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F Neumann

Publications and source records attributed to F Neumann.

At least 55 records · Page 3Linked to original sources
PubMed1995

The influence of optimization target selection on the structure of arterial tree models generated by constrained constructive optimization.

The computational method of constrained constructive optimization was used to generate complex arterial model trees by optimization with respect to a target function. Changing the target function also changes the tree structure obtained. For a parameterized family of target functions a series of trees was created, showing visually striking differences in structure that can also be quantified by appropriately chosen numerical indexes. Blood transport path length, pressure profile, and an index for relative segment orientation show clear dependencies on the optimization target, and the nature of changes can be explained on theoretical grounds. The main goal was to display, quantify, and explain the structural changes induced by different optimization target functions.

Animals↗
PubMed1994

The branching angles in computer-generated optimized models of arterial trees.

The structure of a complex arterial tree model is generated on the computer using the newly developed method of "constrained constructive optimization." The model tree is grown step by step, at each stage of development fulfilling invariant boundary conditions for pressures and flows. The development of structure is governed by adopting minimum volume inside the vessels as target function. The resulting model tree is analyzed regarding the relations between branching angles and segment radii. Results show good agreement with morphometric measurements on corrosion casts of human coronary arteries reported in the literature.

Animals↗
PubMed1993

Structural and functional properties of ribosomal protein L7 from humans and rodents.

By subtractive screening of a library made from mRNA of lipopolysaccharide (LPS)-stimulated mouse B lymphocytes we isolated cDNA-clones encoding the ribosomal protein L7. Human L7 mRNA was cloned from activated T-lymphocytes. Although no specific function of L7 in the translation apparatus is known as yet, it should be a critical one as indicated by its high degree of structural conservation during evolution and its regulated expression in lymphoid cells. Human and rodent L7 proteins carry sequences similar to the basic-region-leucine-zipper(BZIP)-motif of DNA-binding eucaryotic transcription factors. We show here that the region of L7 carrying the latter motif mediates L7-dimerization and stable binding to DNA and RNA. A preferential binding to RNA-structures is demonstrated.

Amino Acid Sequence↗
PubMed1992

[Transesophageal echocardiography from the surgical viewpoint].

Following the development of new techniques in echocardiography and especially of Doppler color flow imaging, a new dimension of cardiac surgery has been brought about. The use of transesophageal probes facilitates routine surgery to be performed without interferences and, also, comparability between repeated ultrasonic measurements. Originally, echocardiography was mainly applied for quality control by comparing pre- and postoperative echocardiograms. Now it is equally important in perioperative strategy planning guiding the surgeon's decision throughout the operation as well as in cardiac emergencies. Using intraoperative echocardiography routinely in cardiac surgery establishes a more and more close cooperation between surgeons, cardiologists, and anesthesiologists. In order to evaluate the clinical relevance of echo findings, they have to be repeatedly correlated to surgical realities and to long term results of clinical outcome.

Adult↗
PubMed1992

Effects of coronary artery bypass grafting on global and regional myocardial function. An intraoperative echocardiographic assessment.

The immediate effect of coronary artery bypass grafting on global and regional myocardial function was studied by means of epicardial two-dimensional echocardiography during operations in 20 patients. Echocardiograms were recorded before cardiopulmonary bypass and 5 and 30 minutes after bypass. Global left ventricular function was expressed as percent short-axis area change and regional function as percent fractional area change. Segments were classified according to their baseline function as normal (percent fractional area change greater than 40%), moderately hypokinetic (percent fractional area change 21% to 40%), or severely dysfunctional (percent fractional area change less than 20%). Percent short-axis area change was significantly reduced immediately after cardiopulmonary bypass (from 42.0% +/- 4.6% to 34.9% +/- 3.0%, p less than 0.05) but had returned to baseline 30 minutes after bypass (42.6% +/- 4.0%). Similarly, function of normal and moderately hypokinetic segments decreased significantly immediately after cardiopulmonary bypass (normal segments: percent fractional area change 56% +/- 0.9% before bypass to 42.3% +/- 1.5% after bypass, p less than 0.0001; moderately hypokinetic segments: 31.0% +/- 0.9% to 25.1% +/- 1.4%, p less than 0.002). Both normal and moderately hypokinetic areas regained baseline function by 30 minutes after bypass (normal segments: 53.4% +/- 1.6%; moderately hypokinetic segments: 35.4% +/- 2.0%). In contrast, severely dysfunctional segments were found to be significantly improved immediately after bypass (14.7% +/- 0.9% before bypass to 27.7% +/- 2.1% after bypass, p less than 0.0001). This improvement was maintained 30 minutes after bypass (22.8% +/- 1.5%, p less than 0.001). We conclude that coronary revascularization exhibits an immediate beneficial effect on chronically underperfused myocardium having severely depressed baseline function. However, in normal and moderately hypokinetic areas, the depressant effects of global ischemia and reperfusion prevail in the immediate postbypass period, leading to a global depression of cardiac function.

Angina Pectoris↗
PubMed1991

Early indicators for carcinogenesis in sex-hormone-sensitive organs.

Hormones induce tumours in various target tissues in different species of laboratory animals in long-term toxicity studies. Examples of such tumours are: mammary gland tumours in beagle dogs after long-term treatment with progestogens or progestogen/oestrogen combinations; pituitary and mammary gland tumours in rats and mice after long-term treatment with oestrogens or progestogens with an oestrogenic partial effect; interstitial cell tumours in rats after chronic overstimulation by endogenous luteinising hormone; endometrial carcinomas in rats after chronic treatment with dopamine agonists. As a rule every hormone when given in excessive doses over prolonged periods can induce a tumour in the relevant target organs. Drugs or chemicals which stimulate or inhibit the endogenous hormone production of certain endocrine organs can have the same effect. Tumour induction can be a direct or indirect effect involving specific regulatory mechanisms. In general, the induction is preceded by excessive hyperplasia of the target tissue concerned or with regard to the pituitary where excess production of the stimulating hormone occurs. Tumour induction in chronic toxicity studies can usually be predicted by determining hormone levels in short-term studies. Hormones and drugs or chemicals which induce tumours when given in doses high enough to induce hyperplasia are unlikely to do so by a genotoxic mechanism.

Animals↗
PubMed1991

Cyproterone acetate in the treatment of sexual disorders: pharmacological base and clinical experience.

Cyproterone acetate (CPA) has been discovered more than 25 years ago and it was the first antiandrogen suitable for clinical use. CPA inhibits the action of endogenous and exogenous androgens at all androgen target organs; these include the prostate, seminal vesicles, testes, and the vas deferens. However, this antiandrogen also antagonizes less sex-specific effects of androgens, for example ossification of the epiphyseal cartilage, sebaceous gland function and skin thickness. Indications for CPA: Prostate cancer, androgen induced disorders of the skin (acne, seborrhoea, hirsutism, alopecia), precocious puberty and sexual disorders in men. Concerning sexual deviations clinical trials started in 1966. CPA leads to loss of libido and the ability to achieve erection, followed by the inability to achieve orgasm, after about 14 days of treatment (100-200 mg daily orally or 300 mg weekly i.m.). These effects are reversed in the same order as the onset. About 75 to 80% of patients respond to this therapy. CPA is generally well tolerated. Tiredness, lack of drive, listlessness and depressive moods have been reported as non-specific side-effects. Slight gynecomastia occurs in about 20% of patients. There are no good alternatives in this indication. Pure antiandrogens are unsuitable, because these are unable to inhibit libido sufficiently. Tranquilizers are not very effective, high doses of estrogens are associated with severe (cardiovascular) side effects. Orchidectomy is an irreversible intervention, LHRH analogues are associated with hot flushes and the initial increase in testosterone (flare phenomenon).

Androgen Antagonists↗
PubMed1991

Immediate effects of mammary artery revascularization versus saphenous vein on global and regional myocardial function: an intraoperative echocardiographic assessment.

The immediate effect of coronary artery bypass surgery on global and regional myocardial function using the internal mammary artery (IMA) versus saphenous vein (SV) was studied intraoperatively using transesophageal echocardiography (TEE). Thirty-two patients received an IMA and 10 patients only SV. Transesophageal echocardiography was recorded before thoracotomy, 5 minutes after the end of cardiopulmonary bypass (CPB) and after chest closure. Global and regional left ventricular function were expressed as a percent of the short axis area change (%SAAC) and a percent of the fractional area change (%FAC), respectively. Segments were classified according to their baseline function as normal, %FAC greater than 40%, or dysfunctional, %FAC less than 40%. Only normal segments were considered in this study. No significant change in %SAAC in either group was observed in this study. Internal mammary artery revascularized segments showed a significant decrease in %FAC from 57 +/- 1 before thoractomy to 53 +/- 2 5 minutes after CPB, whereas SV segments showed a significant improvement in %FAC from 56 +/- 1 to 61 +/- 1. Applying strict criteria derived from intraobserver and cycle-to-cycle variability, 17% of IMA segments had deteriorated by more than 36% whereas only 4% of SV segments showed such deterioration. Conversely, 17% of SV segments showed an increase in %FAC by more than 36% and only 3% of IMA segments improved similarily. The observed changes were of short duration and had largely resolved by chest closure.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Simulation of coronary circulation with special regard to the venous bed and coronary sinus occlusion.

The vascular beds of the left circumflex and the left anterior descending coronary arteries are modelled by means of coupled differential equations that consider an arterial, a capillary and a venous section. In a stepwise procedure, experimental data from normal coronary perfusion and coronary sinus occlusion are used to assess the model parameters. For venous distensibility, a non-linear form of pressure-volume relationship proved vital to reproduce the characteristics of the rise in venous pressure after the onset of coronary sinus occlusion. Numerical integration was carried out for normal perfusion and for coronary sinus occlusion, yielding time courses of flows, volumes and pressures within large coronary arteries, capillaries and coronary veins. Coronary sinus occlusion reduces total mean flow by 18% and divides intramyocardial flow between the capillaries and the veins into a forward component of 3.03 mls-1 and a backward component of -1.54 mls-1. This result represents a prediction for a haemodynamic quantity which is therapeutically important but inaccessible to measurement. Varying degrees of systolic myocardial squeezing are studied to display the impact of myocardial contractility and vessel collapse on the mean values and phasic components of intra-myocardial flows.

Blood Pressure↗
PubMed1990

The role of intramyocardial pressure during coronary sinus interventions: a computer model study.

A model consisting of an arterial, a capillary, and a venous compartment was developed to reproduce experimentally determined hemodynamic results of the arterial and venous sides of the coronary circulation. From the model, intramyocardial flow between capillaries and veins, which is inaccessable to measurement, was then estimated. Results are given for normal perfusion and coronary sinus occlusion conditions. For both conditions, intramyocardial pressure was varied within the model in order to study its impact on intramyocardial flow. For low and moderate intramyocardial pressures under coronary sinus occlusion, retrograde flow from veins to capillaries was seen to increase with increasing intramyocardial pressure. However, for very high values of intramyocardial pressure, which are close to left ventricular pressure, retrograde flow declined.

Computer Simulation↗
PubMed1990

Intraoperative echocardiography in cardiac emergencies.

Echocardiography has brought about a new modality of surgical decision making in open heart surgery. Especially in urgent and emergency surgery, echocardiography can provide decisive insight into the underlying pathophysiological processes, improved monitoring of cardiac function, as well as immediate quality control after the procedure. The importance of intraoperative echocardiography for the cardiac surgeon is illustrated in a number of selected case reports.

Aged↗