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Biomedical subjects

A Shitzer

Publications and source records attributed to A Shitzer.

29 records · Page 2Linked to original sources
PubMed1982

Transient temperature profiles in tissues with nonuniform blood flow distributions.

Numerical methods and the bio-heat transfer equation are employed to calculate temperature profiles in tissues subjected to nonuniform blood flow distribution for initial and boundary conditions which simulate experimental physiological situations. Results indicate that one can infer, from sudden changes in temperature distribution, the occurrence of sudden changes in tissue blood flow. However, prediction of blood flow distribution from near equilibrium or steady-state temperature profiles is of poor resolution, and does not appear useful as a practical technique. The methods and results are useful for predictions of temperature profiles in the absence of significant endogenous or exogenous heating; they can be extended to such applications by straightforward methods.

Body Temperature↗
PubMed1980

Controlled destruction and temperature distributions in biological tissues subjected to monoactive electrocoagulation.

An analysis of the temperature fields developed in a biological tissue undergoing a monoactive electrical coagulating process is presented, including thermal recovery following prolonged heating. The analysis is performed for the passage of alternating current and assumes a homogeneous and isotropic tissue model which is uniformly perfused by blood at arterial temperature. Solution for the one-dimensional spherical geometry is obtained by a Laplace transform and numerical integrations. Results obtained indicate the major role which blood perfusion plays in determining the effects of the coagulating process; tissue temperatures and depth of destruction are drastically reduced as blood perfusion increases. Metabolic heat generation rate is found to have negligible effects on tissue temperatures whereas electrode thermal inertia affects temperature levels appreciably. However, electrodes employed in practice would have a low thermal inertia which might be regarded as zero for all practical purposes. It is also found that the depth of tissue destruction is almost directly proportional to the electrical power and duration of application. To avoid excessively high temperatures and charring, it would be advantageous to reduce power and increase the time of application. Results of this study should be regarded as a first approximation to the rather complex phenomena associated with electrocoagulation. They may, nevertheless, serve as preliminary guidelines to practicing surgeons applying this technique.

Blood Circulation↗
PubMed1980

On the relationship between blood perfusion, metabolism and temperature in biological tissue heat balance.

A general, one-dimensional steady-state analysis of the thermal behavior of biological tissues is presented. The three major geometries, i.e., rectangular, cylindrical and spherical, are considered along with boundary conditions of the general type. It is shown that transport of heat inside the tissue may be dominated by conduction, convection by blood perfusion, metabolism or a combination thereof. The role of each of these mechanisms is presented by suitable dimensionless parameters expressed in terms of tissue physical properties. The order of magnitude of these parameters indicates the relative importance of the various mechanisms on the transport of heat inside the tissue. It is further shown that in areas where convection by blood perfusion is dominant, tissue temperatures are almost uniform except for narrow regions near the boundaries. The occurrence of maximum temperatures inside the tissue is also studied along with the combinations of blood perfusion and heating rates which would insure that certain predetermined values are not exceeded. This work also demonstrates that the amount of heat which may be convected into the tissue by the circulatory system depends on the heating rate and the boundary conditions, as well as the blood perfusion rate. This quantity is shown to reach a finite limit as the blood perfusion rate becomes very high.

Blood Physiological Phenomena↗