A shortened approach to measure mitochondrial capacity using Near-Infrared Spectroscopy (NIRS) was evaluated. Comparisons were made between 6-occlusion versus 22-occlusion protocols in two data sets (bicep, forearm). A third data set evaluated four serial 6-occlusion tests. The rate constants were not different between 22-cuff and 6-cuff for bicep (p=0.56) and forearm (p=0.76). The correlations were R2=0.9 for the bicep and R2=0.93 for the forearm. Mitochondrial capacity was not different between the four tests (P>0.05). The 6-Cuff analysis provided the same results in less time. There were no order effects for the rate constants for repeated 6-cuff tests of mitochondrial capacity.
Near-infrared spectroscopy (NIRS) has been used to measure reactive hyperemia following a vascular occlusion. However, the procedures and methods of analysis used have varied. The purpose of the present study is to identify reproducible methods for measuring reactive hyperemia using HbO2 NIRS signals in the calf and foot. Healthy participants (10 male, 10 female) aged 19 to 28 years performed one of two tests: reproducibility trials or elevation protocol (30 and 60 cm limb elevation above the heart). The time to 50% reperfusion (T1/2) and the second (R2q) quartile rates of reperfusion were found to be the most reproducible parameters (coefficient of variation=7.12 to 14.1%). The time to 95% reperfusion (T95) was 12.7% more reproducible on average than the previously reported parameter of time to peak hyperemia. Measures of reperfusion time and rate slowed with increasing limb elevation. Correlations were identified between the calf and foot in the measurements of R2q (R2=0.713, p=0.021), T1/2 (R2=0.673, p=0.033), and T95 (R2=0.792, p=0.006). Half and 95% recovery times and second and third quartile rates expressed good reproducibility and sensitivity to change with reduced perfusion pressure. NIRS measures of reactive hyperemia have the potential to evaluate microvascular perfusion in clinical populations.
Near-infrared spectroscopy (NIRS) was initiated in 1977 by Jobsis as a simple, noninvasive method for measuring the presence of oxygen in muscle and other tissues in vivo. This review honoring Jobsis highlights the progress that has been made in developing and adapting NIRS and NIR imaging (NIRI) technologies for evaluating skeletal muscle O2 dynamics and oxidative energy metabolism. Development of NIRS/NIRI technologies has included novel approaches to quantification of the signal, as well as the addition of multiple source detector pairs for imaging. Adaptation of NIRS technology has focused on the validity and reliability of NIRS measurements. NIRS measurements have been extended to resting, ischemic, localized exercise, and whole body exercise conditions. In addition, NIRS technology has been applied to the study of a number of chronic health conditions, including patients with chronic heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, varying muscle diseases, spinal cord injury, and renal failure. As NIRS technology continues to evolve, the study of skeletal muscle function with NIRS first illuminated by Jobsis continues to be bright.
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