Influence of muscle fibre shortening on estimates of conduction velocity and spectral frequencies from surface electromyographic signals

The study of surface electromyographic (EMG) signals under dynamic contractions is becoming increasingly important. However, knowledge of the methodological issues that may affect such analysis is still limited. The aim of the study was to analyse the effect of fibre shortening on estimates of conduction velocity (CV) and mean power spectral frequency (MNF) from surface EMG signals. Single fibre action potentials were simulated, as detected by commonly used spatial filters, for different fibre lengths. No physiological modifications were included with changes in fibre length, and thus only geometrical artifacts related to fibre shortening were investigated. The simulation results showed that the dependence of CV and MNF on fibre shortening is affected by the fibre location, electrode position and the spatial filter applied. With shortening of up to 50% for a fibre of 50 mm semi-length, the variations in CV and MNF estimates with shortening in bipolar recordings were 0.5% (CV) and 0.7% (MNF) for superficial fibres, and 3.6% and 5.1% for deeper fibres. Using the longitudinal double differential filter, under the same conditions, the percent variation was 0% and 0.2%, and 24.7% and 15.8%, respectively. The main conclusions were, first, muscle fibre shortening can significantly affect estimates of CV and MNF, especially for short fibre lengths. However, for long (semi-length >50 mm) and superficial fibres, this effect is limited for shortenings of up to 50% of the initial fibre length. Secondly, CV and MNF are almost equally affected by changes in muscle length; and, thirdly, sensitivity to fibre shortening depends on the spatial filter applied for signal detection.

Preadipocyte-loaded collagen scaffolds with enlarged pore size for improved soft tissue engineering

Extended soft tissue defects after extensive deep burns or tumor resections are still an unresolved problem in plastic and reconstructive surgery. There is a clinical need for an adequate solution to this problem but currently, no adequate implant material is available for the correction of these defects. Since the autologous transplantation of mature adipose tissue gives poor results, this study explores the advantages of using human preadipocytes in collagen sponges for tissue reconstruction purposes. Human preadipocytes of young adults were isolated, cultured, seeded onto collagen sponges with uniform pore size, and implanted into immunodeficient mice. After 24 hours of incubation in vitro and after explantation at 3, 8, and 12 weeks, sponges were examined for macroscopic appearance, weight, thickness, histology, immuno-histochemistry, and ultrastructure. We find good penetration of cells into the scaffold, layers of adipose tissue, and new vessels on all grafts while controls appear unchanged. These results are promising for improving the reconstruction of soft tissue defects.

Single motor unit analysis from spatially filtered surface electromyogram signals. Part I: spatial selectivity

The aim of the study was to compare experimentally, on the basis of single motor unit (MU) activities, the selectivity of different spatial filters commonly used to detect surface electromyogram (EMG) signals. Surface EMG signals were recorded from the biceps brachii and the upper trapezius muscle of five subjects using a two-dimensional (2D) electrode array consisting of 16 pin electrodes. The subjects performed isometric contractions at different elbow angles and shoulder abduction and flexion. The same monopolar surface EMG signals were filtered using longitudinal single and double differential, transverse single and double differential and normal double differential filters. From the single MU action potentials, extracted by automatic EMG decomposition, indexes of transverse (perpendicular with respect to the fibre direction) and longitudinal (along the fibre direction) selectivity were computed. The number of detected MUs was 46 for the upper trapezius, with the arms held in the sagittal plane, and 52 when the arms were held in the frontal plane; 85 MUs were identified from the biceps brachii contractions. The results showed that transverse selectivity was significantly higher for the 2D and transverse one-dimensional (1D) filters with respect to the 1D longitudinal filters, whereas longitudinal selectivity was higher (i.e. MU action potentials were shorter) for the 2D filter and the longitudinal double differential filter. In particular, the relative attenuation of potential amplitude moving 5 mm from the source was, on average (for the two muscles), 16.5% for the least selective filter in the transverse direction (longitudinal single differential) and 35.7% for the most selective one in the same direction (transverse double differential). The MU action potential duration was, on average, 13.8 ms for the most selective filter in the longitudinal direction (longitudinal double differential) and 18.7 ms for the least selective one (transverse double differential). The normal double differential filter resulted in spatial selectivity indexes that ware not statistically different in the two directions from those of the best filters in each direction.

Single motor unit analysis from spatially filtered surface electromyogram signals. Part 2: conduction velocity estimation

The aim of the study was to compare experimentally conduction velocity (CV) estimates obtained with different estimation methods based on surface electromyogram (EMG) signals detected using five spatial filters. The filters investigated were the longitudinal single and double differential, transverse single and double differential, and normal double differential. The same surface EMG signals detected as described in Part 1 were used in this work. CV was estimated with four commonly used delay estimation techniques, i.e. from the distance between the peak values of two waveforms (with and without polynomial interpolation around the peak), and by the maximum likelihood estimate (MLE) based on two or more surface EMG channels. The average standard deviation of CV estimation (for all the MUs and the two muscles together) was 0.61 m s(-1) and 0.79 m s(-1) for the peak method, with and without interpolation, respectively, and 0.50 m s(-1) and 0.31 m s(-1) for the MLE method, from two and more surface EMG channels, respectively. Moreover, the mean of CV estimates varied by as much as 1 m s(-1) depending on the spatial filter used and the method adopted for CV estimation. Considering the dependence on the spatial filter only, the average (over all estimation methods) CV estimates obtained with the five spatial filters were 4.32 m s(-1) (normal double differential), 4.23 m s(-1) (longitudinal double differential), 4.61 m s(-1) (transverse double differential), 4.64 m s(-1) (transverse single differential) and 4.03 m s(-1) (longitudinal single differential). It was concluded that the comparison of single MU CV values obtained in different studies is critical if different spatial filters and processing techniques are used for their estimation. Higher estimates of CV were attributed to a smaller reduction in non-travelling signal components and thus were assumed to be positively biased.

Preparation of collagen scaffolds and their applications in tissue engineering

Freeze-dried collagen scaffolds can be used for a variety of medical tissue engineering applications. The pore structure of the scaffolds might play a decisive role for the inoculation, growth and differentiation of the cells. For a controlled 3D-cell growth the pore structure needs to be homogeneous and the pore size individually adjustable. For lyophilised scaffolds, the pore structure is determined by the ice crystal morphology during freezing under steady conditions. Scaffolds with a homogeneous pore structure and a range of pore size between 25 and 100 microns were reached. Cells such as preadipocytes, keratinocytes, and fibroblasts showed to adhere well to the collagen matrix.

Thermophysical properties of a monolayer tissue with respect to freeze-drying

Conservation of tissue structures by means of freeze-drying is still limited as the complex mechanisms taking place at molecular/cellular level are not fully understood. The successful application of hydroxyethyl starch (HES) in combination with maltose, sucrose, and trehalose as stabilizers of lipid bilayers/membranes in red blood cells suggests an extended use of this mixture of cryoprotectants. The effectiveness of such cryoprotectant solutions has been linked to changes in the thermophysical properties of cellular structures. This work deals, in a first step, with the thermophysical properties of a model monolayer tissue--onion epidermis--in binary aqueous solutions of dissacharides. First and second order phase transitions, i.e. melting, crystallisation, and glass transition, are characterised by means of Modulated Differential Scanning Calorimetry (MDSC).

[Arm motion analysis: a new method and its clinical application]

AIM

An investigation into the objective criteria of shoulder mobility possesses special meaning for diagnostic documentation, the evaluation of therapy and the effects of rehabilitation in the treatment of diseases of the shoulder. In order to ascertain the criteria which characterise shoulder mobility, it is necessary to have a tool available that is objective, comparable and allows the complexity, variability and range of motion to be recorded. Motion analysis represents one such standard procedure used to measure joint movement.

METHOD

Accordingly, a marker- based motion analysis of the wrist and elbow, a marker-based three-dimensional motion analysis system for the upper extremities was developed. We evaluated 10 healthy subjects without shoulder conditions and 8 patients with impingement syndrome (7 operative, 1 conservative therapy).

RESULTS

The healthy subjects revealed a reproducible motion curve for the specific motion tested. The curves were defined as the normal standard and we used them for comparative purposes. In the treatment group, an improvement of the 3D range of motion could be documented for the affected shoulder following rehabilitation.

CONCLUSION

It can be stated that this newly developed marker-based procedure for the three-dimensional motion analysis is suitable for recording complex unconstrained movements. This was found to be more relevant for the assessment of the ability of patients to manage the physical demands of daily living than traditional clinical tests. Furthermore, the information gained from motion analysis of the upper extremities will play a valuable role in the future for quality control during diagnosis and treatment, as well as for the design of shoulder rehabilitation programs.

A case study in designing speech interaction with a patient monitor

OBJECTIVE

New developments in speech interaction technology warrant the assumption that some of the interaction problems at anesthesia workplaces can be solved using speech interaction. One application might be the documentation of the anesthetic procedure.

METHOD

To investigate this hypothesis, a speech input system was developed for a commercially available patient monitor (Datex-Ohmeda AS/3 Anesthesia Monitor with Record-Keeper), which in addition to standard functions also facilitates the generation of the anesthesia record. The speech input system was based on the IBM ViaVoice speech recognition technology (version Millennium Pro). The speech input device was preliminarily tested by 5 anesthetists wearing surgical masks under laboratory conditions and through retrospectively documenting 4 to 5 anesthetic procedures (each 12 to 17 documentation entries) in a calm situation. The speech interactive documentation procedure was compared with the conventional keyboard documentation procedure.

RESULTS

The test persons achieved an overall word recognition rate between 72% and 92.4%. Between 76.5% and 97.7% of the single word commands could be completed without any corrections. The same qualifier held for 58.5% to 86.3% of the two- and three-word commands. Despite high speech recognition error rates, almost all documentation entries (236 of 238) could be finished using speech interaction. Comparing both documentation techniques, speech interaction was said to be more intuitive and caused less frustration than the keyboard documentation procedure. However, speech interactive documentation was rated less controllable because of the high speech recognition error rates and bccause the auditive feedback dialogues took too long.

CONCLUSIONS

Modern speech recognition tools are still not advanced enough to facilitate the design of applications with an almost natural speech interface and widespread user acceptance. Nevertheless, many tasks in anesthesia have the necessary characteristics to be optimally supported by speech interaction. In contrast to earlier approaches to speech-interactive anesthesia workplaces, successful application today depends on the question of design rather than solely on that of technology. Many of the constraints and drawbacks of current technology can be overcome through appropriate design measures. The goals must focus first on identifying task areas in intensive care where speech-interaction can yield real benefit in terms of work efficiency, and second on developing and evaluating an ergonomic design of speech interaction. The intended users seem to look forward to the incorporation of speech interaction at the workplace.

Evaluation of two new ecological interface approaches for the anesthesia workplace

OBJECTIVE

Currently, vital parameters are commonly displayed as trends along a timeline. However, clinical decisions are more often based upon concepts, such as the depth of anesthesia, that are derived by combining parameter relationships and additional context information. The current displays do not visualize such concepts and therefore do not optimally support the decision process. A new display should present an ecological interface (EI). The principle of EI design is to visualize all of the information necessary for decision making in one single display.

METHODS

In the first approach, we developed an EI that visualizes 35 relevant parameters for anesthesia monitoring. All of the parameters are generated by an anesthesia software simulator. Sixteen anesthetists had to administer two simulated general anesthetics: in one setting working only with the simulator's monitors ("Sim Only"), and in another setting working with the simulator's monitors in combination with the EI ("Combi1"). During each experiment, one unexpected critical incident (either blood loss or a cuff leakage) had to be identified. The control and monitoring behavior was analyzed by recording the subjects' eye movements and think-aloud protocol. With the help of the eye-tracking results, we re-designed the EI. The new EI was then tested with no eye tracking ("Combi2") on eight anesthetists under analogous conditions as in "Combi1."

RESULTS

Cuff leakage was identified significantly quicker in "Combi1" (7 of 8 cases; time (T): 65 s +/- 73 s) than in "SimOnly" (6 of 8 cases; T: 222 s +/- 187 s). Blood loss was identified in 5 of 8 cases (T: 215 s +/- 76 s) in "Combi1" as quickly as in "SimOnly" (all cases; T: 217 s +/- 72 s). In "Combi1," the EI was used as the main source of information (in 43 +/- 19% of time) and was frequently favored when identifying an evolving critical incident. In "Combi2," cuff leakage was identified in 7 of 8 cases (T: 70 s +/- 111 s) as quickly as in "Combi1." Blood loss was identified significantly quicker in all cases (T: 147 s +/- 62 s) in "Combi2" than in "Combi1" and in "SimOnly."

CONCLUSION

The results have shown that appropriately designed EIs may improve the anesthetist's decision making and focus attention on specific problems. Now, the findings have to be tested in future studies by widening the scope using other simulated scenarios and being closer to reality under real conditions in the OR. Eye tracking proved to be a useful method to analyze the anesthetists' decision making and appropriately re-design interfaces.

Area-to-amplitude ratio of the terminal phase of the belly-tendon detected motor unit potentials could be used to recognize reinnervated motor units

Besides the increased number of fibres, the reinnervated motor units (MUs) are characterised by an increased scattering the end-plates, greater desynchronization in the fibres' activation, greater dispersion in the diameters of the MU fibres and thus in propagation velocities along them. As a result, desynchronization in the moments, at which the excitation waves reach the fibres' ends, increases in reinnervated MUs. The possibility to recognize reinnervated MUs in short (hand) muscles on the basis of changes in duration of the terminal (second) phase of the belly-tendon detected motor unit potentials (MUPs) was examined by numerical experiments. A convolution model that took into account the finite fibre length, was used to calculate MUPs for distances typical of surface detection. It was shown that the ratio between the area of the terminal phase and its amplitude, as a measure of duration of the terminal phase, was sensitive to desynchronisation of the waves of excitation. The ratio was independent of the distance from the MU axis and of the volume conductor properties. Basing on the results obtained, we can conclude that the ratio reflects main functional compensations in reinnervated MUs and could be used for discrimination between reinnervated and normal MUs.

The presence of unknown layer of skin and fat is an obstacle to a correct estimation of the motor unit size from surface detected potentials

To overcome problems with a strong distance-dependence of the motor unit potentials (MUPs), different methods to estimate the MU location and size have been proposed. Distance-independence of the exponent of the power function, that describes the MUP distance decline, and homogeneity of the volume conductor, are assumed in all methods. Some of them consider the exponent value as unique, irrespective of persons, muscles and their functional state. One method estimates the current exponent value. We evaluate this method by computer simulation of MUPs in infinite and semi-infinite volume conductor. Our results show that although the first assumption is not fulfilled, it does not affect considerably the estimate of the MU location and size obtained for infinite or semi-infinite homogeneous volume conductor. The errors of the MU location can be insignificant even in inhomogeneous volume conductor with a layer of lower conductivity (skin and fat) between the muscle tissue and electrode. The accurate location of the MU electrical axis is, however, not a sufficient condition for a correct MU size estimation that depends considerably on actual parameters of the layer. Thus, the surface EMG could hardly be considered as non-invasive alternative to macro EMG for detection of the enlarged MUs.

Surface detected potentials of normal and reinnervated motor units: a simulation study for muscles consisted of short fibres

We aimed to check whether the characteristics used up to now in macro EMG to distinguish between normal and reinnervated motor unit potentials (MUPs), were suitable for surface detected MUPs. MUPs produced by normal and reinnervated MUs were simulated with a fast and precise convolution model. An increased number of fibres in the MU territory enhanced the amplitude, area and RMS of the MUP proportionally irrespective of the MU-electrode distance. An increased scatter of the end-plates and greater desynchronization in the fibres' activation decreased the MUP amplitude and affected the temporal characteristics of the MUP (duration of the negative phase and its area to amplitude ratio). The effects were more pronounced at shorter distances. At larger distances, the effect of the MU-electrode distance on temporal and amplitude characteristics of MUPs was much stronger than that of the parameters changed with reinnervation. We conclude that reinnervated MUs consisting of short fibres can not be distinguished from the normal ones by means of characteristics of MUP used in macro EMG. To discriminate reinnervated MUs non-invasively, the MUP amplitude should be normalized in respect of the MU-electrode distance or other MUP characteristics (independent of MU-electrode distance and sensitive to reinnervation) should be used.

Effect of hemolysis on oxygen and hematocrit measurements by near infrared reflectance spectroscopy

A short review of the principles of near infrared reflectance spectroscopy (NIRS) in whole blood is followed by a discussion on the influence of hemolysis. The increase of free plasmahemoglobin (PHb) has a strong influence on the continuous measurement of hematocrit and oxygen saturation (O(2)S) by NIRS. In view of the relative stability of hematocrit values in vivo this effect may be used to detect a change of the hemolysis rate induced by blood pumps in case of malfunction. The aim of this study is, therefore, the assessment of the hemolysis rate within an in vitro mock loop comprising a rotary blood pump by means of NIRS at constant hematocrit levels compared to the photometric reference method. Reflected light is measured by an integrated optical sensor working at three wavelengths (660 nm, 730 nm, and 830 nm). The experimental results demonstrate that the increase of free hemoglobin in plasma due to mechanical pumping leads to a decrease of detected reflected light at all three wavelengths. Influencing parameters such as adhering proteins on the sensor surface and the blood flow rate are briefly discussed. Finally, the possibility of using NIRS sensors for detecting malfunctions of blood pumps in vitro and in vivo is discussed, together with the option of using these sensors for supervision of long-term implantable pumps.

Control of pore structure and size in freeze-dried collagen sponges

Because of many suitable properties, collagen sponges are used as an acellular implant or a biomaterial in the field of tissue engineering. Generally, the inner three-dimensional structure of the sponges influences the behavior of cells. To investigate this influence, it is necessary to develop a process to produce sponges with a defined, adjustable, and homogeneous pore structure. Collagen sponges can be produced by freeze-drying of collagen suspensions. The pore structure of the freeze-dried sponges mirrors the ice-crystal morphology after freezing. In industrial production, the collagen suspensions are solidified under time- and space-dependent freezing conditions, resulting in an inhomogeneous pore structure. In this investigation, unidirectional solidification was applied during the freezing process to produce collagen sponges with a homogeneous pore structure. Using this technique the entire sample can be solidified under thermally constant freezing conditions. The ice-crystal morphology and size can be adjusted by varying the solute concentration in the collagen suspension. Collagen sponges with a very uniform and defined pore structure can be produced. Furthermore, the pore size can be adjusted between 20-40 microm. The thickness of the sponges prepared during this research was 10 mm.

Magnification of the pore size in biodegradable collagen sponges

In tissue engineering cells are often combined with a carrying structure with collagen being a suitable material to form a 3D-scaffold. A process to manufacture collagen sponges with an adjustable and homogeneous structure has been developed at the Helmholtz-Institute. Using this process, collagen suspensions are frozen directionally and subsequently vacuum-dried. One clinical application in which these scaffolds can be used is soft tissue reconstruction. Various soft tissue defects require an adequate replacement, e.g. in the case of severe burn wounds, or after tumour resections. Collagen (type I) sponges, which are cultured with preadipocytes, may be used to regenerate such defects. In this case, pore sizes of approximately 100 microm are desired to allow a complete differentiation of preadipocytes into adipocytes. Based on known technology to manufacture collagen sponges with an adjustable and homogeneous pore structure, research on the increase of pore size beyond the previous limit of 40 microm was necessary in order to enable soft tissue replacement. A scaffold with an average pore size of 100 microm was obtained.

Metabolism of surfactant phosphatidylcholine molecular species in cftr(tm1HGU/tm1HGU) mice compared to MF-1 mice

In cftr(tmIHGU/m1HGU) mice, an animal model designed to study pathophysiologic alterations due to the CFTR defect found in cysticfibrosis, surfactant phospholipids of bronchoalveolar lavage fluid (BALF) are increased. To study the metabolical basis of such increases, we intraperitoneally injected cft(tm1HGU/tm1HGU) mice [methyl-3H]choline and measured [methyl-3H]choline incorporation into phosphatidylcholine (PC) molecular species of lung tissue and BALF after 1.5 to 24 hours. MF1 and MF1 x cftr(tm1HGU/tm1HGU) hybrid mice served as controls. In tissue [methyl-3H]choline incorporation into total PC was constant for 24 hours and identical in control and cftr(tmIHGU/m1HGU) mice. However, from 7.5 to 24 hours there was a shift of [methyl-3H]choline incorporation from palmitoyloleoyl-PC and palmitoyllinoleoyl-PC towards PC species enriched in surfactant, dipalmitoyl-PC, palmitoylmyristoyl-PC, and palmitoylpalmitoleoyl-PC. The relative and absolute 3H-labels of PC species were identical for cftr(tmIHGU/m1HGU) compared to control mice. In BALF [methyl-3H]choline of total PC increased from 1.5 to 24 hours (R2 > .98), mainly due to [methyl-3H]choline-labelled dipalmitoyl-PC, in all experimental groups. In BALF from cftr(tmIHGU/m1HGU) mice, the [methyl-3H]choline label of total PC and individual PC species was significantly increased over control values after 24 hours, but not after 1.5 to 6 hours. Numbers and composition of BALF cells were not different between controls and cftr(tmIHGU/m1HGU) mice. We, conclude that increased alveolar phospholipid in cftr(tmIHGU/m1HGU) mice is likely due to decreased reuptake of surfactant.

Development of the MEDOS/HIA DeltaStream extracorporeal rotary blood pump

The DeltaStream blood pump has been developed for extracorporeal circulation with one focus on potential integration into simplified bypass systems (SBS). Its small size and an embedded electric motor are the basic pump properties. A variation of the impeller design has been performed to optimize hydraulic and hematologic characteristics. A simple impeller design was developed which allows flow and pressure generation for cardiopulmonary bypass applications. The option of a pulsatile flow mode for ventricular assist device applications also was demonstrated in vitro. Impeller washout holes were implemented to improve nonthrombogenicity. The pump was investigated for potential thermal hazards for blood caused by the integrated electric motor. It could be demonstrated that there is no thermal risk associated with this design. Durability tests were performed to assess the lifetime of the pump especially with regard to the incorporated polymeric seal. Seal lifetimes of up to 28 days were achieved using different blood substitutes. In animal tests using either the pump as a single device or in an SBS setup, biocompatibility, low hemolysis, and nonthrombogenicity were demonstrated. In summary, the DeltaStream pump shows great potential for different extracorporeal perfusion applications. Besides heart-lung machine and SBS applications, ventricular assist and extracorporeal membrane oxygenation up to several days also appear promising as potential applications.

An automatic camera-holding system for gynecologic laparoscopy

Ergonomic analysis of conditions prevailing during laparoscopy show that static holding work causes considerable problems. The surgeon's assistant is particularly affected, for example, by holding the endoscope optical system. To minimize strain for the entire operating team and to increase the range of activities that can be performed by the assistant, an automatic surgical camera-holding system was developed. Its value in clinical practice was tested in gynecologic laparoscopy, where it enabled the surgical team to work more comfortably.

Experimental MR imaging-guided interstitial cryotherapy of the brain

BACKGROUND AND PURPOSE

Hyperthermal ablation techniques such as laser or RF ablation require dedicated heat-sensitive MR imaging sequences for monitoring MR imaging--guided interventions. Because cryotherapy does not have these limitations, the purpose of this study was to evaluate the feasibility of MR imaging--guided percutaneous cryotherapy of the brain.

METHODS

An experimental cryoprobe with an outer diameter of 2.7 mm was inserted into the right frontal lobe of 11 healthy pigs under MR imaging control. Freezing procedures were monitored by using an interventional 1.5-T magnet and a gradient-echo sequence with radial k-space trajectories, a fast T2-weighted single-shot spin-echo sequence, and a T1-weighted single-shot gradient-echo sequence. In three animals, the procedure was also monitored by using dynamic CT. A freeze-thaw cycle with a duration of 3 minutes was repeated three times per animal. Follow-up MR images were obtained 3, 7, and 14 days after cryotherapy by using conventional MR sequences. Six animals were killed 7 days after intervention, and five animals were killed 14 days after intervention. The brains were sectioned, and the histologic findings of the lesions were compared with the MR imaging appearance.

RESULTS

No artifacts due to the probe were observed on the MR images or CT scans. The ice formation (mean diameter, 12.5 mm) was very well delineated as a signal-free sphere. MR monitoring of the freezing procedure yielded a significantly higher ice:tissue contrast than did CT. The size of the ice ball as imaged by MR imaging and CT during the intervention correlated well with the MR imaging appearance of the lesions at the 14-day follow-up examination and with the histologic findings. Histologically, coagulation necrosis and gliosis were found, surrounded by a transition zone of edema and a disrupted blood-brain barrier, corresponding to a contrast-enhancing rim around the lesions on follow-up MR images.

CONCLUSION

MR imaging-guided cryotherapy of the brain is possible and allows a precise prediction of the resulting necrosis. MR imaging of the freezing process does not require heat-sensitive sequences and is superior to CT for monitoring of cryoablation.