Skeletal Muscle Oxygen Research Articles

Physiological Profiles: Speed Reserve Ratio, Skeletal Muscle Oxygenation, And Lactate Measurements In Middle-distance Runners

Physiological Profiles: Speed Reserve Ratio, Skeletal Muscle Oxygenation, And Lactate Measurements In Middle-distance Runners

Differences In Skeletal Muscle Oxygenation Of Vastus Laterals And Gastrocnemius During Exhaustive Exercise

Differences In Skeletal Muscle Oxygenation Of Vastus Laterals And Gastrocnemius During Exhaustive Exercise

Understanding exercise (in)tolerance in sickle cell disease: impacts of hemolysis and exercise training on skeletal muscle oxygen delivery.

Sickle cell disease (SCD) is characterized by central (cardiac) and peripheral vascular dysfunctions, significantly diminishing exercise capacity and quality of life. Although central cardiopulmonary abnormalities in SCD are known to reduce exercise capacity and quality of life; the impact of hemolysis and subsequent cell-free hemoglobin (Hb)-mediated peripheral vascular abnormalities on those outcomes are not fully understood. Despite the recognized benefits of exercise training for cardiovascular health and clinical management in chronic diseases like heart failure, there remains substantial debate on the advisability of regular physical activity for patients with SCD. This is primarily due to concerns that prolonged and/or high-intensity exercise might trigger metabolic shifts leading to vaso-occlusive crises. As a result, exercise recommendations for patients with SCD are often vague or nonexistent, reflecting a gap in knowledge about the mechanisms of exercise intolerance and the impact of exercise training on SCD-related health issues. This mini-review sheds light on recent developments in understanding how SCD affects exercise tolerance, with a special focus on the roles of hemolysis and the release of cell-free hemoglobin in altering cardiovascular and skeletal muscle function. Also highlighted here is the emerging research on the therapeutic effects and safety of exercise training in patients with SCD. In addition, the review identifies future research opportunities to fill existing gaps in our understanding of exercise (in)tolerance in SCD.

Effect of Curcumin Intake on Skeletal Muscle Oxygen Saturation Parameters in Older Participants.

Aging is associated with increased reactive oxygen species (ROS) and reduced bioavailability of nitric oxide (NO). Curcumin has been shown to increase NO bioavailability due to its ability to neutralize ROS, preventing oxidative stress. The present study aimed to investigate the effect of curcumin intake on skeletal muscle oxygen parameters and exercise tolerance in response to exercise in older people. Changes in circulating levels of NO metabolites were also investigated. Older subjects consumed 10 g of turmeric root extract from Curcuma longa L. (containing 95.33% of the total curcuminoids) or placebo in a randomized, double-blind, crossover study. A time of 2 h after ingestion, the participants performed one set of rhythmic handgrip exercise until the limit of tolerance, followed by 5 min of recovery. During exercise and exercise recovery, skeletal muscle oxygen saturation parameters were recorded. During exercise, the amplitude of deoxyhemoglobin was greater after curcumin intake compared to placebo (CUR: 13.11 ± 9.52 vs. PLA: 10.22 ± 8.39 μM, p = 0.030). Furthermore, a faster skeletal muscle oxygen resaturation during exercise recovery was observed after curcumin compared to placebo (CUR: 1.01 ± 0.65 vs. PLA: 0.32 ± 0.20%.s-1, p = 0.004). These results were associated with significant changes in plasma nitrite (CUR: 6.82 ± 11.68 vs. PLA: -4.94 ± 17.28%, p = 0.028). There was no statistical difference in the total hemoglobin, exercise time until fatigue, and plasma nitrate between groups. The present study suggests that curcumin improves muscle oxygenation status at the capillary level in older adults by possibly improving muscle oxygen extraction and/or delivery, with no effect on exercise tolerance.

Acute Sleep Deprivation and Cerebral and Skeletal Muscle Oxygenation: A Review and Future Directions

Cerebral and skeletal muscle oxygenation are critical research areas for understanding blood flow and oxygen delivery during various physiological states, including cognitive tasks and exercise. Measuring oxygenated and deoxygenated hemoglobin through functional near-infrared spectrometry (fNIRS) enables non-invasive assessment of cerebral and skeletal muscle oxygenation. Research using fNIRS to explore oxygenation after sleep deprivation (SD) is limited and often contradictory. We reviewed how SD affects cerebral and muscle oxygenation as part of a broader review of how SD affects exercise through altered physiologic and perceptual responses. Herein, we consolidate existing knowledge, identify gaps, and suggest directions for future investigation. A comprehensive literature review was conducted via predefined search parameters using PubMed and Google Scholar, focusing on studies that employed fNIRS to measure cerebral and/or skeletal muscle oxygenation in humans after SD (total or partial) or in individuals with chronically fragmented sleep due to obstructive sleep apnea (OSA). Select studies report increased cerebral oxygenation post-SD, potentially due to compensatory mechanisms and increased brain activity. Contrarily, several studies indicate decreased cerebral oxygenation following SD, potentially due to impaired endothelial function, cortical neurovascular coupling, suppressed brain activity, or decreased oxygen consumption. Cerebral oxygenation may be associated with perceived exertion, suggesting meaningful links to exercise. Interestingly, exercise training may mitigate the effects of SD on oxygenation. The only study investigating skeletal muscle oxygenation with regards to sleep status found a lower tissue saturation index in OSA participants compared to controls, though hemoglobin parameters did not differ. The effect of SD on oxygenation remains equivocal, with no studies fully elucidating the mechanisms underlying these changes. This review is the foundation for an ongoing prospective study investigating the impact of acute SD on exercise capacity and fNIRS-derived cerebral and skeletal muscle oxygenation, with two participants enrolled to date and interim analyses planned at n=5 participants.

Impact of sprint interval training on post-fatigue mitochondrial rate in professional boxers.

Professional boxing is a sport that requires a high aerobic capacity to prevent fatigue and allow athletes to perform over 4-12 rounds. Typically, athletes will go into a heavy training period in a pre-bout camp lasting 6 to 9weeks. This study investigates the impact of 3weeks of repeated Wingate sprint interval training, performed on standard gym ergometer bikes, on skeletal muscle endurance and mitochondrial function. Ten male professional boxers (age: 26 ± 4years, height: 175 ± 5cm, weight: 70 ± 5kg) participated in the study. Baseline testing involved a NIRS monitor attached to the rectus femoris muscle prior to an incremental time to exhaustion test on a treadmill. After the treadmill test participants underwent a series of arterial occlusions to determine mitochondrial function post-volitional exhaustion. Participants then continued their own training for 3weeks and then repeated baseline testing. After the second testing session, participants undertook three weekly sprint sessions consisting of 3 × 30s maximal sprints with 60s recovery. Testing was repeated 3weeks later. The time to exhaustion increased by > 6% after 3weeks of sprint interval training as compared to baseline and control (p < 0.05). Skeletal muscle oxygen saturation (SmO2) at exhaustion was increased by 5.5% after 3weeks of sprint interval training as compared to baseline and control (p = 0.008). Skeletal muscle mitochondrial rate post exhaustion was increased by 160% after 3weeks of sprint interval training as compared to baseline and control (p < 0.001). The study demonstrated that SIT led to increased incremental time to exhaustion, higher SmO2 levels at volitional exhaustion and increased mitochondrial rates in professional boxers. These findings suggest that SIT should be an integral part of a boxe's conditioning regimen to improve performance and safety within the ring.

In vivo optical assessment of cerebral and skeletal muscle microvascular response to phenylephrine.

This study aimed to investigate the simultaneous response of the cerebral and skeletal muscle microvasculature to the same phenylephrine (PE) boluses. A hybrid optical system that combines hyperspectral near-infrared spectroscopy (hs-NIRS) and diffuse correlation spectroscopy (DCS) was used to monitor changes in tissue oxygenation and perfusion. Data were collected from the head and hind limb of seven male Sprague-Dawley rats while administering intravenous (IV) injections of PE or saline to all animals. The response to saline was used as a control. Skeletal muscle oxygenation decreased significantly after PE injection, while a statistically underpowered decrease in perfusion was observed, followed by an increase beyond baseline. Vascular conductance also decreased in the muscle reflecting the drug's vasoconstrictive effects. Tissue oxygenation and perfusion increased in the brain in response to PE. Initially, there was a sharp increase in cerebral perfusion but no changes in cerebral vascular conductance. Subsequently, cerebral flow and vascular conductance decreased significantly below baseline, likely reflecting autoregulatory mechanisms to manage the excess flow. Further, fitting an exponential function to the secondary decrease in cerebral perfusion and increase in muscular blood flow revealed a quicker kinetic response in the brain to adjust blood flow. In the skeletal muscle, PE caused a transient decrease in blood volume due to vasoconstriction, which resulted in an overall decrease in hemoglobin content and tissue oxygen saturation. Since PE does not directly affect cerebral vessels, this peripheral vasoconstriction shunted blood into the brain, resulting in an initial increase in oxygenated hemoglobin and oxygen saturation.

Young users of electronic cigarettes exhibit reduced cardiorespiratory fitness.

Electronic nicotine delivery systems, often referred to as e-cigarettes, are popular tobacco products frequently advertised as safer alternatives to traditional cigarettes despite preliminary data suggesting a potential negative cardiovascular impact. Cardiorespiratory fitness is a critical cardiovascular health marker that is diminished in individuals who consume traditional tobacco products. Whether the use of e-cigarettes impacts cardiorespiratory fitness is currently unknown. Thus, the purpose of this study was to investigate the impact of regular e-cigarette use on cardiorespiratory fitness in young healthy adults. Twenty-six users of e-cigarettes (ECU, 13 males, and 13 females; age: 24 ± 3 yr; e-cigarette usage 4 ± 2 yr) and 16 demographically matched nonusers (NU, 6 males, and 10 females; age: 23 ± 3 yr) participated in this study. Cardiorespiratory fitness was measured by peak oxygen consumption (V̇o2peak) during a cardiopulmonary exercise test. Measurements of chronotropic response, hemodynamic, oxygen extraction, and utilization were also evaluated. Our results suggest that regular users of e-cigarettes exhibited significantly lower peak oxygen consumption when compared with nonusers, even when controlled by fat-free mass and lean body mass. Hemodynamic changes were not different between both groups during exercise, whereas lower chronotropic responses and skeletal muscle oxygen utilization were observed in users of e-cigarettes. Results from the present study demonstrate that young, apparently healthy, regular users of e-cigarettes exhibit significantly reduced cardiorespiratory fitness, lower chronotropic response, and impaired skeletal muscle oxygen utilization during exercise. Overall, our findings contribute to the growing body of evidence that supports adverse effects of regular e-cigarette use on cardiovascular health.NEW & NOTEWORTHY E-cigarettes are tobacco products frequently used by youth and young adults. Little is known about the long-term health effects of their prolonged use. Results from the present study demonstrate that young, apparently healthy, regular users of e-cigarettes exhibit significantly reduced cardiorespiratory fitness, a marker of cardiovascular health and a predictor of all-cause mortality. We also identified that the young users of e-cigarettes present with lower chronotropic response and impaired skeletal muscle oxygen utilization during exercise.

Acute effects of manual breathing assist technique on lung volume and dyspnea in individuals with severe chronic obstructive pulmonary disease: A quasi-experimental study.

Manual breathing assist technique (MBAT) is a common physical therapy technique used to facilitate airway clearance and improve ventilation and oxygenation. The effects during and immediately after intervention in individuals with chronic obstructive pulmonary disease (COPD) are unknown. This study aimed to investigate the acute effects and potential mechanisms of MBAT on lung volume, dyspnea, and oxygenation in individuals with COPD. This non-randomized quasi-experimental pre-test/post-test study included participants from pulmonary rehabilitation programs at Tagami Hospital (COPD group) and a community exercise program (Healthy group). During a single session, MBAT was applied during the expiration of every breath for 10 minutes. Dyspnea and lung volumes (tidal volume; VT, inspiratory capacity; IC, inspiratory reserved capacity; IRV, expiratory reserve capacity; ERV) were collected at baseline and after MBAT. Pulse oximetry (SpO2), skeletal muscle oxygenation (SmO2), and oxy- and deoxy-hemoglobin (O2Hb and HHb) using near-infrared spectroscopy (NIRS) were collected at baseline, during, and after MBAT. Between-group comparisons were conducted using the Mann-Whitney U-test and chi-square analyses. Within-group changes before and after MBAT were analyzed using the Wilcoxon signed-rank test. The Kruskal-Wallis test was used to detect differences in NIRS variables in each phase and over time. Thirty participants with COPD, matched for age and sex, were included, with 15 individuals per group. The difference scores of VT, IRV, and IC were significantly higher in the Healthy group than in the COPD group, but improvements in dyspnea and SpO2 were significantly higher in the COPD group. Compared to baseline, ERV decreased significantly in both groups, with dyspnea and SpO2 improving significantly only in the COPD group. Inspiratory accessory muscle ΔO2Hb and ΔHHb were significantly higher and lower (respectively) during MBAT in the COPD group compared to the Healthy group. Additionally, only the COPD group had increased SmO2 during and after MBAT compared to baseline. MBAT in patients with COPD had acute physiological effects in reducing dyspnea by facilitating expiration and decreasing the recruitment of accessory respiratory muscles. MBAT may help individuals with COPD reduce dyspnea before exercise therapy in a pulmonary rehabilitation program.

Identifying the Mechanisms of a Peripherally Limited Exercise Phenotype in Patients With Heart Failure With Preserved Ejection Fraction.

We identified peripherally limited patients using cardiopulmonary exercise testing and measured skeletal muscle oxygen transport and utilization during invasive single leg exercise testing to identify the mechanisms of the peripheral limitation. Forty-five patients with heart failure with preserved ejection fraction (70±7 years, 27 females) completed seated upright cardiopulmonary exercise testing and were defined as having a (1) peripheral limitation to exercise if cardiac output/oxygen consumption (VO2) was elevated (≥6) or 5 to 6 with a stroke volume reserve >50% (n=31) or (2) a central limitation to exercise if cardiac output/VO2 slope was ≤5 or 5 to 6 with stroke volume reserve <50% (n=14). Single leg knee extension exercise was used to quantify peak leg blood flow (Doppler ultrasound), arterial-to-venous oxygen content difference (femoral venous catheter), leg VO2, and muscle oxygen diffusive conductance. In a subset of participants (n=36), phosphocreatine recovery time was measured by magnetic resonance spectroscopy to determine skeletal muscle oxidative capacity. Peak VO2 during cardiopulmonary exercise testing was not different between groups (central: 13.9±5.7 versus peripheral: 12.0±3.1 mL/min per kg; P=0.135); however, the peripheral group had a lower peak arterial-to-venous oxygen content difference (central: 13.5±2.0 versus peripheral: 11.1±1.6 mLO2/dL blood; P<0.001). During single leg knee extension, there was no difference in peak leg VO2 (P=0.306), but the peripherally limited group had greater blood flow/VO2 ratio (P=0.024), lower arterial-to-venous oxygen content difference (central: 12.3±2.5 versus peripheral: 10.3±2.2 mLO2/dL blood; P=0.013), and lower muscle oxygen diffusive conductance (P=0.021). A difference in magnetic resonance spectroscopy-derived phosphocreatine recovery time was not detected (P=0.199). Peripherally limited patients with heart failure with preserved ejection fraction identified by cardiopulmonary exercise testing have impairments in oxygen transport and utilization at the level of the skeletal muscle quantified by invasive knee extension exercise testing, which includes an increased blood flow/V̇O2 ratio and poor muscle diffusive capacity. URL: https://www.clinicaltrials.gov; Unique identifier: NCT04068844.

Microvascular Reactivity Is Greater Following Blood Flow Restriction Resistance Exercise Compared with Traditional Resistance Exercise.

Perlet, MR, Hosick, PA, Licameli, N, and Matthews, EL. Microvascular reactivity is greater following blood flow restriction resistance exercise compared with traditional resistance exercise. J Strength Cond Res XX(X): 000-000, 2024-Chronic blood flow restriction (BFR) resistance exercise can improve muscular strength, hypertrophy, and microvasculature function, but the acute microvascular effects are unknown. We aimed to test the effects of acute BFR resistance exercise on postexercise microvascular reactivity in an exercising muscle and nonexercising muscle compared with traditional resistance exercise (TRE). Twenty-five adults (men = 14, women = 11, age: 22 ± 3 years, body mass: 71.69 ± 14.49 kg, height: 170 ± 10 cm) completed barbell back squat 1-repetition maximum (1RM) testing followed by 2 randomized and counterbalanced resistance exercise visits separated by ≥48 hours. The 2 visits involved either BFR (4 sets of 30-15-15-15 repetitions at 30% 1RM, with 60-second rest intervals) or TRE (4 sets of 10 repetitions at 70% 1RM, 60-second rest intervals). During each exercise visit, a pre- and postbarbell back squat vascular occlusion test was performed using near-infrared spectroscopy to measure skeletal muscle oxygen (SmO2) in the vastus lateralis (VL) and flexor carpi radialis (FCR). Two-way repeated-measures ANOVA found an interaction effect (p = 0.020) for SmO2 reactivity in the VL. Post hoc analysis found greater reactive hyperemia postexercise in the VL for the BFR condition (p < 0.001) but not the TRE condition (p ≥ 0.05). There were no time, condition, or interaction effects (all p > 0.05) for the same analysis in the FCR. This analysis suggests that BFR, but not TRE, lead to acutely improved microvasculature function. Moreover, it suggests that the effects of BFR resistance exercise are local to the exercised or occluded limb and not systemic.

Reliability of near-infrared spectroscopy in measuring muscle oxygenation during squat exercise

Monitoring of changes in skeletal muscle oxygenation during exercise has increased in recent years. Tissue oxygenation, which is related to fatigue and muscle hypertrophy, is often measured using near-infrared spectroscopy (NIRS). ObjectivesThis study aimed to determine the test-retest reliability of a non-portable NIRS (NIRO200Nx) during the full-squat exercise and recovery in young healthy men. DesignTwenty-five male participants (21.8 ± 2.6 years) were recruited for this original research. Each participant completed an 8-repetition test with a load that elicited a velocity of 1 m·s−1. The test was conducted twice, with a 48-hour washout period between sessions. MethodsThe NIRS measured the changes of oxygenated-Hemoglobin (O2Hb), deoxygenated-Hemoglobin (HHb) and Tissue Oxygenation Index (TOI) in both Vastus Lateralis and Vastus Medialis during rest, exercise, and recovery. Coefficient of Variation (CV), Standard Error Measurement (SEM) and Intraclass Correlation Coefficient (ICC) were used to evaluate the reliability of the data. Significance was set at p < 0.05. ResultsThe results indicated that TOI had good to acceptable absolute reliability (CVTOI = 2.7–10.2 %). A good relative relativity for the overall test was found for Vastus Medialis O2Hb (ICC = 0.851), HHb (ICC = 0.852), and TOI (ICC = 0.864), and Vastus Lateralis O2Hb (ICC = 0.898), HHb (ICC = 0.899), and TOI (ICC = 0.897). ConclusionsWe conclude that NIRO200Nx is a reliable instrument for measuring muscle oxygen saturation through the TOI parameter in not-to-failure dynamic resistance exercises (1 set of 8 reps against ∼40 % 1 repetition maximum). Tissue oxygenation assessment could be a new way of individualizing exercise through dynamic resistance exercises.

The effect of self-identified arm dominance on exercising forearm hemodynamics and skeletal muscle desaturation.

The human forearm model is commonly employed in physiological investigations exploring local vascular function and oxygen delivery; however, the effect of arm dominance on exercising forearm hemodynamics and skeletal muscle oxygen saturation (SmO2) in untrained individuals is poorly understood. Therefore, the purpose of this study was to explore the effect of self-identified arm dominance on forearm hemodynamics and SmO2 in untrained individuals during submaximal, non-ischemic forearm exercise. Twenty healthy individuals (23±4 years, 50% female; 80% right-handed) completed three-minute bouts of supine rhythmic (1 second contraction: 2 second relaxation duty cycle) forearm handgrip exercise at both absolute (10kg; 98N) and relative (30% of maximal voluntary contraction) intensities in each forearm. Beat-by-beat measures of forearm blood flow (FBF; ml/min), mean arterial blood pressure (MAP; mmHg) and flexor digitorum superficialis SmO2 (%) were obtained throughout and averaged during the final 30 seconds of rest, exercise, and recovery while forearm vascular conductance was calculated (FVC; ml/min/100mmHg). Data are Δ from rest (mean±SD). Absolute force production did not differ between non-dominant and dominant arms (97±11 vs. 98±13 N, p = 0.606) whereas relative force production in females did (69±24 vs. 82±25 N, p = 0.001). At both exercise intensities, FBFRELAX, FVCRELAX, MAPRELAX, and the time constant tau for FBF and SmO2 were unaffected by arm dominance (all p>0.05). While arm dominance did not influence SmO2 during absolute intensity exercise (p = 0.506), the non-dominant arm in females experienced an attenuated reduction in SmO2 during relative intensity exercise (-14±10 vs. -19±8%, p = 0.026)-though exercise intensity was also reduced (p = 0.001). The present investigation has demonstrated that arm dominance in untrained individuals does not impact forearm hemodynamics or SmO2 during handgrip exercise.

Interaction of macro- and microvascular function underlies brachial artery flow-mediated dilation in humans.

Brachial artery flow-mediated dilation (BAFMD) is induced by hyperemic wall shear rate (WSR) following forearm ischemia. In older adults, there appears to be a reduced brachial hyperemic WSR and altered stimulus-response relationship compared with young adults. However, it is unclear if an altered forearm microvascular response to ischemia influences brachial hyperemic WSR in older adults. We determined associations between brachial hyperemic WSR and forearm skeletal muscle oxygen saturation in young and older adults. Healthy young (n = 17, 29 ± 7 yr) and older (n = 32, 65 ± 4 yr) adults participated in the study. BAFMD by a multigate spectral Doppler system and forearm skeletal muscle oxygen saturation by near-infrared spectroscopy were concurrently measured. When compared with the young, older adults showed reduced oxygen extraction kinetics (OE, 0.15 [0.12-0.17] vs. 0.09 [0.05-0.12]%s-1) and magnitude (So2deficit, 3,810 ± 1,420 vs. 2,723 ± 1,240%s) during ischemia, as well as oxygen resaturation kinetics (So2slope, 2.5 ± 0.7 vs. 1.7 ± 0.7%s-1) upon reperfusion (all P < 0.05). When OE in the young and So2slope in older adults were stratified by their median values, young adults with OE above the median had greater hyperemic WSR parameters compared with those below the median (P < 0.05), but So2slope in older adults did not show clear differences in hyperemic WSR parameters between those above/below the median. This study demonstrates that, in addition to a reduced microvascular response to ischemia, there may be a dissociation between microvascular response to ischemia and brachial hyperemic WSR in older adults, which may result in a further impairment of BAFMD in this cohort.NEW & NOTEWORTHY Microvascular response to ischemia and subsequent reperfusion is diminished in older adults compared with the young. Furthermore, there appears to be a dissociation between the microvascular response to ischemia and brachial hyperemic WSR in older adults, which may further disturb the BAFMD process in this cohort. A reduced BAFMD in older adults may be a result of multiple alterations occurring both at macro- and microcirculation.

#1553 Effects of proteinuria on muscle oxygenation and microvascular reactivity in patients with pre-dialysis CKD: a post-hoc analysis

Abstract Background and Aims Vascular dysfunction is a hallmark of CKD. Previous studies showed an impaired microvascular reactivity in the skeletal muscles, which deteriorates in advanced CKD stages. This analysis aims to examine the impact of proteinuria on skeletal muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with pre-dialysis CKD. Method 66 patients with CKD stage 2-4 were included in this post-hoc analysis; 24-h urine samples were used for evaluation of proteinuria. Continuous measurement of muscle oxygenation [tissue saturation index (TSI%)] via near-infrared-spectroscopy at rest, during occlusion-reperfusion and during a 3-min handgrip exercise (at 35% of maximal-voluntary-contraction). Results The study groups were similar in terms of age (proteinuric vs nonproteinuric: 68.4 ± 10.6 vs 67.2 ± 10.8; p = 0.676), eGFR (41.3 ± 18.9 vs 46.3 ± 14.8; p = 0.248) and BMI (28.4 ± 4.9 vs 28.1 ± 4.8; p = 0.803). Resting muscle oxygenation did not differ between study groups (proteinuric vs nonproteinuric: 63.35 ± 4.09 vs 62.34 ± 3.21; p = 0.280). During occlusion, proteinuric CKD patients had marginally lower TSI occlusion magnitude (25.77 ± 7.87 vs 29.95 ± 10.34; p = 0.074) but no difference in occlusion slope (−0.09 ± .03 vs -.10 ± .04; p = 0.134). During reperfusion, the TSI reperfusion slopes were significantly lower in proteinuric CKD (slope to max 1.03 ± .45 vs 1.39 ± 0.69; p = 0.035 and 10-sec slope: 1.34 ± .63 vs 1.92 ± .75; p = 0.002); hyperemic response was numerically lower in proteinuric CKD (7.13 ± 4.27 vs 8.89 ± 4.68; p = 0.131). Finally, during exercise no differences were detected in the average muscle oxygenation between-group (10.76 ± 6.05 vs 10.65 ± 5.39; p = 0.943). Conclusion Although no differences in resting muscle oxygenation were detected, CKD patients with proteinuria showed more impaired skeletal muscle oxidative capacity (as suggested by lower TSI magnidute during occlusion), and miscrovascular reactivity during reperfusion.

Sourcebook update: using near-infrared spectroscopy to assess skeletal muscle oxygen uptake.

Monitoring the metabolic cost or oxygen consumption associated with rest and exercise is crucial to understanding the impact of disease or physical training on the health of individuals. Traditionally, measuring the skeletal muscle oxygen cost associated with exercise/muscle contractions can be rather expensive or invasive (i.e., muscle biopsies). More recently, specific protocols designed around the use of near-infrared spectroscopy (NIRS) have been shown to provide a quick, noninvasive easy-to-use tool to measure skeletal muscle oxygen consumption ([Formula: see text]). However, the data and results from NIRS devices are often misunderstood. Thus the primary purpose of this sourcebook update is to provide several experimental protocols students can utilize to improve their understanding of NIRS technology, learn how to analyze results from NIRS devices, and better understand how muscle contraction intensity and type (isometric, concentric, or eccentric) influence the oxygen cost of muscle contractions.NEW & NOTEWORTHY Compared to traditional methods, near-infrared spectroscopy (NIRS) provides a relatively cheap and easy-to-use noninvasive technique to measure skeletal muscle oxygen uptake following exercise. This laboratory not only enables students to learn about the basics of NIRS and muscle energetics but also addresses more complex questions regarding skeletal muscle physiology.

Relationship among muscle strength, muscle endurance, and skeletal muscle oxygenation dynamics during ramp incremental cycle exercise.

Peak oxygen uptake (VO2), evaluated as exercise tolerance, is a strong predictor of life prognosis regardless of health condition. Several previous studies have reported that peak VO2 is higher in those with a greater decrease in muscle oxygen saturation (SmO2) in the active muscles during incremental exercise. However, the skeletal muscle characteristics of individuals exhibiting a greater decrease in SmO2 during active muscle engagement in incremental exercise remain unclear. This study aimed to clarify the relationship among muscle strength, muscle endurance, and skeletal muscle oxygenation dynamics in active leg muscles during incremental exercise. Twenty-four healthy young men were included and categorized into the non-moderate-to-high muscular strength and endurance group (those with low leg muscle strength, endurance, or both; n = 11) and the moderate-to-high muscular strength and endurance group (those with both moderate-to-high leg muscle strength and endurance; n = 13). All participants underwent cardiopulmonary exercise testing combined with near-infrared spectroscopy to assess whole-body peak VO2 and the change in SmO2 at the lateral vastus lateralis from rest to each exercise stage as skeletal muscle oxygenation dynamics. A linear mixed-effects model, with the change in SmO2 from rest to each stage as the dependent variable, individual participants as random effects, and group and exercise load as fixed effects, revealed significant main effects for both group (P = 0.001) and exercise load (P < 0.001) as well as a significant interaction between the two factors (P < 0.001). Furthermore, multiple-comparison test results showed that the change in SmO2 from rest to 40%-100% peak VO2 was significantly higher in the moderate-to-high muscular strength and endurance group than in the non-moderate-to-high muscular strength and endurance group. Maintaining both muscle strength and endurance at moderate or higher levels contributes to high skeletal muscle oxygenation dynamics (i.e., greater decrease in SmO2) during moderate- or high-intensity exercise.

Population pharmacokinetic modelling and simulation of tranexamic acid in adult trauma patients.

The aim of this study is to describe the disposition of tranexamic acid (TXA) in adult trauma patients and derive a dosing regimen that optimizes exposure based on a predefined exposure target. We performed a population pharmacokinetic (popPK) analysis of participants enrolled in the Tranexamic Acid Mechanisms and Pharmacokinetics in Traumatic Injury (TAMPITI) trial (≥18 years with traumatic injury, given ≥1 blood product and/or requiring immediate transfer to the operating room) who were randomized to a single dose of either 2 or 4g of TXA ≤2h from time of injury. PopPK analysis was conducted using nonlinear mixed-effects modelling (NONMEM). Simulations were then performed using the final model to generate estimated plasma TXA concentrations in 1000 simulated participants. Dosing schemes were evaluated to determine maintenance of TXA plasma concentrations >10mg/L for ≥8h after administration of the initial dose. TXA PK was best described by a two-compartment model with proportional residual error and allometric scaling on all parameters. Platelet count, skeletal muscle oxygen saturation measured by near-infrared spectroscopy and interleukin-8 concentration were significant covariates on TXA clearance. Based on simulations, a 2g IV bolus dose, repeated 3h later, best achieved the target exposure. According to simulations from a popPK model of TXA, a 2g IV bolus with a repeated dose 3h later would be most likely to maintain concentrations >10mg/L for 8h in >95% of adult trauma patients and should be considered for patients with ongoing haemorrhage.

EFFECTS OF PROTEINURIA ON MUSCLE OXYGENATION AND MICROVASCULAR REACTIVITY IN PATIENTS WITH PRE-DIALYSIS CKD: A POST-HOC ANALYSIS

Objective: Vascular dysfunction is a hallmark of CKD. Previous studies showed an impaired microvascular reactivity in the skeletal muscles, which deteriorates in advanced CKD stages. This analysis aims to examine the impact of proteinuria on skeletal muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with pre-dialysis CKD. Design and method: 66 patients with CKD stage 2-4 were included in this post-hoc analysis; 24-h urine samples were used for evaluation of proteinuria. Continuous measurement of muscle oxygenation [tissue saturation index (TSI%)] via near-infrared-spectroscopy at rest, during occlusion-reperfusion and during a 3-min handgrip exercise (at 35% of maximal-voluntary-contraction). Results: The study groups were similar in terms of age (proteinuric vs nonproteinuric: 68.4±10.6 vs 67.2±10.8; p=0.676), eGFR (41.3±18.9 vs 46.3±14.8; p=0.248) and BMI (28.4±4.9 vs 28.1±4.8; p=0.803). Resting muscle oxygenation did not differ between study groups (proteinuric vs nonproteinuric: 63,35±4,09 vs 62,34±3,21; p=0.280). During occlusion, proteinuric CKD patients had marginally lower TSI occlusion magnitude (25,77±7,87 vs 29,95±10,34; p=0.074) but no difference in occlusion slope (-0,09±.,03 vs -,10±.,04; p=0.134). During reperfusion, the TSI reperfusion slopes were significantly lower in proteinuric CKD (slope to max 1,03±.,45 vs 1,39±.0,69; p=0.035 and 10-sec slope: 1,34±.,63 vs 1,92±.,75; p=0.002); hyperemic response was numerically lower in proteinuric CKD (7,13±.4,27 vs 8,89±.4,68; p=0.131). Finally, during exercise no differences were detected in the average muscle oxygenation between-group (10,76±6,05 vs 10,65±5,39; p=0.943). Conclusions: Although no differences in resting muscle oxygenation were detected, CKD patients with proteinuria showed more impaired skeletal muscle oxidative capacity (as suggested by lower TSI magnidute during occlusion), and miscrovascular reactivity during reperfusion.

Contributors to Diminished Cardiorespiratory Fitness in Young Users of Electronic Cigarettes

Background: Cardiorespiratory fitness, an independent marker of cardiovascular health, represents the ability of respiratory, cardiovascular, and muscular systems to effciently deliver and utilize oxygen (O2) during exercise. Recently, reduced cardiorespiratory fitness was identified in young and healthy, regular users of electronic (e-) cigarettes; however, its limiting factors are not established. Thus, the purpose of this study was to investigate the contributors to impaired cardiorespiratory fitness in young regular users of e-cigarettes. Methods: An evaluation of hemodynamics, chronotropic response, and oxygen utilization during exercise was completed in nineteen regular users of e-cigarettes (EU, age: 23±3 yr; e-cigarette usage 4±2 yr.) and sixteen demographically matched non-users (NU, age: 23±3 yr.). Hemodynamics were accessed via a non-invasive signal morphology impedance cardiography device, while chronotropic responses were measured as changes in peak heart rate (HR). Oxygen extraction ratio (difference in arterial and venous O2 content) at baseline and peak exercise was also recorded. Fold changes from rest to peak exercise were assessed to provide insight into potential factors that limit cardiorespiratory fitness. Results: At peak exercise, users of e-cigarettes exhibited significantly higher chronotropic incompetence ( p=0.033) and lower ( p=0.047) peak HR than non-users, with no differences in other hemodynamic assessments. Significantly ( p=0.025) lower skeletal muscle O2 extraction (EU=51±11 vs. NU=61±10%) was also observed in users of e-cigarettes during peak exercise. Fold changes in chronotropic (HR; p=0.915) and hemodynamic (cardiac output; p=0.279) responses were similar between both groups, while significant ( p=0.048) differences in oxygen extraction ratio were identified between the users of e-cigarettes (0.5±0.3 fold change) and non-users (0.8±0.3 fold change). Conclusions: Results from our study demonstrate that young, regular users of e-cigarettes exhibit abnormal chronotropic responses and impaired skeletal muscle oxygen utilization during exercise when compared to non-users, suggesting reduced cardiovascular and muscle health. Overall, our findings contribute to the growing body of evidence that supports the negative effects of regular e-cigarette use on young individuals. Supported in part by a Rapid Response Project NIDA/FDA (PRM). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.