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.

Pulmonary vascular resistance distribution and recruitment of microvascular surface area.

To test the hypothesis that the distribution of hemodynamic resistance is involved in the control of pulmonary capillary surface area, we measured permeability-surface area product (PS) and longitudinal resistance distribution (LRD) as functions of perfusion rate in isolated rabbit lungs under zone II conditions (n = 10) and through the zone II-III transition (n = 4). PS, considered to be indicative of functioning capillary surface area, was measured with the aid of the diffusion-limited tracer [14C]propanediol, whereas LRD was determined using a viscous bolus technique. LRD was seen to change character with increasing flow and increasing PS/surface area, becoming bimodal with low central resistance as full capillary recruitment was approached in zone III.

Deduction of pulmonary microvascular hematocrit from indicator dilution curves.

We have developed a new model describing the relationship between plasma and red cell tracers flowing through the lung. The model is the result of an analysis of the transport of radiolabeled plasma albumin between two flowing phases and shows that differences between red cell and plasma tracer curves are related to microvascular hematocrit. The model was tested in an isolated, blood-perfused dog lung preparation in which we injected 51Cr-labeled red cells and 125I-labeled plasma albumin into the pulmonary artery.

Postischemic hypoperfusion during unilateral lung reperfusion in vivo.

The incomplete restoration of blood flow during reperfusion may amplify injury by prolonging ischemia; this "no-reflow" has been studied extensively in systemic organs. Our goal was to examine lung blood flow and microvascular function, specifically to determine whether blood flow is altered during lung reperfusion injury in vivo. In a unilateral lung model of ischemia-reperfusion in awake sheep, we measured pulmonary vascular resistance in each lung by radiolabeled microspheres.

Analysis of the influences of the E5 transforming protein on kinetic parameters of epidermal growth factor binding and metabolism.

The E5 protein of the bovine papillomavirus induces cellular transformation when transfected into NIH 3T3 cells, and the extent of focal transformation is enhanced by cotransfection with the epidermal growth factor (EGF) receptor (Martin et al., Cell 59:21-32, 1989). To determine whether E5 affects EGF:receptor interactions we analyzed the kinetics of 125I-EGF processing using a mathematical model that enabled us to evaluate rate constants for ligand association (ka), dissociation (kd), internalization (ke), recycling (kr), and degradation (kh).

Modeling the effect of flow heterogeneity on coronary permeability-surface area.

In 11 anesthetized pigs, the left anterior descending coronary artery (LAD) was cannulated and pump perfused with blood before and during maximum adenosine vasodilation. For LAD plasma flows (F) ranging from 0.42 to 3.

Multiple autophosphorylation site mutations of the epidermal growth factor receptor. Analysis of kinase activity and endocytosis.

We have utilized site-directed mutants to study the role of autophosphorylation of the epidermal growth factor (EGF) receptor in the regulation of receptor kinase activity and ligand-induced endocytosis. A single mutation of the major autophosphorylation site, Y1173, and a double mutation of two autophosphorylation sites, Y1173 and Y1148, did not inhibit kinase activity in vivo, using PLC gamma 1 as a specific substrate for the EGF receptor kinase. The simultaneous mutation of three major autophosphorylation sites (Y1173, Y1148, Y1068), however, caused more than a 50% decrease in EGF-induced tyrosine phosphorylation of PLC gamma 1.

Effects of ligation and embolization on Kf and multiple tracer measurements in dog lungs.

In isolated blood-perfused dog lungs, the capillary filtration coefficient (Kf) and the permeability-surface area product of urea (PS) were measured to determine their responses to two different methods of altering filtration area: lobe ligation (LL, n = 5) and glass bead embolization (GBE, n = 4) during constant perfusion rates (700 +/- 45 ml/min). When two of three lobes were ligated, Kf decreased (1.36 +/- 0.

Rate constants for binding, dissociation, and internalization of EGF: effect of receptor occupancy and ligand concentration.

We measured the kinetic parameters for interaction of epidermal growth factor (EGF) with fetal rat lung (FRL) cells under two sets of experimental conditions and applied sensitivity analysis to see which parameters were well-defined. In the first set of experiments (method 1), the kinetics of internalization and dissociation of radiolabeled EGF were measured with a temperature-shift protocol in medium initially devoid of free ligand. The initial concentration of radiolabeled EGF bound to the cell surface corresponded to levels of receptor occupancy ranging from approximately 200 receptors per cell to approximately 18,000 receptors per cell, a level at which EGF binding approaches saturation.

Exercise training increases coronary transport reserve in miniature swine.

Female yucatan miniature swine were trained on a treadmill (ET) or were cage confined (C) for 16-22 wk. The ET pigs had increased exercise tolerance, heart weight-to-body weight ratio, and skeletal muscle oxidative capacity. After anesthesia the left anterior descending coronary artery was cannulated and pump perfused with blood while aortic, central venous, and coronary perfusion pressures, electrocardiogram, heart rate, and coronary blood flow were monitored.

Reperfusion of the ischemic canine myocardium: effect on vascular exchange and resistance.

In order to see if changes in hemodynamic resistance following reperfusion of ischemic myocardium could be related to alterations in microvascular exchange, we measured resistance (R), permeability surface-area for sucrose (PS), and distribution volumes for tritiated water (V) and for sucrose (VS) in nine anesthetized dogs in which blood to the left anterior descending coronary artery was supplied via a shunt from the carotid artery. Measurements were made during four periods: baseline, reduced coronary artery flow, reperfusion, and a second period of reduced flow. Increase in resistance following reperfusion (R2 = 1.

Effect of exogenous adenosine on resistance, capillary permeability-surface area and flow in ischemic canine myocardium.

The effects of adenosine on capillary-tissue exchange have not been evaluated. Although adenosine is a known vasodilator, its effects on nutritive flow are unknown. We therefore measured the influence of adenosine on resistance and capillary exchange in normal and mildly ischemic myocardium in 11 anesthetized, heparinized dogs.

Tracer exchange in the normal and ischemic coronary circulation.

Proper function of the coronary blood-tissue exchange system may be important in the preservation of myocardium threatened by ischemia. We have undertaken studies aimed at elucidating the functions of this system under baseline and ischemic conditions. The exchange of [14C]sucrose between the coronary capillaries and extravascular space has been studied with the multiple-tracer method.

Effects of hyaluronidase and protamine on resistance and transport after coronary flow reduction in heparinized dogs.

We have measured the effects of hyaluronidase, protamine and a mixture of the two drugs on coronary flow resistance and transcapillary exchange in 20 heparinized, anesthetized dogs in which flow to the left anterior descending coronary artery was supplied through an extracorporeal shunt from the carotid artery. Multiple-tracer measurements were made by injecting a mixture of isotopes into the shunt and sampling from the coronary sinus. These were carried out under base-line conditions, after 1 hr of reduced flow to the left anterior descending coronary artery and after a 2nd hr during which the drug under study was infused into the ischemic zone.

Concurrent increases in resistance and transport after coronary obstruction in dogs.

We have extended earlier studies on coronary vascular permeability-surface area (PS) for [14C]sucrose to include observations of the transcoronary flow resistance before and after partial occlusion of the left anterior descending coronary artery. Multiple-tracer (MT) studies were conducted on 13 anesthetized dogs by inserting an isotope mixture (125I-albumin, 51Cr-red blood cells, [14C]sucrose, 3HOH) into a cannula connecting the carotid and the left anterior descending coronary artery. Analysis of blood sampled from the coronary sinus allowed calculation of PS, extravascular 3HOH volume (VT), and extravascular [14C]sucrose volume (VS).

Chemorheological studies of the effect of heparin on the course of coagulation.

The influence of sodium heparin on viscoelastic change during coagulation was determined in vitro for whole blood samples from ten normal subjects at heparin concentrations ranging from 0 to 1.45 units/(ml whole blood). A four-parameter chemorheological model was used to describe the time course of coagulation as measured by the Weissenberg Rheogoniometer.