Biomedical subjects

J B Bassingthwaighte

Publications and source records attributed to J B Bassingthwaighte.

149 records · Page 9Linked to original sources

PubMedDate not supplied

Nonlinear model for capillary-tissue oxygen transport and metabolism.

Oxygen consumption in small tissue regions cannot be measured directly, but assessment of oxygen transport and metabolism at the regional level is possible with imaging techniques using tracer 15O-oxygen for positron emission tomography. On the premise that mathematical modeling of tracer kinetics is the key to the interpretation of regional concentration-time curves, an axially-distributed capillary-tissue model was developed that accounts for oxygen convection in red blood cells and plasma, nonlinear binding to hemoglobin and myoglobin, transmembrane transport among red blood cells, plasma, interstitial fluid and parenchymal cells, axial dispersion, transformation to water in the tissue, and carriage of the reaction product into venous effluent. Computational speed was maximized to make the model useful for routine analysis of experimental data. The steady-state solution of a parent model for nontracer oxygen governs the solutions for parallel-linked models for tracer oxygen and tracer water. The set of models provides estimates of oxygen consumption, extraction, and venous pO2 by fitting model solutions to experimental tracer curves of the regional tissue content or venous outflow. The estimated myocardial oxygen consumption for the whole heart was in good agreement with that measured directly by the Fick method and was relatively insensitive to noise. General features incorporated in the model make it widely applicable to estimating oxygen consumption in other organs from data obtained by external detection methods such as positron emission tomography.

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PubMedDate not supplied

Physiology and theory of tracer washout techniques for the estimation of myocardial blood flow: flow estimation from tracer washout.

The time course of washout of tracer from the myocardium provides an estimate of the flow per unit volume when the blood-tissue exchange is flow-limited. Methods of testing for the flow-limitation and for the absence of influences of low permeability or diffusion on the washout include the uses of paired or multiple tracers and the examination for similarity of the shapes of the residue function or washout curves at varied coronary blood flows. A conceptual framework for these studies is provided by a clearance-flow diagram for the myocardium where capillaries are long compared to radial intercapillary distances. This anatomic-physiologic framework coupled with a probabilistic, general analytic approach and with various experimental approaches to tracer studies of mass transport through the heart provides a general basis for methods of estimating myocardial blood flow in the whole organ and in its component regions.

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PubMedDate not supplied

GGOPT: an unconstrained non-linear optimizer.

GGOPT is a derivative-free non-linear optimizer for smooth functions with added noise. If the function values arise from observations or from extensive computations, these errors can be considerable. GGOPT uses an adjustable mesh together with linear least squares to find smoothed values of the function, gradient and Hessian at the center of the mesh. These values drive a descent method that estimates optimal parameters. The smoothed values usually result in increased accuracy.

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PubMedDate not supplied

Power-law kinetics of tracer washout from physiological systems.

Recent studies suggest that the tail of the washout of tracer-labeled substances from physiological systems can exhibit power-law behavior. In this work we develop a theoretical interpretation of the power-law behavior of the flow-limited washout of tracer-labeled water from the myocardium. Using minimal assumptions concerning the complicated structure of the coronary network we show that the washout from a heterogeneous flow system is given by h(t) approximately equal to A x p1 (V/t)(-beta), where beta is close to 3, p1 is the probability density of flows through the system, V is a constant volume associated with each pathway, and A is a constant. This prediction fits observed power-law washout behavior of tracer water in the heart. This theory is general enough to lead us to speculate that close examination of transport in other heterogeneity-perfused systems is likely to reveal similar power-law behavior.

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PubMedDate not supplied

The fractal nature of myocardial blood flow emerges from a whole-organ model of arterial network.

Mammalian hearts exhibit a heterogeneous spatial distribution of blood flows, but flows in near-neighbor regions correlate strongly. Also, tracer (15)O-water washout after injection into the inflow shows a straight log-log relationship between outflow concentration and time. To uncover the role of the arterial network in governing these phenomena, morphometric data were used to construct a mathematical model of the coronary arterial network of the pig heart. The model arterial network, built in a simplified three-dimensional representation of tissue geometry, satisfies the statistical morphometric data on segment lengths, diameters and connectivities reported for real arterial networks. The model uses an avoidance algorithm to position successive vascular segments in the network. Assuming flows through the network to be steady, the calculated regional flow distributions showed (1) the degree of heterogeneity observed in normal hearts; (2) spatial self-similarity in local flows; (3) fractal spatial correlations, all with the same fractal dimension found in animal studies; (4) pressure distributions along the model arterial network comparable to those observed in nature, with maximal resistances in small vessels. In addition, the washout of intravascular tracer showed tails with power law slopes that fitted h(t) = at(-alpha-1) with the exponents alpha = 2 for the reconstructed networks compared with those from experimental outflow concentration-time curves with alpha = 2.1+/-0.3. Thus, we concluded that the fractal nature of spatial flow distribution in the heart, and of temporal intravascular washout, are explicable in terms of the morphometry of the coronary network.

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