The effects of acute ischaemia on intramyocardial oxygen tensions

Determining critical values of calculated parameters within a physiologic model

To determine the critical value of calculated but not readily measurable variables of a physiologic model, we examine clinical studies of similar variables and establish the critical values. The calculated variables considered in this study are the partial pressure of oxygen in the myocardium and in the gray matter of the brain. Partial pressure target values of 29 mmHg for cerebral tissue and 23 mmHg for myocardial tissue were determined to be suitable for a critical threshold. We validated these with a physiologic model test by ensuring that these corresponded to a reasonable value of cardiac output, vital sign commonly used to evaluate patient well being. These values can be used for future analysis of physiologic monitors' alarm systems when using physiologic models.

Myocardial oxygen supply under critical conditions, the effects of hemodilution and fluorocarbons

This article reviews the factors influencing myocardial oxygen supply and demand. The regulative mechanisms in coronary blood flow, especially in critical conditions, are explained. Myocardial oxygenation in coronary artery disease is discussed with special reference to pharmacological intervention. An extensive evaluation of the effects of hemodilution on both the healthy and diseased heart is presented. Effects of hemodilution with fluorocarbons for the treatment or prevention of myocardial ischemia are shown with the aid of intramyocardial oxygen partial pressure measurements.

Tissue oxygen tension in the cerebral cortex of the rabbit

Polarographic techniques were employed to measure oxygen partial pressure using 10 micron glass-protected gold microelectrodes. When inserting the electrode into the cortex, a PO2-profile is produced. The average PO2 was about 9 mm Hg. Nearly all measurements were below 25 mm Hg and measurements above 50 mm Hg were rare. When the FiO2 was increased from 0.3 to 1.0, tissue PO2 increased, then gradually decreased. This is probably due to vasoconstriction of pre-capillary sphincters. Acute hypoxia showed the opposite effect, but the autoregulation does not seem to be so effective. When CO2 was added to the inspiratory gas mixture the PO2 increased and showed little tendency to return to normal values. This increase in PO2 is due to the direct effect of CO2 and H+ on the blood vessels, causing vasodilation, and therefore an increase in blood flow and tissue oxygenation.