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Biomedical subjects

M Eiselt

Publications and source records attributed to M Eiselt.

At least 37 records · Page 2Linked to original sources
PubMed1997

Quantitative analysis of discontinuous EEG in premature and full-term newborns during quiet sleep.

To assess the spatio-temporal structure of discontinuous EEG tracing in mature and immature newborns, we analysed mean spectral power in frequency bands between 0.8 and 16.8 Hz in 6 full-term newborns and 7 premature newborns < 32 weeks of conceptional age. The most striking results showed a significantly higher mean spectral power for the first half of bursts than for the second half recorded in > 2.8-14.8 Hz frequency bands. This pattern was more pronounced in premature than in full-term newborns. No clear differences were observed in comparisons between the first and the second half of the interburst periods. In addition, as far as mid and high frequency band spectra were considered, the mean spectral power of burst was, in both groups, higher in the right as compared to the left occipital regions.

Brain↗
PubMed1997

Influence of tissue resistivities on neuromagnetic fields and electric potentials studied with a finite element model of the head.

Modeling in magnetoencephalography (MEG) and electroencephalography (EEG) requires knowledge of the in vivo tissue resistivities of the head. The aim of this paper is to examine the influence of tissue resistivity changes on the neuromagnetic field and the electric scalp potential. A high-resolution finite element method (FEM) model (452,162 elements, 2-mm resolution) of the human head with 13 different tissue types is employed for this purpose. Our main finding was that the magnetic fields are sensitive to changes in the tissue resistivity in the vicinity of the source. In comparison, the electric surface potentials are sensitive to changes in the tissue resistivity in the vicinity of the source and in the vicinity of the position of the electrodes. The magnitude (strength) of magnetic fields and electric surface potentials is strongly influenced by tissue resistivity changes, while the topography is not as strongly influenced. Therefore, an accurate modeling of magnetic field and electric potential strength requires accurate knowledge of tissue resistivities, while for source localization procedures this knowledge might not be a necessity.

Adipose Tissue↗
PubMed1997

Glutamine and other amino acid losses during continuous venovenous hemodiafiltration.

Serum amino grams and daily losses of glutamine (Gln) and other amino acids (AAs) into diafiltrate were measured during the first 5 days of continuous venovenous hemodiafiltration (CVVHDF) in 6 ICU patients with acute renal failure (ARF). Four patients had ARF as a part of multiple organ failure (MOF) of septic origin, and 2 patients had isolated ARF because of primary renal disease. During the study, all the patients received defined total parenteral nutrition (TPN). The mean daily AA losses into dialysate were relatively low (0.61 +/- 0.1 gN) and reached 4.5% of the daily AA substitution. Gln represented 32.7 +/- 5.9% of the total AA losses (0.19 +/- 0.04 gN). Serum levels of Gln (p = 0.002) and of most other AAs were significantly lower in the patients than in the control subjects (AA analysis in 16 healthy volunteers). Phenylalanine (Phe) was the only AA that was increased significantly (p < 0.01) in the patients. The mean patient serum concentrations of Phe and tyrosine were significantly higher (p < 0.03) than the correspondent concentrations in dialysate, but the lysine concentration was higher in dialysate (p < 0.03). The serum and dialysate concentrations of other AAs did not differ. Gln in serum decreased significantly (p < 0.03) on the second day of CVVHDF but returned to the baseline levels subsequently. Serum concentrations of Phe increased on the second day of CVVHDF (p < 0.05). Serum concentrations of other AAs remained stable during the whole study. We conclude that Gln losses into dialysate during CVVHDF are relatively low, but CVVHDF itself may induce changes in Gln metabolism and distribution that are reflected by a decrease of serum Gln levels at the institution of this treatment. Therefore, the need for Gln supplementation in ICU patients is even greater in the first days of CVVHDF.

Acute Kidney Injury↗
PubMed1997

[Deterministic-chaotic and spectral-functional analysis of heart rate and respiratory movements].

After an introduction into the analysis of periodical-linear and deterministic- chaotic characteristics of heart rate fluctuations and respiratory movements their physiological background and clinical aspects are debated. Using the example of own results at the mature rabbit and new-born pig different relations of periodical-linear and deterministic-chaotic characteristics in dependence on the experimental status and neurovegetative blockades are demonstrated. From the data assignments of these characteristics are derived.

Animals↗
PubMed1996

Deterministic--chaotic and periodic properties of heart rate and arterial pressure fluctuations and their mediation in piglets.

OBJECTIVE: Only the simultaneous analysis of periodic and nonlinear properties of heart rate fluctuations (HRF) can describe completely this complex physiological process. Up to now there is, apart from a study of our own, no systematic and correlative investigation using both parameter groups, also not in early development. Thus, we tried to describe in this manner these properties of HRF, the corresponding mean arterial pressure fluctuations (MAPF) and respiratory movements (RM) and their mutual relations in neonatal pig. METHODS: In 6 term newborn piglets, periodic properties of HRF, RM, and MAPF were analyzed by spectral and coherence analysis, and deterministic-chaotic properties by calculation of correlation dimension (CD), Lyapunov exponent (LE), and construction of phase space plots. The assumption of deterministic chaotic components was supported by Theiler's test for nonlinearity, by always positive leading LEs, and by the results of a nonlinear deterministic model. These analyses were done in sleep states, general anaesthesia, hypoxic hypoxia, in ventilated state, and during cholinergic and additional beta-adrenergic blockade. RESULTS: In all experimental states, HRF and MAPF have periodic and nonlinear, very probably deterministic-chaotic properties, but in different relations. In anaesthetized piglets, periodic properties of HRF and MAPF dominate. In hypoxia the decreasing LE and CD of HRF and CD of MAPF were connected with increasing MAPF power density. Cholinergic blockade caused a decreased overall HRF and MAPF power and a decreasing LE and CD, but beta-adrenergic blockade decreased a small part of power density of both in 0.02-0.08 Hz only. The results of CD, LE, Theiler's test and the low dimensional deterministic model data suggested mainly deterministic-chaotic properties in the nonlinear part of HRF and MAPF. CONCLUSIONS: Already in neonatal piglets, both periodic and nonlinear, very probably deterministic chaotic properties of HRF and MAPF exist which change both during hypoxia and cholinergic blockade. They are partly cholinergically and--to a small extent--also beta-adrenergically mediated. The decrease of nonlinear complexity of HRF and MAPF during hypoxia suggests characteristic pathological change even in early development.

Anesthesia, General↗
PubMed1995

Application of optimized pattern recognition units in EEG analysis: common optimization of preprocessing and weights of neural networks as well as structure optimization.

The main goal of this study is to demonstrate the possibility of training the Neural Network (multilayer perceptron) classifier and preprocessing units simultaneously, i.e., that properties of preprocessing are chosen automatically during the training phase. In the first realization step, adaptive recursive estimation of the power within a frequency band was used as a preprocessing unit. To improve the efficiency of special units, the power and momentary frequency estimation was replaced by methods that are based on adaptive Hilbert transformers. The strategy was developed to obtain optimized recognition units that can be efficiently integrated into strategies for monitoring the cerebral status of neonates. Therefore, applications (e.g., in neonatal EEG pattern recognition) will be shown. Additionally, a method of minimizing the error function was used, where this minimization is based on optimizing the network structure. The results of structure optimization in the field of EEG pattern recognition in epileptic patients can be demonstrated.

Algorithms↗
PubMed1994

Heart rate and heart rate variability during sleep in small-for-gestational age newborns.

To assess the influence of intrauterine growth retardation on heart rate (HR) and HR variability during sleep, we performed polygraphic recordings in 10 small-for-gestational age (SGA) and 16 appropriate-for-gestational age (AGA) newborns. Both groups were clinically and neurologically normal and were at 37 to 41 wk conceptional age. RR intervals were analyzed using the short-time Fourier transform in three frequency bands: 1) high frequency, with a period 3-8 heartbeat; 2) mid frequency, with a period 10-25 heartbeat; and 3) low frequency, with a period 30-100 heartbeat. In both active and quiet sleep, SGA newborns significantly differed from AGA newborns by having a shorter RR interval (p < 0.01) and lower amplitude of HR variability in all bands (p < 0.05) except low frequency in quiet sleep. Quiet sleep differed from active sleep by having a longer RR interval (p < 0.05), higher high-frequency variability (p < 0.02) in both SGA and AGA newborns, and lower low-frequency variability (p < 0.005 for AGA newborns). Our data give evidence of clear modifications of both sympathetic and parasympathetic HR control in the at-risk SGA population. Similarity of between-state characteristics suggests maintained CNS control of HR in SGA as well as in AGA newborns. We speculate that between-group HR and HR variability differences may be related to augmented metabolic rate in SGA compared with AGA newborns.

Basal Metabolism↗
PubMed1993

Heart-rate variability in low-risk prematurely born infants reaching normal term: a comparison with full-term newborns.

To investigate the influence of prematurity and postnatal age on the maturation of the autonomic nervous system function, we analysed heart-rate and heart-rate variability in twelve prematurely born infants (< 37 weeks gestational age) reaching the conceptional age of 37-41 weeks. These neonates were compared with sixteen 37-41 week conceptional age newborns (< 10 days postnatal age). Heart-rate variability was analysed by spectral analysis of interbeat intervals using Short-Time Fourier Transform. We found that during both active and quiet sleep, the durations of RR-intervals were shorter and the amplitude of heart-rate variability in different frequency bands was lower in prematures reaching term than in newborns of the same conceptional age (P < 0.001). Between-state comparison showed differences in both groups. In both groups, low-frequency heart-rate variability was higher in active sleep than in quiet sleep. Between-state differences of RR-intervals and high-frequency heart-rate variability were present only in newborns (P < 0.01). Discrimination between newborns and prematures reaching term, based on RR-intervals and heart-rate variability, was correct in both sleep states with errors between 7 to 16%. However, in both newborns and prematures reaching term, between-state discrimination showed less reliable results, especially for quiet sleep discrimination with 24% (in PRT) and 20% (in NB) of errors. Our results, especially information given by factor analysis, suggest that the differences between newborns and prematures reaching term, concerning RR-interval and heart-rate variability, may be related to a changed balance between the sympathetic and parasympathetic nervous systems with a diminished parasympathetic component of heart rate control in prematures reaching term, as compared to newborns.

Discriminant Analysis↗
PubMed1993

Sleep state organization in premature infants of less than 35 weeks' gestational age.

To assess sleep organization in premature infants of < 35 wk gestational age (w GA), we performed polygraphic recordings in 24 neurologically normal neonates (eight per group): artificially ventilated 27-30 and 31-34 w GA infants and nonventilated 31-34 w GA infants. Sleep states were defined by concordance of EEG and rapid eye movement criteria. Uninterrupted active sleep periods of > 13 min and quiet sleep periods of > 5 min were observed in all babies, except in one 33 w GA ventilated infant. Intervals from the beginning of recording to the 1st quiet sleep period varied from 0 to 63 min and intervals to the beginning of the longest sleep cycle varied from 5 to 84 min. Nonventilated 31-34 w GA infants had longer sleep cycles (p < 0.02), principally because of longer active sleep periods. However, percentages of different states in the cycles were similar in all groups. When body movements were required for state definition, amounts of active and quiet sleep diminished and the percentage of indeterminate sleep was augmented significantly. In conclusion, our study demonstrated that 1) sleep state differentiation is present as soon as 27 w GA; and 2) artificial ventilation, performed in a highly specialized neonatal intensive care unit, does not modify sleep organization of neurologically normal premature infants. We hypothesize that this "earlier" sleep state differentiation, compared with previous data, may be related to improvements in neonatal intensive care over recent years.

Electroencephalography↗
PubMed1992

Sigh-related heart rate changes during sleep in premature and full-term newborns.

The functional linkage in the cardio-respiratory system demands precise coordination of their activity. Sighs provide an opportunity to study the interaction and the maturation of the autonomic nervous system. In 4 groups of normal, sleeping newborns (31 to 41 weeks conceptional age [wCA], 2 to 10 days postnatal age) we investigated heart rate changes caused by sighs by means of polygraphy. In full-term (39-41 wCA) and near-term newborns (37-38 wCA) sighs during quiet sleep (QS) were accompanied by heart rate acceleration (p < 0.01) and thereafter by heart rate deceleration (p < 0.01). During active sleep (AS) only heart rate acceleration (p < 0.01) was observable. In prematures (35-36 wCA) acceleration could be observed in QS (p < 0.01) and AS (p < 0.01) but no deceleration in QS. In prematures of 31-34 wCA no changes during AS and QS could be detected. Body movements caused heart rate acceleration but no heart rate deceleration. In conclusion, it can be hypothesized that heart rate acceleration may be caused by reduced vagotonus initiated by augmented lung volume and movements. Sigh-related changes responsible for heart rate deceleration occur solely during quiet sleep. In prematures of 31-34 wCA these reflexes are not developed.

Electroencephalography↗
PubMed1991

Use of discrete Hilbert transformation for automatic spike mapping: a methodological investigation.

On the basis of discrete Hilbert transform (DHT) realised by fast Fourier transform (FFT), a new strategy for automatic spike mapping is introduced. The further computation of the EEG time series after DHT results in the time series of the momentary power and the momentary frequency. Both are used for the solution of the main requirements of automatic spike mapping. The spike-mapping concept introduced meets the requirements of efficient automatic spike detection and also has an insensitivity with regard to EMG interference and transient signal components, a frequent cause of false positive detections. Additionally, there are advantages if the momentary power of the spike is mapped instead of the spike potential. The use of momentary power makes a combination of power spectral mapping and spike-mapping strategies possible.

Algorithms↗
PubMed1991

Using discrete Hilbert transformation for interval-related calculation of the respiration rate in neonates.

From the basis of the fast Fourier transformation (FFT), the discrete Hilbert transformation (DHT) is used to compute the instantaneous respiration rate in neonates. This interval-related computation of respiration rate must be combined with a concept of adaptive filtration of the respiratory movements. This strategy is performed by adaptive recursive estimations of mean values with different adaptation constants. Additionally, a frequency band limitation is carried out on the basis of the peak characteristic of the power spectrum (respiratory movements). By means of the adaptive estimation of the variance of respiratory movements, an amplitude-time window is calculated to choose between epochs with breaths and apnoea.

Algorithms↗
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

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

[Prognostic predictive value of neonatal ultrasonic studies of the CNS and of EEG monitoring for the psychomotor development at 1 year of age].

The prognostic value of cranial ultrasound and EEG-monitoring for the developmental outcome at 1 year of age in 209 premature and full-term newborns was studied retrospectively. The first ultrasound examination was performed within the first three days of life. Further investigations were done depending on type of severity of the findings. The investigation was completed by EEG-monitoring in 41 patients. The infants were investigated for psychomotor development. 158 infants were found normally developed. Abnormal neonatal ultrasound findings were registered in 18.9% of them. Developmental retardation was observed in 46 infants. 54.3% of them had abnormal ultrasound findings. 2/3 of infants with neonatal major brain insults like IVH III-IV or leukomalacia showed serious neurological handicaps, whereas subependymal bleedings seem to be without influence onto the development. In contrast pathologic EEG's were of higher prognostic value. None of the infants with a abnormal EEG was developed normally.

Brain Diseases↗
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↗