Search PubMed⌕ Search

Biomedical subjects

A Ernst

Publications and source records attributed to A Ernst.

At least 91 records · Page 5Linked to original sources
PubMed1994

Feasibility of recanalization of human coronary arteries using high-intensity ultrasound.

To investigate the feasibility of ultrasonic recanalization of obstructed human coronary arteries in vitro, high-intensity ultrasound was applied to 16 coronary arteries obtained at autopsy, using a prototype instrument enabling insonification through a catheter tip. It was a 119 cm long, 0.95 mm thick wire in an 8Fr catheter connected to an external ultrasonic transformer and power generator. A 5 MHz phased-array 2-dimensional echocardiography instrument was used to determine minimal luminal diameter and percent diameter narrowing before and after ultrasound application. The ultrasonic energy was delivered at 21.5 kHz and with a 52 +/- 19 micrometer average amplitude of tip displacement. The mean percent luminal diameter narrowing, flow rate and mean pressure gradient before ultrasound exposure were 74 +/- 11%, 97 +/- 61 ml/min, and 92 +/- 18 mm Hg, respectively. After recanalization, the mean percent luminal diameter narrowing decreased to 45 +/- 17% (p < 0.001), the mean flow rate increased to 84 +/- 92 ml/min (p < 0.001), and the mean pressure gradient was reduced to 45 +/- 24 mm Hg (p < 0.001). Of the debris particles, 95% had a diameter < 9 microns (range 5 to 12). Arterial perforation occurred in 5 of 16 arteries (31%) and all 5 occurred due to stiff wire manipulation and without ultrasound application. Mechanical fracture of the wire occurred in 8 cases (50%). No signs of thermal injury were found on histology. Thus, ultrasonic recanalization of human coronary arteries in vitro is feasible. It may reduce obstruction and improve blood flow. Debris sizes are sufficiently small to minimize the hazard of peripheral embolization.

Adult↗
PubMed1994

[Galvanic labyrinth stimulation--medical history aspects].

The reaction of the vestibular system to a galvanic stimulus was described for the first time by Purkinje in 1820. The vertiginous response that could be elicited was experimentally and clinically investigated by neurologists in the following years. In the fifties of this century, the method was included into neurotological diagnostics. The main objection was to use it in the differential diagnosis of cerebellopontine angle (CPA) lesions. After imaging procedures, such as computerised tomography and magnetic resonance imaging, were introduced, galvanic testing is nowadays only used as part of the test battery of cochlear implant candidates to differentiate between a peripheral or retrolabyrinthine vestibular lesion.

Animals↗
PubMed1994

[Noninvasive assessment of intracochlear pressure and patency of the cochlear aqueduct in normal probands with TMD (tympanic membrane displacement) analysis].

The intracochlear pressure cannot yet be evaluated in patients with certain audiological neuro-otological diseases. However, it seems to be of importance in the diagnosis and pathogenesis of Ménière's disease and related disorders. The present paper is aimed at introducing a setup to indirectly assess intracochlear and intracranial pressure changes and the design and philosophy of this technique. It is possible to describe a normal range of the measured values in healthy controls although large interindividual variations occur. In addition, the positional changes of the registered parameters enable assessment of the patency of the cochlear aquaeduct. This seems to be important in some diseases, such as stapes gusher.

Acoustic Impedance Tests↗
PubMed1994

Utilization of light for nitrogen fixation by a new synechocystis strain is extended by its low photosynthetic efficiency.

Performance of photosynthesis and nitrogenase activity in a novel cyanobacterium, Synechocystis sp. strain BO 8402, isolated from Lake Constance, located at the northern fringe of the Alps in central Europe, and of a stable derivative, strain BO 9201, were examined. Strain BO 8402 is characterized by an extraordinarily high level of autofluorescence originating from paracrystalline phycobiliprotein-linker complexes located in inclusion bodies (W. Reuter, M. Westermann, S. Brass, A. Ernst, P. Böger, and W. Wehrmeyer, J. Bacteriol. 176:896-904, 1994). Energy transfer between paracrystalline phycobiliproteins and the photosystems is inefficient, resulting in a high oxygen compensation point and a decreased growth rate. The derivative strain BO 9201 exhibits hemidiscoidal phycobilisomes that support a high growth rate, even under low light intensities. Because of the differences in photosynthetic performance, anaerobic light-stimulated nitrogenase activity is maintained at higher light intensity in the original strain BO 8402 than in the derivative strain BO 9201. The results indicate that the formation of paracrystalline phycobiliproteins in Synechocystis sp. strain BO 8402 represents a hitherto-unknown means for a unicellular cyanobacterium to extend its capacity to fix nitrogen in the light.

Journal Article↗
PubMed1994

Characterization of devA, a gene required for the maturation of proheterocysts in the cyanobacterium Anabaena sp. strain PCC 7120.

Mutant M7, obtained by transposon mutagenesis of the cyanobacterium Anabaena sp. strain PCC 7120, is impaired in the development of mature heterocysts. Under aerobic conditions, the mutant is unable to fix N2 because of a deficiency of at least two components of the oxygen-protective mechanisms: a hemoprotein-coupled oxidative reaction and heterocyst-specific glycolipids. DNA contiguous with the inserted transposon was recovered from the mutant and sequenced. The transposon had inserted itself within a 732-bp open reading frame designated devA. The wild-type form of devA, obtained from a lambda-EMBL3 library of Anabaena sp. DNA, had the identical sequence. Directed mutagenesis of devA in the wild-type strain showed that the phenotype of the mutant was caused by insertion of the transposon. The wild-type form of devA on a shuttle vector complemented the mutation in M7. Expression of devA by whole filaments, monitored following nitrogen stepdown by using luxAB as the reporter, increased ca. eightfold during differentiation; the increase within differentiating cells was much greater. The deduced sequence of the DevA protein shows strong similarity to the ATP-binding subunit of binding protein-dependent transport systems. The product of devA may, therefore, be a component of a periplasmic permease that is required for the transition from a proheterocyst to a mature, nitrogen-fixing heterocyst.

ATP-Binding Cassette Transporters↗
PubMed1994

Structure, composition, and assembly of paracrystalline phycobiliproteins in Synechocystis sp. strain BO 8402 and of phycobilisomes in the derivative strain BO 9201.

The phycobiliproteins of the unicellular cyanobacterium Synechocystis sp. strain BO 8402 and its derivative strain BO 9201 are compared. The biliproteins of strain BO 8402 are organized in paracrystalline inclusion bodies showing an intense autofluorescence in vivo. These protein-pigment aggregates have been isolated. The highly purified complexes contain phycocyanin with traces of phycoerythrin, corresponding linker polypeptides LR35PC and LR33PE (the latter in a small amount), and a unique colored polypeptide with an M(r) of 55,000, designated L55. Allophycocyanin and the core linker polypeptides are absent. The substructure of the aggregates has been studied by electron microscopy. Repetitive subcomplexes of hexameric stacks of biliproteins form extraordinary long rods associated side by side in a highly condensed arrangement. Evidence that the linker polypeptides LR35PC and LR33PE stabilize the biliprotein hexamers is presented, while the location and function of the colored linker L55 remain uncertain. The derivative strain BO 9201 contains established hemidiscoidal phycobilisomes comprising phycoerythrin, phycocyanin, and allophycocyanin as well as the corresponding linker polypeptides. The core-membrane linker protein (LCM), and two polypeptides with M(r)s of 40,000 and 45,000 which are present in small amounts, exhibit strong cross-reactivity in Western blot (immunoblot) analysis using an antibody directed against the colored LCM of a Nostoc sp. In contrast, strain BO 8402 exhibits no polypeptide with a significant immunological cross-reactivity in Western blot analysis. Physiological and genetic implications of the unusual pigment compositions of both strains are discussed.

Bacterial Proteins↗
PubMed1994

Intraoperative facial nerve monitoring in the surgery of cerebellopontine angle tumors: improved preservation of nerve function.

The surgery of cerebellopontine angle tumors has shown remarkable progress over the last 20 years due to improved microsurgical techniques. However, the dissection of the facial nerve may lead to postoperative paresis as the result of the surgical trauma and the disruption of blood supply over a large distance. The functional status of the nerve can be intraoperatively monitored by means of intramuscular electromyography of facial muscles and direct electrical stimulation. In this study, the impact of monitoring techniques on the preservation of facial function was evaluated by comparing monitored (n = 30) and unmonitored (n = 34) patients. Both groups were comparable with regard to the size of the tumor, the surgical approach and the duration of operation. All patients were operated by the same surgeon (T.L.) either via the middle fossa or the translabyrinthine approach. The EMG was recorded with needle electrodes from the orbicularis oris and oculi muscles. For electrical stimulation, bipolar forcep electrodes were used delivering rectangular, constant current pulses of 100 microseconds duration and a current strength between 0.05 and 0.8 mA. The mechanically or thermally elicited activity by drilling, direct manipulation or coagulation consisted of bursts and trains which are signs of minor nerve impairment. Their occurrence can lead to a modified surgical technique with a more precise preparation around and at the facial nerve. The immediate postoperative nerve function was normal or showed only a minor impairment (classes I and II according to House and Brackmann) in 87% of the monitored as compared with 74% of the unmonitored patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebellopontine Angle↗
PubMed1994

Intracellular calcium changes by hyposmotic activation of cochlear outer hair cells in the guinea pig.

During continued exposure to a hypotonic solution, isolated outer hair cells (OHCs) from the guinea pig cochlea showed a regulatory volume decrease (RVD) after initial cell swelling. In the absence of extracellular Ca2+, RVD was significantly inhibited. Using Ca(2+)-sensitive dye fura-2, accompanying changes of the intracellular Ca2+ concentrations ([Ca2+]i) of OHC were investigated. Hyposmotic activation resulted in a [Ca2+]i increase associated with cell shortening and swelling. In a Ca(2+)-free solution, [Ca2+]i was not significantly increased during hyposmotic activation although shortening and swelling of the OHC was observed. These results suggest that the increase in [Ca2+]i during hyposmotic activation is mainly based on an influx or extracellular Ca2+ which precedes the RVD.

Animals↗
PubMed1994

Diagnosis of deep vein thrombosis in elderly hip-fracture patients by using the duplex scanning technique.

To detect the incidence of preoperative and postoperative deep vein thrombosis (DVT) in elderly patients with hip fracture, 100 patients aged 65 years and older with either a subcapital or intertrochanteric hip fracture were evaluated by duplex beta-mode ultrasonography. Treatment was based on each scan result: if evidence for DVT was seen, the patient was therapeutically anticoagulated; lacking signs of DVT, patients were treated prophylactically. Before their operation, 77 patients (77%) had normal results of their scans, while DVT was diagnosed in 12 patients (12%). An additional 11 patients (11%) developed DVT after the operation. The total incidence of DVT in this series was 23%.

Aged↗
PubMed1993

Hyposmotic activation hyperpolarizes outer hair cells of guinea pig cochlea.

The electrophysiological responses of isolated guinea pig outer hair cells (OHCs) to hyposmotic activation were studied using the whole-cell patch-clamp technique. The cell swelling by hyposmotic activation hyperpolarized OHCs by 6.6 +/- 2.3 mV from the resting membrane potential of -58.5 +/- 5.9 mV (n = 48). This hyperpolarization was associated with an outward current (97.7 +/- 22.2 pA, n = 15). The hyperpolarization was inhibited by 300 microM quinine, 5 mN Ba2+ and increasing the extracellular K+ to 30 mM from 5 mM. In the absence of extracellular Ca2+ (1 mM EGTA), the hyperpolarization during hyposmotic activation was also abolished while the following depolarization was preserved. 50 microM GdCl3, which is known to block stretch-activated non-specific cation channels, inhibited the hyperpolarization reversibly. 50 microM GdCl3 also inhibited [Ca2+]i increase during hyposmotic activation as shown by the calcium-sensitive dye fura-2. Simultaneously, the [Ca2+]i increase and the hyperpolarization during hyposmotic activation could be observed using the combined method of whole-cell patch clamp and fura-2 technique. It is concluded that the cell swelling by hyposmotic activation may activate the stretch-activated non-specific cation channels in the OHCs which allow a Ca2+ influx. In turn, this [Ca2+]i increase leads to an activation of the Ca(2+)-activated K+ channels at the basolateral membrane of OHCs which results finally in a reversible hyperpolarization of OHCs by K+ efflux.

Animals↗
PubMed1993

Neural mechanisms of tinnitus.

The theoretical concepts underlying the neural origin of tinnitus are outlined. Several neurophysiological models are reviewed critically and the impact of the pathological ensemble spontaneous activity of the auditory system for the diagnosis and therapy of tinnitus is described in more detail.

Animals↗
PubMed1993

Cochlear-motor, transduction and signal-transfer tinnitus: models for three types of cochlear tinnitus.

The present paper reviews possible molecular and cellular mechanisms in the cochlea that might contribute to tinnitus. They constitute a part of a highly integrated network in cochlear sound processing and are divided for easier understanding into three different models, i.e. active motor tinnitus, transduction tinnitus and signal-transfer tinnitus. Some of the steps of the pathophysiological models can even be pharmacologically influenced (as exemplified by experimental applications of lidocaine, calcium channel blocker, benzodiazepine, glutamate and atropine). This provides a rationale for the efficient suppression of tinnitus in some patients by these drugs. The most evident problem of all models in tinnitus, including the ones proposed in this paper, is the lack of objective verification by measurement. Thus, the well-defined clinical situation of each patient is hardly attributable to one of the models suggested. In addition, adequate therapy--perhaps one of the drugs considered--still cannot be based upon a reliable clinical finding.

Animals↗
PubMed1993

Sound preprocessing by ac and dc movements of cochlear outer hair cells.

In inner and outer hair cells, a sound event results mechano-electrically in a receptor potential from the hair cells by the functioning of apical and lateral K(+)-channels. However, after this point, the signal transfer is divided. Inner hair cells (IHC) release an unknown afferent transmitter. By contrast, outer hair cells (OHC) are proposed to produce mechanical ac and dc responses. In our model, the ac components of the sound signal, the carrier frequencies, determine the response of the OHC. Usually, they respond by ac and dc movements. The rapid ac movements of OHC, for which the underlying mechanism is unknown, may respond cycle-by-cycle to and interfere with the carrier frequency of the traveling wave. Near hearing threshold, they could drastically amplify the traveling wave thus contributing to the postulated cochlear amplifier. Active dc movements of the cytoskeleton of the cell body, as well as of the cuticular plate with the sensory hairs, are proposed to respond to millisecond changes of the sound stimulus over time. Such changes could be a modulation of the amplitude (AM), i.e., an increase or decrease of the sound pressure level (SPL), which is reflected in the envelope of the traveling wave. The active mechanical dc response of OHC to the amplitude (AM) and frequency modulation (FM) pattern is then expected to result in dc position changes of the reticular lamina (RL). These should control the operation point of the stereocilia, thus influencing their transfer function and sensitivity. In addition, experimental data suggest that there are modulations of the compliance of the organ of Corti (OC) and changes of its geometry. This dc modulation of micromechanical properties and geometry of the OC by active force generation of OHCs might contribute to automatic gain control, adaptation, TTS, as well as to the homeostasis of the basilar membrane location. In particular, the motile mechanism may protect the vulnerable cochlear partition against high sound pressure levels. Moreover, according to this model, changes of the sound signal with time are expected to be encoded in the actively produced dc movements of the RL. As the signal changes may carry important information (e.g., complex sound signal modulations such as formant transitions in speech), this is extracted and mechanically encoded by the proposed active dc mechanism. It cannot be excluded that the information-carrying dc signal is transferred to inner hair cells contributing to their adequate stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Cochlea↗
PubMed1993

High-resolution mapping of genetic loci of Anabaena PCC 7120 required for photosynthesis and nitrogen fixation.

A physical map of the Anabaena genome permitted the localization of its genes to chromosomal fragments generated by rarely cutting restriction endonucleases and separated by pulsed-field gel electrophoresis. We introduce a novel means of mapping more precisely to c. 20 kb by use of rare restriction sites within vectors bearing cloned sequences that undergo homologous recombination with the genome. We thereby localize and orient genes encoding principal photosynthetic pigments. The relative spacing of loci within a single restriction fragment was determined with even higher resolution, as illustrated for genes required for heterocyst development and nitrogen fixation that were marked with transposons. Small, newly visualized restriction fragments of the chromosome were also mapped.

Anabaena↗
PubMed1993

Volume regulation in guinea pig outer hair cells and the role of intracellular calcium.

Single outer hair cells (OHCs) isolated from the guinea pig cochlea showed a regulatory volume decrease (RVD) after the initial cells swelling despite continued exposure to a hypotonic solution. The accompanying change of the intracellular Ca2+ concentration ([Ca2+]i) in the OHCs was investigated using the Ca(2+)-sensitive dye fura-2. Hyposmotic activation led to a [Ca2+]i increase which was accompanied by cell shortening and swelling. In a nominally Ca(2+)-free solution, however, [Ca2+]i was not significantly increased during hyposmotic activation although shortening and swelling of the OHCs were observed. These results suggest that the increase in [Ca2+]i during hyposmotic activation is mainly based on an influx of extracellular Ca2+.

Animals↗
PubMed1993

[Polypoid pansinusitis in an unusual, extra-intestinal manifestation of Crohn disease].

A 17-year-old female patient with known Crohn's disease developed a polypoid pansinusitis and a peritonsillitis during an acute inflammatory phase of her disease. The symptoms observed in the paranasal sinuses and in the oropharynx disappeared after treatment with cortisone and antibiotics was started. The histological findings in the biopsy specimens taken from the affected regions as well as the course of the disease suggest the extraintestinal manifestation of Crohn's disease.

Adolescent↗