A New Synthetic Conduit for the Treatment of Peripheral Nerve Injuries.

BACKGROUND: Peripheral nerve defects (PND) often cause lifelong physical disability, and the available treatment options are often not satisfactory. PND are usually bridged with an autologous nerve transplant or a nerve guidance conduit (NGC), when coaptation as preferred technique is not possible. The aim of this experimental study was to determine the effectiveness of a novel NGC for regeneration in the treatment of PND. MATERIALS AND METHODS: A conduit made of gelatin with an innovative interior structure was tested for the repair of a 6-mm gap versus direct microsurgical suture repair without gap. RESULTS: We found that bridging the defect with this conduit was as effective as direct microsurgical coaptation without a defect. CONCLUSIONS: This nerve conduit, effective in bridging neural defects, appears as an alternative to autologous nerve grafts, avoiding the problems related to nerve graft harvesting, host-donor differences in diameter, mismatches in number and pattern of fascicles, cross-sectional shape and area, and morbidity of the donor area.

A Novel Approach to Analyze the Progression of Measured Corneal Sub-Basal Nerve Fiber Length in Continuously Expanding Mosaic Images.

Purpose/Aim of the study: A recently proposed technique enables the generation of continuously increasing mosaic images of the corneal sub-basal nerve plexus (SNP) using in vivo corneal confocal microscopy (CCM). The aim of the present study was to investigate the progression of the corneal nerve fiber length (CNFL) measured in the growing mosaic images with regard to their increasing area. MATERIALS AND METHODS: Five large datasets from three healthy volunteers were examined using the proposed CCM technique. Intermediate mosaic images were created and assessed for CNFL. RESULTS: The measured CNFL progression shows both over- and underestimation of the CNFL for small observed areas. Increasing the mosaic image area stabilizes the CNFL values and reduces the moving variance in all five datasets. The relative deviation of means from values of first and second examination of two of the subjects shows high differences for an observed area of <1.5 mm2. CONCLUSIONS: The present examination provides two measures to quantify different area-dependent aspects of the CNFL measured in an expanding mosaic image. The moving variance measures how stable the CNFL can be considered at a certain mosaic size. The relative deviation of means from two repeated CCM examinations on the other hand gives some indication on the level of reliability that can be expected from the measured CNFL. The progression of CNFL in the examined datasets manifests a potentially very high variability for mosaic sizes of less than about 1.5 mm2. Above that size, CNFL progression and the intra-patient relative deviations both stabilize significantly in all five datasets. The results of the present examination suggest a recommendation for a minimum sampled area of the central SNP of 1.5 mm2 for reliable and meaningful measurement of CNFL.

The pupil can control an artificial lens intuitively.

PURPOSE: After cataract surgery, the ability to accommodate is lost. For this reason, a mechatronic IOL is being developed at the moment: The Artificial Accommodation System. This device requires an easily measureable indicator of the distance of the observed object to determine the demand of accommodation. As the pupil constricts with near vision, pupil size might be such an indicator. Our research focused on whether the pupil can control an artificial lens. METHODS: A study with 14 healthy subjects aged between 24 and 64 years was conducted. An artificial lens with variable refractive power was mounted in front of one eye. In this eye, natural accommodation was greatly reduced or absent due to presbyopia, pseudophakia, or iatrogenic cycloplegia. The lens' refractive power was changed in a computer-controlled manner depending on changes in the pupil diameter of the second eye, which could not see the fixation stimulus. The subject's task was to get a clear focused image of the target in different distances. RESULTS: The lens can be controlled by the pupil intuitively (P < 1.8 × 10(-18)). Without prior knowledge, 11/14 subjects passed the first trial, and 31/41 trials were successful. Only one subject was not able to control the lens at all. Most subjects comprehended instantly how to use the unfamiliar lens control to bring a target into focus. CONCLUSIONS: This study emphasizes the plasticity of the visual control system. Positioning accuracy was acceptable, but the control must be optimized to facilitate maintaining a defined refractive power.

Kinetic energy scavenging in a prosthetic foot using a fluidic system.

The use of active prostheses for the lower extremity is limited by the amount of electric energy stored in batteries. A promising way to extend their usage time is to convert motions generated by the human body during walking to electrical energy. A first functioning prototype was designed to transfer kinetic energy from heel contact and forefoot contact to a generator by using a fluidic system. Experimental results show that walking with the system generates an average electrical power of 0.8 W. The design of the energy scavenging system (ESS) is presented and results are discussed.

New synthetic prosthesis for peripheral nerve injuries: an experimental pilot study.

INTRODUCTION: Even the most modern technology has failed to induce satisfactory functional regeneration of traumatically severed peripheral nerves. Delayed neural regeneration and in consequence, slower neural conduction seriously limit muscle function in the area supplied by the injured nerve. This study aimed to compare a new nerve coaptation system involving an innovative prosthesis with the classical clinical method of sutured nerve coaptation. Besides the time and degree of nerve regeneration, the influence of electrostimulation was also tested. METHODS: The sciatic nerve was severed in 14 female Göttingen minipigs with an average weight of 40.4 kg. The animals were randomized into 2 groups: One group received the new prosthesis and the other underwent microsurgical coaptation. In each group, according to the randomization a part of the animals received postoperative electrostimulation. Postoperative monitoring and the stimulation schedule covered a period of 9 months, during which axonal budding was evaluated monthly. RESULTS: The data from the pilot study indicate that results with the nerve prosthesis were comparable with those of conventional coaptation. CONCLUSION: The results indicate that implantation of the nerve prosthesis allows for good and effective neural regeneration. This new and simple treatment option for peripheral nerve injuries can be performed in any hospital with surgical facilities as it does not involve the demanding microsurgical suture technique that can only be performed in specialized centers.

A modular, low-cost robot for zebrafish handling.

The zebrafish (danio rerio) is one of the most important model organisms in modern drug discovery and disease modeling. Handling and analyzing large numbers of zebrafish larvae require an immense manpower and involve time-consuming manual processes. A novel modular, robotic platform for high-throughput screening is being developed at BioRobotLab (KIT). In this article the fish sorter, which is a robotic device for the automation of a manual process in bio analysis, is presented. The fish sorter detects randomly spread zebrafish eggs and larvae up to an age of 120 hours post fertilization (hpf) in Petri dishes and transfers them to standard 96- or 384- well plates. The robot is controlled by an advanced algorithm with sensor-based process control. Fast and precise hardware components lead to a high working speed and success rate >= 95%.

Preserved autonomic regulation in patients undergoing transcatheter aortic valve implantation (TAVI): a prospective, comparative study.

Heart rate and blood pressure variability as well as baroreflex sensitivity (BRS) lead to additional insights on the patients' prognosis after cardiovascular events. The following study was performed to assess the differences in the postoperative recovery of the autonomic regulation after transcatheter aortic valve implantation (TAVI) and surgical aortic valve replacement (SAVR). Fifty-eight consecutive patients were enrolled in a prospective study; 24 underwent TAVI and 34 SAVR. BRS was calculated according to the Dual Sequence Method, heart rate variability (HRV) was evaluated using standard linear as well as nonlinear parameters. HRV and BRS parameters were reduced after surgery in patients with SAVR only (meanNN: p<0.001, sdNN: p<0.05, Shannon: p<0.01, BRS: p<0.01), while these indexes were preserved in patients after TAVI. Simultaneously, an increased complexity of blood pressure (BP) in SAVR patients (fwShannon: p<0.001, fwRenyi4: p<0.001), but not in TAVI patients was recorded. In this study we were able to demonstrate for the first time that, in contrast to patients undergoing conventional open surgery, there are fewer alterations of the cardiovascular autonomic system in patients with TAVI.

Cardiovascular regulation in different sleep stages in the obstructive sleep apnea syndrome.

Heart rate and blood pressure variability analysis as well as baroreflex sensitivity have been proven to be powerful tools for the assessment of autonomic control in clinical practice. Their ability to detect systematic changes caused by different states, diseases and treatments shall be shown for sleep disorders. Therefore, we consider 18 normotensive and 10 hypertensive patients suffering from obstructive sleep apnea syndrome (OSAS) before and after a three-month continuous positive airway pressure (CPAP) therapy. Additionally, an age and sex matched control group of 10 healthy subjects is examined. Linear and nonlinear parameters of heart rate and blood pressure fluctuation as well as the baroreflex sensitivity are used to answer the question whether there are differences in cardiovascular regulation between the different sleep stages and groups. Moreover, the therapeutic effect of CPAP therapy in OSAS patients shall be investigated. Kruskal-Wallis tests between the sleep stages for each group show significant differences in the very low spectral component of heart rate (VLF/P: 0.0033-0.04 Hz, p<0.01) which indicates differences in metabolic activity during the night. Furthermore, the decrease of Shannon entropy of word distribution as a parameter of systolic blood pressure during non-REM sleep reflects the local dominance of the vagal system (p<0.05). The increased sympathetic activation of the patients leads to clear differences of cardiovascular regulation in different sleep stages between controls and patients. We found a significant reduction of baroreflex sensitivity in slow wave sleep in the OSAS patients (Mann-Whitney test, p<0.05) compared to controls, which disappeared after three months of CPAP therapy. Hence, our results demonstrate the ability of cardiovascular analyzes to separate between healthy and pathological regulation as well as between different severities of OSAS in this retrospective study.

Image reconstruction of the subbasal nerve plexus with in vivo confocal microscopy.

PURPOSE: To overcome the anterior corneal mosaic (ACM) phenomenon in in vivo confocal laser scanning microscopy (CLSM) and to reconstruct undistorted images of the subbasal nerve plexus (SNP), facilitating morphometric analysis in the presence of ACM ridges. METHODS: CLSM was performed in five healthy volunteers. An original image processing algorithm based on phase correlation was used to analyze and reduce motion distortions in volume scan image sequences. Three-dimensional tracing of the SNP was performed to reconstruct images containing only the SNP layer, with nerve fibers clearly visible even in ACM areas. RESULTS: Real-time mapping of the SNP revealed the presence of ridges with K-structures underneath them in all cases. The occurrence of K-structures correlated directly with development of ACM observed by slit lamp and resulted in massive deformation at the level of Bowman's membrane, seriously interfering with examination of SNP structures. The average elevation of ACM ridges was 20.6 µm (range, 8.7-34.0 µm). The novel method presented permitted reconstruction of the SNP layer in regions of ACM. CONCLUSIONS: The described method allows the precise analysis and elimination of motion artifacts in CLSM volume scans, in conjunction with the capability to reconstruct SNP structures even in the presence of severe ACM. The robustness and automation of the described algorithms require ongoing development, but this will provide a sound basis for extended studies of corneal nerve regeneration or degeneration and for use in clinical practice.

Robust intraocular acquisition of the accommodation demand using eyeball movements.

The Artificial Accommodation System is a mechatronic lens implant that will restore the ability of the human eye to accommodate. Therefore, the accommodation demand has to be acquired. One possibility is to measure the vergence angle of the eyeballs in reference to an external field. Using the earth magnetic field as reference the proof of this measuring principle was possible. Still there are drawbacks like high responsivity to interferences and limitations of the measuring range. The new approach is to use the gravity field as reference and thus reduce the responsivity to interferences. The measuring range can be expanded by combining both sensing principles.

Impact of sleep deprivation on medium-term psychomotor and cognitive performance of surgeons: prospective cross-over study with a virtual surgery simulator and psychometric tests.

BACKGROUND: Despite recent work hour restrictions, 24-hour calls remain an important part of patient care. The aim of this study was to assess the impact of 24-hour night calls on the psychomotor and cognitive skills of surgeons with a virtual surgery simulator (VSS) and psychometric tests. We hypothesized that sleep loss impairs surgical skills and concentration performance. METHODS: Seventeen surgery residents (test group) and 13 medical students (reference group) performed a 5-day training program on the VSS. The test group was then assessed during a night call on 4 test points (8 am and 4 pm on the on-call day, 8 am on the postcall day, and 8 am on the recovery day) to assess the effects of sleep loss on these surgery residents. The reference group performed the same tests but without a night call. RESULTS: The training resulted in a homogenous performance level for both groups. The average time for the test group was 26 minutes. The analysis between rested and sleep-deprived participants (6.5 +/- 0.9 vs 2.9 +/- 1.4 hours of night sleep) in the on-call part showed no performance differences. No impairment was found for the VSS and the cognitive tests within the test group between the start of the working day and the start of the postcall day after the night of relative sleep loss. The subgroup analysis showed no significant differences regarding the amount of night sleep and laparoscopic experience. CONCLUSION: No performance impairment was found for surgeons with a VSS and standardized cognitive tests after a night of relative sleep loss. Although there is no doubt that sleep deprivation ultimately impairs human functioning, typical surgical skills do not necessarily deteriorate with a limited amount of sleep loss under clinical conditions.

Depression of cardiovascular autonomic function is more pronounced after mitral valve surgery: evidence for direct trauma.

The analysis of baroreflex sensitivity (BRS) and heart rate variability (HRV) leads to additional insights into patients' prognosis after cardiovascular events. The following study was performed to assess the differences in the post-operative recovery of autonomic regulation after mitral valve (MV) and aortic valve (AV) surgery with a heart-lung machine. Among the 43 consecutive male patients enrolled in a prospective study, 26 underwent isolated AV surgery and 17 isolated MV surgery. Blood pressure as well as ECG signals were recorded the day before, 24 hours after and one week after surgery. BRS was calculated according to the dual sequence method, and HRV was calculated using standard linear as well as nonlinear parameters. There were no major differences between the two groups in the pre-operative values. At 24 hours a comparable depression of HRV and BRS in both groups was observed, while at 7 days there was partial recovery in AV patients, which was absent in MV patients: p(AV versus MV)<0.001. While the response of the autonomic system to surgery is similar in AV and MV patients, there is obviously a decreased ability to recover in MV patients, probably attributed to traumatic lesions of the autonomic nervous system by opening the atria. Ongoing research is required for further clarification of the pathophysiology of this phenomenon and to establish strategies to restore autonomic function.

Autonomic control in patients experiencing atrial fibrillation after cardiac surgery.

BACKGROUND: Atrial fibrillation (AF) occurs in 20-40% of patients after open heart surgery and leads to an increased morbidity and prolonged hospital stay. Earlier studies have demonstrated that depressed baroreflex function predicts mortality and major arrhythmic events in patients surviving myocardial infarction. Cardiac surgery per se leads to decreased baroreflex sensitivity (BRS) and heart rate variability (HRV). Hence, the present study was aimed at analyzing the impact of the cardiovascular autonomous system on the development of postsurgical AF. METHODS AND RESULTS: The study covered 51 patients who consecutively underwent aortic valve replacement, coronary artery bypass surgery, or combined procedures. Noninvasive blood pressure and ECG were recorded the day before and 24 hour after surgery. BRS, linear as well as nonlinear HRV parameters were calculated using established methods. Eighteen patients developed AF during the first postoperative week, while 33 remained in sinus rhythm (SR) throughout the observation period. Patients with postoperative (PostOp) AF exhibited a significantly reduced preoperative (PreOp) BRS in terms of bradycardic and tachycardic regulation (average delayed slope [ms/mmHg]: SR: PreOp: 9.83 +/- 3.26, PostOp: 6.02 +/- 2.29, Pre-Post: P < 0.001; AF: PreOp: 7.59 +/- 1.99, PostOp: 6.39 +/- 3.67, Pre-Post: P < 0.044; AF vs SR: PreOp: P < 0.01, PostOp: ns). In both groups, surgery caused a decrease of BRS and HRV. Analysis of nonlinear dynamics revealed a tendency toward decreased system complexity caused by the operation; this trend was significant in patients remaining in sinus rhythm. CONCLUSIONS: Patients experiencing postoperative AF obviously suffer from an impaired BRS before surgery already. These findings may be used to guide prophylactic antiarrhythmic therapy.

Automated feature assessment in instrumented gait analysis.

A methodological modular framework is presented for automated assessment of gait patterns. The processing steps of data selection, gait parameter calculation and evaluation are not limited to a specific field of application and are largely independent of case-based clinical expert knowledge. For these steps, a variety of mathematical methods was used and the validity of the approach to assess gait parameters tested by applying it to the clinical problem of Botulinum Toxin A (BTX-A) treatment of the spastic equinus foot. A set of 3670 parameters was ranked by relevance for classification of a group of 42 diplegic cerebral palsy (CP) patients and an age-matched reference group. The same procedure was performed for pre- and post-therapeutic data sets of these patients. Gait parameters of high relevance coincided well with results of previous studies based on partly manual and more subjective parameter selection. A norm distance measure is introduced to facilitate the quantification of deviations from a normal walking pattern and can be used as an overall scalar measure to evaluate differences in gait patterns or as a set of measures attributing each joint angle separately.

A prospective randomized study to test the transfer of basic psychomotor skills from virtual reality to physical reality in a comparable training setting.

OBJECTIVE: To test whether basic skills acquired on a virtual endoscopic surgery simulator are transferable from virtual reality to physical reality in a comparable training setting. SUMMARY BACKGROUND DATA: For surgical training in laparoscopic surgery, new training methods have to be developed that allow surgeons to first practice in a simulated setting before operating on real patients. A virtual endoscopic surgery trainer (VEST) has been developed within the framework of a joint project. Because of principal limitations of simulation techniques, it is essential to know whether training with this simulator is comparable to conventional training. METHODS: Devices used were the VEST system and a conventional video trainer (CVT). Two basic training tasks were constructed identically (a) as virtual tasks and (b) as mechanical models for the CVT. Test persons were divided into 2 groups each consisting of 12 novices and 4 experts. Each group carried out a defined training program over the course of 4 consecutive days on the VEST or the CVT, respectively. To test the transfer of skills, the groups switched devices on the 5th day. The main parameter was task completion time. RESULTS: The novices in both groups showed similar learning curves. The mean task completion times decreased significantly over the 4 training days of the study. The task completion times for the control task on Day 5 were significantly lower than on Days 1 and 2. The experts' task completion times were much lower than those of the novices. CONCLUSIONS: This study showed that training with a computer simulator, just as with the CVT, resulted in a reproducible training effect. The control task showed that skills learned in virtual reality are transferable to the physical reality of a CVT. The fact that the experts showed little improvement demonstrates that the simulation trains surgeons in basic laparoscopic skills learned in years of practice.

Two multiarticulated hydraulic hand prostheses.

PURPOSE: Consumers want new prosthetic hand designs that have increased functionality, better cosmetic appearance, and lower weight. METHODS: New lightweight hands that fulfill these demands can be designed by integrating a hydraulic system with small fluidic actuators at the digit joints. RESULTS: Two different designs of lightweight experimental prosthetic hand are presented. The weight of the first hand is reduced by 50% compared to a conventional prosthetic hand, whereas the functionality of the second hand is increased by additional prehension types. Optionally, a tactile feedback system can be integrated. Due to multiple articulated digits and flexible materials, both hands are able to conform to the shape of an object held. This significantly reduces the necessary grip force and results in stable holding of an object. For a natural appearance, the hands are covered with a cosmetic silicone rubber glove.

Virtual reality in laparoscopic surgery.

Although the many advantages of laparoscopic surgery have made it an established technique, training in laparoscopic surgery posed problems not encountered in conventional surgical training. Virtual reality simulators open up new perspectives for training in laparoscopic surgery. Under realistic conditions in real time, trainees can tailor their sessions with the VR simulator to suit their needs and goals, and can repeat exercises as often as they wish. VR simulators reduce the number of experimental animals needed for training purposes and are suited to the pursuit of research in laparoscopic surgery.