Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 127, April 1974

This special bibliography lists 279 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1974

Evaluation and Correlation of Morphological, Blood Flow and Physiological Retinal Changes in a Rat Model of Glaucoma with a Combined Optical Coherence Tomography and Electroretinography System

Glaucoma is a chronic disease associated with progressive dysfunction of the retinal ganglion cells (RGC), reduction of the retinal blood flow, thinning of the retinal nerve fiber layer (RNFL) and deformation of the optical nerve head (ONH). It is the second leading cause of blindness worldwide, with an estimate of 64.3 million people between the ages of 40 to 80 years affected in 2013, 76.7 million by 2020, and 111.8 million by 2040. Currently, there is no cure for glaucoma and any clinically available pharmaceutical or surgical approaches to treating the disease can only slow its progression. Therefore, early detection and treatment are essential for managing the glaucoma progression. Elevated intraocular pressure (IOP) is one of the most well studied and documented pathogenic risk factors for open-angle glaucoma (OAG), and as such, numerous animal models have been developed to study the acute and chronic IOP elevation effect on the ONH structure, retinal blood perfusion and RGC function. However, most of these studies utilized static chronic IOP elevation, while the relation between the IOP dynamics and the progression of glaucoma is still poorly understood. Joos et al proposed a rat model of glaucoma that utilized a dynamic approach to IOP elevation by use of a vascular loop that consists of short duration (~1h), intermittent IOP elevation. This model resembles closely the daily IOP spiking observed in glaucomatous patients, especially during the early stages of the disease. Better understanding of how the retina (human and animal) responds to such intermittent spikes of the IOP can provide ophthalmologists with valuable information on the origins and early stages of glaucoma development when treatment would be most efficient, as well as insights into developing new therapeutic approaches for glaucoma. Over the past few decades, a number of ex-vivo and in-vivo optical imaging modalities ranging from histopathology to confocal microscopy and optical coherence tomography (OCT) have been used to image changes in the morphology of the retina and the optic nerve head (ONH) in human subjects and animal models of OAG. Laser Doppler Flowmetry, Doppler OCT (DOCT) and Optical Coherence Angiography (OCTA) have been utilized to image and quantify changes in the total retinal blood flow and the blood perfusion in retinal capillaries during IOP elevation. Furthermore, electroretinography (ERG) has been used to assess changes in the retinal function (response to visual stimulation) during elevated IOP. However, all previous studies collected information about the morphological, functional and blood flow / perfusion changes in the retina during elevated IOP separately, at different time points, which prevented the researchers from correlating those changes and uncovering the relationship between them, typically referred to as neurovascular coupling. Since OCT provides both intensity and phase information in a single acquisition, this imaging technology is able to assess changes in the retinal morphology, function and blood flow/perfusion in-vivo and simultaneously. Therefore, the main goals of this PhD project were to: • Develop a combined OCT+ERG imaging system that can image in-vivo and record simultaneously, changes in the retinal morphology, retinal response to visual stimulation and retinal blood flow / perfusion at normal and elevated IOP. • Test the performance of the OCT+ERG system in a rat model of glaucoma. • Utilize the OCT+ERG technology and the dynamic IOP rat model of glaucoma based on the vascular loop, to investigate the effects of acute and chronic IOP elevation to ischemic and non-ischemic IOP levels on the rat retina. • Utilize the OCT+ERG technology to investigate neurovascular coupling in the rat retina at normal and abnormal IOP levels. Results from this PhD research have been published or summarized in manuscripts that are currently under review. Therefore, this PhD thesis was prepared in such a way that individual manuscripts represent separate thesis chapters

Micromachined Magnetoelastic Sensors and Actuators for Biomedical Devices and Other Applications.

Magnetoelastic materials exhibit coupling between material strain and magnetization; this coupling provides the basis for a number of wireless transducers. This thesis extends past work on microfabricated magnetoelastic sensors in three ways. First, a new class of strain sensors based on the ΔE effect are presented. Two sensor types are described – single and differential. The single sensor has an active area of 7×2 mm2 and operates at a resonant frequency of 230.8 kHz with a sensitivity of 13×103 ppm/mstrain and a dynamic range of 0.05-1.05 mstrain. The differential sensor includes a strain-independent 2×0.5 mm2 reference resonator in addition to a 2.5×0.5 mm2 sensing element. The sensor resonance is at 266.4 kHz and reference resonance is at 492.75 kHz. The differential sensor has a dynamic range of 0-1.85 mstrain, a sensitivity of 12.5×103¬¬ ppm/mstrain, and is temperature compensated in the 23-60°C range. Second, fluidic actuation by resonant magnetoelastic devices is presented. This transduction is performed in the context of an implantable device, specifically the Ahmed glaucoma drainage device (AGDD). Aspherical 3D wireless magnetoelastic actuators with small form factors and low surface profiles are integrated with the AGDD; the fluid flow generated by the actuators is intended to limit cellular adhesion to the implant surface that ultimately leads to implant encapsulation and failure. The actuators measure 10.3×5.6 mm2 with resonant frequencies varying from 520 Hz to 4.7 kHz for the different actuator designs. Flow velocities up to 266 μm/s are recorded at a wireless activation range of 25-30 mm, with peak actuator vibration amplitudes of 1.5 μm. Finally, detection techniques for improving the measurement performance of wireless magnetoelastic systems are presented. The techniques focus on decoupling of the excitation magnetic signal from the sensor response to improve measurement sensitivity and noise immunity. Three domains – temporal, frequency, and spatial – are investigated for signal feedthrough. Quantitative results are presented for temporal and frequency domain decoupling. Temporal decoupling is used to measure strain sensors with resonant frequencies in the 125 kHz range, whereas frequency domain decoupling is implemented to measure 44 kHz magnetoelastic resonators.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/116647/1/venkatp_1.pd

System Level Challenges for Microfabricated Magnetoelastic Transducers in Implantable Biomedical Applications

Magnetoelastic devices have potential utility as sensors and actuators in implanted biomedical applications because of their inherent passive wireless nature which avoids the need for batteries and simplifies the implanted module. This work focuses on addressing system level challenges in two applications, one requiring an actuator and one a sensor. The first application is mitigation of glaucoma valve encapsulation; challenges addressed in this application include the integration of an actuator onto the valve and especially the development of an acoustomagnetic interrogation module for verifying actuator functionality. The second application is biliary stent monitoring; challenges include protection of the sensor during and after deployment, and development of an interrogation module with vastly increased wireless range. An Ahmed glaucoma valve (AGV) is used in the treatment of glaucoma to drain fluid from the eye and decrease the elevated intraocular pressure. However, adhesion of cells and encapsulation of the AGV often lead to its failure. The magnetoelastic system described in this work consists of a magnetoelastic actuator integrated onto the AGV that can agitate the nearby liquid and potentially mitigate encapsulation, and an interrogation module to excite the actuator. The interrogation module addresses the signal feedthrough and clinical utility challenges by implementing physical domain decoupling and tailored signal processing. The in situ experiments with the system resulted in the first recorded acoustic signatures from a magnetoelastic sensor in an implanted environment; the measured signal-to-noise ratio was 3-6. In vivo experiments performed on live rabbits along with the in situ results indicate that the magnetoelastic system does not adversely affect the health of the animal and can feasibly provide sufficient wireless range and actuation amplitudes after implantation. A magnetoelastic system for biliary stent monitoring consists of a magnetoelastic sensor integrated into the stent, and an interrogation module to communicate with the sensor. The change in the resonant response of the sensor by mass loading and viscosity shifts due to sludge accumulation can diagnose early occlusion and allow timely intervention. A self-biased sensor is designed and fabricated, decreasing the footprint considerably while preserving its resonant frequency. In vitro experiments mimicking sludge accumulation were performed, and the ratio of the shift in resonant frequency to the quality factor was found to be well-correlated with occlusion. The receiver operator characteristic of this parameter indicated an accuracy of 97.84% for a detection threshold of 50% decrease in flow rate through the stent due to occlusion. To protect the sensor during and after endoscopic deployment, a Nitinol reinforced polymer hybrid package is designed and used. In vitro tests utilizing bile-resistant bacterial cultures were conducted to evaluate the effect of the packaged sensor itself on the stent occlusion dynamics. Non-inferiority statistical tests performed on the results indicate that the instrumented stent is not inferior to the normal stent in terms of the occlusion time (p-value < 0.05). The implementation of the interrogation module addresses challenges, including wireless range, signal feedthrough, and clinical utility, and these are solved in part by time domain decoupling and signal processing techniques. The complete magnetoelastic system was successfully demonstrated in vivo, with the sensor-integrated stent implanted in the bile duct of a live pig at a wireless range of ≈17.15 cm with a signal to noise ratio ≈106. These are the first reported signals from a stent-integrated magnetoelastic sensor implanted in a live animal.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/153381/1/rampmn_1.pd

Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program

The activities are reported of the NASA Biomedical Applications Team at Southwest Research Institute between 25 August, 1972 and 15 November, 1973. The program background and methodology are discussed along with the technology applications, and biomedical community impacts

Aerospace Medicine and Biology. A continuing bibliography with indexes

This bibliography lists 244 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1981. Aerospace medicine and aerobiology topics are included. Listings for physiological factors, astronaut performance, control theory, artificial intelligence, and cybernetics are included

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 122, December 1973

This special bibliography lists 343 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1973

Doctor of Philosophy

dissertationThis dissertation provides an in-depth evaluation of microstimulation of the primary visual cortex (V1) using chronically implanted Utah Electrode Arrays (UEAs) in macaque monkeys for use as a visual prosthesis. Within the scope of this dissertation are several significant contributions. First, a minimally invasive and robust device for head fixation was developed. In comparison to other available designs, this device improved long-term outcomes by providing a stronger, less invasive interface that reduced the risk of infection. This device made it possible to acquire chronic microstimulation data in macaque monkeys. It has been tested on three animals and has provided a stable interface for over two years. Second, this dissertation is the first to describe the factors influencing the performance and safety of microstimulation of V1 with the UEA. Two UEAs were implanted in V1 of two macaque monkeys, and experiments were performed several months following implantation. The electrical and recording properties of the electrodes and the high-resolution visuotopic organization of V1 were measured. In addition, threshold stimulation levels that evoked behavioural responses using single electrodes were determined. Periodic microstimulation at currents up to 96 pA did not impair the ability to record neural signals and did not affect the animal's vision where the UEAs were implanted. It was discovered, however, that microstimulation at these levels evoked behavioural responses on only 8 of 82 systematically stimulated electrodes. It was suggested that the ability to evoke behavioral responses may depend on the location of the electrode tips within the cortical layers of V1, the distance of the electrode tips to neuronal somata, and the inability of nonhuman primates to recognize and respond to a generalized set of evoked percepts. Finally, this dissertation is the first to describe the spatial and temporal characteristics of microstimulation of V1 with the UEA over chronic time periods. Two years after implantation, it was found that consistent behavioural responses could be evoked during simultaneous stimulation of multiple contiguous electrodes. Saccades to electrically-evoked targets using groups of nine electrodes showed that the animal could discriminate spatially distinct percepts with a resolution comparable to the current epiretinal prostheses. These results demonstrate chronic perceptual functionality and provide evidence for the feasibility of a UEA-based visual prosthesis for the blind

Aerospace Medicine and Biology: Cumulative index, 1979

This publication is a cumulative index to the abstracts contained in the Supplements 190 through 201 of 'Aerospace Medicine and Biology: A Continuing Bibliography.' It includes three indexes-subject, personal author, and corporate source