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C Bos

Publications and source records attributed to C Bos.

34 records · Page 2Linked to original sources
PubMed1996

The effect of blood flow on oxygen extraction pressures calculated in a model of pointlike erythrocyte sources for rat heart.

A mathematical description of pericapillary oxygen gradients that takes into account the particulate nature of blood is possible in terms of erythrocytes as pointlike sources. The formulation in terms of quasi-stationary sources [1] is extended to account for moving erythrocytes. The extended model is semianalytical and can be used to estimate the extraction pressure (EP), which quantifies the effect on partial pressure of oxygen (pO2) in the tissue far from the erythrocytes. Simulations have been done for rat heart muscle tissue around a capillary. For low hematocrit (Hct; 20%) and low blood velocity EP is highest, higher than the pO2 drop in a surrounding typical tissue cylinder. This means that the impediment to O2 release close to the capillary can be larger than that to transport further into the tissue. Increasing the hematocrit decreases EP, that is, it facilitates O2 release. Increasing the blood velocity decreases EP at low Hct values but has the opposite effect at high Hct values (> 35%). For zero velocity, results are the same as with the quasi-stationary model.

Animals↗
PubMed1996

Reconsidering the effect of local plasma convection in a classical model of oxygen transport in capillaries.

In 1970, Aroesty and Gross investigated the influence of local plasma convection in between two successive red blood cells (RBC) in a capillary on the local oxygen transfer into tissue by combining convectional and diffusional oxygen transport. They concluded that the effect of local plasma convection on oxygen transport in the capillaries was insignificant. Here it is shown that this result was due to their choice of flat oxygen concentration profiles as boundary conditions. In fact, the plasma motion can be of importance when more realistic oxygen concentrations are used as boundary conditions. The fluxes of oxygen through the capillary wall could be up to 50% larger as compared to those of Aroesty and Gross, especially for low hematocrit values and for maximally working muscle. Since the boundary concentrations in the model of the current paper are fixed, chosen not to be influenced by the transport processes, calculations will not show to what extent motion really enhances the oxygen transport, and should be considered as rough indications of the effect of plasma motion. The results in this investigation indicate that in capillaries motion has to be taken into account under conditions of low hematocrit or high RBC velocity.

Biological Transport↗
PubMed1996

An etiologic study of Paget's disease.

The objective of this case-control questionnaire study was to determine whether a history of measles or of dog ownership occurred with different frequencies in Paget's disease patients and in age- and sex-matched controls. Clustering of Paget's disease cases in geographic foci was also looked for, as well as a difference in the prevalence of Paget's disease according to whether the subsoil was composed of rocks from the primary or the tertiary-quaternary geologic periods. Completed questionnaires were obtained from 247 Paget's disease patients and 281 controls. Paget's disease was significantly associated with a history of measles (odds ratio, 2.46) but not with a history of mumps (odds ratio, 0.79) or with dog ownership (odds ratio, 0.97). The 174 cases of Paget's disease in subjects from the study district were distributed throughout the district, with no geographic clustering. This result was confirmed by the analysis of the ratios of Paget's disease cases over the total population in each county in the study district. The incidence of Paget's disease was slightly higher in areas with a primary subsoil, but the difference was not statistically significant (chi-square, 0.79; P = 0.37).

Aged↗
PubMed1996

The effect of separate red blood cells on capillary tissue oxygenation calculated with a numerical model.

In simplified models that describe large quantities of capillaries the capillary content is considered to be homogeneous for oxygen transport; but, in reality, the capillaries contain discrete red blood cells (RBCs), and this discreteness will affect oxygen transport from the capillary to the tissue. This was previously investigated with an analytical model, where RBCs were modelled as point-like sources. A numerical approach is used in this investigation, and the results are compared with the analytical model. In both models the effect of the particulate nature of blood depends on the haematocrit and on the RBC velocity. There is only a minor difference between the two models. For rat hearts, the correction factor used in this study, the extraction pressure, can be up to 3 kPa (23 mmHg).

Animals↗
PubMed1995

Mathematical model of erythrocytes as point-like sources.

A new approach to investigate the effect of pericapillary gradients, caused by the particulate nature of blood, on oxygen partial pressure (pO2) in tissue is presented. The blood erythrocytes are modeled as point-like sources, which makes the system independent of the geometry of the erythrocytes. This model is semi-analytical and is developed to estimate the pO2 far from the erythrocytes. It does so through calculation of the extraction pressure, which accounts for the capillary oxygen drop as compared to homogeneous blood. It is particularly useful to estimate pO2 in regions where the oxygen concentration is low. Simulations have been performed for a cylindrical tissue geometry and parameters are chosen for rat heart muscle. In accordance with the literature, for a fixed total oxygen supply low hematocrit values result in a lower pO2 at the border of the tissue cylinder than high values do. Also a decrease in hematocrit results in higher values for the extraction pressure. Finally, it was found that the effect of the particulate nature of blood is most distinct at low hematocrit values.

Animals↗
PubMed1994

Local plasma convection can be important for oxygen release in tissue capillaries.

Aroesty and Gross investigated the effect of mixing in gaps between two successive RBCs on the local mass transfer at the capillary wall. They found that the effect was insignificant. In this presentation it is shown that their conclusion results from their choice of boundary conditions. When boundary concentrations are chosen which are more similar to those in diffusional models the flux at the capillary wall increases significantly when mixing increases. The calculations presented indicate that mixing of plasma may enhance oxygen transport, although it is impossible to assess the physiological importance. To be able to investigate that, a model has to be developed that includes oxygen transport in both the RBCs and tissue, the oxygen release in the RBCs, and the oxygen consumption in the tissue.

Animals↗
PubMed1993

Tetrasomy 5p mosaicism in a boy with delayed growth, hypotonia, minor anomalies, and an additional isochromosome 5p [46,XY/47,XY, + i(5p)].

We describe a 1-year-old boy with a rare de novo 46,XY/47,XY, + i(5p) mosaicism (ratios 28/3 in peripheral blood lymphocytes and 2/12 in skin fibroblasts). The boy, born after a pregnancy of 34 weeks, had lung hypoplasia, persistent hypotonia, and postnatal growth failure. Craniofacial anomalies were also present. His clinical manifestations correspond to those described in trisomy 5p patients. Prenatal diagnosis on maternal age indication had shown normal male chromosomes in 16 cells in the short term culture of a chorionic villus sampling. Retrospectively, 1 out of 217 cells in this culture showed the i(5p). Several mechanisms could have resulted in the formation of this 46/47, + i(5p) mosaic. Postzygotic local incorrect ligation during chromatid replication, followed by a second replication offers an attractive model on theoretical grounds since it needs only one step to explain both isochromosome formation and mosaicism. Differences between the various tissues in selection pressure on cells with the isochromosome might explain the different ratios of mosaicism found.

Aneuploidy↗
PubMed1976

Sertoli cell tumors of ovary: light microscopic and ultrastructural study with histogenetic considerations.

Two cases of pure Sertoli cell tumors of the ovary are presented. The tumors were grey to brown and generally solid, but with several cystic areas. They showed a highly differentiated, but variable, histologic patterns with solid cords of neoplastic cells, as well as tubular formations. Ultrastructurally, the basal part of the cells rested on a nonfibrillary basement membrane layer while the free border showed occasional cilia. Laterally, the cells showed tight junctions and desmosomes. Abundant rough endoplasmic reticulum and some cystically dilated smooth endoplasmic reticulum were evident. The theories regarding the histogenesis are discussed. Enough similarities, both by light and by electron microscopy, are presented between these tumors and the Sertoli cell to justify classifying these ovarian tumors as Sertoli cell in type. The development of cilia is considered to be a manifestation of focal metaplasia of the neoplastic Sertoli cell.

Cell Nucleus↗
PubMedDate not supplied

MR-guided balloon angioplasty: in vitro demonstration of the potential of MRI for guiding, monitoring, and evaluating endovascular interventions.

The purpose of this study was to demonstrate the potential of MRI for guiding, monitoring, and evaluating endovascular interventions. This was done by investigating the feasibility of MR-guided balloon angioplasty in a stenosed vessel model. Catheters and guidewires were prepared for susceptibility-based MR visualization by incorporating paramagnetic markers into their walls. Near real-time monitoring (up to 1 image/sec) of the interventional procedure was achieved by using a dynamic two-dimensional gradient-echo technique. Devices were localized by on-the-fly subtraction of a baseline image from consecutive dynamic images and by merging the subtraction images with a previously acquired road map. All steps involved in balloon angioplasty, from the introduction and placement of a guidewire to the positioning of a catheter across the stenosis, inflation of the balloon, and dilatation of the stenosis could adequately be monitored with MR fluoroscopy. The beneficial effect of dilatation could be substantiated by a reduction of stenosis-related hypointensities and hyperintensities in the posttreatment MR angiogram as compared to the pretreatment angiogram and by a posttreatment increase of the volumetric flow rate.

Angioplasty, Balloon↗
PubMedDate not supplied

Perceptions and knowledge of preservice and inservice teachers about early literacy instruction.

A major conclusion from the last decade of research on children with poor reading performance is that early, systematic instruction in phonological awareness and letter-sound correspondences improves early reading and spelling skills and results in a reduction of the number of students who are reading below grade level. To teach reading to at-risk students and students with learning disabilities, teachers need to have positive perceptions regarding the role of systematic, explicit instruction, as well as knowledge of English language structure. The purpose of this study was to examine the perceptions and knowledge of general educators at two professional levels toward early literacy instruction for students at risk for reading failure. Unfortunately, our findings are similar to those obtained by Moats in 1994: Many general education teachers, at both preservice and inservice levels, are not prepared adequately for this challenging task.

Adult↗