Biomedical subjects

W Gabriel

Publications and source records attributed to W Gabriel.

At least 19 recordsLinked to original sources

PubMed2005

How stress selects for reversible phenotypic plasticity.

Stress occurring in periods shorter than life span strongly selects for reversible phenotypic plasticity, for maximum reliability of stress indicating cues and for minimal response delays. The selective advantage of genotypes that are able to produce adaptive reversible plastic phenotypes is calculated by using the concept of environmental tolerance. Analytic expressions are given for optimal values of mode and breadth of tolerance functions for stress induced and non-induced phenotypes depending on (1) length of stress periods, (2) response delay for switching into the induced phenotype, (3) response delay for rebuilding the non-induced phenotype, (4) intensity of stress, i.e. mean value of the stress inducing environment, (5) coefficient of variation of the stress environment and (6) completeness of information available to the stressed organism. Adaptively reversible phenotypic plastic traits will most probably affect fitness in a way that can be described by simultaneous reversible plasticity in mode and breadth of tolerance functions.

Computer Simulation↗

PubMed2000

Fixation of clonal lineages under Muller's ratchet.

For clonal lineages of finite size that differ in their deleterious mutational effects, the probability of fixation is investigated by mathematical theory and Monte Carlo simulations. If these fitness effects are sufficiently small in one or both lineages, then the lineage with the less deleterious effects will become fixed with high probability. If, however, in both lineages the deleterious effects are larger than a threshold s(c), then the probability of fixation is independent of the fitness effects and depends only on the initial frequencies of the lineages. This threshold decreases with decreasing genomic mutation rate U and increases with population size N. (For N = 10(5), we have s(c) approximately = 0.1 if U = 1, and s(c) approximately = 0.015 if U = 0.1). Above the threshold, the competition is not driven by the ratio of mean fitnesses of the lineages, but by the relative sizes of the zero-mutation classes, which are independent of the fitness effects of the mutations. After the loss of the zero-mutation class of a lineage, the other lineage will spread to fixation with high probability and within a short time span. If the mutation rates of the lineages differ substantially, the lineage with the lower mutation rate is fixed with very high probability unless the lineage with the larger mutation rate has very slightly deleterious mutational effects. If the mutation rates differ by not more than a few percent, then the lineage with the higher mutation rate and the more deleterious effects can become fixed with appreciable probability for a certain range of parameters. The independence of the fixation probability on the fitness effects in a single population leads to dramatic effects in metapopulations: lineages with more deleterious effects have a much higher fixation probability. The critical value s(c), above which this phenomenon occurs, decreases as the migration rate between the subpopulations decreases.

Animals↗

PubMed1992

Survival of small populations under demographic stochasticity.

We estimate the mean time to extinction of small populations in an environment with constant carrying capacity but under stochastic demography. In particular, we investigate the interaction of stochastic variation in fecundity and sex ratio under several different schemes of density dependent population growth regimes. The methods used include Markov chain theory, Monte Carlo simulations, and numerical simulations based on Markov chain theory. We find a strongly enhanced extinction risk if stochasticity in sex ratio and fluctuating population size act simultaneously as compared to the case where each mechanism acts alone. The distribution of extinction times deviates slightly from a geometric one, in particular for short extinction times. We also find that whether maximization of intrinsic growth rate decreases the risk of extinction or not depends strongly on the population regulation mechanism. If the population growth regime reduces populations above the carrying capacity to a size below the carrying capacity for large r (overshooting) then the extinction risk increases if the growth rate deviates from an optimal r-value.

Animals↗

PubMed1982

[Prevention of aviation accidents from the forensic medicine viewpoint].

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Accidents, Aviation↗

PubMed1979

[Development of anaesthetic technique for endolaryngeal surgery 1960--1976 (author's transl)].

In 1960 direct laryngoscopy in combination with general anaesthesia with relaxation and intermittent positive negative pressure ventilation via a smallbore blocker tube was introduced. When, in 1965, microlaryngoscopy was developed it was exclusively performed with this technique. Since 1960, 44, 464 ear, nose or throat operations were carried out. 3,305 (7.4%) were endolaryngeal operations. 943 of them were performed in surface analgesia. 2,363 microlaryngoscopic operations were done under general anaesthesia. 22.5 per cent of the patients were women and 77.5 per cent were men. Their age varied between 6 weeks and 86 years. 2.4 per cent were children under 6 years of age and 33 per cent were aged over 60 years. The main advantages of this method over "open laryngeal surgery" are: 1. it provides a large measure of safety for the patient since even old and obese persons with a rigid rib cage can be adequately ventilated; the cuff prevents aspiration; there is no danger of the patient waking up during relaxation since he is being kept ventilated with a mixture of nitrous oxide-oxygen and halothane. Ventilation via the blocker tube begins immediately after intubation and not, as in open jet ventilation, after insertion of the laryngoscope. 2. The surgeon and his team are not exposed to the risk of infection since, in contrast to the "open larynx" methods, the closed system effectively prevents the escape of pathogenic micro-organisms.

Adolescent↗

PubMed1978

[EEG tracings in cerebral death (author's transl)].

In diagnosing electrocerebral silence (isoelectric tracing) the investigator must be sure to exclude the possibility of an artefact. With the methods available up to now for testing the proper functioning of electroencephalographic equipment it has not been possible entirely to avoid errors. A new method is described for the rapid and quantitatively exact testing of EEG equipment including electrodes and cables and the correct recording of isoelectric tracings.

Brain Death↗

PubMed1977

[Anaesthesia for the relief of dyspnoea caused by fibrin membranes in the larynx and trachea (author's transl)].

Three cases of life-endangering airway obstruction by fibrin membranes are reviewed which developed in a 17-year-old girl with virus pneumonia, in a 21-year-old girl with a history of thrombopathy after general anaesthesia with naso-tracheal intubation and in a 23-year-old woman after short anaesthesia with orotracheal intubation. Possible causal factors, the clinical symptoms and the therapeutic measures taken by the anaesthetist are discussed. Since these cases are generally in a state of severe respiratory collapse by the time treatment is initiated general anaesthesia with muscle relaxation should be attempted only if the anaesthesist is certain that he can effectively ventilate the patient before and during the operation. Otherwise it is better to apply assisted ventilation with oxygen and halothane via a mask until a clear air passage has been restored. Administration of anticholine drugs and control of shock are essential.

Adolescent↗

PubMed1976

[Life-threathening tracheal obstruction following intubation in a case of Willebrand-Jürgens disease].

A case of severe dyspnoea is reported which occurred in a 21-years-old woman with Willebrand-Jürgens disease four days after intubation during a dental operation. A 34 Charrière catheter was introduced into the glottis after a 22 Charrière catheter had failed to pass the obstruction. The patient was then artificially ventilated by means of a Spiromat and was subsequently tracheotomized after her cardio-pulmonary condition had become stabilized. The cause of the dyspnoea was a fibrin clot of 5-6 cm length. Three weeks after the tracheotomy and one week after extubation the patient was discharged from hospital in a satisfactory condition. The factors responsible for the development of the fibrin clot are discussed. If there is persistent stridor and aphonia after extubation a laryngologist should be consulted.

Adult↗

PubMed1975

[Duration of relaxation in the laryngeal and forearm muscles after succinyldicholine administration (author's transl)].

During laryngeal surgery with succinyldicholine relaxation it was noticed that the effects of the drug faded most quickly in the laryngeal muscles. To substantiate this observation an electromyographic study was made in 36 patients. 116 comparable action potentials were simultaneously recorded from the interarytenoid and flexor carpiulnaris muscles on a 4-track magnetic tape. An analysis of the recordings showed that action potentials in the larynx always re-appeared before those in the arm muscles. These results are different from those obtained by Spillmann who recorded action potentials in the tongue and arm. The time-lag between resumption of electrical activity in the larynx and the arm averaged 58 seconds. Possible causes of this difference are discussed. Succinyldicholine becomes effective 30 seconds after intravenous injection and its effects last 60-90 seconds. Recording the action potentials in the larynx during anaesthesia allows the accurate timing of further doses of muscle relaxants.

Action Potentials↗

PubMed1975