicentre REVASK registry.

BACKGROUND AND PURPOSE: In contrast to anterior circulation stroke (ACS), there is no evidence from randomized trials that mechanical thrombectomy (MT) with modern stent retrievers or thromboaspiration is safe and effective in posterior circulation stroke (PCS). METHODS: The present analysis was based on the prospective multicentre Registry on Revascularization in Ischemic Stroke Patients (REVASK) in Germany. Demographic data, periprocedural times and complications, recanalization rates, and functional outcome at discharge and after 3 months were compared between 139 consecutive patients with PCS (84.9% basilar artery, 16.5% vertebral artery and 4.3% posterior cerebral artery occlusion) and 961 patients with ACS treated with MT. RESULTS: Compared to ACS, PCS patients were significantly younger (65 vs. 69 years, P = 0.021) and had a lower median National Institutes of Health Stroke Scale (NIHSS) score at baseline (12 vs. 15, P = 0.024). Patients with PCS had a significantly longer time delay between symptom onset and both start and end of the MT procedure. Successful recanalization and thrombectomy passes did not significantly differ between the two groups. No symptomatic intracranial haemorrhage occurred in PCS compared to 3% in ACS (P = 0.010). The median NIHSS score at discharge was 3 in PCS and 4 in ACS. Favourable functional outcome at 3 months (modified Rankin Scale 0-2 38.0% vs. 42.6%, P = 0.392) and mortality (33.7% vs. 30.8%, P = 0.539) did not differ significantly between PCS and ACS. CONCLUSIONS: The study suggests that MT in PCS shows a lower risk of symptomatic intracranial haemorrhage and similar effectiveness compared to ACS. PCS patients also seem to benefit from MT started beyond 6 h after symptom onset.

Influence of Circulating Endothelin-1 and Asymmetric Dimethylarginine on Whole Brain Circulation Time in Multiple Sclerosis.

Blood-brain barrier (BBB) breakdown, inflammatory and immune cell activation, and chronic cerebral hypoperfusion are features of multiple sclerosis (MS). The aim is to determine the influence of endothelin-1 (ET1) and asymmetric dimethylarginine (ADMA) on cerebral circulation time (CCT) in patients with MS. In all, 64 patients with MS (39 relapsing-remitting [RR]-MS; 25 secondary progressive [SP]-MS subtype) and 37 controls (C) were studied. Cerebral circulation time was obtained by angiography. Plasmatic ET1 and ADMA were measured by enzyme-linked immunosorbent assay. Lesion load (LL) and brain volume (BV) were obtained by magnetic resonance imaging. Cerebral circulation time was correlated to ET1, ADMA, LL, BV, disease duration (DD), and Expanded Disability Status Scale (EDSS). In MS, both ET1 and ADMA were significantly higher than C (P < .0001); CCT was approximately 2 times lower than C (P < .0001) and significantly slower in SP than in RR-MS (P = .0215). Cerebral circulation time significantly correlated with ET1 in SP-MS (r = 0.38), whereas in RR-MS CCT significantly correlated with DD (r = 0.75). The LL, BV, and EDSS did not correlate with CCT. Endothelin-1 significantly influences CCT delay in SP-MS. Diversely, CCT in RR-MS is independent of ET1 and correlates significantly with DD. We conclude that in RR-MS, DD responds to neurovascular damage accumulation. It is supposed that high ET1 and ADMA levels stem from a protective response to early insults, aimed at opposing nitric oxide overproduction, whereas persistent pathological ET1 and ADMA levels translate into detrimental long-term effects, due to increased brain micro-vessel resistance.

Sympathetic control of the brain circulation: Appreciating the complexities to better understand the controversy.

Although the human cerebral circulation is richly innervated with sympathetic nerve fibers, the role of sympathetic nerve activity (SNA) on the regulation of cerebral blood flow (CBF) remains debated. Several issues may be responsible for the conflicting conclusions reported in the animal vs. human literature in regards to the sympathetic control of the brain circulation. Furthermore, due to the physiological consequences associated with SNA blockade (e.g. changes in blood pressure and cardiac output), and differences in methodology (e.g. assessment of CBF), interpretation of the role of SNA in CBF regulation in humans is challenging. The goals of this brief review are to provide an overview of the role of neural control in the regulation of CBF, with a focus on SNA and discuss the likely reasons behind the controversial influence of SNA on CBF regulation. A final objective of this article is to critically review the various methods available to measure CBF and highlight their strengths and weaknesses to provide insight in SNA regulation of CBF.

Yawning reduces facial temperature in the high-yawning subline of Sprague-Dawley rats.

BACKGROUND: Yawning is a stereotyped behavior that enhances blood flow to the skull, and the resulting counterflow has been hypothesized as a mechanism for brain cooling. Studies have shown that yawns are strongly associated with physiological and pathological conditions that increase brain temperature, and that they are followed by equivalent decreases in brain temperature. However, measured reductions in cranial or facial temperatures following yawning have yet to be reported, to our knowledge. To accomplish this, we used a subline of Sprague-Dawley rats that yawn at a much greater rate (20 yawns/h) than do outbred Sprague-Dawley rats (2 yawns/h). RESULTS: Using an infrared camera, we effectively evaluated thermal changes in the cornea and concha of these rats before, during, and after yawns. The maximum temperature in both regions significantly decreased 10 s following yawns (concha: -0.3 °C, cornea: -0.4 °C), with a return to basal temperatures after 20 s. CONCLUSIONS: This study is the first clear demonstration of yawning-induced thermal cooling on the surface of the face, providing convergent evidence that this behavior plays a functional role in thermoregulation. As other studies have demonstrated that yawning is capable of reducing cortical brain temperature, our current data support the idea that yawning functions as a thermoregulator, affecting all structures within the head.