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Biomedical subjects

R M Schmitt

Publications and source records attributed to R M Schmitt.

At least 19 recordsLinked to original sources
PubMed1996

[Flow rates of roentgen contrast media of different viscosity in 4.1 Charrière coronary catheters].

The studies presented here investigated the obtainable flows of different contrast media (Iopromide 370 mg iodine/ml, ZK 119 095 370 mg iodine/ml, ZK 139 129 370 mg iodine/ml, Iopamidol 370 mg iodine/ml, Iopromide 300 mg iodine/ml, ZK 119 095 300 mg iodine/ml, ZK 139 129 300 mg iodine/ml, Iopamidol 300 mg iodine/ml, aqua dest.) in 4.1 Charrière coronary catheters. The measurements of the flow achieved by a standardised power of 100 N show that the highest values are reached with the substance ZK 119 095 (both for 300 mg iodine/ml and 370 mg iodine/ml). On comparison of the catheter types there are no differences in the delivery rate. The x-ray contrast-media, however, are significantly different: the lowest iodine delivery rate is found for iopromide 370 with 384.5 mg iodine/s; the highest rate for the test substance ZK 119 095 with 648.9 mg iodine/s. Although contrast media with low viscosity contain considerably less iodine/ml it is possible to achieve an iodine density in coronary vessels by about 86% higher than that achieved by contrast media with 370 mg iodine/ml. Therefore, the possibility to choose a viscosity-adapted x-ray contrast-medium allows the use of very thin cardiac catheter systems without leading to a worsening of picture quality.

Cardiac Catheterization↗
PubMed1994

Cerebral autoregulation of preterm neonates--a non-linear control system?

The low frequency cerebral blood flow velocity (CBFV) oscillations in neonates are commonly attributed to an under-dampened immature linear type cerebral autoregulation, and the 'instability' is regarded as causative for peri-intraventricular haemorrhage/periventricular leukomalacia. In contrast, oscillations susceptible to frequency entrainment are a fundamental part of the stable function of non-linear control systems. To classify the autoregulation an observational study was done on the relationship between CBFV oscillations, heart rate variability, and artificial ventilation. In 10 preterm neonates (gestational age 26 to 35 weeks) we serially Doppler traced arterial CBFV continuously for 12 minutes between days 1 and 49 of life. The individual time series of CBFV and heart rate were subjected to spectral analysis. Forty six of 47 tracings showed significant low frequency CBFV oscillations. Low frequency heart rate oscillations were not a prerequisite thereof. All patients with < 30% of total power in the low frequency band of CBFV oscillations were on the ventilator. Three of them demonstrated a shift of spectral power from low frequency to a frequency equal or harmonic to the ventilator rate indicating entrainment. The findings of CBFV oscillations combined with entrainment classify the autoregulation as a non-linear system. It is suggested that entrainment by periodic high amplitude stimuli might challenge the regulatory capacity to its limits thus increasing the risk for cerebral damage.

Blood Flow Velocity↗
PubMed1993

Simultaneous influence of blood pressure, PCO2, and PO2 on cerebral blood flow velocity in preterm infants of less than 33 weeks' gestation.

In extremely preterm infants, the protective capacity for cerebral blood flow (CBF) autoregulation may be impaired or absent, which increases the risk for developing cerebral lesions. The purpose of this study was to quantify the simultaneous influence of several vital parameters, such as mean arterial blood pressure (MABP), PCO2, and PO2, on cerebral blood flow velocity (CBFv), which is used as a measure for CBF. In 16 mechanically ventilated infants of < 33 wk gestation, the CBFv in the internal carotid artery was measured every minute for 1 h by a computer-controlled pulsed Doppler device. MABP and transcutaneous PCO2 and PO2 were recorded as well. A multiple linear regression analysis was performed in each patient to determine the individual MABP, PCO2, and PO2 reactivities as a measure for CBF autoregulation. The medians (and ranges) of the whole group were an MABP reactivity of 7.5% (-12.5 to 20.1%) rise in CBFv/1 kPa rise in MABP, a PCO2 reactivity of 32.7% (-8.1 to 79.5%) rise in CBFv/1 kPa rise in PCO2, and a PO2 reactivity of -3.1% (-14.2 to 7.9%) fall in CBFv/1 kPa rise in PO2. In preterm infants, the individual's capacity for MABP-, PCO2-, and PO2-dependent CBF autoregulation can be estimated by means of the present method, even if the vital parameters change simultaneously.

Blood Flow Velocity↗
PubMed1992

Embryonic stem cells and in vitro hematopoiesis.

To study hematopoietic differentiation a variety of in vitro systems have been established using hematopoietic precursors derived from various explanted adult and fetal tissues. In this prospective we describe and discuss the potential of a novel system for studying the earliest stages of hematopoietic development. In addition, some of the applications of this system as a unique in vitro model for studying other developmental systems are discussed. Murine embryonic stem cells (ESC), which are totipotent and can be maintained undifferentiated indefinitely in vitro, have the capacity to differentiate in vitro into hematopoietic precursors of most, if not all, of the colony forming cells found in normal bone marrow. This potential can be exploited to study the control of the early stages of hematopoietic induction and differentiation. Recent results have indicated that there is a strong transcriptional activation, in a well defined temporal order, of many of the hematopoietically relevant genes. Examples of the genes expressed early during the induction of hematopoiesis include erythropoietin (Epo) and its receptor as well as the Steel (SI) factor (SLF) and its receptor (c-kit). Several other genes, including CSF-1, IL-1, and G-CSF were expressed during the later stages of hematopoietic differentiation. Contrasting with these observations, IL-3 and GM-CSF were not expressed during the first 24 days of ES cell differentiation suggesting that neither factor is necessary for the induction of hematopoietic precursors. Although these studies are just beginning, this system is easily manipulated and gives us an approach to understanding the control of the induction and differentiation of the hematopoietic system in ways not previously possible.

Animals↗
PubMed1991

Hematopoietic development of embryonic stem cells in vitro: cytokine and receptor gene expression.

A novel system to study early hematopoietic development is described. This report documents the in vitro capacity of murine embryonic stem (ES) cells to differentiate into hematopoietic precursors of most, if not all, of the colony-forming cells found in normal bone marrow. This system is used to correlate the genetic expression of cytokines, their receptors, the beta-globins, and the hematopoietic cell surface markers throughout the time course of ES cell differentiation with the hematopoietic development that occurs in these cultures. Our results indicate that there is a strong transcriptional activation, in a well-defined temporal order, of most of these genes including erythropoietin (Epo), CSF-1, IL-4, beta-globins, as well as the receptors for Epo, CSF-1, and IL-4. IL-3 and GM-CSF were not expressed during the first 24 days of ES cell differentiation. In contrast, the Steel (Sl) factor (SLF) was expressed early and underwent substantial up-regulation during this differentiation, and its receptor, c-kit, was expressed relatively constantly throughout the culture period. Our results are consistent with the conclusion that SLF, Epo, IL-4, and IL-6 are important during the early stages of ES cell differentiation and hematopoietic development. Furthermore, these results argue strongly that IL-3 and GM-CSF are not critical to early hematopoiesis. This system offers a unique in vitro model for studying hematopoietic development at the earliest possible stages.

Animals↗
PubMed1990

Endosonography of pararectal lymph nodes. In vitro and in vivo evaluation.

One hundred thirteen patients with carcinoma of the rectum were evaluated for lymph node metastases by endorectal ultrasound. With the use of 7.5 MHz and based on different echo patterns, two main groups of lymph nodes can be differentiated: hypoechoic and hyperechoic lymph nodes. Compared with pathologic findings, hypoechoic lymph nodes represent metastases, whereas hyperechoic lymph nodes are visualized due to unspecific inflammation. Lymph node metastases can be predicted with a sensitivity of 72 percent and inflammatory lymph nodes with a specificity of 83 percent. The physical basis of the differentiation of lymph nodes was assessed in vitro by the determination of ultrasound parameters (speed of sound, acoustic impedance, attenuation, and backscattered amplitude). The attenuation coefficient of benign lymph nodes [2.5 dB/(MHz x cm)] is significantly higher than the mean value of lymph node metastases [1.3 db/(MHz x cm)]. The results demonstrate that involved nodes can principally be differentiated from not involved nodes. Micrometastases, mixed lymph nodes, and changing echo patterns within inflammatory nodes explain the accuracy rate of 78 percent.

Acoustics↗
PubMed1990

A 100-element ultrasonic circular array for endoscopic application in medicine and NDT.

In this paper we focus on a new developed ultrasonic circular array for endoscopic application in medicine and NDT. The new device consists of 100 strip elements. The diameter of this array is just 10 mm. The arrays are conceived for frequencies between 3.5 and 7.5 MHz, the band width has an amount of 50%. The mathematical algorithm, monochromatic and broadband simulations of the soundfield are shown and problems with grating lobes are discussed. Furthermore the process of manufacturing is discussed and partially depicted. We present the final results and ultrasonic images obtained from tissue aquivalent phantoms representing medical application and from special test specimens representing NDT- Application.

Algorithms↗
PubMed1985

The effect of acute and chronic femoral artery ligation on the blood flow through the gastrocnemius muscle of the rat examined using laser Doppler flowmetry and xenon-133 clearance.

In this investigation the resting gastrocnemius muscle blood flow of the anaesthetized rat was evaluated using a recently developed laser Doppler flowmeter and the xenon-133 clearance technique. The perfusion of the microvasculature of the muscle was measured in normal control rats and in animals in which the supplying femoral artery had been acutely (1 h-1 week) or chronically (8-12 weeks) ligated. The laser Doppler flowmeter allowed continuous measurements of the muscle perfusion. Such measurements revealed a rhythmic fluctuation in the perfusion of the gastrocnemius muscle. The xenon-133 clearance technique did not allow continuous recording of muscle blood flow and rhythmical flow changes could not be observed. Acute ligation of the femoral artery reduced the mean muscle perfusion by 41% and 52% when assessed by laser Doppler flowmetry and xenon-133 clearance respectively. In comparison to animals without femoral artery ligation the hyperaemic response, following release of a tourniquet around the thigh or of an abdominal aortic occlusion, was markedly attenuated. Chronic ligation of the femoral artery reduced the mean muscle perfusion by 33% and 32% when assessed by laser Doppler flowmetry and xenon-133 clearance respectively. In these animals the hyperaemia, following tourniquet-induced muscle ischaemia, was reduced, compared to normal animals, but was more pronounced than observed in acutely ligated animals. In the chronically ligated animals abdominal aortic occlusion did not produce sustained muscle ischaemia and consequently no hyperaemic response was observed upon release of the aortic occlusion. We conclude that, as judged by the comparability of the results obtained using xenon-133 clearance, the laser Doppler flowmeter is a useful and sensitive new tool for the examination of the perfusion of tissue blood flow. The results suggest that chronic ligation of the rat femoral artery induces circulatory changes which mimic those seen in claudicants.

Animals↗
PubMed1984

Ultrasonic computed tomography of the breast. Improvement of image quality by use of cross-correlation time-of-flight and phase-insensitive attenuation measurements.

The authors present two methods of reducing refraction artifacts in ultrasonic computed tomography of the breast. Measuring the time of flight of sonic pulses by cross-correlation instead of leading-edge detection significantly reduces distortion and improves resolution in speed-of-sound images. Phase-insensitive reception of pulse energy across a large aperture array is shown to be superior to a conventional single-element transducer for attenuation imaging.

Breast Diseases↗
PubMedDate not supplied

Evaluation of the Xe-133 clearance method for indirect placental blood flow determination.

The Xe-133 clearance method, chosen by several groups for indirect placental blood flow (PBF) determination, is evaluated using a placenta-fetus compartment model first introduced by Moll (1973). The placenta is modelled as a strong concurrent, counter-current or cross-current exchange system. The fetal circulatory system is simplified by dividing it into two major branches: the umbilical circulation and the fetal tissue or systemic circulation. Following an arbitrary labelling of maternal arterial blood, Xe-133 concentrations in myometrium, placenta and fetus are derived from the model and are used to calculate placental clearance rates. The dependence of clearance rates on maternal and fetal PBF, on the distribution of fetal cardiac output, and on the effect of recirculation times, is considered in the three different arrangements of maternal and fetal placental vessels.

Animals↗
PubMedDate not supplied

Median and spatial low-pass filtering in ultrasonic computed tomography.

To reduce noise- and reconstruction-related artifacts in ultrasound computed tomography, the use of combined median and Hamming-weighted spatial low-pass filtering is evaluated. The evaluation of the reconstruction filters uses both computer-generated projections of a known object with the least mean-square error criterion as well as a more subjective evaluation of conventional ultrasonic attenuation and speed of sound images.

Breast↗
PubMedDate not supplied

[The flow of contrast media in coronary catheters: study of the structural quality in interventional cardiology].

In the present study we investigated the contrast medium flow in 8 different types of left heart catheter having two different diameters (each n = 5). Using a 10 ml syringe and the contrast medium Ultravist 370, we calculated a mean value of 94.24 N + 16.01 for the maximum manual injection force in 18 test subjects. For the sake of simplicity, the figure of 100 N was defined as standardized manual force (which is within the standard deviation). If the maximally admissible static pressure of 82.5 bar is not to be exceeded, flow rates of not more than 16-17 ml/s are possible with 5.2 Fr. catheters, and 21-23 ml/s and 1.46 ml/s for 5.2 Fr. catheters, and between 1.99 ml/s and 2.17 ml/s for 6 Fr. catheters. Thus, a 50% higher flow can be achieved with 6 Fr. catheters as compared with 5.2 Fr. catheters at the same injection force. The iodine delivery rates are between 506 mg iodine/s and 539 mg iodine/s for 5.2 Fr. catheters, and between 738 mg iodine/s and 804 mg iodine/s for 6 Fr. catheters. The figures for the jet stream.

Cardiac Catheterization↗