Muscle Near-Infrared Spectroscopy Signals versus Venous Blood Hemoglobin Oxygen Saturation in Skeletal Muscle

Purpose The study aimed to examine the relationship between near-infrared spectroscopy (NIRS) signals and venous hemoglobin oxygen saturation (O(2)Hb%) and venous oxygen concentration (CvO(2)). Methods Gastrocnemius muscles (GS) in six dogs were surgically isolated and pump perfused. NIRS signals were recorded, and venous blood samples were collected at constant flow rates (control flow, high flow, and low flow) at rest as well as during electrically stimulated tetanic muscle contractions at rates of one contraction per 2 s (1/2 s) and two contractions per 3 s (2/3 s). Similar data were also collected at three different inspired O-2 percentages (12%, 21%, and 100%) with constant blood flow. Results Complete data from five animals were analyzed; all data from one animal were deleted because of erratic oxy-NIRS signals. Venous O(2)Hb% ranged from 7.6% to 97.5% across the various experimental conditions. After the NIRS signals were normalized to the physiological range, a high linear correlation was seen between the deoxygenated heme signal (HHbMb%) and the venous O(2)Hb% (R-2 = 0.92 0.05), between the oxygenated heme signal (HbMbO(2)%) and the venous O(2)Hb% (R-2 = 0.92 +/- 0.03), between the HHbMb% and the CvO(2) (R-2 = 0.89 +/- 0.06), and between the HbMbO(2)% and the CvO(2) (R-2 = 0.90 +/- 0.05). The overall relationships between HHbMb%, HbMbO(2)%, and venous O(2)Hb% as well as between HHbMb%, HbMbO(2)%, and CvO(2) were also linear and highly correlated with R-2 values ranging from 0.81 to 0.90. Conclusion In this controlled canine muscle model, NIRS signals are highly correlated with venous O(2)Hb% and CvO(2) across a wide range of physiological conditions. The practical application of our results is that for an individual muscle or perhaps muscle group, normalized NIRS HHbMb and HbMbO(2) signals accurately reflect the mean venous O-2 saturation of the interrogated muscle tissue.