Inertial Gait Phase Detection for control of a drop foot stimulator: Inertial sensing for gait phase detection

An Inertial Gait Phase Detection system was developed to replace heel switches and footswitches currently being used for the triggering of drop foot stimulators. A series of four algorithms utilising accelerometers and gyroscopes individually and in combination were tested and initial results are shown. Sensors were positioned on the outside of the upper shank. Tests were performed on data gathered from a subject, sufferer of stroke, implanted with a drop foot stimulator and triggered with the current trigger, the heel switch. Data tested includes a variety of activities representing everyday life. Flat surface walking, rough terrain and carpet walking show 100% detection and the ability of the algorithms to ignore non-gait events such as weight shifts. Timing analysis is performed against the current triggering method, the heel switch. After evaluating the heel switch timing against a reference system, namely the Vicon 370 marker and force plates system. Initial results show a close correlation between the current trigger detection and the inertial sensor based triggering algorithms. Algorithms were tested for stairs up and stairs down. Best results are observed for algorithms using gyroscope data. Algorithms were designed using threshold techniques for lowest possible computational load and with least possible sensor components to minimize power requirements and to allow for potential future implantation of sensor system.     

Estimation of the kinetic-optimized stimulus intensity envelope for drop foot gait rehabilitation

The purpose of present study is to estimate the optimal stimulus intensity envelope for drop foot rehabilitation based on a kinetic perspective. The voluntary and electric-stimulated elicited dorsiflexion torque responses of 11 healthy subjects were measured. During dorsiflexion, we recorded the tibialis anterior (TA) electromyography (EMG) or the stimulation intensity at four angles of the ankle joint. From these measurements, we derived two approximate equations that estimate dorsiflexion produced by either voluntary contraction or by electrical stimulation using a sigmoid function and a stepwise-regression analysis. We then tested the predictive capability of the model using Pearson correlation. Both equations indicated high correlation coefficients. Finally, we derived a relation between the TA EMG amplitude and stimulation intensity. From the obtained equation, we determined the optimal stimulus amplitude. We assume that the derived stimulus intensity envelope, calculated from EMG amplitude and angle of ankle joint, satisfies kinetic demand.     

Estimation of the kinetic-optimized stimulus intensity envelope for drop foot gait rehabilitation

The purpose of present study is to estimate the optimal stimulus intensity envelope for drop foot rehabilitation based on a kinetic perspective. The voluntary and electric-stimulated elicited dorsiflexion torque responses of 11 healthy subjects were measured. During dorsiflexion, we recorded the tibialis anterior (TA) electromyography (EMG) or the stimulation intensity at four angles of the ankle joint. From these measurements, we derived two approximate equations that estimate dorsiflexion produced by either voluntary contraction or by electrical stimulation using a sigmoid function and a stepwise-regression analysis. We then tested the predictive capability of the model using Pearson correlation. Both equations indicated high correlation coefficients. Finally, we derived a relation between the TA EMG amplitude and stimulation intensity. From the obtained equation, we determined the optimal stimulus amplitude. We assume that the derived stimulus intensity envelope, calculated from EMG amplitude and angle of ankle joint, satisfies kinetic demand.     

Automated setup of functional electrical stimulation for drop foot using a novel 64 channel prototype stimulator and electrode array: Results from a gait-lab based study

Functional electrical stimulation is commonly used to correct drop foot following stroke or multiple sclerosis. This technique is successful for many patients, but previous studies have shown that a significant minority have difficulty identifying correct sites to place the electrodes in order to produce acceptable foot movement. Recently there has been some interest in the use of ‘virtual electrodes’, the process of stimulating a subset of electrodes chosen from an array, thus allowing the site of stimulation to be moved electronically rather than physically. We have developed an algorithm for automatically determining the best site of stimulation and tested it on a computer linked to a small, battery-powered prototype stimulator with 64 individual output channels. Stimulation was delivered via an 8 × 8 array adhered to the leg by high-resistivity self-adhesive hydrogel. Ten participants with stroke (ages 53–71 years) and 11 with MS (ages 40–80 years) were recruited onto the study and performed two walks of 10 m for each of the following conditions: own setup (PS), clinician setup (CS), automated setup (AS) and no stimulation (NS). The PS and CS conditions used the participant's own stimulator with two conventional electrodes; the AS condition used the new stimulator and algorithm. Outcome measures were walking speed, foot angle at initial contact and the Borg Rating of Perceived Exertion.Mean walking speed with no stimulation was 0.61 m/s; all FES setups significantly increased speed relative to this (AS p < 0.05, PS p < 0.01, CS p < 0.01). Speed for PS (0.72 m/s) was faster than both AS (0.65 m/s, p < 0.01) and CS (0.68 m/s, p < 0.05). Frontal plane foot orientation at heel-strike was more neutral for AS (0.3° everted) than in the NS (11.2° inverted, p < 0.01), PS (4.5° inverted, p < 0.05) and CS (3.1° inverted, p < 0.05) conditions. Dorsiflexion angles for AS (4.2°) were larger than NS (?3.0°, p < 0.01), not different to PS (4.3°, p > 0.05) and less dorsiflexed than CS (6.0°, p < 0.05).This proof of principle study has demonstrated that automated setup of an array stimulator produces results broadly comparable to clinician setup. Slower walking speed for automated and clinician setups compared to the participants’ own setup may be due to the participants’ lack of familiarity with responses different to their usual setups. Automated setup using the method described here seems sufficiently reliable for future longer-term investigation outside the laboratory and may lead to FES becoming more viable for patients who, at present, have difficulty setting up conventional stimulators.     

Writing through a robot: a proof of concept for a brain-machine interface

This paper describes a non-invasive human brain-actuated robotic arm experiment, which allows remote writing. In the local environment, the participant decides on an arbitrary word to transmit. A mental speller interface is then used to select the letters. A robot arm placed in the remote environment writes the word on a whiteboard in real time. A multidisciplinary framework such as the one presented here exemplifies a class of interactive applications with possible relevance in a variety of fields, such as entertainment and clinical environments.     

Serial triggering of TCRs: a basis for the sensitivity and specificity of antigen recognition

Sensitivity of antigen detection by B cells correlates with high-affinity binding. This paradigm does not appear to hold for the T-cell receptor (TCR), which is able to bind its ligand — peptide in the context of major histocompatibility complex (MHC) — with low affinity. Here, Salvatore Valitutti and Antonio Lanzavecchia propose that the efficiency of T-cell antigen recognition is dependent upon optimal kinetics of the TCR—peptide—MHC interaction, allowing serial engagements and triggering of many TCRs by a few peptide—MHC complexes.     

Qualitative haemodynamic validation of a percutaneous temporary aortic valve: a proof of concept study

The concept of temporary aortic valves has been suggested in the clinical settings of acute aortic regurgitation and transcatheter aortic valve replacement procedure (TAVR). In TAVR, suggestions have been made to pre-treat or remove the diseased aortic valve prior to implantation of the replacement valve. A successful temporary aortic valve must demonstrate the ability to prevent life-threatening haemodynamics of massive aortic regurgitation. A novel temporary aortic valve (TAV) design, comprised of inflatable balloon elements as a check-valve, can readily be deployed and retrieved via a catheter-system. A simple flow model is set up to test the TAV's performance in severe aortic regurgitation. With induced aortic regurgitation, placement of the TAV is found to increase the distal aortic diastolic pressure, to reduce the widened pulse pressure, to protect proximal aorta-left ventricle from diastolic pressure elevation and to reduce the aortic regurgitant volume. In conclusion, continued development of the TAV system can lead to a successful temporary aortic valve to be used in various appropriate clinical settings.     

Testing a mobile mindful eating intervention targeting craving-related eating: feasibility and proof of concept

Theoretically driven smartphone-delivered behavioral interventions that target mechanisms underlying eating behavior are lacking. In this study, we administered a 28-day self-paced smartphone-delivered intervention rooted in an operant conditioning theoretical framework that targets craving-related eating using mindful eating practices. At pre-intervention and 1-month post-intervention, we assessed food cravings among adult overweight or obese women (N = 104; M age = 46.2 ± 14.1 years; M BMI = 31.5 ± 4.5) using ecological momentary assessment via text message (SMS), self-reported eating behavior (e.g., trait food craving), and in-person weight. Seventy-eight participants (75.0%) completed the intervention within 7 months (‘all completers’), and of these, 64 completed the intervention within 3 months (‘timely completers’). Participants experienced significant reductions in craving-related eating (40.21% reduction; p < .001) and self-reported overeating behavior (trait food craving, p < .001; other measures ps < .01). Reductions in trait food craving were significantly correlated with weight loss for timely completers (r = .30, p = .020), this pattern of results was also evident in all completers (r = .22, p = .065). Taken together, results suggest that smartphone-delivered mindful eating training targeting craving-related eating may (1) target behavior that impacts a relative metabolic pathway, and (2) represent a low-burden and highly disseminable method to reduce problematic overeating among overweight individuals. ClinicalTrials.gov registration: NCT02694731.     

Tumor bracketing and safety margin estimation using multimodal marker seeds: a proof of concept

Accurate tumor excision is crucial in the locoregional treatment of cancer, and for this purpose, surgeons often rely on guide wires or radioactive markers for guidance toward the lesion. Further improvement may be obtained by adding optical guidance to currently used methods, in the form of intra-operative fluorescence imaging. To achieve such a multimodal approach, we have generated markers that can be used in a pre-, intra-, and post-operative setting, based on a cocktail of a dual-emissive inorganic dye, lipids, and pertechnetate. Phantom experiments demonstrate that these seeds can be placed accurately around a surrogate tumor using ultrasound. Three-dimensional bracketing provides delineation of the entire lesion. Combined with the multimodal nature, this provides the opportunity to predetermine the resection margins by validating the placement accuracy using multiple imaging modalities (namely, x ray, MRI, SPECT/CT, and ultrasound). The dual-emissive fluorescent properties of the dye provide the unique opportunity to intra-operatively estimate the depth of the seed in the tissue via multispectral imaging: emission green λmax=520 nm≤5 mm penetration versus emission red λmax=660 nm≤12 mm penetration. By using particles with different colors, the original geographic orientation of the excised tissue can be determined.     

Three dimensional inertial sensing of foot movements for automatic tuning of a two-channel implantable drop-foot stimulator

A three dimensional inertial sensing system for measuring foot movements during gait is proposed and tested. It can form the basis for an automated tuning system for a two-channel implantable drop-foot stimulator. The foot orientation and position during the swing phase of gait can be reconstructed on the basis of three-dimensional measurement of acceleration and angular velocity, using initial and final conditions during mid-stance. The foot movements during gait of one stroke person using the implanted two-channel stimulator were evaluated for several combinations of stimulation parameters for both channels. The reconstructed foot movements during gait in this person indicated that the channel stimulating the deep peroneal nerve contributes mainly to dorsiflexion and provides some reduction of inversion seen without stimulation, while the channel activating the superficial peroneal nerve mainly provides additional reduction of inversion. This agrees with anatomical knowledge about the function of the muscles activated by both branches of the peroneal nerve. The inertial sensor method is expected to be useful for the clinical evaluation of foot movements during gait supported by the two-channel drop-foot stimulator. Furthermore, it is expected to be applicable for the automated balancing of the two stimulation channels to ensure optimal support of gait.     

Continuously microscopically observed and process-controlled cell culture within the SlideReactor: proof of a new concept for cell characterization

Certain cell types, especially primary human cells, favor a well-defined culture environment offering continuous supply of nutrients and oxygen and waste product removal. Several bioreactors based on special matrices or hollow fibers have been developed that provide such conditions. However, characterization of matrix re-organization or growth of tissue within these systems is possible only after culture termination. Evaluation of the influence of certain medium additives or culture conditions (e.g., temperature, oxygenation) on cell viability, expansion, and differentiation within these systems remains a challenging task. The SlideReactor, a miniaturized hollow fiber-based bioreactor, was developed to enable the observation of cells during culture. An operation concept offering predefined conditions for various cell types has been designed. For proof of concept, primary human cells (hepatocytes, fibroblasts, keratinocytes) and cell lines (HepG2, HuH7, C3A, WiDr, SkHep1) were cultured and observed. A series of experiments (n=40) showed the feasibility of the set-up; determination of process parameters and continuous observation is possible. The SlideReactor may serve as a simple and cost-efficient tool for cell characterization and optimization of cell-culture conditions.     

A dynamic model for simulating a trip and fall during gait

The purpose of this study was to develop an analytical model to simulate a trip and fall during gait. The human body was modeled as a 12 degree-of-freedom linkage system. The kinematics of the lower extremity for one cycle of gait were obtained for a healthy subject using an optoelectronic three-dimensional data acquisition system. Inverse dynamics was used to compute the moments about the hip, knee and ankle joints of the lower extremity. These moments were then used as input actuators to the joints in to a forward dynamics model to simulate the swing phase of gait from toe-off to heel-strike. An optimization procedure to minimize errors associated with the computed experimental torque was applied to correct for mathematical instability. An experiment was performed to measure the three-dimensional foot--obstacle contact force for a healthy subject tripping on an obstacle during gait. The contact force was applied to the swing limb of the forward dynamics model for 0.09 s beginning at 0.04 s after toe-off. Tripping on an obstacle followed by a muscle-relaxed fall was simulated. The simulation results were visualized with animation software.     

An endotracheal intubation confirmation system based on carina image detection: a proof of concept

In this paper, a novel system for automatic confirmation of endotracheal intubation is proposed. The system comprises a miniature CMOS sensor and electric wires attached to a rigid stylet. Video signals are continuously acquired and processed by the algorithm implemented on a PC/DSP. The system is based on detection of the carina image as an anatomical landmark of correct tube positioning and it thus utilizes direct visual cues. Detection of the carina is performed based on unsupervised clustering, using a greedy-Gaussian mixture framework. The performance of the proposed system was initially evaluated using a mannequin model. A scientific prototype was assembled and used to perform repeated intubations on the model and collect a database of video signals which were processed off-line. The videos were categoried by a medical professional into carina, upper-trachea, and esophagus. An accuracy of 100% was achieved in discriminating between the carina and other anatomical structures including esophagus and upper-trachea. As an additional validation, the system was tested using a dataset of 231 video images recorded from five human subjects during intubation. The system correctly classified 120 out of 125 non-carina images (i.e. a sensitivity of 96.0%), and 100 out of 106 carina images (i.e. a specificity 94.3%). Using a 10th-order median filter, applied on the frame-based classification results, a 100% accuracy rate was obtained.     

Expansion anchors for use in anterior cruciate ligament (ACL) reconstruction: establishing proof of concept in a benchtop analysis

The current method for graft fixation in bone tendon-bone anterior cruciate ligament (ACL) reconstruction is the interference screw. Although this method of fixation provides for adequate graft fixation with respect to strength, intraoperative placement is difficult and the failure rate is high. To address these concerns, we have designed and fabricated prototype expansion anchors that could be expanded to anchor the graft in the bone tunnel. As a first step in assessing the validity of this concept, in the current work, we demonstrate that these systems are of comparable fixation strength (biomechanical pullout testing) to the standard interference screw, are smaller at the time of insertion and thus provide for increased visibility and ease of placement. The increased visibility should result in better placement and reduced failure rates. The increased ease of placement should result in significant savings in decreased OR time.     

Anti-metatype antibody reactivity: a model for T-cell receptor recognition

Anti-metatype (Met) antibodies are anti-immunoglobulins that specifically recognize an antibody-liganded active site but lack specificity for either the ligand or the idiotype. As proposed here by Edward Voss, anti-metatype-metatype immunoglobulin interactions may serve as a model for the interaction of the T-cell receptor (TCR) with antigen-MHC (class I/class II) complexes: the anti-metatype immunoglobulin reagent simulates the TCR and the liganded antibody mimics the antigen-MHC complex. Such a model addresses the dilemma of two macromolecules interacting with the same antigenic determinant and may represent a rational approach to improve understanding of the initiation and regulation of the immune response.