Skeletal Muscle Blood Flow Research Articles

Skeletal muscle blood flow response to local PO2 is impaired in high fat diet fed Sprague Dawley and Zucker Diabetic Sprague Dawley rats

Objective: Quantify the capillary blood flow responses to dynamic changes in oxygen concentrations ([O2]) in 27-week-old Sprague Dawley (SD) and Zucker Diabetic Sprague Dawley (ZDSD) type 2 diabetic (T2D) rats during hyperinsulinemic-euglycemic clamp. Hypothesis: Chronic hyperglycemia and elevated insulin in T2D causes impaired oxygen mediated blood flow regulation leading to functional defects in capillary network blood flow distribution at rest, during hyperinsulinemia, and in response to oxygen challenges. Methods: 8 SD and 10 ZDSD rats were fed high fat (HF) diet upon arrival at 15 weeks old, transitioned to a HF and high sugar diet from 16-19 weeks old, to induce T2D in the ZDSD strain, before being returned to HF until intravital video microscopy (IVVM). At 27 weeks of age, animals were fasted overnight and on the morning of the experiment animals were anaesthetized, mechanically ventilated, and catheters were introduced for systemic monitoring, fluid resuscitation and anaesthetic administration. The extensor digitorum longus muscle was isolated, blunt dissected, and reflected over a microfluidic gas exchange chamber fitted in the stage of an inverted microscope. Microvascular blood flow responses to sequential changes in [O2] (7%-12%-2%-7%) were recorded at baseline and during hyperinsulinemic-euglycemic clamp. Hyperinsulinemic-euglycemic clamp was achieved by simultaneous infusion of insulin (2U/hr/kg) and variable rate of 50% glucose until euglycemia was reached (5-7 mM). ZDSD rats with fasting blood glucose <20 mM on the day of IVVM were excluded from the hyperglycemic group. Analysis of IVVM videos was completed offline using custom MATLAB software. Animal protocols were approved by Memorial University’s Animal Care Committee. Results: SD red blood cell (RBC) saturation (SO2) significantly increased in response to 12% [O2] at both baseline and clamp (62.0 ± 5.9 vs. 75.8 ± 3.8 %, p <0.0001, and 62.7 ± 8.2 vs. 76.7 ± 6.5 %, p = 0.0001), RBC SO2 significantly decreased with 2% [O2] under both conditions compared to 7% (62.0 ± 5.9 vs. 38.1 ± 6.3 %, p <0.0001, and 62.7 ± 8.2 vs. 46.0 ± 9.5 %, p <0.0001). RBC velocity, supply rate (SR) and hematocrit showed no change from 7% (174.8 ± 59.7 μm/s, 10.7 ± 3.4 cells/s, and 27.5 ± 3.8 %) in response to increased or decreased [O2]. ZDSD rats had a significant increase between baseline and clamp in RBC SR at 12% (19.5 ± 3.3 vs 23.7 ± 9.1 cells/s, p = 0.0151) as well as at 2% (14.9 ± 2.6 vs 23.9 ± 8.0 cells/s, p = 0.0295). However, there was no change in RBC velocity or hematocrit in the ZDSD strain in response to imposed [O2] changes at baseline and clamp. Conclusion: SD and ZDSD animals lacked expected responses in capillary RBC velocity, SR, and hematocrit to imposed local [O2] changes both at baseline and during euglycemic clamp. This finding suggests that both hyperglycemia in T2D and high fat feeding alone affects microvascular blood flow responses to acute changes in local oxygen concentrations. This project was supported by the Canadian Institute of Health Research through a project grant to GMF. Studentships were supported by Memorial University's School of Graduate Studies and the Faculty of Medicine. This is the full abstract presented at the American Physiology Summit 2023 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.

Sympathetic and hemodynamic responses to exercise in heart failure with preserved ejection fraction.

Excessive sympathetic activity during exercise causes heightened peripheral vasoconstriction, which can reduce oxygen delivery to active muscles, resulting in exercise intolerance. Although both patients suffering from heart failure with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively) exhibit reduced exercise capacity, accumulating evidence suggests that the underlying pathophysiology may be different between these two conditions. Unlike HFrEF, which is characterized by cardiac dysfunction with lower peak oxygen uptake, exercise intolerance in HFpEF appears to be predominantly attributed to peripheral limitations involving inadequate vasoconstriction rather than cardiac limitations. However, the relationship between systemic hemodynamics and the sympathetic neural response during exercise in HFpEF is less clear. This mini review summarizes the current knowledge on the sympathetic (i.e., muscle sympathetic nerve activity, plasma norepinephrine concentration) and hemodynamic (i.e., blood pressure, limb blood flow) responses to dynamic and static exercise in HFpEF compared to HFrEF, as well as non-HF controls. We also discuss the potential of a relationship between sympathetic over-activation and vasoconstriction leading to exercise intolerance in HFpEF. The limited body of literature indicates that higher peripheral vascular resistance, perhaps secondary to excessive sympathetically mediated vasoconstrictor discharge compared to non-HF and HFrEF, drives exercise in HFpEF. Excessive vasoconstriction also may primarily account for over elevations in blood pressure and concomitant limitations in skeletal muscle blood flow during dynamic exercise, resulting in exercise intolerance. Conversely, during static exercise, HFpEF exhibit relatively normal sympathetic neural reactivity compared to non-HF, suggesting that other mechanisms beyond sympathetic vasoconstriction dictate exercise intolerance in HFpEF.

Microbiota Mediate Enhanced Exercise Capacity Induced by Exercise Training.

We investigated the effects of gut microbes, and the mechanisms mediating the enhanced exercise performance induced by exercise training, i.e., skeletal muscle blood flow, and mitochondrial biogenesis and oxidative function in male mice. All mice received a graded exercise test before (PRE) and after exercise training via forced treadmill running at 60% to 70% of maximal running capacity 5 d·wk -1 for 5 wk (POST). To examine the role of the gut microbes, the graded exercise was repeated after 7 d of access to antibiotic (ABX)-treated water, used to eliminate gut microbes. Peripheral blood flow, mitochondrial oxidative capacity, and markers of mitochondrial biogenesis were collected at each time point. Exercise training led to increases of 60% ± 13% in maximal running distance and 63% ± 11% work to exhaustion ( P < 0.001). These increases were abolished after ABX ( P < 0.001). Exercise training increased hindlimb blood flow and markers of mitochondrial biogenesis and oxidative function, including AMP-activated protein kinase, sirtuin-1, PGC-1α citrate synthase, complex IV, and nitric oxide, all of which were also abolished by ABX treatment. Our results support the concept that gut microbiota mediate enhanced exercise capacity after exercise training and the mechanisms responsible, i.e., hindlimb blood flow, mitochondrial biogenesis, and metabolic profile. Finally, results of this study emphasize the need to fully examine the impact of prescribing ABX to athletes during their training regimens and how this may affect their performance.

Adrenergic control of skeletal muscle blood flow during chronic hypoxia in healthy males.

Sympathetic transduction is reduced following chronic high-altitude (HA) exposure; however, vascular α-adrenergic signaling, the primary mechanism mediating sympathetic vasoconstriction at sea level (SL), has not been examined at HA. In nine male lowlanders, we measured forearm blood flow (Doppler ultrasound) and calculated changes in vascular conductance (ΔFVC) during 1) incremental intra-arterial infusion of phenylephrine to assess α1-adrenergic receptor responsiveness and 2) combined intra-arterial infusion of β-adrenergic and α-adrenergic antagonists propranolol and phentolamine (α-β-blockade) to assess adrenergic vascular restraint at rest and during exercise-induced sympathoexcitation (cycling; 60% peak power). Experiments were performed near SL (344 m) and after 3 wk at HA (4,383 m). HA abolished the vasoconstrictor response to low-dose phenylephrine (ΔFVC: SL: -34 ± 15%, vs. HA; +3 ± 18%; P < 0.0001) and markedly attenuated the response to medium (ΔFVC: SL: -45 ± 18% vs. HA: -28 ± 11%; P = 0.009) and high (ΔFVC: SL: -47 ± 20%, vs. HA: -35 ± 20%; P = 0.041) doses. Blockade of β-adrenergic receptors alone had no effect on resting FVC (P = 0.500) and combined α-β-blockade induced a similar vasodilatory response at SL and HA (P = 0.580). Forearm vasoconstriction during cycling was not different at SL and HA (P = 0.999). Interestingly, cycling-induced forearm vasoconstriction was attenuated by α-β-blockade at SL (ΔFVC: Control: -27 ± 128 vs. α-β-blockade: +19 ± 23%; P = 0.0004), but unaffected at HA (ΔFVC: Control: -20 ± 22 vs. α-β-blockade: -23 ± 11%; P = 0.999). Our results indicate that in healthy males, altitude acclimatization attenuates α1-adrenergic receptor responsiveness; however, resting α-adrenergic restraint remains intact, due to concurrent resting sympathoexcitation. Furthermore, forearm vasoconstrictor responses to cycling are preserved, although the contribution of adrenergic receptors is diminished, indicating a reliance on alternative vasoconstrictor mechanisms.

Abstract 10465: Abnormal Post Exercise Skeletal Muscle Microvascular Response and Metabolism Correlate With Patient Reported Outcomes in Patients With Intermittent Claudication From Peripheral Artery Disease

Background and Aims: Intermittent claudication (IC) in patients with peripheral artery disease (PAD) is thought to be caused by reduced lower extremity macrovascular blood flow. However, the ankle-brachial index (ABI) (a macrovascular measure) does not correlate well with patient-reported outcome measures. We aimed to study microvascular and metabolic skeletal muscle responses to exercise in patients with IC using positron emission tomography (PET). Methods: We enrolled 19 patients with IC (ABI &amp;lt; 0.90 and imaging/angiographic evidence of PAD) and 12 healthy controls (HCs) (normal ABI). All subjects underwent rest perfusion imaging of the legs with 13 N-ammonia or 11 C-acetate PET followed by a graded treadmill test. Subjects exercised until limited by claudication or the end of the 20-minute protocol. Subjects then underwent immediately post-exercise PET imaging of the legs. Skeletal muscle blood flow (SMBF) was quantified in each leg at rest and immediately post-exercise. Skeletal muscle oxygen utilization (SMVO 2 ) normalized to SMBF was also quantified for patients who underwent imaging with 11 C-acetate. Peripheral artery questionnaire (PAQ) summary score was obtained for all subjects. Results: We found that SMBF was increased post-exercise in all subjects, and stress/rest SMBF was higher in the legs of subjects with PAD than in the legs of HCs ( Figure 1A ). We also found that stress SMVO 2 /SMBF was higher in legs of patients with PAD than in the legs of HCs ( Figure 1B ). There was a moderate, significant correlation between limb stress/rest SMBF and PAQ score ( Figure 1C ) and a strong, significant correlation between limb stress SMVO 2 /SMBF and PAQ score ( Figure 1D ). Conclusions: In conclusion, we found that SMBF increased in all subjects after treadmill exercise and paradoxically to the greatest degree in patients with IC. We also found that PET-derived markers of post-exercise microvascular perfusion and metabolism correlated with patient-reported outcomes.

AKG/OXGR1 promotes skeletal muscle blood flow and metabolism by relaxing vascular smooth muscle

Abstract In response to contraction during exercise, skeletal muscle growth and metabolism are dynamically regulated by nerve action, blood flow, and metabolic feedback. α-Ketoglutarate (AKG), a bioactive intermediate in the tricarboxylic acid cycle released during exercise, has been shown to promote skeletal muscle hypertrophy. However, the underlying mechanism of AKG in regulating skeletal muscle development and metabolism is still less known. 2-Oxoglutarate receptor 1 (OXGR1), the endogenous AKG receptor, is found to be distributed in the vascular smooth muscle (VSM) of skeletal muscles. OXGR1 knockout results in skeletal muscle atrophy, accompanied by decreased expression of myosin heavy chain I (MyHC I), capillary density, and endurance exercise capacity. Furthermore, the study found that dietary AKG supplementation increased mice endurance exercise distance, MyHC I/MyHC IIb ratio, arteriole, and capillary densities in skeletal muscle. Meanwhile, acute AKG administration gradually increased the blood flow in the lower limbs. Further, by using OXGR1 global knockout and OXGR1 VSM-specific (MYH11-Cre × OXGR1-FloxP) knockdown models, we found that OXGR1 in VSM is essential for AKG-induced improvement of skeletal muscle performances. According to the in vitro study, AKG expanded the cell area in VSM with a decreased intracellular pH by OXGR1. Our results demonstrated a novel role of AKG/OXGR1 in VSM of skeletal muscle to regulate blood flow and then enhance slow muscle fiber conversion and capillarization. These findings provide a theoretical basis for the AKG/OXGR1 signaling pathway to maintain human muscle function and improve meat production and livestock and poultry meat quality.

Does sympathetic vasoconstriction contribute to metabolism: Perfusion matching in exercising skeletal muscle?

The process of matching skeletal muscle blood flow to metabolism is complex and multi-factorial. In response to exercise, increases in cardiac output, perfusion pressure and local vasodilation facilitate an intensity-dependent increase in muscle blood flow. Concomitantly, sympathetic nerve activity directed to both exercising and non-active muscles increases as a function of exercise intensity. Several studies have reported the presence of tonic sympathetic vasoconstriction in the vasculature of exercising muscle at the onset of exercise that persists through prolonged exercise bouts, though it is blunted in an exercise-intensity dependent manner (functional sympatholysis). The collective evidence has resulted in the current dogma that vasoactive molecules released from skeletal muscle, the vascular endothelium, and possibly red blood cells produce local vasodilation, while sympathetic vasoconstriction restrains vasodilation to direct blood flow to the most metabolically active muscles/fibers. Vascular smooth muscle is assumed to integrate a host of vasoactive signals resulting in a precise matching of muscle blood flow to metabolism. Unfortunately, a critical review of the available literature reveals that published studies have largely focused on bulk blood flow and existing experimental approaches with limited ability to reveal the matching of perfusion with metabolism, particularly between and within muscles. This paper will review our current understanding of the regulation of sympathetic vasoconstriction in contracting skeletal muscle and highlight areas where further investigation is necessary.

Skeletal muscle blood flow during exercise is reduced in a rat model of pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is characterized by exercise intolerance. Muscle blood flow may be reduced during exercise in PAH; however, this has not been directly measured. Therefore, we investigated blood flow during exercise in a rat model of monocrotaline (MCT)-induced pulmonary hypertension (PH). Male Sprague-Dawley rats (∼200 g) were injected with 60 mg/kg MCT (MCT, n = 23) and vehicle control (saline; CON, n = 16). Maximal rate of oxygen consumption (V̇o2max) and voluntary running were measured before PH induction. Right ventricle (RV) morphology and function were assessed via echocardiography and invasive hemodynamic measures. Treadmill running at 50% V̇o2max was performed by a subgroup of rats (MCT, n = 8; CON, n = 7). Injection of fluorescent microspheres determined muscle blood flow via photo spectroscopy. MCT demonstrated a severe phenotype via RV hypertrophy (Fulton index, 0.61 vs. 0.31; P < 0.001), high RV systolic pressure (51.5 vs. 22.4 mmHg; P < 0.001), and lower V̇o2max (53.2 vs. 71.8 mL·min-1·kg-1; P < 0.0001) compared with CON. Two-way ANOVA revealed exercising skeletal muscle blood flow relative to power output was reduced in MCT compared with CON (P < 0.001), and plasma lactate was increased in MCT (10.8 vs. 4.5 mmol/L; P = 0.002). Significant relationships between skeletal blood flow and blood lactate during exercise were observed for individual muscles (r = -0.58 to -0.74; P < 0.05). No differences in capillarization were identified. Skeletal muscle blood flow is significantly reduced in experimental PH. Reduced blood flow during exercise may be, at least in part, consequent to reduced exercise intensity in PH. This adds further evidence of peripheral muscle dysfunction and exercise intolerance in PAH.

Isolated knee extensor exercise training improves skeletal muscle vasodilation, blood flow, and functional capacity in patients with HFpEF.

Patients with HFpEF experience severe exercise intolerance due in part to peripheral vascular and skeletal muscle impairments. Interventions targeting peripheral adaptations to exercise training may reverse vascular dysfunction, increase peripheral oxidative capacity, and improve functional capacity in HFpEF. Determine if 8 weeks of isolated knee extension exercise (KE) training will reverse vascular dysfunction, peripheral oxygen utilization, and exercise capacity in patients with HFpEF. Nine HFpEF patients (66 ± 5 years, 6 females) performed graded IKE exercise (5, 10, and 15 W) and maximal exercise testing (cycle ergometer) before and after IKE training (3x/week, 30 min/leg). Femoral blood flow (ultrasound) and leg vascular conductance (LVC; index of vasodilation) were measured during graded IKE exercise. Peak pulmonary oxygen uptake (V̇O2; Douglas bags) and cardiac output (QC; acetylene rebreathe) were measured during graded maximal cycle exercise. IKE training improved LVC (pre: 810 ± 417, post: 1234 ± 347 ml/min/100 mmHg; p = 0.01) during 15 W IKE exercise and increased functional capacity by 13% (peak V̇O2 during cycle ergometry; pre:12.4 ± 5.2, post: 14.0 ± 6.0 ml/min/kg; p = 0.01). The improvement in peak V̇O2 was independent of changes in Q̇c (pre:12.7 ± 3.5, post: 13.2 ± 3.9 L/min; p = 0.26) and due primarily to increased a‐vO2 difference (pre: 10.3 ± 1.6, post: 11.0 ± 1.7; p = 0.02). IKE training improved vasodilation and functional capacity in patients with HFpEF. Exercise interventions aimed at increasing peripheral oxidative capacity may be effective therapeutic options for HFpEF patients.

Age-related impairments in ATP release by red blood cells as an important contributor to declines in skeletal muscle blood flow in older adults.

Age-related impairments in ATP release by red blood cells as an important contributor to declines in skeletal muscle blood flow in older adults.

Global REACH 2018: increased adrenergic restraint of blood flow preserves coupling of oxygen delivery and demand during exercise at high-altitude.

Chronic exposure to hypoxia (high-altitude, HA; >4000m) attenuates the vasodilatory response to exercise and is associated with a persistent increase in basal sympathetic nerve activity (SNA). The mechanism(s) responsible for the reduced vasodilatation and exercise hyperaemia at HA remains unknown. We hypothesized that heightened adrenergic signalling restrains skeletal muscle blood flow during handgrip exercise in lowlanders acclimatizing to HA. We tested nine adult males (n=9) at sea-level (SL; 344 m) and following 21-28days at HA (∼4300m). Forearm blood flow (FBF; duplex ultrasonography), mean arterial pressure (MAP; brachial artery catheter), forearm vascular conductance (FVC; FBF/MAP), and arterial and venous blood sampling (O2 delivery ( ) and uptake ( )) were measured at rest and during graded rhythmic handgrip exercise (5%, 15% and 25% of maximum voluntary isometric contraction; MVC) before and after local α- and β-adrenergic blockade (intra-arterial phentolamine and propranolol). HA reduced ΔFBF (25% MVC: SL: 138.3±47.6 vs. HA: 113.4±37.1mlmin-1 ; P=0.022) and Δ (25% MVC: SL: 20.3±7.5 vs. HA: 14.3±6.2mlmin-1 ; P=0.014) during exercise. Local adrenoreceptor blockade at HA restored FBF during exercise (25% MVC: SLα-β blockade : 164.1±71.7 vs. HAα-β blockade : 185.4±66.6mlmin-1 ; P=0.947) but resulted in an exaggerated relationship between and ( / slope: SL: 1.32; HA: slope: 1.86; P=0.037). These results indicate that tonic adrenergic signalling restrains exercise hyperaemia in lowlanders acclimatizing to HA. The increase in adrenergic restraint is necessary to match oxygen delivery to demand and prevent over perfusion of contracting muscle at HA. KEY POINTS: In exercising skeletal muscle, local vasodilatory signalling and sympathetic vasoconstriction integrate to match oxygen delivery to demand and maintain arterial blood pressure. Exposure to chronic hypoxia (altitude, >4000m) causes a persistent increase in sympathetic nervous system activity that is associated with impaired functional capacity and diminished vasodilatation during exercise. In healthy male lowlanders exposed to chronic hypoxia (21-28days; ∼4300m), local adrenoreceptor blockade (combined α- and β-adrenergic blockade) restored skeletal muscle blood flow during handgrip exercise. However, removal of tonic adrenergic restraint at high altitude caused an excessive rise in blood flow and subsequently oxygen delivery for any given metabolic demand. This investigation is the first to identify greater adrenergic restraint of blood flow during acclimatization to high altitude and provides evidence of a functional role for this adaptive response in regulating oxygen delivery and demand.

Impact of supervised exercise on skeletal muscle blood flow and vascular function measured with MRI in patients with peripheral artery disease.

Supervised exercise is a common therapeutic intervention for patients with peripheral artery disease (PAD), however, the mechanism underlying the improvement in claudication symptomatology is not completely understood. The hypothesis that exercise improves microvascular blood flow is herein tested via temporally resolved magnetic resonance imaging (MRI) measurement of blood flow and oxygenation dynamics during reactive hyperemia in the leg with the lower ankle-brachial index. One hundred and forty-eight subjects with PAD were prospectively assigned to standard medical care or 3 mo of supervised exercise therapy. Before and after the intervention period, subjects performed a graded treadmill walking test, and MRI data were collected with Perfusion, Intravascular Venous Oxygen saturation, and T2* (PIVOT), a method that simultaneously quantifies microvascular perfusion, as well as relative oxygenation changes in skeletal muscle and venous oxygen saturation in a large draining vein. The 3-mo exercise intervention was associated with an improvement in peak walking time (64% greater in those randomized to the exercise group at follow-up, P < 0.001). Significant differences were not observed in the MRI measures between the subjects randomized to exercise therapy versus standard medical care based on an intention-to-treat analysis. However, the peak postischemia perfusion averaged across the leg between baseline and follow-up visits increased by 10% (P = 0.021) in participants that were adherent to the exercise protocol (completed >80% of prescribed exercise visits). In this cohort of adherent exercisers, there was no difference in the time to peak perfusion or oxygenation metrics, suggesting that there was no improvement in microvascular function nor changes in tissue metabolism in response to the 3-mo exercise intervention.NEW & NOTEWORTHY Supervised exercise interventions can improve symptomatology in patients with peripheral artery disease, but the underlying mechanism remains unclear. Here, MRI was used to evaluate perfusion, relative tissue oxygenation, and venous oxygen saturation in response to cuff-induced ischemia. Reactive hyperemia responses were measured before and after 3 mo of randomized supervised exercise therapy or standard medical care. Those participants who were adherent to the exercise regimen had a significant improvement in peak perfusion.

Rho-kinase inhibition improves haemodynamic responses and circulating ATP during hypoxia and moderate intensity handgrip exercise in healthy older adults.

Skeletal muscle haemodynamics and circulating adenosine triphosphate (ATP) responses during hypoxia and exercise are blunted in older (OA) vs. young (YA) adults, which may be associated with impaired red blood cell (RBC) ATP release. Rho‐kinase inhibition improves deoxygenation‐induced ATP release from OA isolated RBCs. We tested the hypothesis that Rho‐kinase inhibition (via fasudil) in vivo would improve local haemodynamic and ATP responses during hypoxia and exercise in OA. Healthy YA (25 ± 3 years; n = 12) and OA (65 ± 5 years; n = 13) participated in a randomized, double‐blind, placebo‐controlled, crossover study on two days (≥5 days between visits). A forearm deep venous catheter was used to administer saline/fasudil and sample venous plasma ATP ([ATP]V). Forearm vascular conductance (FVC) and [ATP]V were measured at rest, during isocapnic hypoxia (80% SpO2), and during graded rhythmic handgrip exercise that was similar between groups (5, 15 and 25% maximum voluntary contraction (MVC)). Isolated RBC ATP release was measured during normoxia/hypoxia. With saline, ΔFVC was lower (P < 0.05) in OA vs. YA during hypoxia (∼60%) and during 15 and 25% MVC (∼25–30%), and these impairments were abolished with fasudil. Similarly, [ATP]V and ATP effluent responses from normoxia to hypoxia and rest to 25% MVC were lower in OA vs. YA and improved with fasudil (P < 0.05). Isolated RBC ATP release during hypoxia was impaired in OA vs. YA (∼75%; P < 0.05), which tended to improve with fasudil in OA (P = 0.082). These data suggest Rho‐kinase inhibition improves haemodynamic responses to hypoxia and moderate intensity exercise in OA, which may be due in part to improved circulating ATP. Key points Skeletal muscle blood flow responses to hypoxia and exercise are impaired with age. Blunted increases in circulating ATP, a vasodilator, in older adults may contribute to age‐related impairments in haemodynamics.Red blood cells (RBCs) are a primary source of circulating ATP, and treating isolated RBCs with a Rho‐kinase inhibitor improves age‐related impairments in deoxygenation‐induced RBC ATP release.In this study, treating healthy older adults systemically with the Rho‐kinase inhibitor fasudil improved blood flow and circulating ATP responses during hypoxia and moderate intensity handgrip exercise compared to young adults, and also tended to improve isolated RBC ATP release.Improved blood flow regulation with fasudil was also associated with increased skeletal muscle oxygen delivery during hypoxia and exercise in older adults.This is the first study to demonstrate that Rho‐kinase inhibition can significantly improve age‐related impairments in haemodynamic and circulating ATP responses to physiological stimuli, which may have therapeutic implications.

0153 Bright light exposition potentiates the vasodilation promoted by dynamic handgrip exercise

Abstract Introduction Bright light (~5000 lux) directed at human skin increases plasma nitric oxide concentration promoting vasodilation, with increased skeletal muscle blood flow (BF) and decreased blood pressure (BP). The same stimulus directed at the eyes increases sympathetic activity, promoting vasoconstriction and increased BP. If bright light potentiates or mitigates the vasodilation promoted during exercise is unknown. Therefore, this study aimed to compare the effect of different intensities of lights on vasodilation of the active skeletal muscle during dynamic handgrip exercise. Methods Eleven healthy and physically inactive adult men (29±6 years) participated of the current study. All experiments were conducted between June and July 2021, beginning at 5 PM and under constant environmental conditions. Subjects performed dynamic handgrip exercise using the dominant arm at a 90º angle in the supine position with 2 s cycles of contraction and relaxation for 6 min at 40% of maximal voluntary contraction during the three experimental condition in a randomized order: (BL) 5000 lux, Control light (CL) 500 lux, and Dim light (DL) ≤8 lux. In each condition, (BL, CL or DL), subjects remained in a rested state for 20 min before 1 min of baseline assessment followed by exercise. Conditions were always separated by 20 min of washout (under CL). Assessments comprised BF, vascular conductance (VC), and diameter of brachial artery of exercising arm (Ultrasound); BP measured in the rest arm (Photoplethysmography) and heart rate (ECG). Two-way ANOVA for repeated measures, p≤0.05. Results Baseline were not different (p&amp;gt;0.05). During exercise, BF and VC increased in the three conditions, however it was potentiated by BL (p &amp;lt; 0.0001 and p &amp;lt; 0.0001, respectively) compared with CL (+19% and +15%, respectively) and with DL (+12% and +11%, respectively). Arterial diameter increased similarly in the three conditions. Mean BP increased in the three conditions, however it was attenuated in the BL compared with DL (-23%) and similar to CL (&amp;lt;0.0001). Conclusion Bright light can potentiate skeletal muscle vasodilation during a small-mass muscle exercise attenuating the increase of BP. Support (If Any) The São Paulo Research Foundation - FAPESP 2020/11588-2.

Longitudinal Changes in Skeletal Muscle Metabolism, Oxygen Uptake, and Myosteatosis During Cardiotoxic Treatment for Early-Stage Breast Cancer

BackgroundWhile cardiotoxic chemotherapy is known to negatively impact cardiac function and hemoglobin levels, the impact on skeletal muscle has been understudied among patients. The purpose was to longitudinally characterize myosteatosis (muscle fat), skeletal muscle metabolism, and oxygen (O2) consumption during cardiotoxic chemotherapy for breast cancer.Patients and MethodsThirty-four patients with stage I-III breast cancer were enrolled before trastuzumab-containing and/or anthracycline-containing chemotherapy. We used magnetic resonance imaging to non-invasively quantify thigh myosteatosis (fat-water imaging), and lower leg metabolism (31P spectroscopy), O2 consumption (custom techniques), and peak power output during single-leg plantarflexion exercise at pre-, mid-, end-chemotherapy, and 1-year. We also measured pulmonary VO2peak and maximal leg press strength.ResultsDuring chemotherapy, VO2peak and leg press strength decreased while peak plantarflexion power output was maintained. At mid-chemotherapy, hemoglobin decreased (16%) and lower leg blood flow increased (37%) to maintain lower leg O2 delivery; exercise Pi:PCr and myosteatosis increased. Between mid- and end-chemotherapy, lower leg O2 extraction (28%) and O2 consumption (21%) increased, while plantarflexion exercise efficiency (watts/O2 consumed) decreased. At one year, VO2peak and leg press strength returned to pre-chemotherapy levels, but lower leg exercise O2 extraction, consumption and Pi:PCr, and myosteatosis remained elevated.ConclusionLower leg skeletal muscle blood flow and O2 extraction adapt to compensate for chemotherapy-related hemoglobin reduction for small muscle mass exercise but are insufficient to maintain large muscle mass exercise (pulmonary VO2peak, leg press strength). The excess O2 required to perform work, increased Pi:PCr ratio and myosteatosis together suggest suppressed fat oxidation during chemotherapy.

Cerebrovascular Dynamics During Light Exercise

Cerebral blood flow (CBF) dynamic response to moderate‐intensity exercise has a time delay (TD) of ~ 40s. This is dramatically longer compared to other physiological responses to exercise (e.g. skeletal muscle blood flow &lt;10 s) and CBF response to other stimuli (e.g. hypercapnia, thigh cuff occlusion, ~ 10‐20 s). A possible explanation is that a rest‐to‐exercise transition induces a brief hypotensive response due to intensity dependent rapid vasodilation of the periphery (exercise‐onset hypotension, EoH).PurposeTo determine if the magnitude and timing of EoH, effectively reduces CBF at exercise onset causing the longer observed TD. To test this, we modelled CBF kinetic response to light‐intensity exercise to mitigate the magnitude of EoH and determine if components of the CBF response were quickened in young healthy adults.Methods26 young healthy adults (13 Women, 23.8 ± 4 yrs; 23.9 ± 2.9 kg/m2) completed a rest (2min seated quietly, BL) to exercise (3 minutes at 50W, EX) transition on a recumbent cycle ergometer. Middle cerebral artery velocity (MCAv; transcranial doppler) and mean arterial pressure (MAP; finger photoplethysmography) were measured on a heartbeat‐by‐heartbeat basis. End‐tidal CO2 (EtCO2) was measured using breath‐by‐breath capnography. Cerebral vascular conductance index (CVCi) was calculated as (CVCi = MCAv/MAP *100 mmHg). Change in MCAv data (ΔMCAv = MCAvEX‐MCAvBL) were averaged into 2 s bins and fit to a monoexponential model (ΔMCAv(t)= Amp(1‐e‐(t‐TD)/ τ)). Time delay (TD), tau (τ), and mean response time (MRT = TD + τ) were obtained from the model. Several subjects (N=11) exhibited little to no TD (TD &lt; 1 s), these subjects (FAST) were separated out and compared to individuals with longer TDs (TD ≥ 3 s; SLOW). Comparisons were made using an independent t‐test.ResultsAll data is mean±SD. In total, subjects exhibited a TD of 15.4 ± 18.2 s, τ of 79.8 ± 139.7, and MRT of 95.3 ± 134.9 s. This coincided with a ΔMAPNADIR (‐14.5 ± 8.2 mmHg), ΔMCAvNADIR (‐5.7 ± 5.8 cm/s) which occurred at similar times (14.0 ± 17.2 vs. 18.6 ± 14.4 s; p=0.30 MAPNADIR vs. MCAvNADIR), and ΔCVCiMAX (25.3 ± 34.0 cm/s/100mmHg). When data were split, the FAST group experienced a faster TD compared to SLOW (0.01 ± 0.01 vs. 26.8 ± 16.4 s; p&lt;0.001). ΔMCAvNADIR although different (‐1.0 ± 4.0 vs. ‐9.1 ± 4.2 cm/s; p&lt;0.001, FAST vs. SLOW), occurred at similar times (20.5 ± 17.3 vs. 17.3 ± 12.5 s; p=0.59, FAST vs. SLOW). ΔMAPNADIR (‐14.4 ± 10.4 vs. ‐14.6 ± 6.5 mmHg; p=0.97) and CVCiMAX (22.1 ± 25.4 vs. 27.6 ± 39.9 cm/s/100mmHg; p=0.56 FAST vs. SLOW) were not different between groups. There were no other differences between groups regrading demographic, EtCO2, or other kinetic variables.DiscussionOur data indicates EoH is related to the initial drop in CBF and TD during light‐exercise is faster (15.9 s) when compared to previous research during moderate‐intensity exercise (~40 s). However, our data identifies fast responders who have minimal TD and MCAvNADIR responses without differing EoH at the same absolute exercise intensity. Therefore, these data reveal monoexponential CBF models ignore initial perturbances to CBF and disregard potentially important cerebrovascular mechanisms occurring prior to model predicted blood flow increases.

Rapid Onset Vasodilation: Impact of Cardiorespiratory Fitness

IntroductionHigher cardiorespiratory fitness is associated with greater vascular function that leads to improved regulation of skeletal muscle blood flow during exercise. Rapid onset vasodilation (ROV) describes the immediate increase in blood flow following a single contraction, which is integral to support greater blood flow during exercise. As such, blood flow regulation during exercise hyperemia is important. However, it is unclear if cardiorespiratory fitness plays a role in ROV of small muscle mass in young, healthy individuals.PurposeTo investigate the relationship of cardiorespiratory fitness on ROV following a single handgrip (HG) contraction in young, healthy adults.MethodsCardiorespiratory fitness (VO2peak) was assessed during a maximal cycle ergometer test in 14 volunteers (M/F, 6/8; 28 ± 5yrs; 24.8 ± 4.1kg/m2). Brachial velocity and diameter were measured using duplex Doppler ultrasound for 10 cardiac cycles prior to and 20 cardiac cycles following the first cardiac cycle after a single 30% of maximal voluntary handgrip contraction. Brachial artery blood flow (FBF) was calculated for each cardiac cycle: (diameter2/2)*π*velocity*60. Peak forearm (brachial) blood flow (FBFpeak) was determined as the maximal FBF from baseline following the first cardiac cycle after the single HG contraction. Time to peak blood flow response was determined as the time to reach FBFpeak and heart rate was measured using a three‐lead ECG. The relationship between FBFpeak and time to peak blood flow was tested using a multivariate regression analysis with cardiorespiratory fitness and sex as independent variables.ResultsCardiorespiratory fitness (VO2peak: 30.6 ± 8.0mL/kg/min); β for VO2peak= 0.162 [0.003, 0.327]) was the only predictor of time to peak blood flow response, F(1,12)= 4.602, p= 0.05, R2= 0.217, r= 0.526, while sex (β for time to peak= ‐106.5 [‐156.9, ‐56.2]) was the only predictor of FBFpeak, F(1,12)= 21.245, p&lt;0.001, R2= 0.609, r= 0.799, indicating that females had a lower FBFpeakoverall.ConclusionOur data suggests blood flow responsiveness (e.g., time to peak) is positively associated with cardiorespiratory fitness and these data contribute to our understanding of potential mechanisms between improved blood flow regulation commonly associated with greater cardiorespiratory fitness. More research is necessary to fully elucidate the role biological sex has on these relationships, but our data suggest there may be sex differences in certain blood flow responses.

Acute Heat Exposure Improves Microvascular Function in Skeletal Muscle of Aged Humans

Acute heat exposure improves microvascular function in the leg of aged adults as assessed using post‐occlusive reactive hyperemia. However, reactive hyperemia measures whole‐limb blood flow and cannot isolate perfusion among various tissues. Thus, it is unclear if the skeletal muscle circulation contributes to the improvement in microvascular function observed following acute heat exposure. We tested the hypothesis that acute hot water immersion would improve microvascular function in the vastus lateralis of aged adults. Seven aged adults (1 man, 71 ± 4 yrs) were immersed to the umbilicus for 60 min in thermoneutral (36 °C) or hot (40 °C) water. Body core temperature was measured via a telemetric pill. Two microdialysis probes were placed in the vastus lateralis ~30 min after immersion. Microdialysis was utilized to bypass the cutaneous circulation and directly assess endothelial‐dependent and endothelial‐independent microvascular function in skeletal muscle by measuring the local blood flow response to a graded infusion of acetylcholine (ACh, 27.5 and 55.0 mM) and sodium nitroprusside (SNP, 21 and 42 mM), respectively. Local blood flow was measured using the ethanol washout technique. Body core temperature increased by Δ1.1 ± 0.3 °C during hot water immersion but was relatively unchanged during thermoneutral immersion (Δ0.1 ± 0.3 °C). Baseline skeletal muscle blood flow did not differ between thermal conditions for the ACh probe (P= 0.9), nor the SNP probe (P= 0.7). The hyperemic response to 27.5 mM ACh did not differ between thermal conditions (thermoneutral immersion, Δ11.3 ± 11.5 ml/min/100g vs. hot water immersion, Δ18.6 ± 16.8 ml/min/100g; P = 0.7). However, the hyperemic response to 55.0 mM ACh was increased with prior hot water immersion (thermoneutral immersion, Δ30.7 ± 16.9 ml/min/100g vs. hot water immersion, Δ56.2 ± 19.7 ml/min/100g; P &lt; 0.01). Similarly, the hyperemic response to 21 mM SNP did not differ between thermal conditions (thermoneutral immersion, Δ16.9 ± 16.8 ml/min/100g vs. hot water immersion, Δ18.2 ± 18.8 ml/min/100g; P= 0.9), but was increased with prior hot water immersion during the infusion of 42 mM SNP (thermoneutral immersion, Δ29.3 ± 14.4 ml/min/100g vs. hot water immersion, Δ58.5 ± 31.2 ml/min/100g; P = 0.02). These data suggest that acute heat exposure improves endothelial‐dependent and endothelial‐independent microvasculature function in skeletal muscle of aged humans. Furthermore, these data highlight the therapeutic potential of heat therapy to attenuate the hypoperfusion of skeletal muscle that occurs in aged adults during conditions that require an elevated blood supply such as exercise.

Gastric inhibitory polypeptide as the new candidate for the interaction of skeletal muscle blood flow and glucose disposal.

Gastric inhibitory polypeptide as the new candidate for the interaction of skeletal muscle blood flow and glucose disposal.

Evaluation of Local Skeletal Muscle Blood Flow in Manipulative Therapy by Diffuse Correlation Spectroscopy.

Manipulative therapy (MT) is applied to motor organs through a therapist’s hands. Although MT has been utilized in various medical treatments based on its potential role for increasing the blood flow to the local muscle, a quantitative validation of local muscle blood flow in MT remains challenging due to the lack of appropriate bedside evaluation techniques. Therefore, we investigated changes in the local blood flow to the muscle undergoing MT by employing diffuse correlation spectroscopy, a portable and emerging optical measurement technology that non-invasively measures blood flow in deep tissues. This study investigated the changes in blood flow, heart rate, blood pressure, and autonomic nervous activity in the trapezius muscle through MT application in 30 volunteers without neck and shoulder injury. Five minutes of MT significantly increased the median local blood flow relative to that of the pre-MT period (p < 0.05). The post-MT local blood flow increase was significantly higher in the MT condition than in the control condition, where participants remained still without receiving MT for the same time (p < 0.05). However, MT did not affect the heart rate, blood pressure, or cardiac autonomic nervous activity. The post-MT increase in muscle blood flow was significantly higher in the participants with muscle stiffness in the neck and shoulder regions than in those without (p < 0.05). These results suggest that MT could increase the local blood flow to the target skeletal muscle, with minimal effects on systemic circulatory function.