A method for assessing heterogeneity of blood flow and metabolism in exercising normal human muscle by near-infrared spectroscopy

• Published in: Journal of applied physiology (1985) Vol. 118; no. 6; pp. 783 - 793
• Main Authors: Vogiatzis, Ioannis, Habazettl, Helmut, Louvaris, Zafeiris, Andrianopoulos, Vasileios, Wagner, Harrieth, Zakynthinos, Spyros, Wagner, Peter D.
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 15.03.2015
• Subjects: Adult; Blood pressure; Exercise - physiology; Exercise Test - methods; Heterogeneity; Humans; Hypoxia; Hypoxia - physiopathology; Infrared spectroscopy; Male; Metabolism; Muscular system; Oxygen - metabolism; Oxygen Consumption - physiology; Physiology; Quadriceps Muscle - physiology; Regional Blood Flow - physiology; Rest - physiology; Saturation; Spectroscopy, Near-Infrared - methods; Spectrum analysis; Young Adult; oxygen uptake; exercise; near infrared spectroscopy; muscle blood flow
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00458.2014

Heterogeneity in the distribution of both blood flow (Q̇) and O 2 consumption (V̇o 2 ) has not been assessed by near-infrared spectroscopy in exercising normal human muscle. We used near-infrared spectroscopy to measure the regional distribution of Q̇ and V̇o 2 in six trained cyclists at rest and during constant-load exercise (unloaded pedaling, 20%, 50%, and 80% of peak Watts) in both normoxia and hypoxia (inspired O 2 fraction = 0.12). Over six optodes over the upper, middle, and lower vastus lateralis, we recorded 1) indocyanine green dye inflow after intravenous injection to measure Q̇; and 2) fractional tissue O 2 saturation (Sti O 2 ) to estimate local V̇o 2 -to-Q̇ ratios (V̇o 2 /Q̇). Varying both exercise intensity and inspired O 2 fraction provided a (directly measured) femoral venous O 2 saturation range from about 10 to 70%, and a correspondingly wide range in Sti O 2 . Mean Q̇-weighted Sti O 2 over the six optodes related linearly to femoral venous O 2 saturation in each subject. We used this relationship to compute local muscle venous blood O 2 saturation from Sti O 2 recorded at each optode, from which local V̇o 2 /Q̇ could be calculated by the Fick principle. Multiplying regional V̇o 2 /Q̇ by Q̇ yielded the corresponding local V̇o 2 . While six optodes along only in one muscle may not fully capture the extent of heterogeneity, relative dispersion of both Q̇ and V̇o 2 was ∼0.4 under all conditions, while that for V̇o 2 /Q̇ was minimal (only ∼0.1), indicating in fit young subjects 1) a strong capacity to regulate Q̇ according to regional metabolic need; and 2) a likely minimal impact of heterogeneity on muscle O 2 availability.