Non-invasive approach of motor unit recording during muscle contractions in humans

Information about the structural and functional characteristics of the motor unit (MU) is highly relevant for the diagnosis of neuromuscular disorders. Electromyography (EMG) is a suitable method for obtaining the information needed. The problem is the separation of the activity of one MU from others which are simultaneously active. Such investigations of single MU activity have commonly used invasive methods, e.g. employing a needle or a wire. Conventional surface-EMG methods have limited resolution and detect, at high contraction levels, multiple MU superimposed one on the other. The separation of the activity of a single MU can be achieved in a non-invasive way when highly specialised acquisition techniques are used. One approach, called high spatial resolution EMG (HSR-EMG), is based on the use of multi-electrode arrays in combination with a two-dimensional Laplace filter. The HSR-EMG permits the completely non-invasive detection of single MU activity even during maximal voluntary contractions. First applications have shown that the method provides a deeper insight into the functional and structural characteristics of the MU. In this paper the application of HSR-EMG to the diagnosis of neuromuscular disorders will be presented, and the latest results will be given of its application in the evaluation of treatment of patients with plexus lesion.

Development of recommendations for SEMG sensors and sensor placement procedures

The knowledge of surface electromyography (SEMG) and the number of applications have increased considerably during the past ten years. However, most methodological developments have taken place locally, resulting in different methodologies among the different groups of users.A specific objective of the European concerted action SENIAM (surface EMG for a non-invasive assessment of muscles) was, besides creating more collaboration among the various European groups, to develop recommendations on sensors, sensor placement, signal processing and modeling. This paper will present the process and the results of the development of the recommendations for the SEMG sensors and sensor placement procedures. Execution of the SENIAM sensor tasks, in the period 1996-1999, has been handled in a number of partly parallel and partly sequential activities. A literature scan was carried out on the use of sensors and sensor placement procedures in European laboratories. In total, 144 peer-reviewed papers were scanned on the applied SEMG sensor properties and sensor placement procedures. This showed a large variability of methodology as well as a rather insufficient description. A special workshop provided an overview on the scientific and clinical knowledge of the effects of sensor properties and sensor placement procedures on the SEMG characteristics. Based on the inventory, the results of the topical workshop and generally accepted state-of-the-art knowledge, a first proposal for sensors and sensor placement procedures was defined. Besides containing a general procedure and recommendations for sensor placement, this was worked out in detail for 27 different muscles. This proposal was evaluated in several European laboratories with respect to technical and practical aspects and also sent to all members of the SENIAM club (>100 members) together with a questionnaire to obtain their comments. Based on this evaluation the final recommendations of SENIAM were made and published (SENIAM 8: European recommendations for surface electromyography, 1999), both as a booklet and as a CD-ROM. In this way a common body of knowledge has been created on SEMG sensors and sensor placement properties as well as practical guidelines for the proper use of SEMG.

Movement biomechanics goes upwards: from the leg to the arm

The analysis of lower limb movements has been well established in biomechanics research and clinical applications for a long time. For these studies, powerful and very advanced tools have been developed to measure movement parameters and reaction forces. The main focus of interest aims towards gait movements while the understanding of the basic concepts is supported by numerous models. Definitions of physiological ranges and detection of pathological changes in movements open an increasingly valuable clinical field of application. If, however, the primary function of the upper extremities as highly variable and adaptive organ for manipulating tasks is the subject of interest, the situation becomes considerably more complex. The nature of free arm movements is completely different from being restricted, repeatable or cyclic as compared to gait. Therefore, the transfer of the knowledge and experience gained in lower extremity movement analysis to the analysis of upper extremities turns out to be difficult. A proposal for how to proceed in measurements, e.g. where to place the markers and how to calculate movements and angles of segments involved, will be discussed which results in the description of the joint movements of wrist, elbow and shoulder joint. The definition of the motion is a specific step in upper extremity motion analysis which is important in terms of repeatability and significance of the results. An example of assessing movement disorders in children with plexus lesion will illustrate the implications and the potential of upper extremity movement analysis in clinical applications.

Variation of the HES concentration for the cryopreservation of keratinocytes in suspensions and in monolayers

It has recently been shown that keratinocytes, both in suspension and in monolayers, can be successfully cryopreserved with hydroxyethyl starch (HES) (6, 9). HES is a nontoxic biodegradable macromolecule which is clinically approved as a plasma expander and which has already been used for the cryopreservation of red blood cells (10, 11). In this study we varied the HES concentration between 0 and 10 wt% in 2% steps for suspended cells and between 0, 4, 6, 8, and 10 wt% for monolayer cells in order to determine the effect on the survival rate and metabolic activity after cryopreservation. The experiments with the suspended cells were performed both with and without NCS. Cryopreserved keratinocytes can be transplanted onto patients for the treatment of deep dermal burns and leg ulcers. In this study, we achieved a survival rate of 80% for the suspended cells (10 wt% HES, 3 degrees C/min) and a survival rate of even 88% when the cells were cryopreserved as a monolayer using the same parameters. The addition of NCS did not improve the results for the suspended cells significantly.

[CRIGOS: development of a compact robot for image-guided orthopedic surgery]

In this paper, we present a medical robot system dedicated to support the surgeon during challenging tasks within orthopedic interventions. The main goal of this work is to develop a system as technically simple as the surgical requirements allow to keep its cost and complexity to a minimum. Therefore, we primarily focus on calibrated X-ray imaging for image acquisition, an easy registration procedure and robotic execution using a positioning device with simple parallel kinematics. Examples of different orthopedic interventions using the compact robot system for image-guided orthopedic surgery (CRIGOS) are presented, as well as various modes of execution of the device.

A small pulsatile blood pump for ventricular support during end-stage heart failure

A displacement blood pump to support the natural heart of patients for recovery from end-stage heart failure has been developed. This electromechanical pusher plate pump has a very compact and extremely flat design. The design goal was achieved by developing a novel gear system based on the principle of a swash plate. The blood pump and cannulae can be placed within the thoracic cavity between the lungs and ribcage. The first labtype model delivers an output of 3.1 L/min against an aortic pressure of 100 mm Hg at 120 bpm.

CRIGOS: a compact robot for image-guided orthopedic surgery

The CRIGOS (compact robot for image-guided orthopedic surgery) project was set up for the development of a compact surgical robot system for image-guided orthopedic surgery based on user requirements. The modular system comprises a compact parallel robot and a software system for planning of the surgical interventions and for supervision of the robotic device. Because it is not sufficient to consider only technical aspects in order to improve in clinical routine the therapeutic outcome of conventional interventions, a user-centered and task-oriented design process has been developed which also takes human factors into account. The design process for the CRIGOS system was started from requirement analysis of various orthopedic interventions using information gathered from literature, questionnaires, and workshops with domain experts. This resulted in identification of conventional interventions for which the robotic system would improve the medical and procedural quality. A system design concept has been elaborated which includes definitions of components, functionalities, and interfaces. Approaches to the acquisition of calibrated X-rays will be presented in the paper together with design and evaluation of a first human-computer interface. Finally, the first labtype parallel robot based on low-cost standard components is presented together with the first evaluation results concerning positioning accuracy.

Ergonomic evaluation of an ecological interface and a profilogram display for hemodynamic monitoring

OBJECTIVE

Comprehensive monitoring of the patient state and subsequent decision making is an essential part of the task of an anaesthetist. The physicians' decision making process is based upon a concept of partly abstract physiologic parameters such as depth of anaesthesia or contractility. This concept is derived from the measured parameters given on todays' trend displays in addition to context information available for the anaesthetist. We investigated two alternative approaches of display design for hemodynamic monitoring: 1) integrated displays based on ecological interface design, and 2) profilogram displays based on intelligent alarms.

METHOD

To evaluate differences in decision making, the two displays and a trend display were compared in an experimental set-up with computer simulated vital parameter curves. From a start state with random parameter deviations from the ideal state, subjects had to achieve the ideal circulatory performance as fast as possible by manipulating vasomotor tone, heart rate, blood volume and contractility. To analyse subjects' decision making process, eye-tracking, event-logging, and the method of think aloud protocols were used. Twenty anaesthesiologists performed 113 experiments (approximately 2 with each display).

RESULTS

The anaesthetists failed to achieve the task in 37% using the trend display, in 19% using the profilogram display, and in 13% using the ecological interface. Hence, a safer task solution was possible with the ecological interface and the profilogram display but at the expense of various performance parameters such as higher trial time, more interactions with the simulated system, and more frequent eye movements. In contrast to the trend display and the profilogram display, where anaesthetists were mainly focussed on controlling the left atrial pressure, such an behaviour was less observed with the ecological interface.

CONCLUSION

Our results have shown that subjects came to more effective solutions with the traditional trend display. The main reason for this result may be their years of experience with this kind of display type. Regarding safe and goal-intended decision finding, the results are encouraging for further experiments with redesigned ecological displays. But these displays ought to have smoother changes with respect to the traditional trend displays. Furthermore, new experiments have to be performed under real or fairly real (e.g. together with an anaesthesia simulator) conditions to underline the positive results for ecological interfaces.

Freeze-drying of red blood cells: how useful are freeze/thaw experiments for optimization of the cooling rate?

A red blood cell suspension, prepared according to a high-yield HES cryopreservation protocol, was frozen at selected cooling rates of 50, 220, 1250, 4200, and 13,500 K/min. After either thawing or vacuum-drying, the cell recovery was determined using a modified saline stability test. As expected, the recovery of thawed samples followed the theory of Mazur's two-factor hypothesis. The best result was found at a cooling rate of 220 K/min. In contrast, the recovery of freeze-dried and rehydrated samples was very poor at that rate, but maximal at 4200 K/min where thawing caused almost complete hemolysis. This discrepancy is attributed to different damaging mechanisms involved with the respective sample processing subsequent to freezing. While thawing leads to increased devitrification and recrystallization at supraoptimal cooling rates for cryopreservation, the resultant almost vitreous sample structure seems to be advantageous for vacuum-drying. It can be concluded that freeze/thaw experiments are not sufficient for optimization of the cooling rate for freeze-drying.

Cryopreservation of keratinocytes in a monolayer

The cryopreservation of cells in tissues is one of the major challenges in current cryobiology, especially with regard to the progressively increasing field of tissue engineering. It is very questionable whether protocols which were developed for the cryopreservation of isolated cells are also applicable for cells in more complex structures, such as tissues. As a starting point toward cryopreservation of these three-dimensional structures, the aim of this study was to find an optimum cryopreservation protocol for keratinocytes in a monolayer (two-dimensional structure). These epidermal cells can be transplanted as a monolayer grown on an appropriate matrix for the treatment of deep-dermal burns and leg ulcers. The successful cryopreservation of such transplants would offer the advantage of long-term storage and immediate availability of the transplant. In our study, the variables investigated were the cryoprotective solution and the cooling rate. In order to find a nontoxic cryoprotective agent (CPA) which could be transplanted without an additional washing step, we included hydroxyethyl starch (HES) as a possible CPA in our experimental protocol with the commonly used CPAs Me(2)SO, glycerol, and ethylene glycol. For the evaluation, the cell survival rate was determined by dye exclusion (trypan blue) and the cell metabolism was investigated by cell activity assay (alamarBlue). In conclusion, the cryopreservation protocol with 10 wt.-% HES resulted not only in the highest survival rate (72%) but also in the highest metabolic activity of the cells after thawing; comparable values for the other CPAs were: Me(2)SO, 48%; glycerol, 8%; and ethylene glycol, 10%.

Platelet function and hemolysis in centrifugal pumps: in vitro investigations

The effects of centrifugal pumps on blood components other than erythrocytes, namely platelets and their interaction with the coagulation system, are not very well known. In a comparative study with three centrifugal pumps (BioMedicus BP-80, St. Jude Isoflow, and Sarns Delphin) and the Stockert roller pump hemolysis, platelet counts, thromboplastin and partial thromboplastin times, as well as resonance thrombography (RTG) parameters for the assessment of platelet and coagulation function were evaluated in vitro. Normalized indices of hemolysis (NIH) with ACD anticoagulation after 360 minutes were 0.008+/-0.004 (Isoflow), 0.018+/-0.017 (BP-80), 0.085+/-0.051 (Delphin), and 0.049+/-0.010 g/1001 (roller pump). Plasmatic coagulation was activated in all circuits. Platelet function was severely inhibited by the BP-80, indicated by increase in RTG platelet time to 358%+/-150% of initial values compared to 42%+/-29% (Isoflow), 40%+/-20% (Delphin), and 12%+/-10% (roller pump). Fibrin polymerization was affected similarly. The large surface area of the BP-80 leads to an extensive activation of platelets and plasminogen.

A marker-based measurement procedure for unconstrained wrist and elbow motions

A protocol is proposed to obtain the joint angles of wrist and elbow from tracked triads of surface markers on each limb segment. Cuffs placed on the limb support the rigidity of the triads. Additional markers are used to mark the approximate positions of joints. Corrections of surface marker data for skin motion are derived from a priori knowledge about plausible joint motions. In addition, ill-conditioned states are trapped when the elbow is nearly fully extended. The protocol is applied to sample motions which demonstrate the use and the effect of the corrections. The results show that the model assumptions are reasonable and that accurate joint rotations can be obtained. The correction steps prove to be an essential part of upper-extremity movement analysis.

Leakage flow at mechanical heart valve prostheses: improved washout or increased blood damage?

BACKGROUND AND AIMS OF THE STUDY

An essential problem of mechanical heart valve (MHV) prostheses is the risk of thromboembolic events and consequent need of lifetime anticoagulation due to unnatural hemodynamics that results in traumatization of red blood cells and platelets. The precise spatial and tidal localization of blood-damaging events within the flow is poorly understood. The present study addresses the question whether leakage flow at MHV, which is claimed to improve washout in the hinge areas of microthrombi and platelet-activating agents, is responsible for significant blood damage.

METHODS

This study investigated leakage flow in vitro, primarily within turbulent leakage jets of currently used mechanical valves. St. Jude Medical, Sorin Bicarbon, Duromedics-Edwards and CarboMedics valves were analyzed in the mitral position of a circulatory mock loop. Jet configuration was determined by echocardiography; velocity and shear stress distributions within jets were measured using laser-Doppler anemometry (LDA). A blood damage index (BDI) was developed in terms of lactate dehydrogenase release by platelets and hemoglobin release by red blood cells (RBC), as a function of exposure time and shear stresses within the flow field. BDIs were validated by direct measurement of hemolysis caused by leakage flow, using porcine blood.

RESULTS

All valves showed characteristic and reproducible jet patterns, mainly emerging from the hinge areas. Maximum velocities up to 1.7 m/s were measured. Maximum turbulent shear stresses > 80 Pa were found. The investigated MHV revealed significant differences in calculated BDIs. The Sorin Bicarbon had a significantly lower BDI for RBC damage, as well as for platelet damage; this was validated by direct hemolysis measurements.

CONCLUSIONS

The relevance of the leakage-induced blood damage was demonstrated from a literature investigation of hemolysis as a function of valve type and implant position.

Imaging of interstitial cryotherapy--an in vitro comparison of ultrasound, computed tomography, and magnetic resonance imaging

RATIONALE AND OBJECTIVES

To evaluate the imaging capabilities of ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) in monitoring interstitial cryotherapy and to compare them with visual control.

METHODS

An experimental MR-compatible, vacuum-insulated and liquid nitrogen-cooled cryoprobe was inserted under in vitro conditions into a porcine liver, which was kept at a temperature of 37 +/- 1 degrees C, in a water bath with continuous stirring. The freezing procedure was controlled macroscopically, by US (Toshiba Sonolayer, 7.5-MHz linear array transducer), by CT (Siemens Somatom Plus, slice thickness 2-8 mm, 165-210 mA at 120 kV), and by MRI (Philips Gyroscan ACS-NT, FFE TR/TE/FA = 15/5.4/25 degrees, T1-SE 550/20, T2-TSE 1800/100) after the iceball reached its maximum size.

RESULTS

The maximum iceball diameter around the probe tip was 12.0 mm by visual control, 12.4 mm by US, 12.7 mm by CT, and within 12.8 mm by spin echo sequences and 11 mm by gradient echo sequence. Due to the nearly signal-free appearance of the frozen tissue on MR images, the ice/tissue contrast on T1-weighted and gradient echo images was superior to T2-weighted images and CT images. Sonographically, the ice formation appeared as a hyperechoic sickle with nearly complete acoustic shadowing.

CONCLUSION

Due to the better ice/tissue contrast, T1-weighted or gradient echo MR images were superior to CT and US in monitoring interstitial cryotherapy. Gradient echo sequences generally underestimated the ice diameter by 15%.

Procedure for the semi-automatic detection of gastro-oesophageal reflux patterns in intraluminal impedance measurements in infants

The diagnosis of gastro-oesophageal reflux (GOR) is of great interest for paediatric gastroenterologists. pH monitoring is the commonly used procedure for GOR diagnosis but a major amount of postprandial GOR is missed due to the mostly non-acidic gastric contents in infants. The multiple intraluminal impedance technique is based on the recording of the impedance changes during bolus transport inside the oesophagus. It is the first method which allows the pH-independent, long-term registration of GOR. The use of the impedance technology in clinical practice has been limited so far by the time-consuming, visual evaluation of the impedance traces. The new approach of a semi-automatic analysis of the impedance measurements allows the automated detection of reflux patterns. It is based on event marking and an optimised feature description of the impedance traces combined with a fuzzy system for pattern recognition. The classifier is developed and tested on 50 investigations in infants. Compared to the comprehensive, multiple visual evaluation the achieved precision is 75% sensitivity and 48% positive prediction. In comparison to a single visual evaluation the analysis of the automatically proposed patterns corresponds to a 96% reduction of the evaluation time with no loss of precision. Thus the applicability of the impedance technology is enhanced significantly. A combined measurement of pH and impedance gives evidence about the occurrence of GOR, its pH and the acidic exposure of the oesophagus.

[Combined pH measurement and multiple impedance variation assessments--validation of a new technique for detection of non-acid reflux in the esophagus]

In 10 patients with gastroesophageal reflux disease, defective lower esophageal sphincter and normal motility pH and impedance were measured parallel over 24 hours. All patients had a reflux score > 40 with a total of 736 reflux episodes registered by the pH metry of which 724 (sensitivity: 98.9%) were recognized by impedancemetry and with additional 292 reflux phases registered at a stomach pH > 4 by the impedancemetry of which none was recognized by the pH metry as a reflux of pH > 7. With the multiple impedancemetry a reliable recognition of gastroesophageal reflux is possible, independently of the pH and this makes it possible to recognize gastroesophageal reflux also at a non acid milieu of the stomach, e.g. under acid suppression medication or after stomach resection.

Freeze-drying of red blood cells at ultra-Low temperatures

The hemolysis of human red blood cells (RBCs) after freeze-drying and resuspension depends on the vacuum-drying temperature. In an experimental study, RBCs were first solidified based on a modified high-yield cryopreservation protocol in the presence of hydroxyethyl starch and maltose. Afterward, they were vacuum-dried in a special low-temperature freeze-drying device at selected shelf temperatures between -5 and -65 degrees C. Subsequently, the dried samples were resuspended in an isotonic, phosphate-buffered saline solution. The hemolysis was determined according to a modified saline stability test. It decreases with a decreasing shelf temperature until a minimum is reached at -35 degrees C. A further decrease of the shelf temperature has no beneficial effect; the hemolysis even increases. To interpret these results, we assume that the hemolysis depends on two contrary damaging effects: (1) the higher the shelf temperature, the higher the probability of structural damages occurring during drying; (2) the lower the shelf temperature, the lower the driving force for water transport; this may lead to an incomplete intracellular dehydration which means that the cells are not in a glassy state at ambient temperature.

[Experimental MRI-controlled cryotherapy of the brain with almost real-time imaging by radial k-space scanning]

PURPOSE

To test radial k-space scanning by MR fluoroscopy to guide and control MR-guided interstitial cryotherapy of the healthy pig brain.

METHODS

After MR tomographic planning of the approach, an MR-compatible experimental cryotherapy probe of 2.7 mm diameter was introduced through a 5 mm burr hole into the right frontal brain of five healthy pigs. The freeze-thaw cycles were imaged using a T1-weighted gradient echo sequence with radial k-Space scanning in coronal, sagittal, and axial directions.

RESULTS

The high temporal resolution of the chosen sequence permits a continuous representation of the freezing process with good image quality and high contrast between ice and unfrozen brain parenchyma. Because of the interactive conception of the sequence the layer plane could be chosen as desired during the measurement. Ice formation was sharply demarcated, spherically configurated, and was free of signals. Its maximum diameter was 13 mm.

CONCLUSIONS

With use of the novel, interactively controllable gradient echo sequence with radial k-space scanning, guidance of the intervention under fluoroscopic conditions with the advantages of MRT is possible. MR-guided cryotherapy allows a minimally-invasive, precisely dosable focal tissue ablation.

Non-invasive detection of the single motor unit action potential by averaging the spatial potential distribution triggered on a spatially filtered motor unit action potential

For research as well as diagnostic applications the non-invasive detection of the activity of single motor units is of interest. The most direct information is expected to be found in monopolarly recorded data. But when an array of surface electrodes is used for the monopolar recordings of the potential distribution on the skin, in most cases an additional invasive needle electrode is utilized to detect the exact points in time when a certain motor unit is firing. With this supplementary information, an averaging of the monopolar EMG tracings can be performed. In this paper, a completely non-invasive methodology is presented which replaces the invasive needle by a spatial filtering procedure. The EMG signals from the m. biceps brachii are recorded monopolarly with an electrode array. Afterwards, a spatial filtering procedure, called normal double differentiating filter, is applied to the data. The EMG signals obtained are investigated by means of an amplitude threshold to distinguish the activity of different motor units. The point of the maximum amplitude of the selected peaks then is used as trigger point to average the monopolar EMG data. The time courses of the motor unit action potential signals found after applying the described procedure show similar shapes, while two different components are to be identified: corresponding to the spread of the excitation, one is referring to stationary, the other to travelling events. These results justify the possibility to replace the needle electrode to obtain a trigger event in the future by the non-invasive spatial filtering procedure.