Effect of individual structured and qualified feedback on improving clinical performance of dental students in clinical courses-randomised controlled study.

AIM: Analysis of the effect of individual structured and qualified feedback (FB) on practical skills development of dental students during clinical courses. METHODS: Fifty-three final-year dental students at Jena University Hospital participated in this prospective randomised controlled interventional study. Two calibrated assessors evaluated 128 pre- and post-assessments of 4 different dental treatment steps performed by dental students during the integrated clinical course in restorative dentistry and prosthodontics and the clinical course paediatric dentistry. The assessment included direct observation, graded and non-grading evaluation and was documented with a specific FB assessment tool. Dental students in the intervention group (IG) received an elaborated, structured and qualified FB after the pre-assessment that focussed on individual strengths and weaknesses, providing specific suggestions for improvement and establishing a personal learning goal. Participants were randomly allocated to the IG and the control group (CG). RESULTS: In both groups, dental students significantly enhanced their performance, but the difference was higher in the IG than in the CG. Large effect sizes (ES) were observed in all observed items, but FB had largest effect size in improving technical skills (ES = 1.6), followed by management (ES = 1.3) and communication skills (ES = 0.8). Factors with the highest influence on FB in enhancing dental students' clinical performance were their insight into their own mistakes or omissions, the observed dental treatment step and the duration of FB. CONCLUSION: Individual structured and qualified FB is an effective method to enhance dental students' professional performances and to individually guide the learning process.

Quadratic Phase Couplings in the EEG of Premature and Full-term Newborn during Quiet Sleep.

INTRODUCTION: This article is part of the Focus Theme of Methods of Information in Medicine on "Biosignal Interpretation: Advanced Methods for Neural Signals and Images". OBJECTIVES: The aim of this study was to compare rhythmicities in the quadratic phase coupling (QPC) in the tracé discontinue EEG patterns (TD) of premature newborns and the tracé alternant EEG patterns (TA) of full-term newborns by means of time-variant bispectral analysis. Both pattern occur during quiet sleep and are characterized by an ongoing sequence of interburst and burst patterns. The courses of time-variant bispectral measures during the EEG burst most likely indicate specific interrelations between cortical and thalamocortical brain structures. METHODS: The EEG of a group of premature (n = 5) and of full-term (n = 5) newborns was analysed. Time-variant QPC was investigated by means of time-variant parametric bispectral analysis. The frequency plain [0.5 Hz, 1.5 Hz] x [3 Hz, 6 Hz] was used as the region-of-interest (ROI). RESULTS: QPC rhythms with a frequency of 0.1 Hz (8 - 11 s) were found in all full-term newborns at all electrodes. For the premature newborns the QPC rhythms were less stable and slower (< 0.1 Hz, 11 -  17 s) at all electrodes and showed a higher inter-individual variation than for the full-term newborns. Statistically, the adaptation of a linear mixed model revealed a difference of about 5 s between both groups of newborns. CONCLUSIONS: The comparison of the results of both groups of newborns indicates a development in the interaction between cortical, thalamocortical and neurovegetative structures in the neonatal brain.

Time-variant partial directed coherence in analysis of the cardiovascular system. A methodological study.

Time-variant partial directed coherence (tvPDC) is used for the first time in a multivariate analysis of heart rate variability (HRV), respiratory movements (RMs) and (systolic) arterial blood pressure. It is shown that respiration-related HRV components which also occur at other frequencies besides the RM frequency (= respiratory sinus arrhythmia, RSA) can be identified. These additional components are known to be an effect of the 'half-the-mean-heart-rate-dilemma' ('cardiac aliasing' CA). These CA components may contaminate the entire frequency range of HRV and can lead to misinterpretation of the RSA analysis. TvPDC analysis of simulated and clinical data (full-term neonates and sedated patients) reveals these contamination effects and, in addition, the respiration-related CA components can be separated from the RSA component and the Traube-Hering-Mayer wave. It can be concluded that tvPDC can be beneficially applied to avoid misinterpretations in HRV analyses as well as to quantify partial correlative interaction properties between RM and RSA.

Dynamics of directed interactions between brain regions during interburst-burst EEG patterns in quiet sleep of full-term neonates.

The study investigates time-variant directed interactions between brain regions during the interburst-burst EEG pattern (tracé alternant) characteristic of quiet sleep in healthy neonates. The transition from interburst to burst is of particular interest as the generation of the EEG characteristics at burst onset reflects timing and time-variant interplay between the cortical and the thalamo-cortical brain structures. To study the dynamics of the interactions, time-variant partial directed coherence (PDC), a measure of effective connectivity, was used which allows analysis in the time-frequency range. The main results of the grand mean PDC analysis are: (1) PDC time-frequency patterns are frequently associated with phase-locked oscillations. (2) Interhemispheric interactions are dominant between frontal, central and occipital electrodes and intrahemispheric interactions are much less substantial. (3) An interaction breakdown for the frequency ranges 1-4 Hz (Fp(1) ⇒ Fp(2)) and 0.5-3 Hz (Fp(2) ⇒ Fp(1)) exists which lasts about 2.5s and which is located at about burst onset. (4) Strong interactions in the high-frequency range 3.5-4.5 Hz between the frontal electrodes can be observed for both directions at the burst onset. It can be concluded that the evolution of strong interactions in the high-frequency range, which starts shortly before or at the burst onset from frontal regions to anteroposterior directions as well as the frontal interhemispheric interactions, are associated with the burst onset generation. Additionally, the collapsing of the interactions before burst onset and after the burst are indicative of neuronal reorganisation processes.

Time-variant analysis of phase couplings and amplitude-frequency dependencies of and between frequency components of EEG burst patterns in full-term newborns.

OBJECTIVE: Burst activity of the 'trace alternant' (TA) EEG pattern in the quiet sleep of full-term newborns is investigated to explore the timing and the time-variant coupling characteristics of and between a burst's oscillatory components. The working hypothesis is that signal properties provide information about the neuronal initiation processes of the burst, and about the coupling and interrelation dynamics between cortical low-frequency oscillations and high-frequency spindles in thalamic structures which substantially contribute to the burst pattern. METHODS: For time-variant phase-locking index (PLI), phase-synchronization index (PSI), quadratic phase coupling (QPC) measures, and amplitude-frequency dependency analyses the Gabor and the Hilbert transformation, both implemented as fast Fourier transformation-based approaches, were used. Additionally, models of mutually coupled Duffing oscillators were adapted to the burst data derived from the neonates ('measured bursts'), and the corresponding 'modeled burst' simulations were analyzed in comparison to the measured bursts. RESULTS: A strong phase-locking of the high-frequency oscillations and synchronization between low- and high-frequency oscillatory activity at burst onset can be observed. The QPC courses and the amplitude of all oscillations rise slightly before or at the burst onset and reach their maximum within the following 1-3 s after onset. Additionally, correlative envelope-envelope and envelope-frequency couplings within and between the burst oscillations can be demonstrated. All theses time-variant signal properties can be simulated by the model. CONCLUSIONS: The amplitude-independent phase measures point to a phase stabilization of high-frequency oscillatory activity which occurs before the initiation of the low-frequency oscillation. This finding points to a trigger process in which the thalamus is initially involved. After burst onset the cortical low-frequency oscillation modulates the high-frequency oscillatory activities, where modulation and additional coupling effects can be explained by three mutually coupled oscillators. SIGNIFICANCE: The model-based analysis strategy offers an up-to-date methodological guideline and sets a new standard of analysis for the investigation of EEG patterns and event-related potentials.

Coordination of the EEG and the heart rate of preterm neonates during quiet sleep.

Aim of this study was to confirm that EEG bursts are associated with heart rate (HR) accelerations, and to investigate the synchronicity between quadratic phase couplings (QPC) courses of the EEG and HR before and during burst activity during quiet sleep in preterm newborns. The time-courses of QPC between frequency components of the EEG ([0.25-1.0 Hz]<-->[4.0-6.0 Hz]) as well as between the Mayer-Traube-Hering (MTH) wave and the frequency component of the HR associated to the respiratory sinus arrhythmia (RSA) ([0.02-0.15 Hz]<-->[0.4-1.5 Hz]) were investigated in five preterm neonates. During quiet sleep, the EEG alternates between burst and interburst activity. The burst onsets were used to trigger an averaging procedure for the EEG, HR, and QPC courses. It can be demonstrated that the envelopes of the EEG rise after the burst onset accompanied by an acceleration of HR before or at the burst maximum. The QPC courses show that the HR's QPC increases before or at the burst onset whereas the increase of the EEG's QPC is delayed. The synchronous changes of EEG and HR as well as of the corresponding QPC courses indicate a coupling between cortical, thalamocortical and neurovegetative brain structures. Such a coupling might be mediated by the MTH waves in the blood pressure.

Autonomic organization of respirocardial function in healthy human neonates in quiet and active sleep.

BACKGROUND AND AIM: It is not known on which time scales the nonlinear respirocardial interactions occur. This work's aim is to quantitatively assess functional respirocardial organization during quiet and active sleep of healthy full-term neonates by autonomic information flow (AIF) without limitation on specific time scales. Representing respirocardial interactions on a global time scale AIF carries information on a wider scope of interdependencies than known linear and nonlinear measures described. It assesses the complexity of heart rate fluctuations (HRF) and respiratory movements (RM) and their interaction comprising both linear and nonlinear properties. Thus, we hypothesized AIF to characterize novel aspects of sleep state-dependent respirocardial interaction. METHODS: RM and ECG-derived HRF of six healthy full-term neonates were studied. We analyzed their power spectra, coherence, auto- and cross-correlation and complexity estimated on local ("next sample" prediction) and global time scales (an integral over AIF predicting for all time lags in HRF and RM). RESULTS: We found the global AIF of HRF and RM to differ significantly between active and quiet sleep in all neonates, whereas on a local time scale this applied to the HRF AIF only. HRF complexity was larger in quiet than in active sleep. Respirocardial interaction was less complex in quiet versus active sleep in the high frequency band only. CONCLUSION: Complex sleep state-related changes of respirocardial interdependencies cannot be identified completely on the local time scale. Considering the global time scale of respirocardial interactions allows a more complete physiological interpretation with regard to the underlying autonomic dynamics.

Time-variant parametric estimation of transient quadratic phase couplings between heart rate components in healthy neonates.

The heart rate variability (HRV) can be taken as an indicator of the coordination of the cardio-respiratory rhythms. Bispectral analysis using a direct (fast Fourier transform based) and time-invariant approach has shown the occurrence of a quadratic phase coupling (QPC) between a low-frequency (LF: 0.1 Hz) and a high-frequency (HF: 0.4-0.6 Hz) component of the HRV during quiet sleep in healthy neonates. The low-frequency component corresponds to the Mayer-Traube-Hering waves in blood pressure and the high-frequency component to the respiratory sinus arrhythmia (RSA). Time-variant, parametric estimation of the bispectrum provides the possibility of quantifying QPC in the time course. Therefore, the aim of this work was a parametric, time-variant bispectral analysis of the neonatal HRV in the same neonates used in the direct, time-invariant approach. For the first time rhythms in the time course of QPC between the HF component and the LF component could be shown in the neonatal HRV.

Time-variant parametric estimation of transient quadratic phase couplings during electroencephalographic burst activity.

OBJECTIVES: Electroencephalographic burst activity characteristic of burst-suppression pattern (BSP) in sedated patients and of burst-interburst pattern (BIP) in the quiet sleep of healthy neonates have similar linear and non-linear signal properties. Strong interrelations between a slow frequency component and rhythmic, spindle-like activities with higher frequencies have been identified in previous studies. Time-varying characteristics of BSP and BIP prevent a definite patternrelated analysis. A continuous estimation of the bispectrum is essential to analyze these patterns. Parametric bispectral approaches provide this opportunity. METHODS: The adaptation of an AR model leads to a parametric bispectrum by using the transfer function of the estimated AR filter. Time-variant parametric bispectral approaches require an estimation of AR parameters which consider higher order moments to preserve phase information. Accordingly, a time-variant parametric estimation of the bispectrum was introduced. Data driven simulations were performed to provide optimal parameters. BSP (12 patients) and BIP (6 neonates) were analyzed using this novel approach. RESULTS: Significant differences in the time course of burst pattern during BSP and burst-like pattern before the onset of BSP could be shown. A rhythmic quadratic phase coupling (period 10 sec) was identified during BIP in all neonates. CONCLUSION: Quadratic phase couplings during BSP increases in the time course depending on depth of sedation. The visually detected burst activity in BIP is only the temporarily observable EEG correlate of a hidden neural process. Time-variant bispectral approaches offer the possibility of a better characterization of underlying neural processes leading to improved diagnostic tools used in clinical routine.

On the spatio-temporal organisation of quadratic phase-couplings in 'tracé alternant' EEG pattern in full-term newborns.

OBJECTIVE: The time courses of quadratic phase-coupling (QPC) of electroencephalographic burst and interburst patterns of the 'trace alternant' (TA) in full-term newborns have been quantified. METHODS: Using the Gabor expansion, a fast Fourier transformation based method, biamplitude, bicoherence and phase-bicoherence time courses of both burst and interburst patterns have been determined (common average reference EEG recordings). With a frequency resolution of 0.25 Hz and a frequency grid of 1-1.5 <==> 3.5-4.5 Hz (region-of-interest), a number of 15 frequency pairs result. These pairs have been investigated. RESULTS: The burst and the interburst patterns are characterized by temporally and topographically different QPC profiles. All differences are dominant at the electrode Fp1 followed by Fp2. There is a significant difference (combined multiple and global test strategy) in the QPC characteristics between both patterns within the time period from 0.75 to 1.5 s after the pattern onset at electrode Fp1. The maximal QPC in burst patterns (especially at Fp1) can be observed during this time period. In contrast to this finding, maximal QPC in interburst patterns (at Fp1) are reached immediately after the onset and at 3 s. Summarising all findings, a QPC-rhythm of 0.1 Hz during TA can be assumed. CONCLUSIONS: It can be assumed that the QPC rhythm of the TA is generated by a pattern-spanning time-variant phase-locking process and there are indications for a possible correspondence between the QPC rhythm and vegetative rhythms. SIGNIFICANCE: This study showed that advanced, time-variant analysis methods quantifying QPC rhythms are able to add new scientific information to the understanding of nature, characteristics and significance of TA in the neonatal EEG.

[Pulmonary plasma catecholamine levels and pulmonary hypertension in congenital heart disease]. / Pulmonale Plasmakatecholaminspiegel bei Patienten mit angeborenen Herzfehlern und erhöhtem pulmonalarteriellen Fluss.

Plasma catecholamines may play a role in the pathogenesis of pulmonary hypertension in congenital heart disease with increased pulmonary blood flow. At cardiac catheterization, blood samples were obtained before and after passage of the lung in patients with congenital heart disease with normal pulmonary blood flow (n=39), elevated pulmonary blood flow with normal pulmonary pressure and normal pulmonary vascular resistance (PVR) in patients with atrial septal defect (ASD) (n=57) or ventricular septal defect (VSD) (n=12), and increased pulmonary blood flow, pressure and vascular resistance in patients with ASD, VSD or both (n=22), or in patients with primary pulmonary hypertension (n=4). Plasma catecholamines were determined by reversed phase high performance liquid chromatography and electrochemical detection (HPLC-ECD). In patients with elevated PVR elevated norepinephrine levels (NE) were observed. In contrast, epinephrine levels (E) were not associated with the development of pulmonary hypertension. Patients with primary pulmonary hypertension had the highest levels of NE while patients with associated Down's syndrome had significantly lower epinephrine levels. Pulmonary plasma norepinephrine levels are increased in patients with elevated pulmonary vascular resistance. Whether this phenomena is the cause or sequalae of pulmonary hypertension needs further examination. In the future, plasma catecholamines may serve as a diagnostic feature or may result in further therapeutic options.

Functional interactions within the newborn brain investigated by adaptive coherence analysis of EEG.

To assess functional cortical organization in newborns during quiet sleep we investigated instantaneous interhemispheric coherences in six healthy full-term subjects using linked ear reference and average reference. Tracé alternant was the most frequent EEG pattern during quiet sleep of these newborns and consists of burst and interburst periods. The calculation of coherence was performed by means of time-variant autoregressive models on the basis of Kalman filtering. Coherence changes simultaneously with the appearance of these burst and interburst periods. The highest level of coherence was observed during burst periods in comparison with interburst periods. The lowest level of coherence was observed just before the burst started. During burst, maximal coherence was reached at different moments--late in the low frequency band (0.5-1.5 Hz; about 3 s after the burst started) and earlier in higher frequency bands (> 2 Hz, about 2 s). Interhemispheric coherence depended on the region being investigated. A significant level of coherence could be observed over frontal, temporal and occipital regions. Our data demonstrate significant modification of interhemispheric coherence during quiet sleep of full-term newborns and, irrespective of the immaturity of the brain, these coherences differ significantly between cortical regions.

Technique for the quantification of transient quadratic phase couplings between heart rate components.

A technique for the time-variant analysis of quadratic phase coupling (QPC) in heart rate data is introduced and tested in 6 human neonates during quiet sleep. The set up of the approach is based up on the assumption that QPCs in the heart rate variability (HRV) are related to amplitude modulation effects. The application of the biamplitude deals with the detection of the coupling pattern and the bicoherence is used for the statistical quantification of coupling. By means of the results of bispectral analysis the time-variant processing has been adapted. The frequency-selective complex demodulation of the HRV leads to the envelope of the respiratory sinus arrhythmia (RSA), this has been used as one input for a time-variant coherence analysis. The other input is the low-pass filtered 10-second-rhythm of the HRV. A time-continuous quantification of the QPC, caused by amplitude modulation (10-second-rhythm modulates the RSA), is possible using this approach. According to our observed results in neonatal HRV both a phase co-ordination between the 10-second-rhythm and RSA as well as a non-linear coupling (amplitude modulation) between these HRV components can be seen.

Relations between early prespike magnetic field changes, interictal discharges, and return to basal activity in the neocortex of rabbits.

To evaluate possible prespike field synchronizations, its relation to both interictal discharges and postspike return to baseline, penicillin-induced cortical interictal discharges were recorded in anaesthetized rabbits by magnetoencephalography (MEG) and electrocorticography (EcoG). Statistical parameters of spatial (global field power (GFP)) and temporal properties (Z-parameter) of field synchronization were calculated. In our previous report, three types of prespike field synchronization were found before the onset of interictal spike. We report here that the continuous and fluctuating, but not the abrupt prespike increases, were more often associated with a spike and wave pattern of interictal discharge than with a spike alone. Furthermore, the postspike return of these statistical parameters shows the same three patterns as the prespike field synchronizations, but in the inverse time sequence. More often than not pre- and postspike pattern were of the same type. The results suggest an influence of prespike field synchronization upon interictal discharge and subsequent field return dynamics.

Early magnetic field changes preceding the intracortical penicillin induced spikes.

Events preceding interictal activity were studied using a combination of magnetoencephalography (MEG), electrocorticography (ECoG), and intracortical field potential recordings in rabbits. We measured MEG signals simultaneously with ECoG before and during interictal discharges induced by penicillin injected in the cortex (group 1: n = 12, medial cortex, regio retrosplenialis granularis; group 2: n = 4, cortical convexity, regio retrosplenialis agranularis; control group: n = 5); in group 3 (n = 12) a 16-channel depth electrode array was used to calculate the current source density in the cortical area exhibiting interictal epileptiform discharges. The modified Z-parameter as a lumped measure of magnetic field pattern changes and the global field power as a lumped measure of changes of field amplitude differences were calculated. In almost all recordings of both group 1 and 2, the Z-parameter of intra-individual MEG data became significantly larger than the control condition before the earliest change of the interictal spike recorded at the penicillin injection site (20-310 ms earlier, median: 91 ms, n = 151). The increase in Z-parameter in averaged MEG data of group 1 was significantly correlated with time as early as 790 ms before the spike (Pearson correlation coefficient, P < 0.05). After the start of the early increase of the Z-parameter, the global field power also began to increase before the ECoG spike. These results suggest a prespike field recruitment nearly 1 s before an interictal spike.

Adaptable preprocessing units and neural classification for the segmentation of EEG signals.

In this contribution, a methodology for the simultaneous adaptation of preprocessing units (PPUs) for feature extraction and of neural classifiers that can be used for time series classification is presented. The approach is based upon an extension of the backpropagation algorithm for the correction of the preprocessing parameters. In comparison with purely neural systems, the reduced input dimensionality improves the generalization capability and reduces the numerical effort. In comparison with PPUs with fixed parameters, the success of the adaptation is less sensitive to the choice of the parameters. The efficiency of the developed method is demonstrated via the use of quadratic filters with adaptable transmission bands as preprocessing units for the segmentation of two different types of discontinuous EEG: discontinuous neonatal EEG (burst-interburst segmentation) and EEG in deep stages of sedation (burst-suppression segmentation).

[High-resolution magnetoencephalography--studies with a small-volume phantom]. / Hochauflösende Magnetoenzephalographie--Untersuchungen mit einem kleinvolumigen Phantom.

To investigate the spatiotemporal organisation of neuronal processes in an animal model using magnetoencephalography (MEG), a high temporal resolution (ms) and an appropriate spatial resolution of about 1 mm is necessary. With the aim of determining the localization error and the resolution power of high-resolution MEG systems, we developed a phantom capable of simulating the characteristics of animal models. The phantom enables us to variably position at least two magnetic field sources to within 0.1 mm. For source localization on the basis of the magnetic field data, a spatial filtering algorithm was used. The investigation of a 16-channel micro SQUID-MEG system with a current dipole orientated tangentially to the phantom surface produced the following localization data (min ... max, x, y--horizontal plane, z--depth); systematic localization error e(x) = 1.16 ... 1.67 mm, e(y) = -1.01 ... -1.28 mm, e(z) = -5.22 ... -7.64 mm, standard deviation of the individual measurements perpendicular to the dipole axis s(perp) = 0.05 ... 0.22 mm, along this axis s(long) = 0.20 ... 1.73 mm, in the depths sz = 0.17 ... 3.17 mm. The "goodness of fit" was > 95%. Separation of two dipoles was still possible for parallel dipoles at a distance apart of d(parallel) = 0.03 mm and for those oriented perpendicularly to each other at a distance apart of d(perp) = 0.10 mm. On the basis of these results we conclude that the MEG system can achieve a resolution sufficient to permit the investigation of neuronal microstructures. The spatial errors detected were related to sensor position in the cryostatic vessel as well as to external low-frequency noise.

A 16-channel SQUID-device for biomagnetic investigations of small objects.

Biomagnetic investigations in basic physiological research using animals require measurement devices different from commercial biomagnetometers used in human investigations. Two major problems have to be tackled in the design of such biomagnetometers. First, the spatial sampling needs to be much higher. Second, the distance between pick-up coils and the sources needs to be much shorter in order to compensate the worse signal-to-noise ratio (SNR) due to the smaller pick-up coils. We designed and built a 16-channel biomagnetic measurement system meeting these design criteria. The pick-up coil diameter of this new biomagnetometer is 6.7 mm, thus allowing 16 channels on an area of 3.2x3.2 cm2. The pick-up coils are located 3 mm above the dewar outer bottom, hence the closest distance to the cortical surface can be a few millimetres. We provide as an example of first measurements performed with the new biomagnetometer investigations of epileptic spikes in adult rabbits by simultaneous magnetoencephalogram (MEG) and electrocorticogram (ECoG) recordings. The high SNR of the recorded MEG and the simultaneously detected electric potentials allow investigations of the spatio-temporal pattern of neuronal processes of epileptiform spikes with signal strengths of about 3.5 pT.