Dynamic response of the coronary circulation to a rapid change in its perfusion in the anaesthetized goat.

1. We tested predictions of a mathematical formulation of a hypothesis of dynamic control of coronary blood flow by tissue oxygen tension. 2.

Dynamics of coronary adjustment to a change in heart rate in the anaesthetized goat.

1. We have previously shown that steady-state coronary flow during auto-regulation and metabolic rate changes is predicted by a mathematically expressed theory which assigns control of coronary vascular resistance to tissue PO2. Our present purpose was to test the applicability of this theory to the non-steady state as exemplified by a sudden step change in heart rate.

Rate of decrease of myocardial O2 consumption due to cardiac arrest in anesthetized goats.

The rate of change of myocardial O2 consumption, MVO2, has been measured during the transition from beating to cardiac arrest. Cardiac arrest was achieved by destruction of the bundle of His by injection of formalin and induced by 25 s interruption of pacing. The left main coronary artery was perfused under constant pressure and the great cardiac vein was drained under controlled pressure.

Model of the coronary circulation based on pressure dependence of coronary resistance and compliance.

The effect of pressure-dependent changes in vascular volume, resistance and capacitance in the coronary micro-circulation, has been studied by a distributed mathematical model of the coronary micro-vasculature in the left ventricular wall. The model does not include regulation of coronary blood flow and is evaluated only for the fully dilated coronary vasculature. The left ventricular wall was thought to consist of eight parallel layers, each of them with an arteriolar, capillary and venular compartment.

Quantification of arteriolar density and embolization by microspheres in rat myocardium.

We developed a technique for in vitro determination of arteriolar densities. Hearts, obtained from anesthetized rats and perfused by the Langendorff method, were fully dilated with adenosine and were arrested with an elevated potassium concentration. After a stabilization period, the hearts were perfused with a buffered fixative for some minutes to obtain a nonvital vasculature.

Intramyocardial blood volume change in first moments of cardiac arrest in anesthetized goats.

The effect of cardiac relaxation on the intramyocardial blood volume was studied by measuring the integrated difference between arterial inflow and great cardiac venous outflow. In nine anesthetized goats, the left main coronary artery was perfused under constant pressure. The great cardiac vein was drained under pressure control.

Quantification of O2 consumption and arterial pressure as independent determinants of coronary flow.

The steady-state relationship between coronary arterial blood flow (CBF) and both myocardial O2 consumption (MVO2) and coronary arterial pressure (P) was explored in anesthetized dogs and goats. Both species were subjected to constant pressure perfusion of the left main coronary artery by an external pressure-controlling circuit. In addition a group of goats was studied with normal aortic perfusion using an occluder around the left main coronary artery to vary coronary arterial pressure.

Coronary diastolic pressure-flow relation and zero flow pressure explained on the basis of intramyocardial compliance.

In the controversy about the mechanisms determining the high zero flow pressures and the further interpretation of coronary diastolic pressure flow relations, this paper takes a stand in favor of intramyocardial compliance as the primary cause of the high zero flow pressures. An attempt has been made to estimate the compliance distribution within the coronary circulation and to show the specific effect of intramyocardial compliance on arterial and venous pressure-flow relations. Since no data are available on the distensibility of coronary arterioles and capillaries, these data were taken from studies on mesenteric vessels.

Coronary circulation in the presence of vascular disease.

This paper discusses three specific aspects of coronary circulation as they relate to the patient with coronary artery disease. Firstly, the normal autoregulatory and metabolic control of the coronary circulation is considered in the light of current understanding of the relevant processes. Secondly, the implications of microcirculatory heterogeneities are discussed.

Oxygen and coronary vascular resistance during autoregulation and metabolic vasodilation in the dog.

The hypothesis that tissue oxygen tension controls coronary vascular resistance during changes in perfusion pressure and oxygen consumption was expressed in a simplified mathematical form capable of making quantitative predictions. The predictive value of this formulation of the hypothesis was tested in experiments on anaesthetized mongrel dogs subjected to constant-pressure perfusion of the left main coronary artery, with measurements of coronary blood flow and arterio-venous oxygen content differences. Coronary venous oxygen content was used as an index of tissue oxygenation.

Early colour deprivation in the pigeon.

When cats and monkeys are deprived of specific stimuli during an early sensitive period the development of their visual system is known to be affected. In pigeons, pattern discrimination learning has been shown to be affected by monocular deprivation [2]. Our study was set up to examine whether colour discrimination learning could be affected by colour deprivation.

Forward coronary flow normally seen in systole is the result of both forward and concealed back flow.

Normally systolic coronary blood flow is almost entirely forward. As perfusion pressure was lowered through the autoregulatory range in open-chest dogs, net systolic back flow appeared at approximately 70 mm Hg. Imposing a series resistance (Rs), which impedes both forward and back flow, abolished this reverse flow and resulted in net forward systolic flow.

Can a single vasodilator be responsible for both coronary autoregulation and metabolic vasodilation?

To test the hypothesis that both coronary autoregulation and metabolic vasodilation can be mediated by the same substance, we have analysed measured autoregulation curves with the aid of a simple mass balance model. In an open-chest dog preparation, increasing the heart rate by pacing results in a nearly parallel shift of the autoregulation curve to a higher flow (Q) level. We assume a unique relationship between vascular conductance and interstitial concentration of a vasodilating substance [A].

Plasma protein concentration and control of coronary vascular resistance in isolated rat heart.

Isolated externally paced (300 beats/min) rat hearts were perfused at constant pressure (70 mmHg) using a modified Krebs-Henseleit solution with (n = 52) and without (n = 15) washed bovine red cells. Albumin concentration varied from 1 to 10 g/dl. With increasing albumin concentration in blood-perfused hearts, wet-to-dry weight ratio, peak reactive hyperemic flow, and control geometric resistance were decreased, whereas oxygen consumption, control flow, and minimal geometric resistance remained constant.

Diffusion coefficients of oxygen and hemoglobin as obtained simultaneously from photometric determination of the oxygenation of layers of hemoglobin solutions.

The oxygenation of layers of deoxygenated hemoglobin solutions after a sudden exposure to a gas containing oxygen at a partial pressure P1 has been studied by a photometric method. Layer thicknesses varied between 50 and 250 micron, hemoglobin concentrations between 0.1 and 0.

A theoretical analysis of nonsteady-state oxygen transfer in layers of hemoglobin solution.

The oxygenation of layers of hemoglobin solutions thick enough to ensure chemical equilibrium between oxygen and hemoglobin has been analyzed theoretically assuming simultaneous diffusion of oxygen and oxyhemoglobin. The dimensionless transfer equation was solved for the finite and semi-infinite situation, the parameters being 1) the ratio of bound to physically dissolved oxygen after equilibration (H), 2) the ratio of carrier-mediated to free oxygen flux at steady state (D), and 3) the dimensionless saturation curve (characterized by phi 50). A parametric analysis provided plots of the dimensionless oxygenation time against these three dimensionless parameters.

Transient oxygen uptake during myocardial reactive hyperemia in the dog.

Oxygen uptake during myocardial hyperemia (MRH) following occlusions of 2.5-30 s was studied in nine anesthetized open-chest dogs by continuous measurement of left anterior coronary blood flow and anterior coronary vein oxygen saturation with electromagnetic flowmeter and fiber-optic catheters, respectively. The ratio of excess oxygen uptake to debt multiplied by 100% was defined as the oxygen repayment ratio (RR) and varied between -50% and +150% (mean 78%).

Use of a wedge cuvette in thin layer photometry and its application to oximetry.

A wedge cuvette was constructed by fixing 2 glass plates at a known angle with a spacer at one end. This resulted in a thin layer with thickness varying from 0 to 250 micrometer. By measuring the intensity of a beam of light through the thin layer as a function of distance along the wedge (and thus layer thickness), the absorption coefficient at the light wavelength used could be obtained without a separate measurement of I0, the reference light intensity.