K. Alex Shorter

A portable powered ankle-foot orthosis for rehabilitation

Innovative technological advancements in the field of orthotics, such as portable powered orthotic systems, could create new treatment modalities to improve the functional out come of rehabilitation. In this article, we present a novel portable powered ankle-foot orthosis (PPAFO) to provide untethered assistance during gait. The PPAFO provides both plantar flexor and dorsiflexor torque assistance by way of a bidirectional pneumatic rotary actuator. The system uses a portable pneumatic power source (compressed carbon dioxide bottle) and embedded electronics to control the actuation of the foot. We collected pilot experimental data from one impaired and three nondisabled subjects to demonstrate design functionality. The impaired subject had bilateral impairment of the lower legs due to cauda equina syndrome. We found that data from nondisabled walkers demonstrated the PPAFOs capability to provide correctly timed plantar flexor and dorsiflexor assistance during gait. Reduced activation of the tibialis anterior during stance and swing was also seen during assisted nondisabled walking trials. An increase in the vertical ground reaction force during the second half of stance was present during assisted trials for the impaired subject. Data from nondisabled walkers demonstrated functionality, and data from an impaired walker demonstrated the ability to provide functional plantar flexor assistance.

A new approach to detecting asymmetries in gait

BACKGROUND Traditional parameters used to assess gait asymmetries, e.g., joint range of motion or symmetry indices, fail to provide insight regarding timing and magnitude of movement deviations among lower limb joints during the gait cycle. This study evaluated the efficacy of a new approach for quantifying aspects of gait asymmetry. METHODS Asymmetric gait was simulated by joint bracing. The dominant leg knee or ankle was constrained in ten healthy young adult males. Kinematic data were collected during three-minute trials for treadmill-walking conditions: unbraced, knee-braced, and ankle-braced. We created a regions of deviation analysis, which compared asymmetric walking (flexion/extension behavior) relative to normative (group-averaged unbraced) data. Symmetry/asymmetry between bilateral joint pairs was quantified and the behavior of specific joints relative to normative data was assessed using this analysis. FINDINGS While traditional measures (e.g., maximum range of motion) grossly detected asymmetries due to bracing, these new analyses identified significant regions of asymmetry. Knee-bracing affected the knee during mid-swing, but also increased ankle asymmetry during both terminal stance and mid-swing and hip asymmetry during mid-stance and mid-swing. Ankle-bracing created asymmetries at the ankle (terminal stance and initial swing) and hip (terminal stance), but none at the knee. INTERPRETATION Region of deviation analysis effectively identified the timing and magnitude of deviations throughout the gait cycle, and provided information about the impact of a joint-mobility perturbation on neighboring joints. This new methodology will be useful in clinical settings to identify, characterize, and monitor recovery from asymmetric behaviors associated with injuries or pathologies.

A pneumatic power harvesting ankle-foot orthosis to prevent foot-drop

BackgroundA self-contained, self-controlled, pneumatic power harvesting ankle-foot orthosis (PhAFO) to manage foot-drop was developed and tested. Foot-drop is due to a disruption of the motor control pathway and may occur in numerous pathologies such as stroke, spinal cord injury, multiple sclerosis, and cerebral palsy. The objectives for the prototype PhAFO are to provide toe clearance during swing, permit free ankle motion during stance, and harvest the needed power with an underfoot bellow pump pressurized during the stance phase of walking.MethodsThe PhAFO was constructed from a two-part (tibia and foot) carbon composite structure with an articulating ankle joint. Ankle motion control was accomplished through a cam-follower locking mechanism actuated via a pneumatic circuit connected to the bellow pump and embedded in the foam sole. Biomechanical performance of the prototype orthosis was assessed during multiple trials of treadmill walking of an able-bodied control subject (n = 1). Motion capture and pressure measurements were used to investigate the effect of the PhAFO on lower limb joint behavior and the capacity of the bellow pump to repeatedly generate the required pneumatic pressure for toe clearance.ResultsToe clearance during swing was successfully achieved during all trials; average clearance 44 ± 5 mm. Free ankle motion was observed during stance and plantarflexion was blocked during swing. In addition, the bellow component repeatedly generated an average of 169 kPa per step of pressure during ten minutes of walking.ConclusionThis study demonstrated that fluid power could be harvested with a pneumatic circuit built into an AFO, and used to operate an actuated cam-lock mechanism that controls ankle-foot motion at specific periods of the gait cycle.

Bottlenose dolphins modify behavior to reduce metabolic effect of tag attachment.

Attaching bio-telemetry or -logging devices (‘tags’) to marine animals for research and monitoring adds drag to streamlined bodies, thus affecting posture, swimming gaits and energy balance. These costs have never been measured in free-swimming cetaceans. To examine the effect of drag from a tag on metabolic rate, cost of transport and swimming behavior, four captive male dolphins (Tursiops truncatus) were trained to swim a set course, either non-tagged (n=7) or fitted with a tag (DTAG2; n=12), and surface exclusively in a flow-through respirometer in which oxygen consumption () and carbon dioxide production (; ml kg−1 min−1) rates were measured and respiratory exchange ratio (/) was calculated. Tags did not significantly affect individual mass-specific oxygen consumption, physical activity ratios (exercise /resting ), total or net cost of transport (COT; J m−1 kg−1) or locomotor costs during swimming or two-minute recovery phases. However, individuals swam significantly slower when tagged (by ~11%; mean ± s.d., 3.31±0.35 m s−1) than when non-tagged (3.73±0.41 m s−1). A combined theoretical and computational fluid dynamics model estimating drag forces and power exertion during swimming suggests that drag loading and energy consumption are reduced at lower swimming speeds. Bottlenose dolphins in the specific swimming task in this experiment slowed to the point where the tag yielded no increases in drag or power, while showing no difference in metabolic parameters when instrumented with a DTAG2. These results, and our observations, suggest that animals modify their behavior to maintain metabolic output and energy expenditure when faced with tag-induced drag.

Invariant Density Analysis: Modeling and Analysis of the Postural Control System Using Markov Chains

In this paper, a novel analysis technique, invariant density analysis (IDA), is introduced. IDA quantifies steady-state behavior of the postural control system using center of pressure (COP) data collected during quiet standing. IDA relies on the analysis of a reduced-order finite Markov model to characterize stochastic behavior observed during postural sway. Five IDA parameters characterize the model and offer physiological insight into the long-term dynamical behavior of the postural control system. Two studies were performed to demonstrate the efficacy of IDA. Study 1 showed that multiple short trials can be concatenated to create a dataset suitable for IDA. Study 2 demonstrated that IDA was effective at distinguishing age-related differences in postural control behavior between young, middle-aged, and older adults. These results suggest that the postural control system of young adults converges more quickly to their steady-state behavior while maintaining COP nearer an overall centroid than either the middle-aged or older adults. Additionally, larger entropy values for older adults indicate that their COP follows a more stochastic path, while smaller entropy values for young adults indicate a more deterministic path. These results illustrate the potential of IDA as a quantitative tool for the assessment of the quiet-standing postural control system.

Smoothing spline analysis of variance models: A new tool for the analysis of cyclic biomechanical data

Cyclic biomechanical data are commonplace in orthopedic, rehabilitation, and sports research, where the goal is to understand and compare biomechanical differences between experimental conditions and/or subject populations. A common approach to analyzing cyclic biomechanical data involves averaging the biomechanical signals across cycle replications, and then comparing mean differences at specific points of the cycle. This pointwise analysis approach ignores the functional nature of the data, which can hinder one׳s ability to find subtle differences between experimental conditions and/or subject populations. To overcome this limitation, we propose using mixed-effects smoothing spline analysis of variance (SSANOVA) to analyze differences in cyclic biomechanical data. The SSANOVA framework makes it possible to decompose the estimated function into the portion that is common across groups (i.e., the average cycle, AC) and the portion that differs across groups (i.e., the contrast cycle, CC). By partitioning the signal in such a manner, we can obtain estimates of the CC differences (CCDs), which are the functions directly describing group differences in the cyclic biomechanical data. Using both simulated and experimental data, we illustrate the benefits of using SSANOVA models to analyze differences in noisy biomechanical (gait) signals collected from multiple locations (joints) of subjects participating in different experimental conditions. Using Bayesian confidence intervals, the SSANOVA results can be used in clinical and research settings to reliably quantify biomechanical differences between experimental conditions and/or subject populations.

From the track to the ocean : using flow control to improve marine bio-logging tags for cetaceans

Bio-logging tags are an important tool for the study of cetaceans, but superficial tags inevitably increase hydrodynamic loading. Substantial forces can be generated by tags on fast-swimming animals, potentially affecting behavior and energetics or promoting early tag removal. Streamlined forms have been used to reduce loading, but these designs can accelerate flow over the top of the tag. This non-axisymmetric flow results in large lift forces (normal to the animal) that become the dominant force component at high speeds. In order to reduce lift and minimize total hydrodynamic loading this work presents a new tag design (Model A) that incorporates a hydrodynamic body, a channel to reduce fluid speed differences above and below the housing and wing to redirect flow to counter lift. Additionally, three derivatives of the Model A design were used to examine the contribution of individual flow control features to overall performance. Hydrodynamic loadings of four models were compared using computational fluid dynamics (CFD). The Model A design eliminated all lift force and generated up to ~30 N of downward force in simulated 6 m/s aligned flow. The simulations were validated using particle image velocimetry (PIV) to experimentally characterize the flow around the tag design. The results of these experiments confirm the trends predicted by the simulations and demonstrate the potential benefit of flow control elements for the reduction of tag induced forces on the animal.

The next generation of multi-sensor acoustic tags: Sensors, applications, and attachments

From Kooyman’s 1963 wind-up kitchen timer TDR, multi-sensor tags have evolved significantly over the last twenty years. These advancements, including high fidelity acoustics, have been driven by improved sensing and electronics technology, and resulted in highly integrated mechatronics systems for the study of free ranging animals. In the next decade, these tags will continue to improve, and promising work has begun in three key areas: (i) new sensors; (ii) expanding uses of existing sensors; and (iii) increasing attachment duration and reliability. The addition of rapid acquisition GPS and the inclusion of gyroscopes to separate the dynamic acceleration of the animal from gravitational acceleration, are underway but not widely available to the community. Existing sensors could be used for more and different applications, e.g., measuring ambient ocean noise. Tags attached to pinnipeds in the Southern Ocean, for example, could provide noise measurements from remote areas. Finally, attachment duration has b...

Actuation Timing Strategies for a Portable Powered Ankle Foot Orthosis

Ankle-foot orthoses (AFOs) are used to assist persons with lower-limb neuromuscular impairments. We have developed the portable powered AFO (PPAFO). This device uses a bidirectional pneumatic actuator powered by a CO2 bottle to provide dorsiflexor and plantarflexor torque assistance. The PPAFO operates tether-free, allowing for use outside of the laboratory. This system has been tested on one impaired and multiple healthy subjects. Timing of the assistance provided by the PPAFO has been determined by: 1) direct event detection using sensor feedback with threshold triggers, and 2) state estimation in which gait events are estimated using a cross-correlation based algorithm. Direct event detection, while simple to implement, can be unreliable for subjects with certain gait impairments. State estimation, while more complicated to implement, provides access to state information that cannot be directly measured by the AFO, which allows for greater flexibility in assistance timing. Current hardware limitations and future work are also discussed.Copyright

A framework for enhanced localization of marine mammals using auto-detected video and wearable sensor data fusion

Accurate biological agent localization offers the opportunity for both researchers and institutions to gain new knowledge about individual and group behaviors of biosystems. This paper presents a sensor-fusion approach for tracking biological agents, combining the data from automated video logging with magnetic, angular rate, and gravity (MARG) and inertial measurement unit (IMU) data, with professionally managed dolphins as the representative example. Our method of video logging allows for accurate and automated dolphin location detection using a combination of Laplacian of Gaussian (LoG) and multi-orientation elliptical blob detection. These data are combined with MARG/IMU measurements to generate a localization estimate through a series of drift-correcting Kalman and gradient-descent filters, finalized with Incremental Smoothing and Mapping (iSAM2) pose-graph localization.