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At least 883 records · Page 49Linked to original sources
PubMed1989

[Conception of a decompression table].

After a given time at bottom, different tissues become saturated to different extents with nitrogen. In diving back to the surface a hydrostatic decompression occurs first, followed by the desaturation process some time later. It is during this time interval that all important events are taking place, namely: either a monophasic desaturation, whereby inert nitrogen gas is given off at the alveolar capillary interface. or a biphasic desaturation takes place, giving rise to gas bubbles in the blood-stream as well as in the tissues. We may then encounter pathologies which are benign incidents or, worse, lead to decompression sickness grade II. Since Paul Bert dedicated his thoughts in 1878 to this problem, numerous authors tried to explain this time delay, for trying to suppress it would be entirely unrealistic. Unfortunately, mathematical reasoning has too often overshadowed physiological thinking in these matters. We also stuck to Haldane's concept of 1908, in incorporating Workman's improvements of 1965. This method is based on two main principles: 1. all calculations were done with several "tissues" in mind. Their anatomical boundaries are of no importance as, only their desaturation half-times are relevant. 2. a natural limit is given by the critical saturation-coefficient (CS). It expresses the ratio between the partial pressure of the dissolved gas and the reduction of hydrostatic pressure during ascent (given as pressure gradient). Through experience we were able to put up tables which were more and more safe, in examining foremost the CS ratio and the desaturation times of certain tissues. Several examples are given, the values of which are statistically highly significant, as they incorporate the results of more than 60,000 air dives.

Decompression↗
PubMed2006

Validity of the Children's Category Test-Level 1 in a clinical sample with heterogeneous forms of brain dysfunction.

Validity of the Children's Category Test-Level 1 (CCT-1) was evaluated in 123 children with various forms of brain dysfunction. Confirmatory factor analyses indicated that the CCT-1 is composed of two factors. The first factor was composed of subtests II and III, and was named "Conceptual Discrimination", while the second was composed of subtests IV and V, and was named "Conceptual Memory". Both factors were more highly correlated with mathematical achievement than with reading or writing achievement. Comparisons between traumatic brain injury (TBI) and Attention-Deficit/Hyperactivity Disorder (ADHD) groups indicated that the Conceptual Discrimination factor was more sensitive to TBI than the Conceptual Memory factor. Also, the total error composite T-score was not particularly sensitive to ADHD. Findings indicate that the composite T-score should be interpreted with caution because it does not appear sensitive to milder forms of brain dysfunction and because the CCT-1 is a multidimensional procedure.

Brain Diseases↗
PubMed1992

Introduction to modeling.

A model is a representation of structure and a mathematical model describes mathematically the relationship between variables and/or parameters. Numerous types of mathematical models have been used to study biological systems that are of interest to nutritionists. This paper introduces some concepts that relate to the dynamic behavior of biological systems and discusses two modeling approaches that can be used in conjunction with kinetic studies. The two approaches, empirical compartmental modeling and model-based compartmental analysis, are subcategories of compartmental analysis. The objective of this brief introduction to modeling is to encourage more nutritionists to use compartmental analysis and other forms of mathematical modeling in their research.

Animals↗
PubMed1989

Metabolic dynamics in the human red cell. Part I--A comprehensive kinetic model.

The experimental investigation of the red cell over the last three decades has accumulated extensive biochemical data on its enzymes and metabolites. The goal of this work is to provide a unified theoretical framework for the integration and consistent interpretation of these data by means of a comprehensive mathematical metabolic model of the red cell. This model is described in four parts. Here, we describe the general conception, scope and the biological assumptions of the model. The model is comprised of dynamic mass balances based on stoichiometry and enzyme kinetics with the imposed physico-chemical constraints of osmotic balance and electroneutrality.

Erythrocytes↗
PubMed1984

A unifying concept for carcinogenic risk assessments: comparison with radiation-induced leukemia in mice and men.

This paper presents a new, general mathematical dose-response model which can use human, animal and cell culture data to predict the incidence of leukemia as a result of exposure to ionizing radiations. The model is based on simple considerations of fundamental biological processes of carcinogenic initiation, carcinogenic promotion and competing risk due to other toxic or disease reactions. The model can be used to predict the risk of leukemia for either human or animal populations which have been (or will be) treated with any radiation dose-time treatment protocol of interest. The model is both an extension and an outgrowth of earlier work done for the Oak Ridge dosimetry program in support activities for the Atomic Bomb Casualty Commission (formerly) and the Radiation Effects Research Foundation (currently).

Animals↗
PubMed1978

Cardiovascular trauma from angiographic jets--validation of a theoretic concept in dogs.

The relationship of angiographic injections to cardiovascular trauma was determined. The aorta of dogs was studied by a mathematic model that (a) defines the kinetic energy of contrast-media jets emanating from the exit holes of catheters and (b) enables precise correlation of energy levels to potential trauma. A universal curve independent of the Reynolds number of the jet readily determines how far the jet penetrates intravascular blood. A traumatic histopathologic spectrum was found for those injections predicted by the model to be traumatic. The curve enables the angiographer to calculate the safe operating range of any catheter.

Angiography↗
PubMed1980

A proposed model for the prediction of response to endocrine therapy in breast cancer from the estrogen receptor status of one site and the number of metastatic sites.

A mathematical model for prediction of response to endocrine therapy of breast cancer has been developed based on a clonal concept of metastatic spread. The model includes an expression of the likelihood of response of an estrogen receptor-positive site and an expression of the concordance of receptor assays when multiple sites are assayed. Both of these are raised to a power function based on the number of sites of metastases to yield a predicted response rate. An excellent fit of the predictions of this mathematical model and response data from a series of patients receiving endocrine therapy was observed. This model provides a worthwhile insight into the biology of response to endocrine therapy. The model may be extended and refined through additional analyses.

Binding Sites↗
PubMed1998

Self-concept in children: equivalence of measurement and structure across gender and grade of Harter's Self-Perception Profile for Children.

In this study, we tested a Dutch version of Harter's (1985) Self-Perception Profile for Children for equivalence of measurement and structure across gender and age (grade), using the LISREL confirmatory factor analytic model. The sample consisted of 758 Flemish 4th, 5th, and 6th graders (8-13 years old, M = 10.5 years old). Support was found for equivalence of structure for boys and girls, for 4th and 5th graders, and for 5th and 6th graders. Equivalence of measurement was only partially found. The relation between items and factors was invariant across gender and grade. The error of measurement however was not equivalent, indicating that the items had not the same reliability for boys and girls and across all grade groups.

Adolescent↗