Comparison of femoral blood gases and muscle near-infrared spectroscopy at exercise onset in humans

Abstract

We hypothesized that near-infrared spectroscopy (NIRS) measures of hemoglobin and/or myoglobin O2 saturation (IR-SO2) in the vascular bed of exercising muscle would parallel changes in femoral venous O2 saturation (SfvO2) at the onset of leg-kicking exercise in humans. Six healthy subjects performed transitions from rest to 48 +/- 3 (SE)-W two-legged kicking exercise while breathing 14, 21, or 70% inspired O2. IR-SO2 was measured over the vastus lateralis muscle continuously during all tests, and femoral venous and radial artery blood samples were drawn simultaneously during rest and during 5 min of exercise. In all gas-breathing conditions, there was a rapid decrease in both IR-SO2 and SfvO2 at the onset of moderate-intensity leg-kicking exercise. Although SfvO2 remained at low levels throughout exercise, IR-SO2 increased significantly after the first minute of exercise in both normoxia and hyperoxia. Contrary to the hypothesis, these data show that NIRS does not provide a reliable estimate of hemoglobin and/or O2 saturation as reflected by direct femoral vein sampling.

NIRS Measurement of O2 Dynamics in Contracting Blood and Buffer Perfused Hindlimb Muscle

“…Surprisingly, the Mb contributes nearly 50% to the NIRS deoxy signal (Table 1). Researchers usually ignore the Mb contribution in human muscle experiments [14,18]. Previous rat hindlimb experiments that applied chemical infusion to modify the muscle O 2 uptake have suggested that 90% of the NIRS signal comes from Hb [9].…”

l-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans

“…However, it is known that muscle NIRS measures manifest significant special heterogeneities across the contracting quadriceps (29), so it is unclear whether a lower [HHb] amplitude during moderate-intensity exercise and the increased TOI during severe-intensity exercise at a discrete site of the vastus lateralis is reflective of an improved matching between muscle O 2 delivery and muscle V O 2 across the contracting quadriceps. Indeed, some studies report good agreement between NIRS markers of muscle oxygenation and mixed venous PO 2 or oxygenation (39), while other studies do not (38). It has also been suggested that the interpretation of NIRS data may be complicated by increased skin blood flow (30,40), as develops during exercise.…”

Estimated contribution of hemoglobin and myoglobin to near infrared spectroscopy

“…The only condition that showed a significant correlation was during the hypoxic breathing condition; normoxic and hyperoxic conditions showed NIRS oxygenation levels increasing while femoral venous oxygen saturation decreased. Due to the marked differences in NIRS oxygenation and femoral venous oxygenation, McDonald et al (1999) concluded that NIRS was not an accurate assessment of venous blood oxygenation during exercise. It should be noted, however, that there are several limitations to this study.…”