Using portable near-infrared spectroscopy (NIRS), we characterized lower limb spastic vs. non-spastic muscle hemodynamic responses to the Modified Ashworth Scale (MAS; functional spasticity scale) and passive ankle range-of-motion (ROM) tests. This 12-wk observational study in an out-patient spasticity clinic had baseline, ~6-wk, and ~12-wk time points. Within-individual (contralateral control) and between-group (patient vs. control) measurements were compared. Spastic hemodynamic responses to MAS and ROM assessments were irregular and highly variable. Non-spastic hemodynamic changes followed three clear, repeatable patterns. NIRS may be useful in developing a hemodynamic/metabolic spasticity index.
We investigated central fatigue during maximal exercise (EXmax) after 12×20-min respiratory muscle endurance training (eRMT) sessions over 4 weeks using cerebral near-infrared spectroscopy (NIRS; left, right prefrontal cortices: LPFC, RPFC); and self-reported effort perceptions (RPE). Healthy participants improved eRMT performance with no spirometry changes. Pre-eRMT, EXmax oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin increases were larger in LPFC than RPFC. Post-eRMT, EXmax O2Hb, HHb, and tHb increases were smaller in LPFC than RPFC. Post-eRMT EXmax RPE were smaller. eRMT-induced LPFC-to-RPFC hemodynamic shifts during EXmax may facilitate decreased RPE.
This pilot study investigated hemodynamics in bone and muscle of the same leg during resistance exercise, using near-infrared spectroscopy (NIRS). Total (tHb) and oxygenated (O2Hb) hemoglobin increased in bone but decreased in muscle. Absolute peak tHb and O2Hb changes in bone were much smaller than absolute antipeak changes in muscle. Bone tHb and O2Hb reached an initial peak quickly and then decreased progressively; muscle tHb and O2Hb decreased initially and then plateaued. Bone perfusion changes during exercise appear independent of metabolism, suggesting that bone hemodynamics measured using NIRS during resistance training are driven by blood vessel compression and release.
This study investigated the influence of moderate-intensity exercise (EX; 20 min cycling exercise, 60% heart rate reserve) on executive function (EF) and prefrontal cortex (PFC) hemodynamics, compared to control (CON; 20 min seated, listening to statistics audio recording). EF tests were Go/NoGo, Task Switching, and Reading Span. Near-infrared spectroscopy (NIRS) measured total hemoglobin concentration (tHb). Compared to CON, right PFC tHb was elevated from baseline at 0 and 15 min post-EX during Go/NoGO and Task Switching, and at 0 min post-EX during Reading Span. In both EX and CON, tHb was unchanged during “rest” between EF tests.
The purpose of this study was to test the hypothesis that mobile, wireless near-infrared spectroscopy (NIRS) instruments can be used during standard lung function tests to measure adaptations in respiratory muscle metabolism over weeks to months. In eight varsity soccer players at 0 weeks and after 16 weeks of routine training, commercially available mobile, wireless NIRS instruments were used to measure oxygenation and hemodynamics in the sternocleidomastoid (SCM, accessory inspiration muscle). During maximal expiratory pressure (MEP) and forced vital capacity (FVC) maneuvers we determined peak or antipeak changes relative to baseline in oxygenation and hemodynamics: Δ%Sat (muscle oxygen saturation), ΔtHb (total hemoglobin), ΔO2Hb (oxygenated hemoglobin), and ΔHHb (deoxygenated hemoglobin). Subjects reported that the average training load was ~13.3 h/week during the 16 study weeks, compared to ~10.4 h/week during 12 prior weeks. After 16 weeks of training compared to 0 weeks we found statistically significant increases in SCM Δ%Sat (57.7%), ΔtHb (55.3%), and ΔO2Hb (56.7%) during MEP maneuvers, and in SCM Δ%Sat (64.8%), ΔtHb (29.4%), and ΔO2Hb (51.6%) during FVC maneuvers. Our data provide preliminary evidence that NIRS measurements during standard lung function tests are sufficiently sensitive to detect improvements or declines in respiratory muscle metabolism over periods of weeks to months due to training, disease, and rehabilitation exercise.
Our goal was to use 2-channel frequency domain near-infrared spectroscopy (NIRS) to investigate the hemodynamic and metabolic mechanisms underlying hyperglycemia-associated long-term memory impairment. We hypothesized that prefrontal cortex (PFC) oxygen saturation (%Sat) and perfusion (tHb, i.e. total hemoglobin) would decrease due to hyperglycemia during learning, and then increase during recall. During learning, participants’ blood glucose was manipulated with beverages containing either 47.4 mg saccharine control (CON, n = 10), or 50 g dextrose + 23.7 mg saccharine (GLC, n = 10). In the Symbol-Digit Modalities Test (SMDT) participants matched nine symbols to corresponding digits (1-9 inclusive), completing 105 learning and 15 testing trials on day 1 and 15 testing trials on day 2. From learning to recall, CON SMDT performance was unchanged, but GLC SMDT performance was decreased 11% (P = 0.0173). There were significant interactions (2-way ANOVA) between the CON-GLC treatment effects and the learning-recall effects for both PFC perfusion and oxygen saturation. Specifically, comparing learning to recall, CON exhibited no tHb differences but for GLC there was a large tHb decrease during learning with a partial recovery toward CON values during recall (P = 0.0012); and, comparing learning to recall, CON exhibited a large %Sat decrease but GLC exhibited a large %Sat increase (P = 0.021). We speculate that, during learning, after overnight fasting (CON) the PFC demands more hemodynamic and metabolic resources and “works” harder, but with readily available sugar (GLC) the PFC exhibits decreased “effort.”
During orthopedic procedures, the tourniquets used to maintain bloodless surgical fields cause ischemia and then reperfusion (I/R), leading to oxidative muscle injury. Established methods exist neither for monitoring orthopedic I/R nor for predicting the extent of tourniquet-associated oxidative injury. To develop a predictive model for tourniquet-associated oxidative muscle injury, this study combined real-time near-infrared spectroscopy (NIRS) monitoring of I/R with Western blotting (WB) for oxidized proteins. We hypothesized strong correlations between NIRS-derived I/R indices and muscle protein oxidation. In 17 patients undergoing ankle fracture repair, a thigh tourniquet was inflated on the injured limb (300 mmHg). Using a continuous-wave (CW) NIRS setup, oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin were monitored bilaterally (tourniquet versus control) in leg muscles. Leg muscle biopsies were collected unilaterally (tourniquet side) immediately after tourniquet inflation (pre) and before deflation (post). Average ischemia duration was 43.2±14.6 min. In post-compared to pre-biopsies, muscle protein oxidation (quantified using WB) increased 172.3%±145.7% (P<0.0005). Changes in O2Hb and tHb were negatively correlated with protein oxidation (respectively: P=0.040, R2=0.25 and P=0.003, R2=0.58). Reoxygenation rate was positively correlated with protein oxidation (P=0.041, R2=0.25). These data indicate that using CW NIRS, it is possible to predict orthopedic tourniquet-associated muscle oxidative injury noninvasively.
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