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Biomedical subjects

U Zwiener

Publications and source records attributed to U Zwiener.

At least 73 records · Page 4Linked to original sources
PubMed1993

Ketamine-diazepam N2O combination anesthesia--a new "circulatory-system-sparing" type of anesthetic in experimental surgery.

For studying the hemodynamics of the greater and lesser circulatory system in animals, the impact of general anesthesia upon cardiovascular functions should be as small, as possible. The marked circulation-depressing effect of halothane, which has so far been given preference for experiments on large animals, was confirmed by the present study of the miniature pig. There was a significant decrease in MAP, cardiac index and dp/dtmax/IP, and an increase in PAPp. Useful insights into hemodynamics, derived from experiments modeling the heart, lungs or vascular system cannot be gained for a cardiovascular system, the functions of which are greatly altered by such an anesthesia. As a new form of anesthesia with minimal cardiovascular influence, the ketamine-diazepam N2O combination, which has already been successfully applied in operations on the open human heart, is introduced into experimental surgery.

Anesthesia, General↗
PubMed1991

Experimental and clinical main forms of hypoxic-ischaemic brain damage and their monitoring.

A short review of main pathogenetic forms of hypoxic-ischaemic brain damage and its consequences for causally orientated therapy and monitoring is given. Different pathogenetic components act in several combinations. In these processes disturbances of the cardio-vascular system, of the haemorheology mainly at the level of microvessels, and disturbances of the blood brain barrier are involved. Furthermore, there are relevant disturbances of the neuronal metabolism such as accumulation of cytosolic Ca++ or disturbances caused by the effect of radicals, lipid peroxidation and changes of protein synthesis. Nowadays, chances of a cause-related therapy are increased by improved evaluation of main pathogenetic components especially regarding secondary brain damage. To evaluate these components in detail, animal models must be more clinically related, especially regarding long-term studies. The increasing knowledge about critical thresholds of reversible and irreversible brain changes also favours effective cerebral function monitoring. The main conclusions from previous experimental as well as clinically related studies indicate the necessity of very early therapeutical interventions.

Brain↗
PubMed1991

Interaction between systemic circulation and brain injuries in newborns.

In several studies different pathogenetic mechanisms of metabolic and/or cardiovascular origin were shown depending on the type of hypoxic or hypoxic/hypercapnic stress and conditions of animals (normal developed or intrauterine growth retarded newborn piglets). Thus, in normal-weight piglets the prevention of compensatory hyperventilation owing to severe hypoxia (artificially ventilated animals) leads to critical, i.e. lethal acidosis. In intrauterine growth retarded piglets, a severe hypoxia cannot be vitally compensated because of the restricted circulatory centralization. Moreover, a limited cerebrovascular dilatation during moderate hypoxia/hypercapnia produces a critical state of the metabolic supply in those animals.

Adaptation, Physiological↗
PubMed1991

Parameters for sensitive cerebral monitoring during the neonatal period in intensive care medicine.

In order to bring about further reduction of neonatal mortality and morbidity, immediate and highly sensitive detection of brain-threatening situations is necessary. We investigated 52 newborns by means of 8-channel EEG recorded with normal (15 mm/s) and compressed write-out (1 cm/min). A correct estimation of amplitude of background activity was possible by both methods. For differentiation between healthy newborns and newborns at risk, the right hemisphere amplitude of the interburst period was the most appropriate. The amplitude of the continuous EEG and the interburst period was reduced in the group of newborns at risk. In the group of the most severely disturbed newborns there was an amplitude difference between both hemispheres with greater reduction over the right hemisphere. These results emphasize the importance of the amplitude of background activity for prognostication and the necessity of using 2 interhemispheric derivations for an independent estimation of changes in both hemispheres.

Brain↗
PubMed1991

Experimental and clinical studies of neonatal eeg mapping--methodical prerequisites and data interpretation.

To investigate whether the sampling theorem was fulfilled up to now in experimental and clinical EEG-mapping of neonates and to determine the "smearing effect" of EEG transmission by the leading media up to the skin, EEG-maps from 5 slightly anaesthetized term newborn piglets and 8 healthy human newborns were calculated. A spatial sampling rate of 1-2 cycles per cm is necessary for a sufficient reproduction of surface EEG topology in newborn piglets showing activity maxima within motor projection zones. In human neonates, 8-channel mapping gave insufficient results, whereas state and EEG pattern related 16-channel maps provided sufficiently constant, but not complete pattern. Simultaneous maps from epidural and epiossal, and epiossal, and surface recordings in newborn piglets showed only small "smearing" effects. We conclude, the more topical interpretation chances exist, like in neonates with smaller "smearing" effects of transmission media, the more complete uptake of original data for mapping is necessary. Up to now, it is done seldomly.

Animals↗
PubMed1991

[Quantification of artefacts in surface EMG by validating the lower frequency limit in clinico-physiologic studies].

The surface-EMG becomes more and more important because computer assisted analysing systems can be applied. The occurrence of artefacts makes it very difficult to compare several recorded EMG channels with each other. In this study a frequency related quantification of movement artefacts and ECG-related influences on the EMG is carried out to select a suitable lower cut-off frequency for surface-EMG investigations. In 764 monopolar surface-EMG-recordings of the neck and back muscles the solely artefact-caused part of EMG-segments was analysed and quantified by means of modelling methods.

Adult↗
PubMed1990

Characteristics of heart rate fluctuations and respiratory movements during orienting, passive avoidance and flight-fight behaviour in rabbits.

In the present study different heart rate patterns were demonstrated to accompany flight-fight behaviour, orienting behaviour and passive avoidance in rabbits. Flight-fight behaviour was characterized by markedly increased heart rate and diminished overall heart rate variability. The effect was mediated by vagal inhibition and beta-adrenergic activation in a type-specific relation. Orienting behaviour was accompanied by a smaller heart rate increase and the exaggeration of slow heart rate fluctuations. The latter effect was absent during beta-adrenergic blockade suggesting a behaviourally provoked beta-adrenergic activation. Single beta-adrenergic blockade did not change the characteristics of the heart rate fluctuations at rest. During passive avoidance a vagally mediated heart rate deceleration was followed by a slow heart rate return toward the initial heart rate level. This level was not reached during beta-adrenergic blockade. The enhanced overall heart rate variability during passive avoidance was mainly caused by strengthened respiratory-induced heart rate fluctuations and, furthermore, by exaggerated slow rhythmical heart rate fluctuations. The latter effect was not observed during beta-adrenergic blockade and is referred to as an orienting component within passive avoidance. Three individual behavioural types may be differentiated in rabbits 'Weisses Gross-Silber' by stable behavioural characteristics i.e. spontaneous motor activities, preferred postures at rest and coping behaviour. The results of the present study suggest that different neurovegetative reaction types, i.e. dominating beta-adrenergic or vagal activation are correlated with stable behavioural characteristics, especially in terms of preferring active or passive coping behaviour, respectively.

Animals↗
PubMed1990

Determination of regional blood flow in abdominal organs and other structures in normal female rats and in rats with TAA-induced chronic liver injury using 99mTc labelled HSA-microsphere technique.

A method for simultaneous determination of cardiac output and regional blood flow distribution in a chronically instrumented, unrestrained rat preparation for different experimental conditions (i.e. conscious, free movement; general anesthesia) and in an experimental chronic liver injury model is described. The use of a modified radioactive microsphere reference sample method using 99mTc labelled HSA-microspheres provides valid measurements of cardiac output [255 +/- 21.6 ml/(min.kg b.wt.)] and of the determined blood flow rates of abdominal organs (with separate determination of arterial and portal-venous hepatic blood flow rates; the latter by means of arterial blood flow measurement of the gastrointestinal tract and the spleen), the myocard, the adrenals, the kidneys, and various brain regions. Furthermore, it is demonstrated that this measuring approach with chronical preparation can also advantageously be used in pharmacological or pathogenetical studies, especially because of the simple measuring equipment and the comparatively low costs that offer a broader application.

Abdomen↗
PubMed1990

Heart rate fluctuations in rabbits during different behavioural states.

Heart rate fluctuations (HRF) were investigated in 18 adult female rabbits (Weisses Grosssilber) in chronical experiments at rest, during motor activity, passive and active avoidance. Pharmacological blockades of the neurovegetative transmission were used to determine the characteristics of neurovegetative mediation during the behavioural states examined. Mean heart rate was always increased during vagal blockade and decreased during beta-adrenergic blockade. At rest the HRF in rabbits are mainly vagally mediated. Vagal blockade reduced the overall heart rate variability by more than 50%. Vagal blockade did not abolish respiratory heart rate fluctuations. If the mean respiratory frequency is greater than half of the mean heart rate frequently occurring in rabbits, the respiratory HRF are generated not synchronously with respiration but in a slower frequency range according to the physiologic effect of "cardiac aliasing". The movement related heart rate increase was absent if the movements were performed during combined beta adrenergic and vagal blockade. The heart rate reaction during passive avoidance was characterized by a heart rate deceleration abolished by vagal blockade. Respiratory HR were increased. Furthermore, the heart rate was returned to the previous mean level and the slow HRF not induced by respiration increased, mediated by beta adrenergic activation. Vagal blockade and beta adrenergic blockade diminished the heart rate acceleration and reduced the overall heart rate variability by more than 50% during active avoidance. Combined vagal and beta-adrenergic blockade fully abolished the heart rate acceleration effect during active avoidance. The ratio of the vagal to sympathetic reaction components differed in behavioural types.

Adrenergic alpha-Antagonists↗
PubMed1990

EEG spectral analysis in newborns with and without severe brain damage at different conceptional ages. A preliminary report.

Spectral power (SP) analysis of neonatal discontinuous EEG pattern of bilateral Fp-T and T-0 derivations has been performed in 5 newborns with no or mild brain damage and in 5 newborns with severe brain damage matched for conceptional age (30-39, week). Discontinuous EEG was separated in interburst and burst intervals. SP of all frequency bands was depressed in newborns with severe brain damage, with the depression being more pronounced during interburst intervals. Surprisingly, a prominent depression of the SP of the derivations of the right hemisphere and of the delta frequency bands of severely handicapped newborns was found. Calculation of coherence between homologous bipolar derivations does not improve the possibilities to separate both groups.

Brain Damage, Chronic↗
PubMed1990

[EEG and evoked potential mapping].

By spectral EEG-mapping and EP-mapping, especially the topologic dimension of electrical brain activity can be evaluated for clinical use. On the other hand, this method allows the highest solution from all functional imaging procedures within the time dimension of brain activity. On the other hand, the ability of topological solution is limited. But the latter is probably better than hitherto assumed and surprisingly well at least regarding neonates. However, several methodological prerequisites described here must be fulfilled. From the pathophysiological point of view, the limits must be considered besides the diagnostic possibilities. Meanwhile, spectral EEG-mapping and EP-mapping are diagnostically used in all main fields of traditional EEG-analysis, like seizures and in the preadiagnostics of tumors a.o. Also in the diagnostics of cerebrovascular disease including transient ischemic attacks, the EEG-mapping and/or EP-mapping are useful within the total diagnostics. There is a similar situation in the diagnostics of degenerative brain disorders. But the significance of frequently described changes inpsychoses, partly also neuroses and other functional disorders is not clear. Altogether, this non-invasive, economically most favourable method for the functional imaging procedures in brain diagnostics is promising to extent the routine diagnostics also to a more precise manner.

Brain↗
PubMed1989

[The rheologic effects of ultraviolet irradiation of autologous blood with and without lymphocytes].

Eliminating the lymphocytes from ultra-violet radiated blood specimens, we observed a decreased effect by this retransfused blood on the whole blood viscosity after 9 radiations to 18%. Also the other changes, like reduced plasma viscosity, plasma fibrinogen and alpha 2-macroglobulin level almost completely disappeared. Thus, the essential part of this effect must be mediated by the lymphocytes, or lymphocytes are necessary for this process.

Adult↗
PubMed1989

Cardiac aliasing--a possible cause for the misinterpretation of cardiorespirographic data in neonates.

Cardiac aliasing is a physiological phenomenon generating respiratory sinus arrhythmia in a frequency range lower than that of respiration if the mean respiration rate exceeds half of the mean heart rate. This was found in 8 out of 39 healthy fullterm newborns, 5 out of 33 fullterm and 3 out of 63 preterm newborns during intensive care. Quantification of cardiorespirographic data is considerably impaired in those cases when the mean respiration rate markedly exceeds half of the mean heart rate (two out of the 39 healthy full term newborns).

Arrhythmia, Sinus↗