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At least 109 records · Page 6Linked to original sources
PubMed1999

[Abdominal actinomycosis presenting as a malignant tumor--report of a case and review of the literature].

Actinomyces israelii is a normal inhabitant in the gastrointestinal tract of humans, it rarely causes disease. Abdominal involvement occurs in only 20 percent of all cases and can mimic malignant diseases, tuberculosis and inflammatory bowel disease. A case of a 36 years old female patient with abdominal actinomycosis and review of the literature is reported. Symptoms was presented as an acute abdomen associated with painful epigastric and left subcostal mass. The pathologic process infiltrated the retroperitoneal space simulated sarcoma or lymphoma. Diagnosis was established only at the second laparotomy, when histologic examination of the removed lymph node disclosed actinomycosis. The patient is completely free of symptoms 6 month after the second operation.

Abdomen↗
PubMed1992

The influence of prior exercise at anaerobic threshold on decompression sickness.

This study was conducted to examine the effects of exercise prior to decompression on the incidence of altitude decompression sickness (DCS). In a balanced, two-period, crossover trial, 39 healthy individuals (29 males, 10 females) of mean (S.D.) age 32.5 (7.7) years and body mass index 23.7 (3.4) were each exposed twice, without denitrogenation, to an altitude of 6,400 m (21,000 ft) in a hypobaric chamber. Under the experimental condition, subjects exercised at their predetermined anaerobic threshold levels for 30 min each day for 3 d prior to altitude exposure; the other condition was a non-exercise control. Under both conditions, subjects performed exercise simulating space extravehicular activities at altitude for a period of 3 h, while breathing 100% oxygen. There were nine preferences (untied responses) for DCS, four under control and five under experimental conditions; all were Type I, pain-only bends. No carryover effect between exposures was detected, and the test for treatment differences showed p = 0.56 (95% confidence interval = 0.34-0.58) for symptoms. No significant difference in DCS preferences was found after subjects exercised up to their anaerobic threshold levels during the days prior to decompression.

Adult↗
PubMedDate not supplied

[Mathematical model of intracranial blood-cerebrospinal fluid dynamics system applied to the study of extreme conditions].

A mathematical model of cerebral blood and lymph circulation that can be used to study various effects (simulated space flight factors, functional loads) on the human body was developed. Biophysical patterns that determine relationships between cerebral blood and lymph circulation as well as between fluid volumes and pressures (P and V) are discussed. Involvement of the mechanism of brain circulation autoregulation in cerebral blood and lymph circulation is considered. The model was applied to study responses of cerebral blood and lymph circulation to various exposures such as orthostatic and antiorthostatic tests and provocative tests which led to intracranial pressure shifts and modified the ratio between volumes and pressures in different hydrodynamic systems. The modelling data were consistent with clinical, physiological and experimental observations which demonstrate an adequacy of the above model.

Aerospace Medicine↗
PubMedDate not supplied

[Nutritional corrections of histamine and serotonin levels in exposure to hypokinesia and neuro-emotional stress].

The content of histamine and serotonin was measured in test subjects exposed to: I experimental series--bed rest at an angle of +6, -2 or -6 degrees; II experimental series--neuro-emotional stress, III experimental series--an increased concentration of ammonium in the enclosure. The exposure to the factors that simulated space flight effects (i. e., orthostatic hypokinesia at -6 degrees and neuro-emotional stress and anticipation of rotation in the centrifuge) led to an increase of histamine and serotonin and a decrease of histaminepectic activity. Consumption of selected nutritional agents a day before and on the day of exposure to the neuro-emotional stress improved the content of histamine and serotonin as well as histamine-pectic activity.

Adult↗
PubMedDate not supplied

[Potential use of ultrasonic bioecholocation as a noninvasive method for assessing human intracranial volumetric ratios].

Potential applications of the method of ultrasonic echo location for determining intracranial fluid volume relations are discussed. The data presented give evidence that variations in the attenuation coefficient and propagation pattern of the ultrasonic signal may reflect changes in both hemodynamics and intracranial pressure. Simultaneous invasive investigations may help quantitate ultrasonic echo location results. The review shows that ultrasonic echo location of the brain can be used to determine variations in the intracranial volume relations induced by simulated space flights and to make well documented diagnoses.

Adaptation, Physiological↗
PubMedDate not supplied

[General patterns of bone atrophy in the absence of a weight load on the skeleton].

The rate of atrophic changes in spongy bones of the weightless man was estimated, using studies of human, dog and rat bones, as well as observations of neurological patients bed-stricken for a long time. Taking into consideration data on the literature on the bone status and mineral balance in real and simulated space flights, two models were built. The models make it possible to estimate osteoporosis of spongy bones of the axial skeleton in the absence of weight loading. One of the models--an intraspecies model for the human population--is based on the experimentally found rate of the physiological rearrangement of various spongy bones. The other--interspecies--model is built with reference to the parameters determining the rate, i. e. bone density and metabolism. The average monthly rates of axial bone losses calculated by means of the two independent methods are essentially identical. The data obtained allow prediction of the decrease of tolerance to head-to-feet impact acceleration as a function of flight duration.

Adult↗
PubMed1993

European isolation and confinement study. Blood pressure, volume-regulating hormones, and electrolytes.

In the ISEMSI confinement experiment we observed three main reactions concerning blood volume regulation: first, a stress activation produced by the high workload that the subjects had to accomplish, both before the isolation period and during the two first weeks of isolation; second, a typical defense reaction to the environment occurred, at least during the two initial days of isolation and later perhaps between crew members themselves; and third, a change in blood volume regulating hormone levels may have been the result of the increase of sympathetic system activity and of dehydration. Confinement is certainly a good and valid method to simulate space station life (with the absence of weightlessness). So, it is interesting to use these confinement studies to perform biological and physiological experiments to obtain greater knowledge, but also to prepare and validate new scientific protocols or new scientific equipment suitable for spaceflights. Even more so, confinement is a good way to prepare and train crew members for long-term space missions. It would seem desirable to confirm the scientific results obtained during the ISEMSI campaign, and especially those for the regulation of the blood volume. This will be done during the next confinement experiment, called EXEMSI, in which four subjects will be subjected to 60 days of confinement.

Adult↗
PubMed1976

[Animal experimental studies on the effects of noise stress on male fertility].

Psychic stress is able to cause male infertility. Stieve found out aspermatogenesis in executed men. Cockett et al. immobilized 5 Macaca-Monkeys 15 to 40 days in capsule module under simulated space flight conditions and detected severe testicular degeneration. Carosi and Calabro reported about workers exposed to industrial noise over a period of years; the number of offspring was found to be much lower than in non exposed families. We examined the effect of noise on the fertility of 21 male guinea pigs. Sounding of 110 dB lasted 3-5 hours daily over a period of 22-31 days. Histological examination of the testicular tissue did not show any disorder of spermatogenesis. We believe that the negative result is attributed to failings in the test arrangement. Sounding only lasted for a maximum of 31 days. However, the duration of spermatogenesis in guinea pigs is about 40 days. Moreover the sounding maximum was only 5 hours per day, yet the time of recovery took 4-5 times longer every day. Consequently the daily short-term depression of the neuroendrocrinium affected the gonadotropine secretion in similarity to the daily biorhythmic variation. Therefore the expected inhibition of fertility by the neuroendrocrinic way could not be demonstrated. Our experiments also revealed another problem. In noise-exposed guinea pigs there was 8.2 per cent tubuli contorti without complete spermatogenesis. Moreover, in the control group even 9.9 per cent of the tubuli was found to be sperm-free. It is not clear why such a contrary reaction occurred. However, it is possible that hormonal stimulation increased temporarily as a result of noise stress. It should be noted that this effect has also been reported by Arguellis.

Acoustic Stimulation↗
PubMed1994

Rethinking "shape space": evidence from simulated docking suggests that steric shape complementarity is not limiting for antibody-antigen recognition and idiotypic interactions.

The concept of "shape space" is based on the assumption that the relevant properties of individual molecules can be adequately specified by a finite list of N parameters; and that cij, the affinity between molecules i and j, can be specified by an equation of the form: cij = f(xi, xj), where xi and xj are N-dimensional vectors representing the absolute positions of molecules i and j in an objective, referential "shape space", and f is an appropriate function. We have performed simulated docking of the combining sites of immunoglobulin molecules, based on their crystallographic structures. The results suggest that shape complementarity cannot account for the specificity of idiotypic interactions, since in the simulations each pair of docked proteins had a buried surface area as great as that occurring in known complexes. It therefore seems likely that the atomic interactions accounting for the specificity of immunoglobulin recognition are highly relational. This casts doubt on the basic assumptions underlying the shape-space concept, at least in the simple form hitherto used in theoretical modelling of the immune system. In order to be realistic, the dimensionality N would have to be high (more than 20), and the function f would be irregular and discontinuous. Alternatively, if the equation cij = f(xi, xj) is interpreted as a purely formal construction in an abstract "inversion space", its validity is entirely relative to the empirical affinity matrix on which the construction is based. We conclude that at present there is no sure way of adequately characterizing the internal structure of idiotypic affinity matrices; and that models of the immune system should therefore aim at being generic and robust with respect to the structure of the idiotypic affinity matrices of unselected immunoglobulins.

Algorithms↗
PubMed1997

Novel methods of sampling phase space in the simulation of biological systems.

New advances in molecular dynamics and Monte Carlo simulations have led to impressive increases in the speed of sampling phase space for complex biological systems. These methods have been combined with new fast algorithms for computing long range electrostatic interactions for new polarizable force fields. In addition, new methods for sampling low energy molecular conformations allow the rapid determination of thermodynamically dominant regions on the potential-energy surface. Accurate measures of the rate of phase-space sampling should allow both the optimization and the comparison of methods for a particular problem of interest.

Algorithms↗
PubMed1993

MRI simulation using the k-space formalism.

An MRI simulation method, together with a corresponding computer program, using the k-space formalism has been developed. It uses a FFT algorithm to generate the ideal NMR signal from a user defined object. The k-space trajectory given by a pulse sequence is calculated. And it is used to select elements from the ideal NMR signal. This selection of elements mimic the sampling of the signal in an actual MRI experiment. During the sampling procedure changes in signal amplitude due to relaxation and excitation are introduced as well as signal phase changes due to movement or flow. Artifacts due to stimulated echoes and transversal magnetization that propagate through several repetition periods are also handled. The usefulness of the method is demonstrated by calculations using standard spin-echo sequence as well as modifications introduced in order to generate angiographical images and flow phase images. Further more a fast pulse sequence, echo planar imaging (EPI), is also simulated. The method is faster than previously presented ones. It is capable of generating images (128 x 128 matrix), including more than eight different T1 and T2 combinations, in less than 3 min on a standard 386/387 type IBM compatible PC.

Algorithms↗
PubMed1996

[Training with a simulator--experiences in space flight].

High technology and automation have not been able to significantly improve flight safety within the last two decades. The main cause of aviation accidents was and is human error. Therefore, the most powerful tools to reduce risks in aviation deal with the human operator on the flight deck. Pilot selection, training and teamwork are of the utmost importance. The simulator is a valuable training aid. Simulation provides realistic scenarios that can be used to train optimal pilot behavior in emergency situations. Many complex abnormal situations can be only managed in teamwork. That is the reason why training programmes for improved team behavior (crew resource management) are becoming more and more important.

Accidents, Aviation↗
PubMed1985

Psychosocial factors affecting simulated and actual space missions.

As space missions become longer and broader in scope, and as crews become more heterogeneous, psychological and interpersonal factors will take on increasing importance. In order to isolate instructive psychosocial issues and trends, a review was made of over 60 American and Russian simulation and spaceflight studies and reports. Although the missions accomplished most of their goals, psychological and social stresses were evident in the crew members. Psychosocial problems tended to relate to mission length. There was evidence that the use of appropriate psychological testing and interpersonal sensitivity training could improve crew selection and ameliorate problems in the simulation studies. It is time to apply this knowledge to actual spaceflight conditions.

Adaptation, Psychological↗
PubMed2000

P-SPACE: a program for simulating spatial behavior in small groups.

P-SPACE is a computer program that simulates spatial behavior in a small group of individuals. The program describes how interpersonal distances change through time as a result of changes in microlevel features, such as the minimization of local dissatisfaction. Agents are located in a two-dimensional lattice and can move some discrete space units at each discrete time unit within their neighborhood. A nonsymmetrical matrix of ideal distances between agents must be specified. Agents move in order to minimize their dissatisfaction, defined as a function of the discrepancy between possible future distances and ideal distances between agents. At each iteration, agents will move to those cells in their neighborhoods for which the function is minimized. Depending on the specific values in the ideal-distance matrix, different kinds of social dynamics can be simulated.

Electronic Data Processing↗