title: Validation of a high-power, time-resolved, near-infrared spectroscopy system for measurement of superficial and deep muscle deoxygenation during exercise.
abstract: Near-infrared assessment of skeletal muscle is restricted to superficial tissues due to power limitations of spectroscopic systems. We reasoned that understanding of muscle deoxygenation may be improved by simultaneously interrogating deeper tissues. To achieve this, we modified a high-power (∼8 mW), time-resolved, near-infrared spectroscopy system to increase depth penetration. Precision was first validated using a homogenous optical phantom over a range of inter-optode spacings (OS). Coefficients of variation from 10 measurements were minimal (0.5-1.9%) for absorption (μa), reduced scattering, simulated total hemoglobin, and simulated O2 saturation. Second, a dual-layer phantom was constructed to assess depth sensitivity, and the thickness of the superficial layer was varied. With a superficial layer thickness of 1, 2, 3, and 4 cm (μa = 0.149 cm(-1)), the proportional contribution of the deep layer (μa = 0.250 cm(-1)) to total μa was 80.1, 26.9, 3.7, and 0.0%, respectively (at 6-cm OS), validating penetration to ∼3 cm. Implementation of an additional superficial phantom to simulate adipose tissue further reduced depth sensitivity. Finally, superficial and deep muscle spectroscopy was performed in six participants during heavy-intensity cycle exercise. Compared with the superficial rectus femoris, peak deoxygenation of the deep rectus femoris (including the superficial intermedius in some) was not significantly different (deoxyhemoglobin and deoxymyoglobin concentration: 81.3 ± 20.8 vs. 78.3 ± 13.6 μM, P > 0.05), but deoxygenation kinetics were significantly slower (mean response time: 37 ± 10 vs. 65 ± 9 s, P ≤ 0.05). These data validate a high-power, time-resolved, near-infrared spectroscopy system with large OS for measuring the deoxygenation of deep tissues and reveal temporal and spatial disparities in muscle deoxygenation responses to exercise.
authors.affiliation: Applied Physiology Laboratory, Kobe Design University, Kobe, Japan; s-koga@kobe-du.ac.jp.
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Koga
authors.affiliation: Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas;
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Barstow
authors.affiliation: Applied Physiology Laboratory, Kobe Design University, Kobe, Japan;
authors.forename: Dai
authors.initials: D
authors.lastname: Okushima
authors.affiliation: Rehabilitation Clinical Trials Center, Division of Respiratory & Critical Care Physiology & Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California;
authors.forename: Harry B
authors.identifier: http://orcid.org/0000-0002-7884-0726
authors.initials: HB
authors.lastname: Rossiter
authors.affiliation: Kobe University, Kobe, Japan; and.
authors.forename: Narihiko
authors.initials: N
authors.lastname: Kondo
authors.affiliation: Hamamatsu Photonics K.K., Hamamatsu, Japan.
authors.forename: Etsuko
authors.initials: E
authors.lastname: Ohmae
authors.affiliation: Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas;
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
mesh_terms: D000293:Adolescent; D001642:Bicycling; D004867:Equipment Design; D015444:Exercise; D005080:Exercise Test; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D009211:Myoglobin / Q000378:metabolism; D010092:Oximetry / Q000295:instrumentation / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D052097:Quadriceps Muscle / Q000000981:diagnostic imaging / Q000378:metabolism*; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared / Q000295:instrumentation / Q000379:methods; D014463:Ultrasonography; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D009211:Myoglobin; C055547:deoxymyoglobin; C100003:deoxyhemoglobin; D010100:Oxygen
keywords: heterogeneity; kinetics; oxygen consumption; oxygen delivery; oxygen utilization