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Biomedical subjects

J Wittmann

Publications and source records attributed to J Wittmann.

At least 19 recordsLinked to original sources
PubMed1995

[Simulation as a method for solving medical technical problems].

The present paper first presents a comprehensive overview of the methodological aspects of simulation. It lists the various approaches to the modelling of real-world systems and emphasizes the respective constraints on the interpretation of model data. For this purpose, a classification of typical applications of simulation models is given, and is followed by a discussion of three structurally different ways of constructing a model. The correct matching of these modelling concepts to the particular application problem in hand is discussed, with special consideration being given to the drawing of conclusions from, and the interpretation of, the simulation results. To round of the classification, the simulation models are differentiated in accordance with the nature of their implementation. By defining application type, modelling concept and model implementation, an understanding of the validity and appropriate application of any industrial model is derived.

Computer Simulation↗
PubMed1991

Respiratory function of catecholamines during the late period of avian development.

To study the function of catecholamines in the late period of avian embryogenesis, the time course of plasma catecholamines, the release of catecholamines by hypoxia and finally the effect of adrenergic agents on blood parameters and on circulation were recorded. The experiments reveal a temporary increase in plasma adrenaline and noradrenaline shortly before internal pipping occurs. On the other hand a premature increase of plasma catecholamines is induced by hypoxia. Furthermore, treating the embryo with adrenergic agents such as adrenaline, noradrenaline and phenylephrine resulted in changes of blood gas parameters: increase of PO2, O2-saturation and negative base excess, decrease of PCO2 and HCO3-. In addition, exogenous adrenaline and noradrenaline released an increase in the blood flow and an enhanced hemoglobin content in the chorioallantoic membrane, but not in the kidneys. Finally, adrenaline caused a decrease of 2,3 DPG and an increase of lactate in the plasma. The data indicate that hypoxia, which is formed normally towards the end of embryogenesis, induces an increased secretion of catecholamines which in turn improves the blood gas status. In this way the embryo is protected from deleterious hypoxic damages. This conclusion has been derived from experiments, in which the release of catecholamines was blocked under hypoxia. Under these conditions a significant increase in the mortality rate was observed.

2,3-Diphosphoglycerate↗
PubMed1991

The influence of thiourea on the development of the cultured quail embryo.

Although thyroid hormones are known to promote embryonic development, it is still questionable whether the hormones of the thyroid gland exert a stimulatory effect on the early embryo. In attempting to elucidate the thyroid function in this period, we tried to block the synthesis of thyroid hormones by thiourea and followed the embryogenesis under these conditions. The experiments were performed with cultured quail embryos (Coturnix coturnix japonica), which seemed especially suitable for those studies. The results demonstrate that thiourea causes a decrease of the survival rate, DNA-synthesis and of the excretion of uric acid into the allantoic liquid. Furthermore, it exerts an inhibitory effect on weight gain and developmental stages. On the basis of these results it seems very likely, that thyroid hormones exert a stimulatory effect on the development of quail embryos earlier than assumed previously.

Animals↗
PubMed1989

Accelerating and retarding effects of dexamethasone on the development of the avian lung.

Fertile eggs from Bovans hybrid were treated with dexamethasone on day 17 of incubation. This treatment resulted in a stimulation of the surfactant synthesis as recorded by the increased uptake of 14C-choline into the pulmonary phosphatidylcholine and the accumulation of lipoid vacuoles. On the other hand, dexamethasone caused a delay in pulmonary fluid absorption till day 19. This delay seems to be caused by a retarded onset of lung circulation. This conclusion has been derived from the lowered pulmonary hemoglobin content at this developmental stage. On the basis of the activities of ornithokallikrein and the angiotensin converting enzyme, ornithokinin may be involved in the retarded onset of circulation.

Animals↗
PubMed1988

Formation and changes of the subembryonic liquid from turned, unturned, and cultured Japanese quail eggs.

Japanese quail eggs belonging to the same flock of hens were incubated under different conditions: group 1 eggs were turned 3 times a day, group 2 eggs were left unturned, and group 3 eggs were cultured and left unturned. The results indicate that failure to turn eggs results in a delayed efflux of liquid and glucose from albumen and from the subembryonic liquid. Furthermore, the major difference between unturned and cultured eggs was that in the first group the glucose levels and in the second group the lactate levels of the subembryonic liquid were increased. It is suggested that reduced glucose supply may be involved in the disturbance of development of unturned and cultured eggs.

Animals↗
PubMed1987

Activity of putative pulmonary ornithokallikrein and angiotensin-converting enzyme during the onset of lung respiration in the chick embryo.

We have assayed a proteinase from chicken lungs, the properties of which were comparable to those of ornithokallikrein, the enzyme that catalyzes the formation of ornithokinin. The activity of this pulmonary proteinase showed an accelerated increase during the development of lung respiration (paranatal period). In contrast, the increase in the activity of angiotensin-converting enzyme (ACE), which degrades kinin, was not enhanced at this developmental stage. L-thyroxine administration accelerated the onset of lung respiration and the associated changes in the activities of ornithokallikrein and ACE. Thiourea, on the other hand, retarded the onset of lung respiration. Concomitantly, there was no pronounced increase in ornithokallikrein activity and no attenuation of the increase in ACE activity. Furthermore, the development of lung circulation, as measured by pulmonary hemoglobin concentration, paralleled the ornithokallikrein activity. The results suggest that the increase in ornithokallikrein activity and the suppression of ACE activation during the paranatal period help adapt the embryo to the neonatal period.

Animals↗
PubMed1987

Lung development under the influence of thiourea and L-thyroxine. Retarding and toxic effects of thiourea.

Chick embryos were treated on day 17 of incubation with 32.8 mumol thiourea or 18.9 nmol L-thyroxine. As was already known from previous studies, hatching was delayed and accelerated, respectively, under these conditions. The premature induction of hatching by L-thyroxine was accompanied by an advanced development of the pulmonary structure and of the circulation and by a premature absorption of the parabronchial liquid. Thiourea exerted an opposite effect on these parameters. In several cases the structural formation of the parabronchii was suppressed after treatment with thiourea. Furthermore, parabronchial liquid accumulated in those embryos, the hatching of which was suppressed. It is suggested that these changes represent a toxic effect of thiourea rather than a retardation of pulmonary development.

Animals↗
PubMed1987

[Respiratory and non-respiratory functions of the lung].

With the development of higher organisms, the problem of gas exchange of each single cell had to be resolved. Nature gave preference to the development of a specific organ for gas exchange (lungs, gills) as opposed to a system of gas exchange involving the whole organism. In vertebrates, the latter has been developed only in lungless salamanders (Desmognatus fuscus) and in the embryos of the oviparous species. Mammalian embryos also do not use their lungs during the prenatal period, however, in contrast to the oviparous species gas exchange is performed via the maternal respiratory apparatus. The transition from the pre- to the neonatal period is more problematic in mammals than in oviparous species. The critical situation is caused by the fact that mammalian lungs must be inflated within a comparatively short period of time. In oviparous species, however, the development of lung respiration lasts several hours. Several lines of evidence indicate that lungs are also involved in blood pressure changes occurring during the perinatal period. In this context the pulmonary regulation of bradykinin and prostaglandin metabolism has been emphasized. It has been recognized that lungs of adults serve not only as a gas exchange organ, but are involved in the synthesis, activation or inactivation of substances which exert an influence mainly on blood pressure. In this function, lungs are especially suitable due to their position between the venous and arterial circulation. Therefore, it is not surprising that disturbances in the pulmonary function result in manifold pathological processes.

Animals↗
PubMed1986

Activation of hepatic and inactivation of renal xanthine dehydrogenase activity by dexamethasone during the prenatal period in chick eggs.

In the experiments reported here, the effect of dexamethasone on hepatic and renal xanthine dehydrogenase toward the end of incubation was studied. Dexamethasone injected on day 17 of incubation into the chick eggs increased the hepatic and decreased the renal activity of xanthine dehydrogenase. Furthermore, dexamethasone was found to accelerate fetal development as measured by the precocious decrease of thymidine uptake into nuclear DNA and by the increased fetus weight/egg weight ratio. The data suggest that an activation of xanthine dehydrogenase is caused by a hatching-independent factor and by a factor related to the hatching process.

Animals↗
PubMed1985

[Fiberoptic bronchoscopy in intensive care medicine--functional efficacy and methodological side effects].

A prospective study was performed to determine the side effects of fiberoptic bronchoscopy on cardiopulmonary function, the influence of bronchial lavage on cardiopulmonary function, and the functional efficacy of fiberoptic bronchoscopy in obstructive atelectasis due to retained secretions. In 17 patients endotracheal intubation was immediately followed by a significant (P less than 0.01) rise in arterial, pulmonary artery and pulmonary capillary wedge pressure, heart rate, and cardiac output. There were no statistically significant differences in arterial blood gases and intrapulmonary right-to-left shunt. Two patients showed circulatory changes indicative of a heart insufficiency on the left side. A significant increase (P less than 0.001) in intrapulmonary right-to-left shunt from 12% to 17.5%, a significant decline in arterial oxygen tension of 15 mm Hg, and a significant increase of cardiac output from 6.4 to 7.71/min following saline solution lavage (20 ml in each bronchus) were observed in nine patients. The results indicate that bronchial lavage is the essential mechanism for the decline in arterial oxygen tension induced by fiberoptic bronchoscopy. In patients with unstable cardiopulmonary status, the cardiovascular response during bronchoscopy may be hazardous and the bronchoscopist should be aware of the pathophysiologic side effects involved. Fifteen therapeutic bronchoscopies were performed in five critically ill patients with obstructive atelectasis, due to retained secretions. Following the procedure, Qs/Qt declined from 23.9% to 15%, cardiac output from 9.3 to 7.31/min, and arterial Po2 increased from 58.9 to 70.9 mm Hg. The differences were statistically significant (P less than 0.0001). The therapeutic value of fiberoptic bronchoscopy in the treatment of obstructive atelectasis is demonstrated by the significant improvement in cardiopulmonary status.

Arrhythmias, Cardiac↗
PubMed1984

Lung respiration, somatic activity and gas metabolism in embryonic chicks prevented from hatching by thiourea.

Treating chick embryos with high doses of thiourea (32.8 mumol) on day 17 of incubation resulted in prevention of hatching and of active breathing. Furthermore, thiourea also prevented the increase of O2 consumption and the marked increase of somatic activity associated with the final hatching act. These findings provide evidence for the importance of active breathing in the prenatal period to initiate pipping and hatching of the avian embryo.

Animals↗
PubMed1983

Gas exchange, blood gases and acid-base status in the chick before, during and after hatching.

To study the transition from chorioallantoic to pulmonary gas exchange in birds, blood gases and acid--base variables were measured in chicks of domestic fowl before, during and after hatching. Measurements were made in samples of 'venous' blood (from allantoic arteries or the right ventricle, respectively) entering the gas exchanger (chorioallantois or lungs, respectively) and arterialized blood (from allantoic veins or the left ventricle, respectively) leaving the gas exchanger. Also, O2 uptake was measured and blood flow of the gas exchanger was determined according to the Fick principle. During the last days of incubation PO2 decreased PCO2 increased in both arterialized and 'venous' blood, but the changes of pH were small due to a concomitant increase in bicarbonate concentration, in accordance with the results of previous studies. After external pipping and hatching pronounced hypocapnia developed, but the respiratory alkalosis was partiallY compensated by a transitory non-respiratory reduction of bicarbonate. In spite of arterial hypoxia at the end of incubation and some loss of blood during hatching, blood O2 transport was not seriously impaired during pipping and hatching as revealed by 'venous' blood gases. The blood gases and pH of 17-day-old chicks were close to those of adult chickens.

Acid-Base Equilibrium↗
PubMed1983

Activation of xanthine dehydrogenase during the prenatal period through L-thyroxine, thiourea and cycloheximide.

Xanthine dehydrogenase activity in the liver of embryonic chicks has been shown to be inducible by L-thyroxine, thiourea, and cycloheximide. Results reported here indicate different mechanisms underlying the activation through L-thyroxine on the one hand, and through thiourea and cycloheximide on the other. Using hepatocyte suspension and homogenized liver, it has been shown that prenatal activation of xanthine dehydrogenase results in increased rate of uric acid formation from nucleic acids and purine derivatives, but not from amino acids.

Animals↗
PubMed1983

Motility pattern and lung respiration of embryonic chicks under the influence of L-thyroxine and thiourea.

Pressure changes in the air cell and at the egg shell have been used to monitor respiratory and somatic movements of embryonic chicks. During the prehatching period a phase of reduced activity is observed. Pulmonary respiration is initiated during this phase. Exogenous L-thyroxine exerts an accelerating effect on the hatching process and on the onset of the phase of reduced motility and of lung respiration. In thiourea-treated embryos the opposite effects on the hatching process and on the motility and respiration pattern are registered. When, however, the egg shell above the air cell was sealed with glue, times of hatching and of the beginning of lung respiration were similar to those of controls, although pipping the egg shell occurred earlier than normal. It is suggested that the effects of L-thyroxine and thiourea on the hatching process are caused by a premature or delayed onset, respectively, of pulmonary respiration.

Animals↗