Ankle strategy assistance to improve gait stability using controllers based on in-shoe center of pressure in 2 degree-of-freedom powered ankle-foot orthoses: a clinical study.

BACKGROUND: Although the ankle strategy is important for achieving frontal plane stability during one-leg stance, previously developed powered ankle-foot orthoses (PAFOs) did not involve ankle strategies because of hardware limitations. Weakness of movement in frontal plane is a factor that deteriorates gait stability and increases fall risk so it should not be overlooked in rehabilitation. Therefore, we used PAFO with subtalar joint for frontal plane movement and tried to confirm that the existence of it is important in balancing through clinical experiments. METHODS: We developed a proportional CoP controller to assist ankle strategy or stabilizing moment and enhance eversion to compensate for the tilting moment with 2 dof PAFO. It was true experimental study, and we recruited seven healthy subjects (30 ± 4 years) who did not experience any gait abnormality participated in walking experiments for evaluating the immediate effect of subtalar joint of PAFO on their gait stability. They walked on the treadmill with several cases of controllers for data acquisitions. Indices of gait stability and electromyography for muscle activity were measured and Wilcoxon signed-rank tests were used to identify meaningful changes. RESULTS: We found that subjects were most stable during walking (in terms of largest Lyapunov exponents, p < 0.008) with the assistance of the PAFO when their electromyographic activity was the most reduced (p < 0.008), although postural sway increased when a proportional CoP controller was used to assist the ankle strategy (p < 0.008). Other indices of gait stability, kinematic variability, showed no difference between the powered and unpowered conditions (p > 0.008). The results of the correlation analysis indicate that the actuator of the PAFO enhanced eversion and preserved the location of the CoP in the medial direction so that gait stability was not negatively affected or improved. CONCLUSIONS: We verified that the developed 2 dof PAFO assists the ankle strategy by compensating for the tilting moment with proportional CoP controller and that wearer can walk in a stable state when the orthosis provides power for reducing muscle activity. This result is meaningful because an ankle strategy should be considered in the development of PAFOs for enhancing or even rehabilitating proprioception. Trial registration 7001988-202003-HR-833-03.

Terrain Feature Estimation Method for a Lower Limb Exoskeleton Using Kinematic Analysis and Center of Pressure.

While controlling a lower limb exoskeleton providing walking assistance to wearers, the walking terrain is an important factor that should be considered for meeting performance and safety requirements. Therefore, we developed a method to estimate the slope and elevation using the contact points between the limb exoskeleton and ground. We used the center of pressure as a contact point on the ground and calculated the location of the contact points on the walking terrain based on kinematic analysis of the exoskeleton. Then, a set of contact points collected from each step during walking was modeled as the plane that represents the surface of the walking terrain through the least-square method. Finally, by comparing the normal vectors of the modeled planes for each step, features of the walking terrain were estimated. We analyzed the estimation accuracy of the proposed method through experiments on level ground, stairs, and a ramp. Classification using the estimated features showed recognition accuracy higher than 95% for all experimental motions. The proposed method approximately analyzed the movement of the exoskeleton on various terrains even though no prior information on the walking terrain was provided. The method can enable exoskeleton systems to actively assist walking in various environments.

Design of an Artificial Neural Network Algorithm for a Low-Cost Insole Sensor to Estimate the Ground Reaction Force (GRF) and Calibrate the Center of Pressure (CoP).

As an alternative to high-cost shoe insole pressure sensors that measure the insole pressure distribution and calculate the center of pressure (CoP), researchers developed a foot sensor with FSR sensors on the bottom of the insole. However, the calculations for the center of pressure and ground reaction force (GRF) were not sufficiently accurate because of the fundamental limitations, fixed coordinates and narrow sensing areas, which cannot cover the whole insole. To address these issues, in this paper, we describe an algorithm of virtual forces and corresponding coordinates with an artificial neural network (ANN) for low-cost flexible insole pressure measurement sensors. The proposed algorithm estimates the magnitude of the GRF and the location of the foot plantar CoP. To compose the algorithm, we divided the insole area into six areas and created six virtual forces and the corresponding coordinates. We used the ANN algorithm with the input of magnitudes of FSR sensors, 1st and 2nd derivatives of them to estimate the virtual forces and coordinates. Eight healthy males were selected for data acquisition. They performed an experiment composed of the following motions: standing with weight shifting, walking with 1 km/h and 2 km/h, squatting and getting up from a sitting position to a standing position. The ANN for estimating virtual forces and corresponding coordinates was fitted according to those data, converted to c script, and downloaded to a microcontroller for validation experiments in real time. The results showed an average RMSE the whole experiment of 31.154 N for GRF estimation and 8.07 mm for CoP calibration. The correlation coefficients of the algorithm were 0.94 for GRF, 0.92 and 0.76 for the X and Y coordinate respectively.

The effects of operating height and the passage of time on the end-point performance of fine manipulative tasks that require high accuracy.

Sustained shoulder abduction, which results from an inappropriate worktable height or tool shape and long task hours, leads to an accumulation of muscle fatigue and subsequent work-related injuries in workers. It can be alleviated by controlling the table height or ergonomic tool design, but workers who are doing some types of work that require a discomfortable posture, such as minimally invasive surgery, cannot avoid these situations. Loads to the shoulder joint or muscles result in several problems, such as muscle fatigue, deterioration of proprioception or changing movement strategies of the central nervous system, and these are critical to work that requires a high accuracy of the upper extremities. Therefore, in this paper, we designed and conducted an experiment with human participants to discuss how an inappropriate height of the work-table affects the task performance of workers who are performing a fine manipulative task that requires high accuracy of the end point. We developed an apparatus that can control the height and has four touch screens to evaluate the end-point accuracy with two different heights. Eighteen adults (9 women and 9 men) participated in the experiments, and the electromyography of their shoulder muscles, their movement stability, and task performance were measured for the analysis. We found that inappropriate height of a table brings about muscle fatigue, and time elapsed for conducting tasks accelerated the phenomenon. Task performance deteriorated according to increased fatigue, and improved movement stability is not enough to compensate for these situations.

Policy Design for an Ankle-Foot Orthosis Using Simulated Physical Human-Robot Interaction via Deep Reinforcement Learning.

This paper presents a novel approach for designing a robotic orthosis controller considering physical human-robot interaction (pHRI). Computer simulation for this human-robot system can be advantageous in terms of time and cost due to the laborious nature of designing a robot controller that effectively assists humans with the appropriate magnitude and phase. Therefore, we propose a two-stage policy training framework based on deep reinforcement learning (deep RL) to design a robot controller using human-robot dynamic simulation. In Stage 1, the optimal policy of generating human gaits is obtained from deep RL-based imitation learning on a healthy subject model using the musculoskeletal simulation in OpenSim-RL. In Stage 2, human models in which the right soleus muscle is weakened to a certain severity are created by modifying the human model obtained from Stage 1. A robotic orthosis is then attached to the right ankle of these models. The orthosis policy that assists walking with optimal torque is then trained on these models. Here, the elastic foundation model is used to predict the pHRI in the coupling part between the human and robotic orthosis. Comparative analysis of kinematic and kinetic simulation results with the experimental data shows that the derived human musculoskeletal model imitates a human walking. It also shows that the robotic orthosis policy obtained from two-stage policy training can assist the weakened soleus muscle. The proposed approach was validated by applying the learned policy to ankle orthosis, conducting a gait experiment, and comparing it with the simulation results.

Effects of the degree of freedom and assistance characteristics of powered ankle-foot orthoses on gait stability.

We studied the use of powered ankle-foot orthoses (PAFOs) and walking stability of the wearers, focusing on the ankle joint, which is known to play a critical role in gait stability. Recognizing that the subtalar joint is an important modulator of walking stability, we conducted the walking experiment on a treadmill by applying varying assistance techniques to the 2-degree-of-freedom (DOF) PAFO, which has the subtalar joint as the rotating axis, and the commonly used 1-DOF PAFO. The participants were 8 healthy men (mean±SD: height, 174.8±7.1 cm; weight, 69.8±6.5 kg; and age, 29.1±4.8 years) with no history of gait abnormality. Center of pressure (COP) was measured with an in-shoe pressure sensor, and stability was estimated on the basis of the angular acceleration measured with the inertial measurement unit attached to the trunk. The experimental results of the 2-DOF PAFO, with or without assistance, showed a significantly higher stability than those of the 1-DOF PAFO (up to 23.78%, p<0.0326). With the 1-DOF PAFO, the stability deteriorated with the increase in the degree of assistance provided. With the 2-DOF PAFO, this tendency was not observed. Thus, the importance of the subtalar joint was proven using PAFOs. The mean position analysis of the COP during the stance phase confirmed that the COP highly correlated with stability (Pearson correlation coefficient: -0.6607). Thus, we conclude that only the 2-DOF PAFO can maintain walking stability, regardless of the assistance characteristics, by preserving the COP in the medial position through eversion. Awareness regarding the role of the subtalar joint is necessary during the manufacture or use of PAFOs, as lack of awareness could lead to the degradation of the wearer's gait stability, regardless of effective assistance, and deteriorate the fundamental functionality of PAFO.

Design of a Pneumatic Actuated Ankle-Foot Orthosis which has Talocrural and Subtalar Joint.

As aging progresses, risk of falls in elderly people increases due to the decreasing the range of motion (RoM) of eversion and the weakening of the plantar flexor. Balance training is performed to reduce the risk of falls and powered ankle-foot orthosis (PAFO) can be utilized in this process. The elderly can conduct training on the narrow roads or on the rugged ground with assistance on rotation of eversion and propulsion by PAFO. However, existing PAFOs were developed just by considering the talocrural joint which make the rotation of sagittal plane of ankle which is called by plantar flexion and dorsiflexion. So, we developed the 2 Degree of Freedom (DoF) PAFO which has the Talocrural and Subtalar joints for frontal plane rotation which is called inversion and eversion. We established the coordinate system and calculated the spatial formulas for talocrural and subtalar joint based on anatomical data. Developed PAFO has the pneumatic artificial muscle (PAM) as an actuator which is controlled by solenoid valve with PWM methods, light-weight 3D printed body and knee orthosis for interfacing with wearer in three area which are thigh, shank and foot. The total weight of developed PAFO is 2. 14kg and it can be 1. 44kg without the weight of knee orthosis (0.7kg). Measurement sensors for PAFO were the absolute encoders to measure the angle of talocrural and subtalar joint, tensile loadcell to measure the magnitude of force from PAM, pressure sensor to measure the pressure of PAM and FSR sensor to judge the phase of the gait cycle. The results of the paper show the validation of design, kinematics and functional capacity for human subject experiments with proportional myoelectric control (PMc) of developed PAFO.

A design of RF stimulator which is similar to temperature distribution by moxibustion (preliminary study).

We developed a novel radio-frequency (RF) stimulator to mimic heat effects similar to the temperature distributions created by moxibustion in porcine tissue. Moxibustion is a traditional Oriental medicine technique using moxa, which is utilized not only to cure disease, but also to increase immunity. However, it may lead to undesired effects including severe pains, blisters, and burns because of the difficulty of controlling heat intensity during the process. To overcome these problems, a novel RF stimulator that can conduct thermal energy to the deep tissue of the body and also easily control the power of heat stimulation was proposed. RF stimulating protocols were designed to mimic the temperature profiles of two types of moxibustion. In our results, the temperature distributions created by the proposed protocols were similar to those attained by moxibustion. It was also shown that the proposed protocols were more effective than moxibustion for transferring heat effects into deep tissues.

Development of a cardiorespiratory monitoring system based on pressure change of aircushion.

Heartbeat and respiration are fundamental vital signs used for estimation of patient's status. In this study, we have proposed a simple method to monitor the heartbeat and respiration based on displacements of human body which occur due to periodic heartbeat and breathing.

Novel algorithm for the hemiplegic gait evaluation using a single 3-axis accelerometer.

This paper suggests the novel algorithm for the estimating gait parameters of the hemiplegic patients using a 3-axis accelerometer. The signal processing for algorithm consists of a bandpass filter and a least square acceleration filter. To evaluate the performance of the algorithm, the correlation coefficients of the stride and the step time between the 3-axis accelerometer and the Vicon motion analysis system are compared. In consequence, correlation coefficient ranged from 0.90 to 0.99 for patients and ranged from 0.92 to 0.99 for normal subjects. The results showed that the novel algorithm is very useful for estimating not only hemiplegic gait but also normal gait.

Adaptive noise canceling of electrocardiogram artifacts in single channel electroencephalogram.

A new method for estimating and eliminating electrocardiogram (ECG) artifacts from single channel scalp electroencephalogram (EEG) is proposed. The proposed method consists of emphasis of QRS complex from EEG using least squares acceleration (LSA) filter, generation of synchronized pulse with R-peak and ECG artifacts estimation and elimination using adaptive filter. The performance of the proposed method was evaluated using simulated and real EEG recordings, we found that the ECG artifacts were successfully estimated and eliminated in comparison with the conventional multi-channel techniques, which are independent component analysis (ICA) and ensemble average (EA) method. From this we can conclude that the proposed method is useful for the detecting and eliminating the ECG artifacts from single channel EEG and simple to use for ambulatory/portable EEG monitoring system.

Results of Curative Radiotherapy Alone in Patients with Uterine Cervical Carcinomas.

PURPOSE: To evaluate the role of curative radiotherapy alone in the treatment of uterine cervical carcinomas, by a retrospective analysis with respects to survival and pelvic control, and to find any risk factors of failure. MATERIALS AND METHODS: Between Jan. 1990 and Dec. 1995, a total of 187 patients, diagnosed with uterine cervical carcinomas in FIGO stages greater than IA, were treated by curative radiotherapy alone with no chemotherapy. The ages of the patients ranged from 26 to 80 years, with a median of 60 years. The number of patients diagnosed with squamous cell carcinomas were 183 (97.9%). The number of patients with FIGO stage IB1, IB2, IIA, IIB, IIIA, IIIB and IVA were 61 (32.6%), 7 (3.7%), 43 (23.0%), 62 (33.3%), 3 (1.6%), 7 (3.7%) and 4 (2.1%), respectively. External radiotherapy was performed with 6 MV or 10 MV X-rays, with a dose range of 19.8 Gy~ 50.4 Gy (median; 30.6), to whole pelvis. Intracavitary radiation (ICR) was then performed using a high-dose rate remote controlled afterloader with radioisotopes of Co-60 and Cs-137. The fraction size of the ICR was 5 Gy twice a week, and was delivered up to total doses of 10 Gy~ 55 Gy (median; 40). After the ICR, additional pelvic external radiotherapy with midline shielding width of 4 cm was performed with the dose range of 0~30.6 Gy (median; 19.8), and the resultant total doses of A points ranged between 49.8 Gy and 86.0 Gy (median; 70.6). RESULTS: The five-year overall survival rates of FIGO IB1, IB2, IIA, IIB, III and IVA were 88.3%, 83.3%, 86.1%, 65.2%, 60.0% and 50.0%, respectively (p=0.005). The pelvic control rates of each stage were 90.1%, 85.7%, 86.1%, 69.4%, 68.6% and 50.0%, respectively (p=0.03). From the multivariate analysis, the radiation response and tumor diameter were found to be significant factors affecting the overall survival. The significant factors influencing pelvic control were the radiation response and pre-treatment hemoglobin level. CONCLUSION: The radiation response and tumor diameter were significant factors affecting survival, so patients with tumor diameters greater than 4 cm should be considered for a combined modality, such as concurrent chemoradiotherapy.