Possibility of Monitoring Mitochondrial Activity In Isometric Exercise Using NIRS.

Abstract

379 Oxygen debt is a controversial topic and there is debate that mitochondrial activity is initiated with work output. Recent NMR studies suggested it may take 30 sec to 1 min for mitochondria to fully respond to the ATP requirement, which is different from In Vivo studies. We aimed to solve the problem by monitoring directly tissue oxygenation by NIRS using isometric finger flexor exercise 30,50, and 90%Vmax intensities. The NIR gives an information of changes in muscle oxygenation, which consists of the following factors; oxygen supply, or blood flow and oxygen demand, or VO2. Thus, we can obtain oxygen metabolism information in the case of known blood flow(isometric exercise does not alter blood flow) by the calculated amount of deoxyhemoglobin (Hb) and oxyhemoglobin (HbO2) in an optically visible volume of the muscle. The hemoglobin signal that transmits information of oxygenation, comes from rather vessels whose diameters are less than 2 mm. We roodel an optically visible muscle oxygen transport/circulation system; based upon hemoglobin and myoglobin. It can be divided into three compartments; in-flow, metabolic, and out-flow. The in-flow and out-flow compartment do not attribute to oxygen transport and metabolic compartment but does have a oxygen transporting function. According to our model we present here, based upon a modified Fick equation, the rate of deoxygenation is a function of metabolism, or oxygen consumption and mixing term in the venous compartment, which may delay information of VO2. The time constants are weighted by the increased VO2 and venous blood volume relative to a oxygen transferable volume. We compared the rate of deoxygenation to that with cuff ischemia to eliminate the mixing time. The results show the linear regression of 0.88; 12% smaller values in the deoxygenation than that during cuff ischemia, with r2=0.85, showing the mixing function by the blood flow is minimal. The results indicate that we can estimate oxygen consumption by the rate of deoxygenation during isometric exercise. Supported in part by NIH HL44125