Highly accurate thermal flow microsensor for continuous and quantitative measurement of cerebral blood flow.

Cerebral blood flow (CBF) plays a critical role in the exchange of nutrients and metabolites at the capillary level and is tightly regulated to meet the metabolic demands of the brain. After major brain injuries, CBF normally decreases and supporting the injured brain with adequate CBF is a mainstay of therapy after traumatic brain injury. Quantitative and localized measurement of CBF is therefore critically important for evaluation of treatment efficacy and also for understanding of cerebral pathophysiology. We present here an improved thermal flow microsensor and its operation which provides higher accuracy compared to existing devices. The flow microsensor consists of three components, two stacked-up thin film resistive elements serving as composite heater/temperature sensor and one remote resistive element for environmental temperature compensation. It operates in constant-temperature mode (~2 °C above the medium temperature) providing 20 ms temporal resolution. Compared to previous thermal flow microsensor based on self-heating and self-sensing design, the sensor presented provides at least two-fold improvement in accuracy in the range from 0 to 200 ml/100 g/min. This is mainly achieved by using the stacked-up structure, where the heating and sensing are separated to improve the temperature measurement accuracy by minimization of errors introduced by self-heating.

Supracerebellar Transtentorial Approach for Occipital Meningioma to Maximize Visual Preservation: Technical Note.

BACKGROUND AND IMPORTANCE: Surgery for resection of tentorial meningiomas compressing primary visual cortex carries a significant risk of worsening vision. This concern is especially acute in patients with a preexisting visual deficit. Approaches that involve mechanical retraction of the occipital lobe further threaten visual function. The supracerebellar transtentorial (SCTT) approach, which does not carry a risk of occipital retraction injury, should be considered for patients with occipital tentorial meningiomas to maximize functional visual outcomes. CLINICAL PRESENTATION: A 54-yr-old woman underwent 2 resections and radiation therapy for a right occipital oligodendroglioma as a teenager. She was left with a complete left homonymous hemianopsia. The patient now presented with progressive vision loss in her remaining right visual field. Imaging revealed a left occipital superiorly projecting tentorial meningioma. To preserve her remaining visual function the SCTT approach was chosen for resection. A Simpson grade 1 removal was achieved without disrupting the occipital lobe pia or requiring mechanical cerebellar retraction. A diagnosis of a WHO grade II meningioma (presumably radiation induced) was made. The patient's vision returned to premorbid baseline 1 wk after surgery. CONCLUSION: The SCTT approach should be considered for the surgical management of patients with occipital tentorial meningiomas when visual preservation is at risk. This approach avoids transgression of visual cortex and minimizes the risk of venous infarction or contusions from retraction injury.

Lateral Supraorbital Craniotomy for Tuberculum Sella Meningioma Resection.

Tuberculum sella meningioma can be approached by either open or endoscopic approaches. The aim of this video case presentation is to highlight the nuances of the lateral supraorbital craniotomy for tuberculum sella meningioma resection. The authors present a 34-year-old female patient who presented with decreased right eye visual acuity (20/60), afferent pupillary defect, and nasal field cut due to a tuberculum sella meningioma. The tumor was partially encasing the left A1 artery, severely displacing the optic apparatus, and minimally invading the right optic canal. The lateral supraorbital craniotomy was considered the most suitable approach to this tumor. The operative nuances and pitfalls of this approach are detailed in the video. Gross total resection of the tumor was achieved and confirmed with postoperative MRI. The patient's vision gradually improved and she was discharged on the fourth postoperative day. The minimally invasive lateral supraorbital craniotomy for tuberculum sella meningioma is a suitable approach in selected cases. The link to the video can be found at: https://youtu.be/yG8q6YH2D9k .

Neuroprotective Effects of Trigeminal Nerve Stimulation in Severe Traumatic Brain Injury.

Following traumatic brain injury (TBI), ischemia and hypoxia play a major role in further worsening of the damage, a process referred to as 'secondary injury'. Protecting neurons from causative factors of secondary injury has been the guiding principle of modern TBI management. Stimulation of trigeminal nerve induces pressor response and improves cerebral blood flow (CBF) by activating the rostral ventrolateral medulla. Moreover, it causes cerebrovasodilation through the trigemino-cerebrovascular system and trigemino-parasympathetic reflex. These effects are capable of increasing cerebral perfusion, making trigeminal nerve stimulation (TNS) a promising strategy for TBI management. Here, we investigated the use of electrical TNS for improving CBF and brain oxygen tension (PbrO2), with the goal of decreasing secondary injury. Severe TBI was produced using controlled cortical impact (CCI) in a rat model, and TNS treatment was delivered for the first hour after CCI. In comparison to TBI group, TBI animals with TNS treatment demonstrated significantly increased systemic blood pressure, CBF and PbrO2 at the hyperacute phase of TBI. Furthermore, rats in TNS-treatment group showed significantly reduced brain edema, blood-brain barrier disruption, lesion volume, and brain cortical levels of TNF-α and IL-6. These data provide strong early evidence that TNS could be an effective neuroprotective strategy.

Evaluation of microelectrode materials for direct-current electrocorticography.

OBJECTIVE: Direct-current electrocorticography (DC-ECoG) allows a more complete characterization of brain states and pathologies than traditional alternating-current recordings (AC-ECoG). However, reliable recording of DC signals is challenging because of electrode polarization-induced potential drift, particularly at low frequencies and for more conducting materials. Further challenges arise as electrode size decreases, since impedance is increased and the potential drift is augmented. While microelectrodes have been investigated for AC-ECoG recordings, little work has addressed microelectrode properties for DC-signal recording. In this paper, we investigated several common microelectrode materials used in biomedical application for DC-ECoG. APPROACH: Five of the most common materials including gold (Au), silver/silver chloride (Ag/AgCl), platinum (Pt), Iridium oxide (IrOx), and platinum-iridium oxide (Pt/IrOx) were investigated for electrode diameters of 300 µm. The critical characteristics such as polarization impedance, AC current-induced polarization, long-term stability and low-frequency noise were studied in vitro (0.9% saline). The two most promising materials, Pt and Pt/lrOx were further investigated in vivo by recording waves of spreading depolarization, one of the most important applications for DC-ECoG in clinical and basic science research. MAIN RESULTS: Our experimental results indicate that IrOx-based microelectrodes, particularly with composite layers of nanostructures, are excellent in all of the common evaluation characteristics both in vitro and in vivo and are most suitable for multimodal monitoring applications. Pt electrodes suffer high current-induced polarization, but have acceptable long-term stability suitable for DC-ECoG. Major significance. The results of this study provide quantitative data on the electrical properties of microelectrodes with commonly-used materials and will be valuable for development of neural recordings inclusive of low frequencies.

Combined age- and trauma-related proteomic changes in rat neocortex: a basis for brain vulnerability.

This proteomic study investigates the widely observed clinical phenomenon, that after comparable brain injuries, geriatric patients fare worse and recover less cognitive and neurologic function than younger victims. Utilizing a rat traumatic brain injury model, sham surgery or a neocortical contusion was induced in 3 age groups. Geriatric (21 months) rats performed worse on behavioral measures than young adults (12-16 weeks) and juveniles (5-6 weeks). Motor coordination and certain cognitive deficits showed age-dependence both before and after injury. Brain proteins were analyzed using silver-stained two-dimensional electrophoresis gels. Spot volume changes (>2-fold change, p<0.01) were identified between age and injury groups using computer-assisted densitometry. Sequences were determined by mass spectrometry of tryptic peptides. The 19 spots identified represented 13 different genes that fell into 4 general age- and injury-dependent expression patterns. Fifteen isoforms changed differentially with respect to both age and injury (p<0.05). Further investigations into the nature and function of these isoforms may yield insights into the vulnerability of older patients and resilience of younger patients in recovery after brain injuries.