M. Fennema

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.

Cardiovascular Responses, Hemodynamics and Oxygen Transport to Tissue during Moderate Isovolemic Hemodilution in Pigs

In conclusion, in contrast to many reports obtained from dogs, in pigs the rise in CO during moderate isovolemic hemodilution is, besides the increased venous return, more induced by increased work performance of the heart and less by a decreased SVR. The rise in CO did not compensate for the decrease in oxygen transport capacity. Our results confirm most of the reported findings in humans at the same stage of hemodilution. Besides changes in hemodynamics, in our study a gradual decreased oxygen affinity of hemoglobin could be observed. That the pig animal model for studying hemodilution and oxygen transport to the tissue is more appropriate than the dog model is open to discussion.

Oxygen Supply to the Myocardium

This paper concerns aspects of oxygenation of the myocardium in relation to coronary artery flow and in relation to areas of ischaemic hypoxia. These results were obtained during the course of experiments designed to set up a myocardial ischaemia model and to investigate the effects of haemodilution on myocardial oxygenation. These studies involved the use of various inspired oxygen concentrations (FIO2’s) and cross-clamping of a terminal branch of the left anterior descending coronary artery, (Faithfull et al 1983a). The paper is inevitably somewhat ‘anecdotal’ in nature, but nevertheless does throw some light on the complicated nature of the oxygenation of myocardial tissue.

Tissue Oxygenation by Fluorocarbons

Fluorocarbons have a very high solubility for oxygen and this was very dramatically shown by Clark and Gollan (1966), when they were able to demonstrate survival of mice completely immersed in these liquids for extended periods of time. The animals were able to obtain sufficient oxygen by respiring the liquid and after removal showed no apparent ill effects from the experience.

PO2-Profiles in Human Muscle Tissue as Indicator of Therapeutical Effect in Septic Shock Patients

Automatically stepwise driven pO2 electrodes were transcutaneously inserted into muscle tissue of severely ill septic shock patients. The pO2 profile was plotted from 200 individual measurements registered during 5 minutes and a histogram plotted for documentation. Arterial and venous blood gases, cardiac output, systemic and pulmonary vascular resistance were measured continuously on-line. In septicemia multiple drug schemes are suggested all intending to increase oxygen supply to the tissue and to improve oxygen demand/supply mismatch. So far the attending physician is bound to conclude and continue respectively change the treatment scheme according to the above described macrophysiological parameters. Perfusion distribution and local inhomogenities of tissue oxygen supply remain undetected. In the described study pretreatment pO2 profiles in musculus quadriceps femoris were obtained and measurements repeated in intervals of 10 minutes after start of pharmacological treatment. The changes of pO2 profiles of 20 patients, monitored in such a way over days and weeks, were carefully correlated to the described cardiocirculatory parameters and blood gas analyses. Dopamine was used to improve cardiac function and tissue oxygen supply as well. The investigations show that resulting changes of cardiovascular and blood gas parameters do not always indicate that tissue oxygen supply has really improved. On the other hand there was never an improvement in tissue oxygen supply when no changes of the other parameters had occurred. It is advised to add as a further diagnostic parameter tissue pO2 measurements to get insight if improvement in cardiac and pulmonary function really has the intended effect of improvement of tissue oxygen supply.

The Effects of Acute Ischaemia on Intramyocardial Oxygen Tensions

Most of the studies of myocardial oxygen tensions (PmO2) that have been performed in the beating heart have been carried out in dogs (Rude et al 1982, Rude et al 1984, Moss 1968, Schuchhardt 1985, Reyes et al 1978, van der Laarse 1978). This species is known to have a number of microscopic collateral vessels in contrast to humans and pigs that have few such structures (Berne and Rubio 1979). As far as we are aware, no studies have been performed to determine the distribution of PmO2 values in the myocardium of the pig. Neither have studies been made of minute-to-minute changes in PmO2 distribution during conditions of acute myocardial ischemia. This paper reports our work in these areas.

Factors that Determine the Oxygen Supply of the Cell and their Possible Disruption

Oxygen transport to tissue and cell occurs in three major steps: 1. oxygen uptake in the lung; 2. oxygen transport in blood; 3. diffusion of oxygen from the capillaries, through the tissue and into the cell.

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.

Continuous Intra-Arterial PO2 Monitoring During Thoracic Surgery

Intermittent blood gas sampling has several disadvantages, the most important being that samples are usually taken at set intervals, or when changes in oxygenation are suspected--when it is too late. Another problem is inaccuracy caused by careless blood sample handling. Continuous intravascular PaO2 monitoring eliminates these problems. This study shows that the Continucath sensor is an easy-to-use and reliable monitor, with specific early warning capabilities for hypoxia, thereby improving anesthetic and intensive care management. Its characteristics are: a stabilization period of 10 minutes, a 90% response time of 90 seconds, temperature dependence of 4% per degree celsius, a flow dependence of less than 1% if the flow is more than 5 cm/sec, a drift of less than 0.7% per hour, a correlation coefficient of 0.92 when compared to blood gas analysis during surgery.

Prophylaxis and treatment of myocardial ischaemia by haemodilution with fluorocarbon emulsions.

Fluorocarbons (PFCs), largely inert chemicals with a high solubility for respiratory and other gases, are available in emulsified form in the plasma substitute Fluosol-DA 20% (FDA). This has an oxygen solubility of 0.75 ml per 100 mmHg (Zander and Makowski, 1982; Grote et al., 1985), about two and a half times that in plasma. To take advantage of this difference a high inspired concentration of oxygen is usually administered.