Regional measurement of the Gd-DTPA tissue partition coefficient in canine myocardium.

Quantifiable MRI perfusion studies using the contrast agent Gd-DTPA require measurement or estimation of the tissue partition coefficient (lambda) for tracer kinetic modeling. Radiotracer techniques were used to obtain regional lambda measurements from the left ventricles of five dogs. Measurements were analyzed to determine whether spatial heterogeneity was a major component of lambda variability.

Effects of flow heterogeneity on the measurement of capillary exchange in the lung.

The effects of flow heterogeneity on the measurement of transcapillary escape of small molecules for perfused in situ sheep lungs were evaluated. Lungs were studied at five flows (1.5-5.

The use of microsoft excel as a user interface for biological simulations.

We used Microsoft Excel 4.0 for Windows running on a PC-486 to develop a user interface for two biological simulation models: a lung fluid balance model and a fractal model of the pulmonary circulation. The simulation programs were written in the C programming language, while the user interface was written in the macro language of Excel.

Parameter identification in coronary pressure flow models: a graphical approach.

The confident identification of parameters is important in the practical application of physiological models. However, the task of parameter identification is often complicated by interactions among parameters and by the fact that the sensitivity of the model to changes in a given parameter is generally a function of all the other parameters. Here we illustrate a graphical approach to parameter identification that allows the modeler to visualize the behavior of the model, the sensitivity functions, and certain functions characteristic of parameter interdependence.

Exercise training-induced increase in coronary transport capacity.

The objective of this study was to measure effects of exercise training on coronary flow heterogeneity, microvascular transport, and hemodynamics. Five miniature swine were trained on a treadmill (ET) for 16 wk; five control pigs (C) were confined to cages for the same period. At the end of that period we used the multiple indicator dilution method to measure permeability-surface area product (PS) to EDTA over a range of flow (F) in an anesthetized, open-chest preparation.