Learning to walk with an adaptive gain proportional myoelectric controller for a robotic ankle exoskeleton

Abstract Background Robotic ankle exoskeletons can provide assistance to users and reduce metabolic power during walking. Our research group has investigated the use of proportional myoelectric control for controlling robotic ankle exoskeletons. Previously, these controllers have relied on a constant gain to map user’s muscle activity to actuation control signals. A constant gain may act as a constraint on the user, so we designed a controller that dynamically adapts the gain to the user’s myoelectric amplitude. We hypothesized that an adaptive gain proportional myoelectric controller would reduce metabolic energy expenditure compared to walking with the ankle exoskeleton unpowered because users could choose their preferred control gain. Methods We tested eight healthy subjects walking with the adaptive gain proportional myoelectric controller with bilateral ankle exoskeletons. The adaptive gain was updated each stride such that on average the user’s peak muscle activity was mapped to maximal power output of the exoskeleton. All subjects participated in three identical training sessions where they walked on a treadmill for 50 minutes (30 minutes of which the exoskeleton was powered) at 1.2 ms-1. We calculated and analyzed metabolic energy consumption, muscle recruitment, inverse kinematics, inverse dynamics, and exoskeleton mechanics. Results Using our controller, subjects achieved a metabolic reduction similar to that seen in previous work in about a third of the training time. The resulting controller gain was lower than that seen in previous work (β=1.50±0.14 versus a constant β=2). The adapted gain allowed users more total ankle joint power than that of unassisted walking, increasing ankle power in exchange for a decrease in hip power. Conclusions Our findings indicate that humans prefer to walk with greater ankle mechanical power output than their unassisted gait when provided with an ankle exoskeleton using an adaptive controller. This suggests that robotic assistance from an exoskeleton can allow humans to adopt gait patterns different from their normal choices for locomotion. In our specific experiment, subjects increased ankle power and decreased hip power to walk with a reduction in metabolic cost. Future exoskeleton devices that rely on proportional myolectric control are likely to demonstrate improved performance by including an adaptive gain.http://deepblue.lib.umich.edu/bitstream/2027.42/115879/1/12984_2015_Article_86.pd

Contemporary outcomes of complete atrioventricular septal defect repair: Analysis of the Society of Thoracic Surgeons Congenital Heart Surgery Database

ObjectiveContemporary outcomes data for complete atrioventricular septal defect (CAVSD) repair are limited. We sought to describe early outcomes of CAVSD repair across a large multicenter cohort, and explore potential associations with patient characteristics, including age, weight, and genetic syndromes.MethodsPatients in the Society of Thoracic Surgeons Congenital Heart Surgery Database having repair of CAVSD (2008-2011) were included. Preoperative, operative, and outcomes data were described. Univariate associations between patient factors and outcomes were described.ResultsOf 2399 patients (101 centers), 78.4% had Down syndrome. Median age at surgery was 4.6 months (interquartile range, 3.5-6.1 months), with 11.8% (n = 284) aged ≤2.5 months. Median weight at surgery was 5.0 kg (interquartile range, 4.3-5.8 kg) with 6.3% (n = 151) < 3.5 kg. Pulmonary artery band removal at CAVSD repair was performed in 122 patients (4.6%). Major complications occurred in 9.8%, including permanent pacemaker implantation in 2.7%. Median postoperative length of stay (PLOS) was 8 days (interquartile range, 5-14 days). Overall hospital mortality was 3.0%. Weight < 3.5 kg and age ≤ 2.5 months were associated with higher mortality, longer PLOS, and increased frequency of major complications. Patients with Down syndrome had lower rates of mortality and morbidities than other patients; PLOS was similar.ConclusionsIn a contemporary multicenter cohort, most patients with CAVSD have repair early in the first year of life. Prior pulmonary artery band is rare. Hospital mortality is generally low, although patients at extremes of low weight and younger age have worse outcomes. Mortality and major complication rates are lower in patients with Down syndrome

Aortic valve replacement in neonates and infants: An analysis of the Society of Thoracic Surgeons Congenital Heart Surgery Database

ObjectiveWe sought to describe early outcomes of aortic valve replacement in neonates and infants across a large multicenter cohort.MethodsNeonates and infants in the Society of Thoracic Surgeons Congenital Heart Surgery Database undergoing nontruncal aortic valve replacement with the Ross-Konno procedure, Ross procedure, or homograft replacement from 2000 to 2009 were included. Preoperative characteristics, operative data, and early outcomes are described.ResultsA total of 160 patients (43 neonates, 117 infants) from 47 centers were included. Society of Thoracic Surgeons–defined preoperative risk factors were present in 76 patients (48%) and were most prevalent in neonates (67%) and patients undergoing homograft aortic valve replacement (93%). Concomitant arch repair or mitral valve surgery was performed in 30 patients (19%) and 19 patients (12%), respectively. Postoperative mechanical circulatory support was used in 17 patients (11%). Overall in-hospital mortality was 18% and was highest for neonates (28%) and patients undergoing homograft aortic valve replacement (40%). Concomitant arch repair was associated with higher in-hospital mortality (33% vs 15%, P = .02), whereas concurrent mitral valve surgery was not (21% vs 18%, P = .73). Postoperative mechanical circulatory support was also associated with increased in-hospital mortality (65% vs 13%, P < .0001).ConclusionsNeonates and infants undergoing aortic valve replacement are a high-risk group, with hospital mortality comparable with some of the highest risk procedures in this age group. The requirement for arch repair or postoperative mechanical circulatory support was associated with an increased risk of death in this cohort

Motor modules during adaptation to walking in a powered ankle exoskeleton

Abstract Background Modules of muscle recruitment can be extracted from electromyography (EMG) during motions, such as walking, running, and swimming, to identify key features of muscle coordination. These features may provide insight into gait adaptation as a result of powered assistance. The aim of this study was to investigate the changes (module size, module timing and weighting patterns) of surface EMG data during assisted and unassisted walking in an powered, myoelectric, ankle-foot orthosis (ankle exoskeleton). Methods Eight healthy subjects wore bilateral ankle exoskeletons and walked at 1.2 m/s on a treadmill. In three training sessions, subjects walked for 40 min in two conditions: unpowered (10 min) and powered (30 min). During each session, we extracted modules of muscle recruitment via nonnegative matrix factorization (NNMF) from the surface EMG signals of ten muscles in the lower limb. We evaluated reconstruction quality for each muscle individually using R2 and normalized root mean squared error (NRMSE). We hypothesized that the number of modules needed to reconstruct muscle data would be the same between conditions and that there would be greater similarity in module timings than weightings. Results Across subjects, we found that six modules were sufficient to reconstruct the muscle data for both conditions, suggesting that the number of modules was preserved. The similarity of module timings and weightings between conditions was greater then random chance, indicating that muscle coordination was also preserved. Motor adaptation during walking in the exoskeleton was dominated by changes in the module timings rather than module weightings. The segment number and the session number were significant fixed effects in a linear mixed-effect model for the increase in R2 with time. Conclusions Our results show that subjects walking in a exoskeleton preserved the number of modules and the coordination of muscles within the modules across conditions. Training (motor adaptation within the session and motor skill consolidation across sessions) led to improved consistency of the muscle patterns. Subjects adapted primarily by changing the timing of their muscle patterns rather than the weightings of muscles in the modules. The results of this study give new insight into strategies for muscle recruitment during adaptation to a powered ankle exoskeleton.https://deepblue.lib.umich.edu/bitstream/2027.42/140718/1/12984_2017_Article_343.pd

Pediatric Cardiac Surgical Patterns of Practice and Outcomes in Europe and China:An Analysis of the European Congenital Heart Surgeons Association Congenital Heart Surgery Database

Background: The European Congenital Heart Surgeons Association (ECHSA) Congenital Heart Surgery Database (CHSD) was founded in 1999 and is open for worldwide participation. The current dataset includes a large amount of surgical data from both Europe and China. Thepurposeofthisanalysisistocomparepatternsof practice and outcomes among pediatric congenital heart defect surgeries in Europe and China using the ECHSA-CHSD. Methods: We examined all European (125 centers, 58,261 operations) and Chinese (13 centers, 23,920 operations) data in the ECHSA-CHSD from 2006-2018. Operative mortality, postoperative length of stay, median patient age and weight were calculated for the ten benchmark operations for China and Europe, respectively. Results: Benchmark procedure distribution frequencies differed between Europe and China. In China, ventricular septal defect repair comprised approximately 70% of procedures, while Norwood operations comprised less than one percent of all procedures. Neonatal cardiac procedures were rare in China overall. For procedures in STAT mortality category 1, Chinese centers had lower operative mortality rates, while procedures in categories 3 and 5 mortality is lower in European centers. Operative mortality over the time period decreased from 3.89% to 1.64% for the whole cohort, with a sharper decline in China. This drop coincides with an increase of submitted procedures over this 13-year-period. Conclusion: Chinese centers had higher program-matic volume of congenital heart surgeries, while European centers have a more complex case mix. Palliation for patients with functionally univentricular heart was performed less commonly in China. These comparison of patterns of practice and outcomes demonstrate opportunities for continuing bidirectional transcontinental collaboration and quality improvement

Oral Contraceptive Pills Are Not a Risk Factor for Deep Vein Thrombosis or Pulmonary Embolism After Arthroscopic Shoulder Surgery

Background: Worldwide, more than 100 million women between the ages of 15 and 49 years take oral contraceptive pills (OCPs). OCP use increases the risk of venous thromboembolism (VTE) through its primary drug, ethinylestradiol, which slows liver metabolism, promotes tissue retention, and ultimately favors fibrinolysis inhibition and thrombosis. Purpose: To evaluate the effects of OCP use on VTE after arthroscopic shoulder surgery. Study Design: Cohort study; Level of evidence, 3. Methods: A large national payer database (PearlDiver) was queried for patients undergoing arthroscopic shoulder surgery. The incidence of VTE was evaluated in female patients taking OCPs and those not taking OCPs. A matched group was subsequently created to evaluate the incidence of VTE in similar patients with and without OCP use. Results: A total of 57,727 patients underwent arthroscopic shoulder surgery from 2007 to 2016, and 26,365 patients (45.7%) were female. At the time of surgery, 924 female patients (3.5%) were taking OCPs. The incidence of vascular thrombosis was 0.57% (n = 328) after arthroscopic shoulder surgery, and there was no significant difference in the rate of vascular thrombosis in male or female patients (0.57% vs 0.57%, respectively; P \u3e .99). The incidence of VTE in female patients taking and not taking OCPs was 0.22% and 0.57%, respectively (P = .2). In a matched-group analysis, no significant difference existed in VTE incidence between patients with versus without OCP use (0.22% vs 0.56%, respectively; P = .2). On multivariate analysis, hypertension (odds ratio [OR], 2.00; P \u3c .001) and obesity (OR, 1.43; P = .002) were risk factors for VTE. Conclusion: OCP use at the time of arthroscopic shoulder surgery is not associated with an increased risk of VTE. Obesity and hypertension are associated with a greater risk for thrombolic events, although the risk remains very low. Our findings suggest that patients taking OCPs should be managed according to the surgeon’s standard prophylaxis protocol for arthroscopic shoulder surgery

Pediatric Cardiac Surgical Patterns of Practice and Outcomes in Japan and Europe

Objectives: The Japan Cardiovascular Surgery Database-Congenital section (JCVSD-Congenital) and the European Congenital Heart Surgeons Association (ECHSA) Congenital Heart Surgery Database (CHSD) share the same nomenclature. We aimed at comparing congenital cardiac surgical patterns of practice and outcomes in Japan and Europe using the JCVSD-Congenital and ECHSA-CHSD. Methods and Results: We examined Japanese (120 units, 63,365 operations) and European (96 units, 90,098 operations) data in JCVSD-Congenital and ECHSA-CHSD from 2011 to 2017. Patients' age and weight, periprocedural times, mortality at hospital discharge, and postoperative length of stay were calculated for ten benchmark operations. There was a significantly higher proportion of ventricular septal defect closures and Glenn operations and a significantly lower proportion of coarctation repairs, tetralogy of Fallot repairs, atrioventricular septal defect repairs, arterial switch operations, truncus repairs, Norwood operations, and Fontan operations in JCVSD-Congenital compared to ECHSA-CHSD. Postoperative length of stay was significantly longer following all benchmark operations in JCVSD-Congenital compared to ECHSA-CHSD. Mean STAT mortality score (Society of Thoracic Surgeons European Association for Cardio-Thoracic Surgery mortality score) was significantly higher in JCVSD-Congenital (0.78) compared to ECHSA-CHSD (0.71). Mortality at hospital discharge was significantly lower in JCVSD-Congenital (4.2%) compared to ECHSA-CHSD (6.0%, P < .001). Conclusions: The distribution of the benchmark procedures and age at the time of surgery differ between Japan and Europe. Postoperative length of stay is longer, and the mean complexity is higher in Japan compared to European data. These comparisons of patterns of practice and outcomes demonstrate opportunities for continuing bidirectional transcontinental collaboration and quality improvement

Case complexity scores in congenital heart surgery: A comparative study of the Aristotle Basic Complexity score and the Risk Adjustment in Congenital Heart Surgery (RACHS-1) system

ObjectiveThe Aristotle Basic Complexity score and the Risk Adjustment in Congenital Heart Surgery system were developed by consensus to compare outcomes of congenital cardiac surgery. We compared the predictive value of the 2 systems.MethodsOf all index congenital cardiac operations at our institution from 1982 to 2004 (n = 13,675), we were able to assign an Aristotle Basic Complexity score, a Risk Adjustment in Congenital Heart Surgery score, and both scores to 13,138 (96%), 11,533 (84%), and 11,438 (84%) operations, respectively. Models of in-hospital mortality and length of stay were generated for Aristotle Basic Complexity and Risk Adjustment in Congenital Heart Surgery using an identical data set in which both Aristotle Basic Complexity and Risk Adjustment in Congenital Heart Surgery scores were assigned. The likelihood ratio test for nested models and paired concordance statistics were used.ResultsAfter adjustment for year of operation, the odds ratios for Aristotle Basic Complexity score 3 versus 6, 9 versus 6, 12 versus 6, and 15 versus 6 were 0.29, 2.22, 7.62, and 26.54 (P < .0001). Similarly, odds ratios for Risk Adjustment in Congenital Heart Surgery categories 1 versus 2, 3 versus 2, 4 versus 2, and 5/6 versus 2 were 0.23, 1.98, 5.80, and 20.71 (P < .0001). Risk Adjustment in Congenital Heart Surgery added significant predictive value over Aristotle Basic Complexity (likelihood ratio χ2 = 162, P < .0001), whereas Aristotle Basic Complexity contributed much less predictive value over Risk Adjustment in Congenital Heart Surgery (likelihood ratio χ2 = 13.4, P = .009). Neither system fully adjusted for the child’s age. The Risk Adjustment in Congenital Heart Surgery scores were more concordant with length of stay compared with Aristotle Basic Complexity scores (P < .0001).ConclusionsThe predictive value of Risk Adjustment in Congenital Heart Surgery is higher than that of Aristotle Basic Complexity. The use of Aristotle Basic Complexity or Risk Adjustment in Congenital Heart Surgery as risk stratification and trending tools to monitor outcomes over time and to guide risk-adjusted comparisons may be valuable

Databases for Congenital Heart Defect Public Health Studies Across the Lifespan

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139106/1/jah31841_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139106/2/jah31841.pd