Muscle Oxygen Saturation Research Articles

Concentric and eccentric pedaling-type interval exercise on a soft robot for stable coronary artery disease patients: Toward a personalized protocol

Background: Cardiovascular diseases are the leading causes of death worldwide, and coronary artery disease (CAD) is one of the most common causes of death in Europe. Leading cardiac societies recommend exercise as an integral part of cardiovascular rehabilitation because it reduces the morbidity and mortality of patients with CAD. Continuous low-intensity exercise using shortening muscle actions (concentric, CON) is a common training modality during cardiovascular rehabilitation. However, a growing clinical interest has been recently developed in high-intensity interval training (HIIT) for stable patients with CAD. Exercise performed with lengthening muscle actions (eccentric, ECC) could be tolerated better by patients with CAD as they can be performed with higher loads and lower metabolic cost than CON exercise. Objective: We developed a clinical protocol on a soft robot to compare cardiovascular and muscle effects of repeated and work-matched CON versus ECC pedaling-type interval exercise between patients with CAD during cardiovascular rehabilitation. This study aims to ascertain whether the developed training protocols affect peak oxygen uptake (VO2peak), peak aerobic power output (Ppeak), and parameters of muscle oxygen saturation (SmO2) during exercise, and anaerobic muscle power. Methods: We will randomize 20-30 subjects to either the CON or ECC group. Both groups will perform a ramp test to exhaustion before and after the training period to measure cardiovascular parameters and SmO2. Moreover, the aerobic skeletal muscle power (Ppeak) is measured weekly during the 8-week training period using a simulated squat jump and a counter movement jump on the soft robot and used to adjust the training load. The pedaling-type interval exercise on the soft robot is performed involving either CON or ECC muscle actions. The soft robotic device being used is a closed kinetic chain, force-controlled interactive training, and testing device for the lower extremities, which consists of two independent pedals and free footplates that are operated by pneumatic artificial muscles. Results: The first patients with CAD, who completed the training, showed protocol-specific improvements, reflecting, in part, the lower aerobic training status of the patient completing the CON protocol. Rehabilitation under the CON protocol, more than under the ECC protocol, improved cardiovascular parameters, that is, VO2peak (+26% vs −6%), and Ppeak (+20% vs 0%), and exaggerated muscle deoxygenation during the ramp test (248% vs 49%). Conversely, markers of metabolic stress and recovery from the exhaustive ramp test improved more after the ECC than the CON protocol, that is, peak blood lactate (−9% vs +20%) and peak SmO2 (+7% vs −7%). Anaerobic muscle power only improved after the CON protocol (+18% vs −15%). Conclusions: This study indicates the potential of the implemented CON and ECC protocols of pedaling-type interval exercise to improve oxygen metabolism of exercised muscle groups while maintaining or even increasing the Ppeak. The ECC training protocol seemingly provided a lower cardiovascular stimulus in patients with CAD while specifically enhancing the reoxygenation and blood lactate clearance in recruited muscle groups during recovery from exercise. Trial Registration: ClinicalTrials.gov NCT02845063; https://clinicaltrials.gov/ct2/show/NCT02845063

Hemorrhage simulated by lower body negative pressure provokes an oxidative stress response in healthy young adults.

We characterize the systemic oxidative stress response in young, healthy human subjects with exposure to simulated hemorrhage via application of lower body negative pressure (LBNP). Prior work has demonstrated that LBNP and actual blood loss evoke similar hemodynamic and immune responses (i.e. white blood cell count), but it is unknown whether LBNP elicits oxidative stress resembling that produced by blood loss. We show that LBNP induces a 29% increase in F2-isoprostanes, a systemic marker of oxidative stress. The findings of this investigation may have important implications for the study of hemorrhage using LBNP, including future assessments of targeted interventions that may reduce oxidative stress, such as novel fluid resuscitation approaches.

Functional Electrical Stimulation Changes Muscle Oxygenation in Patients with Chronic Obstructive Pulmonary Disease During Moderate-Intensity Exercise: A Secondary Analysis

We previously showed that functional electrical stimulation during cycle ergometry (FES-cycling) increased oxygen consumption (VO2), indicating that metabolism during exercise was increased. However, the effects on muscle oxygenation have never been studied. The aim of this secondary analysis was to analyse changes in muscle oxygenation during an FES-cycling session. Eight patients with chronic obstructive pulmonary disease who were participating in a pulmonary rehabilitation programme were enrolled. Each participant carried out 30 minutes of cycle ergometry with a constant load at 50% of peak oxygen uptake, either (i) with FES or (ii) without (Placebo-FES). Oxygenation of the vastus lateralis (VL) muscle over time was measured using near-infrared spectroscopy (NIRS) during both sessions. External power output on the cycle ergometer was the same in both conditions. There were no differences in dyspnoea between the groups, although the concentrations of deoxygenated haemoglobin and myoglobin (deoxy(Hb + Mb)) in the VL were significantly greater during Placebo-FES than FES-Cycling (respectively +212 ± 65% vs. +84 ± 29%; p < 0.001), as was the decrease in muscle oxygen saturation (StO2) (p < 0.001). When adjusted for VO2, there was a greater increase over time in the deoxy(Hb + Mb)/VO2 ratio during Placebo-FES than FES-cycling (p < 0.0001). FES-cycling could be a useful strategy to decrease muscular deoxy(Hb + Mb) and limit decreases in muscle StO2, however this should be confirmed in larger studies.

Differences in muscle oxygenation between young and middle-aged recreationally active men during high-volume resistance exercise

The aim of this study was to compare muscle oxygenation of the vastus lateralis during a high-volume isokinetic resistance exercise protocol (HVP) between young adult (YA) and middle-aged adult (MA) men. Twenty recreationally trained men were assigned to either the YA (age 21.8±2.0 years, body mass 90.7±11.6 kg, body height 179±4.7 cm) or MA (age 47.0±4.4 years, body mass 96.1±21.6 kg, body height 177±7.7 cm) group. The HVP consisted of eight sets of 10 repetitions of unilateral isokinetic concentric knee extension and eccentric knee flexion at 60°·s-1. Changes in tissue hemoglobin saturation index (TSI), tissue oxygenated hemoglobin concentration (O2Hb), deoxygenated hemoglobin (HHb), and muscle oxidation index (O2Hb-HHb) were measured during the exercise session using the near-infrared spectroscopy (NIRS). Data were analyzed using two-way mix factorial analyses of variance. Prior to exercise, TSI was significantly greater (p=.024) for YA compared to MA. Significant decreases in O2Hb and O2Hb-HHb and increases in HHb were observed during each of the eight sets relative to the rest periods (p&amp;lt;.05) for both groups. The average change during the eight sets of the HVP revealed a significantly higher (p=.036) level of HHb and a lower (p=.029) level of O2Hb-HHb for MA compared to YA. A significant negative correlation was also noted at baseline between O2Hb-HHb index and the cross-sectional area of the vastus lateralis muscle (r=-.45, p=.045). During a high- volume resistance exercise, MA experienced reduced muscle oxygen saturation levels compared to YA. These results may be attributed to reductions in local tissue oxidative capacity and reduced blood delivery occurring during middle-age, and possibly due to group differences in muscle morphology.

Predictors of feelings of energy differ from predictors of fatigue

ABSTRACT Background: Studies examining energy and fatigue as a bipolar mood have focused on a single variable, usually fatigue, when studying these moods. Objective: The purpose of this study was to identify factors predicting feelings of energy and fatigue separately while simultaneously examining multiple domains related to these mood states in graduate health sciences students. Method: Seventy-seven participants were recruited from a Physician Assistant, Physical Therapy and Occupational Therapy program at a small school in Northern New York. Participants completed a series of surveys to measure mood, diet, mental work load intensity on school days and non-school days, and physical activity. Participants also completed the Trail-making Test Part B task on an iPad and their Resting Metabolic Rate (RMR) and muscle oxygen consumption mVO2 was measured. A backwards linear regression was used to determine the relationship between energy, fatigue and multiple variables. Results: The predictor variables accounted for 46.1% and 22.7% of the variance in fatigue and energy, respectively. More fatigue was associated with worse sleep quality, more time spent sitting and higher perceived intensity of mental workload on non-school days. More energy was associated with better sleep quality, higher muscle oxygen saturation, lower RMR, and faster psychomotor performance. Conclusion: The results of this study indicate that energy and fatigue are separate, yet overlapping constructs that are predicted with different accuracy by different variables. Our results indicate that small lifestyle changes may be necessary to improve feelings of fatigue but comprehensive interventions may be necessary to improve feelings of energy and fatigue.

Evaluation of Cardiovascular System Reactions when Different Muscle Groups are Activated

Research background and hypothesis. In our study, the dynamics of working muscle oxygen saturation of participants in the fi nal stages of provocative bicycle ergometer test was different. According to this, we hypothesized, that different central and peripheral reaction of cardiovascular system would dominate during local and regional exercises, too.Research aim was to evaluate central and peripheral reaction of cardiovascular system when different muscle groups are activated. Research methods. Twenty seven healthy men (age 32 ± 1.8 years, body mass index 25.3 ± 0.6 kg / m 2 ) participated in the study. All participants performed provocative bicycle ergometer test, electrocardiogram and oxygen saturation were registered. The participants performed three exercises activating different muscle groups: calf, forearm and back extension.Research results. Variation of heart rate and oxygen saturation values highlighted the difference between arm and leg training exercises. However, the load for arms and legs was individualised, both Groups A and B were different according to the dynamics of heart rate and oxygen saturation indices. Heart rate reaction to the physical load for the back muscles was unusual - heart rate decreased during the fi rst seconds of the back load. Oxygen saturation was lower in resting back muscles compared to those of resting arm and leg muscles (p &lt; 0.05). Discussion and conclusions. The analysis of heart rate and oxygen saturation values has revealed that each functional muscle group of the human organism contains not only general but also individual activating features both integrating regulatory systems and forming a certain activation of metabolism in working muscles.Keywords: heart rate, oxygen saturation, variation of indices.

PO-096 Correlation between Muscle oxygen and Cardiopulmonary of young cyclists at Ventilation threshold

Objective To investigate the relationship between Near-infrared spectroscopy (NIRS)-derived muscle oxygen saturation (SmO2) and Cardiopulmonary indexes at the Ventilatory threshold (VT1 and VT2) during Cardiopulmonary exercise test (CPET) ofyoung cyclists.&#x0D; Methods 12 young cyclists performed a maximal incremental exercise test to exhaustion on a friction-braked cycle ergometer (Monark 839E, Sweden).Heart rate (Polar RS400, Finland) and respiratory gas exchange were measured during the Resting and exercise phases using a breath-by-breath system. SmO2 of active muscles during cycling was measured by NIRS monitors (Fortiori Design LLC, USA), and three of the monitors were placed on both vastus lateralis (VLL &amp; VLR) and left gastrocnemius lateralis (GLL) of left leg. The resting value of the SmO2 of the GLL (SmO2-GLL), the left vastus lateralis (SmO2-VLL), and the right vastus lateralis (SmO2-VLR) was recorded as a baseline. Then after VT1 and VT2 of each subject were measured by the V-slope method during a CPET, values of muscle oxygen corresponding to the three lower limb sites at two ventilation thresholds was recorded to reflect the muscle oxygenation level at the anaerobic threshold; And the change of muscle oxygen relative to the baseline was calculated to reflect the degree of muscle deoxygenation, which is termed as deoxygenation indexes(ΔSmO2-GLL, ΔSmO2-VLL, ΔSmO2-VLR); As well, Cardiopulmonary indexes including Heart rate (HR), Minute ventilation (VE), Relative oxygen uptake (VO2R), Carbon dioxide production (VCO2) and Respiratory exchange rate (RER) at the Ventilatory threshold were measured. All Results were expressed as mean ± standard deviation. Finally, Pearson correlation analysis was used to determine the relationship between multi-site muscle oxygen saturation of lower extremities and Cardiopulmonary indexes (HR, VE, VO2R, VCO2, RER). The significance level was defined as p&lt;0.05.&#x0D; Results Each subject performed their best to complete the aerobic capacity test. The average VO2peak of the 12 subjects was 42.77 ± 9.69 ml/kg/min (Male: 47.38 ± 9.41 ml/kg/min; Female: 36.31 ± 3.33 ml/kg/min). At rest, the calf and thigh SmO2 were 67.92%± 6.84% (SmO2-GLL), 61.42% ± 13.77% (SmO2-VLL), 64.83% ± 10.62% (SmO2-VLR)respectively; HR, VE, VO2, VO2R, VCO2 and RER were 112.08 ± 14.38, 25.96 ± 8.74 L / min 0.94 ± 0.32 L/min, 15.82 ± 4.30 ml/kg/min, 0.81 ± 0.24 L/min,0.88 ± 0.12 L/min, and 0.38 ± 0.07, respectively. Correlation analysis shows that when adolescent athletes reached the anaerobic threshold level, there was a significant correlation between muscle oxygen and cardiopulmonary: At the time of VT1, for Oxygenation index, SmO2 of GLL was highly negatively correlated with HR (r=-0.69,p&lt;0.05), VE (r=-0.71, p&lt;0.01), VO2R (r=-0.65, p&lt;0.05), VCO2 (r=-0.66, p&lt;0.05) and RER (r=-0.58, p&lt;0.05); SmO2-VLL was also highly negatively correlated with VE (r=-0.70, p&lt;0.05), VO2R (r=-0.70, p&lt;0.05), VCO2 (r=-0.66, p&lt;0.05); Additionally, there is also high inverse correlation between SmO2-VLR and HR (r=-0.66, p&lt;0.05), VE (r=-0.70, p&lt;0.05), VO2R (r=-0.66, p&lt;0.05), VCO2 (r=-0.68, p&lt;0.05), RER (r=-0.60, p&lt;0.05). In terms of deoxygenation indexes, ΔSmO2-GLL was highly negatively correlated with VE (r=-0.61, p&lt;0.05), VO2R (r=-0.64, p&lt;0.05) and VCO2 (r=-0.59, p&lt;0.05); While, ΔSmO­2-VLL was highly negatively correlated with HR (r=-0.62, p&lt;0.05), VE (r=-0.72, p&lt;0.01),VO2R (r=-0.80, p&lt;0.01) and VCO2(r=-0.84, p&lt;0.01); ΔSmO2-VLR was correlated with HR (r=-0.75, p&lt;0.01), VE (r=-0.62, p&lt;0.05), VO2R (r=-0.58, p&lt;0.05) and RER (r=-0.74, p&lt;0.01), and it also shows highly negative correlation. When VT2 occurred, only SmO2 of the GLL in the oxygenation indexes was highly positively correlated with HR (r=0.65, p&lt;0.05), there was no correlation between GLL-SmO2 and any other gas exchange indexes. In terms of muscle deoxygenation indexes, only ΔSmO2 in the thigh VLR was significantly negatively correlated with RER (r=-0.75, p&lt;0.01).&#x0D; Conclusions Based on these results, there is a high correlation between NIRS-derived regional muscle oxygen saturation (Oxygenation and Deoxygenation indexes) of lower extremities and cardiopulmonary index (HR, VE, VO2R, VCO2, RER) during CPET of young cyclists at first Ventilatory threshold, however, it is still unclear whether there is a significant correlation between muscle oxygen saturation of lower extremities and other cardiopulmonary indexes when second Ventilatory threshold occurs except Heart rate or Minute ventilation.

The effects of ultrasound and shockwave treatment on muscle regional oxygen saturation using near-infrared spectroscopy

ABSTRAKTWstęp: Terapeutyczne fale ciśnieniowe są często stosowane w leczeniu różnych schorzeń układu mięśniowo-szkieletowego, niemniej jednak efekt biologiczny ich odziaływania wciąż nie został w pełni poznany. W przedstawionych badaniach oceniono wpływ fal dźwiękowych o różnej sile bodźca stosowanych w terapii falą ultradźwiękową (ultrasound therapy – UST) i pozaustrojową radialną falą uderzeniową (radial extracorporeal shockwave therapy – rESWT) na wysycenie tlenem tkanki mięśniowej i temperaturę powierzchniową w kontekście potencjalnego efektu troficznego przy użyciu spektroskopii bliskiej podczerwieni (near-infrared spectroscopy).Materiały i metody: Badaniem objęto 41 zdrowych ochotników, w tym 27 poddanych UST i 14 rESWT, w wieku 22–48 lat. Pomiar saturacji tkankowej i temperatury powierzchni obszaru mięśnia podgrzebieniowego wykonano 4-krotnie: bezpośrednio przed (T0) i po (T1) oraz 15 (T2) i 30 min po aplikacji bodźca (T3). Saturacje mięśni zmierzono na 2 głębokościach: 20 mm (czujnik 1 – S1) i 12,5 mm (czujnik 2 – S2).Wyniki: Wartość regionalnej perfuzji tkankowej (rSO2 [%]) istotnie zmniejszyła się natychmiast oraz po 15 i 30 min od UST. Wartości początkowe, wynoszące 71,26 ±5,47% (S1) i 88,26 ±2,89% (S2) dla odpowiednich głębokości, znacząco spadły po bodźcowaniu odpowiednio do 68,89 ±5,26% (T2) i 68,93 ±5,12% (T3) na głębokości 20 mm i 86,63 ±5,37% (T1) i 86,52 ±3,38% (T2) na głębokości 12,5 mm.Wnioski: Uzyskane wyniki wskazują, że tylko leczenie za pomocą UST ma znaczący wpływ na zmiany oksymetrii regionalnej, co tłumaczy się ich działaniem przekrwiennym i termicznym w tkankach głębokich, które z kolei indukują dysocjacje tlenu z hemoglobiny do tkanek i efekt troficzny.

A single dose of beetroot juice improves endothelial function but not tissue oxygenation in pregnant women: a randomised clinical trial.

Beetroot juice (BJ) consumption has been associated with improved cardiovascular health owing to an increase in NO bioconversion. This study evaluates the effect of BJ consumption on macrovascular endothelial function (flow-mediated dilation (FMD)) and muscle oxygen saturation (StO2) parameters in pregnant women within a randomised, crossover, double-blind design in which twelve pregnant women consumed a single dose (140 ml) of BJ or placebo (PLA). Urinary nitrate was assessed before (T0) and 150 min after BJ/PLA consumption. FMD was used to evaluate macrovascular endothelial function, and near-IR spectroscopy was used to evaluate muscle StO2 parameters during the occlusion and reperfusion phases, which were taken at baseline (PRE) and 120 and 140 min after BJ/PLA consumption, respectively. A significant increase in urinary nitrate was observed at 150 min after BJ consumption when compared with T0 (BJ: 0·20 (sd 0·13) v. T0: 0·02 (sd 0·00), P=0·000) and PLA intervention (PLA: 0·02 (sd 0·00), P=0·001). FMD improved after BJ consumption when compared with PRE (BJ: 11·00 (sd 1·67) v. PRE: 5·53 (sd 1·17), P=0·000) and PLA (5·34 (sd 1·31), P=0·000). No significant difference between PLA and PRE in FMD (P=1·000) was observed. In StO2 parameters, a difference was not observed after BJ consumption compared with PRE and PLA intervention. The data demonstrate that a single dose of 140 ml of BJ consumption improves macrovascular endothelial function, but not StO2 parameters.

Muscle blood content and muscle oxygen saturation in response to head down and head up tilt

As microgravity alters blood distribution and flow in muscle tissue, in the present study, blood content and oxygen saturation in extremity muscles were evaluated by an analogous body tilting model. For this purpose, the supine resting posture was compared with successive head down tilt (HDT) and head up tilt (HUT) in ten well trained male volunteers. Muscle oxygen saturation and total hemoglobin content were measured using near infrared spectroscopy sensors attached on the gastrocnemius, vastus lateralis and biceps brachii muscles of each body side. Simultaneously, continuous and noninvasive recordings of arterial blood pressure and heart rate variability were performed. The test protocol consisted of the following stages (5 min each): supine, 6o HDT, 15o HDT, 30o HDT, supine, 6o HUT, 15o HUT, and 30o HUT postures in successive order. The evolution of the rhythmic components in the recorded time series were analyzed by wavelet based multiscale time-frequency distributions, and synchronization between measurement sites by wavelet phase synchronization indexing. A support vector machine (SVM) algorithm was employed for classification of posture in relation to muscle total hemoglobin content or oxygen saturation. Increasing or decreasing gravitational impact due to the posture changes resulted in significant increases or decreases of total hemoglobin content in the muscles, but showed no linear relation to muscle oxygen saturation. This effect was stronger pronounced as the respective extremity part was located more centrifugal to the body tilting axis. Blood pressure and heart rate did not influence muscle oxygen saturation. The two major rhythmic components in the cardiovascular system, the 0.1 Hz and respiratory rhythm, were only weakly displayed in the muscle oxygen saturation time series. Oscillations of muscle oxygen saturation in the very low frequency band displayed left-right synchrony. SVM was able to classify postural changes of muscle blood content with good accuracy but not those of muscle oxygen saturation. These results imply that muscle oxygen saturation during acute postural changes may be mainly regulated by neural drive to the micro-vascular circulation and not by systemic cardiovascular kinetics.

Comparisons of Traditional Metabolic Markers and Compensatory Reserve as Early Predictors of Tolerance to Central Hypovolemia in Humans.

Circulatory shock remains a leading cause of death in both military and civilian trauma. Early, accurate and reliable prediction of decompensation is necessary for the most efficient interventions and clinical outcomes. Individual tolerance to reduced central blood volume can serve as a model to assess the sensitivity and specificity of vital sign measurements. The compensatory reserve (CRM) is the measurement of this capacity. Measurements of muscle oxygen saturation (SmO2), blood lactate, and end tidal CO2 (EtCO2) have recently gained attention as prognostic tools for early assessment of the status of patients with progressive hemorrhage, but lack the ability to adequately differentiate individual tolerance to hypovolemia. We hypothesized that the CRM would better predict hemodynamic decompensation and provide greater specificity and sensitivity than metabolic measures. To test this hypothesis, we employed lower body negative pressure on healthy human subjects until symptoms of presyncope were evident. Receiver operating characteristic area under the curve (ROC AUC), sensitivity, and specificity were used to evaluate the ability of CRM, partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), SmO2, lactate, EtCO2, potential of hydrogen (pH), base excess and hematocrit (Hct) to predict hemodynamic decompensation. The ROC AUC for CRM (0.94) had a superior ability to predict decompensation compared with pO2 (0.85), pCO2 (0.62), SmO2 (0.72), lactate (0.57), EtCO2 (0.74), pH (0.55), base excess (0.59), and Hct (0.67). Similarly, CRM also exhibited the greatest sensitivity and specificity. These findings support the notion that CRM provides superior detection of hemodynamic compensation compared with commonly used clinical metabolic measures.

Calf Muscle Oxygen Saturation during 6-Minute Walk Test and Its Relationship with Walking Impairment in Symptomatic Peripheral Artery Disease

Impaired microcirculation is associated with poor walking capacity in symptomatic peripheral artery disease (PAD) patients during treadmill test; however, this test does not simulate the efforts of daily walking of these patients. Thus, the aim of the study was to describe the microcirculation responses during a 6-minute walk test (6MWT) and to analyze the relationship between microcirculation indicators and walking impairment in symptomatic PAD patients. Thirty-four patients were included (mean age=67.6±11.2 years). Their clinical characteristics were collected, and they performed a 6MWT, in which the initial claudication distance (ICD) and total walking distance (TWD) were recorded. During and after the 6MWT, calf muscle oxygen saturation (StO2) parameters were monitored continuously to measure microcirculation behavior. The association between calf muscle StO2 parameters and walking impairment were analyzed by Pearson or Spearman correlations. Walking impairment was not associated with any StO2 parameters during exercise. In contrast, after 6MWT, recovery time of StO2 (r=-0.472, P=0.008) and recovery time to maximal StO2 (r=-0.402, P=0.019) were negatively correlated with ICD. Furthermore, the distance walked under claudication symptoms (ΔTWD-ICD) was positively correlated with recovery time to maximal StO2 (r=0.347, P=0.048). In symptomatic PAD patients, shorter ICD values during a 6MWT are associated with a delayed recovery in calf muscle StO2 after exercise. Calf muscle StO2 parameters decrease subtly during 6MWT, suggesting that the degree of ischemia in the calf muscle during ground walking, simulating efforts of the daily walking, is relatively low.

Impact of Remote Ischemic Preconditioning Post-application Delay on Muscle Oxygenation during Subsequent Cycling Intervals

INTRODUCTION: Remote ischemic preconditioning (RIPC) involves brief, repeated bouts of manually-imposed blood flow restriction of the arms or legs. The alternating periods of occlusion and reperfusion lead to endothelial adaptations, capable of enhancing blood flow and oxygen delivery. PURPOSE: The aim of this study was to investigate the effect of a lower limb RIPC protocol, with either a 5-min or 45-min post-application delay, on muscle oxygen saturation within that same limb at rest and during short- duration intense cycling. METHODS: Subjects included recreationally aerobically trained college-aged students (23± 3 years, 173.5± 5.4 cm, 69.2± 4.0 kg, 15.2± 4.0 % BF, 2peak VO : 46.6± 1.1 mL•kg-1•min-1 at 215± 19 W). All subjects randomly completed four experimental trials: RIPC with 5-min delay, RIPC with 45-min delay, SHAM with 5-min delay, and SHAM with 45-min delay. For the RIPC conditions, each subject received 5-min of alternating-leg blood flow occlusion using a blood pressure cuff (220 mmHg) placed on the upper thighs for a total of 40 min. After a 5 or 45-min delay, the subjects completed 5, 1-min cycle sprints separated by 2 min of recovery. The SHAM conditions were identical to the RIPC, however, subjects laid supine for the same 40-min duration with alternating-leg cuff inflation to 20 mmHg. Muscle oxygen saturation was measured continuously using a portable NIRS-based sensor placed over the vastus lateralis (VL). RESULTS: RIPC decreased muscle oxygen saturation in the VL in a replicable manner (MD: 29.5± 13.4%, mean occlusion slope: -5.0± 2.4 %•min-1, mean reperfusion slope: 38.5± 22.4%•min-1) while SHAM conditions left muscle oxygen saturation largely unchanged (MD: 2.9± 1%). Mean VL oxygen saturation (RIPC45:71.9± 0.7%; RIPC5: 67.3± 1.7%; SHAM45: 72.0± 4.4%; SHAM5: 69.9± 3.0%) and preservation of muscle oxygen saturation (MD: RIPC45: -12.4± 6.2%; RIPC5: -14.4± 9.9%; SHAM45: -11.6± 6.4%; SHAM5: -13.0± 7.1%) during high intensity cycling intervals varied minutely between experimental conditions. CONCLUSIONS: The muscle oxygenation response during a standard occlusion/reperfusion protocol may lack assumed constancy. Furthermore, the use of RIPC and the length of the delay following RIPC did not greatly alter the muscle oxygenation response to repetitive high-intensity cycling intervals.

Evaluating Near Infrared Spectroscopy Signals From Skeletal Muscle

Near Infrared Spectroscopy (NIRS) uses the relative absorption of light at 850 and 760nm to determine skeletal muscle oxygen saturation. There are currently disagreements in the literature over how to report oxygen saturation and the relative contributions of hemoglobin and myoglobin. PURPOSE: 1) Compare the separate 850nm (HbO2) and 760nm (HHb)signals during rest, ischemia, and reperfusion, and 2) test whether electrical stimulation to increase metabolic rate changes oxygen saturation values during 5-6 minutes of complete ischemia. METHOD: Ten participants ages = 20-29 years were measured. NIRS measurements were made in the forearm flexor muscles at rest, after 30 seconds of 6 Hz electrical stimulation, during and after 5-6 minutes of complete ischemia produced by arterial occlusion preceded by 30 seconds of 6 Hz electrical stimulation. After 5-6 minutes of ischemia 30 seconds of 6 Hz electrical stimulation was performed. RESULTS: Six Hz stimulation for 30 s increased metabolic rate for HbO2 and HHb; 6.2+3.1 and 5.5+2.7 fold over rest, respectively. Six Hz stimulation during cuff ischemia did not change either the HHb or HbO2 values (p>0.05). There was significantly greater (p<0.05) pulsitility associated with heart rate in the HbO2 (0.78+0.41% range) compared to HHb (0.16+0.09% range). Pulse size increased during reperfusion; HbO2 (2.37+0.38% range) compared to HHb (0.96+0.32% range). CONCLUSIONS: The difference in the magnitude of pulsitility between HbO2 and HHb signals suggests different anatomical locations for these signals, further suggesting that using various ratios of HbO2 and HHb signals should be performed with caution. Increasing metabolic rate with electrical stimulation during complete ischemia did not further change the NIRS signals, suggesting complete ischemia is obtained with 5-6 minutes of complete cuff occlusion. Keywords: Skeletal Muscle, Near Infrared Spectroscopy (NIRS), Oxygen consumption, Hemoglobin, Myoglobin

Comparison of Measures of Compensatory Reserve and Tissue Oxygen in Differentiating Tolerance to Simulated Hemorrhage

BackgroundWe previously reported that average measurements of compensatory reserve (CRM) and muscle oxygen saturation (SmO2) obtained from a large cohort of humans provided earlier indication of reduced central blood volume than standard vital signs (e.g., blood pressure, heart rate, arterial oxygen saturation). Additionally, CRM was more sensitive and specific in earlier prediction of decompensation than SmO2 overall.ObjectiveIn the present study, we hypothesized that CRM derives its superior predictive qualities from its ability to differentiate between individuals with high (HT) and low (LT) tolerance to central hypovolemia compared with measures of SmO2.MethodsContinuous noninvasive measures of CRM (calculated from feature changes in the photoplethysmographic arterial waveforms) were collected from 55 healthy volunteer subjects before and during stepwise lower body negative pressure (LBNP) to the point of presyncope. Near infrared spectroscopy was used on the forearm to obtain measures of deep SmO2, hydrogen ion concentration ([H+]), and hemoglobin volume (HbT; decreases reflect vasoconstriction). Using a progressively increasing stepwise protocol, tolerance group was defined by those subjects who did (HT) or did not (LT) complete 60 mmHg LBNP. Data were analyzed using generalized estimating equations (GEE) to account for the repeated measures design.ResultsOf 55 participants, there were 35 (64%) HT and 20 (36%) LT, 26 (47%) males and 29 females (53%), with a mean age of 28 years (SD=7), height of 172 cm (SD=10) and weight of 72 kg (SD=15). CRM decreased by 97% in a linear fashion across progressive LBNP levels from baseline to −90 mm Hg, while SmO2 decreased by only 39% from baseline to −90 mm Hg. The slope for CRM values across progressive LBNP levels differed significantly between LT and HT individuals (slope difference −0.14; p=0.03). The slope for SmO2 values did not differ between LT and HT individuals across LBNP levels (slope difference=0.06; p=0.18).ConclusionConsistent with our hypothesis, CRM exhibited greater reduction across progressive LBNP levels than SmO2. These data support the notions that: 1) CRM can enable more accurate triage of casualties than SmO2 due to superior ability to differentiate those individuals at highest risk for shock; and 2) continuous monitoring of CRM can allow for earlier detection of continued casualty deterioration.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Countdown before voluntary exercise induces muscle vasodilation with decreased muscle sympathetic nerve activity in humans

We examined whether countdown (CD) before voluntary bicycle ergometer exercise induced cerebro‐cardiovascular responses and, if so, whether these responses to CD were altered by postural change from the semi‐recumbent to supine position. Young men (n=14) performed voluntary cycle exercise in the semi‐recumbent position while middle cerebral artery blood flow velocity (CBF; Doppler ultrasonography), heart rate (HR), blood pressure (finger photoplethysmography), oxygen consumption rate (VO2), oxygen saturation in the right thigh muscle (StO2; near‐infrared spectrometry), cardiac output (CO; cZ method) and total peripheral resistance (TPR) were measured. The subjects repeated 8 trials, intermitted by more than 5‐min rest. In 4 trials randomly selected from 8 trials, the onset of exercise was signaled by a 30‐sec CD, whereas in the remaining 4 trials, exercise was started without CD. We found that CD increased CBF, HR, CO, mean blood pressure, and VO2 sequentially, decreasing TPR with increased StO2. To assess efferent signals causing vasodilation and the effects of posture change from the semi‐recumbent to supine position, other groups of subjects underwent the same exercise protocol but using only right leg in the semi‐recumbent (n=10) or supine (n=8) positions while muscle sympathetic nerve activity (MSNA; microneurography) and StO2 were measured in the left and right leg, respectively. We found that CD decreased MSNA burst frequency and total MSNA (both, P&lt;0.05), which were significantly correlated with the increase in StO2 (both, P&lt;0.001). However, these responses to CD were nearly abolished by the postural change. Thus, CD before starting voluntary exercise induced cerebro‐cardiovascular responses from central system to effector organs in a sequential manner in the semi‐recumbent position, but these responses were minimized while in the supine position.Support or Funding InformationThis study was supported by grants from the Japan Society for the Promotion of Science (24689014 and 15H04680).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Validation of a novel wearable, wireless technology to estimate oxygen levels and lactate threshold power in the exercising muscle.

There is a growing interest in monitoring muscle oxygen saturation (SmO2), which is a localized measure of muscle oxidative metabolism and can be acquired continuously and noninvasively using near‐infrared spectroscopy (NIRS) methods. Most NIRS systems are cumbersome, expensive, fiber coupled devices, with use limited to lab settings. A novel, low cost, wireless, wearable has been developed for use in athletic training. In this study, we evaluate the advantages and limitations of this new simple continuous‐wave (CW) NIRS device with respect to a benchtop, frequency‐domain near‐infrared spectroscopy (FDNIRS) system. Oxygen saturation and hemoglobin/myoglobin concentration in the exercising muscles of 17 athletic individuals were measured simultaneously with the two systems, while subjects performed an incremental test on a stationary cycle ergometer. In addition, blood lactate concentration was measured at the end of each increment with a lactate analyzer. During exercise, the correlation coefficients of the SmO2 and hemoglobin/myoglobin concentrations between the two systems were over 0.70. We also found both systems were insensitive to the presence of thin layers of varying absorption, mimicking different skin colors. Neither system was able to predict the athletes’ lactate threshold power accurately by simply using SmO2 thresholds. Instead, the proprietary software of the wearable device was able to predict the athletes’ lactate threshold power within half of one power increment of the cycling test. These results indicate this novel wearable device may provide a physiological indicator of athlete's exertion.

Multiday Pomegranate Extract Supplementation Decreases Oxygen Uptake During Submaximal Cycling Exercise, but Cosupplementation With N-acetylcysteine Negates the Effect.

Pomegranate extract (POMx) has been suggested as an ergogenic aid due to its rich concentration of polyphenols, which are proposed to enhance nitric oxide bioavailability, thereby improving the efficiency of oxygen usage and, consequently, endurance exercise performance. Although acute POMx supplementation improves aerobic exercise performance in untrained individuals, trained athletes appear to require chronic supplementation for a similar effect. Furthermore, the combination of POMx with a thiol antioxidant may prove more effective than POMx alone, due to the protective effects of thiols on nitric oxide. Thus, this study hypothesized that multiday POMx supplementation would decrease the oxygen uptake (VO2) required by trained cyclists to perform submaximal exercise and increase performance during a time trial, and that thiol (N-acetylcysteine [NAC]) cosupplementation would enhance these effects. Eight cyclists completed four 8-day supplementation periods: POMx only, NAC only, POMx + NAC (BOTH), and placebo. Following supplementation, they performed submaximal cycling and a 5-min time trial, with VO2 and muscle oxygen saturation (SmO2) being recorded. A three-way (POMx × NAC × Intensity) repeated-measures analysis of variance with a Fisher's least significant difference post hoc assessment was performed for dependent variables (p ≤ .05). VO2 during submaximal exercise was reduced with POMx versus placebo (-2.6ml·min-1·kg-1, p = .009) and BOTH (-2.5ml·min-1·kg-1, p < .05) and increased with NAC (+1.9ml·min-1·kg-1, p < .03), despite no main effect of treatment on SmO2 or performance. It appears that POMx's high polyphenol content reduced the VO2 required during submaximal exercise. However, NAC cosupplementation annulled this effect; thus, NAC may interact with nitric oxide to reduce its bioavailability.

Changes in Spinal Muscle Oxygenation and Perfusion During the Biering-Sørensen Test: Preliminary Results of a Study Employing NIRS-Based Muscle Oximetry.

We measured muscle perfusion in healthy subjects during the Biering-Sørensen (BS) test (the gold standard for evaluating back muscle endurance) using a commercial near-infrared spectroscopy (NIRS) device. We analysed data sets of five female healthy subjects (age: 34 ± 15years) who reached the maximum of 4 min during the BS test. Muscle oxygenation (SmO2) and perfusion ([tHb]) were measured using the Moxy NIRS device (Fortiori Design LLC, Hutchinson, USA). Probes were set unilaterally on M. longissimus, M. iliocostalis and M. multifidus. Additionally, mean arterial blood pressure (MAP), pulse pressure (PP), heart rate (HR), arterial oxygen saturation (SpO2) and lactate (pre, task, post) were measured. We observed (i) a large inter-subject variability in the SmO2 and [tHb] responses in the three muscles (i.e., SmO2 desaturations in the in M. longissimus across subjects during the task ranging from 1.1% to -56.6%), and (ii) a consistent response of the systemic signals in all subjects (i.e., increase in MAP, PP and HR). Lactate changes (post task minus task period) correlated with changes in PP and SmO2 of the multifidus muscle. Our preliminary results showed that during the BS test the response in the peripheral muscles was more variable than the central systemic response. A goal for future investigations is to explain this variability in the periphery by considering, for example, subject-specific changes in systemic cardiovascular activity, lactate and in the microvascular perfusion of muscle tissue.

Ischemic Preconditioning Does Not Alter Performance in Multidirectional High-Intensity Intermittent Exercise.

Purpose: Research dealing with ischemic preconditioning (IPC) has primarily focused on variables associated to endurance performance with little research about the acute responses of IPC on repeated multidirectional running sprint performance. Here we aimed to investigate the effects of IPC of the arms and the legs on repeated running sprint performance with changes-of-direction (COD) movements.Methods: Thirteen moderately-to-well-trained team-sport athletes (7 males; 6 females; age: 24 ± 2 years, size: 175 ± 8 cm, body mass: 67.9 ± 8.1 kg) performed 16 × 30 m all-out sprints (15 s rest) with multidirectional COD movements on a Speedcourt with IPC (3 × 5 min) of the legs (IPCleg; 240 mm Hg) or of the arms (remote IPC: IPCremote; 180–190 mm Hg) 45 min before the sprints and a control trial (CON; 20 mm Hg).Results: The mean (±SD) time for the 16 × 30 m multidirectional COD sprints was similar between IPCleg (Mean t: 16.0 ± 1.8 s), IPCremote (16.2 ± 1.7 s), and CON (16.0 ± 1.6 s; p = 0.50). No statistical differences in oxygen uptake (mean difference: 0%), heart rate (1.1%) nor muscle oxygen saturation of the vastus lateralis (4.7%) and biceps brachii (7.8%) between the three conditions were evident (all p > 0.05).Conclusions: IPC (3 × 5 min) of the legs (220 mm Hg) or arms (180–190 mm Hg; remote IPC) applied 45 min before 16 × 30 m repeated multidirectional running sprint exercise does not improve sprint performance, oxygen uptake, heart rate nor muscle oxygen saturation of the vastus lateralis muscle when compared to a control trial.