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H Klostermann

Publications and source records attributed to H Klostermann.

9 recordsLinked to original sources
PubMed2000

Frequency modulation of the ion-acoustic instability.

In a double-plasma device with a negatively biased grid separating source and target chamber, the ion-acoustic instability is recorded during the injection of an ion beam whose velocity is chosen between the ion-acoustic velocity and twice this value. The observed broad power spectra of the density fluctuations are found to be related to a strong modulation of the frequency inside the bursts of unstable waves. This modulation is interpreted as being a consequence of the existence of propagating strongly nonlinear coherent structures that arise in the course of the nonlinear spatiotemporal evolution of the ion-acoustic instability.

Journal Article↗
PubMed2000

On-off intermittency at the onset of the ion-acoustic instability in a laboratory plasma

The ion-ion beam instability is experimentally studied just above threshold in a laboratory double-plasma device. Intermittent bursts of unstable waves are recorded in the target plasma and the distribution of the recurrence times of the bursts is estimated. At the onset of instability, the measurements are in agreement with the expected evolution deduced from a theoretical model that combines the normal form of a supercritical Hopf-Andronov bifurcation and the parametric noisy deviations from threshold typical of on-off intermittency. In both the experiment and the model, the distribution of the recurrence times of the bursts decays as an inverse power law and the evolution of the mean laminar length when the control parameter is increased beyond threshold exhibits a power law of exponent -1.

Journal Article↗
PubMed1992

Advanced computer programs for drug dosing that combine pharmacokinetic and symbolic modeling of patients.

In this paper, we describe our design for advanced drug dosing programs that "reason" using a combination of Bayesian pharmacokinetic modeling and symbolic modeling of patient status and drug response. Our design is similar to the design of the Digitalis Therapy Advisor program, but extends this previous work by incorporating a Bayesian pharmacokinetic model, performing a "meta-level" analysis of drug concentrations to identify sampling errors and changes in pharmacokinetics, and including the results of this analysis in reasoning for dosing and therapeutic monitoring recommendations. The design has been implemented in a program for aminoglycoside antibiotics called Aminoglycoside Therapy Manager. The program is user-friendly and runs on low-cost general-purpose hardware. The initial validation study showed that the program was as accurate in predicting future drug concentrations as an expert using commercial Bayesian forecasting software and that its dosing recommendations were similar to those of an expert.

Aminoglycosides↗
PubMed1992

Practical computer-assisted dosing for aminoglycoside antibiotics.

In principle, computer-assisted individualization of antibiotic dosing offers the prospect of better patient outcomes through improved dosing precision. In practice, however, the expertise in pharmacokinetics required to operate these programs has precluded their use by most physicians and pharmacists. We developed a computer program for individualization of dosing of aminoglycoside antibiotics under conditions in which access to experts in pharmacokinetics is impractical. The program is accurate, yet it requires less effort for data collection than previous drug dosing programs did. The program generates advice on a broad spectrum of topics, including dose adjustment, interpretation of measured drug concentrations in blood, and recommendations for monitoring drug concentrations. We tested its performance by prospectively comparing it with a clinical pharmacokinetic consultation service in a series of 78 consecutive patients. There were no differences in accuracy or bias in the prediction of drug concentrations. The rate of agreement between the program's dosing recommendations and those of the consultation service was 67 percent. This rate of agreement is typical of interexpert variation. In a stratified set of 24 of the 41 instances with significant disagreement regarding the recommended dose, experts ranked the program's recommendations as highly as those of the consultation service (95% confidence interval for difference in rank, -0.30 less than chi less than 0.47). The results suggest that expert systems can be coupled with pharmacokinetic dosing programs to deliver high-quality clinical recommendations for administration of antimicrobial agents.

Adult↗
PubMed1990

Changes in cerebral haemodynamics in cases of post-lumbar puncture headache: a prospective transcranial Doppler ultrasound study.

We used transcranial Doppler ultrasonography in 45 patients to investigate if changes in haemodynamics in the major arteries of the brain base occurred after lumbar puncture and whether or not patients with or without post-lumbar puncture headache differ with respect to their cerebral haemodynamic parameters before and after lumbar puncture. Before lumbar puncture, patients with post-lumbar puncture headache differed from patients without post-lumbar puncture headache in that they showed significantly higher flow velocities and significant asymmetry of flow velocities with lateralization to the right (p less than or equal to 0.05). Patients without post-lumbar puncture headache, on the other hand, showed non-significant flow velocity lateralization to the left. Forty-eight hours after lumbar puncture, both groups demonstrated symmetrical flow velocities. In addition, only patients with post-lumbar puncture headache showed a significant reduction in the flow velocity of the right middle cerebral artery (p less than or equal to 0.05). These findings suggest that it is not only absolute flow velocity that plays a part in the event of headache, the interhemispheric relation of cerebral haemodynamics also plays a fundamental role.

Adult↗
PubMed1990

[Hemodynamic reactions in the area supplied by the middle cerebral artery in post-puncture headache].

We used transcranial Doppler ultrasonography to investigate whether a change in hemodynamics in the major arteries of the brain base occurred after diagnostic lumbar puncture. On the day before diagnostic lumbar puncture the flow in the right and left middle cerebral artery was measured in 36 patients using transcranial Doppler ultrasonography. 48 hours after lumbar puncture a second ultrasound examination was performed. We found that only patients with post-lumbar puncture headache (PLPS) showed a significant reduction in the flow of the right middle cerebral artery (p less than or equal to .05). These findings support the puncture-hole-seepage theory as pathogenetic principle of PLPS.

Adult↗
PubMed1976

Distribution and diaplacental passage of infused 3H-fenoterol hydrobromide (partusisten) in the gravid rabbit.

Tritium-labelled fenoterol hydrobromide was infused into an ear-vein of pregnant rabbits over a period of 4 hours. Two doses were used. The tritum concentrations in the blood of the dams and the amniotic fluid were determined from samples obtained during infusion and up to 11 hours after completion of infusion. The tritium concentrations were also determined in selected organ samples from dams and fetuses, taken immediately and 5 and 11 hours after infusion. Within 1.5 hours after commencement of infusion, the tritium activity in the whole blood of the dams reached a plateau on a level corresponding to the dose administered. Immediately after completion of infusion, the level of radioactivity fell rapidly. The tritium concentration in the amniotic fluid began to rise far more slowly after a time lag, so that approximately 2 hours after completion of infusion, the concentrations in maternal whole blood and amniotic fluid were equal. As the amniotic fluid level fell at a slower rate than the maternal whole blood level, the former somewhat exceeded the latter at this advanced stage of the study. The tritium distribution patterns of the dams indicate rapid elimination via kidneys and intestine. The tritium concentration in all the tissue fell rapidly after completion of infusion. The lung and uterus have a slightly greater affinity. The tritium concentrations in the fetal organs remained below those in the organs of the dams for the whole duration of the study. The highest radioactive concentration in the fetuses was found in the urine. Further observation of the rapid conversion of fenoterol hydrobromide into conjugates leads us to expect only minimal amounts of active substance to be found in the fetuses after infusion.

Amniotic Fluid↗
PubMed1969

Cell kinetic studies in mixed leukocyte cultures: an in vitro model of homograft reactivity.

The recognition phase of homograft immunity can be studied in vitro in the mixed leukocyte culture reaction. In this reaction, at the end of seven days, up to 30 per cent of the lymphocytes in culture "respond" to a single allogeneic cell stimulus. This paper presents evidence that the lymphocytes responding in culture divide with the generation time of 18-21 hours, with some asynchrony, and that a large percentage of the cells found at the end of the culture period may be the products by division of a small number of cells initially responding. Two estimates are made of the frequency of the initially responding unit (the cell(s) responsible for initiating the response). These are probably minimum estimates and are in the range of 1 in 200 to 1 in 2000 cells which can initially respond. This very high frequency of responding units as compared with the responding units in immediate type hypersensitivity (antibody production) is discussed.

Autoradiography↗