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Biomedical subjects

B Brehmer

Publications and source records attributed to B Brehmer.

16 recordsLinked to original sources

Dynamic decision making: human control of complex systems.

This paper reviews research on dynamic decision making, i.e., decision making under conditions which require a series of decisions, where the decisions are not independent, where the state of the world changes, both autonomously and as a consequence of the decision maker's actions, and where the decisions have to be made in real time. It is difficult to find useful normative theories for these kinds of decisions, and research thus has to focus on descriptive issues. A general approach, based on control theory, is proposed as a means to organize research in the area. An experimental paradigm for the study of dynamic decision making, that of computer simulated microworlds, is discussed, and two approaches using this paradigm are described: the individual differences approach, typical of German work in the tradition of research on complex problem solving, and the experimental approach. In studies following the former approach, the behaviour of groups differing in performance is compared, either with respect to strategies or with respect to performance on psychological tests. The results show that there are wide interindividual differences in performance, but no stable correlations between performance in microworlds and scores on traditional psychological tests have been found. Experimental research studying the effects of system characteristics, such as complexity and feedback delays, on dynamic decision making has shown that decision performance in dynamic tasks is strongly affected by feedback delays and whether or not the decisions have side effects. Although neither approach has led to any well-developed theory of dynamic decision making so far, the results nevertheless indicate that we are now able to produce highly reliable experimental results in the laboratory, results that agree with those found in field studies of dynamic decision making. This shows that an important first step towards a better understanding of these phenomena has been taken.

Computer Simulation

Asymptomatic mandibular third molars: oral surgeons' judgment of the need for extraction.

Ten oral surgeons were asked to judge the need for extraction of asymptomatic mandibular third molars. Thirty-six mandibular third molars with equal distribution of angular position, impaction status, and patient's sex and age were selected. To estimate the consistency of judgment, the 36 cases were duplicated so that, in all, 72 cases were judged. The judgment of the oral surgeons was compared with that of 30 general dental practitioners (GDPs). The number of mandibular third molars the oral surgeons proposed to extract varied from 3 to 21 of 36 teeth. The mean number of molars proposed for extraction was 12 for the oral surgeons and 13 for the GDPs. There was no third molar that all the observers in the two groups agreed should be extracted. About three times as many observers in both groups proposed extraction of molars partially covered by soft tissue. The oral surgeons were unanimous in their judgment not to extract 11 molars, and the GDPs were also unanimous in judgment not to extract two of these. The mean intraobserver agreement within the two groups was comparable, 94% for the oral surgeons and 92% for the GDPs. We conclude that there is a great variation among oral surgeons in their judgment on the need for removal of asymptomatic mandibular third molars. A similar variation in judgment also was observed among GDPs.

Adolescent

General dental practitioners' evaluation of the need for extraction of asymptomatic mandibular third molars.

Thirty general dental practitioners were asked to evaluate the need for extraction of asymptomatic mandibular third molars. Thirty-six mandibular third molars with equal distribution of angular positions, impaction status, males and females and age groups were selected. To estimate the consistency of the evaluation, the 36 cases were duplicated so that, in all, 72 teeth were evaluated. The number of molars proposed to be extracted by the observers varied from 0 to 26. There was no third molar which all observers agreed should be extracted. The two molars which most observers, 25 and 23 of altogether 30 observers, proposed to be extracted were partially covered by soft tissue. The decision not to extract two molars was unanimous. Both of these were completely covered by bone tissue and positioned vertically. The mean overall intra-observer agreement for the therapeutical decision was 92%, with a range of 69-100%. The length of professional experience of the observer did not influence the evaluation whether or not to extract. We conclude that there is a great variation among general dental practitioners regarding their evaluation on the need for removal of asymptomatic mandibular third molars.

Adult

[Differential diagnosis of acute scrotum by nuclear medicine study].

Sixty-four patients with acute scrotal pain were examined by radionuclide scrotal scanning. We compared clinical, surgical and radionuclide findings. The scrotal scanning is a rapid, non invasive and painless examination with high accuracy in inflammatory disease. But two falsely negative scans in acute testicular torsion warn against this simple method. Torsion of the appendix testis were not recognized by scanning.

Acute Disease

Radionuclide scrotal imaging: a useful diagnostic tool in patients with acute scrotal swelling?

Fifty-four patients complaining of acute painful scrotal swelling were submitted to urgent radionuclide scrotal imaging. Clinical and surgical findings were compared with the results of radionuclide studies. Radionuclear scrotal imaging is an easy rapid none invasive investigation with high accuracy in inflammatory disease of the scrotal content. Two falsely negative examinations confirmed by surgical exploration, however, warn against relying on this method as a single test in the diagnosis of acute testicular torsion.

Epididymitis

[Value of lymphography in teratoid testicular tumors (author's transl)].

In 72 patients with malignant testicular tumors lymphograms were reviewed and correlated with the microscopic findings of the resected lymphnodes. In 55 patients (76%) the roentgenographic diagnosis was confirmed by histology. In 6 patients lymphography was false positive as microscopic examination of the resected lymphnodes showed. In 4 patients lymphography was considered negative but metastatic disease proven microscopically from retroperitoneal lymphnodes. Out of 7 patients with questionable positive lymphograms 2 had retroperitoneal metastases confirmed by microscopic examination. The limits, errors and value of lymphography in patients with testicular tumors are discussed.

Adolescent

[Replacement of the trigonum vesicae by silicone rubber in mini pigs (author's transl)].

Prostheses of the trigonum vesicae made of silicone rubber and covered with a textile layer were implanted in 18 mini pigs. Investigations were done in two series: in the first the prostheses were covered on the outside with a narrow woven textile layer, in the second with Dacron-velour. While the narrow woven textile-lined prostheses were rejected into the urinary bladder after a short period, the Dacron-velour-lined prostheses remained well attached to the bladder wall.

Animals

[Ureteroureterostomies: indications and results (author's transl)].

Thirteen unilateral ureteroureterostomies and twenty-five transureteroureterostomies (TUU) were performed since 1968. In 22 of these, a transureteroureterocutaneostomy (TUUC) was done. Indications, operative procedures, results and complications are discussed. No complications due to the anastomosis were found. In six cases stenosis of the ureterocutaneostomy was demonstrated which, in four instances, made another form of urinary diversion necessary. Ureteroureterostomies should only be performed with well functioning kidneys and with one well preserved ureter. TUUC is recommended in cases with at least one dilated ureter.

Abdominal Muscles

[Combined surgical and cytostatic therapy in patients with advanced metastatic nonseminomatous testicular cancer (author's transl)].

Lymphadenectomy and chemotherapy were carried out on 18 patients with grossly disseminated nonseminomatous testicular cancer. Of the 14 patients so far evaluable, remission was obtained in 13 (92%), complete remission in 7 (50%). Results suggest that even when the disease is advanced, lymphadenectomy is of diagnostic, therapeutic, and palliative value.

Adult

Ultrastructural characteristics of "aging" of human prostate cells in monolayer cell culture.

Monolayer tissue culture cells from benign nodular hyperplasia of the prostate transferred at 1-2 weeks intervals were examined under the electron microscope after the 3rd, 9th, and 10th transfers. Changes seen after 9 to 10 transfers were interpreted as an "aging process" and consisted of the presence of lysosomes of various types and variations in the mitochondria profile. These changes were described in detail and illustrated and compared to the ultrastructural appearance of monolayer cell cultures in the early transfer stage.

Animals

Variable errors set a limit to adaptation.

This paper argues that variable error introduces a limit to the extent to which a person can be adapted to his or her environment in general, and for the extent to which the driver can be adapted to the traffic environment in particular. This is because variable error turns what is a deterministic and stable world into an uncertain one where it is only possible to be adapted in a statistical sense. A series of experiments are then discussed. These experiments show that drivers match their utilization of perceptual information to the validity of this information, i.e., they treat uncertainty introduced by variable error in the perceptual system in the same manner as they treat uncertainty in the physical system. This supports the main hypothesis of the paper. A driver may mitigate the effects of variable error by having a safety margin, but the relation between speeds and accident rates (predicted from the current hypothesis) shows that this adaptation is not effective enough. Safety authorities may mitigate the effects of variable error by decreasing the variability of the driving environment, e.g., by introducing speed limits.

Accidents, Traffic