Journal of Applied Physiology AJP: Endocrinology and Metabolism
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J Appl Physiol 99: 2463-2469, 2005; doi:10.1152/japplphysiol.00709.2005
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LETTER TO THE EDITOR

Kinetics of muscle oxygen use, oxygen content, and blood flow during exercise

ABSTRACT

Ferreira, Leonardo F., Dana K. Townsend, Barbara J. Lutjemeier, and Thomas J. Barstow. Muscle capillary blood flow kinetics estimated from pulmonary O2 uptake and near-infrared spectroscopy. J Appl Physiol 98: 1820–;1828, 2005. First published January 7, 2005; doi:10.1152/japplphysiol.00907.2004.— The near-infrared spectroscopy (NIRS) signal (deoxy-hemoglobin concentration; [HHb]) reflects the dynamic balance between muscle capillary blood flow (cap) and muscle O2 uptake (O2m) in the microcirculation. The purposes of the present study were to estimate the time course of cap from the kinetics of the primary component of pulmonary O2 (O2p) and [HHb] throughout exercise, and compare the cap kinetics with the O2p kinetics. Nine subjects performed moderate- (M; below lactate threshold) and heavy-intensity (H, above lactate threshold) constant-work-rate tests. O2p (l/min) was measured breath by breath, and [HHb] (µM) was measured by NIRS during the tests. The time course of cap was estimated from the rearrangement of the Fick equation [cap = O2m/(a-v)O2, where (a-v)O2 is arteriovenous O2 difference] using O2p (primary component) and [HHb] as proxies of O2m and (a-v)O2, respectively. The kinetics of [HHb] [time constant ({tau}) + time delay [HHb]; M = 17.8 ± 2.3 s and Ç = 13.7 ± 1.4 s] were significantly (P < 0.001) faster than the kinetics of O2 [{tau} of primary component ({tau}P); M = 25.5 ± 8.8 s and H = 25.6 ± 7.2 s] and cap [mean response time (MRT); M = 25.4 ± 9.1 s and H = 25.7 ± 7.7 s]. However, there was no significant difference between MRT of cap and {tau}P-O2 for both intensities (P = 0.99), and these parameters were significantly correlated (M and H; r = 0.99; P < 0.001). In conclusion, we have proposed a new method to noninvasively approximate cap kinetics in humans during exercise. The resulting overall cap kinetics appeared to be tightly coupled to the temporal profile of O2m.

 

REPLY

Leonardo F. Ferreira and Thomas J. Barstow

Kansas State University
Manhattan, Kansas
e-mail: tbarsto{at}ksu.edu




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