Human-In-The-Loop Optimization of A Wearable Robot Using Foot Pressure Sensors

Background: Individuals with below-knee amputation (BKA) experience increased physical effort when walking, and the use of a robotic ankle-foot prosthesis (AFP) can reduce such effort. Our prior study on a robotic AFP showed that walking effort could be reduced if the robot is personalized to the wearer. The personalization is accomplished using human-in-the-loop (HIL) optimization, in which the cost function is based on a real-time physiological signal indicating physical effort. The conventional physiological measurement, however, requires a long estimation time, hampering real-time optimization due to the limited experimental time budget. In addition, the physiological sensor, based on respiration uses a mask with rigid elements that may be difficult for the wearer to use. Prior studies suggest that a symmetry measure using a less intrusive sensor, namely foot pressure, could serve as a metric of gait performance. This study hypothesized that a function of foot pressure, the symmetric foot force-time integral, could be used as a cost function to rapidly estimate the physical effort of walking; therefore, it can be used to personalize assistance provided by a robotic ankle in a HIL optimization scheme. Methods: We developed a new cost function derived from a well-known clinical measure, the symmetry index, by hypothesizing that foot force-time integral (FFTI) symmetry would be highly correlated with metabolic cost. We conducted experiments on human participants (N = 8) with simulated amputation to test the new cost function. The study consisted of a discrete trial day, an HIL optimization training day, and an HIL optimization data collection day. We used the discrete trial day to evaluate the correlation between metabolic cost and a cost function using symmetric FFTI percentage. During walking, we varied the prosthetic ankle stiffness while measuring foot pressure and metabolic rate. On the second and third days, HIL optimization was used to find the optimal stiffness parameter with the new cost function using symmetric FFTI percentage. Once the optimal stiffness parameter was found, we validated the performance with comparison to a weight-based stiffness and control-off conditions. We measured symmetric FFTI percentage during the stance phase, prosthesis push-off work, metabolic cost, and user comfort in each condition. We expected the optimized prosthetic ankle stiffness based on the newly developed cost function could reduce the energy expenditure during walking for the individuals with simulated amputation. Results: We found that the cost function using symmetric foot force-time integral percentage presents a reasonable correlation with measured metabolic cost (Pearson’s R > 0.62). When we employed the new cost function in HIL ankle-foot prosthesis parameter optimization, 8 individuals with simulated amputation reduced their cost of walking by 15.9% (p = 0.01) and 16.1% (p = 0.02) compared to the weight-based and control-off conditions, respectively. The symmetric FFTI percentage for the optimal condition tended to be closer to the ideal symmetry value (50%) compared to weight-based (p = 0.23) and control-off conditions (p = 0.04). Conclusion: This study suggests that foot force-time integral symmetry using foot pressure sensors can be used as a cost function when optimizing a wearable robot parameter.

Lower limb kinetic comparisons between the chasse step and one step footwork during stroke play in table tennis

Background Biomechanical footwork research during table tennis performance has been the subject of much interest players and exercise scientists. The purpose of this study was to investigate the lower limb kinetic characteristics of the chasse step and one step footwork during stroke play using traditional discrete analysis and one-dimensional statistical parameter mapping. Methods Twelve national level 1 table tennis players (Height: 172 ± 3.80 cm, Weight: 69 ± 6.22 kg, Age: 22 ± 1.66 years, Experience: 11 ± 1.71 year) from Ningbo University volunteered to participate in the study. The kinetic data of the dominant leg during the chasse step and one step backward phase (BP) and forward phase (FP) was recorded by instrumented insole systems and a force platform. Paired sample T tests were used to analyze maximum plantar force, peak pressure of each plantar region, the force time integral and the pressure time integral. For SPM analysis, the plantar force time series curves were marked as a 100% process. A paired-samples T-test in MATLAB was used to analyze differences in plantar force. Results One step produced a greater plantar force than the chasse step during 6.92–11.22% BP (P = 0.039). The chasse step produced a greater plantar force than one step during 53.47–99.01% BP (P < 0.001). During the FP, the chasse step showed a greater plantar force than the one step in 21.06–84.06% (P < 0.001). The one step produced a higher maximum plantar force in the BP (P = 0.032) and a lower maximum plantar force in the FP (P = 0) compared with the chasse step. The one step produced greater peak pressure in the medial rearfoot (P = 0) , lateral rearfoot (P = 0) and lateral forefoot (P = 0.042) regions than the chasse step during BP. In FP, the chasse step showed a greater peak pressure in the Toe (P = 0) than the one step. The one step had a lower force time integral (P = 0) and greater pressure time integral (P = 0) than the chasse step in BP, and the chasse step produced a greater force time integral (P = 0) and pressure time integral (P = 0.001) than the one step in the FP. Conclusion The findings indicate that athletes can enhance plantarflexion function resulting in greater weight transfer, facilitating a greater momentum during the 21.06–84.06% of FP. This is in addition to reducing the load on the dominant leg during landing by utilizing a buffering strategy. Further to this, consideration is needed to enhance the cushioning capacity of the sole heel and the stiffness of the toe area.

Skeletal Muscle Specific Calpastatin Overexpression Mitigates Muscle Weakness in Aging and Extends Lifespan

Calpain activation has been postulated as a potential contributor to the loss of muscle mass and function associated with both aging and disease but limitations of previous experimental approaches have failed to completely examine this issue. We hypothesized that mice overexpressing calpastatin, an endogenous inhibitor of calpain (CalpOX), solely in skeletal muscle would show an amelioration of the aging muscle phenotype. We assessed 4 groups of mice (age in months): (1) young wild type (5.71±0.43) (WT); (2) young CalpOX (5.6±0.5); (3) old WT (25.81±0.56); and (4) old CalpOX (25.91±0.60) for diaphragm and limb muscle (extensor digitorum longus, EDL) force frequency relations. Aging significantly reduced diaphragm and EDL peak force in old WT mice, and decreased the force-time integral during a fatiguing protocol by 48% and 23% in aged WT diaphragm and EDL, respectively. In contrast, we found that CalpOX mice had significantly increased diaphragm and EDL peak force in old mice, similar to that observed in young mice. The impact of aging on the force-time integral during a fatiguing protocol was abolished in the diaphragm and EDL of old CalpOX animals. Surprisingly, we found that CalpOX had a significant impact on longevity, increasing median survival from 20.55 months in WT mice to 24 months in CalpOX mice (p = 0.0006).

Foot Posture and Plantar Loading With Ankle Bracing

Context Arch height is one important aspect of foot posture. An estimated 20% of the population has pes planus and 20% has pes cavus. These abnormal foot postures can alter lower extremity kinematics and plantar loading and contribute to injury risk. Ankle bracing is commonly used in sport to prevent these injuries, but no researchers have examined the effects of ankle bracing on plantar loading. Objective To evaluate the effects of ankle braces on plantar loading during athletic tasks. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants A total of 36 participants (11 men, 25 women; age = 23.1 ± 2.5 years, height = 1.72 ± 0.09 m, mass = 66.3 ± 14.7 kg) were recruited for this study. Intervention(s) Participants completed walking, running, and cutting tasks in 3 bracing conditions: no brace, lace-up ankle-support brace, and semirigid brace. Main Outcome Measure(s) We analyzed the plantar-loading variables of contact area, maximum force, and force-time integral for 2 midfoot and 3 forefoot regions and assessed the displacement of the center of pressure. A 3 × 3 mixed-model repeated-measures analysis of variance was used to determine the effects of brace and foot type (α = .05). Results Foot type affected force measures in the middle (P range = .003–.047) and the medial side of the foot (P range = .004–.04) in all tasks. Brace type affected contact area in the medial midfoot during walking (P = .005) and cutting (P = .01) tasks, maximum force in the medial and lateral midfoot during all tasks (P &lt; .001), and force-time integral in the medial midfoot during all tasks (P &lt; .001). Portions of the center-of-pressure displacement were affected by brace wear in both the medial-lateral and anterior-posterior directions (P range = .001–.049). Conclusions Ankle braces can be worn to redistribute plantar loading. Additional research should be done to evaluate their effectiveness in injury prevention.

666Impact of local left atrial wall thickness on the incidence of acute pulmonary vein reconnection after ablation index-guided ablation

Background/Introduction Pulmonary vein reconnection is considered a major determinant of atrial fibrillation (AF) recurrence after pulmonary vein isolation (PVI). Ablation Index (AI)-guided ablation allows for the creation of ablation lesions of consistent depth and may reduce the incidence of pulmonary vein reconnection after PVI. However, anatomical and imaging studies have demonstrated an important inter- and intra-patient variability of left atrial wall thickness, which can result in non-transmural ablation lesion formation in thicker segments. Purpose The present study aimed to investigate the impact of local left atrial wall thickness on the incidence of acute pulmonary vein reconnection after AI-guided AF ablation. Methods Consecutive AF patients who underwent cardiac computed tomography (CT) imaging prior to AI-guided ablation between December 2017 and September 2019 were studied. AI targets were 500 for anterior/roof and 380 for posterior/inferior segments with a maximum interlesion distance of 6 mm. Occurrence of acute pulmonary vein reconnection after initial PVI was assessed after a 30-minute waiting period. Ablation procedures were analysed offline to determine minimum AI, force-time integral, contact force, ablation duration, power, impedance drop and maximum interlesion distance for each segment according to a 16-segment model. Pulmonary vein antrum wall thickness was assessed for each segment on reconstructed CT images based on patient-specific thresholds in Hounsfield Units, using a previously described method. Results Seventy patients (63% paroxysmal AF, 67% male, mean age 63 ± 8 years) who underwent preprocedural CT imaging and AI-guided AF ablation were studied. Acute reconnection (AR) occurred in 27/1152 segments (2%, 15 anterior/roof, 12 posterior/inferior) in 17/70 (24%) patients. Anterior/roof segments were thicker than posterior/inferior segments (1.48 [1.23-1.80] vs. 1.13 [1.00-1.30] mm; p &lt; 0.01). Reconnected segments were characterised by a greater local atrial wall thickness, both in anterior/roof (1.83 [1.60-2.00] vs. 1.47 [1.20-1.80] mm; p &lt; 0.01) and posterior/inferior (1.38 [1.25-1.50] vs. 1.13 [1.00-1.27] mm; p &lt; 0.01) segments (Figure 1). Minimum AI, force-time integral, contact force, ablation duration, power, impedance drop and maximum interlesion distance were not associated with acute pulmonary vein reconnection. Conclusion Local atrial wall thickness is associated with acute pulmonary vein reconnection after AI-guided PVI. Individualised AI targets based on local wall thickness may be of use to create transmural ablation lesions and prevent pulmonary vein reconnection after PVI. Abstract Figure. Impact of wall thickness on reconnection

Benefit of Contact Force–Guided Catheter Ablation for Treating Premature Ventricular Contractions

We evaluated whether an irrigated contact force–sensing catheter would improve the safety and effectiveness of radiofrequency ablation of premature ventricular contractions originating from the right ventricular outflow tract. We retrospectively reviewed the charts of patients with symptomatic premature ventricular contractions who underwent ablation with a contact force–sensing catheter (56 patients, SmartTouch) or conventional catheter (59 patients, ThermoCool) at our hospital from August 2013 through December 2015. During a mean follow-up of 16 ± 5 months, 3 patients in the conventional group had recurrences, compared with none in the contact force group. Complications occurred only in the conventional group (one steam pop; 2 ablations suspended because of significantly increasing impedance). In the contact force group, the median contact force during ablation was 10 g (interquartile range, 7–14 g). Times for overall procedure (36.9 ± 5 min), fluoroscopy (86.3 ± 22.7 s), and ablation (60.3 ± 21.4 s) were significantly shorter in the contact force group than in the conventional group (46.2 ± 6.2 min, 107.7 ± 30 s, and 88.7 ± 32.3 s, respectively; P &lt;0.001). In the contact force group, cases with a force-time integral &lt;560 gram-seconds (g-s) had significantly longer procedure and fluoroscopy times (both P &lt;0.001) than did those with a force-time integral ≥560 g-s. These findings suggest that ablation of premature ventricular contractions originating from the right ventricular outflow tract with an irrigated contact force–sensing catheter instead of a conventional catheter shortens overall procedure, fluoroscopy, and ablation times without increasing risk of recurrence or complications.

Abstract 17376: Risk of Early Reablation Post Cryoballoon Ablation

Introduction: Post-ablation radiofrequency tissue friability has been described; however, tissue friability post cryoablation has not been well studied. We report a case of left atrial perforation with normal contact force radiofrequency ablation 22 days after initial cryoballoon ablation. Description: A 59-year-old male with persistent atrial fibrillation, severe biatrial enlargement, non-ischemic cardiomyopathy (EF of 20%), underwent initial cryoballoon pulmonary vein isolation with left atrial roof cryoablation with restoration of sinus rhythm and no complications. Patient presented 22 days later with sustained atrial flutter and heart rate over 130 bpm refractory to aggressive medical management, cardioversion, and acute on chronic congestive heart failure. Early re-ablation was performed with electrophysiology study and 3D activation map confirming ectopic atrial tachycardia foci arising from left atrial roof, anterior to the border of previously cryo-ablated region. St. Jude TactiCath™ contact force ablation catheter, was used to ablate this foci, and termination within 5 seconds of ablation was observed. Using the Force-Time Integral index to guide further ablation, the surrounding area was ablated for an additional 20 seconds at 30 W with a maximum recorded contact force throughout the procedure of 35 grams, and an average of 10-15 grams.A decrease in systolic blood pressure from 120 mmHg to 80 mmHg was noted, and intracardiac ultrasound confirmed 1.5 cm of pericardial effusion. Successful pericardiocentesis and reversal of anticoagulation was performed with ongoing bleeding, and eventual surgical intervention was required. On direct visualization during surgery, the left atrial roof perforation was confirmed, and was noted to be very friable and difficult to retain suture for repair. Patient did well post-operatively and was discharged with no recurrence of arrhythmias. Conclusions: Despite standard of care monitoring, including force-time integral index and contact-sensing catheters, atrial perforation occurred likely due to increased tissue friability post initial cryoablation. The optimal timing for repeat ablation is not completely understood, and extreme caution and avoidance of early re-ablation risk is prudent.