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Biomedical subjects

M Kohl

Publications and source records attributed to M Kohl.

At least 19 recordsLinked to original sources
PubMed2005

[Morbidity and mortality of extremely low gestational age infants in Schleswig-Holstein. Follow-up at three to six years corrected age of infants < 27 + 0 weeks gestation in Schleswig-Holstein, Germany].

BACKGROUND: Regional, population-based outcome studies of extremely preterm infants may help to assess the quality of neonatal care across centres and explain variation. PATIENTS AND METHODS: We included all extremely low gestational age infants (< 27 + 0 gestational age = ELGA) of six paediatric hospitals in Schleswig-Holstein born during 1997 to 1999. The surviving children were evaluated at the corrected age of three to six years with the developmental test ET 6-6. The end point major disability was determined as subnormal scores in the developmental test ET 6-6 (< 2 SD), or any of the following diagnoses: cerebral palsy, blindness, deafness, epilepsy and/or hydrocephalus requiring a shunt system. RESULTS: 130 infants with gestational age (GA) < 27 + 0 weeks were identified. 85 survived until discharge and 82 survived until follow-up. 63 children (77% of all possible cases) participated in the developmental test. Neonatal survival increased with gestational age: 0/1 GA = 22 weeks, 3/10 GA = 23 weeks, 12/25 GA 24 = weeks, 28/43 GA = 25 weeks, 42/51 GA = 26 weeks. At follow-up 24 children had a major disability, among those were 14 children with multiple major disabilities. There was no significant correlation between major disability and gestational age. CONCLUSIONS: In a regional neonatal care system only infants of 25 to 26 weeks gestation but not those of lower GA show good survival rates. Major disability of extremely preterm infants seems to be independent of gestational age.

Cause of Death↗
PubMed2004

Measurement of the exclusive 3He(e,e'p) reaction below the quasielastic peak.

New, high-precision measurements of the 3He(e,e(')p) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross-section, but significant differences remain.

Journal Article↗
PubMed2004

Antenatal corticosteroid therapy in premature infants.

OBJECTIVE: The objective was to examine the effect of antenatal corticosteroid treatment on premature infants, with special attention to any possible adverse effects on neonatal outcome. METHODS: A retrospective chart review of all singleton and multiple pregnancies delivered in our perinatal center between 1991 and 1999, who had a birth weight of < or =1,500 g and who were subsequently admitted to our neonatal intensive care unit. Three hundred and sixty-five infants were included in the study and divided into two groups. One group had a gestational age below 28 weeks (< or =196 days) and one group was 28 weeks (>196 days) onward. RESULTS: Antenatal corticosteroid therapy reduced the duration of mechanical ventilation, the need for supplementary oxygen, and the need for exogenous surfactant in neonates born at >196 days's gestation (p<0.05). Corticosteroid treatment seemed to benefit the respiratory distress syndrome (RDS; p=0.051) in this group. There were less cases of necrotizing enterocolitis and neonatal death in the group with corticosteroid treatment (p<0.05). Before 28 weeks' gestation, all parameters that were examined (e.g., duration of mechanical ventilation, need for supplemental oxygen, need for exogenous surfactant, RDS) showed no significant differences between those pregnancies pre-treated with corticosteroids or those not treated with corticosteroids. There was no adverse effect of corticosteroids on chorioamnionitis and early onset sepsis in pregnancies with a premature rupture of the membranes. Repeated corticosteroid treatment had no effect on birth weight, but did not improve neonatal outcome either. The interval between last corticosteroid treatment and delivery had no influence on RDS. There was no effect of corticosteroids on periventricular leukomalacia and intraventricular hemorrhage. Regression analysis showed a higher risk of severe RDS in multiple gestations. CONCLUSION: Antenatal betamethasone treatment reduces perinatal morbidity and mortality after 28 weeks' gestation. We found no adverse effects and also no benefit of repetitive corticosteroid treatment. The interval between last corticosteroid treatment and delivery did not influence the incidence of RDS. Dose, timing, and rate of antenatal corticosteroids should be reconsidered in multiple gestations.

Adrenal Cortex Hormones↗
PubMed2002

Prenatal sonographic features of Harlequin ichthyosis.

Harlequin ichthyosis (HI) is a severe and usually fatal congenital keratinization disorder with autosomal recessive inheritance. For over a decade, prenatal diagnosis of HI relied on fetoscopic or sonographically guided skin biopsies, and, therefore, was limited to previously affected families. Only a few cases of prenatal sonographic diagnosis have been published and the sonographic findings are variable. We report a case of HI, in which the typical features were detected during fetal life but the condition remained undiagnosed at 35 weeks' gestational age in this pregnancy complicated by premature rupture of membranes, oligohydramnios and intrauterine growth retardation. The documented prenatal findings were a flat profile with absent nose; a large mouth, widely gaping open; dysplastic ears; abnormal fixed position of the hands; and edema of thighs and feet; and intrauterine growth retardation. Following elective cesarean section the infant died of septicemia 12 days post-partum despite etretinate and antibiotic treatment. The sonographic features of HI are discussed together with those previously reported and an attempt is made to delineate sonographic markers of this rare disorder.

Adult↗
PubMed2002

Cross talk in the Lambert-Beer calculation for near-infrared wavelengths estimated by Monte Carlo simulations.

Using the modified Lambert-Beer law to analyze attenuation changes measured noninvasively during functional activation of the brain might result in an insufficient separation of chromophore changes ("cross talk") due to the wavelength dependence of the partial path length of photons in the activated volume of the head. The partial path length was estimated by performing Monte Carlo simulations on layered head models. When assuming cortical activation (e.g., in the depth of 8-12 mm), we determine negligible cross talk when considering changes in oxygenated and deoxygenated hemoglobin. But additionally taking changes in the redox state of cytochrome-c-oxidase into account, this analysis results in significant artifacts. An analysis developed for changes in mean time of flight--instead of changes in attenuation--reduces the cross talk for the layers of cortical activation. These results were validated for different oxygen saturations, wavelength combinations and scattering coefficients. For the analysis of changes in oxygenated and deoxygenated hemoglobin only, low cross talk was also found when the activated volume was assumed to be a 4-mm-diam sphere.

Absorption↗
PubMed2001

Neutral pion threshold production at Q(2) = 0.05 GeV(2)/c(2) and chiral perturbation theory.

New data are presented on the p(e,e'p)pi(0) reaction at threshold at a four-momentum transfer of Q(2) = 0.05 GeV(2)/c(2). The data were taken with the three-spectrometer setup of the A1 Collaboration at the Mainz Microtron MAMI. The complete center of mass solid angle was covered up to a center of mass energy of 4 MeV above threshold. Combined with measurements at three different values of the virtual photon polarization epsilon, the structure functions sigma(T), sigma(L), sigma(TT), and sigma(TL) are determined. The results are compared with calculations in heavy baryon chiral perturbation theory and with a phenomenological model. The measured cross section is significantly smaller than both predictions.

Journal Article↗
PubMed2001

Linear aspects of changes in deoxygenated hemoglobin concentration and cytochrome oxidase oxidation during brain activation.

We used near infrared spectroscopy (NIRS) to investigate the vascular and metabolic response to brain activation in human primary and adjacent secondary visual cortex. NIRS is able to measure concentration changes in deoxygenated hemoglobin ([deoxy-Hb]) (which mainly contribute to the blood oxygenation level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI)) as well as concentration changes of oxygenated hemoglobin ([oxy-Hb]) and corpuscular blood volume ([total-Hb] = [oxy-Hb] + [deoxy-Hb]) and changes in the redox status of the cytochrome c oxidase ([Cyt-Ox]), a putative parameter for cellular oxygenation. A sound understanding of the transfer functions between stimulus parameters, neuronal activity, and vascular/metabolic parameters is important for interpretation of data acquired with indirect neuroimaging techniques like fMRI, especially in event-related design studies. In the present study we tested whether the vascular/metabolic response to stimulation can be described as a linear and time invariant system. Since linearity is a property attributed to systems that satisfy the scaling and superposition properties, as a first simple test, superposition of the responses obtained from short duration visual stimuli was used to predict the responses of longer duration stimuli. Our results showed that the predictions of [deoxy-Hb] and [Cyt-Ox] responses to stimuli of 6- to 24-s duration were satisfactory whereas predictions of [oxy-Hb] and [total-Hb] were insufficient. In a second step, a calculated convolution function of an assumed impulse response function and the stimulus function was fitted with the measured [deoxy-Hb] and [Cyt-Ox] curves to obtain amplitude, time delay, and time constant parameters. We show that predictions of cellular and vascular oxygenation responses to visual stimulation are good for 6- to 24-s stimuli duration under the assumption of a linear transfer characteristic. This model is not valid for corpuscular volume changes which affect mainly the [oxy-Hb] response. Noninvasive NIRS is shown to be a suitable method to get more direct information about neuronal-activity-associated changes in cerebral parameters which are partly reflected in BOLD signal but are not fully understood yet.

Adult↗
PubMed2000

Somatosensory evoked fast optical intensity changes detected non-invasively in the adult human head.

This work is the first to report optical intensity changes (DeltaI/I approximately 0.05%) with a latency between 60 and 160ms after electrical median nerve stimulation at 5Hz detected non-invasively through the intact adult human skull in volunteers. The signal is localised and reproducible when measuring at the same position on successive examinations. Compared to previous reports of fast optical changes in the human adult by a single group (Psychophysiology, 32 (1995) 505) the here reported changes are much smaller. They are in line with results from a photon transport calculation on a head model employing data from exposed cortical tissue. The origin of the signal found here is still unclear, however, they might be the non-invasive equivalent to the scattering changes found in exposed cortical tissue studies (J. Neurophysiol., 78 (1997) 1707).

Adult↗
PubMed2000

Surface excitations of a bose-einstein condensate

Surface modes in a Bose-Einstein condensate of sodium atoms have been studied. We observed excitations of standing and rotating quadrupolar and hexadecapolar modes. The modes were excited with high spatial and temporal resolution using the optical dipole force of a rapidly scanning laser beam. This novel technique is very flexible and should be useful for the study of rotating Bose-Einstein condensates and vortices.

Journal Article↗
PubMed2000

Rapid detection of expansions by PCR and non-radioactive hybridization: application for prenatal diagnosis of myotonic dystrophy.

The mutation specific for myotonic dystrophy (DM) is an unstable expanded CTG repeat located in the 3'-untranslated region of the myotonin protein kinase gene. Expansion of the CTG repeat shows a positive correlation with the severity of the disease and increases in successive generations of DM patients. Children with the congenital form of DM show the most severe phenotype and have large expansions, usually > 1000 repeats. For pregnant women with DM, prenatal diagnosis of DM may be offered. To reduce the time between chorionic villus sampling or amniocentesis and final results of DNA analysis in these cases, a fast and efficient method has been developed. This method combines direct PCR analyses for normal alleles with a nested PCR system followed by non-radioactive hybridization with a single-stranded probe.

Adult↗
PubMed2000

Spontaneous low frequency oscillations of cerebral hemodynamics and metabolism in human adults.

UNLABELLED: We investigated slow spontaneous oscillations in cerebral oxygenation in the human adult's visual cortex. The rationale was (1) to demonstrate their detectability by near infrared spectroscopy (NIRS); (2) to analyze the spectral power of as well as the phase relationship between the different NIRS parameters (oxygenated and deoxygenated hemoglobin and cytochrome-oxidase; oxy-Hb/deoxy-Hb/Cyt-ox). Also (3) influences of functional stimulation and hypercapnia on power and phase shifts were investigated. The results show that-in line with the literature-low frequency oscillations (LFO) centred around 0.1 s(-1) and even slower oscillations at about 0.04 s(-1) (very low frequency, VLFO) can be distinguished. Their respective power differs between oxy-Hb, deoxy-Hb, and Cyt-ox. Either frequency (LFO and VLFO) is altered in magnitude by functional stimulation of the cortical area examined. Also we find a change of the phase shift between the vascular parameters (oxy-Hb, tot-Hb) and the metabolic parameter (Cyt-ox) evoked by the stimulation. It is shown that hypercapnia attenuates the LFO in oxy-Hb and deoxy-Hb. CONCLUSIONS: (1) spontaneous vascular and metabolic LFO and VLFO can be reproducibly detected by NIRS in the human adult. (2) Their spectral characteristics and their response to hypercapnia are in line with those described in exposed cortex (for review see (Hudetz et al., 1998)) and correspond to findings with transcranial doppler sonography (TCD) (Diehl et al., 1995) and fMRI (Biswal et al., 1997). (3) The magnitude of and phase relation between NIRS-parameters at the LFO may allow for a local noninvasive assessment of autoregulatory mechanisms in the adult brain.

Adult↗
PubMed2000

Near-infrared spectroscopy: does it function in functional activation studies of the adult brain?

Changes in optical properties of biological tissue can be examined by near-infrared spectroscopy (NIRS). The relative transparency of tissues including the skull to near-infrared light is the prerequisite to apply the method to brain research. We describe the methodology with respect to its applicability in non-invasive functional research of the adult cortex. A summary of studies establishing the 'typical' response in NIRS vascular parameters, i.e. changes in the concentration of oxygenated and deoxygenated haemoglobin, over an activated area is followed by the validation of changes in the cytochrome-oxidase redox state in response to a visual stimulus. Proceeding from these findings a rough mapping of this metabolic response over the motion-sensitive extrastriate visual area is demonstrated. NIRS measures concentration changes in deoxygenated haemoglobin [deoxy-Hb] which are assumed to be the basis of fMRI BOLD contrast (blood oxygenation level-dependent). The method is therefore an excellent tool to validate assumptions on the physiological basis underlying the fMRI signal, due to its high specificity as to the parameters measured. Questions concerning the concept of 'activation'/'deactivation' and that of the linearity of the vascular response are discussed. To challenge the method we finally present results from a complex single-trial motor paradigm study testing the hypothesis, that premotor potentials (contingent negative variation) can be examined by functional techniques relying on the vascular response. Some of the work described here has been published elsewhere.

Adult↗
PubMed2000

Physical model for the spectroscopic analysis of cortical intrinsic optical signals.

We used Monte Carlo simulations and the diffusion approximation to estimate correction terms for the analysis of reflectance spectra of cortical intrinsic optical signals. These corrections depend on scattering and absorption properties, i.e. they are dependent on assumptions on the tissue blood content and oxygen saturation. The analysis was applied to reflectance spectra acquired during whisker barrel stimulation in the rat where attenuation spectra were converted to changes in oxygenated and deoxygenated haemoglobin concentration. The description of the experimental data as judged by the residual and sensitivity to variations of wavelength was considerably improved when the correction terms were included. Inclusion of the correction does have a considerable impact on the time course of deoxyhaemoglobin concentration changes. In contrast to the calculation without correction terms, there is no indication for an early increase in deoxyhaemoglobin ('early dip'). This finding might further current interpretation of the coupling between neuronal activation and oxygen extraction and supply.

Absorption↗
PubMed2000

Saccadic suppression induces focal hypooxygenation in the occipital cortex.

This study investigated how a decrease in neuronal activity affects cerebral blood oxygenation employing a paradigm of acoustically triggered saccades in complete darkness. Known from behavioral evidence as saccadic suppression, electrophysiologically it has been shown in monkeys that during saccades an attenuation of activity occurs in visual cortex neurons (Duffy and Burchfiel, 1975). In study A, using blood oxygen level-dependent (BOLD) contrast functional magnetic resonance imaging (fMRI), the authors observed signal intensity decreases bilaterally at the occipital pole during the performance of saccades at 2 Hz. In study B.1, the authors directly measured changes in deoxyhemoglobin [deoxy-Hb] and oxyhemoglobin [oxy-Hb] concentration in the occipital cortex with near-infrared spectroscopy (NIRS). Whereas a rise in [deoxy-Hb] during the performance of saccades occurred, there was a drop in [oxy-Hb]. In a second NIRS study (B.2), subjects performed saccades at different rates (1.6, 2.0, and 2.3 Hz). Here the authors found the increase in deoxy-Hb and the decrease of oxy-Hb to be dependent on the frequency of the saccades. In summary, the authors observed a focal hypooxygenation in the human visual cortex dependent on the saccade-frequency in an acoustically triggered saccades paradigm. This could be interpreted as evidence that corresponding to the focal hyperoxygenation observed in functional brain activation, caused by an excessive increase in cerebral blood flow (CBF) over the increase in CMRO2 during decreased neuronal activity CBF, is more reduced than oxygen delivery.

Acoustic Stimulation↗
PubMed2000

Oximetry based on diffuse photon density wave differentials.

The quantification of tissue optical properties for calculating blood saturation and hemoglobin concentration using measurements of diffuse photon density waves at some distance away from an intensity-modulated light source, generally requires the determination of the amplitude and phase of this light source. This determination may become a severe impediment for measurements performed in the clinical environment. In this work we extend a self-calibrating methodology developed for constant wave and modulation depth-phase measurements, to include amplitude and phase measurements of diffuse photon density waves. The method uses amplitude and phase changes of intensity modulated light, under the assumption of known index of refraction and invariant reduced scattering coefficient mu's, to quantify the absorption coefficient mu(a) without requiring initial amplitude and phase knowledge. Quantification of the mu(a) at selected time points during a measurement can then be employed to calibrate numerical solutions of the diffusion equation and compute the mu(a) for the remaining time points of the experiment. It is shown that the method is quite insensitive to the knowledge of the exact mu's value so that an assumption on the average mu's value for the tissue measured may be employed. The sensitivity of calculating blood saturation and hemoglobin concentration, as a function of the deviation of the mu's used in the calculation versus the real mu's value is investigated using simulated data. It is also demonstrated that the saturation calculation is especially insensitive to the mu's guess. The performance of the method to quantify blood oxygen saturation and the concentrations of oxy- and deoxy-hemoglobin is examined with experimental measurements at two wavelengths on specially constructed blood model phantoms. To validate the method the measurements are monitored by a time-resolved spectrometer. The method is shown to be accurate to within +/-5% in calculating blood saturation and to within +/-10% in calculating hemoglobin concentration compared to the results obtained with the time-resolved spectrometer and the expected theoretical values.

Algorithms↗
PubMed1999

Intussusception in preterm infants: case report and literature review.

UNLABELLED: Intussusception is an extremely rare disorder in preterm infants. An infant of 29 weeks gestational age with this condition is reported and a retrospective analysis of 17 previously reported cases presented. In the reviewed preterm infants, risk factors for intussusception seemed to be multifactorial. Clinical features included severe abdominal distension (17/17), gastric aspirates (13/17), commonly bilious, bloody stools (10/17) and rarely a palpable abdominal mass (5/17). Diagnostic features were signs of small bowel obstruction on the abdominal radiographs. Signs and symptoms were similar to those seen in necrotizing enterocolitis, therefore difficulties in establishing a correct diagnosis led to an average delay of 7 days between the onset of symptoms and abdominal surgery, increasing the risk of developing a compromised bowel. CONCLUSION: The differential diagnosis of an intussusception should be considered in preterm infants with acute abdominal distension and tenderness.

Diagnosis, Differential↗