Effects of assuming constant optical scattering on measurements of muscle oxygenation by near-infrared spectroscopy during exercise

• Published in: Journal of applied physiology (1985) 2007-01, Vol.102 (1), p.358-367
• Main Authors: Ferreira, Leonardo F, Hueber, Dennis M, Barstow, Thomas J
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Exercise; Exercise - physiology; Exercise Test; Female; Fundamental and applied biological sciences. Psychology; Hemoglobin; Hemoglobins - metabolism; Humans; Kinetics; Male; Mathematics; Muscle, Skeletal - metabolism; Muscular system; Myoglobin - metabolism; Oxygen; Oxygen - metabolism; Oxyhemoglobins - metabolism; Spectroscopy, Near-Infrared - methods; Spectrum analysis; Studies; Time Factors
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00920.2005

1 Departments of Kinesiology and Anatomy and Physiology, Kansas State University, Manhattan, Kansas; and 2 ISS Inc., Champaign, Illinois Submitted 28 July 2005 ; accepted in final form 25 September 2006 The aim of this study was to examine the effects of assuming constant reduced scattering coefficient (µ ) on the muscle oxygenation response to incremental exercise and its recovery kinetics. Fifteen subjects (age: 24 ± 5 yr) underwent incremental cycling exercise. Frequency domain near-infrared spectroscopy (NIRS) was used to estimate deoxyhemoglobin concentration {[deoxy(Hb+Mb)]} (where Mb is myoglobin), oxyhemoglobin concentration {[oxy(Hb+Mb)]}, total Hb concentration (Total[Hb+Mb]), and tissue O 2 saturation (Sti ), incorporating both continuous measurements of µ and assuming constant µ . When measuring µ , we observed significant changes in NIRS variables at peak work rate [deoxy(Hb+Mb)] (15.0 ± 7.8 µM), [oxy(Hb+Mb)] (–4.8 ± 5.8 µM), Total[Hb+Mb] (10.9 ± 8.4 µM), and Sti (–11.8 ± 4.1%). Assuming constant µ resulted in greater ( P < 0.01 vs. measured µ ) changes in the NIRS variables at peak work rate, where [deoxy(Hb+Mb)] = 24.5 ± 15.6 µM, [oxy(Hb+Mb)] = –9.7 ± 8.2 µM, Total[Hb+Mb] = 14.8 ± 8.7 µM, and Sti = –18.7 ± 8.4%. Regarding the recovery kinetics, the large 95% confidence intervals (CI) for the difference between those determine measuring µ and assuming constant µ suggested poor agreement between methods. For the mean response time (MRT), which describes the overall kinetics, the 95% confidence intervals were MRT – [deoxy(Hb+Mb)] = 26.7 s; MRT – [oxy(Hb+Mb)] = 11.8 s, and MRT – Sti = 11.8 s. In conclusion, µ changed from light to peak exercise. Furthermore, assuming a constant µ led to an overestimation of the changes in NIRS variables during exercise and distortion of the recovery kinetics. tissue oxygen saturation; incremental exercise; kinetics; recovery Address for reprint requests and other correspondence: T. J. Barstow, Dept. of Kinesiology, 1A Natatorium, Kansas State Univ., Manhattan, KS, 66506–0302 (e-mail: tbarsto{at}ksu.edu )