An overview of FDA medical device regulation as it relates to deep brain stimulation devices.

The United States Food and Drug Administration (FDA) is charged with assuring the safety and effectiveness of a variety of medical products and the FDA's Center for Devices and Radiological Health is responsible for premarket and postmarket regulation of medical devices. In this paper, we review--from device classification and clinical studies to the final marketing application--FDA's premarket requirements and postmarket requirements as they relate to deep brain stimulation devices.     

Heat and Fluid Flow in an Optical Switch Bubble

The Agilent all-optical bubble switch uses bubbles in an organic fluid index matched to a silica planar lightwave circuit. The bubble is created and sustained by heaters that are deposited on an attached silicon substrate. Testing of the bubble shows how heater power and ambient pressure affect bubble shape, size, and optical reflection characteristics. Heat and fluid flow in the bubble were modeled in 2D and 3D using the homogeneous bubble model in the Flow3D modeling software. Fluid condensing on the trench wall causes a dimple on the bubble and hence nonoptimum optical reflection. To aid understanding, the bubble, silica walls, and heaters were also modeled as a thermal resistance network. Because the pressure drop across the bubble wall is fixed, the bubble size is determined by P_res/DeltaT_t , where P_res is the heater power and DeltaT_t is the temperature difference between the bubble and the substrate. Heating the trench walls beyond the bubble temperature with heaters located underneath the trench wall will dry out the trench wall and give a stable optical reflection. As DeltaT_t approaches zero, a bubble is sustained without any heater power and with zero fluid flow. This "static" bubble provides for a very stable optical reflection     

Homologous and heterologous desensitisation of somatostatin-induced increases in intracellular Ca2+ and inositol 1,4,5-trisphosphate in CHO-K1 cells expressing human recombinant somatostatin sst5 receptors

The mechanisms responsible for somatostatin (SRIF)-induced increases in intracellular Ca2+ concentration ([Ca2+]i) and subsequent desensitisation were studied in CHO-K1 cells expressing human sst5 receptors (CHOsst5 cells). To study the nature of the desensitisation, interactions with uridine triphosphate (UTP) were examined. SRIF (pEC50 7.10) and UTP (pEC50) 5.14) caused concentration-dependent increases in [Ca2+]i but the SRIF maximum was about 40% of that to UTP. SRIF-, but not UTP-, induced increases in [Ca2+]i were transient and abolished by pertussis toxin. SRIF and UTP caused sustained increases in Ins(1,4,5)P3 but the SRIF maximum was about 30% of that to UTP. Removal of [Ca2+]e attenuated the SRIF-induced peak rise in [Ca2+]i but had no effect on the peak increases in Ins(1,4,5)P3. UTP-induced increases in [Ca2+]i and Ins(1,4,5)P3 were attenuated in the absence of [Ca2+]e. Following pre-exposure to SRIF (1 microM) or UTP (100 microM) for 5 min, subsequent SRIF responses were desensitised. Similar results were obtained in the absence of [Ca2+]e. Pre-exposure to SRIF had no effect on subsequent responses to UTP but in the absence of [Ca2+]e, responses to UTP were attenuated. The results suggest that SRIF but not UTP-induced increases in [Ca2+]i in CHOsst5 cells are mediated by pertussis toxin sensitive G proteins and are caused by an entry of extracellular Ca2+ and release from an Ins(1,4,5)P3 sensitive Ca2+ store. Homologous or heterologous desensitisation of agonist-induced increases in [Ca2+]i could be demonstrated in the presence or absence of extracellular Ca2+ respectively, and the latter appeared to involve depletion of a common intracellular Ca2+ store.     

Aging and memory for words and action events: Effects of item repetition and list length.

We were concerned with the effects of item repetition, list length, and class of item on free recall in elderly as compared with young adults. In Experiment 1, samples of young and elderly adults recalled a list of 27 words and a list of 27 action events (minitasks performed by the subjects). Some items were presented once and some twice. Although the younger subjects showed better recall on both types of lists, the older sample benefited from item repetition as much as did the younger sample. This finding was replicated in Experiment 2. A second finding in Experiment 2 was a significant aging effect in the recall of long but not of short lists of both words and action events. The absence of an Age?×?Repetition Effect interaction was ascribed to the strength nature of the repetition manipulation. The age effects in the recall of the long lists were attributed to possible deficits in retrieval proficiency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of a thick-film capillary column for the analysis of organic acids in body fluids

Contradictory evidence as to the effects of alcohol on early information processing stages has been obtained from behavioral and psychophysiological investigations. In the present study, choice reaction times, error rates, and event-related potentials (ERPs) were recorded in a task in which variations in stimulus discriminability and of the (task irrelevant) correspondence between stimulus location and response location were orthogonally combined. Both discriminability and stimulus-response correspondence affected reaction time and electrophysiological chronometric measures as expected. However, no behavioral effects of alcohol were observed, possibly because of strategic adjustments. Psychophysiological chronometric measures indicated that alcohol leaves the initial flow of perceptual evidence to motor stages unimpaired, whereas it appears to increase the duration of stimulus evaluation. Interestingly, a number of alcohol effects appeared in the ERP amplitudes. Decrements in early ERP components indicate alcohol-induced impairments of involuntary visual attention and/or the automatic stimulus location-dependent activation of response channels. In contrast, a strong enhancement of a late slow-wave component under alcohol may reflect the investment of processing resources in order to maintain normal performance levels.     

Investigation of the thermal, mechanical, and fracture properties of alumina-epoxy composites

A combination of dynamic shear rheology, thermomechanical analysis (TMA), scanning electron microscopy (SEM), Near-Edge X-ray Absorption Fine Structure (NEXAFS), and fracture toughness testing was utilized to characterize the thermal, mechanical, chemical, and fracture properties of alumina (α-Al₂O₃)-filled epoxy resins as a function of average filler size, size distribution, particle shape, loading, and epoxy crosslink density. In general the cured properties of the filled composites were robust. Small changes in particle size, shape, and size distribution had little impact on the final properties. Resin crosslink density and filler loading were the most critical variables, causing changes in all properties. However, most applications could likely tolerate small changes in these variables also. SEM and NEXAFS characterization of the fracture surfaces revealed that the fracture occurs at the filler interface and the interfacial epoxy composition is similar to the bulk resin, indicating a weak epoxy-alumina interaction. These results are critical for implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency.     

The predictive value of electrodiagnostic studies in carpal tunnel syndrome

In recent years, electrodiagnostic studies have become an expected component in the work up and evaluation of carpal tunnel syndrome. We conducted a retrospective review of 460 carpal tunnel decompressions to determine whether the accuracy of diagnosis and the prediction of therapeutic outcome could be related to the positivity and severity of findings on preoperative electrical studies. The 349 patients (460 hands) were divided into two groups: group 1 consisted of hands with the clinical diagnosis of carpal tunnel syndrome but with normal electrodiagnostic studies (n = 62); in group 2 the hands had a clinical diagnosis of carpal tunnel syndrome with confirmatory electrodiagnostic studies (n = 398). The number and distribution of signs and symptoms of carpal tunnel syndrome were not statistically different between these two groups. There was not a statistically significant difference in the success rate of surgery or the incidence of complications. The similarities between these two groups suggests that the distinction between them (the positivity of electrodiagnostic studies) is an artificial one and that the clinical diagnosis of carpal tunnel syndrome is sufficient to predict the presence of the disease, as well as outcome of surgery. On the basis of these data, strict adherence to electrodiagnostic studies to confirm the diagnosis will exclude 13 percent of the patients with legitimate carpal tunnel syndrome from receiving appropriate therapy.