AN EXPERIMENTAL APPROACH FOR EVALUATION OF THE O₂ BALANCE IN LOCAL MYOCARDIAL REGIONS IN VIVO

Abstract

SUMMARYQuantitative evaluation of myocardial oxygen balance can be accomplished by measurement of oxygen supply, demand, and intracellular oxygen concentration. Experimentally, these parameters are often related to coronary blood flow, cardiac contractility, and mitochondrial NADH redox level, respectively. Methods were developed to measure these three parameters in a local region on the myocardial surface in open-chest dogs. Local coronary blood supply was measured with the aid of a small surface thermistor, and cardiac work with a miniature strain gauge arch. NADH oxidation-reduction state was recorded using surface fluorometry through a fibre optic light guide. Transient anoxia produced by nitrogen breathing caused a rapid but reversible elevation in NADH levels, which was not always accompanied by a concomitant change in contractile force. Elevation of heart rate resulted in a rise in intramitochondrial NADH followed by an increase in coronary flow. In spite of the increased flow, NADH levels remained elevated, indicating a change in the 02 balance; this may indicate that autoregulation does not necessarily result in total compensation.

Mitochondrial function in vivo evaluated by NADH fluorescence: from animal models to human studies

“…When hemoglobin was eliminated from the brain (perfused with a fluorochemical), no blood volume changes could occur, and indeed no changes in reflectance were observed (174). In the heart, anoxia did not have a great effect on reflectance and the observed change was in the same direction as in the brain (114). In a partially ischemic brain (147) or when N 2 cycles were repeated many times (157), the typical decrease inreflectanceduring anoxia was also minimal, due to the low brain capacity to increase its blood volume to compensate for low PO 2 .…”

“…This is the main artifact in monitoring tissue NADH fluorescence, and it has been discussed by many investigators. During the past 30 years, we have used fiber optic surface fluorometry to monitor the brain exposed to various conditions, as well as other organs such as the heart (114,189). Hence, evidence for the involvement of blood volume artifacts and their correction have been drawn from various published experiments.…”

“…In monitoring other organs, a micromanipulator can be used to hold the light guide above the organ (133,161). In the heart, this problem has been solved by using a light guide-holding cannula connected to the heart muscle by three sutures (114,115,195). In brain preparations, even while the animal was undergoing hyperbaric convulsions or decapitation, only very small artifact changes in the traces were measured from the brain, indicating that the movement has only a negligible effect on NADH measurements.…”

In Vivo Study of Tissue Oxygen Metabolism using Optical and Nuclear Magnetic Resonance Spectroscopies

“…Attempts have been made to measure the fluorescence of heart NADH but interference from blood hemoglobin as well as from myoglobin absorption was not completely eliminated (93). Similarly, myoglobin and hemoglobin absorption cannot be separated in vivo in heart and skeletal tissue.…”

Effect of coronary vasodilators and pacing upon regional oxygen balance of the ischaemic myocardium

“…Since this may influence the vitality of ischaemic myocardial cells, we have developed an experimental approach for evaluating the oxygen balance in local areas of the ventricular myocardium (KEDEM & MAYEVSKY, 1976;KEDEM et al, 1981b & c). These techniques include measurements of local coronary blood supply (using a thermistor probe), local isometric contractile force and intracellular NADH redox level.…”