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P van Leeuwen

Publications and source records attributed to P van Leeuwen.

At least 19 recordsLinked to original sources
PubMed2006

[Short time variation of foetal heart rate: therapeutic management and effect on heart rate variation in the context of chronic hypotension in the 27th week of gestation].

The non-stress test is the most commonly used method in prepartal surveillance. Due to the high intra- and interobserver variability involved in subjective evaluation, the computer-assisted analysis is gaining in importance. Some studies have shown that low foetal STV may be associated with higher rates of acidosis and intrauterine mortality. Other factors influencing STV are largely not known. Low STV has been found as an effect of cortisone. In this case report, we illustrate the relevance of haemodilation therapy in the context of essential hypertension in the 27 (th) week of gestation and its effect on SVT. The treatment led to a prolongation of pregnancy to the 32 (nd) week. At the start of treatment STV increased to 4.5 ms and dropped back below this value concurrently with centralisation as documented by Doppler sonography. STV correlated clearly with the foetal condition. However, STV is dependent on numerous factors which should be investigated in further studies in order to determine appropriate reference values.

Cardiotocography↗
PubMed2005

[Magnetocardiography--a possible supplementary method for early detection of fetal distress in high-risk pregnancies].

Ever since the first report on fetal magnetocardiography by Kariniemi in 1974 numerous studies have examined cardiac activity in healthy fetuses using this technique. Recently there has been an increase in reports on the identification of fetal pathological states, in particular in the diagnosis of fetal arrhythmias, using magnetocardiography. Other possible applications of this non-invasive method include the assessment of intrauterine growth retardation and fetal stress. In a patient with gestational hypertension and asymmetric growth retardation without pathological ultrasound findings, fetal magnetocardiography showed a reduced beat-to-beat heart rate variability indicating signs of fetal stress. On the day following the magnetocardiographic recording, fetal Doppler ultrasonography findings indicated an incipient brain sparing effect. The fetal growth retardation was reflected in the duration of the fetal cardiac time intervals. We conclude that fetal magnetocardiography non-invasively enables the timely identification of pathological fetal conditions.

Adult↗
PubMed2005

Application of inulin-type fructans in animal feed and pet food.

The inulin-type fructans are non-digestible oligosaccharides that are fermented in the gastrointestinal tract of farm animals and pets. This review focuses on the various effects of inulin-type fructans in pigs, poultry, calves and companion animals. Effects of the inulin-type fructans on gut microflora, digestion and availability of nutrients, gut morphology, fermentation characteristics and animal performance are discussed. Inulin-type fructans can support animal performance and health by affecting nutrient digestion, gut microflora and gut morphology, although results vary depending on composition of the basal diet, inclusion level, type of fructan, adaptation period and experimental hygienic conditions.

Animal Feed↗
PubMed2004

Morphology of the small intestinal mucosal surface of broilers in relation to age, diet formulation, small intestinal microflora and performance.

1. Three experiments were performed to relate morphological characteristics of the small intestinal mucosal surface to age, dietary factors, small intenstinal microflora and performance of broilers. Characterisation of the small intestinal mucosal surface using a dissecting microscope was based on the orientation of the villi, villus shape and the presence of convoluted villi. 2. In Trial 1, the morphological changes of the mucosal surface were studied weekly in the period from 7 to 28 d of age. At d 7 mainly tongue- and leaf-shaped villi together with some ridge-shaped ones were observed in the middle section of the small intestine, displaying a regular zigzag pattern on 53% of the mucosal surface. During the period from d 7 to 14, the area with ridge-shaped villi increased from 7 to 63% and did not change significantly over the next 2 weeks. 3. In Trial 2, three protein sources, soy isolate (SI), wheat gluten (WG), hydrolysed wheat gluten (HWG) and SI with added L-glutamine (SI + Gln), were studied with respect to their effect as dietary components on villus morphology in the mid-small intestine and performance. Diets were fed with (0 to 14 d) and without pectin (14 to 21 d). Feed conversion ratio on the HWG diet improved in comparison to the native WG diet. During the period 0 to 14 d of age the mucosal area with zigzag-oriented villi increased when the pectin diet was supplemented with Gln. Moreover, weight gain of birds fed the SI + Gln diet increased in the period 41 to 21 d. 4. In Trial 3, a study was made of the morphological response of the villi to a stimulation of microbial activity in the digesta after addition of highly methylated pectin to the soybean meal (SBM) diet. This was performed with and without inoculation of a non-virulent Salmonella typhimurium on d 7. By d 21 the birds fed the pectin diet showed impaired weight gain and higher feed conversion. The pectin affected the mucosal surface by decreasing the area with the zigzag pattern and increasing the area with convoluted, mainly ridge-shaped villi. The Salmonella typhimurium infection increased the effects of pectin on performance and mucosal morphology.

Animal Feed↗
PubMed2004

Reproducibility and reliability of fetal cardiac time intervals using magnetocardiography.

We investigated several factors which may affect the accuracy of fetal cardiac time intervals (CTI) determined in magnetocardiographic (MCG) recordings: observer differences, the number of available recording sites and the type of sensor used in acquisition. In 253 fetal MCG recordings, acquired using different biomagnetometer devices between the 15th and 42nd weeks of gestation, P-wave, QRS complex and T-wave onsets and ends were identified in signal averaged data sets independently by different observers. Using a defined procedure for setting signal events, interobserver reliability was high. Increasing the number of registration sites led to more accurate identification of the events. The differences in wave morphology between magnetometer and gradiometer configurations led to deviations in timing whereas the differences between low and high temperature devices seemed to be primarily due to noise. Signal-to-noise ratio played an important overall role in the accurate determination of CTI and changes in signal amplitude associated with fetal maturation may largely explain the effects of gestational age on reproducibility. As fetal CTI may be of value in the identification of pathologies such as intrauterine growth retardation or fetal cardiac hypertrophy, their reliable estimation will be enhanced by strategies which take these factors into account.

Adult↗
PubMed2002

Multicentre study of fetal cardiac time intervals using magnetocardiography.

OBJECTIVE: A database with reference values of the durations of the various waveforms in a magnetocardiogram of fetuses in uncomplicated pregnancies is assessed. This database will be of help to discriminate between pathologic and healthy fetuses. A fetal magnetocardiogram is a recording of the magnetic field in a location near the maternal abdomen and reflects the electric activity within the fetal heart. It is a non-invasive method, which can be used with nearly 100% reliability from the 20th week of gestation onward. DESIGN: Durations of the waveforms were assembled from averaged magnetocardiograms and statistically processed. SETTING: Fetal magnetocardiograms were measured with different magnetocardiographs. All measurements were carried out in magnetically shielded rooms. SAMPLE: Fetal magnetocardiograms were obtained for 582 healthy patients. METHOD: The durations of the waveforms were extracted from fetal magnetocardiograms measured at the cooperating centres. The variables collected included the duration of the P-wave, the PR interval, the PQ interval, the QRS complex, the QT interval and the T-wave and QTc value. The results were compared with values extracted from electrocardiograms of fetuses measured via electrodes attached to the maternal abdomen, from electrocardiograms measured during labour using a scalp electrode, and from electrocardiograms recorded in newborns, that were found in the literature. MAIN OUTCOME MEASURES: Values of the durations are given as a function of gestational age including the regression line as well as the bounds marking the 90%, 95% and 98% prediction interval. RESULTS: The durations of the P-wave, the PR interval, the QRS complex, the QT interval and QTc value increase linearly with gestational age. The durations of the PQ interval and the T-wave are independent of fetal age. CONCLUSION: The values found agree with those found in the literature. The scatter of the data is wide due to the variation in normal physiology, the measuring system and signal processing and the subjectivity of the researcher. However, the system can define normal ranges and may be used in diagnosis.

Analysis of Variance↗
PubMed2002

[Simulation of coupling behavior of heart rhythms for study of phase synchronization].

Biological systems exhibit numerous rhythmic processes. In the human, rhythms produced by e.g. the cardiac and respiratory systems show signs of synchronisation, reflecting a physiological coupling of the underlying oscillating processes. When examining such rhythms for evidence of coupling, it is difficult to distinguish between epochs of coincidental (numerical) and real (physiological) synchronisation. The objective of this study was to simulate model rhythms in order to examine the conditions under which coupling may be recognised and the influence of noise on this recognition. Different model rhythms with adjustable noise were implemented. The synchronisation between pairs of such rhythms was examined with the help of synchrograms. Functions were used to simulate coupling. The results of the simulation were compared to real fetal-maternal cardiac rhythms. The simulation showed that heart rate variability may be an important factor in distinguishing between coincidental and real synchronisation.

Computer Simulation↗
PubMed2002

[Magnetoneurographic registration of evoked summation action fields over lumbar vertebrae following transcutaneous tibial nerve stimulation].

Goal of this study was the development of a protocol for the registration of evoked magnetic fields over the lumbar spine using off-the-shelf equipment. Three subjects in a sitting position with their torso bent slightly forward were stimulated at the tibial nerve with a commercially available stimulator. Neuromagnetic fields were registered over a circular, 800 cm2 area of the lumbosacral spine using a 61-channel 4D-Neuroimaging biomagnetometer. After appropriate signal processing, dipolar magnetic fields with a field strength 5-17 fT peak-to-peak amplitude were detected in three out of four registrations. Location and orientation of these fields concurred with the expected evoked compound action currents along the course of the nerve fibers.

Adult↗
PubMed2000

Does texture analysis improve breast ultrasound precision?

OBJECTIVE: To evaluate the possibility of distinguishing between benign and malignant breast tumors using a computer-aided evaluation of echogenicity and echostructure of ultrasound findings at certain focal points. STUDY DESIGN: The ultrasound images from 89 cases of breast tumor were documented under standardized conditions using a linear array machine and 7.5 MHz transducer. In each sonographic image, the maximum area of the 'region of interest' of the tumor was marked and then subjected to consecutive statistical analysis and correlation with the histological findings. For evaluation of tumor status eight parameters of first and second order texture statistics (gray level histogram, Fourier analysis, co-occurrence matrix) were applied. RESULTS: Benign tumors were clearly distinguished from carcinomas in the evaluation of the co-occurrence matrix and the Fourier analysis on the basis of Wilcoxon and Student t-test (P < 0.05) but not in the gray level histogram. Using logistic regression a sensitivity of 73.8% and a specificity of 54.2% were obtained. A statistically significant difference between benign tumors and moderately differentiated together with poorly differentiated carcinomas could be demonstrated. CONCLUSION: This study concludes that texture analysis appears to distinguish between benign and most malignant tumors. A computer texture analyzing system is able to improve the subjective assessment of ultrasound images of the breast but can not replace it. Where the limits of subjective assessment of a given tumor are reached, computerized texture analysis will provide additional information in the differentiation of benign from malignant findings.

Breast Neoplasms↗
PubMed2000

Entropies of short binary sequences in heart period dynamics.

Dynamic aspects of R-R intervals have often been analyzed by means of linear and nonlinear measures. The goal of this study was to analyze binary sequences, in which only the dynamic information is retained, by means of two different aspects of regularity. R-R interval sequences derived from 24-h electrocardiogram (ECG) recordings of 118 healthy subjects were converted to symbolic binary sequences that coded the beat-to-beat increase or decrease in the R-R interval. Shannon entropy was used to quantify the occurrence of short binary patterns (length N = 5) in binary sequences derived from 10-min intervals. The regularity of the short binary patterns was analyzed on the basis of approximate entropy (ApEn). ApEn had a linear dependence on mean R-R interval length, with increasing irregularity occurring at longer R-R interval length. Shannon entropy of the same sequences showed that the increase in irregularity is accompanied by a decrease in occurrence of some patterns. Taken together, these data indicate that irregular binary patterns are more probable when the mean R-R interval increases. The use of surrogate data confirmed a nonlinear component in the binary sequence. Analysis of two consecutive 24-h ECG recordings for each subject demonstrated good intraindividual reproducibility of the results. In conclusion, quantification of binary sequences derived from ECG recordings reveals properties that cannot be found using the full information of R-R interval sequences.

Electrocardiography, Ambulatory↗
PubMed1999

Spatial and temporal variations in the magnetic fields produced by human gastrointestinal activity.

Magnetoenterography (MENG) is a new, non-invasive technique that measures gastrointestinal magnetic signals near the body surface. This study was undertaken to evaluate the temporal and spatial characteristics of the magnetic signals generated by gastric and duodenal slow wave activity. The gastrointestinal magnetic fields of eight normal subjects were measured for 60 minutes in both the fasting and fed state using 36 magnetic sensors simultaneously. The results were displayed as a succession of maps over time showing the temporal evolution of the spatial distribution of the signal over the upper abdomen. In all subjects, slow wave activity of the stomach centred at 3.0 +/- 0.5 cycles min-1 in both the fasting and fed state was observed. The duodenal signal at 11.0 +/- 1.0 cycles min-1 was observed in four subjects. The spatial distribution of these two signals is distinctly different. The observed spatial and temporal variations are described in terms of a model used previously to explain the potentials observed in electrogastrography (EGG).

Adult↗
PubMed1999

Magnetocardiography in the diagnosis of fetal arrhythmia.

OBJECTIVE: To examine the possible use of magnetocardiography in the diagnosis of fetal arrhythmias. DESIGN: Investigation of routinely examined pregnant women, as well as women referred because of arrhythmias or other reasons. PARTICIPANTS: Sixty-three women between the 13th and 42nd week of pregnancy. METHODS: Recording of 189 fetal magnetocardiograms, of which 173 traces (92%) demonstrated sufficient fetal signal strength to permit evaluation. After digital subtraction of the maternal artefact, all fetal complexes were identified and the recording was examined for arrhythmic events. RESULTS: Short bradycardic episodes, not associated with any pathological condition, were found in 26% of all recordings, usually in mid-pregnancy. In 12 cases, isolated extrasystoles of no clinical importance could be identified. There were nine traces which revealed multiple arrhythmias including ventricular and supraventricular ectopic beats, bigeminy and trigeminy, sino-atrial block and atrio-ventricular conduction disturbances. Furthermore, two cases with tachycardia were found. CONCLUSION: Magnetocardiography offers a simple noninvasive method for examination of the fetal cardiac electrophysiological signal. It may thus be useful in the identification and classification of clinically relevant arrhythmia and aid in decisions concerning treatment.

Adult↗
PubMed1999

Musical rhythms in heart period dynamics: a cross-cultural and interdisciplinary approach to cardiac rhythms.

The purpose of this study was to expand classic heart period analysis methods by techniques from ethnomusicology that explicitly take complex musical rhythm principles into consideration. The methods used are based on the theory of African music, the theory of symbolic dynamics, and combinatorial theory. Heart period tachograms from 192 24-h electrocardiograms of 96 healthy subjects were transformed into binary symbol sequences that were interpretable as elementary rhythmic (percussive) patterns, the time lines in African music. Using a hierarchical rhythm pattern scheme closely related to the Derler Rhythm Classification (from jazz theory), we calculated the predominance and stability of pattern classes. The results show that during sleep certain classes, specific to individuals, occurred in a cyclically recurrent manner and many times more often than expected. Simultaneously, other classes disappeared more or less completely. Moreover, the most frequent classes obviously originate from phase-locking processes in autonomic regulation (e.g., between respiratory and cardiac cycles). In conclusion, the new interdisciplinary method presented here demonstrates that heart period patterns, in particular those occurring during night sleep, can be interpreted as musical rhythms. This method may be of great potential use in music therapy research.

Adult↗
PubMed1996

Apparent ileal dry matter and crude protein digestibility of rations fed to pigs and determined with the use of chromic oxide (Cr2O3) and acid-insoluble ash as digestive markers.

Two experiments were conducted to determine apparent ileal DM and crude-protein (CP) digestibilities in rations fed to pigs. An evaluation was made of Cr2O3 and HCl-insoluble ash as digestive markers. In addition, the effects of body weight (BW) on apparent ileal DM and CP (N x 6.25) digestibilities were studied. In Expt 1, thirteen barrows averaging 35 kg BW were fitted with post-valve T-caecum (PVTC) cannulas to determine the apparent ileal DM and CP digestibilities of a wheat gluten-bran ration (B2) and a soyabean-meal ration (E1). Immediately after morning feeding ileal digesta samples were collected on an hourly basis for a total of 12 h. Subsequently. N and marker contents were determined in the samples. The postprandial patterns of N and Cr passage were more similar than those of N and HCl-insoluble ash. Therefore Cr2O3 is more suitable as a marker than HCl-insoluble ash. The apparent ileal CP digestibility coefficient of ration B2 derived using Cr2O3 as a marker was significantly (P < 0.05) higher by 0.018 compared with the value obtained using HCl-insoluble ash. The corresponding values for ration E2 obtained using Cr2O3 and HCl-insoluble ash were both 0.825. In Expt 2, apparent ileal DM and CP digestibilities were determined in eighteen rations using twelve barrows also fitted with PVTC cannulas (BW from 40 to 100 kg). The protein sources for these rations were from different groups of feedstuffs. In four and three of the rations apparent ileal DM and CP digestibilities respectively were significantly different (P < 0.05) when assessed using the two markers. The digestibility coefficients were not systematically higher or lower for either marker. Absolute differences were < 0.049 on average. Significant effects of live weight on apparent ileal CP digestibilities were found.

Animal Feed↗
PubMed1996

[Determination of respiratory frequency from respiratory sinus arrhythmia].

In the clinical setting, the observation of undisturbed spontaneous respiration and direct measurement of an "unbiased" respiratory rate is not a practical option. However, the respiratory modulation of the heart rate (respiratory sinus arrhythmia, RSA) offers a possibility of recording the respiratory rate indirectly. The present work introduces a novel procedure for extracting the respiratory rate from the ECG, and compares the results thus obtained with those of a previously applied method. The latter is based on the determination of dominant peaks in the amplitude spectrum of a five-minute RR interval time series. The new method presented here is based on the band pass filtering of a one-minute RR interval time series with subsequent analysis of the maxima, minima and zero crossings of the resulting RSA curve. The methods were compared by determining the respiratory rates of 16 healthy male subjects measured in 15 different experimental situations, including spontaneous and controlled breathing. The respiratory rate as determined by thermistor recording of nasal breath temperature was used as control. The mean deviation from directly measured respiratory rate was 2.9 min-1 for the new and 7.2 min-1 for the previous method. The new method proved superior under all conditions except controlled breathing at low frequencies. The present study thus demonstrates the high precision of respiratory rate determined indirectly by analysing the RSA curve. Since it requires no special instrumentation, this procedure is ideally suited for clinical application, and permits the continuous recording of respiratory rate over long periods of time.

Adult↗
PubMed1995

[Magnetocardiography for assessment of fetal heart actions].

Magnetocardiography provides a new, alternative method for fetal surveillance. This method allows the registration of changes in the magnetic field produced by the fetal cardiac system. In comparison to fetal ECG, the fetal magnetocardiogram (fMCG) is not affected by intermediate tissue, in particular by the insulating effect of the vernix caseosa. Furthermore fMCG's with a good signal noise ratio can be obtained in the second trimester. A multichannel biomagnetometer allows the non-invasive measurement of the magnetic signals produced by the fetus. Examples of dta and evaluation techniques are given. Signal processing software allows the identification of all fetal beats in a data set, permitting the calculation of an averaged beat and the evaluation of signal morphology and cardiac time intervals. Furthermore it is possible to produce a beat to beat time series with high temporal resolution, making the evaluation of heart rate variability with measures from the time, frequency, and phase domain accessible. Particularly the latter are of interest in investigating changes in temporal complexity of the fetal cardiac system. Magnetocardiography thus holds the promise of improved antenatal surveillance as of the second trimester.

Adult↗