Quantification of extra-cerebral and cerebral hemoglobin concentrations during physical exercise using time-domain near infrared spectroscopy

Abstract

Fitness is known to have beneficial effects on brain anatomy and function. However, the understanding of mechanisms underlying immediate and long-term neurophysiological changes due to exercise is currently incomplete due to the lack of tools to investigate brain function during physical activity. In this study, we used time-domain near infrared spectroscopy (TD-NIRS) to quantify and discriminate extra-cerebral and cerebral hemoglobin concentrations and oxygen saturation () in young adults at rest and during incremental intensity exercise. In extra-cerebral tissue, an increase in deoxy-hemoglobin () and a decrease in were observed while only cerebral increased at high intensity exercise. Results in extra-cerebral tissue are consistent with thermoregulatory mechanisms to dissipate excess heat through skin blood flow, while cerebral changes are in agreement with cerebral blood flow () redistribution mechanisms to meet oxygen demand in activated regions during exercise. No significant difference was observed in oxy- () and total hemoglobin (). In addition , and increased with subject's peak power output (equivalent to the maximum oxygen volume consumption; peak) supporting previous observations of increased total mass of red blood cells in trained individuals. Our results also revealed known gender differences with higher hemoglobin in men. Our approach in quantifying both extra-cerebral and cerebral absolute hemoglobin during exercise may help to better interpret past and future continuous-wave NIRS studies that are prone to extra-cerebral contamination and allow a better understanding of acute cerebral changes due to physical exercise.

Changes in neurovascular coupling during cycling exercise measured by multi-distance fNIRS: a comparison between endurance athletes and physically active controls

“…Regarding decreased HHb concentrations, these findings are reasonable and can be explained by previous studies demonstrating that more complex movements are associated with cortical activation increases in SMA and adjacent premotor areas (Orgogozo and Larsen 1979). Even though cortical processing during a rhythmic alternating activity such as cycling has mainly been investigated in prefrontal brain regions by means of fNIRS (Auger et al 2016; Giles et al 2014; Rupp et al 2008), recent studies pointed to the important role of motor-related brain regions in cycling. For example, using PET, Christensen et al (2000) observed an activation in M1 and SMA during active and passive cycling as two conditions of a rhythmic alternating activity in leg muscles.…”

“…These findings were confirmed in fNIRS studies showing increased oxygenation (Takehara et al 2017) and deoxygenation (Jung et al 2015) with elevating exercise intensities. Furthermore, previous studies revealed exercise-induced activations in prefrontal cortex (PFC) showing that Hb and HHb levels respond as a function of both exercise load and duration in both experts (Rupp et al 2008) and non-experts (Auger et al 2016; Giles et al 2014; Jung et al 2015). However, previous studies focusing on neurovascular coupling at several intensity levels show that there is no consensus concerning the type of exercise (incremental tests with short stages vs. constant-load exercises), duration of exercise (Giles et al 2014; Tsubaki et al 2016) and intensity (Auger et al 2016; Byun et al 2014; Giles et al 2014; Takehara et al 2017; Tsubaki et al 2018).…”

“…In general, as a confirmatory hypothesis based on the literature, we expected endurance athletes (EA) to show superior values in peak power output (PPO) and maximum oxygen consumption volume ( V O 2 max) (Kostić 2017; Rankovic et al 2010) as assessed by ICT, indicating clear differences in training status as compared to active control participants (ACP). Furthermore, we hypothesized to observe neurovascular coupling alterations (increase in Hb and decrease in HHb) in motor-related brain regions such as M1, SMA and premotor cortex (PMC) in dependence of exercise intensity (Auger et al 2016; Giles et al 2014; Kenville et al 2017) assessed by multi-distance fNIRS measurements during short-term and submaximal constant-load cycling exercises as well as an intensity-dependent increase of cardiorespiratory parameters such as V O 2 and heart rate (HR). Additionally, we assumed, in line with the “neural efficiency” hypothesis (Dunst et al 2014), that EA would show less neurovascular coupling at distinct intensity levels as compared to ACP.…”

Method to improve the depth sensitivity of diffuse reflectance measurements to absorption changes in optically turbid medium

“…The distance-resolved NIRS technique may allow to reduce such extracerebral contamination [8,9], however the time-resolved near infrared spectroscopy (trNIRS) technique still remains the most advanced approach. The trNIRS allows to gather more information about the tissue of interest, in comparison to cwNIRS technique [10][11][12]. It was reported that trNIRS allows to estimate optical properties of the tissue (absorption and reduced scattering coefficients µ a and µ s ') considered as a homogenous medium [13].…”

The Optical Effective Attenuation Coefficient as an Informative Measure of Brain Health in Aging

“…Although here we computed EAC values in healthy adults, an important application of EAC mapping would be to investigate people with pathological conditions that affect both oxygenation and anatomy (e.g., superficial hemorrhages, strokes, etc. ), or where subtle, regional and perhaps temporary physiological [71] or pathological alterations of oxygenation (such as concussion [72]) are suspected. In fact, in this paper we only considered the generation of static EAC maps (i.e., the average maps across the recording period) to maximize SNR.…”