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Biomedical subjects

G Rau

Publications and source records attributed to G Rau.

At least 73 records · Page 4Linked to original sources
PubMed1998

In vitro calcification of pericardial bioprostheses.

BACKGROUND AND AIM OF THE STUDY: The lifetime of bioprosthetic heart valves is limited by calcification. To investigate the calcification behavior of bioprostheses and gain insight into the etiology of valve calcification, a test protocol for accelerated valve calcification was developed. This protocol includes a pulsatile valve tester, a synthetic calcification fluid, and non-destructive radiographic assessment of calcification sites. About 40 porcine bioprostheses from different manufacturers have been investigated previously using this test protocol and showed that valves exhibited different calcification patterns and even different degrees of calcification within their leaflets. A positive correlation of calcification versus tissue anomalies/stress concentrations (r = 0.72; n = 29 valves) and lipid deposits (r = 0.81) was found. In the present study, bovine pericardial valves were investigated in comparison with porcine valves. METHODS: Four bovine pericardial and two porcine mitral valves (Baxter) with a tissue annulus diameter (TAD) of 29 mm (one 27 mm) were investigated in parallel under identical test conditions. The valves were cyclically loaded at 300 per min with a delta p of 110 mmHg at 37 degrees C for up to 19 x 10(6) cycles. The synthetic calcification fluid was changed weekly. Sites of calcification were assessed by microradiography. Radiographs were analyzed by PC images processing with respect to the degree of calcification, defined as calcified surface area in relation to total leaflet surface area. RESULTS: This analysis showed that, for bovine pericardial valves, the mean degree of calcification increased by 14% and 20% after 12 and 19 x 10(6) cycles, respectively. Under identical conditions, the mean degree of calcification of porcine valves increased by 28% and 37%. CONCLUSIONS: Pericardial valves appear less prone to calcification than porcine valves. Further studies must be performed in order to prove this finding since, as recognized previously in porcine valves, other factors such as tissue or manufacturing anomalies may be as important as the tissue source itself.

Animals↗
PubMed1998

In vitro thrombogenicity testing of artificial organs.

Thromboembolic complications remain as one of the main problems for blood contacting artificial organs such as heart valves, bloodpumps and others. In vitro evaluation of thrombogenesis in prototypes has not previously been part of the standard evaluation of these devices. In comparison to hemolysis testing, evaluation of the thrombogenic potential is more difficult to perform because of the complexity of the blood coagulation system. We present an in vitro testing procedure that allows the accelerated examination of the thrombogenic potential of different types of blood pumps. Additionally, first results are presented that indicate the reliability of the accelerated clotting test for mechanical heart valves. Results for the centrifugal pump BioMedicus and two microaxial pumps have shown typical thrombus formation at locations such as bearings. The results indicate that the accelerated clotting test is an excellent addition to the much more expensive animal testing of artificial organs or assist devices. In vitro testing permits studies of thrombus formation to be performed at an early stage and at low costs and also facilitates a more precise investigation of device areas known to be potential hot spots for thrombus formation.

Animals↗
PubMed1998

[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.

Electric Impedance↗
PubMed1997

Diagnostic yield of noninvasive high spatial resolution electromyography in neuromuscular diseases.

High Spatial Resolution electromyography (HSR-EMG), a new kind of noninvasive surface EMG based on a spatial filtering technique, was evaluated with respect to the diagnosis of neuromuscular diseases. HSR-EMG measurements were recorded from 61 healthy subjects and 72 patients with different neuromuscular diseases and analyzed quantitatively. The results indicate that a few parameters such as muscular conduction velocity, dwell time over root mean square, autocorrelation function, and chi-value are sufficient to recognize and classify specific signal alterations due to neuromuscular disorders. A diagnostic evaluation procedure calculating automatically the most probable diagnosis from the parameter results could assign the correct diagnosis to about 81% of the investigated patients and healthy subjects. Myopathic disorders were recognized with a sensitivity of 85% (specificity: 97%), neuropathic disorders with a sensitivity of 68% (specificity: 98%). We conclude that HSR-EMG shows a diagnostic validity similar to that described in literature for needle EMG. Moreover, the noninvasive technique provides the advantage of a simple and painless application.

Adolescent↗
PubMed1997

Noninvasive approach to motor unit characterization: muscle structure, membrane dynamics and neuronal control.

The standard surface EMG reflects the compound activity of a high number of motor units which is finally due to its low spatial resolution in the detection of the potential distribution on the skin surface. Therefore, detailed information about the structural and functional characteristics of the muscle consisting of populations of motor units, like the functional anatomy, the excitation spread or the innervation pattern cannot be obtained from the standard surface EMG. A novel noninvasive EMG-procedure with high spatial resolution (HSR-EMG) allows in contrast to the standard surface EMG even the detection of the single motor unit activity. In this way, the noninvasive determination of detailed information about the muscle structure, the membrane dynamics and the neuronal control becomes possible. First applications of the HSR-EMG have shown that especially the noninvasively measured conduction velocity of the excitation is highly affected by physiological details, like the muscle temperature, the relative muscle fibre diameter or inhomogeneities in the connective tissue forming part of the volume conductor around the muscle. From the results of the HSR-EMG investigations it can be concluded that the information about the structural and functional characteristics of the muscle as well as a deeper insight in the active state of the muscle is essential for a correct interpretation of the standard surface EMG.

Animals↗
PubMed1997

Design and validation of an intelligent patient monitoring and alarm system based on a fuzzy logic process model.

The process of patient care performed by an anaesthesiologist during high invasive surgery requires fundamental knowledge of the physiologic processes and a long standing experience in patient management to cope with the inter-individual variability of the patients. Biomedical engineering research improves the patient monitoring task by providing technical devices to measure a large number of a patient's vital parameters. These measurements improve the safety of the patient during the surgical procedure, because pathological states can be recognised earlier, but may also lead to an increased cognitive load of the physician. In order to reduce cognitive strain and to support intra-operative monitoring for the anaesthesiologist an intelligent patient monitoring and alarm system has been proposed and implemented which evaluates a patient's haemodynamic state on the basis of a current vital parameter constellation with a knowledge-based approach. In this paper general design aspects and evaluation of the intelligent patient monitoring and alarm system in the operating theatre are described. The validation of the inference engine of the intelligent patient monitoring and alarm system was performed in two steps. Firstly, the knowledge base was validated with real patient data which was acquired online in the operating theatre. Secondly, a research prototype of the whole system was implemented in the operating theatre. In the first step, the anaesthetists were asked to enter a state variable evaluation before a drug application or any other intervention on the patient into a recording system. These state variable evaluations were compared to those generated by the intelligent alarm system on the same vital parameter constellations. Altogether 641 state variable evaluations were entered by six different physicians. In total, the sensitivity of alarm recognition is 99.3%, the specificity is 66% and the predictability is 45%. The second step was performed using a research prototype of the system in anaesthesiological routine. The evaluation of 684 events yielded a sensitivity, specificity and predictability of the alarm recognition of more than 99%.

Anesthesiology↗
PubMed1997

Principles of high-spatial-resolution surface EMG (HSR-EMG): single motor unit detection and application in the diagnosis of neuromuscular disorders.

The most detailed information about the structural and functional characteristics of the muscle can be gained from the single motor unit (MU) action potential. In addition, information about the activity of a single MU is essential for the diagnosis of neuromuscular disorders. Due to the low spatial resolution of conventional bipolar surface electromyography (EMG), the resulting signal is a superposition of a large number of simultaneous active MUs. The difficulty is in separating the activity of a single MU from simultaneous active adjacent MUs. In contrast to other non-invasive EMG procedures, the high-spatial-resolution-EMG (HSR-EMG), which is based on the use of a multi-electrode array in combination with a spatial filter procedure, allows the detection of single MU activity in a non-invasive way. It opens access to the excitation spread and enables the determination of the conduction velocity in single MUs, and the localization of the endplate region. In addition, HSR-EMG detects changes in the electrical activities of the MUs which are typical in neuromuscular disorders. Using HSR-EMG it was possible to identify 97% of all investigated volunteers and patients with muscular or neuronal disorders. Therefore, HSR-EMG is suitable as a tool for the non-invasive diagnosis of neuromuscular disorders.

Journal Article↗
PubMed1997

Improvement of spatial resolution in surface-EMG: a theoretical and experimental comparison of different spatial filters.

The conventional bipolar surface electromyography (EMG) technique detects, due to its low spatial resolution, the superimposed electromyographic activity of a large number of motor units (MU's). In superficial muscles the isolated action potentials of the most superficial MU's can be recorded noninvasively by means of surface electrodes, if the method of spatial filtering, in connection with electrode arrays, is used. Up to now, only filters with an anisotropic transfer function have been used. As the surface potential distribution generated by the excitation of the MU's contains spatial frequencies in the anisotropic range of those filters, it can be assumed that isotropic spatial filters detect the single MU activity more effectively. In the present study, different isotropic and anisotropic filters have been compared by means of theoretical field simulations and experiments in volunteers. A tripole model for an excited MU was used as the basis for simulating the spatial extension of the filter response for each of the investigated filters. The spatial extension is an indicative of the spatial resolution. For the experimental validation, the total number of single motor units was not directly investigated, but the signal-to-noise ratio (SNR) has been determined. Therefore, the potential distribution generated on the skin surface during maximum voluntary contraction has been simultaneous spatially filtered with each of the investigated filters. The simulations show that an isotropic spatial filtering procedure reduces the spatial extension of the filter response and improves the spatial resolution of the EMG-recording arrangement in comparison to anisotropic spatial filters up to 30%. In other words, the spatial selectivity of the arrangement is increased. This improvement in the filter performance is more pronounced for MU's located close to the skin surface than for MU's more distantly located. Additionally, this theoretical improvement in selectivity depends on the direction of the excitation spread relative to the filter alignment. However, the investigations also show that isotropic filters offer an advantage, compared to anisotropic filters, only when the investigated MU is located extremely close to the filter input. The results of the simulations can be confirmed by the experimental investigations. An improvement of 11% in the SNR, relative to anisotropic spatial filters, can be established when using an isotropic spatial filter. This experimental improvement in selectivity is less than the theoretical improvement because the experimentally investigated MU's have less portion in the anisotropic range of the filters than the simulated one at best.

Anisotropy↗
PubMed1997

The implantable fuzzy controlled Helmholtz-left ventricular assist device: first in vitro testing.

To perform first experimental tests for validation of a new left ventricular assist device (LVAD) with a high efficiency energy converter, a new pump design and a novel type of perfusion control, a functional labtype, were manufactured. With a stroke volume of 65 ml, a total pump housing volume of 450 ml (including valves and connectors), and a weight of 430 g, it is one of the smallest and lightest implantable pulsatile electromechanical LVADs. Pulsatile operation is generated by a special reduction and displacement gear which transforms a uniform rotational movement of a sensorless, electronically commutated DC motor into a translatory pusher plate movement. A prolonged duration for filling (60% of the cycle time) supports full-empty pumping and consequently a high overall pump efficiency. Active adaptation of output flow to organ perfusion demand is achieved by changing the rotational speed of the motor by means of a sensorless fuzzy controller, which detects preload and afterload induced effects at the motor current input. First in vitro test results obtained within a circulatory mock loop that simulates physiological preloads and afterloads are presented. They comprise preload sensitivity and the function of the novel perfusion controller as well as preload and afterload related flow data. The results prove the feasability of the energy conversion with the novel gear and control concept for an implantable electromechanical pulsatile LVAD.

Animals↗
PubMed1997

A new blood pump for cardiopulmonary bypass: the HiFlow centrifugal pump.

Centrifugal blood pumps are considered to be generally superior to the traditionally used roller pumps in cardiopulmonary bypass. In our institute a new lightweight centrifugal sealless blood pump with a unique spherical thrust bearing and with a magnetic coupling was developed, the HiFlow. The small design makes the pump suitable for applications in complex devices or close to a patient. Hemolysis tests were carried out in which the BioMedicus pump BP-80 and a roller pump were used as reference. The centrifugal pump HiFlow showed the least blood trauma within the group of investigated pumps. In summary, the HiFlow pump concept with its low priming volume and limited contact surfaces shows great potential for clinical applications in cardiopulmonary bypass. Also, the possibility of using the pump as a short-term assist device with an option of a pulsatile driving mode was demonstrated.

Animals↗
PubMed1997

Abnormal postprandial duodenal chyme transport in patients with long standing insulin dependent diabetes mellitus.

BACKGROUND: Patients with long standing diabetes mellitus frequently have upper gut dysmotility. Gastroparesis has been well studied, whereas detailed data on duodenal motor function are limited. AIMS: To characterise postprandial duodenal chyme transport in such patients. METHODS: Intraluminal multiple impedance measurement, recently introduced as a novel technique for investigation of chyme transport, was used to study postprandial duodenal chyme flow in 10 patients with long standing insulin dependent diabetes mellitus with gastroparesis, and 10 healthy volunteers. RESULTS: Four distinct transport patterns of chyme, termed bolus transport events (BTEs), were found in both groups and could be characterised as: short distance propulsive; simple long distance propulsive; retrograde; and complex long distance propulsive. Diabetic patients had significantly lower numbers of propulsive BTEs (p < 0.01), and higher proportions of retrograde BTEs and complex long distance BTEs (p < 0.05) than control subjects, whereas the proportion of simple long distance BTEs was significantly lower (p < 0.05). The mean propagation velocities of the BTEs were similar in both groups. CONCLUSION: Abnormal postprandial duodenal chyme transport was found in patients with long standing insulin dependent diabetes mellitus. This is characterised by transport disorganisation and may result in disturbed chyme clearance.

Adult↗
PubMed1997

Dynamics of esophageal bolus transport in healthy subjects studied using multiple intraluminal impedancometry.

The dynamics of a bolus transport through the esophagus are largely unexplored. To study this physiological process, we applied multiple intraluminal impedancometry in 10 healthy subjects. Three different protocols were used: 1) liquid bolus administered with subject supine, 2) liquid bolus with subject upright, or 3) semisolid bolus with subject supine. Transit of different parts of a bolus (bolus head, body, and tail) was analyzed at different anatomic segments, namely the pharynx and the proximal, middle, and distal thirds of the esophagus. A characteristic pattern of bolus transport was seen in all subjects. Impedance changes related to air were observed preceding the bolus head. The bolus head propelled significantly faster than did the bolus body and tail. Pharyngeal bolus transit was significantly faster than esophageal bolus transit. Within the esophagus, bolus propulsion velocity gradually decreased. Bolus transport was significantly accelerated in the upright position and delayed with increase of bolus viscosity. In conclusion, the dynamics of a bolus transport from the pharynx into the stomach are complex. It varies within both different anatomic segments and different parts of the bolus and depends on bolus characteristics and test conditions. The spatial and temporal resolution of a bolus transport can be obtained by the impedance technique.

Adult↗
PubMed1997

A new in vitro test method for calcification of bioprosthetic heart valves.

To investigate the calcification behavior of different bioprosthetic heart valves and verify possible hypotheses of the etiology of valve calcification, an accelerated pulse tester for bioprostheses was developed, whereby up to ten valves can be tested under identical test conditions. Each valve was mounted in a separate compartment on a piston and cyclically moved through a calcifying solution at frequencies of up to 800/min at 37 degrees C: An appropriate calcifying solution was evaluated by incubation tests of bovine and porcine tissue. Calcification was confirmed by measuring Ca and phosphate depletion by atomic absorption spectroscopy, von Kossa staining, EDAX, and microradiography. The first tests were successfully carried out on porcine valves that had been nondestructively assessed for tissue/stress anomalies by holographic interferometry prior to the calcification test. The tests showed that 75% of irregular fringe pattern areas corresponded to the calcification areas.

Animals↗
PubMed1997

Approach to computer-based medication planning and coordination support in intensive care units.

Due to more and more complex diagnosis and therapy measures, the critical care of patients requires an extensive work organisation which comprises patient, doctors, nurses and external services (e.g., central laboratory). In this organisation, the documentation plays a major role for the planning and coordination of work procedures and information flow within the medical staff. Various studies in intensive care units (ICU) reveal that the complex work organisation and the related information flow are faulty. Breakdowns are often caused by a lack of coordination between doctors and nurses and by poor transparency of work procedures. A typical example is the incorrect application of a doctor's medication orders by a nurse because she might have overseen a plan modification. This intransparency increases the strain on the medical staff and might result in critical effects on the patient. One approach to design a computer support for medication planning as well as the coordination when executing medication plans is given by work flow models. This paper shows that work flow models could be used to improve deficiencies in medication planning and coordination. Furthermore, it is demonstrated how such a support can be mediated to the user through an appropriately designed user interface.

Communication↗
PubMed1996

Comparison of passive and active perfusion catheters: an in vitro study in a pulsatile coronary flow model.

Perfusion balloon catheters are designed to provide continuous transcatheter blood flow and thereby reduce myocardial ischemia during coronary angioplasty. To compare the transcatheter flow rates of active and passive (auto-) perfusion catheters, a well-controlled experimental study was performed in a circulation model that duplicates the phasic, predominantly diastolic flow pattern of the left coronary artery. Mean diastolic coronary driving pressure varied between 20 and 100 mm Hg. For the autoperfusion catheters, a strong relationship between transcatheter flow and diastolic coronary driving pressure was found. For example, a coronary driving pressure of 80 mm Hg provided a coronary flow of 30 ml/min (RX-Perfusion [RP], ACS), 28 ml/min (Speedflow [SF], Schneider), 20 ml/min (Lifestream [LS], ACS), and 19 ml/min (Flowtrack [FT], ACS). Reduction of driving pressure to 40 mm Hg decreased the absolute transcatheter flow, which was now 16 ml/min (RP), 13 ml/min (SF), and 10 ml/min (LS and FT). The relative catheter flow (the ratio of absolute flow to baseline coronary flow rate without a catheter in place), was independent of actual coronary driving pressure and ranged between 21% +/- 1% (RP) and 14% +/- 1% (FT and LS). For the active perfusion system (Coreflo, Leocor, a maximal transcatheter flow of 82 ml/min was found. Using this active perfusion system, the relative catheter flow increased with decreasing coronary driving pressure:80 --> 40 mm Hg: 56% --> 107%. For all catheters, the distal perfusion decreased between 30% (3.0 mm RP) and 50% (3.0 mm LS) by a 0.014-inch guidewire placed through the inner channel of the catheter. Because of the strong relationship between coronary driving pressure and transcatheter flow, the residual flow through all autoperfusion catheters becomes critical (<20 ml/min), when the coronary driving pressure drops below 50 mm Hg. By contrast, active perfusion systems are independent of the actual coronary driving pressure and are therefore advantageous for prolonged dilation in patients with low aortic pressure.

Angioplasty, Balloon, Coronary↗