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At least 1,135 records · Page 63Linked to original sources
PubMed2000

In vivo spectroscopy in dermatology: methods and new fields of application.

BACKGROUND: The human skin is an easily accessible organ on which non-invasive examination methods can be applied. Remittance spectroscopy uses registration of the proportion of reflected light from the skin surface. Optical characteristics of skin are determined by scattering, reflection and absorption. The remittance is influenced by various test conditions and topography. Spectroscopic methods are applied for determination of microcirculation, measuring of erythema and pigmentation and in pharmacology and toxicology of applied drugs. CONCLUSION: The standardization of spectroscopic measurement of human skin is essential to reduce error sources. In future a better investigation of skin structures and molecules, which are responsible for optical characteristics of skin and a more precise evaluation of spectroscopic signals are necessary to get more information about the state of skin and to develop new fields of applications, such as early diagnosis of skin diseases or monitoring of metabolic processes.

Erythema↗
PubMed1975

[On-line monitoring of cardiac output with a new pulse contour computer (author's transl)].

A new pulse contour cardiac output computer, operating from the aortic pressure wave form was tested in cardiac surgical patients. Reference cardiac output was measured by thermal dilution technique. Satisfactory agreements were obtained between the thermal dilution and the COC-pulse-contour cardiac outputs when rapid variations of cardiac output occurred as well as slowly developing changes. The results show that the computation of the stroke volume from the aortic pressure wave form offers a simple, clinically useful method for on-line monitoring of cardiac output in critically ill patients. Possible error sources are discussed.

Aorta↗
PubMed1991

[Sex differences in schizophrenic diseases].

Sex differences in schizophrenic diseases have been known for a long time but have also been subject to long-term neglect by psychiatric epidemiological research, although a study of these sex differences could, in our opinion, yield valuable pointers to pathogenic factors involved in this group of diseases the aetiology of which still awaits clarification. For this reason we initiated large-scale investigations focussed on this topic. The paper presented here discusses a few initial results, basing on data of Mannheim and National Danish Case Records and on our own study on schizophrenia, the latter being a representative record of 392 patients hospitalised for the first time in the Rhine-Neckar region and the eastern part of the Palatinate. First of all, sex differences at the age at which the disease appeared for the first time, were studied while paying close attention to artifacts and other, usually neglected methodical error sources. The difference in the average age of the sexes at first hospitalisation was confirmed, and also--using an instrument specially developed for that purpose--at the onset of the disease. At the time the first signs of the disease are noticed and the first schizophrenic symptoms become apparent, men are about 3 to 4 years younger than women. On the other hand, the cumulative lifetime risk--calculated up to 60 years of age--seems to be the same for both sexes. It appears that there are no sex differences in the pattern of symptoms of the disease at the time of initial hospital admittance, in respect of both the most common and the characteristic signs and symptoms. There were significant although quantitatively not very great differences in respect of patient behaviour which displays socially positive aspects somewhat more often in women and socially negative ones distinctly more often in men. In respect of the course of the disease we could not find any marked sex differences over a period of 10 years after onset of the disease; however, this is presently based only on the Danish case record data and on criteria of the course of the disease, such as number and duration of inpatient treatments.

Adolescent↗
PubMed1997

[CT volumetry of the liver before transplantation].

PURPOSE: Purpose of the study was to assess the predictive accuracy of preoperative CT volumetry for water displacement volume after liver transplantation. METHODS: In a retrospective study the liver volume of 52 patients who underwent an orthotopic liver transplantation, was calculated preoperatively based on incremental and spiral computed tomography (CT). The calculated values were compared with the liver volume measured by water displacement and weight of the extirpated liver. RESULTS: Marked differences of 19-21.5% were seen between calculated CT volume and water displacement volume for the entire group, and of 12.4-16.9% for livers with a plausible physical liver density (0.9 and 1.1 g/cm3). In this group, 68-86% of the livers were in the acceptable tolerance range for a predictive accuracy (+10% to -20%). Other error sources, such as the breathing shift of the abdominal organs and interobserver variability (1.5-2.7%), were of minor importance for volume calculation. CONCLUSION: In conclusion, both incremental CT and spiral CT are reliable methods for the preoperative estimation of the liver volume, whereas best accordance with the corrected water displacement volume was obtained using the individual segmentation thresholds.

Adolescent↗
PubMed1992

[Evoked otoacoustic emissions as a screening test for hearing evaluation in newborn and premature infants?].

The purpose of this study was the evaluation of evoked otoacoustic emissions (EOAE) for the screening of infant hearing. EOAE and brainstem-evoked response audiometry (BERA) were performed in 40 infants at a special care unit at the Universitäts-Klinik, Göttingen. Both examinations were performed under non-optimal conditions, reflecting a realistic screening situation. The purpose was to determine robust analysis criteria and possible error sources. A comparison of both tests shows that sensitivity and specificity are insufficient for reliable screening. The EOAE test does not yield the threshold of hearing. There is no sharp boundary with the BERA threshold for the detectability of an EOAE. Sensitivity and specificity have not been accurately determined so far due to the relatively small number of infants with impaired hearing tested. Nevertheless, the results show that EOAE should be applied as a supplement to conventional audiometry for infants. It is capable of excluding conductive and severe cochlear hearing losses and is by itself not a reliable screening test.

Audiometry, Evoked Response↗
PubMed2005

Methods and potentials of magnetic resonance imaging for monitoring radiofrequency hyperthermia in a hybrid system.

INTRODUCTION: Non-invasive thermometry (NIT) is a valuable and probably indispensable tool for further development of radiofrequency (RF) hyperthermia. A hybridization of an MRI scanner with a hyperthermia system is necessary for a real-time NIT. The selection of the best thermographic method is difficult, because many parameters and attributes have to be considered. METHODS: In the hybrid system (Siemens Symphony/BSD-2000-3D) the standard methods for NIT were tested such as T1, diffusion (ADC: apparent diffusion coefficient) and proton-resonance-frequency shift (PFS) method. A series of three-dimensional datasets was acquired with different gradient-echo sequences, diffusion-weighted EPI spin-echo sequences and calculated MR-temperatures in the software platform AMIRA-HyperPlan. In particular for the PFS-method, corrective methods were developed and tested with respect to drift and other disturbances. Experiments were performed in phantoms and the results compared with direct temperature measurements. Then the procedures were transferred to clinical applications in patients with larger tumours of the lower extremity or the pelvis. RESULTS: Heating experiments and MR-thermography in a homogeneous cylindrical phantom give an excellent survey over the potentials of the methods. Under clinical conditions all these methods have difficulties due to motion, physiological changes, inhomogeneous composition and susceptibility variations in human tissues. The PFS-method is most stable in patients yielding reasonable MR temperature distributions and time curves for pelvic and lower extremity tumours over realistic treatment times of 60-90 min. Pooled data exist for rectal tumour recurrencies and soft tissue sarcomas. The fat tissue can be used for drift correction in these patients. T1 and diffusion-dependent methods appear less suitable for these patients. The standard methods have different sensitivities with respect to the various error sources. The advantages and pitfalls of every method are discussed with respect to the literature and illustrated by the phantom and patient measurements. CONCLUSIONS: MR-controlled RF hyperthermia in a hybrid system is well established in phantoms and already feasible for patients in the pelvic and lower extremity region. Under optimal conditions the temperature accuracy might be in the range of 0.5 degrees C. However a variety of developments, especially sequences and post-processing modules, are still required for the clinical routine.

Humans↗
PubMed1986

Evaluation of an ISO draft proposal for sampling and analysis of chlorinated hydrocarbon solvent vapors in workplace atmospheres.

The ISO draft proposal for sampling and analysis of chlorinated hydrocarbon solvent vapors in workplace atmospheres (ISO/TC 146/SC 2/WG4 N41) has been evaluated by means of a round-robin test. For this purpose, the repeatability and reproducibility for the determination of tetrachloromethane, trichloromethane, 1,1,1-trichloroethane, trichloroethene were determined at three concentration levels. Furthermore, parameters such as breakthrough and loss on storage were determined. Samples were taken by 11 participants from six countries. After statistical evaluation of the results, it appeared that improvements were necessary for the determination of tetrachloromethane and trichloromethane. For the other three compounds, repeatability and reproducibility were sufficient. Possible error sources and possibilities for improvements are discussed.

Air Pollutants, Occupational↗
PubMed1987

Nurses as evaluators of the humanistic behavior of internal medicine residents.

The reliability of a 13-item questionnaire designed to assess the humanistic behaviors of internal medicine residents and the reliability of nurses as raters of those behaviors were examined. Twenty-five residents were evaluated by 10 or 11 nurses on two general medicine services and on cardiology and hematology-oncology services in a large, highly specialized department of internal medicine. Using an application of generalizability theory, which extends beyond classical test theory to establish estimates of multiple-error sources, the investigators calculated reliability-like coefficients for each of the services. The coefficients were .95 and .85 for the two general medicine services, .67 for cardiology, and .88 for hematology-oncology. These findings indicate that the questionnaire is a reliable instrument for assessing humanistic behavior and identifying reliable raters in groups of nurses.

Clinical Competence↗
PubMedDate not supplied

The association between lack of male circumcision and risk for HIV infection: a review of the epidemiological data.

BACKGROUND AND OBJECTIVES: Whether male circumcision reduces the risk of acquiring human immunodeficiency virus (HIV) infection remains controversial. STUDY DESIGN: As there have now been a number of studies conducted that have examined this issue, we undertook to review their findings. Thirty epidemiological studies identified in the literature that investigated the association between male circumcision status and risk for HIV infection were reviewed. RESULTS: Eighteen cross-sectional studies from six countries reported a statistically significant association, four studies from four countries found a trend toward an association. Four studies from two countries found no association. Two prospective studies reported significant associations, as did two ecological studies. In studies in which significant associations were demonstrated, measures of increased risk ranged from 1.5 to 8.4. The groups in which positive associations were found included sexually transmitted disease (STD) clinic and hospital patients, outpatient clinic and HIV screening clinic attenders, long-distance truck drivers, and general community members. CONCLUSION: Potential sources of error, assessment of causality, implications of the findings, and future research needs are discussed. Because a substantial body of evidence links noncircumcision in men with risk for HIV infection, consideration should be given to male circumcision as an intervention to reduce HIV transmission.

Bias↗
PubMed2004

Tagged-particle dynamics in a hard-sphere system: mode-coupling theory analysis.

The predictions of the mode-coupling theory of the glass transition (MCT) for the tagged-particle density-correlation functions and the mean-squared displacement curves are compared quantitatively and in detail to results from Newtonian- and Brownian-dynamics simulations of a polydisperse quasi-hard-sphere system close to the glass transition. After correcting for a 17% error in the dynamical length scale and for a smaller error in the transition density, good agreement is found over a wide range of wave numbers and up to five orders of magnitude in time. Deviations are found at the highest densities studied, and for small wave vectors and the mean-squared displacement. Possible error sources not related to MCT are discussed in detail, thereby identifying more clearly the issues arising from the MCT approximation itself. The range of applicability of MCT for the different types of short-time dynamics is established through asymptotic analyses of the relaxation curves, examining the wave-number and density-dependent characteristic parameters. Approximations made in the description of the equilibrium static structure are shown to have a remarkable effect on the predicted numerical value for the glass-transition density. Effects of small polydispersity are also investigated, and shown to be negligible.

Journal Article↗
PubMed2002

Velocity bias and fluctuation in the standard dual beam Doppler reconstruction algorithm.

Bias and fluctuation of the standard velocity reconstruction algorithm for dual beam vector Doppler velocity estimation systems are analyzed; both magnitude and angle properties are considered. Bias can arise from any of the error sources known to affect single beam systems in addition to both translation and angle misregistration between the two sample volumes; standard deviation is the result of random temporal fluctuations in Doppler frequency estimates in each beam. Approximate closed-form expressions for both biases and standard deviations of the velocity estimates are derived, and the performance of a typical practical dual beam system is discussed as an illustration of the theory.

Algorithms↗
PubMed1977

Gas chromatographic on-column methylation technique for the simulataneous determination of antiepileptic drugs in blood.

An on-column methylation technique (OCMT) is described for the simultaneous, gas chromatographic determination in blood of ethosuximide (ES), phenobarbital (PB), primidone (PD), phenytoin (DPH), and 5-ethyl-5-phenylhydantoin (EPH). Multiple internal standards are employed in the OCMT, in order to eliminate or to minimize greatly error sources common to the technology of gas chromatography and to compensate for the different chemical dispositions of the antiepileptic drugs in an OCMT. The internal standards used in the OCMT were as follows: alpha,alpha,beta-trimethylsuccinimide (TMS) was used for the determination of ES; 5-ethyl-5-para-tolylbarbituric acid (MPB), for PB; 5-ethyl-5-(para-tolyl) hexahydropyrimidine-4,6-dione (MPD), for PD; and 5-(para-tolyl)-5-phenylhydantoin (MPPH), for EPH and DPH. The use of ether, the buffering of the plasma sample at pH 7.6, and the use of dilute (0.30-0.35 M) trimethyl-phenylammonium hydroxide (TMPAH) contributed to the specificity of the extraction scheme of the OCMT. The precision and accuracy of the OCMT was attributed to the use of appropriate, multiple internal standards. A method is described for the preparation of standard solutions of drugs in blank plasma (biological matrix) and for the use of the standards in calibration and daily intra-laboratory control of the OCMT.

Anticonvulsants↗
PubMed2001

Experimental determination of average turbulent heat transfer and friction factor in stator internal rib-roughened cooling channels.

In gas turbine cooling design, techniques for heat extraction from the surfaces exposed to the hot stream are based on the increase of the inner heat transfer areas and on the promotion of the turbulence of the cooling flow. This is currently obtained by casting periodic ribs on one or more sides of the serpentine passages into the core of the blade. Fluid dynamic and thermal behaviour of the cooling flow have been extensively investigated by means of experimental facilities and many papers dealing with this subject have appeared in the latest years. The evaluation of the average value of the heat transfer coefficient most of the time is inferred from local measurements obtained by various experimental techniques. Moreover the great majority of these studies are not concerned with the overall average heat transfer coefficient for the combined ribs and region between them, but do focus just on one of them. This paper presents an attempt to collect information about the average Nusselt number inside a straight ribbed duct. Series of measurements have been performed in steady state eliminating the error sources inherently connected with transient methods. A low speed wind tunnel, operating in steady state flow, has been built to simulate the actual flow condition occurring in a rectilinear blade cooling channel. A straight square channel with 20 transverse ribs on two sides has been tested for Re of about 3 x 10(4), 4.5 x 10(4) and 6 x 10(4). The ribbed wall test section is electrically heated and the heat removed by a stationary flow of known thermal and fluid dynamic characteristics.

Journal Article↗
PubMed2006

Dendritic voltage-gated K+ conductance gradient in pyramidal neurones of neocortical layer 5B from rats.

Voltage-gated potassium channels effectively regulate dendritic excitability in neurones. It has been suggested that in the distal apical dendrite of layer 5B (L5B) neocortical pyramidal neurones, K+ conductances participate in active dendritic synaptic integration and control regenerative dendritic potentials. The ionic mechanism for triggering these regenerative potentials has yet to be elucidated. Here we used two-electrode voltage clamp (TEVC) to quantitatively record K+ conductance densities of a sustained K+ conductance in the soma and apical dendrite of L5B neurones of adult rats. We report that the somatic and proximal dendritic sustained voltage-gated K+ conductance density is more than 10-fold larger than previous estimates. The results obtained using TEVC were corroborated using current-clamp experiments in combination with compartmental modelling. Possible error sources, including inaccurate measurement of the passive membrane parameters and unknown axonal and basal dendritic conductance distributions, were shown not to distort the density estimation considerably. The sustained voltage-gated K+ conductance density was found to decrease steeply along the apical dendrite. The steep negative K+ conductance density gradient along the apical dendrite may help to define a distal, low-threshold region for amplification of distal synaptic input in L5B pyramidal neurones.

Animals↗
PubMed1996

Fracture of articular cartilage.

Crack formation and propagation is a significant element of the degeneration process in articular cartilage. In order to understand this process, and separate the relative importance of structural overload and material failure, methods for measuring the fracture toughness of cartilage are needed. In this paper, two such methods are described and used to measure fracture properties of cartilage from the canine patella. A modified single edge notch (MSEN) specimen was used to measure J, and a trouser tear test was used to measure T, both measures of fracture toughness with units of kN/m. A pseudo-elastic modulus was also obtained from the MSEN test. Several potential error sources were examined, and results for the MSEN test compared with another method for measuring the fracture parameter for urethane rubber. Good agreement was found. The two test methods were used to measure properties of cartilage from the patellae of 12 canines: 4-9 specimens from each of 12 patellae, with 5 right-left pairs were tested. Values of J ranged from 0.14-1.2 kN/m. J values correlated with T and were an average of 1.7 times larger than T. A variety of failure responses was seen in the MSEN tests, consequently a grade of 0 to 3 was assigned to each test, where 0 represented a brittle-like crack with minimal opening and 3 represented plastic flow with no crack formation. The initial cracks in 12/82 specimens did not propagate and were assigned to grade 3. The method for reducing data in the MSEN test assumed pseudo-elastic response and could not be used for the grade 3 specimens. Stiffness did not correlate with J. Neither J nor T was statistically different between right-left pairs, but varied between animals. The test methods appear useful for providing a quantitative measure of fracture toughness for cartilage and other soft materials.

Animals↗
PubMed1985

Pressure measurements during speech production using semiconductor miniature pressure transducers: impact on models for speech production.

It appears that temperature instabilities are a major obstacle hindering the use of semiconductor strain gauge pressure transducers in speech research, especially when absolute pressure data are mandatory. In this paper a simple and reliable method for an in vivo calibration of this kind of transducer is described. The most important error source, the drift of the zero pressure level due to temperature changes, is discussed, and an estimation of the measurement accuracy which can be obtained is given. Moreover, some registrations of subglottal, supraglottal, and transglottal pressure are presented. It is shown that the pressure recordings allow us to obtain estimates of the volume flow in the trachea and pharynx. Analysis of those waveforms appears to lead to new insights into the physical processes underlying voice production. Specifically, an independent glottal contribution to the skewing of the glottal flow pulses is identified.

Calibration↗
PubMed1998

Measurement of optic disc size: equivalence of methods to correct for ocular magnification.

AIMS: To compare methods available to correct the magnification of images that result from the optics of the eye and identify errors, and source of error, of the methods. METHODS: 11 methods were applied to ocular biometry data from three independent cohorts. Each method was compared with the method of Bennett, which uses most biometric data. The difference between each method and Bennett's is the "error" of the method. The relation between the error and axial length, ametropia, and keratometry was explored by linear regression analysis. RESULTS: Methods using axial length had the lowest mean (+0.5 to +2.6%) and standard deviation (0.6 to 1.2%) of errors. Of methods using keratometry and ametropia only, the lowest mean (-1.4% to +4.4%) and standard deviation (2.9 to 4.3%) of errors was found for a new method described in this paper, and that used by the Heidelberg retina tomograph (HRT). The highest mean error (+2.2 to +7.1%) was found for Littmann's method. Littmann's correction was larger than the HRT's by 3.5 to 3.7%. The mean difference between the new and HRT methods and the "abbreviated axial length" method of Bennett is -1.3 to +2.0%. The error of the "keratometry and ametropia" methods is related to axial length. CONCLUSIONS: Methods using axial length are most accurate. The abbreviated axial length method of Bennett differs little from more detailed calculations and is appreciably more accurate than methods using keratometry and ametropia alone. If axial length is unknown, the new and the HRT methods give results closest to the abbreviated axial length method.

Aged↗