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Biomedical subjects

J Doll

Publications and source records attributed to J Doll.

67 records · Page 4Linked to original sources
PubMed1979

Calculation of residence time distributions of intravascular radioactive tracers in fields of external registration.

Because of the physiological significance of the mean velocity of blood flow, indicator dispersion models are of special interest and possess practical relevance, if biological and extraneous variables can be altered. The variables being considered are flow characteristics of the streaming blood, tracer distribution at the entrance into the flow system, and the area in which impulses are collected to form the time-activity curve. Using a simplified version of the general convective diffusion equation (diffusion model) in which the diffusion constant D includes all propagation and mixing of the tracer, a simple numerical method can be applied. The method is used to determine influences of injection and changed regions of interest on the time-activity curve and the following parameters: appearance times, peak times, mean circulation times, and the times of the first inflection points. For this purpose, the range of D was determined in 14 patients by applying experimental data to the model. The calculations on the variables show, that the advantage of this method is its applicability to any experimental case by simply adapting the input data to the recordings.

Blood Circulation↗
PubMed1977

[Automated method of determining blood circulation time in nuclear medicine cardiology].

In this paper a method of computer-assisted evaluation of circulation times using a scintillation camera is described. Eight segments of the central circulation are defined on a graphic display unit. Then the analysis of time-activity curves and the normalization of circulation times to hear rate is performed. The automatic analysis is based upon the hydrodynamic meaning of the first inflection point of a time-activity curve. The differences between inflection points are nearly identical with appearance time differences under the experimental conditions used in 131 cases. A mathematical model is presented to defined the conditions for this behaviour and to explain some deviations observed if time differences exceeded a certain value. It can be shown that the method described is largely independent of extraneous influences. It offers haemodynamically relevant parameters that correspond to the minimal cardiac transit times.

Blood Circulation Time↗
PubMed1976

[Clinical significance of kidney imaging in bone scintigraphy].

The results of the examination of 62 patients who had undergone skeletal scintigraphy with 18-F and a urologic examination, were evaluated to determine whether the 18-F incorporation in the kidneys might indicate the presence of renal disease. Patients with and without renal disease demonstrated a similar 18-F incorporation in the kidneys. Our data indicate that a side different 18-F renal activity is without clinical significance.

Bone Diseases↗
PubMed1975

[Three-stage method in lung scintigraphy: ventilation, diffusion and perfusion (author's transl)].

A combination of three stages--ventilation, "perfusion" and diffusion-- has proved to be the optimal method in the scientigraphic exmaination of the lung. 85mCrypton is preferred for ventilation studies compared with 133Xenon, in view of its more suitable radiation energy and lower solubility. In the pre and post-operative investigation of the lungs, ventilation estimations are essential, providing a more reliable perameter than "perfusion estimations". The results from "perfusion" measurements with MAA or microspheres frequently do not correspond with those obtained by 133Xenon. It is still debatable whether the use of MAA or microspheres provide perfusion values and it would be better at present to speak of MAA fixation results.

Adult↗
PubMedDate not supplied

Experimental metastasis correlates with cyclic AMP accumulation in B16 melanoma clones.

Metastasis is a complex process whereby tumour cells from a primary neoplastic growth disseminate throughout the body and establish secondary tumour foci in distant organs. Biochemical traits associated with, or essential for, the expression of the metastatic phenotype have not yet been identified. In the course of examining stimulation of the B16 murine melanoma adenylate cyclase by melanocyte-stimulating hormone (MSH) and by the diterpene forskolin, we noted that tumour cell clones isolated from common parent cell populations differed widely in their responses to these agonists. We report here that the accumulation of cyclic AMP induced by MSH or forskolin shows a strong positive correlation with the ability of B16 melanoma clones to form pulmonary tumour colonies when injected intravenously (i.v.) into syngeneic mice ('experimental metastasis'). In parallel in vitro analyses of cyclic AMP metabolism and in vivo assays of experimental metastasis using replicate cell preparations, highly metastatic tumour cell clones consistently show greater than a 30-fold increase in cellular cyclic AMP when exposed to MSH or forskolin. By contrast, clones with limited metastatic abilities respond to the same agonists with only a two- to threefold increase in cellular cyclic AMP. These data suggest that cyclic AMP metabolism is linked with biochemical pathways that are responsible for the formation of experimental metastasis by the B16 melanoma.

Animals↗
PubMedDate not supplied

[Fulminating pneumococcal septicemia (author's transl)].

Two cases of fulminating pneumococcal septicemia (FSP) are reported, and 47 confirmed cases were discovered after a review of the published literature. The syndrome is that of a malignant infection with fever, collapse, and disseminated intravascular coagulation, with a rapid mortal outcome in most cases. Etiologically, FSP is usually the consequence of functional or anatomical asplenia, and the relative frequency of this affection after splenectomy following trauma confirms this observation. Lack of a splenic filter and a deficiency in the phagocytic system are the reasons for microbial proliferation in the blood, and the lymphocytic defence mechanisms are inactive because of the absence of any focus of infection.

Adult↗