Recent developments in near-infrared spectroscopy (NIRS) for the assessment of local skeletal muscle microvascular function and capacity to utilise oxygen

Abstract

Purpose of reviewContinuous wave near infrared spectroscopy (CW NIRS) provides non-invasive technology to measure relative changes in oxy- and deoxy-haemoglobin in a dynamic environment. This allows determination of local skeletal muscle O2 saturation, muscle oxygen consumption (trueV˙O2) and blood flow. This article provides a brief overview of the use of CW NIRS to measure exercise-limiting factors in skeletal muscle.Recent findingsNIRS parameters that measure O2 delivery and capacity to utilise O2 in the muscle have been developed based on response to physiological interventions and exercise. NIRS has good reproducibility and agreement with gold standard techniques and can be used in clinical populations where muscle oxidative capacity or oxygen delivery (or both) are impaired. CW NIRS has limitations including: the unknown contribution of myoglobin to the overall signals, the impact of adipose tissue thickness, skin perfusion during exercise, and variations in skin pigmentation. These, in the main, can be circumvented through appropriate study design or measurement of absolute tissue saturation.SummaryCW NIRS can assess skeletal muscle O2 delivery and utilisation without the use of expensive or invasive procedures and is useable in large population-based samples, including older adults.

Characterising skeletal muscle haemoglobin saturation during exercise using near-infrared spectroscopy in chronic kidney disease

“…This specific device has been validated in healthy participants [41]. The calf muscle was selected as it plays a key role in walking ability and gait [42] and is less influenced by adiposity when compared to other parts of the body [20]. …”

“…The spectra of the two main chromophores [oxyhemoglobin (O 2 Hb) and deoxyhemoglobin (HHb)] is used quantify the percentage of Hb/Mb O 2 [i.e., O 2 Hb/(O 2 Hb + HHb) × 100] saturation in the microvasculature [9, 20]. …”

“…Near-infrared spectroscopy (NIRS) can be used to measure muscle-oxidative metabolism in vivo [9, 11, 12, 20]. NIRS measures the attenuation (reduction in intensity) of light in the near-infrared spectrum to quantify the chromophores, mainly haemoglobin (Hb) and myoglobin (Mb), present in the muscle tissue [21].…”

“…The absorbance of near-infrared light differs depending on whether the molecules are in an oxygenated or deoxygenated state. Unfortunately, the spectral absorbance of Hb and Mb is indistinguishable and attenuation in the muscle is attributed to both [20]. Recent data suggests Mb contributes ~ 50–70% of the NIRS signal and is likely to increase during exercise [21].…”

“…NIRS-derived estimates of mitochondrial oxidative capacity are based on the relationship between oxidative phosphorylation and phosphocreatine (PCr) recovery following exercise [12]. Recent studies have demonstrated the post-exercise recovery kinetics of oxygen metabolism by NIRS is a valid and reproducible proxy model of assessing in vivo mitochondrial respiratory capacity and skeletal muscle-oxidative phosphorylation [9, 11, 20, 30]. Strong agreeability between NIRS and PCr measured by 31P MRS have been observed [9, 11, 20, 31].…”