COMPARISON OF MUSCLE NEAR-INFRARED SPECTROSCOPY AND FEMORAL BLOOD-GASES DURING STEADY-STATE EXERCISE IN HUMANS

Near-infrared spectroscopy (NIRS) is a noninvasive way of measuring mu scular oxygenation. We evaluated the relationship between NIRS signal [infrared muscle oxygen saturation (IR-S-O2mus)] and the femoral venou s oxygen saturation (Sfv(O2)) during cycling exercise. Six healthy sub jects performed a 30-min steady-state exercise at 80% maximal oxygen u pdate in normoxia and hypoxia (inspired O-2 fraction = 0.105). IR-S-O2 mus was recorded continuously throughout the tests with the NIRS probe located on the vastus lateralis. During exercise, blood samples were withdrawn every 5 min from radial artery and femoral vein catheters. I n normoxia, IR-S-O2mus initiated a transient nonsignificant decrease a t 5 min, then returned to preexercise level, whereas Sfv(O2) showed a fast decrease, reaching 18% saturation at 10 min without further chang e. By contrast, in hypoxia, IR-S-O2mus and Sfv(O2) demonstrated a para llel decrease then stabilized at 10 min. We conclude that IR-S-O2mus a ppears to parallel Sfv(O2) when both the arterial and venous oxygen co ntents decrease during steady-state exercise in hypoxia, whereas IR-S- O2mus does not follow Sfv(O2) change in normoxia.