Recovery Rate Constant Research Articles

Near-InfraRed Spectroscopy Provides a Reproducible Estimate of Muscle Aerobic Capacity, but Not Whole-Body Aerobic Power.

Near-infrared spectroscopy (NIRS) during repeated limb occlusions is a noninvasive tool for assessing muscle oxidative capacity. However, the method's reliability and validity remain under investigation. This study aimed to determine the reliability of the NIRS-derived mitochondrial power of the musculus vastus lateralis and its correlation with whole-body (cycling) aerobic power (V̇O2 peak). Eleven healthy active men (28 ± 10 y) twice (2 days apart) underwent repeated arterial occlusions to induce changes in muscle oxygen delivery after 15 s of electrical muscle stimulation. The muscle oxygen consumption (mV̇O2) recovery time and rate (k) constants were calculated from the NIRS O2Hb signal. We assessed the reliability (coefficient of variation and intraclass coefficient of correlation [ICC]) and equivalency (t-test) between visits. The results showed high reproducibility for the mV̇O2 recovery time constant (ICC = 0.859) and moderate reproducibility for the k value (ICC = 0.674), with no significant differences between visits (p > 0.05). NIRS-derived k did not correlate with the V̇O2 peak relative to body mass (r = 0.441, p = 0.17) or the absolute V̇O2 peak (r = 0.366, p = 0.26). In conclusion, NIRS provides a reproducible estimate of muscle mitochondrial power, which, however, was not correlated with whole-body aerobic capacity in the current study, suggesting that even if somewhat overlapping, not the same set of factors underpin these distinct indices of aerobic capacity at the different (peripheral and whole-body systemic) levels.

Analysis of electrical stimulation and voluntary muscle contraction on skeletal muscle oxygen uptake and mitochondrial recovery using near-infrared spectroscopy.

This investigation was to compare differences in skeletal muscle oxygen consumption ([Formula: see text]) and mitochondrial recovery between voluntary (VOL) and electrically stimulated (ES) plantarflexion contractions. Twelve men and women (26 ± 4.0years; 171.8 ± 5.1cm; 74.0 ± 13.7kg) were seated in a chair with their right knee fully extended and right foot secured to a force transducer. ES electrodes and a near-infrared spectroscopy device were placed on the gastrocnemius. Participants performed ES plantarflexion contractions across a range of stimulation intensities at frequencies of 1 and 2Hz and similar VOL contractions. Cuff occlusion occurred immediately following each series of contractions to measure [Formula: see text]. A standardized mitochondrial function assessment protocol was also performed to calculate K-constants between work-matched ES and VOL contractions. For mitochondrial assessments, there were no significant differences between ES and VOL rate constants (2.03 ± 0.98 vs. 1.25 ± 1.35min-1, p = 0.266). ES resulted in a significantly greater workrate-[Formula: see text] slope at 1Hz (0.007 ± 0.007 vs. 0.001 ± 0.002% [Formula: see text]/s/N, p = 0.014) and 2Hz (0.010 ± 0.010 vs. 0.001 ± 0.001% [Formula: see text]/s/N, p = 0.012), as well as a significantly greater workrate-[Formula: see text] Y-intercept at 2Hz (1.603 ± 1.513 vs. 0.556 ± 0.564% [Formula: see text]/s, p = 0.035) but not 1Hz (0.579 ± 0.448 vs. 0.442 ± 0.357% mV̇O2/s, p = 0.535) when compared to VOL. ES results in a significantly greater [Formula: see text] at similar work rates compared to VOL, however, the mitochondrial recovery rate constants were similar. The greater mVO2 with ES may partially contribute to the increased rate of fatigue during ES exercise in individuals with muscle paralysis.

Microvascular and oxidative stress responses to acute high-altitude exposure in prematurely born adults

Premature birth is associated with endothelial and mitochondrial dysfunction, and chronic oxidative stress, which might impair the physiological responses to acute altitude exposure. We assessed peripheral and oxidative stress responses to acute high-altitude exposure in preterm adults compared to term born controls. Post-occlusive skeletal muscle microvascular reactivity and oxidative capacity from the muscle oxygen consumption recovery rate constant (k) were determined by Near-Infrared Spectroscopy in the vastus lateralis of seventeen preterm and seventeen term born adults. Measurements were performed at sea-level and within 1 h of arrival at high-altitude (3375 m). Plasma markers of pro/antioxidant balance were assessed in both conditions. Upon acute altitude exposure, compared to sea-level, preterm participants exhibited a lower reperfusion rate (7 ± 31% vs. 30 ± 30%, p = 0.046) at microvascular level, but higher k (6 ± 32% vs. −15 ± 21%, p = 0.039), than their term born peers. The altitude-induced increases in plasma advanced oxidation protein products and catalase were higher (35 ± 61% vs. −13 ± 48% and 67 ± 64% vs. 15 ± 61%, p = 0.034 and p = 0.010, respectively) and in xanthine oxidase were lower (29 ± 82% vs. 159 ± 162%, p = 0.030) in preterm compared to term born adults. In conclusion, the blunted microvascular responsiveness, larger increases in oxidative stress and skeletal muscle oxidative capacity may compromise altitude acclimatization in healthy adults born preterm.

Determination of three stages for molybdenite flotation kinetics in seawater

ABSTRACT This research mainly investigated the flotation kinetics of molybdenite in seawater based on four flotation models. Molybdenite flotation presented an excellent agreement with the first-order model with rectangular distribution. The ultimate cumulative recovery (R ∞) and flotation rate constant (k) of molybdenite decreased in seawater, mainly due to the divalent cations, with the impact of Mg2+ being significantly greater than that of Ca2+. The addition of sodium silicate (SS) and sodium hexametaphosphate (SH) increased the flotation recovery and rate, probably due to the positive role of dispersants on preventing the attachment of seawater precipitates onto molybdenite surface. In addition, three different stages of flotation kinetics were proposed to reveal the molybdenite flotation for the first time, with the highest flotation recovery and rate being found at Stage I. However, seawater showed a negative role on Stage I, i.e. resulting in a longer duration and lower recovery, as compared to that in pure water. The addition of both SS and SH improved the flotation kinetics at Stage I, with SH being more significant. Therefore, it is more feasible to eliminate the negative effects of seawater on molybdenite flotation at the initial stage (Stage I).

Near-infrared Spectroscopy Estimation Of Combined Muscle Oxidative Capacity And Oxygen Diffusion Capacity In Humans

PURPOSE: Muscle oxygen uptake (mV̇O2) depends on both O2 supply (convective and diffusive O2 delivery) and O2 demand (ATP utilization rate and mitochondrial function). The mV̇O2 recovery rate constant (k) measured by near-infrared spectroscopy (NIRS), in the presence of non-limiting O2 availability, is associated with muscle oxidative capacity in vivo. However, when O2 availability is limiting, k may be limited by muscle O2 diffusing capacity (DmO2). We aimed to determine associations of: i) k obtained in different O2 availability conditions with ex vivo mitochondrial function and ii) the difference in k (∆k) between conditions of non-limiting and limiting O2 availability with capillary-to-fiber ratio (C:F). METHODS: 12 healthy participants volunteered (28 ± 5 yrs; V̇O2peak 37.1 ± 8.0 ml*kg-1*min-1). On visits 1 and 2, k of the vastus lateralis (VL) was measured by NIRS during 10-15 intermittent arterial occlusions performed immediately after moderate intensity constant work-rate exercise. The duration and timing of occlusions were manipulated to maintain TSI in a 10% range change either below (LOW) or above (HIGH) the mid-point of the functional range from a prolonged occlusion. ∆k is the difference between LOW and HIGH k measurements. On visit 3, the VL was biopsied to measure C:F and maximal O2 flux using saturating substrates for complexes I + II by high-resolution respirometry (HRR). RESULTS: O2 flux was 37.7 ± 10.6 and 56.8 ± 19.8 pmol*s-1*mg-1 wet weight in maximal ADP-stimulated phosphorylating state and maximal noncoupled state, respectively. C:F ratio ranged 2.15 to 2.49. k was greater in HIGH (3.15 ± 0.45 min-1) than in LOW (1.56 ± 0.79 min-1, p < 0.0001). k was significantly correlated with both HRR measurements in HIGH (r = 0.72 - 0.69), but not in LOW (r = -0.24 - -0.28). ∆k ranged -0.19 to -3.19 min-1, and was inversely correlated with C:F ratio (r = -0.68, p = 0.01). CONCLUSION: These data show that mV̇O2 recovery rate constant (k) reflected muscle oxidative capacity only under conditions of non-limiting O2 availability. Moreover, ∆k, obtained under different O2 availability conditions, was associated with C:F ratio, a mediator of DmO2. Thus, assessment of muscle k and ∆k using NIRS under HIGH and LOW TSI conditions provides a non-invasive window on both muscle oxidative capacity and muscle O2 diffusive capacity.

NIRS-Estimated Muscle Oxidative Capacity And Capillary-To-Fiber Ratio Differs By Sex And Muscle In Endurance Trained Athletes

The relationship between muscle oxidative capacity and muscle diffusing capacity (DmO2), and how this differs among muscles or by sex in endurance trained athletes in vivo is unknown. Estimates of muscle oxidative capacity and capillary-to-fiber ratio (C:F; a mediator of DmO2) can be assessed by near infra-red spectroscopy (NIRS): muscle oxidative capacity is proportional to the recovery rate constant (k) of muscle V̇O2, and C:F is proportional to the change in k (∆k) when tissue saturation (TSI) is reduced. PURPOSE: To determine the role of sex on k and ∆k in the vastus lateralis (VL) and medial gastrocnemius (GS) in endurance trained athletes. METHODS: Twenty-six competitive college-level endurance athletes volunteered: 14 women (20 ± 1 yrs) and 12 men (27 ± 7 yrs). The NIRS assessments were administered using controlled arterial occlusions to maintain TSI in ±5% bands at each of HIGH (averaging 87% of functional range) and LOW (24%) TSI. k was measured in HIGH and ∆k was calculated from the difference in k between HIGH and LOW. RESULTS: k was lower in females than males (mean difference [95% confidence interval]: -0.61[-0.12,-1.08] min-1, p = 0.014, partial ηp2 = 0.13) and lower in VL than GS (-0.83[-0.35,-1.31] min-1, p = 0.001, ηp2 = 0.22), but there was no muscle-by-sex interaction (p = 0.860) (Table). ∆k tended to be greater in females (-0.43[-0.98,0.13] min-1, p = 0.131, ηp2 = 0.05) and in GS (-0.40[0.95,0.16] min-1, p = 0.159, ηp2 = 0.05), but there was no interaction (p = 0.676). CONCLUSIONS: Overall, both GS and VL muscle oxidative capacity was lower in female than male endurance trained athletes with similar training history. We also found that oxidative capacity in medial GS was greater than VL in these endurance-trained athletes. In females, there was a trend towards greater NIRS-derived estimates of C:F, a mediator of DmO2, suggesting potential differential training adaptations in muscle oxidative capacity and DmO2 to achieve maximal myocellular oxidation rates between sexes.

Near-infrared spectroscopy estimation of combined skeletal muscle oxidative capacity and O2 diffusion capacity in humans.

The final steps of the O2 cascade during exercise depend on the product of the microvascular‐to‐intramyocyte PO2 difference and muscle O2 diffusing capacity (DmO2). Non‐invasive methods to determine DmO2 in humans are currently unavailable. Muscle oxygen uptake (mV˙O2) recovery rate constant (k), measured by near‐infrared spectroscopy (NIRS) using intermittent arterial occlusions, is associated with muscle oxidative capacity in vivo. We reasoned that k would be limited by DmO2 when muscle oxygenation is low (k LOW), and hypothesized that: (i) k in well oxygenated muscle (k HIGH) is associated with maximal O2 flux in fibre bundles; and (ii) ∆k (k HIGH – k LOW) is associated with capillary density (CD). Vastus lateralis k was measured in 12 participants using NIRS after moderate exercise. The timing and duration of arterial occlusions were manipulated to maintain tissue saturation index within a 10% range either below (LOW) or above (HIGH) half‐maximal desaturation, assessed during sustained arterial occlusion. Maximal O2 flux in phosphorylating state was 37.7 ± 10.6 pmol s−1 mg−1 (∼5.8 ml min−1 100 g−1). CD ranged 348 to 586 mm–2. k HIGH was greater than k LOW (3.15 ± 0.45 vs. 1.56 ± 0.79 min–1, P < 0.001). Maximal O2 flux was correlated with k HIGH (r = 0.80, P = 0.002) but not k LOW (r = –0.10, P = 0.755). Δk ranged –0.26 to –2.55 min–1, and correlated with CD (r = –0.68, P = 0.015). mV˙O2 k reflects muscle oxidative capacity only in well oxygenated muscle. ∆k, the difference in k between well and poorly oxygenated muscle, was associated with CD, a mediator of DmO2. Assessment of muscle k and ∆k using NIRS provides a non‐invasive window on muscle oxidative and O2 diffusing capacity. Key points We determined post‐exercise recovery kinetics of quadriceps muscle oxygen uptake (mV˙O2) measured by near‐infrared spectroscopy (NIRS) in humans under conditions of both non‐limiting (HIGH) and limiting (LOW) O2 availability, for comparison with biopsy variables.The mV˙O2 recovery rate constant in HIGH O2 availability was hypothesized to reflect muscle oxidative capacity (k HIGH) and the difference in k between HIGH and LOW O2 availability (∆k) was hypothesized to reflect muscle O2 diffusing capacity. k HIGH was correlated with phosphorylating oxidative capacity of permeabilized muscle fibre bundles (r = 0.80). ∆k was negatively correlated with capillary density (r = −0.68) of biopsy samples.NIRS provides non‐invasive means of assessing both muscle oxidative and oxygen diffusing capacity in vivo.

Bilateral NIRS measurements of muscle mitochondrial capacity: Feasibility and repeatability

BackgroundNon‐invasive determination of mitochondrial capacity via near infrared spectroscopy (NIRS) typically involves voluntary exercise of a single muscle group followed by as many as 26 brief ischemic cuff occlusions to determine a single recovery rate constant (k).PurposeTo determine the within‐ and between‐visit repeatability of a shortened bilateral NIRS protocol, and to establish the feasibility of hamstring k measurements.MethodsSixteen young (eight women, eight men; 22 ± 3 years) active adults underwent a bilateral electrical stimulation protocol in which multiple (n = 4) measurements of k for the vastus lateralis (VL) and medial hamstring (MH) muscles were determined on two visits. Repeatability (CV% and intraclass correlations, ICC) and equivalency across visits were assessed for both muscles.ResultsMean k values in the VL were consistent with published values and within‐visit ICCs were moderately high for both muscles in both sexes. In men, average k values on visit 2 were within 1% (VL muscle) and 5% (MH muscle) of the values on visit 1 (all p > 0.78). In women, average k values were 10%–15% lower on visit 2 (p = 0.01 and p = 0.15 for MH and VL) with the largest between‐visit differences in a subset of participants with the most days between visits.ConclusionsThis bilateral NIRS protocol is time efficient and provides valid estimates of k in both sexes and muscle groups with acceptable within‐visit repeatability. Lower than expected between‐visit repeatability in some participants reinforces the need for further investigation of this newly developed protocol to identify and control for experimental and behavioral sources of variation.

Post-exercise intramuscular O2 supply is tightly coupled with a higher proximal-to-distal ATP synthesis rate in human tibialis anterior.

Key points The post‐exercise recovery of phosphocreatine, a measure of the oxidative capacity of muscles, as assessed by 31P MR spectroscopy, shows a striking increase from distal to proximal along the human tibialis anterior muscle.To investigate why this muscle exhibits a greater oxidative capacity proximally, we tested whether the spatial variation in phosphocreatine recovery rate is related to oxygen supply, muscle fibre type or type of exercise.We revealed that oxygen supply also increases from distal to proximal along the tibialis anterior, and that it strongly correlated with phosphocreatine recovery. Carnosine level, a surrogate measure for muscle fibre type was not different between proximal and distal, and type of exercise did not affect the gradient in phosphocreatine recovery rate.Taken together, the findings of this study suggest that the post‐exercise spatial gradients in oxygen supply and phosphocreatine recovery are driven by a higher intrinsic mitochondrial oxidative capacity proximally. Phosphorus magnetic resonance spectroscopy (31P MRS) of human tibialis anterior (TA) revealed a strong proximo‐distal gradient in the post‐exercise phosphocreatine (PCr) recovery rate constant (k PCr), a measure of muscle oxidative capacity. The aim of this study was to investigate whether this k PCr gradient is related to O2 supply, resting phosphorylation potential, muscle fibre type, or type of exercise. Fifteen male volunteers performed continuous isometric ankle dorsiflexion at 30% maximum force until exhaustion. At multiple locations along the TA, we measured the oxidative PCr resynthesis rate (V PCr = k PCr × PCr depletion) by 31P MRS, the oxyhaemoglobin recovery rate constant (k O2Hb) by near infrared spectroscopy, and muscle perfusion with MR intravoxel incoherent motion imaging. The k O2Hb, k PCr, V PCr and muscle perfusion depended on measurement location (P < 0.001, P < 0.001, P = 0.032 and P = 0.003, respectively), all being greater proximally. The k O2Hb and muscle perfusion correlated with k PCr (r = 0.956 and r = 0.852, respectively) and V PCr (r = 0.932 and r = 0.985, respectively), the latter reflecting metabolic O2 consumption. Resting phosphorylation potential (PCr/inorganic phosphate) was also higher proximally (P < 0.001). The surrogate for fibre type, carnosine content measured by 1H MRS, did not differ between distal and proximal TA (P = 0.884). Performing intermittent exercise to avoid exercise ischaemia, still led to larger k PCr proximally than distally (P = 0.013). In conclusion, the spatial k PCr gradient is strongly associated with the spatial variation in O2 supply. It cannot be explained by exercise‐induced ischaemia nor by fibre type. Our findings suggest it is driven by a higher proximal intrinsic mitochondrial oxidative capacity, apparently to support contractile performance of the TA.

Is Lockdown Effective in Limiting SARS-CoV-2 Epidemic Progression?-a Cross-Country Comparative Evaluation Using Epidemiokinetic Tools.

BackgroundTo date, the risk/benefit balance of lockdown in controlling severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) epidemic is controversial.ObjectiveWe aimed to investigate the effectiveness of lockdown on SARS-CoV-2 epidemic progression in nine different countries (New Zealand, France, Spain, Germany, the Netherlands, Italy, the UK, Sweden, and the USA).DesignWe conducted a cross-country comparative evaluation using a susceptible-infected-recovered (SIR)-based model completed with pharmacokinetic approaches.Main MeasuresThe rate of new daily SARS-CoV-2 cases in the nine countries was calculated from the World Health Organization’s published data. Using a SIR-based model, we determined the infection (β) and recovery (γ) rate constants; their corresponding half-lives (t1/2β and t1/2γ); the basic reproduction numbers (R0 as β/γ); the rates of susceptible S(t), infected I(t), and recovered R(t) compartments; and the effectiveness of lockdown. Since this approach requires the epidemic termination to build the (I) compartment, we determined S(t) at an early epidemic stage using simple linear regressions.Key ResultsIn New Zealand, France, Spain, Germany, the Netherlands, Italy, and the UK, early-onset stay-at-home orders and restrictions followed by gradual deconfinement allowed rapid reduction in SARS-CoV-2-infected individuals (t1/2β ≤ 14 days) with R0 ≤ 1.5 and rapid recovery (t1/2γ ≤ 18 days). By contrast, in Sweden (no lockdown) and the USA (heterogeneous state-dependent lockdown followed by abrupt deconfinement scenarios), a prolonged plateau of SARS-CoV-2-infected individuals (terminal t1/2β of 23 and 40 days, respectively) with elevated R0 (4.9 and 4.4, respectively) and non-ending recovery (terminal t1/2γ of 112 and 179 days, respectively) was observed.ConclusionsEarly-onset lockdown with gradual deconfinement allowed shortening the SARS-CoV-2 epidemic and reducing contaminations. Lockdown should be considered as an effective public health intervention to halt epidemic progression.

Ammonia volatilization from flooded rice soil using CAS and OSC methods

Ammonia (NH3-N) volatilization is an important process of nitrogen loss from crop production systems. An essential step in mathematical modeling is the determination of rate constants of urea reactions in soils. Accordingly, an experiment was conducted and reaction rate constant was estimated using two methods of ammonia recovery from urea applied to flooded rice field. Open Static Chamber (OSC) method is very simple and easy to implement in the field whereas Compressed Air Supply (CAS) method is costly and normally used in laboratory conditions. We adapted the CAS method for implementing in the field. The ammonia recovery from both the methods is approximately same and the observed ammonia volatilization was used for estimating reaction rate constants. The estimation of ammonia recovery and reaction rate constants did not vary significantly between the methods, viz. OSC and CAS. The partial differential equations representing nitrogen reaction process were solved using risk solver platform in the MS-EXCEL environment.

Serum Acylglycerols Inversely Associate with Muscle Oxidative Capacity in Severe COPD.

Chronic obstructive pulmonary disease (COPD) is associated with altered metabolism and body composition that accompany poor outcomes. We aimed to determine whether metabolic derangements in COPD are associated with skeletal muscle deconditioning and/or physical inactivity, independent of pulmonary obstruction. We characterized serum metabolites associated with muscle oxidative capacity or physical activity in 44 COPD patients (forced expiratory volume in 1 s [FEV1] = 61% ± 4% predicted) and 63 current and former smokers with normal spirometry (CON) (FEV1 = 93% ± 2% predicted). Medial gastrocnemius oxidative capacity was assessed at rest from the recovery rate constant (k) of muscle oxygen consumption using near-infrared spectroscopy. Step counts and physical activity (average vector magnitude units [VMU] per minute) were measured over 5-7 d using triaxial accelerometry. Untargeted prime and lipid metabolites were measured using liquid chromatography and mass spectrometry. Muscle k (1.12 ± 0.05 vs 1.68 ± 0.06 min, P < 0.0001, d = 1.58) and VMU per minute (170 ± 26 vs 450 ± 50 VMU per minute, P = 0.004, d = 1.04) were lower in severe COPD (FEV1 < 50% predicted, n = 14-16) compared with CON (n = 56-60). A total of 129 prime metabolites and 470 lipids with known identity were quantified. Using sex as a covariate, lipidomics revealed 24 differentially expressed lipids (19 sphingomyelins) in COPD, consequent to a diminished sex difference of sphingomyelins in COPD (false discovery rate [FDR] < 0.05, n = 44). Total, and some individual, fatty acid concentrations were greater in severe COPD than CON (FDR < 0.05, n = 16, d = 0.56-1.02). After adjusting for FEV1% predicted, we observed that grouped diacylglycerides (ρ = -0.745, FDR = 0.03) and triacylglycerides (ρ = -0.811, FDR = 0.01) were negatively associated with muscle oxidative capacity, but not physical activity, in severe COPD (n = 14). Strong negative associations relate impaired mitochondrial function to the accumulation of serum aclyglycerides in severe COPD.

Skeletal Muscle Mitochondrial Plasticity Is Reduced In Liver Transplant Recipients

PURPOSE Sarcopenic obesity is a hallmark of liver transplant recipients, of which the mechanisms are not yet fully understood. Decline in mitochondrial plasticity could play a mechanistic role in muscle wasting, loss of strength, and increased adiposity via impaired energy substrate utilization. The purpose of this study is to determine if skeletal muscle mitochondrial plasticity is reduced in liver transplant (LT) recipients. METHODS In this prospective cohort study, 15 LT patients (Mean±SD; Age: 58±10 years; months since transplant: 55±81 months) and 10 age matched healthy controls (Age: 55±4 years), underwent assessment of mitochondrial oxidative capacity of the wrist flexor muscle group. Near infrared spectroscopy coupled with repeated, transient arterial occlusions, measured the recovery kinetics of oxygen consumption following a 10 second bout of hand grip exercise. Post exercise metabolic recovery rate constant was calculated and reported as an index of mitochondrial oxidative capacity. RESULTS Post exercise metabolic recovery rates were significantly greater in LT recipients (Mean±SEM; Recovery Time Constant: 72±7 s) compared to HC (51±4 s; p=0.03) indicative of diminished mitochondrial plasticity in this patient cohort (Figure 1). CONCLUSION Skeletal muscle mitochondrial plasticity is reduced in LT patients compared to matched healthy controls. Further investigations are warranted to determine the role of mitochondrial dysfunction in the development of sarcopenic obesity and frailty following LT.

Association between muscle aerobic capacity and whole-body peak oxygen uptake.

Decline in skeletal muscle mitochondrial oxidative capacity (MOC) is associated with reduced aerobic capacity and increased risk ofcardiovascular and metabolicdisease. Measuring skeletal muscle MOC may be an alternative method to assess aerobic capacity, especiallyfor individuals unable to perform a whole-body maximum oxygen uptake protocol. In this study, linear regression analysis in two leg muscles was performed to determine whether MOC values could be used to predict whole-body peak oxygen uptake. MOC was measured with near infrared spectroscopy (NIRS) inthemedial gastrocnemius (MG) and vastus lateralis (VL) musclesof 26 participants (age, 27.1 ± 5.8years old). Whole-body peak oxygen uptake (VO2 peak) was determinedby indirect calorimetry during a continuous ramp protocol on a cycle ergometer. VO2 peak values were significantly correlated with the muscle recovery rate constant (k)ofthe MG (kMG,r = 0.59;p < 0.01) and VL (kVL,r = 0.63; p < 0.01) muscles. Summingrecovery rate constantsof both muscles together (kMG + kVL)improved thestrength of thecorrelation with VO2 peak (r = 0.78;p < 0.0001)andcouldexplain amajorityof the variance(R2 = 0.61)between the two measurements. Data suggest that NIRS can provide reliable MOC measurements on two leg muscles that correlate well with whole-body peak oxygen uptake.

Serum Acylglyceride Metabolites are Negatively Associated with Muscle Oxidative Capacity, but Not with Physical Activity, in Severe COPD

RATIONALEChronic obstructive pulmonary disease (COPD) is associated with altered metabolism and body composition that accompany worse outcomes. Serum lipid metabolites are dysregulated in COPD (e.g. sphingolipids, polyunsaturated fatty acids, ceramides). Loss of skeletal muscle mitochondrial oxidative capacity is implicated in mediating the association between hyperlipidemia and COPD. As both oxidative capacity and physical activity are negatively associated with COPD severity, this study aimed to determine whether lipid dysregulation in COPD was associated with muscle oxidative capacity and/or physical inactivity. We hypothesized that alteration of lipid metabolites in COPD would be associated with muscle oxidative capacity, independent of pulmonary function.METHODSCurrent and former smokers with COPD (n=44, FEV1=61±4%pred) and without COPD (CON) (n=63, FEV1=93±2%pred) volunteered. Untargeted prime and lipid metabolites were measured using liquid chromatography and mass spectrometry. Medial gastrocnemius oxidative capacity was assessed at rest from the recovery rate constant (k) of muscle oxygen consumption using near‐infrared spectroscopy. Daily step count and physical activity (average vector magnitude units (VMU)/min) were measured over 7 days by waist‐worn triaxial accelerometer.RESULTSThe k value (1.12±0.05 vs. 1.68±0.06 min−1, P&lt;0.0001) and VMU/min (170±26 vs. 450±50 VMU/min, P=0.004) were lower in severe COPD (FEV1&lt;50%pred, n=14–16) compared with CON. 129 prime metabolites and 470 lipids with known identity were quantified. Using sex as a covariate, lipidomics revealed that 24 lipids (19 sphingomeylins) were differentially expressed in COPD, consequent to a diminished sex difference of sphingomeylins in COPD (FDR&lt;0.05). Total, and some individual, fatty acid concentrations were greater in severe COPD than in CON (FDR&lt;0.05). After adjusting for FEV1%pred, we observed that grouped diacylglyceride (DG; Spearman’s rho = −0.745, FDR=0.03) and triacylglyceride (TG; rho = −0.811, FDR=0.01) were negatively associated with muscle oxidative capacity, but not physical activity, in severe COPD.DISCUSSIONWe found 24 lipids, including 19 sphingomyelins, increased in COPD with sex as covariant; and that sex‐dependent differences in sphingomyelin in CON were diminished COPD. This may contribute to more rapid progression of COPD in women than in men. Strong negative associations between blood lipids and muscle oxidative capacity, but not physical activity, suggest that impaired mitochondrial function may play a role in the accumulation of serum aclyglycerides in severe COPD. These data provide a strong rationale for targeting mitochondrial deficits by exercise training, or other means, to improve outcomes in COPD.Support or Funding InformationShenzhen Technology University (RL); VA MERT I01 BX00435, R01HL111437, R01HL129727 (TKH); Swiss National Science Foundation P300P3_151705 (AA); ATS‐2014‐03, Pulmonary Education and Research Foundation (HBR); R01HL089856; R01HL089897; UL1TR000124.

Reproducibility of NIRS Oxidative Capacity Measurements in the Vastus Lateralis and Medial Hamstring Muscles

Oxidative capacity within selected muscles can be measured non‐invasively using Near Infrared Spectroscopy (NIRS) by employing a series of transient arterial occlusion cuffs after a metabolic stimulus. Traditionally, this protocol involves voluntary contraction of a single limb followed by up to 22 transient ischemic occlusions per measurement. Our lab has adapted an established protocol 1 to develop a novel protocol that allows for an increased number of measurements using fewer (i.e. 6) ischemic occlusions combined with surface electrical stimulation (E‐stim) in both limbs simultaneously. However, reproducibility has not yet been established with this protocol.PURPOSETo determine the within‐day and between‐day reproducibility of this protocol in both the vastus lateralis and medial hamstring muscles.METHODSThe protocol involved 2 NIRS probes placed over the vastus lateralis (VL) muscles or the medial hamstring (MH) muscles in healthy adults to sense changes in muscle oxygenation. E‐stim pads were placed adjacent to the NIRS probe and were used to increase metabolic rate (&gt;3 fold) using a biphasic setting at 20 Hz, with an intensity (mV) that is within the participant’s tolerance. The mitochondrial oxidative capacity protocol involved 4 consecutive sets of 30 seconds of E‐stim followed by 6 x 5 sec cuff inflation/5 sec cuff deflation cycles using upper thigh rapid inflation cuffs. Analysis consisted of calculating oxygenation recovery rate constants (k) for each muscle (i.e., 4 repeated measurements per muscle, per limb) using a customized software program. Coefficient of variation (CV) and intraclass correlation coefficients [ICC(2,k)] were used to assess reproducibility.RESULTSVariability of within‐day repeated tests (CV) averaged 3.8% (0.9%–6.7%) in the VL (n=12) with an average rate constant (min−1) of 1.96 +/− 0.07 and 4.9% (1.0%–14.1%) in the MH (n=10) with an average rate constant (min−1) of 2.05 +/− 0.11. Variability of between‐day repeated tests averaged 11.7% (8.7% – 14.8%) in the VL (n=4) and 10.4% (7.5% – 12.0%) in the MH (n=4). [ICC(2,k)] was calculated as 0.98, 95% CI [0.95, 0.99] for the VL and 0.93, 95% CI [0.81, 0.98] for the MH muscles.CONCLUSIONThese results suggest the proposed protocol demonstrates good to excellent reproducibility in both muscles, with a higher rate associated with the VL. These outcomes provide investigators with an efficient alternative for measuring muscle oxidative capacity non‐invasively in the vastus lateralis and medial hamstring muscles.Support or Funding InformationCenter for Orthopedic Research and Translational Science, Penn State College of MedicineExperimental setup of bilateral NIRS oxidative capacity protocolFigure 1

Investigation on the influence of surface roughness on magnetite flotation from the view of both particle-particle and bubble-particle interactions

It is well known that surface roughness of mineral particles has a significant influence on their flotation behaviors. In this investigation, magnetite was ground in rod and ball mills to generate particles with similar dimension and shape but varying degree of surface roughness, which was quantified using Atomic Force Microscopy (AFM). The influence of surface roughness on the floatability of magnetite particles was performed by flotation tests using an XFG flotation machine. Flotation tests indicated magnetite particles possessed higher surface roughness had higher flotation recovery and larger flotation rate constant. The aggregation behaviors of different rough magnetite particles were compared for the first time via an optical microscopy. Results of the optical microscopic tests revealed that there were a large number of aggregations in the system of particles with higher surface roughness. A proposed model was deduced with the parameters carefully calculated (not arbitrarily selected) to analyze the bubble-particle interaction energy using an Extended DVLO (Derjaguin–Landau–Verwey–Overbeek) theory. The theoretical interaction energy points to lowering energy barrier when magnetite particles are covered with 28.03 nm asperities as compared to 9.47 nm asperities. The effect of surface roughness on mineral flotation was investigated from the view of both particle aggregations and energy barrier of bubble-particle attachment for the first time, which are the primary causes for differences in flotation performance.

Mitochondrial capacity using NIRS and incomplete recovery curves: Proximal and Medial Vastus Lateralis muscle.

To determine the effectiveness of using a 6-occlusion protocol (Mito6) versus one with 22 occlusions (Mito22) to measure muscle mitochondrial capacity. In two independent data sets (bicep n=7, forearm A n=23), recovery curves were analyzed independently using both the Mito6 and Mito22 analyses. A third data set (Forearm B, n=16) was generated on forearm muscles of healthy subjects using four Mito6 tests performed in succession. Recovery rate constants were generated using a MATLAB routine. When calculated from the same data set, the recovery rate constants were not significantly different between the Mito22 and Mito6 analyses for the bicep (1.43+0.33min-1, 1.43+0.35min-1, p=0.81) and the forearm A (1.97+0.40min-1, 1.97+0.43min-1, p=0.90). The correlation between Mito22 and Mito6 recovery rate constants was y=1.07x-0.09, R2=0.90 for the bicep data and 1.00x+0.01, R2=0.85 for the forearm A data. When performing the four Mito6 tests in the Forearm B study; recovery rate constants were not different between tests (1.50±0.51 min-1, 1.42±0.54 min-1, 1.26±0.41 min-1, 1.29±0.47 min-1, P>0.05). Muscle mitochondrial capacity was not different between the Mito6 analysis and the longer Mito22 analysis. The Mito6 protocol was considered more practical as it used fewer ischemic occlusion periods, and multiple tests could be performed in succession in less time. There were no order effects for the rate constants of four repeated Mito6 tests of mitochondrial capacity, supporting the use of multiple tests to improve accuracy.

Near Infrared Spectroscopy Measurements of Mitochondrial Capacity Using Partial Recovery Curves

BackgroundNear-infrared spectroscopy (NIRS) has been used to measure muscle mitochondrial capacity (mVO2max) as the recovery rate constant of muscle metabolism after exercise. The current method requires as many as 50 short ischemic occlusions to generate two recovery rate constants.PurposeTo determine the validity and repeatability of using a 6-occlusion protocol versus one with 22 occlusions to measure muscle mitochondrial capacity. The order effect of performing multiple Mito6 test was also evaluated.MethodIn two independent data sets (bicep n = 7, forearm A n = 23), recovery curves were analyzed independently using both the 6 and 22 occlusion methods. A third data set (forearm B n = 16) was generated on the forearm muscles of healthy subjects using four 6-occlusion tests performed in succession. Recovery rate constants were generated using a MATLAB routine.ResultsWhen calculated from the same data set, the recovery rate constants were not significantly different between the 22 occlusion and 6 occlusion methods for the bicep (1.43 ± 0.33 min–1, 1.43 ± 0.35 min–1, p = 0.81) and the forearm A (1.97 ± 0.40 min–1, 1.97 ± 0.43 min–1, p = 0.90). Equivalence testing showed that the mean difference was not different than zero and the 90% confidence intervals were within 5% of the average rate constant. This was true for the Mito6 and the Mito5∗ approaches. Bland–Altman analysis showed a slope of 0.21 min–1 and an r of 0.045 for the bicep dataset and a slope of −0.01 min–1 and an r of 0.045 for the forearm A dataset. When performing the four 6-occlusion tests; recovery rate constants showed no order effects (1.50 ± 0.51 min–1, 1.42 ± 0.54 min–1, 1.26 ± 0.41 min–1, 1.29 ± 0.47 min–1, P > 0.05).ConclusionThe Mito6 analysis is a valid and repeatable approach to measure mitochondrial capacity. The Mito6 protocol used fewer ischemic occlusion periods and multiple tests could be performed in succession in less time, increasing the practicality of the NIRS mitochondrial capacity test. There were no order effects for the rate constants of four repeated 6-occlusion tests of mitochondrial capacity, supporting the use of multiple tests to improve accuracy.

Effect of electrochemical oxidized kerosene on flotation rate of difficult-to-float fine coal

ABSTRACT In order to recover difficult-to-float fine coal, flotation rates of full-size coal are tested using electrochemical oxidized kerosene as a collector. The flotation rate of coal using oxidized kerosene is higher than that of adopting conventional kerosene. However, its flotation product contained more ash due to poor selectivity of oxidized kerosene. The maximum recovery and flotation rate constant of the model were calculated by Curve Fitting Tool in MATLAB software, and the correlation coefficient R2 of each model is obtained. It is found that the classic first-order kinetic model is the most suitable model for the flotation of kerosene and oxidized kerosene.