Chyme transport patterns in human duodenum, determined by multiple intraluminal impedancometry

To get information about the mechanisms involved in chyme transport during the fasting and postprandial states, the novel procedure of multiple intraluminal impedancometry was evaluated in 14 healthy subjects (6 during fasting, 8 after a test meal). All main features of the migrating motor complex (MMC) cycle were determined. During phase II of the MMC cycle and the postprandial period, different transport patterns of chyme, termed bolus transport events (BTEs), were determined. These were 1) simple long-distance propulsive transport (spreading distance > 16 cm), 2) short-distance propulsive transport, and 3) retrograde transport. A significantly lower number of BTEs was recorded during fasting than postprandially. Short-distance propulsive BTEs predominated during fasting (72%), and long-distance propulsive BTEs predominated after the test meal (76%). Retrograde BTEs were recorded during fasting (4%) and postprandially (8%). In the latter state, complex long-distance propulsive BTEs were also observed (5%), consisting of multiple components. A major proportion of gastric contents was found to be continuously transported to jejunum. In conclusion, impedancometry enables us to determine patterns and parameters of chyme transport during fasting and postprandial states.

A new procedure for the registration of the visual-evoked cortical potential by multichannel recording of the gradient distribution

A new bipolar multichannel visual-evoked cortical potential (VECP) procedure is presented, which can supply objective information on visual field losses. The electrical potential is recorded from 11 electrodes applied to the back of the head in the form of an equidistant rectangular grid. Each neighbouring pair of electrodes feeds one of 14 bipolar channels. The adjacent horizontal and vertical channels are used to calculate an approximation to the direction and amplitude of the electrical field gradients. The gradient distribution is represented by a map of arrows (gradient map) for every instant of the sweep, so that the whole sweep can be plotted as a time series of gradient maps. The maps are easy to scale and are well suited for visual evaluation. Twenty normal subjects were stimulated using checkerboard reversal, partial field patterns to simulate visual field defects. The stimulated area varied between full-, half- and quarter-field, and the particular area stimulated could be clearly seen in the resulting gradient maps. Additionally, we developed a computerized classification procedure that detected 86% of the disturbed visual fields from the gradient recordings.

Fuzzy logic and control: principal approach and potential applications in medicine

During the last few years intelligent machines appeared in nearly all technical areas, such as consumer electronics, robotics, and industrial control systems. There are for example washing machines that work very effectively, need comparably less power than in the past, and have short execution times because they adjust their washing cycles to each set of clothes and change their washing strategies as the clothes become clean. These intelligent systems are based on fuzzy control strategies, i.e., common sense rules are used to describe a system's behavior instead of complex mathematical models. We have applied this new technology to control problems as well as to reasoning problems in biomedical engineering where appropriate mathematical models could not be built due to the complexity of the problem. After a short introduction to the concepts of fuzzy logic two approaches in the field are described: a fuzzy control strategy for the pump rate adjustment of a novel total artificial heart and an intelligent alarm system based on fuzzy inference which supports the anesthetist in monitoring and evaluating the hemodynamic state of a patient undergoing cardiac surgery. These examples indicate the inherent reliability and stability of this technique in the field of complex dynamic systems. Such properties are highly significant especially in medical applications.

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.

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.

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.

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.

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.

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.

[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.

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.

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.

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.

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.