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Biomedical subjects

P Pedersen

Publications and source records attributed to P Pedersen.

At least 73 records · Page 4Linked to original sources
PubMed1983

Detection by replica plating of false revertant colonies induced in the Salmonella-mammalian microsome assay by hexavalent chromium.

The replica plating method as developed by Lederberg has been used to differentiate between "true" and "false" histidine-requiring revertant bacterial colonies which develop on minimal agar plates in the Ames test. Strains of S. typhimurium LT2, TA 100, when exposed to either sodium dichromate or the fumes from the welding of stainless steel, develop colonies whose apparent numbers are directly in proportion to the Cr(VI) content per plate in both cases, over a wide dose range. Replica impressions of the resulting colonies were transferred to Vogel Bonner minimal agar plates and incubated for 48 hr at 37 degrees C. It was then observed that considerable numbers of "false" revertant colonies were obtained at those Cr(VI) doses which resulted in a pronounced toxic effect, albeit with an acceptable level of the bacterial background lawn. No morphological distinction between "true" and "false" revertant colonies could be made. Although it would appear that at low doses (i.e., low toxicity) the true mutagenicity of stainless steel welding fumes can be completely accounted for by the presence of Cr(VI), the dose range over which the mutagenicity assay is reliable cannot be estimated from examination of the background lawn or from an estimate of the degree of survival of the treated cultures. Thus there is raised a serious question concerning the reliability of quantitative data published in bacterial mutagenicity testing where replica testing of the histidine requirement of the resulting "revertant" colonies is not routinely made. It is suggested that the replica technique can easily be developed as a simple and useful tool for the control of histidine requirement and ampicillin resistance in routine mutagenicity testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

[Controlled respiration with a new "jet-ventilator" in the microsurgery of the larynx. An experimental study on dogs (author's transl)].

To combine the open jet-ventilation system with the security of the closed respiration we developed a new "jet-ventilator". Using a modification of the Carden-tube when we closed the upper part of the intratracheal tube, we had to remove the air by suction during the expiration time. With a pressure-analizer and transducer we could prevent negative and high pressure in the trachea. In experimental studies on six dogs we saw good blood gas analyzers as well as good circulatory parameters. With this method we were able to observe ventilation between eight and nine hours.

Animals↗
PubMed1982

[Computerized photodocumentation with automatic exposure technique in ENT endoscopy (author's transl)].

Proper lighting and exposure of color photographs were often the main problem in endophotography. The photographic equipment used for different regions of the body was complicated or troublesome to handle. In most cases, time and many tests were necessary, yet good photographic results were rarely obtained. To facilitate handling and to overcome the numerous exposure problems in photographic documentation an electronic TTL computer flash with autodynamic controlled flash energy was developed at the department of ORL at the University of Freiburg in 1980. With the single-handed endoscopic photographic system and the electronic TTL computer flash with automatic exposure technique, endoscopic photography becomes a simple and successful procedure. Even an unskilled "endophotographer" will be able to handle the described system easily. Getting good photographic results in endophotography is no longer a time-consuming and elaborate procedure.

Computers↗
PubMed1981

[A new laryngoscope for endolaryngeal microsurgery. A contribution to injector respiration (author's transl)].

A new laryngoscope was developed in order to improve visualization of the larynx and to better adapt the instrument to individual clinical circumstances. As such, the Kleinsasser laryngoscope was divided into tow parts, with the width between the two halves changed by adjustment of a screw. The lower part of the instrument can also be moved to provide more space near the larynx. Since the laryngoscope is open laterally, there is more space for the operator, and shorter instruments can be used for endolaryngeal manipulations. The endoscope can be used for intubation as well as for injection of oxygen under pressure at 0.5 bar (with an inspiration-expiration ratio of 1:2 at a frequency of 13/min). With the new instrument, the advantages of the Kleinsasser laryngoscope have been combined with the Killian suspension endoscope.

Humans↗
PubMed1980

Electronic flash unit for endoscopy with autodynamic controlled flash energy for automatic exposure of endophotos. A new method.

A high-speed flash unit for endoscopy with autodynamic controlled flash energy provides accurately exposed photos, irrespective of endoscope, localisation, and film material. This system was developed and tested in clinical practice in the Department of Otorhinolaryngology at the University of Freiburg, FRG. The autodynamic system for controlled flash energy guarantees a correct exposure even in the hands of an unskilled person.

Endoscopes↗
PubMed1980

[Problems of a frequency-specific threshold measurement with the brainstem potentials using the otometric sound pressure signal (damped wavetrain) (author's transl)].

This study aimes at investigating if the damped wavetrain stimulus (Victoreen) may be used in the evaluation of frequency specific thresholds using brainstem potentials. Stimulus frequencies were 1, 4, and 8 kHz. Starting with a control group (10 persons) latency curves for the brainstem potentials were established. The test group included patients with various forms of sensorineural hearing loss in the audiogram. Threshold measurements at the three stimulus frequencies were done with these patients using the potential IV (Jewet V). The latency curves of the normal hearing control group reveal a frequency-specific information being present in the brainstem potentials. This can be derived from latency shifts at different stimulus frequencies. However, investigating patients with a steep slope or a notch in the pure-tone audiogram introduces some difficulties in the ERA-threshold evaluation.

Audiometry, Evoked Response↗
PubMed1979

[A new laryngoscope for endolaryngeal microsurgery. A contribution to injector respiration (author's transl)].

A new laryngoscope was constructed in order to improve visualization of the larynx and to adjust the instrument to individual situation. The Kleinsasser laryngoscope was divided into two parts. The width between these two halfs can be changed by screws. Because the laryngoscope is open laterally there is more space for the operator and shorter instruments can be used.

Laryngoscopes↗
PubMed1979

[Inject-ventilation in bronchoscopy (author's transl)].

Jet ventilation initially described by Sanders has been modified and improved for use with the Storz bronchoscope. Theoretical and technical performance are discussed and the mechanical and physiological properties are dealt with e.g. FiO2, driving and endotracheal pressure, expiratory CO2 concentrations, blood gas analysis, pulmonary artery pressure and electrocardiographic changes. Using this method prolonged diagnostic and surgical procedures, such as cauterisation of bronchial adenoma, removal of foreign bodies from the airways especially of small children and bronchial toilet in status asthmaticus, are rendered free from problems for the anaesthetist. We believe that the inject ventilator is a very useful addition to endotracheal surgery.

Blood Gas Analysis↗
PubMed1977

["On-line artefact rejection" at electric response audiometry (ERA). Use of an active, analog delay line as buffer in combination with a recognition of disturbing signals (author's transl)].

Some brief theoretical considerations about an artefact rejection basing upon the valuation of amplitudes are followed by a report on a new development of an "on-line artefact rejection" which uses an active analog delay line as buffer combined with a recognition of disturbing signals and can easily operate together with simple averagers. The advantages are shown and discussed by means of examples, but also the mistakes which can arise by too great limitations of the signal's level. Technical details are described briefly.

Acoustic Stimulation↗
PubMed1977

[ERA-findings by "cortical hearing disorder" (author's transl)].

Since about the last 2 years the late potential's component N1 (90--110 ms) as well as the early acoustically evoked potentials, appearing in a latency range of 1--8 ms and consisting of the nerve action potential (Pot. I) and the brain-stem potentials (Pot. II-V), were registered at some hearing impaired patients. This procedure enabled us to diagnose a "cortical hearing defect" at five patients: a) three children at an age of 2--3 years; they all have a slight cerebral damage, a hearing impairment and no speech-development; b) a 15 year old girl with a hearing impairment which is on the right side more severe than on the left side, as consequence of an encephalitis; and c) a 50 year old man suffering on both sides from a loss of temporal brain's substance and from a total deafness after an insult of both arteriae meningeae mediae. At all these patients the ERA-findings result in an almost normal behaviour of the bioelectrical transfer of the acoustic stimuli in the region of the brain-stem, whereas the late potential's component N1 showed a pathologic distortion. The ERA-results together with the anammesis make a "cortical hearing disorder" probable at these five patients. The audiograms and the ERA-characteristic lines are shown and discussed.

Adolescent↗
PubMed1975

[Reactions of human neck muscle-fibers to vestibular stimulation (author's transl)].

In healthy human subjects activity from single fibers of the splenius-capitis muscle was recorded by means of a microelectrode. Two types of muscle fibers could be distinguished according to their reaction on vestibular stimulation. The first type reacted only to stimuli (angular acceleration) exceeding 10 degrees per sec2. These units showed no resting activity. The second type had a resting activity between 20 to 40 impulses per second. Their reactions under vestibular stimulation resembled that of primary afferent neurones of the vestibular nerve of other vertebrates. The functional meaning of these findings is discussed.

Animals↗
PubMed1975

[The objective sinumanometry (author's transl)].

Using a pressure chamber for differenatiation of naso-sinal and sino-nasal ventilatory ostial resistance, we examined 300 patients with pathology of the frontal and maxillary sinuses, stimulating physiological conditions. The analysis of the different obstructing factors--before and after washouts--hints to the presence of a surface--active substance in human sinus secretions.

Airway Resistance↗