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Biomedical subjects

Edward S Ahn

Publications and source records attributed to Edward S Ahn.

8 recordsLinked to original sources

Nanostructured biomaterials for tissue engineering bone.

Advances in several critical research fields (processing, catalytic, optical, actuation, electrical, mechanical, etc.) have started to benefit from nanotechnology. Nano-technology can be broadly defined as the use of materials and systems whose structures and components exhibit novel and significantly changed properties when control is gained at the atomic, molecular, and supramolecular levels. Specifically, such advances have been found for materials when particulate size is decreased to below 100 nm. However, to date, relatively few advantages have been described for biological applications (specifically, those involving bone tissue engineering). This chapter elucidates several promising examples of how nanophase materials can be used to improve orthopedic implant applications. These include mechanical advantages as well as altered cell functions, leading to increased bone tissue regeneration on a wide range of nanophase materials including ceramics, polymers, metals, and composites thereof. Such advances were previously unimaginable with conventional materials possessing large micron-sized particulates.

Animals↗

The Strata programmable valve for shunt-dependent hydrocephalus: the pediatric experience at a single institution.

BACKGROUND AND OBJECTIVE: The Medtronic PS Medical Strata valve has pressure flow characteristics that are noninvasively adjusted with a magnetic tool. The objective of this study was to examine its efficacy during our initial experience with it in shunt-dependent children. MATERIALS AND METHODS: A retrospective review of 53 children with a median age of 2.0 years who had 61 Strata valves implanted. CONCLUSION: The Strata valve is efficacious in the treatment of shunt-dependant hydrocephalus in children. The 1-year shunt survival rate of 67.2% is comparable to that previously reported from a multicenter trial. Of the 30 therapeutically aimed adjustments during the study period, 16 (53.3%) resulted in improvement in abnormal signs or symptoms. Our data indicate that adjustments can be used to treat signs or symptoms of cerebrospinal fluid overdrainage or underdrainage, which may obviate the need for additional surgery.

Adolescent↗

Outcome following decompressive craniectomy for malignant swelling due to severe head injury.

OBJECT: The aim of this study was to assess outcome following decompressive craniectomy for malignant brain swelling due to closed traumatic brain injury (TBI). METHODS: During a 48-month period (March 2000-March 2004), 50 of 967 consecutive patients with closed TBI experienced diffuse brain swelling and underwent decompressive craniectomy, without removal of clots or contusion, to control intracranial pressure (ICP) or to reverse dangerous brain shifts. Diffuse injury was demonstrated in 44 patients, an evacuated mass lesion in four in whom decompressive craniectomy had been performed as a separate procedure, and a nonevacuated mass lesion in two. Decompressive craniectomy was performed urgently in 10 patients before ICP monitoring; in 40 patients the procedure was performed after ICP had become unresponsive to conventional medical management as outlined in the American Association of Neurological Surgeons guidelines. Survivors were followed up for at least 3 months posttreatment to determine their Glasgow Outcome Scale (GOS) score. Decompressive craniectomy lowered ICP to less than 20 mm Hg in 85% of patients. In the 40 patients who had undergone ICP monitoring before decompression, ICP decreased from a mean of 23.9 to 14.4 mm Hg (p < 0.001). Fourteen of 50 patients died, and 16 either remained in a vegetative state (seven patients) or were severely disabled (nine patients). Twenty patients had a good outcome (GOS Score 4-5). Among 30-day survivors, good outcome occurred in 17, 67, and 67% of patients with postresuscitation Glasgow Coma Scale scores of 3 to 5, 6 to 8, and 9 to 15, respectively (p < 0.05). Outcome was unaffected by abnormal pupillary response to light, timing of decompressive craniectomy, brain shift as demonstrated on computerized tomography scanning, and patient age, possibly because of the small number of patients in each of the subsets. Complications included hydrocephalus (five patients), hemorrhagic swelling ipsilateral to the craniectomy site (eight patients), and subdural hygroma (25 patients). CONCLUSIONS: Decompressive craniectomy was associated with a better-than-expected functional outcome in patients with medically uncontrollable ICP and/or brain herniation, compared with outcomes in other control cohorts reported on in the literature.

Adult↗

Effects of N-methyl-d-aspartate, glutamate, and glycine on the dorsal column axons of neonatal rat spinal cord: in vitro study.

The effects of N-methyl-D-aspartate (NMDA), glutamate, and glycine on the developmental axons of the neonatal rat spinal cord were investigated. Isolated dorsal column preparations from postnatal day (PN) 0 to 14 Long-Evans hooded rats (n = 119) were used in vitro. Compound action potentials (CAPs) were recorded from the cuneate and gracile fasciculi with a glass micropipette electrode. NMDA (100 microM) significantly increased CAP amplitude in PN 0-6 cords by 21.5 +/- 9.2% (mean +/- standard error of the mean, p < 0.001, n = 8) and in PN 7-14 cords by 6.7 +/- 6.6% (p < 0.001, n = 10). NMDA (10 microM) significantly increased the CAP amplitude by 6.3 +/- 2.9% in PN 0-6 cords (p < 0.01, n = 10). The increase of CAP amplitude induced by NMDA (100 microM) in PN 0-6 cords was significantly greater than that in PN 7-14 cords (p < 0.005). Glutamate (100 microM) significantly increased the CAP amplitude by 8.8 +/- 8.1% in PN 0-6 cords (p < 0.001, n = 29) and 6.7 +/- 7.5% in PN 7-14 cords (p < 0.01, n = 14), and glutamate (10 microM) significantly increased by 6.3 +/- 2.9% in PN 0-6 cords (p < 0.01, n = 21). The amplitudes induced by glutamate (100 microM or 10 microM) did not significantly differ between PN 0-6 and PN 7-14 cords. Application of glycine (100 microM) did not significantly alter CAP amplitudes induced by NMDA (100 microM or 10 microM) and glutamate (100 microM or 10 microM). D(-)-2-amino-5-phosphonopentanoic acid (NMDA receptor antagonist) blocked the effects of NMDA and glutamate. These results suggest that NMDA receptor is present on afferent dorsal column axons and may modulate axonal excitability, especially during the 1st week after birth.

Age Factors↗

Long-term control after resection and gamma knife surgery of an intracranial clear cell meningioma: case report.

Clear cell meningioma (CCM) is a rare variant of meningioma characterized by sheets of polygonal cells with clear cytoplasm, a feature attributable to its high glycogen content. Authors have described its propensity to recur and metastasize despite its benign pathological characteristics. Clinical response to radiation in these reports has varied. The authors present the case of a 7-year-old girl with a large petroclival CCM who underwent a staged subtotal resection and subsequent gamma knife surgery (GKS). Initially, the residual tumor decreased in size, but 6 years later, it had regrown (9 mm in size). A second GKS treatment was performed and the mass completely regressed without further complication. The findings in this case suggest that GKS is a safe and effective adjunct for residual and recurrent CCM after resection. The delayed recurrence also emphasizes the importance of undertaking close follow-up examination after treating this potentially aggressive variant of meningioma.

Cerebellopontine Angle↗

Acute clival and spinal subdural hematoma with spontaneous resolution: clinical and radiographic correlation in support of a proposed pathophysiological mechanism. Case report.

Infratentorial and spinal subdural hematomas (SDHs) from traumatic injury in the pediatric population occur with such rarity that they can present the clinician with a challenge in diagnosis and management. When such hematomas are correctly identified, clinicians must decide whether to evacuate the lesion or manage it expectantly. The authors discuss the case of a 4-year-old child who presented with a clival and spinal SDH after a fall from a fourth-story window. The clinical and radiographic findings support a possible mechanism of evolution of these lesions. There is little evidence to guide management of clival and spinal SDHs. This case supports the evaluation for a spinal SDH when a clival hematoma is diagnosed. In the setting of a good neurological examination, expectant management can be an appropriate method of treatment. Additionally, this case lends insight into the pathophysiology of spinal SDHs. Unlike its intracranial counterpart, the spinal subdural space lacks bridging veins. The mechanism of formation of spinal SDHs after trauma has been heretofore relatively unclear. The images in this case support the hypothesis that redistribution of the clival SDH to dependent areas in the spinal subdural space is a significant mechanism in the evolution of these lesions.

Child, Preschool↗

Synthes Award for Resident Research on Brain and Craniofacial Injury: normoxic ventilatory resuscitation after controlled cortical impact reduces peroxynitrite-mediated protein nitration in the hippocampus.

Resuscitation with 100% ventilatory oxygen is routinely initiated after severe traumatic brain injury (TBI). Despite the objective to improve oxygenation of the injured brain, there are concerns about the increased production of reactive oxygen species (ROS), which can lead to further neuronal damage. 3-nitrotyrosine (3-NT), the product of peroxynitrite-meditated tyrosine residue nitration, has been used as a marker for ROS-induced oxidative damage to proteins. We hypothesized that posttraumatic resuscitation with hyperoxic ventilation with a fraction of inspired oxygen (Fio2, 100%) results in increased ROS-induced damage to proteins compared with resuscitation with normoxic ventilation or room air (Fio2, 21%). Male Sprague-Dawley rats underwent controlled cortical impact (CCI) and were resuscitated with either normoxic or hyperoxic ventilation for 1 hour after injury (n = 5 per group). Sham-operated control groups received 1 hour of normoxic or hyperoxic ventilation without CCI (n = 4-5 per group). Twenty-four hours after injury, rats were perfused with fixative, and hippocampi were evaluated for levels of 3-NT immunostaining. In a second experiment, for a delayed assessment of neuronal survival, another set of rats similarly underwent CCI and normoxic or hyperoxic ventilation for 1 hour (n = 4 per group), and a sham-operated group was used as a control (n = 4). One week after injury, neuronal cell counts and abnormal cell quantification were performed after staining with the neuron-specific NeuN antibody. Quantification of 3-NT staining revealed significantly increased levels in the ipsilateral hippocampus in the hyperoxic CCI group. The normoxic group showed a 51.0% reduction of staining in CA1 when compared with those rats resuscitated with hyperoxia and a 50.8% reduction in CA3 (both P < 0.05). There was no significant difference in staining between the injured normoxic group and the sham-operated groups. In the delayed analysis of neuronal survival, although neuronal counts were reduced in the hippocampus on the injured side in both injured groups, there was no significant difference between hyperoxic and normoxic groups. Similarly, abnormal cell counts were not significantly different between groups.

Animals↗

Is autism due to brain desynchronization?

The hypothesis is presented that a disruption in brain synchronization contributes to autism by destroying the coherence of brain rhythms and slowing overall cognitive processing speed. Particular focus is on the inferior olive, a precerebellar structure that is reliably disrupted in autism and which normally generates a coherent 5-13 Hz rhythmic output. New electrophysiological data reveal that the continuity of the rhythmical oscillation in membrane potential generated by inferior olive neurons requires the formation of neuronal assemblies by the connexin36 protein that mediates electrical synapses and promotes neuronal synchrony. An experiment with classical eyeblink conditioning is presented to demonstrate that the inferior olive is necessary to learn about sequences of stimuli presented at intervals in the range of 250-500 ms, but not at 700 ms, revealing that a disruption of the inferior olive slows stimulus processing speed on the time scale that is lost in autistic children. A model is presented in which the voltage oscillation generated by populations of electrically synchronized inferior olivary neurons permits the utilization of sequences of stimuli given at, or faster than, 2 per second. It is expected that the disturbance in inferior olive structure in autism disrupts the ability of inferior olive neurons to become electrically synchronized and to generate coherent rhythmic output, thereby impairing the ability to use rapid sequences of cues for the development of normal language skill. Future directions to test the hypothesis are presented.

Animals↗