Vascular dysfunction and the age-related decline in critical power.

Ageing results in lower exercise tolerance, manifested as decreased critical power (CP). We examined whether the age-related decrease in CP occurs independently of changes in muscle mass and whether it is related to impaired vascular function. Ten older (63.1 ± 2.5 years) and 10 younger (24.4 ± 4.0 years) physically active volunteers participated. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual X-ray absorptiometry. The CP and maximum power during a graded exercise test (PGXT ) of single-leg knee-extension exercise were determined over the course of four visits. During a fifth visit, vascular function of the leg was assessed with passive leg movement (PLM) hyperaemia and leg blood flow and vascular conductance during knee-extension exercise at 10 W, 20 W, slightly below CP (90% CP) and PGXT . Despite not differing in leg lean mass (P = 0.901) and physical activity (e.g., steps per day, P = 0.735), older subjects had ∼30% lower mass-specific CP (old = 3.20 ± 0.94 W kg-1 vs. young = 4.60 ± 0.87 W kg-1 ; P < 0.001). The PLM-induced hyperaemia and leg blood flow and/or conductance were blunted in the old at 20 W, 90% CP and PGXT (P < 0.05). When normalized for leg muscle mass, CP was strongly correlated with PLM-induced hyperaemia (R2  = 0.52; P < 0.001) and vascular conductance during knee-extension exercise at 20 W (R2  = 0.34; P = 0.014) and 90% CP (R2  = 0.39; P = 0.004). In conclusion, the age-related decline in CP is not only an issue of muscle quantity, but also of impaired muscle quality that corresponds to impaired vascular function.

Physiological assessment of a 16 day, 4385 km ultra-endurance mountain bike race: A case study.

The Tour Divide (TD) is a 4385 km ultra-endurance bicycle race that follows the continental divide from Canada to Mexico. In this case study, we performed a comprehensive molecular and physiological profile before and after the completion of the TD. Assessments were performed 35 days before the start (Pre-TD) and ∼36 h after the finish (Post-TD). Total energy expenditure was assessed during the first 9 days by doubly labelled water (2 H2 18 O), abdominal and leg tissue volumes via MRI, and graded exercise tests to quantify fitness and substrate preference. Vastus lateralis muscle biopsies were taken to measure mitochondrial function via respirometry, and vascular function was assessed using Doppler ultrasound. The 47-year-old male subject took 16 days 7 h 45 min to complete the route. He rode an average of 16.8 h/day. Neither maximal O2 uptake nor maximal power output changed pre- to post-TD. Measurement of total energy expenditure and dietary recall records suggested maintenance of energy balance, which was supported by the lack of change in body weight. The subject lost both appendicular and trunk fat mass and gained leg lean mass pre- to post-TD. Skeletal muscle mitochondrial and vascular endothelial function decreased pre- to post-TD. Overall, exercise performance was maintained despite reductions in muscle mitochondrial and vascular endothelial function post-TD, suggesting a metabolic reserve in our highly trained athlete.

Rapid onset vasodilation during baroreceptor loading and unloading.

The purpose of these experiments was to determine if the increase in vascular conductance following a single muscle contraction (50% of maximal voluntary contraction) (6 male and 6 female subjects) was altered during baroceptor loading and unloading. Rapid onset vasodilation (ROV) was determined by measuring brachial artery blood flow (Doppler ultrasound) and blood pressure (Finapress monitor). Brachial artery vascular conductance was calculated by dividing blood flow by mean arterial pressure. ROV was described by the area under the Δvascular conductance (VC)-time curve during the 30 s following muscle contraction. ROV was determined using chamber pressures of +20, +10, 0, -10, -20, and -40 mmHg (lower body positive and negative pressure, LBPP, and LBNP). We tested the hypothesis that the impact of baroreceptor loading and unloading produces a proportion change in ROV. The level of ROV following each contraction was proportional to the peak force (r2 = 0.393, P = 0.0001). Peak force was therefore used as a covariate in further analysis. ROV during application of -40 mmHg LBNP (0.345 ± 0.229 mL·mmHg-1) was lower than that observed at Control (0.532 ± 0.284 mL·mmHg-1, P = 0.034) and +20 mmHg LBPP (0.658 ± 0.364 mL·mmHg-1, P = 0.0008). ROV was linearly related to chamber pressure from -40 to +20 mmHg chamber pressure (r2 = 0.512, P = 0.022, n = 69) and from -20 to +10 mmHg chamber pressure (r2= 0.973, P < 0.0425, n = 45), Overall, vasoconstrictor tone altered with physiologically relevant baroreceptor loading and unloading resulted in a proportion change in ROV.NEW & NOTEWORTHY Rapid onset vasodilation (ROV) was linearly related to the peak force of each single 1-s muscle contraction. In addition, ROV is reduced by baroreceptor unloading (LBNP: -10, -120, and -40 mmHg) and increased by baroreceptor loading (LBPP: +10 and +20 mmHg). Without accounting for peak force and the level of baroreceptor engagement makes comparison of ROV in subjects of differing muscle size or strength untenable.

Passive heat stress induces mitochondrial adaptations in skeletal muscle.

The mitochondria are central to skeletal muscle metabolic health. Impaired mitochondrial function is associated with various muscle pathologies, including insulin resistance and muscle atrophy. As a result, continuous efforts are made to find ways to improve mitochondrial health in the context of disuse and disease. While exercise is known to cause robust improvements in mitochondrial health, not all individuals are able to exercise. This creates a need for alternate interventions which elicit some of the same benefits as exercise. Passive heating (i.e., application of heat in the absence of muscle contractions) is one potential intervention which has been shown to increase mitochondrial enzyme content and activity, and to improve mitochondrial respiration. Associated with increases in mitochondrial content and/or function, passive heating can also improve insulin sensitivity in the context of type II diabetes and preserve muscle mass in the face of limb disuse. This area of research remains in its infancy, with many questions yet to be answered about how to maximize the benefits of passive heating and elucidate the mechanisms by which heat stress affects muscle mitochondria.

Reliability of the passive leg movement assessment of vascular function in men.

NEW FINDINGS: What is the central question of this study? Use of the passive leg movement (PLM) test, a non-invasive assessment of microvascular function, is on the rise. However, PLM reliability in men has not been adequately investigated, nor has such reliability data, in men, been compared to the most commonly employed vascular function assessment, flow-mediated vasodilation (FMD). What is the main finding and its importance? PLM is a reliable method to assess vascular function in men, and is comparable to values previously reported for PLM in women, and for FMD. Given the importance of vascular function as a predictor of cardiovascular disease risk, these data support the utility of PLM as a clinically relevant measurement. ABSTRACT: Although vascular function is an independent predictor of cardiovascular disease risk, and therefore has significant prognostic value, there is currently not a single clinically accepted method of assessment. The passive leg movement (PLM) assessment predominantly reflects microvascular endothelium-dependent vasodilation and can identify decrements in vascular function with advancing age and pathology. Reliability of the PLM model was only recently determined in women, and has not been adequately investigated in men. Twenty healthy men (age: 27 ± 2 year) were studied on three separate experimental days, resulting in three within-day and three between-day trials. The hyperemic response to PLM was assessed with Doppler ultrasound, and expressed as the absolute peak in leg blood flow (LBFpeak ), change from baseline to peak (ΔLBFpeak ), absolute area under the curve (LBFAUC ), and change in AUC from baseline (ΔLBFAUC ). PLM-induced hyperemia yielded within-day coefficients of variation (CV) from 10.9 to 22.9%, intraclass correlation coefficients (ICC) from 0.82 to 0.90, standard error of the measurement (SEM) from 8.3 to 17.2%, and Pearson's correlation coefficients (r) from 0.56 to 0.81. Between-day assessments of PLM hyperemia resulted in CV from 14.4 to 25%, ICC from 0.75 to 0.87, SEM from 9.8 to 19.8%, and r from 0.46 to 0.75. Similar to previous reports in women, the hyperemic responses to PLM in men display moderate-to-high reliability, and are comparable to reliability data for brachial artery flow mediated vasodilation. These positive reliability findings further support the utility of PLM as a clinical measurement of vascular function and cardiovascular disease risk.

Localized Heat Therapy Improves Mitochondrial Respiratory Capacity but Not Fatty Acid Oxidation.

AIM: Mild heat stress can improve mitochondrial respiratory capacity in skeletal muscle. However, long-term heat interventions are scarce, and the effects of heat therapy need to be understood in the context of the adaptations which follow the more complex combination of stimuli from exercise training. The purpose of this work was to compare the effects of 6 weeks of localized heat therapy on human skeletal muscle mitochondria to single-leg interval training. METHODS: Thirty-five subjects were assigned to receive sham therapy, short-wave diathermy heat therapy, or single-leg interval exercise training, localized to the quadriceps muscles of the right leg. All interventions took place 3 times per week. Muscle biopsies were performed at baseline, and after 3 and 6 weeks of intervention. Mitochondrial respiratory capacity was assessed on permeabilized muscle fibers via high-resolution respirometry. RESULTS: The primary finding of this work was that heat therapy and exercise training significantly improved mitochondrial respiratory capacity by 24.8 ± 6.2% and 27.9 ± 8.7%, respectively (p < 0.05). Fatty acid oxidation and citrate synthase activity were also increased following exercise training by 29.5 ± 6.8% and 19.0 ± 7.4%, respectively (p < 0.05). However, contrary to our hypothesis, heat therapy did not increase fatty acid oxidation or citrate synthase activity. CONCLUSION: Six weeks of muscle-localized heat therapy significantly improves mitochondrial respiratory capacity, comparable to exercise training. However, unlike exercise, heat does not improve fatty acid oxidation capacity.

Passive muscle heating attenuates the decline in vascular function caused by limb disuse.

Limb disuse has profound negative consequences on both vascular and skeletal muscle health. The purpose of this investigation was to determine whether repeated application of passive heat, applied to the knee extensor muscles, could mitigate the detrimental effects of limb disuse on vascular function. This was a randomized, single-blinded placebo controlled trial. Twenty-one healthy volunteers (10 women, 11 men) underwent 10 days of unilateral lower limb immobilization and were randomized to receive either a daily 2 h sham (Imm) or heat treatment (Imm+H) using pulsed shortwave diathermy. Vascular function was assessed with Doppler ultrasound of the femoral artery and the passive leg movement technique. Biopsies of the vastus lateralis were also collected before and after the intervention. In Imm, femoral artery diameter (FAD) and PLM-induced hyperaemia (HYP) were reduced by 7.3% and 34.3%, respectively. Changes in both FAD (4% decrease; P = 0.0006) and HYP (7.8% increase; P = 0.003) were significantly attenuated in Imm+H. Vastus lateralis capillary density was not altered in either group. Immobilization significantly decreased expression of vascular endothelial growth factor (P = 0.006) and Akt (P = 0.001), and increased expression of angiopoietin 2 (P = 0.0004) over time, with no differences found between groups. Immobilization also upregulated elements associated with remodelling of the extracellular matrix, including matrix metalloproteinase 2 (P = 0.0046) and fibronectin (P = 0.0163), with no differences found between groups. In conclusion, limb immobilization impairs vascular endothelial function, but daily muscle heating via diathermy is sufficient to counteract this adverse effect. These are the first data to indicate that passive muscle heating mitigates disuse-induced vascular dysfunction. KEY POINTS: Limb disuse can be unavoidable for many of reasons (i.e. injury, bed rest, post-surgery), and can have significant adverse consequences for muscular and vascular health. We tested the hypothesis that declines in vascular function that result from lower limb immobilization could be mitigated by application of passive heat therapy. This report shows that 10 days of limb immobilization significantly decreases resistance artery diameter and vascular function, and that application of passive heat to the knee extensor muscle group each day for 2 h per day is sufficient to attenuate these declines. Additionally, muscle biopsy analyses showed that 10 days of heat therapy does not alter capillary density of the muscle, but upregulates multiple factors indicative of a vascular remodelling response. Our data demonstrate the utility of passive heat as a therapeutic tool to mitigate losses in lower limb vascular function that occur from disuse.

The role of the endothelium in the hyperemic response to passive leg movement: looking beyond nitric oxide.

Passive leg movement (PLM) evokes a robust and predominantly nitric oxide (NO)-mediated increase in blood flow that declines with age and disease. Consequently, PLM is becoming increasingly accepted as a sensitive assessment of endothelium-mediated vascular function. However, a substantial PLM-induced hyperemic response is still evoked despite nitric oxide synthase (NOS) inhibition. Therefore, in nine young healthy men (25 ± 4 yr), this investigation aimed to determine whether the combination of two potent endothelium-dependent vasodilators, specifically prostaglandin (PG) and endothelium-derived hyperpolarizing factor (EDHF), account for the remaining hyperemic response to the two variants of PLM, PLM (60 movements) and single PLM (sPLM, 1 movement), when NOS is inhibited. The leg blood flow (LBF, Doppler ultrasound) response to PLM and sPLM following the intra-arterial infusion of NG-monomethyl-l-arginine (l-NMMA), to inhibit NOS, was compared to the combined inhibition of NOS, cyclooxygenase (COX), and cytochrome P-450 (CYP450) by l-NMMA, ketorolac tromethamine (KET), and fluconazole (FLUC), respectively. NOS inhibition attenuated the overall LBF [area under the curve (LBFAUC)] response to both PLM (control: 456 ± 194, l-NMMA: 168 ± 127 mL, P < 0.01) and sPLM (control: 185 ± 171, l-NMMA: 62 ± 31 mL, P = 0.03). The combined inhibition of NOS, COX, and CYP450 (i.e., l-NMMA+KET+FLUC) did not further attenuate the hyperemic responses to PLM (LBFAUC: 271 ± 97 mL, P > 0.05) or sPLM (LBFAUC: 72 ± 45 mL, P > 0.05). Therefore, PG and EDHF do not collectively contribute to the non-NOS-derived NO-mediated, endothelium-dependent hyperemic response to either PLM or sPLM in healthy young men. These findings add to the mounting evidence and understanding of the vasodilatory pathways assessed by the PLM and sPLM vascular function tests.NEW & NOTEWORTHY Passive leg movement (PLM) evokes a highly nitric oxide (NO)-mediated hyperemic response and may provide a novel evaluation of vascular function. The contributions of endothelium-dependent vasodilatory pathways, beyond NO and including prostaglandins and endothelium-derived hyperpolarizing factor, to the PLM-induced hyperemic response to PLM have not been evaluated. With intra-arterial drug infusion, the combined inhibition of nitric oxide synthase (NOS), cyclooxygenase, and cytochrome P-450 (CYP450) pathways did not further diminish the hyperemic response to PLM compared with NOS inhibition alone.

Vascular function in continuous-flow left ventricular assist device recipients: effect of a single pulsatility treatment session.

Vascular function is further attenuated in patients with chronic heart failure implanted with a continuous-flow left ventricular assist device (LVAD), likely due to decreased arterial pulsatility, and this may contribute to LVAD-associated cardiovascular complications. However, the impact of increasing pulsatility on vascular function in this population is unknown. Therefore, 15 LVAD recipients and 15 well-matched controls underwent a 45-min, unilateral, arm pulsatility treatment, evoked by intermittent cuff inflation/deflation (2-s duty cycle), distal to the elbow. Vascular function was assessed by percent brachial artery flow-mediated dilation (%FMD) and reactive hyperemia (RH) (Doppler ultrasound). Pretreatment, %FMD (LVAD: 4.0 ± 1.7; controls: 4.2 ± 1.4%) and RH (LVAD: 340 ± 101; controls: 308 ± 94 mL) were not different between LVAD recipients and controls; however, %FMD/shear rate was attenuated (LVAD: 0.10 ± 0.04; controls: 0.17 ± 0.06%/s-1, P < 0.05). The LVAD recipients exhibited a significantly attenuated pulsatility index (PI) compared with controls prior to treatment (LVAD: 2 ± 2; controls: 15 ± 7 AU, P < 0.05); however, during the treatment, PI was no longer different (LVAD: 37 ± 38; controls: 36 ± 14 AU). Although time to peak dilation and RH were not altered by the pulsatility treatment, %FMD (LVAD: 7.0 ± 1.8; controls: 7.4 ± 2.6%) and %FMD/shear rate (LVAD: 0.19 ± 0.07; controls: 0.33 ± 0.15%/s-1) increased significantly in both groups, with, importantly, %FMD/shear rate in the LVAD recipients being restored to that of the controls pretreatment. This study documents that a localized pulsatility treatment in LVAD recipients and controls can recover local vascular function, an important precursor to the development of approaches to increase systemic pulsatility and reduce systemic vascular complications in LVAD recipients.

Acute high-intensity exercise and skeletal muscle mitochondrial respiratory function: role of metabolic perturbation.

Recently it was documented that fatiguing, high-intensity exercise resulted in a significant attenuation in maximal skeletal muscle mitochondrial respiratory capacity, potentially due to the intramuscular metabolic perturbation elicited by such intense exercise. With the utilization of intrathecal fentanyl to attenuate afferent feedback from group III/IV muscle afferents, permitting increased muscle activation and greater intramuscular metabolic disturbance, this study aimed to better elucidate the role of metabolic perturbation on mitochondrial respiratory function. Eight young, healthy males performed high-intensity cycle exercise in control (CTRL) and fentanyl-treated (FENT) conditions. Liquid chromatography-mass spectrometry and high-resolution respirometry were used to assess metabolites and mitochondrial respiratory function, respectively, pre- and postexercise in muscle biopsies from the vastus lateralis. Compared with CTRL, FENT yielded a significantly greater exercise-induced metabolic perturbation (PCr: -67% vs. -82%, Pi: 353% vs. 534%, pH: -0.22 vs. -0.31, lactate: 820% vs. 1,160%). Somewhat surprisingly, despite this greater metabolic perturbation in FENT compared with CTRL, with the only exception of respiratory control ratio (RCR) (-3% and -36%) for which the impact of FENT was significantly greater, the degree of attenuated mitochondrial respiratory capacity postexercise was not different between CTRL and FENT, respectively, as assessed by maximal respiratory flux through complex I (-15% and -33%), complex II (-36% and -23%), complex I + II (-31% and -20%), and state 3CI+CII control ratio (-24% and -39%). Although a basement effect cannot be ruled out, this failure of an augmented metabolic perturbation to extensively further attenuate mitochondrial function questions the direct role of high-intensity exercise-induced metabolite accumulation in this postexercise response.

The role of endothelin A receptors in peripheral vascular control at rest and during exercise in patients with hypertension.

KEY POINTS: Exercise in patients with hypertension can be accompanied by an abnormal cardiovascular response that includes attenuated blood flow and an augmented pressor response. Endothelin-1, a very potent vasoconstrictor, is a key modulator of blood flow and pressure during in health and has been implicated as a potential cause of the dysfunction in hypertension. We assessed the role of endothelin-1, acting through endothelin A (ETA ) receptors, in modulating the central and peripheral cardiovascular responses to exercise in patients with hypertension via local antagonism of these receptors during exercise. ETA receptor antagonism markedly increased leg blood flow, vascular conductance, oxygen delivery, and oxygen consumption during exercise; interestingly, these changes occurred in the presence of reduced leg perfusion pressure, indicating that these augmentations were driven by changes in vascular resistance. These data indicate that ETA receptor antagonism could be a viable therapeutic approach to improve blood flow during exercise in hypertension. ABSTRACT: Patients with hypertension can exhibit impaired muscle blood flow and exaggerated increases in blood pressure during exercise. While endothelin (ET)-1 plays a role in regulating blood flow and pressure during exercise in health, little is known about the role of ET-1 in the cardiovascular response to exercise in hypertension. Therefore, eight volunteers diagnosed with hypertension were studied during exercise with either saline or BQ-123 (ETA receptor antagonist) infusion following a 2-week withdrawal of anti-hypertensive medications. The common femoral artery and vein were catheterized for drug infusion, blood collection and blood pressure measurements, and leg blood flow was measured by Doppler ultrasound. Patients exercised at both absolute (0, 5, 10, 15 W) and relative (40, 60, 80% peak power) intensities. BQ-123 increased blood flow at rest (79 ± 87 ml/min; P = 0.03) and augmented the exercise-induced hyperaemia at most intensities (80% saline: Δ3818±1222 vs. BQ-123: Δ4812±1469 ml/min; P = 0.001). BQ-123 reduced leg MAP at rest (-8 ± 4 mmHg; P < 0.001) and lower intensities (0-10 W; P < 0.05). Systemic diastolic blood pressure was reduced (0 W, 40%; P < 0.05), but systemic MAP was defended by an increased cardiac output. The exercise pressor response (ΔMAP) did not differ between conditions (80% saline: 25 ± 10, BQ-123: 30 ± 7 mmHg; P = 0.17). Thus, ET-1, acting through the ETA receptors, contributes to the control of blood pressure at rest and lower intensity exercise in these patients. Furthermore, the finding that ET-1 constrains the blood flow response to exercise suggests that ETA receptor antagonism could be a therapeutic approach to improve blood flow during exercise in hypertension.

Imaging transcranial Doppler ultrasound to measure middle cerebral artery blood flow: the importance of measuring vessel diameter.

Cerebral blood flow (CBF) is commonly inferred from blood velocity measurements in the middle cerebral artery (MCA), using nonimaging, transcranial Doppler ultrasound (TCD). However, both blood velocity and vessel diameter are critical components required to accurately determine blood flow, and there is mounting evidence that the MCA is vasoactive. Therefore, the aim of this study was to employ imaging TCD (ITCD), utilizing color flow images and pulse wave velocity, as a novel approach to measure both MCA diameter and blood velocity to accurately quantify changes in MCA blood flow. ITCD was performed at rest in 13 healthy participants (7 men/6 women; 28 ± 5 yr) with pharmaceutically induced vasodilation [nitroglycerin (NTG), 0.8 mg] and without (CON). Measurements were taken for 2 min before and for 5 min following NTG or sham delivery (CON). There was more than a fivefold, significant, fall in MCA blood velocity in response to NTG (∆-4.95 ± 4.6 cm/s) compared to negligible fluctuation in CON (∆-0.88 ± 4.7 cm/s) (P < 0.001). MCA diameter increased significantly in response to NTG (∆0.09 ± 0.04 cm) compared with the basal variation in CON (∆0.00 ± 0.04 cm) (P = 0.018). Interestingly, the product of the NTG-induced fall in MCA blood velocity and increase in diameter was a significant increase in MCA blood flow following NTG (∆144 ± 159 ml/min) compared with CON (∆-5 ± 130 ml/min) (P = 0.005). These juxtaposed findings highlight the importance of measuring both MCA blood velocity and diameter when assessing CBF and document ITCD as a novel approach to achieve this goal.

Nitric oxide synthase inhibition with N(G)-monomethyl-l-arginine: Determining the window of effect in the human vasculature.

Nitric oxide synthase (NOS) inhibition with N(G)-monomethyl-l-arginine (L-NMMA) is often used to assess the role of NO in human cardiovascular function. However, the window of effect for L-NMMA on human vascular function is unknown, which is critical for designing and interpreting human-based studies. This study utilized the passive leg movement (PLM) assessment of vascular function, which is predominantly NO-mediated, in 7 young male subjects under control conditions, immediately following intra-arterial L-NMMA infusion (0.24 mg⋅dl-1⋅min-1), and at 45-60 and 90-105 min post L-NMMA infusion. The leg blood flow (LBF) and leg vascular conductance (LVC) responses to PLM, measured with Doppler ultrasound and expressed as the change from baseline to peak (ΔLBFpeak and ΔLVCpeak) and area under the curve (LBFAUC and LVCACU), were assessed. PLM-induced robust control ΔLBFpeak (1135 ± 324 ml⋅min-1) and ΔLVCpeak (10.7 ± 3.6 ml⋅min-1⋅mmHg-1) responses that were significantly attenuated (704 ± 196 ml⋅min-1 and 6.7 ± 2 ml⋅min-1⋅mmHg-1) immediately following L-NMMA infusion. Likewise, control condition PLM ΔLBFAUC (455 ± 202 ml) and ΔLVCAUC (4.0 ± 1.4 ml⋅mmHg-1) were significantly attenuated (141 ± 130 ml and 1.3 ± 1.2 ml⋅mmHg-1) immediately following L-NMMA infusion. However, by 45-60 min post L-NMMA infusion all PLM variables were not significantly different from control, and this was still the case at 90-105 min post L-NMMA infusion. These findings reveal that the potent reduction in NO bioavailability afforded by NOS inhibition with L-NMMA has a window of effect of less than 45-60 min in the human vasculature. These data are particularly important for the commonly employed approach of pharmacologically inhibiting NOS with L-NMMA in the human vasculature.

Impact of acute antioxidant administration on inflammation and vascular function in heart failure with preserved ejection fraction.

Although it is now well established that heart failure with preserved ejection fraction (HFpEF) is associated with marked inflammation and a prooxidant state that is accompanied by vascular dysfunction, whether acute antioxidant (AO) administration can effectively target these disease-related decrements has not been evaluated. Thus, the present study sought to evaluate the efficacy of an acute over-the-counter AO cocktail (600 mg α-lipoic acid, 1,000 mg vitamin C, and 600 IU vitamin E) to mitigate inflammation and oxidative stress, and subsequently improve nitric oxide (NO) bioavailability and vascular function, in patients with HFpEF. Flow-mediated dilation (FMD) and reactive hyperemia (RH) were evaluated to assess conduit vessel and microvascular function, respectively, 90 min after administration of either placebo (PL) or AO in 16 patients with HFpEF (73 ± 10 yr, EF 54-70%) using a double-blind, crossover design. Circulating biomarkers of inflammation (C-reactive protein, CRP), oxidative stress (malondialdehyde and protein carbonyl), free radical concentration (EPR spectroscopy), antioxidant capacity, ascorbate and NO bioavailability (plasma nitrate, [Formula: see text], and nitrite, [Formula: see text]) were also assessed. FMD improved following AO administration (PL: 3.49 ± 0.7%, AO: 5.83 ± 1.0%), whereas RH responses were similar between conditions (PL: 428 ± 51 mL, AO: 425 ± 51 mL). AO administration decreased CRP (PL: 4,429 ± 705 ng/mL, AO: 3,664 ± 520 ng/mL) and increased ascorbate (PL: 30.0 ± 2.9 µg/mL, AO: 45.1 ± 3.7 µg/mL) and [Formula: see text] (PL: 182 ± 21 nM, AO: 213 ± 24 nM) but did not affect other biomarkers. Together, these data suggest that acute AO administration can exert anti-inflammatory effects and improve conduit artery vasodilation, but not microvascular function, in patients with HFpEF.

Oxygen availability and skeletal muscle oxidative capacity in patients with peripheral artery disease: implications from in vivo and in vitro assessments.

Evidence suggests that the peak skeletal muscle mitochondrial ATP synthesis rate ( Vmax) in patients with peripheral artery disease (PAD) may be attenuated due to disease-related impairments in O2 supply. However, in vitro assessments suggest intrinsic deficits in mitochondrial respiration despite ample O2 availability. To address this conundrum, Doppler ultrasound, near-infrared spectroscopy, phosphorus magnetic resonance spectroscopy, and high-resolution respirometry were combined to assess convective O2 delivery, tissue oxygenation, Vmax, and skeletal muscle mitochondrial capacity (complex I + II, state 3 respiration), respectively, in the gastrocnemius muscle of 10 patients with early stage PAD and 11 physical activity-matched healthy control (HC) subjects. All participants were studied in free-flow control conditions (FF) and with reactive hyperemia (RH) induced by a period of brief ischemia during the last 30 s of submaximal plantar flexion exercise. Patients with PAD repeated the FF and RH trials under hyperoxic conditions (FF + 100% O2 and RH + 100% O2). Compared with HC subjects, patients with PAD exhibited attenuated O2 delivery at the same absolute work rate and attenuated tissue reoxygenation and Vmax after relative intensity-matched exercise. Compared with the FF condition, only RH + 100% O2 significantly increased convective O2 delivery (~44%), tissue reoxygenation (~54%), and Vmax (~60%) in patients with PAD ( P < 0.05), such that Vmax was now not different from HC subjects. Furthermore, there was no evidence of an intrinsic mitochondrial deficit in PAD, as assessed in vitro with adequate O2. Thus, in combination, this comprehensive in vivo and in vitro investigation implicates O2 supply as the predominant factor limiting mitochondrial oxidative capacity in early stage PAD. NEW & NOTEWORTHY Currently, there is little accord as to the role of O2 availability and mitochondrial function in the skeletal muscle dysfunction associated with peripheral artery disease. This is the first study to comprehensively use both in vivo and in vitro approaches to document that the skeletal muscle dysfunction associated with early stage peripheral artery disease is predominantly a consequence of limited O2 supply and not the impact of an intrinsic mitochondrial defect in this pathology.

Increased skeletal muscle mitochondrial free radical production in peripheral arterial disease despite preserved mitochondrial respiratory capacity.

NEW FINDINGS: What is the central question of this study? What is the degree to which skeletal muscle mitochondria-derived reactive oxygen species (ROS) production is linked to impaired skeletal muscle function in patients with early-stage peripheral arterial disease (PAD) and what is the impact on mitochondrial respiratory capacity? What is the main finding and its importance? This is the first study to document increased mitochondria-derived reactive oxygen species production associated with elevated intramuscular oxidative stress, despite preserved mitochondrial respiratory function, in patients with PAD. Furthermore, systemic inflammation, mitochondria-derived ROS production and skeletal muscle oxidative stress were strongly correlated to disease severity, as indicated by ankle-brachial index, in patients with PAD. ABSTRACT: Skeletal muscle mitochondrial dysfunction, which is not fully explained by disease-related arterial occlusion, has been implicated in the pathophysiology of peripheral arterial disease (PAD). Therefore, this study comprehensively assessed mitochondrial respiratory function in biopsies from the gastrocnemius of 10 patients with PAD (Fontaine Stage II) and 12 healthy controls (HC). Intramuscular and systemic inflammation, mitochondria-derived reactive oxygen species (ROS) production, and oxidative stress were also assessed to better understand the mechanisms responsible for the proposed PAD-induced mitochondrial dysfunction. Interestingly, mitochondrial respiratory capacity, assessed as complex I (CI) and complex II (CII)-driven State 3 respiration, measured separately and in combination (State 3 CI+II), revealed no difference between the patients with PAD and the HC. However, mitochondria-derived ROS production was significantly elevated in PAD (HC: 1.0 ± 0.9; PAD: 4.3 ± 1.0 AU (mg tissue)-1 ). Furthermore, patients with PAD exhibited significantly greater concentrations of the pro-inflammatory markers tumour necrosis factor α in plasma (HC: 0.9 ± 0.4; PAD: 2.0 ± 0.3 pg ml-1 ) and interleukin 6 in both plasma (HC: 2.3 ± 0.4; PAD: 4.3 ± 0.5 pg ml-1 ) and muscle (∼75% greater). Intramuscular oxidative stress, assessed by protein carbonyls and 4-hydroxynonenal, was significantly greater in PAD compared to HC. Ankle brachial index was significantly correlated with intramuscular inflammation, oxidative stress and mitochondria-derived ROS production. Thus, elevated intramuscular inflammation, oxidative stress and mitochondria-derived ROS production are likely to contribute to the pathophysiology of the skeletal muscle dysfunction associated with PAD, even in the presence of preserved mitochondrial respiratory function in this population.

TRPV1 channels in human skeletal muscle feed arteries: implications for vascular function.

NEW FINDINGS: What is the central question of this study? We sought to determine whether human skeletal muscle feed arteries (SFMAs) express TRPV1 channels and what role they play in modulating vascular function. What is the main finding and its importance? Human SMFAs do express functional TRPV1 channels that modulate vascular function, specifically opposing α-adrenergic receptor-mediated vasocontraction and potentiating vasorelaxation, in an endothelium-dependent manner, as evidenced by the α1 -receptor-mediated responses. Thus, the vasodilatory role of TRPV1 channels, and their ligand capsaicin, could be a potential therapeutic target for improving vascular function. Additionally, given the 'sympatholytic' effect of TRPV1 activation and known endogenous activators (anandamide, reactive oxygen species, H+ , etc.), TRPV1 channels might contribute to functional sympatholysis during exercise. To examine the role of the transient receptor potential vanilloid type 1 (TRPV1 ) ion channel in the vascular function of human skeletal muscle feed arteries (SMFAs) and whether activation of this heat-sensitive receptor could be involved in modulating vascular function, SMFAs from 16 humans (63 ± 5 years old, range 41-89 years) were studied using wire myography with capsaicin (TRPV1 agonist) and without (control). Specifically, phenylephrine (α1 -adrenergic receptor agonist), dexmedetomidine (α2 -adrenergic receptor agonist), ACh and sodium nitroprusside concentration-response curves were established to assess the role of TRPV1 channels in α-receptor-mediated vasocontraction as well as endothelium-dependent and -independent vasorelaxation, respectively. Compared with control conditions, capsaicin significantly attenuated maximal vasocontraction in response to phenylephrine [control, 52 ± 8% length-tensionmax (LTmax ) and capsaicin, 21 ± 5%LTmax ] and dexmedetomidine (control, 29 ± 12%LTmax and capsaicin, 2 ± 3%LTmax ), while robustly enhancing maximal vasorelaxation with ACh (control, 78 ± 8% vasorelaxation and capsaicin, 108 ± 13% vasorelaxation) and less clearly enhancing the sodium nitroprusside response. Denudation of the endothelium greatly attenuated the maximal ACh-induced vasorelaxation equally in the control and capsaicin conditions (∼17% vasorelaxation) and abolished the attenuating effect of capsaicin on the maximal phenylephrine response (denuded + capsaicin, 61 ± 20%LTmax ). Immunohistochemistry identified a relatively high density of TRPV1 channels in the endothelium compared with the smooth muscle of the SMFAs, but because of the far greater volume of smooth muscle, total TRPV1 protein content was not significantly attenuated by denudation. Thus, SMFAs ubiquitously express functional TRPV1 channels, which alter vascular function, in terms of α1 -receptors, in a predominantly endothelium-dependent manner, conceivably contributing to the functional sympatholysis and unveiling a therapeutic target.

Symmorphosis and skeletal muscle V̇O2 max : in vivo and in vitro measures reveal differing constraints in the exercise-trained and untrained human.

The concept of symmorphosis postulates a matching of structural capacity to functional demand within a defined physiological system, regardless of endurance exercise training status. Whether this concept applies to oxygen (O2 ) supply and demand during maximal skeletal muscle O2 consumption (V̇O2 max ) in humans is unclear. Therefore, in vitro skeletal muscle mitochondrial V̇O2 max (Mito V̇O2 max , mitochondrial respiration of fibres biopsied from vastus lateralis) was compared with in vivo skeletal muscle V̇O2 max during single leg knee extensor exercise (KE V̇O2 max , direct Fick by femoral arterial and venous blood samples and Doppler ultrasound blood flow measurements) and whole-body V̇O2 max during cycling (Body V̇O2 max , indirect calorimetry) in 10 endurance exercise-trained and 10 untrained young males. In untrained subjects, during KE exercise, maximal O2 supply (KE Q̇O2max ) exceeded (462 ± 37 ml kg(-1) min(-1) , P < 0.05) and KE V̇O2 max matched (340 ± 22 ml kg(-1) min(-1) , P > 0.05) Mito V̇O2 max (364 ± 16 ml kg(-1) min(-1) ). Conversely, in trained subjects, both KE Q̇O2max (557 ± 35 ml kg(-1) min(-1) ) and KE V̇O2 max (458 ± 24 ml kg(-1) min(-1) ) fell far short of Mito V̇O2 max (743 ± 35 ml kg(-1) min(-1) , P < 0.05). Although Mito V̇O2 max was related to KE V̇O2 max (r = 0.69, P < 0.05) and Body V̇O2 max (r = 0.91, P < 0.05) in untrained subjects, these variables were entirely unrelated in trained subjects. Therefore, in untrained subjects, V̇O2 max is limited by mitochondrial O2 demand, with evidence of adequate O2 supply, whereas, in trained subjects, an exercise training-induced mitochondrial reserve results in skeletal muscle V̇O2 max being markedly limited by O2 supply. Taken together, these in vivo and in vitro measures reveal clearly differing limitations and excesses at V̇O2 max in untrained and trained humans and challenge the concept of symmorphosis as it applies to O2 supply and demand in humans.

Accuracy and precision of quantitative 31P-MRS measurements of human skeletal muscle mitochondrial function.

Although theoretically sound, the accuracy and precision of (31)P-magnetic resonance spectroscopy ((31)P-MRS) approaches to quantitatively estimate mitochondrial capacity are not well documented. Therefore, employing four differing models of respiratory control [linear, kinetic, and multipoint adenosine diphosphate (ADP) and phosphorylation potential], this study sought to determine the accuracy and precision of (31)P-MRS assessments of peak mitochondrial adenosine-triphosphate (ATP) synthesis rate utilizing directly measured peak respiration (State 3) in permeabilized skeletal muscle fibers. In 23 subjects of different fitness levels, (31)P-MRS during a 24-s maximal isometric knee extension and high-resolution respirometry in muscle fibers from the vastus lateralis was performed. Although significantly correlated with State 3 respiration (r = 0.72), both the linear (45 ± 13 mM/min) and phosphorylation potential (47 ± 16 mM/min) models grossly overestimated the calculated in vitro peak ATP synthesis rate (P < 0.05). Of the ADP models, the kinetic model was well correlated with State 3 respiration (r = 0.72, P < 0.05), but moderately overestimated ATP synthesis rate (P < 0.05), while the multipoint model, although being somewhat less well correlated with State 3 respiration (r = 0.55, P < 0.05), most accurately reflected peak ATP synthesis rate. Of note, the PCr recovery time constant (τ), a qualitative index of mitochondrial capacity, exhibited the strongest correlation with State 3 respiration (r = 0.80, P < 0.05). Therefore, this study reveals that each of the (31)P-MRS data analyses, including PCr τ, exhibit precision in terms of mitochondrial capacity. As only the multipoint ADP model did not overstimate the peak skeletal muscle mitochondrial ATP synthesis, the multipoint ADP model is the only quantitative approach to exhibit both accuracy and precision.