Interpretation of Near-Infrared Spectroscopy (NIRS) Signals in Skeletal Muscle

Abstract

NIRS uses the relative absorption of light at 850nm and 760nm, to determine skeletal muscle oxygen saturation. Previous studies have used the ratio of both signals to report muscle oxygen saturation. Purpose: To evaluate the different approaches used to represent muscle oxygen saturation, and to evaluate the pulsations of the O2heme and Heme signal. Method: Twelve participants, ages 20-29years were tested on the forearm flexor muscles using continuous wave NIRS at rest. Measurements were taken during 2-3mins rest, during physiological calibration (5-minuts Ischemia) and during reperfusion.  Results: There was a significant difference in pulse size between O2heme and Heme signal at the three locations (p < 0.05). Resting oxygen saturation was 58.8+9.2%, 69.6+3.9%, and 89.2+6.9% when calibrated using O2heme, TSI, and Heme, respectively.  Conclusion: The difference in magnitude of O2heme and Heme pulse with each heartbeat might suggest different anatomical locations of these signals, which propose calibrating with just one of the signals instead of the ratio of both. Calculations of physiological calibration must account for increased blood volume in the tissue, because of the changes in blood volume which appear to be primarily from the O2heme signal. Resting oxygen levels calibrated with Heme agrees with theoretical oxygen saturation.

Evaluation of transcutaneous near-infrared spectroscopy for early detection of cardiac arrest in an animal model

“…Importantly, TSI (%) does not re ect arterial oxygen saturation (i.e. the amount of oxygen in the arterial stream available to tissues and organs) but rather is an index of oxygenated to total hemoglobin at a microvascular tissue level 34 composed of both arterial and venous components and thus includes "inaccessible" oxygen trapped in the venous stream.…”

The effects of whole‐body vibration amplitude on glucose metabolism, inflammation, and skeletal muscle oxygenation

“…The thickness of adipose tissue superficial to the muscle belly of the gastrocnemius where the NIRS device was attached was determined using B‐mode ultrasound (Logiq 7, GE Medical Systems). After correcting for blood volume change (Ryan et al, 2012), an estimate of muscle oxygen consumption (mVO 2 ) was obtained from the average of %Hbdiff signal during each minute of WBV and converted into milliliters of O 2 per minute per 100 g of tissue {m O 2 [ml O 2 min −1 (100 g) − 1] = abs[([HbDiff/2] × 60)/(10 × 1.04) × 4] × 22.4/1000}, assuming 22.4 L for the volume of gas (STPD) and 1.04 kg l−1 for muscle density [(Lucero et al, 2018; Sanni & McCully, 2019)].…”

Physiological Adaptations to High-Intensity Interval Training Combined with Blood Flow Restriction in Masters Road Cyclists

“…This device has three LEDs, distanced 30, 35, and 40 mm from the one light receiver, each transmitting two wavelengths (±760 and ±850 nm) (27). The difference in absorbance characteristics can be accommodated for changes in absorbance in the region near 850 nm, which is attributed to tissue oxyhemo (+myo)globin (O 2 Hb), and absorbance in the region near 760 nm is assigned to deoxyhemo (+myo)globin (HHb) (28). The tissue saturation index (TSI), which is the ratio of O 2 Hb to total Hb, was calculated as (O 2 Hb)/((O 2 Hb + HHb) × 100) to express in percentage value.…”