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Biomedical subjects

G Rau

Publications and source records attributed to G Rau.

At least 109 records · Page 6Linked to original sources
PubMed1995

[Arteriovenous fistula after osteosynthesis of upper and lower leg fractures].

Two cases of an arteriovenous fistula following osteosynthetic treatment of a distal fracture of the thigh and a fracture of the lower leg are described. A large AV-fistula between the popliteal artery and the popliteal vein resulted in aneurysmal dilatation of the iliac and femoral vessels 10 years later. The AV-fistula of the second case was small and the result of a large aneurysmal spurium in the proximal calf muscles which was discovered 6 years after the initial injury. The treatment course of the large AV-fistula was protracted. The surgical therapy of the large aneurysmal spurium with the small AV-fistula was uncomplicated.

Adult↗
PubMed1995

Hydraulic refinement of an intraarterial microaxial blood pump.

Intravascularly operating microaxial pumps have been introduced clinically proving to be useful tools for cardiac assist. However, a number of complications have been reported in literature associated with the extra-corporeal motor and the flexible drive shaft cable. In this paper, a new pump concept is presented which has been mechanically and hydraulically refined during the developing process. The drive shaft cable has been replaced by a proximally integrated micro electric motor and an extra-corporeal power supply. The conduit between pump and power supply consists of only an electrical power cable within the catheter resulting in a device which is indifferent to kinking and small curvature radii. Anticipated insertion difficulties, as a result of a large outer pump diameter, led to a two-step approach with an initial 6,4mm pump version and a secondary 5,4mm version. Both pumps meet the hydraulic requirement of at least 2.5l/min at a differential pressure of 80-100 mmHg. The hydraulic refinements necessary to achieve the anticipated goal are based on ongoing hydrodynamic studies of the flow inside the pumps. Flow visualization on a 10:1 scale model as well as on 1:1 scale pumps have yielded significant improvements in the overall hydraulic performance of the pumps. One example of this iterative developing process by means of geometrical changes on the basis of flow visualization is illustrated for the 6.4mm pump.

Biomechanical Phenomena↗
PubMed1995

Development, manufacturing and validation of a single-leaflet mechanical heart valve prosthesis.

A new single-leaflet mechanical heart valve prosthesis was developed and evaluated in vitro and in vivo. The basic design of the closing body is S-shaped, with the leading and trailing edges parallel to the flow direction. This closing body has an additional cross camber and a fixed axis of rotation. The bearing pins of the disc are guided within oblong through bores of the housing, resulting in a self-cleaning effect. The valve housing has a nozzle-shaped configuration in order to avoid flow separation at the inlet and to reduce the associated pressure loss. Development and optimization studies were carried out by means of upscale valve models. After manufacturing of the closing body from pyrolytic carbon and of the orifice from titanium final hydrodynamic evaluation was carried out according to ISO 5840. The results were comparable or better than for bileaflet valves, the cavitation threshold was above a left ventricular dP/dt of 5500 mmHg/sec. The excellent in vitro results were confirmed by in vivo animal studies in calves and sheep with implantation times of 12 months and six months, respectively. These studies were carried out at the RWTH Aachen and at the NIH, Washington. Without any anticoagulation treatment the valves showed excellent results, confirming the concept of a valve design based on advanced engineering techniques.

Animals↗
PubMed1995

The effect of left ventricular dP/dt on the in vitro dynamics of the Björk-Shiley Convexo-Concave mitral valve.

Left ventricular (LV) dP/dt is considered an important hemodynamic factor influencing the dynamics of mechanical heart valve prostheses. LV dP/dt is dependent on patient factors including age, cardiac activity, health, and medication. The objective of this study was to determine the effect of LV dP/dt on the closing dynamics of mechanical heart valve prostheses in the mitral position. Eight instrumented 29 mm Björk-Shiley Convexo-Concave (BSCC) heart valves were tested in the pulse duplicator of the Helmholtz Institute. The valves had miniature strain gages mounted at the base of the outlet strut to measure impact loads at closure. Closing velocities were measured with a "light gate" device which was triggered by the closing leaflet. Physiologic pressure and flow waveforms were generated by a computer-controlled hydraulic drive unit. LV dP/dt was varied from 500 to 4000 mmHg/s simulating a wide range of physiologic conditions. It was found that the closing velocity was almost linearly related to LV dP/dt. At 4000 mmHg/s, closing velocities ranged from 1.5 to 2.0 m/s. Impact loads increased monotonically with LV dP/dt and closing velocity. In some valves, impact loads reached 2800 g at LV dP/dt of 4000 mmHg/s, and closing velocities of 2.0 m/s.

Animals↗
PubMed1994

Encapsulation of human erythrocytes by growing ice crystals.

In this study the interaction of human erythrocytes in suspension with a planar ice-liquid interface is investigated. Due to a repulsive van der Waals force repelling the cells from the crystal and an attractive force resulting from the viscous drag of melt flow around the cell a velocity was determined below which the cell is pushed by the growing crystal and above which it is entrapped by the solid phase. The critical velocity for erythrocytes suspended in 0.85 wt% NaCl-D2O solution can be derived from measuring the time periods of pushing and is calculated to be 1.1 microns/s at a temperature gradient of 15.3 K/mm.

Blood Preservation↗
PubMed1994

[Examination procedure in automated determination of far and near vision].

BACKGROUND: Although the measurement of visual acuity at distance is more important in ophthalmological practice, the visual acuity at near should be tested additionally. In a recently published paper we showed that with today's computer technology visual acuity at distance can be measured in standardized procedures according to DIN 58220. We describe here an additional, integrated setup, which allows the measurement of visual acuity also at near. METHODS: For testing visual acuity at near, the whole set of optotypes is presented on a transparent overlay mask in front of a computer monitor which is used as a program-controlled light source. A certain optotype is chosen by illuminating its background. The patient's responses are read via a small console by the computer. The test procedure follows the DIN requirements. RESULTS AND CONCLUSIONS: First reliability tests showed that the test arrangement is qualified for rapid and standardized determination of visual acuity at near and at distance under nearly natural viewing conditions.

Adult↗
PubMed1994

Design improvements of the HIA-VAD based on animal experiments.

Since 1990, development of the Helmholtz-Institute at Aachen ventricular assist device (HIA-VAD) was mainly based on animal tests performed at the University of Groningen. Although various in vitro tests had been performed previously, animal testing resulted in significant improvements of the HIA-VAD with regard to hemodynamics and pump handling. The most important design improvement was a new trileaflet polyurethane valve, which was designed as a blood-pump valve with an emphasis on opening behavior and flow resistance. Excellent hydrodynamic performance and sufficient durability of this new valve were confirmed by various in vitro tests. Further design and manufacturing improvements resulted in a completely transparent pump, which can be easily deaired and optically controlled. Final pump design was evaluated during subsequent animal tests, and the results are very promising in view of an efficient cardiac support system.

Animals↗
PubMed1994

Concept, realization, and first in vitro testing of an intraarterial microaxial blood pump with an integrated drive unit.

The intraaortically located micoraxial pump represents a promising device for temporary cardiac assistance in terms of efficiency and practicability. Due to well-documented problems arising from the concept of a pump unit being driven by an extracorporeally placed motor via a flexible drive shaft cable, a new pump concept is presented. The cable is replaced by a proximally attached microelectric motor that needs only an extracorporeal power supply.

Aorta↗
PubMed1994

The Helmholtz Total Artificial Heart Labtype.

To perform the first experimental tests for validation of a new gear unit concept, the pump chamber, diaphragm, and pusher plate design of an orthotopic electromechanical total artificial heart (TAH) (Helmholtz Labtype) was manufactured. In its early stage of development, it provides some of the most important features of the conceptual final artificial heart. The new gear unit transforms a uniform unidirectional rotational motor movement into translatory pusher plate movements, with resting phase in the end-diastolic position, and the angled pump chamber orientation determines the available space for the motor and gear unit. Furthermore, this labtype provides flexibility with regard to use of different types of structural parts for experimental investigations. The first in vitro test results, obtained with specially designed circulatory mockloops that simulate physiological preload and afterload conditions, are presented. They comprise pressure and flow generation, motor performance, efficiency, and energy consumption. The results prove the feasibility of the new gear unit concept for an electromechanical artificial heart and allow a reliable determination of the necessary performance of the future brushless DC motor for the first in vivo TAH model.

Blood Pressure↗
PubMed1994

Measuring esophageal motility with a new intraluminal impedance device. First clinical results in reflux patients.

BACKGROUND: The study was undertaken to determine the validity of intraluminal impedance measuring for the diagnosis of esophageal motility disorders in reflux patients. METHODS: A new impedance device was used for the detection of esophageal motility patterns in a prospective study with 10 volunteers and 10 patients with reflux esophagitis grade II-III. Perfused manometry was correlated with the impedance tracings. Test meals were saline and curd in three different preparations with liquid to semisolid viscosity. RESULTS: There was a marked delay in esophageal transport with increasing viscosity of the bolus (p < 0.01). A significant (p < 0.001) delay of the bolus transport in the inflamed esophageal areas was seen in reflux patients. A reduced contractility of the lower esophagus and the lower esophageal sphincter was detected by the impedance procedure in reflux patients, indicating that the pathologic motility patterns in reflux esophagitis are most likely secondary to the tissue inflammation. CONCLUSION: We conclude that impedance procedures may give additional significant information about bolus transport and esophageal wall movements.

Adult↗
PubMed1994

Causes and formation of cavitation in mechanical heart valves.

Cavitation may develop on mechanical valvular prostheses in the mitral position; it causes blood damage and, under particularly adverse conditions, it may result in sudden failure of the prosthesis. Therefore, with regard to future development of mechanical heart valves, the pattern of cavitation and its predisposing factors in different types of prostheses were investigated in in vitro studies, which focused on the analysis of valve closure dynamics and the influence of design parameters on the cavitation-inducing pressure drop at the artificial valve. It was found that cavitation is produced primarily by the deceleration of the closing body of the valve. At 900g, the measured deceleration of the closing bodies falls in the range of the decelerations determined in oscillation experiments for investigating cavitation-induced material erosion. The pressure drop produced thereby is overlapped by the pressure drop in accelerated or turbulent flow regions produced by design characteristics at outlet struts, stop faces or sealing lips during backflow through the closing disc. These phenomena exist particularly in regions of high flow velocity, i.e. at the instant of closure at the maximum distance from the bearing axis of the closing body (12 o'clock position). The onset of cavitation is additionally promoted in this position by a tight joint between the closing body and the ring. Oscillations of the closing body generally have a negligible effect on the cavitation behavior. From these relationships one can infer that cavitation can be avoided in future in mechanical heart valves by locally limited design measures. Especially, unsteadiness in the backflow through the closing valve is to be avoided.

Acceleration↗
PubMed1993

Recovery from neurological deficits following biotin treatment in a biotinidase Km variant.

A 15-year-old boy suffered from progressive bilateral optic neuropathy of acute onset at the age of 10 years. Subsequently he developed spastic paraparesis and a predominantly motor type neuro-axonal neuropathy in all limbs. The basic error has been elucidated to be due to an unusual biotinidase Km variant with biphasic enzyme kinetics causing systemic biotin depletion and consequent multiple biotin-dependent carboxylase deficiency. After daily oral substitution with 10 mg biotin metabolic derangements subsided rapidly. Follow-up studies over one year after substitution with biotin demonstrated remarkable recovery from part of the previously present neuro-ophthalmological, motor and cognitive deficits. The previously extinguished flash-evoked visual potentials now showed clear responses after six months of substitution with biotin. In contrast with reports in literature, these findings indicated that neurological damage associated with biotinidase deficiency, rather than being permanent, is to some extent reversible.

Administration, Oral↗
PubMed1993

Clinical application of a noninvasive multi-electrode array EMG for the recording of single motor unit activity.

Using a recently developed noninvasive EMG recording technique with multi-electrode arrays we investigated the pattern and distribution of motor unit action potentials (MUAP) following maximal voluntary contraction of the musculus abductor pollicis brevis. An additional parameter, i.e. muscular conduction velocity (CV) in single motor units, was calculated from the multi-electrode array EMG recordings. From 63 healthy children of various age the normal EMG pattern and CV were derived and compared to the EMG of diagnosed patients known to suffer from Duchenne muscular dystrophy and from spinal muscular atrophy. In normal individuals the muscular CV in neonates was lowest at 1-2 m/s and gradually reached a plateau of 2.9-4 m/s from the age of 4 years onwards. The EMG in 31 children with Duchenne muscular dystrophy showed an abnormal pattern with low amplitude action potentials. In 30 out of 31 patients a significantly lower muscular CV was found. In 10 children with spinal muscular atrophy the EMG showed action potentials of abnormally large amplitude and a reduced recruitment of firing motor units. The muscular CV remained within the normal range. Compared to classical needle EMG the application of this new noninvasive EMG technique in children is painless and offers an easy-to-handle diagnostic tool to differentiate between neuromuscular diseases of denervating or of myopathic origin.

Adolescent↗
PubMed1993

In vitro comparison of bileaflet aortic heart valve prostheses. St. Jude Medical, CarboMedics, modified Edwards-Duromedics, and Sorin-Bicarbon valves.

The hydrodynamic performance of four currently used bileaflet heart valve prostheses (St. Jude Medical, CarboMedics, modified Edwards-Duromedics, and Sorin-Bicarbon) with a nominal tissue anulus diameter of 27 mm were measured in the aortic position. All experiments were performed in nonpulsatile flow and in an electrohydraulic, computer-controlled pulse duplicator simulating the left side of the human circulatory system. Testing conditions were set at cardiac outputs of 3.0, 4.5, 6.5, and 8.0 L/min at a constant heart rate of 70 beats/min. The Sorin-Bicarbon valve had the lowest pressure difference with regard to nonpulsatile (mean 5.4 mm Hg at 30 L/min) and pulsatile (mean 2.2 mm Hg at 8 L/min) flow, followed by the St. Jude Medical, CarboMedics, and modified Edwards-Duromedics valves. The leakage volumes under static and pulsatile flow conditions were lowest for the modified Edwards-Duromedics and Sorin-Bicarbon valves. The energy loss in pulsatile flow was lowest for the Sorin-Bicarbon valve, mainly because its systolic, closure, and leakage energy losses were low. Systolic sequential velocity profiles showed the most even flow distribution pattern for the St. Jude Medical and Sorin-Bicarbon valves. These findings correspond with lower overall Reynolds shear stress levels for the St. Jude Medical and the Sorin-Bicarbon valves than for the modified Edwards-Duromedics and CarboMedics valves.

Aortic Valve↗
PubMed1993

Cavitation threshold with respect to dP/dt: evaluation in 29 mm bileaflet, pyrolitic carbon heart valves.

A total of 15 bileaflet mechanical heart valves were studied in a pulse duplicator at the Helmholtz Institute (Aachen, Germany) under conditions approximating first, a physiological pressure curve and subsequently, a sinusoidal pressure curve. In this study Edwards-Duromedics valves of the modified specification were compared with the earlier version of the Edwards-Duromedics valve as well as with St. Jude Medical valves. Each valve was tested at a series of nine (9) conditions. At each condition, without altering the valve installation or the systemic conditions, each valve was filmed by two separate video systems: the Helmholtz Institute strobe light system and a high speed video recording system. All data, as recorded by each system, was then independently analyzed by both of the two contributing groups and subsequently compared. In this manner, it was possible to objectively verify not only the consistency of the data obtained, but to also determine the relative reliability of the methods for cavitation threshold detection.

Carbon↗
PubMed1992

[Cardiac involvement in the hypereosinophilia syndrome. the importance of echocardiography in the follow-up].

A 51-year-old man and a 39-year-old woman with the hypereosinophilic syndrome developed a restrictive cardiomyopathy in the course of cardiac involvement. Echocardiography demonstrated typical thrombotic obliteration at the apex of both ventricles. Doppler ultrasound showed changes of impaired filling in both ventricles. Glucocorticoid treatment (prednisone, 85 mg daily) had to be drastically reduced (to 10 mg daily) in case 1, because of the development of a Cushing syndrome. The man died 18 months later of advanced heart failure. In the woman the eosinophil count fell after prednisone administration (1 mg/kg daily) and there was no recurrence. But heart failure due to impaired diastolic filling has persisted so that orthotopic cardiac transplantation has been planned.

Adult↗
PubMed1992

Knowledge-based decision support for patient monitoring in cardioanesthesia.

An approach to generating 'intelligent alarms' is presented that aggregates many information items, i.e. measured vital signs, recent medications, etc., into state variables that more directly reflect the patient's physiological state. Based on these state variables the described decision support system AES-2 also provides therapy recommendations. The assessment of the state variables and the generation of therapeutic advice follow a knowledge-based approach. Aspects of uncertainty, e.g. a gradual transition between 'normal' and 'below normal', are considered applying a fuzzy set approach. Special emphasis is laid on the ergonomic design of the user interface, which is based on color graphics and finger touch input on the screen. Certain simulation techniques considerably support the design process of AES-2 as is demonstrated with a typical example from cardioanesthesia.

Anesthesia↗