Intracellular Oxygen Dynamics Observed by NIRS During Skeletal Muscle Contraction

Abstract

Cellular respiration depends upon a coordinated response of the cardiovasculature and metabolism to meet changing energy demands in muscle. Even though the adjustments in blood flow, O2 gradient, and myoglobin (Mb) saturation will enhance O2 flux to the mitochondria at the initiation of contraction, the relative contribution of Mb vs. Hb remains an issue for contentious debate. Some researchers have ascribed no significant role for Mb in supplying O2 during muscle contraction. Since Mb has an extremely high affinity for O2, it cannot readily release its O2 store. Hb must then supply all the O2 from the onset of contraction. This viewpoint underpins many interpretations of the noninvasive near-infrared spectroscopy (NIRS) data. Although NIRS cannot discriminate between the Hb and Mb signals, many researchers have assumed that NIRS monitors only Hb oxygen saturation and desaturation kinetics. The present chapter introduces an experiment system that allows for the observations of Mb saturation during muscle contraction. The results then provide insights into the relative Hb vs. Mb contribution in the NIRS signal and into the mechanisms of oxygen delivery and consumption regulation.