Microstructured Hollow Fiber Membranes: Potential Fiber Shapes for Extracorporeal Membrane Oxygenators.

Extracorporeal membrane oxygenators are essential medical devices for the treatment of patients with respiratory failure. A promising approach to improve oxygenator performance is the use of microstructured hollow fiber membranes that increase the available gas exchange surface area. However, by altering the traditional circular fiber shape, the risk of low flow, stagnating zones that obstruct mass transfer and encourage thrombus formation, may increase. Finding an optimal fiber shape is therefore a significant task. In this study, experimentally validated computational fluid dynamics simulations were used to investigate transverse flow within fiber packings of circular and microstructured fiber geometries. A numerical model was applied to calculate the local Sherwood number on the membrane surface, allowing for qualitative comparison of gas exchange capacities in low-velocity areas caused by the microstructured geometries. These adverse flow structures lead to a tradeoff between increased surface area and mass transfer. Based on our simulations, we suggest an optimal fiber shape for further investigations that increases potential mass transfer by up to 48% in comparison to the traditional, circular hollow fiber shape.

Water as a Blood Model for Determination of CO2 Removal Performance of Membrane Oxygenators.

CO2 removal via membrane oxygenators has become an important and reliable clinical technique. Nevertheless, oxygenators must be further optimized to increase CO2 removal performance and to reduce severe side effects. Here, in vitro tests with water can significantly reduce costs and effort during development. However, they must be able to reasonably represent the CO2 removal performance observed with blood. In this study, the deviation between the CO2 removal rate determined in vivo with porcine blood from that determined in vitro with water is quantified. The magnitude of this deviation (approx. 10%) is consistent with results reported in the literature. To better understand the remaining difference in CO2 removal rate and in order to assess the application limits of in vitro water tests, CFD simulations were conducted. They allow to quantify and investigate the influences of the differing fluid properties of blood and water on the CO2 removal rate. The CFD results indicate that the main CO2 transport resistance, the diffusional boundary layer, behaves generally differently in blood and water. Hence, studies of the CO2 boundary layer should be preferably conducted with blood. In contrast, water tests can be considered suitable for reliable determination of the total CO2 removal performance of oxygenators.

Suitable CO2 Solubility Models for Determination of the CO2 Removal Performance of Oxygenators.

CO2 removal via membrane oxygenators during lung protective ventilation has become a reliable clinical technique. For further optimization of oxygenators, accurate prediction of the CO2 removal rate is necessary. It can either be determined by measuring the CO2 content in the exhaust gas of the oxygenator (sweep flow-based) or using blood gas analyzer data and a CO2 solubility model (blood-based). In this study, we determined the CO2 removal rate of a prototype oxygenator utilizing both methods in in vitro trials with bovine and in vivo trials with porcine blood. While the sweep flow-based method is reliably accurate, the blood-based method depends on the accuracy of the solubility model. In this work, we quantified performances of four different solubility models by calculating the deviation of the CO2 removal rates determined by both methods. Obtained data suggest that the simplest model (Loeppky) performs better than the more complex ones (May, Siggaard-Anderson, and Zierenberg). The models of May, Siggaard-Anderson, and Zierenberg show a significantly better performance for in vitro bovine blood data than for in vivo porcine blood data. Furthermore, the suitability of the Loeppky model parameters for bovine blood (in vitro) and porcine blood (in vivo) is evaluated.

A Robotic System with EMG-Triggered Functional Eletrical Stimulation for Restoring Arm Functions in Stroke Survivors.

BACKGROUND: Robotic systems combined with Functional Electrical Stimulation (FES) showed promising results on upper-limb motor recovery after stroke, but adequately-sized randomized controlled trials (RCTs) are still missing. OBJECTIVE: To evaluate whether arm training supported by RETRAINER, a passive exoskeleton integrated with electromyograph-triggered functional electrical stimulation, is superior to advanced conventional therapy (ACT) of equal intensity in the recovery of arm functions, dexterity, strength, activities of daily living, and quality of life after stroke. METHODS: A single-blind RCT recruiting 72 patients was conducted. Patients, randomly allocated to 2 groups, were trained for 9 weeks, 3 times per week: the experimental group performed task-oriented exercises assisted by RETRAINER for 30 minutes plus ACT (60 minutes), whereas the control group performed only ACT (90 minutes). Patients were assessed before, soon after, and 1 month after the end of the intervention. Outcome measures were as follows: Action Research Arm Test (ARAT), Motricity Index, Motor Activity Log, Box and Blocks Test (BBT), Stroke Specific Quality of Life Scale (SSQoL), and Muscle Research Council. RESULTS: All outcomes but SSQoL significantly improved over time in both groups (P < .001); a significant interaction effect in favor of the experimental group was found for ARAT and BBT. ARAT showed a between-group change of 11.5 points (P = .010) at the end of the intervention, which increased to 13.6 points 1 month after. Patients considered RETRAINER moderately usable (System Usability Score of 61.5 ± 22.8). CONCLUSIONS: Hybrid robotic systems, allowing to perform personalized, intensive, and task-oriented training, with an enriched sensory feedback, was superior to ACT in improving arm functions and dexterity after stroke.

A generic musculoskeletal model of the juvenile lower limb for biomechanical analyses of gait.

The aim of this study was to develop a generic musculoskeletal model of a healthy 10-year-old child and examine the effects of geometric scaling on the calculated values of lower-limb muscle forces during gait. Subject-specific musculoskeletal models of five healthy children were developed from in vivo MRI data, and these models were subsequently used to create a generic juvenile (GJ) model. Calculations of lower-limb muscle forces for normal walking obtained from two scaled-generic versions of the juvenile model (SGJ1 and SGJ2) were evaluated against corresponding results derived from an MRI-based model of one subject (SSJ1). The SGJ1 and SGJ2 models were created by scaling the GJ model using gait marker positions and joint centre locations derived from MRI imaging, respectively. Differences in the calculated values of peak isometric muscle forces and muscle moment arms between the scaled-generic models and MRI-based model were relatively small. Peak isometric muscle forces calculated for SGJ1 and SGJ2 were respectively 2.2% and 3.5% lower than those obtained for SSJ1. Model-predicted muscle forces for SGJ2 agreed more closely with calculations obtained from SSJ1 than corresponding results derived from SGJ1. These results suggest that accurate estimates of muscle forces during gait may be obtained by scaling generic juvenile models based on joint centre locations. The generic juvenile model developed in this study may be used as a template for creating subject-specific musculoskeletal models of normally-developing children in studies aimed at describing lower-limb muscle function during gait.

A Hybrid Robotic System for Arm Training of Stroke Survivors: Concept and First Evaluation.

OBJECTIVE: To develop and evaluate a hybrid robotic system for arm recovery after stroke, combining ElectroMyoGraphic (EMG)-triggered functional electrical stimulation (FES) with a passive exoskeleton for upper limb suspension. METHODS: The system was used in a structured exercise program resembling activities of daily life. Exercises execution was continuously controlled using angle sensor data and radio-frequency identification technology. The training program consisted of 27 sessions lasting 30 min each. Seven post-acute stroke patients were recruited from two clinical sites. The efficacy of the system was evaluated in terms of action research arm test, motricity index, motor activity log, and box & blocks tests. Furthermore, kinematics-based and EMG-based outcome measures were derived directly from data collected during training sessions. RESULTS: All patients showed an improvement of motor functions at the end of the training program. After training, the exercises were in most cases executed faster, smoother, and with an increased range of motion. Subjects were able to trigger FES, but in some cases, they did not maintain the voluntary effort during task execution. All subjects but one considered the system usable. CONCLUSION: The preliminary results showed that the system can be used in a clinical environment with positive effects on arm functional recovery. However, only the final results of the currently ongoing clinical trial will unveil the system's full potential. SIGNIFICANCE: The presented hybrid robotic system is highly customizable, allows to monitor the daily performance, requires low supervision of the therapist, and might have the potential to enhance arm recovery after stroke.

A preliminary muscle activity analysis: Handle based and push-rim wheelchair propulsion.

Approximately ninety percent of the wheelchair users worldwide prefer the conventional push rim mode of propulsion for daily mobility and rehabilitation. Even though push-rim wheelchairs help to promote a healthy life style, the high muscular demand and the non-continuous push motions can lead to serious upper extremity injuries. In this study, muscle EMG data of ten healthy subjects were recorded for a newly introduced handle based propulsion mechanism (HBP) and compared to conventional push-rim propulsion at two workloads, 25 W and 35 W respectively. The results for the mean peak muscle activations at both workloads demonstrate that push-rim propulsion leads to higher peak muscle activity compared to HBP at a similar wheelchair forward velocity of 1.11 m/s. The generation of these high peak muscle activations with increasing loads in push-rim propulsion over time can lead to overuse injuries. Overall, the use of the HBP mechanism is less straining to the muscles and may reduce fatigue during prolonged propulsion.

Basic Performance Tests of the MILL Intravascular CO2 Removal Catheter.

Currently available treatment methods for acute lung failure show high rates of complications. There is an urgent need for alternative treatment methods. A catheter device which can be minimal invasively inserted into the vena cava for intracorporeal gas exchange was developed. Main components of the device are a drive unit and a membrane module. In this study, the flow behavior in a vena cava model with inserted catheter prototype was investigated in experiments and basic computational fluid dynamic (CFD) simulations. Main findings are that the miniature blood pump has suitable characteristics and generates sufficient power to overcome the pressure drop induced in the membrane module, and that the design of the membrane outlet might be critical to avoid additional pressure losses. Parts manufactured with a high resolution 3D printer have proven to be suitable for the prototyping process.

Wrist Kinematics and Kinetics during Wheelchair Propulsion with a Novel Handle-based Propulsion Mechanism.

Wheelchairs are important for daily mobility and recreation of the elderly and physically challenged individuals. The non-ergonomical propulsion design of wheelchairs frequently causes injuries to the upper extremities, especially in the wrist region. In this study, the joint kinematics and kinetics of the wrist joint was analyzed on subjects propelling a novel handle based wheelchair propulsion unit at 1.2m/s speed (20W and 40W respectively). The joint kinematics and the joint moments of the wrist were determined using a 3D musculoskeletal model. The mean values of joint ranges and torques during propulsion at the mentioned speeds were lower when compared to standard wheelchair propulsion with the push-rim, making the novel propulsion mechanism with its compact design an interesting alternative for wheelchair users that might help to avoid or reduce joint injuries.

BRIDGE - Behavioural reaching interfaces during daily antigravity activities through upper limb exoskeleton: Preliminary results.

People with neuromuscular diseases such as muscular dystrophy experience a distributed and evolutive weakness in the whole body. Recent technological developments have changed the daily life of disabled people strongly improving the perceived quality of life, mostly concentrating on powered wheelchairs, so to assure autonomous mobility and respiratory assistance, essential for survival. The key concept of the BRIDGE project is to contrast the everyday experience of losing functions by providing them of a system able to exploit the best their own residual capabilities in arm movements so to keep them functional and autonomous as much as possible. BRIDGE is composed by a light, wearable and powered five degrees of freedom upper limb exoskeleton under the direct control of the user through a joystick or gaze control. An inverse kinematic model allows to determine joints position so to track patient desired hand position. BRIDGE prototype has been successfully tested in simulation environment, and by a small group of healthy volunteers. Preliminary results show a good tracking performance of the implemented control scheme. The interaction procedure was easy to understand, and the interaction with the system was successful.

Quantitative evaluation of the major determinants of human gait.

Accurate knowledge of the isolated contributions of joint movements to the three-dimensional displacement of the center of mass (COM) is fundamental for understanding the kinematics of normal walking and for improving the treatment of gait disabilities. Saunders et al. (1953) identified six kinematic mechanisms to explain the efficient progression of the whole-body COM in the sagittal, transverse, and coronal planes. These mechanisms, referred to as the major determinants of gait, were pelvic rotation, pelvic list, stance knee flexion, foot and knee mechanisms, and hip adduction. The aim of the present study was to quantitatively assess the contribution of each major gait determinant to the anteroposterior, vertical, and mediolateral displacements of the COM over one gait cycle. The contribution of each gait determinant was found by applying the concept of an 'influence coefficient', wherein the partial derivative of the COM displacement with respect to a prescribed determinant was calculated. The analysis was based on three-dimensional measurements of joint angular displacements obtained from 23 healthy young adults walking at slow, normal and fast speeds. We found that hip flexion, stance knee flexion, and ankle-foot interaction (comprised of ankle plantarflexion, toe flexion and the displacement of the center of pressure) are the major determinants of the displacements of the COM in the sagittal plane, while hip adduction and pelvic list contribute most significantly to the mediolateral displacement of the COM in the coronal plane. Pelvic rotation and pelvic list contribute little to the vertical displacement of the COM at all walking speeds. Pelvic tilt, hip rotation, subtalar inversion, and back extension, abduction and rotation make negligible contributions to the displacements of the COM in all three anatomical planes.

Alternative solution of virtual biomodeling based on CT-scans.

In this paper, an alternative method is presented to convert computed tomography (CT)-scans into 3D biomodels. The CT-data of an equine spine was converted into TIF format to work with it in a 2D CAD program. Then the bony structure has been marked manually with closed splines and saved as IGS files for the next procedure with 3D CAD software to create virtual biomodels of every single bone. Therefore, the different layers of the CT-scans were positioned in correct distance and then a closed surface was created to cover all spline-curves. Finally, the cover was filled up with material to create a solid part. This method can be recommended as an alternative way, if CAD software is available only. Especially, if it is necessary to add extra artificial spline-curves to split two or more bones which were unnaturally grown together, working with 3D CAD software is the right solution.

Sensitivity of muscle force estimates to variations in muscle-tendon properties.

The aim of this study was to determine the sensitivity of muscle force estimates to changes in some of the parameters which are commonly used to describe models of muscle-tendon actuation. The sensitivity analysis was performed on three parameters: optimal muscle-fiber length, muscle physiological cross-sectional area (PCSA), and tendon rest length. The muscles selected for the analysis were posterior gluteus medius/minimus, vasti, soleus, and sartorius. Each parameter was perturbed from its nominal value, and an optimization problem was solved to determine the relative influence of each parameter on the calculated values of muscle force. Muscle forces were calculated for a simulated cycle of normal walking. Parameter sensitivity was quantified using two new metrics: an integrated sensitivity ratio, which quantified the effect of changing a single parameter for any muscle on the time history of force developed by that muscle; and a summed cross-sensitivity ratio, which quantified the effect of changing one parameter for any muscle on the time histories of forces developed by all of the other muscles. The results showed that muscle force estimates for walking are most sensitive to changes in tendon rest length and least sensitive to changes in muscle PCSA. For soleus, for example, the integrated sensitivity ratios for tendon rest length were an order of magnitude greater than those for muscle-fiber length and PCSA. For vasti, the integrated sensitivity ratios for tendon rest length were twice as large as those for muscle-fiber length and nearly an order of magnitude greater than those for PCSA. Overall, changes in the tendon rest lengths of vasti and soleus and changes in the fiber length of vasti were most critical to model estimates of muscle force. Our results emphasize the importance of obtaining accurate estimates of tendon rest length and muscle-fiber length, particularly for those actuators that function as prime movers during locomotion (gluteus maximus, gluteus medius/minimus, vasti, soleus, and gastrocnemius).