Muscle Blood Volume Research Articles

Influence of cutaneous and muscular circulation on spatially resolved versus standard Beer-Lambert near-infrared spectroscopy.

The potential interference of cutaneous circulation on muscle blood volume and oxygenation monitoring by near‐infrared spectroscopy (NIRS) remains an important limitation of this technique. Spatially resolved spectroscopy (SRS) was reported to minimize the contribution of superficial tissue layers in cerebral monitoring but this characteristic has never been documented in muscle tissue monitoring. This study aims to compare SRS with the standard Beer–Lambert (BL) technique in detecting blood volume changes selectively induced in muscle and skin. In 16 healthy subjects, the biceps brachii was investigated during isometric elbow flexion at 70% of the maximum voluntary contractions lasting 10 sec, performed before and after exposure of the upper arm to warm air flow. From probes applied over the muscle belly the following variables were recorded: total hemoglobin index (THI, SRS‐based), total hemoglobin concentration (tHb, BL‐based), tissue oxygenation index (TOI, SRS‐based), and skin blood flow (SBF), using laser Doppler flowmetry. Blood volume indices exhibited similar changes during muscle contraction but only tHb significantly increased during warming (+5.2 ± 0.7 μmol/L·cm, an effect comparable to the increase occurring in postcontraction hyperemia), accompanying a 10‐fold increase in SBF. Contraction‐induced changes in tHb and THI were not substantially affected by warming, although the tHb tracing was shifted upward by (5.2 ± 3.5 μmol/L·cm, P < 0.01). TOI was not affected by cutaneous warming. In conclusion, SRS appears to effectively reject interference by SBF in both muscle blood volume and oxygenation monitoring. Instead, BL‐based parameters should be interpreted with caution, whenever changes in cutaneous perfusion cannot be excluded.

Ranolazine's sweet side – improvement of glycaemic control by the novel mechanism of skeletal muscle microvascular recruitment

Type II diabetes mellitus is a major public health problem afflicting in excess of 250 million individuals worldwide. The presence of this condition in patients with coronary artery disease more than doubles their risk for cardiovascular events. Among the most critical factors are the attendant development of endothelial dysfunction and insulin resistance, which contribute to impaired glycaemic control and acceleration of atherosclerosis. Contemporary therapies have important limitations and safety concerns, as treatment with agents in extensive clinical use, including β-adrenergic receptor blocking agents, thiazide diuretics, and calcium channel antagonists, is associated with increased rates of newly diagnosed diabetes as a result of pro-diabetic effects. These limitations have prompted a search for alternative modalities of drug action. In the current issue of The Journal of Physiology, Fu and colleagues (2013) explored whether ranolazine can improve blood flow and distribution of insulin through α-adrenergic receptor-mediated vasodilatation. Ranolazine is a weak competitive antagonist of α-adrenergic receptors (Allely et al. 1993) and in the conscious dog this antagonism is unmasked by activation of the autonomic nervous system (Zhao et al. 2011). Fu and colleagues (2013) reported that in the therapeutic range of doses ranolazine recruited muscle microvasculature, resulting in a significant >2-fold increase in skeletal muscle blood flow and volume and a substantial enhancement of insulin-mediated whole-body disposal in the range of 30%. In addition, ranolazine improved delivery of insulin into skeletal muscle. Ranolazine increased endothelial nitric oxide synthase (eNOS) phosphorylation and cyclic adenosine monophosphate (cAMP) production without affecting endothelial insulin uptake. Isolated phenylephrine pre-constricted arterial rings were relaxed in the presence of ranolazine, indicating an α-adrenergic receptor-mediated effect. This observation is consistent with evidence obtained in vivo in which the vasoconstrictor effect of intracoronary phenylephrine was abolished by ranolazine (Nieminen et al. 2011) and the vasopressor response to methoxamine was blunted by ranolazine in a dose-dependent manner (Wang et al. 2008). Fu and colleagues (2013) also found that the vasodilatory effects on the pre-capillary arterioles occurred via actions on both the endothelium and smooth muscle cells. Overall, their observations indicate that at therapeutic concentrations ranolazine acutely recruits skeletal muscle microvasculature, increasing microvascular exchange surface area and perfusion. This effect, in combination with the drug's α-adrenergically mediated vasodilatation of pre-capillary arterioles, improves insulin delivery to skeletal muscle and glucose use. This intriguing study by Fu and coworkers (2013) raises important questions relevant to potential clinical applications. As the present studies were performed on an acute basis in normal rats, it remains to be determined whether microvascular recruitment persists following chronic administration in a diabetic animal model. Also, is there evidence that this action of ranolazine on muscle microvasculature operates in patients with various degrees of insulin resistance and early and late stage type 2 diabetes? Clinical trials have demonstrated that ranolazine significantly improves glycaemic control as suggested by reduced levels of glycated haemoglobin (HbA1c) in diabetic as well as non-diabetic subjects (Timmis et al. 2006; Morrow et al. 2009; Chisholm et al. 2010; Kosiborod et al. 2013). Use of ranolazine is also attractive in light of the excellent safety profile shown in the MERLIN-TIMI 36 (Metabolic Efficiency With Ranolazine for Less Ischemia in NonST-Elevation Acute Coronary Syndromes Thrombolysis in Myocardial Infarction 36) trial, which enrolled 6560 patients with cardiovascular disease, 2028 (31%) of whom had pre-existing diabetes (Morrow et al. 2009). However, the mechanisms whereby ranolazine reduces HbA1c remain unknown. The clinical implications of this study are multifold and significant. Essentially, the authors have identified mechanisms that may underlie ranolazine's unique salutary effects, which can potentially improve the cardiovascular health of diabetic patients while reducing myocardial ischaemic events and risk for atrial and ventricular arrhythmias. Although considerable further work will be required to assess fully the clinical applicability of Fu and coworkers’ novel findings (2013), available clinical evidence suggests that the basic concept presented in the current study is promising and worthy of vigorous pursuit.

Postural Strategy and Back Muscle Oxygenation during Inspiratory Muscle Loading

Most healthy individuals show a multisegmental control strategy during challenging standing conditions, whereas others show a rigid ankle-steered strategy, which is assumed as suboptimal. Respiratory-demanding tasks exert a perturbing effect on balance, although the underlying mechanisms remain poorly understood. The purpose of this study was to investigate whether inspiratory resistive loading (IRL) affects postural strategy, back muscle oxygenation, and blood volume during postural control. We assessed the acute effects of increased respiratory effort by measuring the center of pressure displacement in 12 healthy individuals during upright standing on an unstable support surface while breathing against an IRL. Simultaneous ankle and back muscle vibration was used to evaluate the proprioceptive strategy (multisegmental vs ankle-steered) during postural control. Back muscles oxygenation and blood volume were assessed using near-infrared spectroscopy (tissue oxygenation index, deoxyhemoglobin, oxyhemoglobin, and combined hemoglobin). An increased proprioceptive gain at the ankles and an decreased gain at the back were observed after approximately 7 min of IRL. Retrospectively, the group was subdivided on the basis of the participants' dominant proprioceptive use during a baseline postural control. During IRL, the ankle-steered group showed an increased reliance on ankle proprioception compared with a multisegmental group (-5.9 ± 3.1 and 1.0 ± 1.9 cm, respectively, P < 0.05). Tissue oxygenation index, deoxyhemoglobin, oxyhemoglobin, and combined hemoglobin declined progressively in the ankle-steered group during the IRL (from baseline (100%) to -1%, -1%, -45%, and -18%, respectively, P < 0.05), whereas no decline was found in the multisegmental group (from baseline (100%) to 134%, 82%, 129%, and 153%, respectively, P > 0.05). Individuals who adopted an ankle-steered strategy during IRL showed a progressive decline in back muscle oxygenation and blood volume. In contrast, IRL did not affect back muscle oxygenation and blood volume in individuals who showed a multisegmental strategy in upright standing.

THU0424 Near-infrared spectroscopy during exercise and recovery in children with juvenile dermatomyositis

BackgroundChildren with Juvenile Dermatomyositis (JDM) suffer from diminished exercise tolerance1-5, a clinical condition that may be linked to microvascular disturbances in the muscle tissue6. Near-infrared spectroscopy (NIRS) may represent a...

Influence of Postexercise Cooling on Muscle Oxygenation and Blood Volume Changes

The aim of this study was to investigate the effects of postexercise cold water immersion (CWI) on tissue oxygenation and blood volume changes after intense exercise. Nine physically active men performed 30 min of continuous running (CR) at 70% of their maximal treadmill velocity (Vmax), followed by 10 bouts of intermittent running at Vmax. After exercise, one of the participants' legs was immersed in a cold water bath (10°C, CWI) to the level of their gluteal fold for 15 min. The contralateral leg remained outside the water bath and served as a control (CON). Vastus lateralis (VL) skin temperature (TskVL), VL oxygenation (tissue oxygenation index [TOI]), and blood volume changes (total hemoglobin [tHb] volume) were monitored continuously throughout exercise and CWI using near-infrared spectroscopy. TskVL, TOI, and tHb were not significantly different between CON and CWI during continuous running and intermittent running, respectively (P > 0.05). In contrast, TskVL was significantly lower in CWI compared with CON throughout immersion, with peak differences occurring at the end of immersion (CON = 35.1 ± 0.6 vs CWI = 16.9°C ± 1.7°C, P < 0.001). tHb was significantly lower during CWI compared with CON at most time points, with peak differences of 20% ± 4% evident at the end of the 15-min immersion (P < 0.01). Likewise, TOI was significantly higher in CWI compared with CON, with peak differences of 2.5% ± 1% evident at the 12th min of immersion (P < 0.05). Postexercise cooling decreased microvascular perfusion and muscle metabolic activity. These findings are consistent with the suggested mechanisms by which CWI is hypothesized to improve local muscle recovery.

Muscle Oxygenation and Blood Volume Reliability during Continuous and Intermittent Running

The reliability of near infrared spectroscopy derived tissue oxygenation index (TOI) and total haemoglobin concentration (tHb) were examined during continuous (CR) and interval (INT) running. In a repeated measures design, 10 subjects twice performed 30 min of CR at 70% of their peak treadmill velocity, followed by 10 bouts of INT at 100%. Between trial reliability of mean and amplitude changes in TOI and tHb during CR were determined. Muscle de-oxygenation and re-oxygenation rates during INT were calculated using 3 analytical methods; i) linear modelling, ii) minimum and maximum values during work/rest intervals, and iii) mean values during work/rest intervals. Reliability was assessed using coefficient of variation (CV; %). During CR, mean TOI was more reliable (3.5%) compared with TOI amplitude change (34.7%), while mean tHb (12%) was similar to both absolute (9.2%) and relative (10.2%) amplitude changes. During INT, de-oxygenation rates analysed via linear modelling produced the lowest CV (7.2%), while analysis using min-max values produced the lowest CV (9.3%) for re-oxygenation rates. In conclusion, while the variables demonstrated CVs lower than reported changes in training-induced adaptations and/or differences between athletes and controls (23- 450%), practitioners are encouraged to consider the advantages/disadvantages of each method when performing their analysis.

Effect of Race Distance on Muscle Oxygenation in Short-Track Speed Skating

Previous work identified an asymmetry in tissue desaturation changes in the left and right quadriceps muscles during on-ice skating at maximal speed in males. The effect of changing race distance on the magnitude of desaturation or leg asymmetry is unknown. Six elite male skaters (age = 23 ± 1.8 yr, height = 1.8 ± 0.1 m, mass = 80.1 ± 5.7 kg, midthigh skinfold thickness = 7 ± 2 mm) and four elite female skaters (age = 21 ± 4 yr, height = 1.6 ± 0.1 m, mass = 65.2 ± 4.3 kg, midthigh skinfold thickness = 10 ± 1 mm) were studied. Subjects completed time trials over three race distances. Blood lactate concentration and O2 uptake measurements were combined with near-infrared spectroscopy measures of muscle oxygenation (TSI) and blood volume (tHb) in the right and left vastus lateralis. Neither race distance nor gender had a significant effect on the magnitude of maximal muscle desaturation (ΔTSI(max)). Pattern of local changes in tHb during individual laps was dependent upon subtle differences in skating technique used for the different race distances. Linear regression analysis revealed asymmetry between the right and left leg desaturation in males during the final stages of each race distance, but not in females. At all race distances, local muscle desaturation reached maximal values much more quickly than global VO(2peak). The use of wearable near-infrared spectroscopy devices enabled measurement of muscle oxygenation during competitive race simulation, thus providing unique insight into the effects of velocity and technique changes on local muscle oxygenation. This may have implications for training and race pacing in speed skating.

Impact of dietary nitrate supplementation via beetroot juice on exercising muscle vascular control in rats

Dietary nitrate (NO(3)(-)) supplementation, via its reduction to nitrite (NO(2)(-)) and subsequent conversion to nitric oxide (NO) and other reactive nitrogen intermediates, reduces blood pressure and the O(2) cost of submaximal exercise in humans. Despite these observations, the effects of dietary NO(3)(-) supplementation on skeletal muscle vascular control during locomotory exercise remain unknown. We tested the hypotheses that dietary NO(3)(-) supplementation via beetroot juice (BR) would reduce mean arterial pressure (MAP) and increase hindlimb muscle blood flow in the exercising rat. Male Sprague-Dawley rats (3-6 months) were administered either NO(3)(-) (via beetroot juice; 1 mmol kg(-1) day(-1), BR n = 8) or untreated (control, n = 11) tap water for 5 days. MAP and hindlimb skeletal muscle blood flow and vascular conductance (radiolabelled microsphere infusions) were measured during submaximal treadmill running (20 m min(-1), 5% grade). BR resulted in significantly lower exercising MAP (control: 137 ± 3, BR: 127 ± 4 mmHg, P < 0.05) and blood [lactate] (control: 2.6 ± 0.3, BR: 1.9 ± 0.2 mm, P < 0.05) compared to control. Total exercising hindlimb skeletal muscle blood flow (control: 108 ± 8, BR: 150 ± 11 ml min(-1) (100 g)(-1), P < 0.05) and vascular conductance (control: 0.78 ± 0.05, BR: 1.16 ± 0.10 ml min(-1) (100 g)(-1) mmHg(-1), P < 0.05) were greater in rats that received BR compared to control. The relative differences in blood flow and vascular conductance for the 28 individual hindlimb muscles and muscle parts correlated positively with their percentage type IIb + d/x muscle fibres (blood flow: r = 0.74, vascular conductance: r = 0.71, P < 0.01 for both). These data support the hypothesis that NO(3)(-) supplementation improves vascular control and elevates skeletal muscle O(2) delivery during exercise predominantly in fast-twitch type II muscles, and provide a potential mechanism by which NO(3)(-) supplementation improves metabolic control.

An Exercise Therapy Program Can Increase Oxygenation and Blood Volume of the Erector Spinae Muscle During Exercise in Chronic Low Back Pain Patients

ObjectiveTo determine whether erector spinae muscle oxygenation (OXY) and blood volume during a progressive isoinertial lifting evaluation (PILE) are modified by an exercise therapy program. DesignPre- (t1) and post- (t2) exercise therapy experimental design. SettingHospital. ParticipantsSubjects with chronic low back pain (LBP group) (n=24) and healthy subjects (control group) (n=24) were evaluated. InterventionExercise program. Main Outcome MeasuresThe control group was evaluated once, and the LBP group was evaluated before (t1) the exercise therapy program and 28 days thereafter (t2). The maximal load lifted, total work, and total power were determined using the PILE test. Continuous-wave near-infrared spectroscopy was used to measure OXY and blood volume during the PILE test. ResultsThe maximal load lifted, total power, and total work were significantly lower in the LBP group (−42%±5%, −46%±6%, and −67%±6% at t1, respectively; P<.05) than the control group. In the LBP subjects, these parameters improved significantly after the exercise therapy program (+20%±3%, +56%±4%, and +61%±5%; P<.05). At each submaximal power (ie, 25, 50, 75, and 100% of maximal load lifted at t1), OXY and blood volume were significantly higher at t2 than t1. One-half recovery time for OXY was significantly higher in the LBP group (at t1 and t2) than in control subjects. ConclusionsThe findings in this study suggest that LBP subjects present an impairment in their capacity to deliver oxygen at the level of the erector spinae muscle, which can be partly restored by an exercise therapy program.

Near‐infrared spectroscopy during exercise and recovery in children with juvenile dermatomyositis

We hypothesized that microvascular disturbances in muscle tissue play a role in the reduced exercise capacity in juvenile dermatomyositis (JDM). Children with JDM, children with juvenile idiopathic arthritis (clinical controls), and healthy children performed a maximal incremental cycloergometric test from which normalized concentration changes in oxygenated hemoglobin (Δ[O2 Hb]) and total hemoglobin (Δ[tHb]) as well as the half-recovery times of both signals were determined from the vastus medialis and vastus lateralis muscles using near-infrared spectroscopy. Children with JDM had lower Δ[tHb] values in the vastus medialis at work rates of 25%, 50%, 75%, and 100% of maximal compared with healthy children; the increase in Δ[tHb] with increasing intensity seen in healthy children was absent in children with JDM. Other outcome measures did not differ by group. The results suggest that children with JDM may experience difficulties in increasing muscle blood volume with more strenuous exercise.

Effect of vibration on muscle perfusion: a systematic review

Vibration has become of increasing interest to health professionals, primarily owing to reports that vibration can increase tissue blood flow. The aim of this review was to investigate the available scientific evidence on the effects of exogenous vibration on skeletal muscle perfusion. The databases searched from inception to December 2010 included Ovid MEDLINE, EMBASE, CINAHL via EbscoHost and CENTRAL. Experimental and observational studies, where exogenous vibration was an intervention, were included in this review. The main outcomes of interest were muscle blood volume, blood flow, blood flow velocity, arterial diameter and muscle temperature. One reviewer selected studies for inclusion, extracted data and assessed the quality of the eligible studies. Percentage change in muscle perfusion outcome was the measure of treatment effect, and regression analysis was used to investigate associations between vibratory load and muscle perfusion. Twenty-two studies with a total of 302 participants were included in this review. Muscle blood volume increased with vibration in five of nine studies and decreased in two studies; muscle blood flow velocity increased with vibration in five of six studies; muscle blood flow increased with vibration in two of three studies; vibration had a positive effect on arterial diameter in three of three studies; vibration had no effect on muscle temperature in two of two studies. The magnitude of increase in muscle perfusion was positively associated with vibratory load (P<0·001). We conclude that vibration increases muscle perfusion with the magnitude of increase positively related to the vibratory load applied.

Effect of high-intensity interval training on the profile of muscle deoxygenation heterogeneity during incremental exercise

This study examines the effect of high-intensity interval training (HIT) on the spatial distribution of muscle deoxygenation during incremental exercise. Young untrained male adults (n = 11) performed an incremental bicycle exercise before and after a running HIT of 6 weeks. Muscle deoxygenation (HHb) and blood volume (Hb(tot)) were monitored continuously by near-infrared spectroscopy at eight sites in the vastus lateralis. The rise in HHb during incremental exercise was significantly higher after training, in comparison with before training (P = 0.020), whereas the rise in Hb(tot) was not affected by training. The standard deviation of HHb and the relative dispersion of HHb at the eight sites were not significantly different irrespective of the intensity of exercise between pre- and post-training. After training, the standard deviation of HHb was greater at 60, 70, and 80 % of VO₂(max) than at rest. Finally, training significantly increased the standard deviation of Hb(tot) (P = 0.036). These results indicate that HIT changes the muscle deoxygenation profile during incremental exercise, suggesting an improvement in the O(2) extraction with training. HIT did not reduce the spatial heterogeneity of muscle deoxygenation and blood volume during incremental exercise. This indicates that the intra-muscular distribution of the VO(2)/O(2) delivery ratio was not improved by 6 weeks HIT.

Effect of Deep Ocean Minerals Intake on Muscle Oxygen Consumption after Acute High Intensity Exercise

High intensity exercise-induced muscle damage leads to increase oxygen consumption in human. The purpose of this study was to investigate the effect of deep-ocean water minerals supplementation on muscle oxygen consumption after a high intensity badminton training session. Ten professional badminton players were recruited for this study, and considered as placebo and deep-ocean water trials. After performing a bout of high intensity training, all subjects were asked to drink either pure or deep-ocean water. Water intake quantity was 1.5 times higher to subjects' dehydration. Muscle oxygenation and oxygen consumption were measured by nearinfrared spectroscopy (NIRS) before and 2-h after training. We found muscle blood volume (80.35 ± 3.71 μM) was significantly decreased, while muscle oxygen consumption (0.79 ± 0.12 mVO2 ml/min/100 g muscle) was significantly increased after training in both trials. However, deep-ocean water received trial showed lower muscle oxygen consumption 2-h after exercise compared to placebo trial. In conclusion, we suggest that deep-ocean water supplementation could suppress the muscle oxygen consumption inducing by high intensity exercise.

Effects of hypoxia on cerebral and muscle haemodynamics during knee extensions in healthy subjects

A hypoxic model was used to investigate changes in localized cerebral and muscle haemodynamics during knee extension (KE) in healthy individuals. Thirty-one young healthy volunteers performed one set of KE until failure under hypoxia (14 % O(2)) or normoxia (21 % O(2)) at 50, 75 or 100 % of 1 repetition maximum, in random order, on three occasions. Prefrontal cerebral and vastus lateralis muscle oxygenation and blood volume (Cox, Mox, Cbv and Mbv, respectively) were recorded simultaneously by near-infrared spectroscopy. Hypoxia induced significant declines in Cox [-0.017 ± 0.016 optical density (OD) units] and Mox (-0.014 ± 0.026 OD units) and increases in Cbv (0.017 ± 0.027 OD units) and Mbv (0.016 ± 0.023 OD units) at rest. Hypoxia significantly reduced total work (TW) performed during KE at each exercise intensity. Cox, Cbv, Mox, and Mbv changes during KE did not differ between normoxia and hypoxia. Correlations between TW done and Cox changes under normoxia (r = 0.04, p = 0.182) and hypoxia (r = 0.05, p = 0.122) were not significant. However, TW was significantly correlated with Mox under both normoxia (R (2) = 0.24, p = 0.000) and hypoxia (R (2) = 0.15, p = 0.004). Since changes in Cox and Mox reflect alterations in the balance between oxygen delivery and extraction in these tissues, which, in the brain, is an index of neuronal activation, we conclude that: (1) limitation of KE performance was mediated peripherally under both normoxia and hypoxia, with no additional effect of hypoxia, and (2) because of the low common variance with Mox additional intramuscular factors likely play a role in limiting KE performance.

Cardiovascular drift and cerebral and muscle tissue oxygenation during prolonged cycling at different pedalling cadences

We hypothesized that a faster cycling cadence could exaggerate cardiovascular drift and affect muscle and cerebral blood volume and oxygenation. Twelve healthy males (mean age, 23.4 ± 3.8 years) performed cycle ergometry for 90 min on 2 separate occasions, with pedalling frequencies of 40 and 80 r·min(-1), at individual workloads corresponding to 60% of their peak oxygen consumption. The main measured variables were heart rate, ventilation, cardiac output, electromyographic activity of the vastus lateralis, and regional muscle and cerebral blood volume and oxygenation. Cardiovascular drift developed at both cadences, but it was more pronounced at the faster than at the slower cadence, as indicated by the drop in cardiac output by 1.0 ± 0.2 L·min(-1), the decline in stroke volume by 9 ± 3 mL·beat(-1), and the increase in heart rate by 9 ± 1 beats·min(-1) at 80 r·min(-1). At the faster cadence, minute ventilation was higher by 5.0 ± 0.5 L·min(-1), and end-tidal CO(2) pressure was lower by 2.0 ± 0.1 torr. Although higher electromyographic activity in the vastus lateralis was recorded at 80 r·min(-1), muscle blood volume did not increase at this cadence, as it did at 40 r·min(-1). In addition, muscle oxygenation was no different between cadences. In contrast, cerebral regional blood volume and oxygenation at 80 r·min(-1) were not as high as at 40 r·min(-1) (p < 0.05). Faster cycling cadence exaggerates cardiovascular drift and seems to influence muscle and cerebral blood volume and cerebral oxygenation, without muscle oxygenation being radically affected.

Imaging of muscle blood volume changes during exercise with Vascular Space Occupancy (VASO) MRI

Large, rapid changes in perfusion accompany exercise, mediated in part by a local vasodilatory response. Impaired vasodilation occurs in diabetes, obesity, and other conditions. VASO MRI was developed to measure blood volume changes in the brain by nulling the signal of blood; vasodilation thus causes a loss of MRI signal intensity. The purpose of this work was to implement VASO for skeletal muscle. Eighteen subjects participated in the optimization of this method. Subjects were placed supine in a Philips 3.0T scanner with their foot on a force transducer, a knee coil around the calf, and an occlusion cuff around the thigh. Anatomical and VASO images were acquired (Fig 1).Maximal plantarflexion contractions were performed for 1–20 seconds, six minutes apart. The cuff was inflated to 240 mm Hg for five minutes, occluding arterial flow; VASO response was monitored for up to fifteen minutes after cuff release. NIRS spectroscopy was also performed to relate observed VASO signal changes to blood oxygenation and volume changes. VASO signal follows a similar time course to NIRS post occlusion.The decrease in VASO signal following a series of three ten second maximal plantarflexion contractions, as shown in Fig 2, should be proportional to increased blood volume demonstrating the promise of this new imaging paradigm to study blood volume changes in exercising muscle. This work was supported by NIH/NIAMS R01 AR050101.

Asymmetry of Quadriceps Muscle Oxygenation during Elite Short-Track Speed Skating

It has been suggested that, because of the low sitting position in short-track speed skating, muscle blood flow is restricted, leading to decreases in tissue oxygenation. Therefore, wearable wireless-enabled near-infrared spectroscopy (NIRS) technology was used to monitor changes in quadriceps muscle blood volume and oxygenation during a 500-m race simulation in short-track speed skaters. Six elite skaters, all of Olympic standard (age = 23 ± 1.8 yr, height = 1.8 ± 0.1 m, mass = 80.1 ± 5.7 kg, midthigh skinfold thickness = 7 ± 2 mm), were studied. Subjects completed a 500-m race simulation time trial (TT). Whole-body oxygen consumption was simultaneously measured with muscle oxygenation in right and left vastus lateralis as measured by NIRS. Mean time for race completion was 44.8 ± 0.4 s. VO2 peaked 20 s into the race. In contrast, muscle tissue oxygen saturation (TSI%) decreased and plateaued after 8 s. Linear regression analysis showed that right leg TSI% remained constant throughout the rest of the TT (slope value = 0.01), whereas left leg TSI% increased steadily (slope value = 0.16), leading to a significant asymmetry (P < 0.05) in the final lap. Total muscle blood volume decreased equally in both legs at the start of the simulation. However, during subsequent laps, there was a strong asymmetry during cornering; when skaters traveled solely on the right leg, there was a decrease in its muscle blood volume, whereas an increase was seen in the left leg. NIRS was shown to be a viable tool for wireless monitoring of muscle oxygenation. The asymmetry in muscle desaturation observed on the two legs in short-track speed skating has implications for training and performance.

Acute l-arginine supplementation increases muscle blood volume but not strength performance

l-Arginine (L-arg) is an amino acid precursor to nitric oxide (NO). Dietary supplements containing L-arg have been marketed with the purpose of increasing vasodilation, thereby elevating blood flow to the exercising muscle and enhancing the metabolic response to exercise. Our goal was to identify the acute effect of L-arg supplementation on biceps strength performance, indicators of NO production (nitrite and nitrate - NOx), and muscle blood volume (Mbv) and oxygenation (Mox) during recovery from 3 sets of resistance exercise. Fifteen males participated in a randomized, double-blind, placebo-controlled study. After withdrawing resting blood samples, the subjects were supplemented with 6 g of L-arg (ARG) or placebo (PLA). Monitoring of Mbv and Mox with near-infrared spectroscopy began 30min after supplementation and lasted for 60min. The exercise protocol (3 sets of 10 maximal voluntary contractions of isokinetic concentric elbow extension at 60°·s(-1), 2-min rest between sets) was initiated 80min after supplementation. Blood samples were drawn at 30, 60, 90, and 120min after supplementation. Repeated measures ANOVA showed that Mbv significantly (p≤ 0.05) increased in ARG compared with the PLA during the recovery period of each set of resistance exercise. NOx, Mox, peak torque, total work, and set total work were not significantly different between groups. We found that acute L-arg supplementation increases Mbv during recovery from sets of resistance exercise with no increase in strength performance. It is still premature to recommend nutritional supplements containing L-arg as an ergogenic aid to increase muscle strength during resistance training in healthy subjects.

Respiratory and locomotor muscle blood-volume and oxygenation kinetics during intense intermittent exercise

In this study, we examined the time course of changes in the blood volume and oxygenation of accessory respiratory (RM) and locomotor (LM) muscles, and the interrelationships of changes in these parameters during maximal incremental intermittent exercise in 15 non-endurance-trained active men. Blood volume and oxygenation of the serratus anterior and of vastus lateralis were measured simultaneously by near-infrared spectroscopy. The respiratory compensation point, and the breakpoints where abrupt changes were apparent in RM and LM blood volume and oxygenation versus time were identified. During exercise, the decreases in RM and LM oxygenation were accentuated in the vicinity of the respiratory compensation point. This was concomitant with a reduction in LM, but not RM, blood volume. The time at which the respiratory compensation point and the breakpoints in RM and LM blood volume and oxygenation were detected (70.2–75.0% exercise time) did not differ, and were inter-correlated (r=0.56 to 0.95). Moreover, the rate of the accelerated fall of oxygenation in the locomotor muscles was correlated with that of the decline in blood volume in that area (r=0.73), and with that of the accelerated fall of oxygenation in the respiratory muscles (r=0.71). The results suggest that the high ventilatory demand, which occurs naturally during intense intermittent exercise in non-endurance-trained individuals, may precipitate an accelerated fall in RM oxygenation, concomitant with a reduction in LM blood volume and an accentuated decline in LM oxygenation. Such responses are likely to occur above the respiratory compensation point during intermittent exercise.

Sternocleidomastoid muscle deoxygenation in response to incremental inspiratory threshold loading measured by near infrared spectroscopy

This study investigated the pattern of changes in muscle oxygenation, deoxygenation and blood volume in the sternocleidomastoid (SCM) in comparison with the parasternal (PS) and intercostal (IC) muscles during a bout of incremental inspiratory threshold loading (ITL) in healthy subjects using near-infrared spectroscopy. During progressive loading, the PS and IC showed a significant increase in oxygenated hemoglobin (5.9 ± 2.3 and 6.8 ± 2.4 μM, P<0.05) and the SCM showed an increase in deoxygenated hemoglobin (17.3 ± 3.8 μM, P<0.05). Total hemoglobin also steadily increased in the SCM whereas it decreased in the quiescent vastus lateralis muscle (20.7 ± 6.1μM vs. -6.6 ± 2.4 μM, P<0.05), which was used as the control muscle during the ITL. Our data suggests that the SCM is recruited progressively during progressive ITL and is accompanied by an increased blood volume and maintenance of O(2)Hb. Blood redistribution away from the nonactive limb muscles during the ITL may provide one source of maintaining inspiratory muscle blood volume and oxygenation during high respiratory motor output.