Inpatient Gastroenterology Consults Have Little Utility Before Transesophageal Echocardiograms in a Prospective Cohort Study.

INTRODUCTION: Despite the well-documented safety of transesophageal echocardiograms (TEEs), inpatient gastroenterology (GI) services are called to clear patients for the procedure when they have GI symptoms or comorbidities ranging from mild to clinically significant. We aimed to assess the clinical utility of such consults in preventing TEE complications. METHODS: We performed a prospective cohort study of all inpatients at our institution who had a TEE ordered from 7/1/2021 through 7/1/2022. Patients' demographic information, indications for TEE, complications from TEE, 30-day readmission rates, GI team recommendations, and results of any GI-related interventions were collected and analyzed. RESULTS: There were 732 patients who had a TEE ordered during our study period, of whom 641 (87.51%) underwent the procedure. Of the 91 (12.49%) who did not have a TEE, none were canceled due to a GI-related concern. There were 23 of 641 patients (3.59%) with complications from the TEE, none of which were GI-related. The GI team was consulted on 36 patients (4.96% of TEEs ordered) and cleared 22 of 36 (61.11%) with no further testing while the remaining 14 of 36 patients (38.89%) underwent workups that were largely normal. Patients who had a GI consult before their TEE had a significantly longer time between their TEE being ordered and the TEE being performed compared with those who did not have a GI consult before their TEE (4.50 days vs 0.77 days, P < 0.01). DISCUSSION: Inpatient GI team workups to clear patients for a TEE found no contraindications to TEEs, did not change patient care plans, and led to increased hospital costs and lengths of stay.

Transition-of-care program from emergency department to gastroenterology clinics improves follow-up.

OBJECTIVES: Patients discharged from the emergency department (ED) with gastrointestinal (GI) symptoms need to appropriately transition their care to a GI outpatient clinic in a timely manner to have their health needs met and avoid significant morbidity. When this transition isn't optimal, patients are lost to follow-up, potentially placing them at risk for adverse events. We sought to study the effectiveness of implementing an electronic medical record (EMR) based transition-of-care (TOC) program from the ED to outpatient GI clinics. METHODS: We performed a retrospective single center cohort study of patients discharged from the ED of a tertiary care academic medical center referred to outpatient GI clinic before (Pre-TOC patients) and after implementation of an EMR based TOC program (TOC patients). We further stratified patients based on the Distressed Communities Index (DCI), which is a composite measure of economic well-being. We compared rates of appointment scheduling and appointment attendance between the two groups, as well as 30-day readmission rates to the ED. We also performed a subgroup analysis to determine if socioeconomic status would affect patient follow-up rates. RESULTS: We included 380 Pre-TOC and 399 TOC patients in our analysis. TOC patients were found to both schedule appointments (50% vs 27% p-value <0.01) as well as show up to appointments (34% vs 24% p-value <0.01) at significantly higher rates compared to Pre-TOC patients. There was no significant difference between 30-day readmission rates between the two groups. In addition, TOC patients from At-Risk and Distressed Communities were over 22 times more likely to schedule an appointment compared to Pre-TOC patients from similar neighborhoods (OR 22.18, 95% CI 4.23-116.32). CONCLUSION: Our study shows that patients who are discharged from the ED with outpatient GI follow-up are more likely to both schedule and show up to appointments with implementation of an EMR-based direct referral program compared to no patient navigation, particularly among patients of lower socioeconomic status.

Younger Patients Do Not Develop More Advanced Polyps on Surveillance Colonoscopy Than Their Index Colonoscopy When Compared With Older Patients.

BACKGROUND AND GOALS: Colonic polyp surveillance guidelines are based on data from patients 50 and above. Given the recent lowering for colorectal cancer (CRC) screening to age 45, the aim of this study was to assess whether existing colonic polyp surveillance guidelines are appropriate to use in younger patients. MATERIALS AND METHODS: We performed a retrospective cohort study of patients who underwent 2 colonoscopies within a 10-year period. Five Risk Stratification Groups (RSG) were developed based on surveillance colonoscopy interval times recommended by the US Multi-Society Task Force (USMSTF) on CRC, and changes in RSG from index to surveillance colonoscopy were compared between 3 age cohorts-those below 45, those 45 to 49, and those 50 and above. Further analysis was performed for patients whose RSG worsened from index to surveillance colonoscopy, as this was defined as an inappropriate surveillance interval. RESULTS: A total of 1895 patients were included in the final analysis. A multivariate regression model showed that a worsened RSG was not significantly associated with age group, both when comparing below 45 to those 50 and above [odds ratio (OR)=0.840, 95% confidence interval (CI): 0.504-1.399, P=0.50] and when comparing those 45 to 49 to those 50 and above (OR=1.416, 95% CI: 0.905-2.216, P=0.13). Only being female was found to be statistically associated with worsened RSG after controlling for other variables (OR=0.652, 95% CI: 0.486-0.875, P<0.01). CONCLUSIONS: Our study found that younger cohorts of patients, both below 45 and those 45 to 49, are not statistically more likely to develop more advanced polyps necessitating a shorter time to surveillance colonoscopy compared with patients 50 years and above. This finding supports using existing colonic polyp surveillance colonoscopy guidelines that were developed for patients 50 years and above in both patients below 45 and those 45 to 49 years old.

Endoscopic Evaluation of Radiologic Distal Esophageal Thickening.

GOALS: We aim to determine the incidence of esophagogastroduodenoscopies (EGDs) primarily performed for imaging findings of distal esophageal thickening (DET). We also aim to determine if patients with imaging findings of DET have a higher incidence of cancer, and to evaluate the risk factors associated with findings of malignancy. BACKGROUND: The growth of diagnostic imaging has led to an increase in incidental findings of DET. This nonspecific finding frequently prompts an EGD for evaluation-many of which demonstrate benign conditions. There may be a misuse of valuable resources. STUDY: We performed a retrospective chart review of 1080 EGDs from January 2016 to July 2018 at the Veterans Affairs Medical Center, comparing EGDs for the indication of imaging report of DET with EGDs for other indications. Patient demographics, clinical history, imaging, procedure, and pathology reports were collected. Descriptive analysis and biostatistical analysis with χ2, Fisher exact, Wilcoxon rank sum, and Kruskal-Wallis tests were utilized in analyzing the data. RESULTS: Of the 1080 total endoscopies, 8.2% (n=88) were done specifically because of the imaging findings of DET. Those who had EGDs performed because of DET had a higher percentage of abnormal esophageal findings and of cancer. A history of Barrett's esophagus, tobacco use, and having gastrointestinal symptoms were not significant predictors of abnormal findings or of cancer for EGDs done for DET. CONCLUSIONS: There may be a role for EGDs performed for radiologic findings of DET. Even those without risk factors for malignancy should have EGDs performed for DET. Radiologists should consider reporting the DET size in order to determine if significant endoscopic findings correlate with wall thickness.

Neuro-mechanical aspects of playing-related mobility disorders in orchestra violinists and upper strings players: a review.

Orchestra musicians are at high risk of neuro-mechanical disorders due to the intense stresses their body withstand, leading to pain and injury. This review presents a comprehensive account of the works on the circumstances and types of playing related mobility disorders of upper strings players, as well as on the relevant neuro-mechanical factors and perspectives to those disorders. The following aspects are considered: asymmetry and imbalance in the musculo-skeletal system, muscle-bone-joint interactions, repetitive overloading and fatigue. An additional factor relates to neuro-muscular redundancy in the motor system, whereby more muscles and tendons than strictly necessary are engaged in performing a motor task, thus making the system indeterminate, with no unique solution. This same task can be performed with different muscle combinations. It is thus of interest to verify whether playing disorders may be alleviated by considering alternative techniques of performance.

Fibrinogen-Based Hydrogel Modulus and Ligand Density Effects on Cell Morphogenesis in Two-Dimensional and Three-Dimensional Cell Cultures.

There is a need to further explore the convergence of mechanobiology and dimensionality with systematic investigations of cellular response to matrix mechanics in 2D and 3D cultures. Here, a semisynthetic hydrogel capable of supporting both 2D and 3D cell culture is applied to investigate cell response to matrix modulus and ligand density. The culture materials are fabricated from adducts of polyethylene glycol (PEG) or PluronicF127 and fibrinogen fragments, formed into hydrogels by free-radical polymerization, and characterized by shear rheology. Control over the modulus of the materials is accomplished by changing the concentration of synthetic PEG-diacrylate crosslinker (0.5% w/v), and by altering the molecular length of the PEG (10 and 20 kDa). Control over ligand density is accomplished by changing fibrinogen concentrations from 3 to 12 mg mL-1 . In 2D culture, cell motility parameters, including cell speed and persistence time are significantly increased with increasing modulus. In both 2D and 3D culture, cells express vinculin and there is evidence of focal adhesion formation in the high stiffness materials. The modulus- and ligand-dependent morphogenesis response from the cells in 2D culture is contradictory to the same measured response in 3D culture. In 2D culture, anchorage-dependent cells become more elongated and significantly increase their size with increasing ligand density and matrix modulus. In 3D culture, the same anchorage-dependent cells become less spindled and significantly reduce their size in response to increasing ligand density and matrix modulus. These differences arise from dimensionality constraints, most notably the encapsulation of cells in a non-porous hydrogel matrix. These insights underscore the importance of mechanical properties in regulating cell morphogenesis in a 3D culture milieu. The versatility of the hydrogel culture environment further highlights the significance of a modular approach when developing materials that aim to optimize the cell culture environment.

Red white and blue - bright light effects in a diurnal rodent model for seasonal affective disorder.

Despite the common use of bright light exposure for treatment of seasonal affective disorder (SAD), the underlying biology of the therapeutic effect is not clear. Moreover, there is a debate regarding the most efficacious wavelength of light for treatment. Whereas according to the traditional approach full-spectrum light is used, recent studies suggest that the critical wavelengths are within the range of blue light (460 and 484 nm). Our previous work shows that when diurnal rodents are maintained under short photoperiod they develop depression- and anxiety-like behavioral phenotype that is ameliorated by treatment with wide-spectrum bright light exposure (2500 lux at the cage, 5000 K). Our current study compares the effect of bright wide-spectrum (3,000 lux, wavelength 420- 780 nm, 5487 K), blue (1,300 lux, wavelength 420-530 nm) and red light (1,300 lux, wavelength range 600-780 nm) exposure in the fat sand rat (Psammomys Obesus) model of SAD. We report results of experiments with six groups of sand rats that were kept under various photoperiods and light treatments, and subjected to behavioral tests related to emotions: forced swim test, elevated plus maze and social interactions. Exposure to either intense wide-spectrum white light or to blue light equally ameliorated depression-like behavior whereas red light had no effect. Bright wide-spectrum white light treatment had no effect on animals maintained under neutral photoperiod, meaning that light exposure was only effective in the pathological-like state. The resemblance between the effects of bright white light and blue light suggests that intrinsically photosensitive retinal ganglion cells (ipRGCs) are involved in the underlying biology of SAD and light therapy.

Diabetes Mellitus and Age are Risk Factors of Interval Colon Cancer: A Case-Control Study.

BACKGROUND AND AIMS: Interval colorectal cancer (CRC) is largely related to a poor endoscopic performance or different biology in the development of the polyp. However, patient-related factors were less investigated for their association with interval cancer. We thus evaluated tumor and patient characteristics as predictors of interval cancer in a population from Israel. METHODS: In this retrospective study, patients that were diagnosed with colon cancer in our institution and had 2 colonoscopies were included. Demographic parameters and tumor characteristics were compared between 84 cases with interval cancer, occurring 1-10 years after a negative colonoscopy, and 983 patients with primary CRC. In addition, patient-related features, including diabetes and diverticulosis, were compared between 51 patients with interval cancer after negative colonoscopy and 255 controls with no cancer and a previous negative colonoscopy. RESULTS: Compared to "positive" controls with primary cancer, patients with interval cancer were older (age 71.3 vs. 67.6, p = 0.003), had proximal tumor location (57 vs. 34%, p < 0.001) and non-advanced (0-2) tumor staging (78.5 vs. 64.8%, p = 0.014). Compared with -"negative" healthy controls, cases with interval cancer had only higher prevalence of diabetes (31 vs. 15%, p = 0.002). No significant differences were seen between patients with interval cancer occurring < 3 years and after 3-10 years. CONCLUSIONS: Patients with Interval cancer tend to be older and have diabetes. These patient groups should be more carefully or more frequently screened for pre-malignant lesions.

Mechanical Impedance and Its Relations to Motor Control, Limb Dynamics, and Motion Biomechanics.

The concept of mechanical impedance represents the interactive relationship between deformation kinematics and the resulting dynamics in human joints or limbs. A major component of impedance, stiffness, is defined as the ratio between the force change to the displacement change and is strongly related to muscle activation. The set of impedance components, including effective mass, inertia, damping, and stiffness, is important in determining the performance of the many tasks assigned to the limbs and in counteracting undesired effects of applied loads and disturbances. Specifically for the upper limb, impedance enables controlling manual tasks and reaching motions. In the lower limb, impedance is responsible for the transmission and attenuation of impact forces in tasks of repulsive loadings. This review presents an updated account of the works on mechanical impedance and its relations with motor control, limb dynamics, and motion biomechanics. Basic questions related to the linearity and nonlinearity of impedance and to the factors that affect mechanical impedance are treated with relevance to upper and lower limb functions, joint performance, trunk stability, and seating under dynamic conditions. Methods for the derivation of mechanical impedance, both those for within the system and material-structural approaches, are reviewed. For system approaches, special attention is given to methods aimed at revealing the correct and sufficient degree of nonlinearity of impedance. This is particularly relevant in the design of spring-based artificial legs and robotic arms. Finally, due to the intricate relation between impedance and muscle activity, methods for the explicit expression of impedance of contractile tissue are reviewed.

Methods for Dynamic Characterization of the Major Muscles Activating the Lower Limb Joints in Cycling Motion.

The functional activation, through electrical stimulation, of the lower limb consisting of several deficient muscles requires well-patterned and coordinated activation of these muscles. This study presents a method for characterizing the parameters of the major muscle groups controlling the ankle and knee joints in cycling motion, the latter having particular significance in the rehabilitation of locomotion. To lower mechanical indeterminacy in the joints the system is reduced by grouping the muscles acting in synergism. The joint torques were calculated by inverse dynamics methods from cycling motion data, including kinematics and foot/pedal reaction loads (forces, moments). The mechanical indeterminacy was resolved by applying optimization criteria and the individual muscle torques were parceled-out from the joint torques. System identification of the individual muscles, part of which being bi-articular, in this non-isometric condition was performed from the relationship between the evaluated force and the measured EMG of each the muscles, using both first and second order linear transfer functions. Feasibility of the presented method was demonstrated through the computation of the coefficients of the muscles involved and validating the results on the experimental data obtained from one subject.

A finite element model of cell-matrix interactions to study the differential effect of scaffold composition on chondrogenic response to mechanical stimulation.

Mechanically induced cell deformations have been shown to influence chondrocyte response in 3D culture. However, the relationship between the mechanical stimulation and cell response is not yet fully understood. In this study a finite element model was developed to investigate cell-matrix interactions under unconfined compression conditions, using a tissue engineered encapsulating hydrogel seeded with chondrocytes. Model predictions of stress and strain distributions within the cell and on the cell boundary were shown to exhibit space-dependent responses that varied with scaffold mechanical properties, the presence of a pericellular matrix (PCM), and the cell size. The simulations predicted that when the cells were initially encapsulated into the hydrogel scaffolds, the cell size hardly affected the magnitude of the stresses and strains that were reaching the encapsulated cells. However, with the inclusion of a PCM layer, larger cells experienced enhanced stresses and strains resulting from the mechanical stimulation. It was also noted that the PCM had a stress shielding effect on the cells in that the peak stresses experienced within the cells during loading were significantly reduced. On the other hand, the PCM caused the stresses at the cell-matrix interface to increase. Based on the model predictions, the PCM modified the spatial stress distribution within and around the encapsulated cells by redirecting the maximum stresses from the periphery of the cells to the cell nucleus. In a tissue engineered cartilage exposed to mechanical loading, the formation of a neo-PCM by encapsulated chondrocytes appears to protect them from initially excessive mechanical loading. Predictive models can thus shed important insight into how chondrocytes remodel their local environment in order to redistribute mechanical signals in tissue engineered constructs.

The influence of biological motifs and dynamic mechanical stimulation in hydrogel scaffold systems on the phenotype of chondrocytes.

Primary bovine chondrocytes and PEG-based hydrogels were used to investigate the effects of scaffold composition and architecture on the cellular response to large dynamic compressive strain stimulation. Proteins and proteoglycans were conjugated to functionalized poly(ethylene glycol) (PEG) and immobilized in PEG hydrogels to create bio-synthetic scaffolds. Second passage articular chondrocytes were encapsulated into four different scaffold compositions: PEG-Proteoglycan (PP), PEG-Fibrinogen (PF), PEG-Albumin (PA), and PEG only and subjected to 15% dynamic compressive strain at 1-Hz frequency. Cellular response was evaluated in terms of cell number, glycosaminoglycans (GAGs), collagen type II and collagen type I accumulation in the constructs following 24h and 28 days of stimulated and static culture. Stimulation of the constructs resulted in an increase in the cell number in all scaffolds, with no statistical difference measured among them. Dynamic stimulation of PP, PF, PA and PEG constructs resulted in a respective increase in the GAGs by 33%, 53.4%, 240.5%, and 284.5%, compared to their static controls. The permissive PEG and PA scaffolds showed a significantly larger relative increase in the GAGs in comparison to the other scaffolds tested. Collagen type II content in the PF, PA and PEG constructs increased by 78%, 1266% and 896% respectively, compared to their static controls. Permissive constructs showed a significantly larger relative increase and final absolute values of GAGs and type II collagen, compared to the PF constructs. Immunostaining for collagen type I, an indicator for chondrocyte de-differentiation, indicated that stimulation inhibited its production. Correlation maps between scaffold properties highlighted the major differences between permissive and instructive scaffolds. These results support the hypothesis that both compressive strain and scaffold bioactivity have an important effect on the chondrocyte metabolic response to mechanical stimulation, and that the 3-D environment surrounding chondrocytes can actively participate in translating mechanical stimulation to the resident cells.

Real-time monitoring of force response measured in mechanically stimulated tissue-engineered cartilage.

Mechanical stimulation improves tissue-engineered cartilage development both in terms of biochemical composition and structural properties. However, the link between the compositional changes attributed to mechanical stimulation and the changing structural properties of the engineered cartilage is poorly understood. We hypothesize that transient events associated with construct stiffening can be documented and used to understand milestones in construct development. To do this, we designed and built a mechanical stimulation bioreactor that can continuously record the force response of the engineered construct in real time. This study documents the transient changes of the stiffness of tissue-engineered cartilage constructs over the first 14 days of their development under cyclic loading. Compressive strain stimulation (15%, 1 Hz) was applied to poly(ethylene glycol) (PEG) hydrogels seeded with primary articular chondrocytes. The average compressive modulus of strain-stimulated constructs was 12.7 +/- 1.45 kPa after 2 weeks, significantly greater (P < 0.01) than the average compressive moduli of both unstimulated constructs (10.7 +/- 0.94 kPa) and nonviable stimulated constructs (11.2 +/- 0.91 kPa). The system was able to document that nearly all of the stiffness increase occurred over the last 2 days of the experiment, where live-cell constructs demonstrated a rapid 20% increase in force response. The system's ability to track significant increases in stiffness over time was also confirmed by Instron testing. These results present a novel view of the early mechanical development of tissue-engineering cartilage constructs and suggest that the real-time monitoring of force response may be used to noninvasively track the development of engineered tissue.

The differential effect of scaffold composition and architecture on chondrocyte response to mechanical stimulation.

This study aims to explore the differential effect of scaffold composition and architecture on chondrogenic response to dynamic strain stimulation using encapsulating PEG-based hydrogels and primary bovine chondrocytes. Proteins and proteoglycans were conjugated to functionalized poly(ethylene glycol) (PEG) and immobilized in PEG hydrogels to create bio-synthetic materials to be used as scaffolds. Four different compositions were tested, including: PEG-Proteoglycan (PP), PEG-Fibrinogen (PF), PEG-Albumin (PA), and PEG only. Primary articular chondrocytes were encapsulated in the hydrogel scaffolds and subjected to 15% dynamic compressive strain stimulation at 1-Hz frequency for 28 days. Stimulation of PP, PF, PA and PEG constructs resulted in a respective increase in the unconfined true compressive modulus by 32%, 45.4%, 33.6%, and 28.2%, compared to their static controls. The PF showed a significantly larger relative increase in the modulus in comparison to all other scaffolds tested. These results support the hypothesis that mechanical stimulation and material bioactivity have a significant effect on the reported chondrocyte response. Similar trends were observed with the swelling ratio of the constructs. These findings indicate that while stimulation causes metabolic changes in chondrocytes seeded in PEG hydrogels, the matrix bioactivity has a significant role in enhancing chondrocyte mechanotransduction in encapsulating scaffolds subjected to physical deformations.

Enhancement of muscle activity by electrical stimulation in cerebral palsy: a case-control study.

The objectives of this study were to compare the effects of low-intensity electrical stimulation of the quadriceps muscle in children with cerebral palsy in the following 2 modes: reconditioning by long-term training of the muscle versus real-time assist to the muscle during motion. To evaluate the force enhancement in the assist mode, we developed a method to dissociate the volitional and the induced components from the total electromyographic signal. The study group, including 5 children with cerebral palsy (mean age, 3.3 years; 0.4 SD), underwent 2 testing sessions: 1 before and 1 after 3-month training by electrical stimulation. Each session included 2 series of trials: 1 with electrical stimulation, as an orthotic assist, and 1 without electrical stimulation. The tests included flexion-extension movements of the knee at a self-selected pace. The results showed that, compared to before training, there was a significant increase in the average motion velocity and a decrease in motion jerk and in knee torque after training in both the electrical stimulation- assisted and -unassisted modes. Of special interest was the significant decrease in quadriceps-hamstrings co-contraction following training by electrical stimulation but not during electrical stimulation-assisted motion. The results obtained for the group with cerebral palsy were statistically different from those of the control group, but this difference decreased after long-term training by electrical stimulation. It was concluded that, in children with cerebral palsy, electrical stimulation is more beneficial in long-term training than when used as a real-time motion assist. Although muscle strength is not affected, more centrally controlled attributes such as co-contraction are improved.

Differential response of adult and embryonic mesenchymal progenitor cells to mechanical compression in hydrogels.

Cells in the musculoskeletal system can respond to mechanical stimuli, supporting tissue homeostasis and remodeling. Recent studies have suggested that mechanical stimulation also influences the differentiation of MSCs, whereas the effect on embryonic cells is still largely unknown. In this study, we evaluated the influence of dynamic mechanical compression on chondrogenesis of bone marrow-derived MSCs and embryonic stem cell-derived (human embryoid body-derived [hEBd]) cells encapsulated in hydrogels and cultured with or without transforming growth factor beta-1 (TGF-beta1). Cells were cultured in hydrogels for up to 3 weeks and exposed daily to compression for 1, 2, 2.5, and 4 hours in a bioreactor. When MSCs were cultured, mechanical stimulation quantitatively increased gene expression of cartilage-related markers, Sox-9, type II collagen, and aggrecan independently from the presence of TGF-beta1. Extracellular matrix secretion into the hydrogels was also enhanced. When hEBd cells were cultured without TGF-beta1, mechanical compression inhibited their differentiation as determined by significant downregulation of cartilage-specific genes. However, after initiation of chondrogenic differentiation by administration of TGF-beta1, the hEBd cells quantitatively increased expression of cartilage-specific genes when exposed to mechanical compression, similar to the bone marrow-derived MSCs. Therefore, when appropriately directed into the chondrogenic lineage, mechanical stimulation is beneficial for further differentiation of stem cell tissue engineered constructs.

Objective measurement of knee extension force based on computer adaptive testing.

False impairment is encountered when tested subjects either unintentionally or deliberately put an artificial upper limit on their force, in which case their true capacity cannot be disclosed in a straight forward measurement. The aim of this study was to develop a computer adaptive testing (CAT) system for directing subjects into generating greater forces than they intended. The system was tested on eleven cooperative female subjects who volunteered to take part in this study. The CAT consisted of interactive testing cycles, each containing a series of isometric tasks of differing intensities. While fulfilling these tasks, the tested subjects were asked to take care not to exceed a self-selected upper force limit (F(ssl)) that they were previously trained to memorize (order of 40% of the maximal voluntary contraction). Visual feedback, displaying the applied force exertions, was provided to the tested subjects but was modified by re-scaling the display in an un-anticipated manner. To confirm the subject's ability to remember her F(ssl), repeatability of joint memory was tested one week after the CAT. The CAT results were successful in causing ten out of the eleven tested participants to exert a higher force than they intended to. Additionally, the CAT algorithm caused a statistically significant higher force than the repeatability test. These results demonstrate the potential of CAT methods in improving the clinical evaluation of muscle strength, particularly in those cases where the subject's cooperation is not sufficient.

Evaluation of methods for extraction of the volitional EMG in dynamic hybrid muscle activation.

BACKGROUND: Hybrid muscle activation is a modality used for muscle force enhancement, in which muscle contraction is generated from two different excitation sources: volitional and external, by means of electrical stimulation (ES). Under hybrid activation, the overall EMG signal is the combination of the volitional and ES-induced components. In this study, we developed a computational scheme to extract the volitional EMG envelope from the overall dynamic EMG signal, to serve as an input signal for control purposes, and for evaluation of muscle forces. METHODS: A "synthetic" database was created from in-vivo experiments on the Tibialis Anterior of the right foot to emulate hybrid EMG signals, including the volitional and induced components. The database was used to evaluate the results obtained from six signal processing schemes, including seven different modules for filtration, rectification and ES component removal. The schemes differed from each other by their module combinations, as follows: blocking window only, comb filter only, blocking window and comb filter, blocking window and peak envelope, comb filter and peak envelope and, finally, blocking window, comb filter and peak envelope. RESULTS AND CONCLUSION: The results showed that the scheme including all the modules led to an excellent approximation of the volitional EMG envelope, as extracted from the hybrid signal, and underlined the importance of the artifact blocking window module in the process. The results of this work have direct implications on the development of hybrid muscle activation rehabilitation systems for the enhancement of weakened muscles.

Partition between volitional and induced forces in electrically augmented dynamic isometric muscle contractions.

Augmentation of force in partially deficient muscles can be achieved by combining electrical stimulation (ES) with their volitional activation (hybrid activation). However, while the overall torque results from the combination of the volitional and the electrically-induced torque components, the exact share between these components is not known. In a previous work, we described a method to resolve the share between the torque components under isometric static contractions. In this work, we extend our analysis to the case of isometric dynamic contractions. Five healthy subjects were instructed to contract their Tibialis Anterior (TA) muscles according to a typical gait-like dynamic torque pattern, that was visually displayed to them, while monitoring their actual ankle torque and TA electromyography (EMG). These experiments were done with and without augmented activation by means of ES. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG signal processing and on precalibration of the dynamic system of the volitional torque versus EMG. The results indicated the quantitative relations between decrease in the volitional torque and the required increase in ES enhancement. The developed method also demonstrated what ES intensity profile is necessary to produce a desired overall torque output. This provides the means for designing an adaptive rehabilitation device for the hybrid activation of deficient muscles.

Immobilized fibrinogen in PEG hydrogels does not improve chondrocyte-mediated matrix deposition in response to mechanical stimulation.

The present investigation aims to explore the role of cell-scaffold interactions and whole cell compression in chondrocyte mechanotransduction using encapsulating poly(ethylene glycol) (PEG) hydrogel scaffolds and primary bovine chondrocytes. Scaffolds made from PEG hydrogels with immobilized fibrinogen molecules were seeded with chondrocytes and subjected to 15% dynamic compressive strain at 1-Hz frequency. Dynamic strain stimulation resulted in a 37% increase in the levels of sulfated glycosaminoglycan (sGAG) after 2 weeks of stimulation, when compared to static controls. Comparing results of the PEG-fibrinogen scaffolds with their respective PEG control group did not show significant differences between the two, even following 2 weeks of dynamic mechanical stimulation. Accordingly, these findings indicate that while cell deformations cause metabolic changes in chondrocytes seeded in PEG hydrogels, it is difficult to ascertain the role of matrix bioactivity in enhancing chondrocyte mechanotransduction in encapsulating scaffolds subjected to physical deformations. This study shows how interactions between mechanical stimulation and scaffold composition are evaluated using an experimental approach and customized biomaterial scaffolds.