Manjunatha Mahadevappa

Perceptual thresholds and electrode impedance in three retinal prosthesis subjects

Three test subjects blind from retinitis pigmentosa were implanted with retinal prostheses as part of a FDA-approved clinical trial. The implant consisted of an extraocular unit that contained electronics for wireless data, power, and generation of stimulus current, and an intraocular unit that consisted of 16 platinum stimulating electrodes arranged in a 4 /spl times/ 4 pattern within a silicone rubber substrate. The array was held to the retina by a small tack. The stimulator was connected to the array by a multiwire cable and was controlled by a computer based external system that allowed precise control over each electrode. Perception thresholds and electrode impedance were obtained on each electrode from the subjects over several months of testing. The electrode distance from the retina was determined from optical coherence tomography imaging of the array and retina. Across all subjects, average thresholds ranged from 24-702 /spl mu/A (1-ms pulse). The data show that proximity to the retina played a role in determining the threshold and impedance, but only for electrodes that were greater than 0.5 mm from the retina.

Brightness preserving dynamic fuzzy histogram equalization

This paper proposes a novel modification of the brightness preserving dynamic histogram equalization technique to improve its brightness preserving and contrast enhancement abilities while reducing its computational complexity. The modified technique, called Brightness Preserving Dynamic Fuzzy Histogram Equalization (BPDFHE), uses fuzzy statistics of digital images for their representation and processing. Representation and processing of images in the fuzzy domain enables the technique to handle the inexactness of gray level values in a better way, resulting in improved performance. Execution time is dependent on image size and nature of the histogram, however experimental results show it to be faster as compared to the techniques compared here. The performance analysis of the BPDFHE along with that for BPDHE has been given for comparative evaluation.

Factors Affecting Perceptual Thresholds in Epiretinal Prostheses

PURPOSE The goal was to evaluate how perceptual thresholds are related to electrode impedance, electrode size, the distance of electrodes from the retinal surface, and retinal thickness in six subjects blind as a result of retinitis pigmentosa, who received epiretinal prostheses implanted monocularly as part of a U.S. Food and Drug Administration (FDA)-approved clinical trial. METHODS The implant consisted of an extraocular unit containing electronics for wireless data, power recovery, and generation of stimulus current, and an intraocular unit containing 16 platinum stimulating electrodes (260- or 520-microm diameter) arranged in a 4 x 4 pattern. The electrode array was held onto the retina by a small tack. Stimulation was controlled by a computer-based external system that allowed independent control over each electrode. Perceptual thresholds (the current necessary to see a percept on 79% of trials) and impedance were measured for each electrode on a biweekly basis. The distance of electrodes from the retinal surface and retinal thickness were measured by optical coherence tomography on a less regular basis. RESULTS Stimulation thresholds for detecting phosphenes correlated with the distance of the electrodes from the retinal surface, but not with electrode size, electrode impedance, or retinal thickness. CONCLUSIONS Maintaining close proximity between the electrode array and the retinal surface is critical in developing a successful retinal implant. With the development of chronic electrode arrays that are stable and flush on the retinal surface, it is likely that the influence of other factors such as electrode size, retinal degeneration, and subject age will become more apparent. (ClinicalTrials.gov number, NCT00279500.).

Long-term stimulation by active epiretinal implants in normal and RCD1 dogs

An epiretinal prosthesis, consisting of an extraocular microelectronic stimulator and an intraocular electrode array, was implanted in one eye of three blind and three sighted dogs. Three dogs (2 blind, 1 normal) were stimulated for 120 days, and two dogs (both normal) for 60 and 103 days respectively for 8-10 h/day at levels of 0.1 mC cm(-2) and 0.05 mC cm(-2), with each stimulus level presented to half of the array. One blind dog was kept as an inactive implant control. During the study period, electroretinograms (ERG) and fundus photographs were recorded. At the end of the study period, the dogs were sacrificed and histological and morphometric evaluation was made of the retina. No inflammatory reaction, neovascularization or hemorrhage was observed during the follow-up examinations. ERGs were unchanged. Stimulus levels used were of sufficient amplitude to elicit cortical evoked potentials. Histological evaluation showed no inflammatory infiltrates or changes in retina morphometry related to electrical stimulation when compared to the unstimulated control eye. Morphometric analysis revealed no consistent differences relating to electrical stimulation. In summary, chronic electrical stimulation of the dog retina at up to 0.1 mC cm(-2) with an epiretinal prosthesis does not appear to adversely affect the retina.

Restoration of gait and motor recovery by functional electrical stimulation therapy in persons with stroke

Purpose. To evaluate the clinical efficacy of functional electrical stimulation (FES) therapy of the tibialis anterior (TA) muscle on gait restoration and enhancing motor recovery with stroke patients. Method. Thirty hemiparetic participants with spastic foot-drop impairments who were at least 3 months post-stroke were recruited from a rehabilitation institute and were assigned either to a control group or a FES group. Both the groups participated in a conventional stroke rehabilitation program for 60 min per day, 5 days a week, for 12-weeks. The FES group received the electrical stimulation to the TA muscle for correction of foot-drop. Results. Functional electric stimulation (FES) resulted in a 26.3% (p < 0.001) improvement of walking speed measured with 10-m walkway, whereas the improvement in the control group was only 11.5% (p < 0.01). The FES group also showed significantly greater improvements compared to control group in other gait parameters (e.g. cadence, step length), physiological cost index (PCI), ankle range of motion, spasticity of calf muscle, Fugl–Meyer scores, and the maximum value of the root mean square (RMSmax), which reflects the capacity of the muscle output. Conclusions. These findings suggest that, the FES therapy combined with conventional therapy treatment more effectively improves the walking ability and enhances the motor recovery when compared with conventional therapy alone in stroke survivors.

Functional electrical stimulation of dorsiflexor muscle: effects on dorsiflexor strength, plantarflexor spasticity, and motor recovery in stroke patients.

OBJECTIVE To evaluate the therapeutic effects of Functional Electrical Stimulation (FES) of the tibialis anterior muscle on plantarflexor spasticity, dorsiflexor strength, voluntary ankle dorsiflexion, and lower extremity motor recovery with stroke survivors. DESIGN We conducted a prospective interventional study. SETTING Rehabilitation ward, physiotherapy unit and gait analysis laboratory. PARTICIPANTS Fifty-one patients with foot drop resulting from stroke. INTERVENTION The functional electrical stimulation (FES) group (n=27) received 20-30 minutes of electrical stimulation to the peroneal nerve and anterior tibial muscle of the paretic limb along with conventional rehabilitation program (CRP). The control group (n=24) treated with CRP only. The subjects were treated 1 hr per day, 5 days a week, for 12 weeks. MAIN OUTCOME MEASURES Plantarflexor spasticity measured by modified ashworth scale (MAS), dorsiflexion strength measured by manual muscle test (MMT), active/passive ankle joint dorsiflexion range of motion, and lower-extremity motor recovery by Fugl-Meyer assessment (FMA) scale. RESULTS After 12 weeks of treatment, there was a significant reduction in a plantarflexor spasticity by 38.3% in the FES group and 21.2% in control group (P< 0.05), between the beginning and end of the trial. Dorsiflexor muscle strength was increased significantly by 56.6% and 27.7% in the FES group and control group, respectively. Similarly, voluntary ankle dorsiflexion and lower-extremity motor function improved significantly in both the groups. No significant differences were found in the baseline measurements among groups. When compared with control group, a significant improvement (p< 0.05) was measured in all assessed parameters in the FES group at post-treatment assessment, thus FES therapy has better effect on recovery process in post-stroke rehabilitation. CONCLUSIONS Therapy combining FES and conventional rehabilitation program was superior to a conventional rehabilitation program alone, in terms of reducing spasticity, improving dorsiflexor strength and lower extremity motor recovery in stroke patients.

Effect of functional electrical stimulation on the effort and walking speed, surface electromyography activity, and metabolic responses in stroke subjects

OBJECTIVE To investigate the effects of functional electrical stimulation (FES) combined with conventional rehabilitation program on the effort and speed of walking, the surface electromyographic (sEMG) activity and metabolic responses in the management of drop foot in stroke subjects. METHODS Fifteen patients with a drop foot resulting from stroke at least 3 months prior to the start of the trial took part in this study. All subjects were treated 1h a day, 5 days a week, for 12 weeks, including conventional stroke rehabilitation program and received 30 min of FES to the tibialis anterior (TA) muscle of the paretic leg in clinical settings. Baseline and post-treatment measurements were made for temporal and spectral EMG parameters of TA muscle, walking speed, the effort of walking as measured by physiological cost index (PCI) and metabolic responses. RESULTS The experimental results showed a significant improvement in mean-absolute-value (21.7%), root-mean-square (66.3%) and median frequency (10.6%) of TA muscle EMG signal, which reflects increased muscle strength. Mean increase in walking speed was 38.7%, and a reduction in PCI of 34.6% between the beginning and at end of the trial. Improvements were also found in cardiorespiratory responses with reduction in oxygen consumption (24.3%), carbon dioxide production (19.9%), heart rate (7.8%) and energy cost (22.5%) while walking with FES device. CONCLUSIONS The results indicate that the FES may be a useful therapeutic tool combined with conventional rehabilitation program to improve the muscle strength, walking ability and metabolic responses in the management of drop foot with stroke patients.

Ultrasonic spectacles and waist-belt for visually impaired and blind person

This paper presents an electronic navigation system for visually impaired and blind people (subject). This system understands obstacles around the subject up to 500 cm in front, left and right direction using a network of ultrasonic sensors. It effectively calculates distance of the detected object from the subject and prepares navigation path accordingly avoiding obstacles. It uses speech feedback to aware the subject about the detected obstacle and its distance. This proposed system uses AT89S52 microcontroller based embedded system to process real time data collected using ultrasonic sensor network. Based on direction and distance of detected obstacle, relevant pre-recorded speech message stored in APR9600 flash memory is invoked. Such speech messages are conveyed to the subject using earphone.

Way-finding Electronic Bracelet for visually impaired people

Way-finding Electronic Bracelet (WEB) for visually impaired (subject) is a portable embedded system for obstacle detection and way-finding. This MSP430G2553 processor based real-time system employs single Maxbotix MB1340 ultrasonic transceiver mounted on customized circular bracelet for detecting obstacle in the range 20 to 600 centimetres. Half duplex wireless communication is used for invoking vibrotactile and audio cues at receiver side. Maintaining a safety margin distance in front, left and right direction, WEB dynamically calculates obstacle distance (if any). Using on-demand hand movements, subject can understand surrounding situations and can perform successful way-finding. WEB system is available with choice of optimum hardware as per wearable comfort and requirement of subject. Preliminary trials on blindfolded subjects, WEB demonstrated substantial potential for cost-effective wearable real-time system with minimum physical interface for mobility of visually impaired people.

Visual task performance in blind humans with retinal prosthetic implants

A prototype electronic retinal prosthesis has been tested in three subjects. The system features an implanted retinal stimulator and an external system for image acquisition, processing, and telemetry. The subjects in general performed better than chance on psychophysical tests involving object detection, object counting, object discrimination, and direction of movement.