Philip D. Parks

Psychomotor vigilance testing of professional drivers in the occupational health clinic: a potential objective screen for daytime sleepiness.

Objective Psychomotor vigilance testing (PVT) rapidly assesses attention, reaction time (RT), and abnormal vigilance. Thus, PVT may be an adjunct to screening drivers for high-risk obstructive sleep apnea (OSA)/excess daytime sleepiness (EDS). Methods: Commercial drivers and emergency responders undergoing occupational examinations took a 10-minute PVT and were instructed to achieve their fastest possible RTs. Participants with maximum RT >5 seconds or ≥2 “super lapses” (RT ≥1000 ms) were categorized as “microsleepers.” Results: Among 193 male participants, the 15 microsleepers (8%) were significantly more obese, but not different on age or Epworth Sleepiness Score. Time of day had no effect on RT. Conclusion: PVT is suitable to occupational clinics and can identify otherwise unrecognized, impaired vigilance. Further studies must validate the PVT abnormalities most predictive of OSA/EDS and vehicular crashes, compared to adiposity measures alone.

An implantable 64-channel neural interface with reconfigurable recording and stimulation

Next generation implantable medical devices will have the potential to provide more precise and effective therapies through adaptive closed-loop controllers that combine sensing and stimulation across larger numbers of electrode channels. A major challenge in the design of such devices is balancing increased functionality and channel counts with the miniaturization required for implantation within small anatomical spaces. Customized therapies will require adaptive systems capable of tuning which channels are sensed and stimulated to overcome variability in patient-specific needs, surgical placement of electrodes, and chronic physiological responses. In order to address these challenges, we have designed a miniaturized implantable fully-reconfigurable front-end system that is integrated into the distal end of an 8-wire lead, enabling up to 64 electrodes to be dynamically configured for sensing and stimulation. Full reconfigurability is enabled by two custom 32×2 cross-point switch (CPS) matrix ASICs which can route any electrode to either an amplifier with reprogrammable bandwidth and integrated ADC or to one of two independent stimulation channels that can be driven through the lead. The 8-wire circuit includes a digital interface for robust communication as well as a charge-balanced powering scheme for enhanced safety. The system is encased in a hermetic package designed to fit within a 14 mm bur-hole in the skull for neuromodulation of the brain, but could easily be adapted to enhance therapies across a broad spectrum of applications.

Package architecture and component design for an implanted neural stimulator with closed loop control

An implanted neural stimulator with closed loop control requires electrodes for stimulation pulses and recording neuron activity. Our system features arrays of 64 electrodes. Each electrode can be addressed through a cross bar switch, to enable it to be used for stimulation or recording. This electrode switch, a bank of low noise amplifiers with an integrated analog to digital converter, power conditioning electronics, and a communications and control gate array are co-located with the electrode array in a 14 millimeter diameter satellite package that is designed to be flush mounted in a skull burr hole. Our system features five satellite packages connected to a central hub processor-controller via ten conductor cables that terminate in a custom designed, miniaturized connector. The connector incorporates features of high reliability, military grade devices and utilizes three distinct seals to isolate the contacts from fluid permeation. The hub system is comprised of a connector header, hermetic electronics package, and rechargeable battery pack, which are mounted on and electrically interconnected by a flexible circuit board. The assembly is over molded with a compliant silicone rubber. The electronics package contains two antennas, a large coil, used for recharging the battery and a high bandwidth antenna that is used to download data and update software. The package is assembled from two machined alumina pieces, a flat base with brazed in, electrical feed through pins and a rectangular cover with rounded corners. Titanium seal rings are brazed onto these two pieces so that they can be sealed by laser welding. A third system antenna is incorporated in the flexible circuit board. It is used to communicate with an externally worn control package, which monitors the health of the system and allows both the user and clinician to control or modify various system function parameters.

Iatrogenic disability and narcotics addiction after lumbar fusion in a worker's compensation claimant

Study Design. Case report. Objective. Describe a case of chronic occupational low back pain with various treatments of questionable efficacy, leading to prolonged disability, iatrogenic narcotic addiction, and opioid-induced hyperalgesia. Summary of Background Data. Concerns about narcotics and other questionable treatments for chronic low back pain are increasing, especially in those with work-related conditions. Methods. Medical record review. Results. The patient had significant, persistent low back symptoms, but good function at work and home. He underwent lumbar fusion to address persistent pain, and subsequently developed failed back surgery syndrome. He was prescribed increasing amounts of opioid analgesics and was recommended for an intrathecal morphine pump, without evaluation of the safety or efficacy of his current regimen. Subsequently, he was hospitalized for opioid detoxification and substance abuse treatment. Conclusion. Patients with chronic low back pain are at risk for receiving ineffective and potentially harmful treatment. A focus on restoring function instead of complete pain relief may lead to better outcomes in these patients.

Neural signal processing and closed-loop control algorithm design for an implanted neural recording and stimulation system.

A fully autonomous intracranial device is built to continually record neural activities in different parts of the brain, process these sampled signals, decode features that correlate to behaviors and neuropsychiatric states, and use these features to deliver brain stimulation in a closed-loop fashion. In this paper, we describe the sampling and stimulation aspects of such a device. We first describe the signal processing algorithms of two unsupervised spike sorting methods. Next, we describe the LFP time-frequency analysis and feature derivation from the two spike sorting methods. Spike sorting includes a novel approach to constructing a dictionary learning algorithm in a Compressed Sensing (CS) framework. We present a joint prediction scheme to determine the class of neural spikes in the dictionary learning framework; and, the second approach is a modified OSort algorithm which is implemented in a distributed system optimized for power efficiency. Furthermore, sorted spikes and time-frequency analysis of LFP signals can be used to generate derived features (including cross-frequency coupling, spike-field coupling). We then show how these derived features can be used in the design and development of novel decode and closed-loop control algorithms that are optimized to apply deep brain stimulation based on a patients neuropsychiatric state. For the control algorithm, we define the state vector as representative of a patients impulsivity, avoidance, inhibition, etc. Controller parameters are optimized to apply stimulation based on the state vectors current state as well as its historical values. The overall algorithm and software design for our implantable neural recording and stimulation system uses an innovative, adaptable, and reprogrammable architecture that enables advancement of the state-of-the-art in closed-loop neural control while also meeting the challenges of system power constraints and concurrent development with ongoing scientific research designed to define brain network connectivity and neural network dynamics that vary at the individual patient level and vary over time.

Predicting local field potentials with recurrent neural networks

We present a Recurrent Neural Network using LSTM (Long Short Term Memory) that is capable of modeling and predicting Local Field Potentials. We train and test the network on real data recorded from epilepsy patients. We construct networks that predict multi-channel LFPs for 1, 10, and 100 milliseconds forward in time. Our results show that prediction using LSTM outperforms regression when predicting 10 and 100 millisecond forward in time.

An implantable, designed-for-human-use peripheral nerve stimulation and recording system for advanced prosthetics

Complex suture prostheses that deliver sensory and position feedback require a more sophisticated integration with the human user. Here a micro-size active implantable system that provides many-degree-of-freedom neural feedback in both sensory stimulation and motor control is shown, as one potential human-use solution in DARPAs HAPTIX program. Various electrical and mechanical challenge and solutions in meeting both sensory /motor performance as well as ISO 14708 FDA-acceptable human use in an aspirin-size active implementation are discussed.Complex suture prostheses that deliver sensory and position feedback require a more sophisticated integration with the human user. Here a micro-size active implantable system that provides many-degree-of-freedom neural feedback in both sensory stimulation and motor control is shown, as one potential human-use solution in DARPAs HAPTIX program. Various electrical and mechanical challenge and solutions in meeting both sensory /motor performance as well as ISO 14708 FDA-acceptable human use in an aspirin-size active implementation are discussed.