Limb Blood Flow Research Articles

Warning: Tourniquets Risk Frostbite in Cold Weather.

We sought to better understand the frostbite risk during first-aid tourniquet use by reviewing information relevant to an association between tourniquet use and frostbite. However, there is little information concerning this subject, which may be of increasing importance because future conflicts against near-peer competitors may involve extreme cold weather environments. Historically, clinical frostbite cases with tourniquet use occurred in low frequency but in high severity when leading to limb amputation. The physiologic response of vasoconstriction to cold exposure leads to limb cooling and causes a reduction of limb blood flow, but cold-induced vasodilation ensues as periodic fluctuations that increase blood flow to hands and feet. In animal experiments, tourniquet use increased the development of frostbite. Evidence from human experiments also supports an association between tourniquet use and frostbite. Clinical guidance for caregiving to casualties at risk for frostbite with tourniquet use had previously been provided but slowly and progressively dropped out of documents. Conclusions: The cause of frostbite was deduced to be a sufficiently negative heat-transfer trend in local tissues, which tourniquet use may worsen because of decreasing tissue perfusion. An association between tourniquet use and frostbite exists but not as cause and effect. Tourniquet use increased the risk of the cold causing frostbite by allowing faster cooling of a limb because of reduced blood flow and lack of cold-induced vasodilation. Care providers above the level of the lay public are warned that first-aid tourniquet use in low-temperature (<0°C [<32°F]) environmental conditions risks frostbite.

Effects of Pemafibrate on Reducing Oxidative Stress and Augmenting Angiogenesis in Ischemic Limb Tissue.

Oxidative damage is observed in the ischemic limbs of patients with arteriosclerosis obliterans. We investigated whether pemafibrate, a selective peroxisome proliferator-activated receptor alpha modulator, reduced oxidative stress in ischemic limbs and consequently rescued limb damage in model mice. We surgically induced hind-limb ischemia in mice and orally administered pemafibrate solution (P-05 group, 0.5 mg/kg/day; P-10 group, 1.0 mg/kg/day) or control solution (control group). Seven days after the surgery, differences in reactive oxygen species (ROS) contents, antioxidative enzyme and transcription factor expression, blood flow, and capillary density in ischemic limbs were assessed. Tissue ROS levels were lower in the P-05 and P-10 groups compared with those in the control group. Although the tissue expression levels of nuclear factor-erythroid 2-related factor 2 increased in the P-10 group compared with that in the control group, no corresponding changes were observed in the tissue expression of four antioxidative enzymes. The limb salvage rates and capillary densities in ischemic limbs were higher in the P-05 and P-10 groups than that in the control group. Pemafibrate treatment reduced oxidative stress and augmented angiogenesis in ischemic limbs, contributing to prevention of limb damage in mice.

High sodium intake differentially impacts brachial artery dilation when evaluated with reactive versus active hyperemia in salt resistant individuals.

This study sought to determine if high sodium (HS) intake in salt resistant (SR) individuals attenuates upper limb arterial dilation in response to reactive (occlusion) and active (exercise) hyperemia, two stimuli with varying vasodilatory mechanisms, and the role of oxidative stress in this response. Ten young, SR participants (9 males, 1 female) consumed a 7-day HS (6,900 mg/day) and a 7-day recommended sodium intake (RI: 2,300 mg/day) diet in a randomized order. On the last day of each diet, brachial artery (BA) function was evaluated via reactive (RH-FMD: 5 min of cuff occlusion) and active [handgrip (HG) exercise] hyperemia after consumption of both placebo (PL) and antioxidants (AO). The HS diet significantly elevated sodium excretion (P < 0.05), but mean arterial blood pressure was unchanged. During the PL condition, the HS diet significantly reduced RH-FMD when compared with RI diet (P = 0.01), but this reduction was significantly restored (P = 0.01) when supplemented with AO (HS + PL: 5.9 ± 3.4; HS + AO: 8.2 ± 2.7; RI + PL: 8.9 ± 4.7; RI + AO: 7.0 ± 2.1%). BA shear-to-dilation slopes, evaluated across all HG exercise workloads, were not significantly different across sodium intervention or AO supplementation. In SR individuals, HS intake impaired BA function when assessed via RH-FMD, but was restored with acute AO consumption suggesting oxidative stress as a contributor to this dysfunction. However, exercise-induced BA dilation was unaltered, potentially implicating an inability of HS intake to influence the mechanisms responsible for effectively maintaining skeletal muscle perfusion during exercise.NEW & NOTEWORTHY This study examined if high sodium (HS) intake in salt resistant (SR) individuals attenuates brachial artery (BA) flow-mediated dilation in response to reactive (occlusion) and active (exercise) hyperemia. In SR individuals, HS intake impaired reactive hyperemia-induced BA dilation, but not exercise-induced BA dilation. This finding suggests that although brachial artery nitric oxide bioavailability may be reduced following HS intake, the redundant mechanisms associated with adequate upper limb blood flow regulation during exercise are maintained.

The Efficacy of HGF/VEGF Gene Therapy for Limb Ischemia in Mice with Impaired Glucose Tolerance: Shift from Angiogenesis to Axonal Growth and Oxidative Potential in Skeletal Muscle

Combined non-viral gene therapy (GT) of ischemia and cardiovascular disease is a promising tool for potential clinical translation. In previous studies our group has developed combined gene therapy by vascular endothelial growth factor 165 (VEGF165) + hepatocyte growth factor (HGF). Our recent works have demonstrated that a bicistronic pDNA that carries both human HGF and VEGF165 coding sequences has a potential for clinical application in peripheral artery disease (PAD). The present study aimed to test HGF/VEGF combined plasmid efficacy in ischemic skeletal muscle comorbid with predominant complications of PAD-impaired glucose tolerance and type 2 diabetes mellitus (T2DM). Male C57BL mice were housed on low-fat (LFD) or high-fat diet (HFD) for 10 weeks and metabolic parameters including FBG level, ITT, and GTT were evaluated. Hindlimb ischemia induction and plasmid administration were performed at 10 weeks with 3 weeks for post-surgical follow-up. Limb blood flow was assessed by laser Doppler scanning at 7, 14, and 21 days after ischemia induction. The necrotic area of m.tibialis anterior, macrophage infiltration, angio- and neuritogenesis were evaluated in tissue sections. The mitochondrial status of skeletal muscle (total mitochondria content, ETC proteins content) was assessed by Western blotting of muscle lysates. At 10 weeks, the HFD group demonstrated impaired glucose tolerance in comparison with the LFD group. HGF/VEGF plasmid injection aggravated glucose intolerance in HFD conditions. Blood flow recovery was not changed by HGF/VEGF plasmid injection either in LFD or HFD conditions. GT in LFD, but not in HFD conditions, enlarged the necrotic area and CD68+ cells infiltration. However, HGF/VEGF plasmid enhanced neuritogenesis and enlarged NF200+ area on muscle sections. In HFD conditions, HGF/VEGF plasmid injection significantly increased mitochondria content and ETC proteins content. The current study demonstrated a significant role of dietary conditions in pre-clinical testing of non-viral GT drugs. HGF/VEGF combined plasmid demonstrated a novel aspect of potential participation in ischemic skeletal muscle regeneration, through regulation of innervation and bioenergetics of muscle. The obtained results made HGF/VEGF combined plasmid a very promising tool for PAD therapy in impaired glucose tolerance conditions.

AhR regulates VEGF expression by promoting STAT1 transcriptional activity, thereby affecting endothelial angiogenesis in acute limb ischemia

BackgroundAngiogenesis has great potential in the treatment of acute limb ischemia (ALI). Here, we aimed to investigate the effect and mechanism of Aryl hydrocarbon receptor (AhR) on angiogenesis in ALI. MethodsThe ALI mouse model was constructed by femoral artery ligation, and the cell ischemia injury was induced by Hypoxia/serum deprivation. The laser doppler perfusion imaging was executed to detect the limb blood flow velocity. The tube formation assay was performed to evaluate angiogenesis. The cell viability was measured by 3-(45)-dimethylthiahiazo(-z-y1)-35-di-phenytetrazoliumromide. The cell migration was detected by wound healing assay. Hematoxylin-eosin, immunohistochemistry, immunofluorescence, dual-luciferase reporter gene assay, and Chromatin immunoprecipitation assay were conducted. ResultsIn ALI models, AhR expression was increased and translocated from cytoplasm to nucleus. Besides, necrosis and inflammatory infiltration were also increased in gastrocnemius tissues of model mice. In addition, AhR loss (LV-sh-AhR) promoted cell viability, angiogenesis, and migration, and also elevated the levels of vascular endothelial growth factor (VEGF), Tie2, and Ang2 in HUVEC models with Hypoxia/serum deprivation injury. Meanwhile, the interaction between AhR and signal transducer and activator of transcription 1 (STAT1), as well as STAT1 and VEGF, has also been confirmed. Co-transfection of LV-sh-AhR and LV-STAT1 suppressed cell viability, angiogenesis, and migration of injured HUVECs. Furthermore, injection of AAV2/9-shAhR in vivo also promoted angiogenesis, which was consistent with the in vitro experimental results. ConclusionsIn ALI models, activated AhR was translocated to the nucleus and down-regulated VEGF expression by promoting the transcriptional activity of STAT1, thereby inhibiting endothelial angiogenesis.

Adipose-derived stem cell-secreted exosomes enhance angiogenesis by promoting macrophage M2 polarization in type 2 diabetic mice with limb ischemia via the JAK/STAT6 pathway

Diabetic lower limb ischemia is an intractable disease that leads to amputation and even death. Recently, adipose-derived stem cell-secreted exosomes (ADSC-Exo) have been reported as a potential therapeutic approach, but its specific mechanism of action is unknown. Studies have found that exosomes derived from stem cells can reduce inflammation and promote tissue repair. Macrophages play an important role in the development and repair of inflammation in lower limb ischemic tissue, but the specific regulation of ADSC-Exo in macrophages has rarely been reported. The present study aimed to verify whether ADSC-Exo could promote angiogenesis by regulating macrophages to reduce the level of inflammation in diabetic ischemic lower limbs. In this study, adipose-derived stem cells (ADSCs) were obtained and identified, and ADSC-Exos were isolated using ultracentrifugation and characterized using transmission electron microscopy, nanoparticle tracking analysis, and western blotting analysis. The uptake of ADSC-Exos by macrophages was observed using immunofluorescence, and macrophage polarization induced by ADSC-Exos was identified by flow cytometry, immunofluorescence and ELISA. The effects of ADSC-Exos on the proliferation, apoptosis, migration and adhesion of macrophages were evaluated using CCK-8 assay, flow cytometry, Transwell assay, scratch and adhesion experiments, and ELISA assay. The polarization-related JAK/STAT6 signaling pathway was explored by using western blotting. A lower limb ischemic model of type 2 diabetic mice was established and ADSC-Exos was intramuscularly injected into the mice. The blood flow in the lower limbs was assessed using a laser Doppler flowmeter, while the level of angiogenesis was determined using immunohistochemistry and immunofluorescence. The results of this study prove that ADSC-Exos induced M2-phenotype polarization of macrophages via the JAK/STAT6 signaling pathway can promote the proliferation, migration and adhesion of M2 macrophages, inhibit the apoptosis of macrophages, and promote the angiogenesis and revascularization of ischemic lower limbs in type 2 diabetic mice. Thus, this study provides a theoretical and experimental basis for the clinical treatment of diabetic lower limb ischemic disease.

Sex differences in blood pressure and inactive limb blood flow responses during dynamic leg exercise with increased inspiratory muscle work.

We hypothesized that, compared with young males, young females have a smaller decrease in blood flow to the inactive limb, accompanied by a smaller increase in arterial blood pressure, during dynamic exercise with increased inspiratory muscle work. Young males and females performed dynamic knee-extension and -flexion exercises for 10 min (spontaneous breathing for 5 min and voluntary hyperpnoea with or without inspiratory resistance for 5 min). Mean arterial blood pressure (MAP) and mean blood flow (MBF) in the brachial artery were continuously measured by means of finger photoplethysmography and Doppler ultrasound, respectively. No sex differences were found in the ΔMAP and ΔMBF (Δ: from baseline) during exercise without inspiratory resistance. In contrast, the ΔMAP during exercise with inspiratory resistive breathing was greater (P < 0.05) in males (+31.3 ± 2.1 mmHg, mean ± SE) than females (+18.9 ± 3.2 mmHg). The MBF during exercise with inspiratory resistance did not change in males (-4.4 ± 10.6 mL/min), whereas it significantly increased in females (+25.2 ± 15.4 mL/min). These results suggest that an attenuated inspiratory muscle-induced metaboreflex in young females affects blood flow distribution during submaximal dynamic leg exercise.

Temporal analysis of skeletal muscle remodeling post hindlimb ischemia reveals intricate autophagy regulation.

Hind limb ischemia (HLI) is the most severe form of peripheral arterial disease, associated with a substantial reduction of limb blood flow that impairs skeletal muscle homeostasis to promote functional disability. The molecular regulators of HLI-induced muscle perturbations remain poorly defined. This study investigated whether changes in the molecular catabolic-autophagy signaling network were linked to temporal remodeling of skeletal muscle in HLI. HLI was induced in mice via hindlimb ischemia (femoral artery ligation) and confirmed by Doppler echocardiography. Experiments were terminated at time points defined as early- (7 days; n = 5) or late- (28 days; n = 5) stage HLI. Ischemic and nonischemic (contralateral) limb muscles were compared. Ischemic versus nonischemic muscles demonstrated overt remodeling at early-HLI but normalized at late-HLI. Early-onset fiber atrophy was associated with excessive autophagy signaling in ischemic muscle; protein expression increased for Beclin-1, LC3, and p62 (P < 0.05) but proteasome-dependent markers were reduced (P < 0.05). Mitophagy signaling increased in early-stage HLI that aligned with an early and sustained loss of mitochondrial content (P < 0.05). Upstream autophagy regulators, Sestrins, showed divergent responses during early-stage HLI (Sestrin2 increased while Sestrin1 decreased; P < 0.05) in parallel to increased AMP-activated protein kinase (AMPK) phosphorylation (P < 0.05) and lower antioxidant enzyme expression. No changes were found in markers for mechanistic target of rapamycin complex 1 signaling. These data indicate that early activation of the sestrin-AMPK signaling axis may regulate autophagy to stimulate rapid and overt muscle atrophy in HLI, which is normalized within weeks and accompanied by recovery of muscle mass. A complex interplay between Sestrins to regulate autophagy signaling during early-to-late muscle remodeling in HLI is likely.

CircCRIM1 Ameliorates Endothelial Cell Angiogenesis in Aging through the miR-455-3p/Twist1/VEGFR2 Signaling Axis.

Background Aging leads to vascular endothelial cell senescence. Decreased expression of VEGFA and VEGFR2 plays a crucial role in impairing angiogenesis in senescent endothelial cells. Noncoding RNAs, including circular RNAs (circRNAs) and microRNAs (miRNAs), regulate endothelial cell proliferation, differentiation, apoptosis, and migration and participate in the occurrence and development of vascular diseases. However, the mechanism of noncoding RNAs in age-related vascular endothelial dysfunction remains unclear. Here, we aimed to identify the circRNA that is associated with VEGF/VEGFR2 signaling pathway activation in angiogenesis. Methods Immunoblotting, quantitative reverse transcription-polymerase chain reaction (qRT–PCR), in vitro and in vivo experiments, luciferase assays, and chromatin immunoprecipitation followed by qRT–PCR (ChIP–qPCR) assays were performed to clarify the roles played by circCRIM1 in mouse aortic endothelial cell (MAEC) angiogenesis. Results CircCRIM1 expression was downregulated in both an aging mouse model of lower limb ischemia in vivo and aging MAECs in vitro. Overexpressing circCRIM1 mediated through a plasmid or adeno-associated virus (AAV) reversed the downregulation of angiogenesis-related phenotype acquisition during aging. MiR-455-3p was confirmed to be a potential target of circCRIM1 through luciferase assays followed by RNA fluorescence in situ hybridization (FISH), which revealed the colocalization of circCRIM1 and miR-455-3p. CircCRIM1 was found to be a competitive endogenous RNA that sponged miR-455-3p and regulated angiogenesis-related phenotypes in MAECs. Furthermore, Twist1 was found to be downstream of miR-455-3p. A ChIP–qPCR assay showed that Twist1 promoted VEGFR2 expression by binding to the promoter region, playing a vital role in angiogenesis. Conclusions Decreased expression of circCRIM1 impaired angiogenesis in aging via the miR-455-3p/Twist1/VEGFR2 axis. Our findings suggest that overexpression of circCRIM1 may be an effective therapeutic strategy for promoting ischemic lower limb blood flow recovery.

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.

Changes In Splanchnic Blood Flow And Blood Pressure During Inspiratory Resistive Breathing

PURPOSE: The hyperpnea during whole-body heavy exercise leads to an increase in respiratory muscle work, which is associated with cardiovascular regulations during exercise (i.e., respiratory muscle metaboreflex). In resting condition, blood flow to inactive limbs is reduced with inspiratory resistive breathing. Furthermore, increasing the work of breathing during dynamic exercise influences inactive limb blood flow. Therefore, it is conceivable that the respiratory muscle-induced metaboreflex is associated with blood flow redistribution during exercise. Redistribution of blood flow is also associated with splanchnic blood flow as well as inactive blood flow. However, influence of respiratory muscle metaboreflex on splanchnic blood flow in humans remains unknown. We hypothesized that blood flow to splanchnic organs would reduce via respiratory muscle-induced metaboreflex. METHODS: Ten healthy young men (20.2 ± 0.4 yrs, mean ± SE) performed two voluntary hyperventilation tests (tidal volume of 40% of vital capacity, a breathing frequency of 40 breaths/min and inspiratory duty cycle of 50%). One trial was voluntary hyperventilation with inspiratory resistance (about 40% of maximal inspiratory pressure), and the trial was terminated when the subject could not maintain the target ventilation (the resistance trial), and the other one was voluntary hyperventilation without inspiratory resistance until the same time as the resistance trial (the non-resistance trial). During trials, mean arterial blood pressure (MAP) was measured using finger photoplethysmography, and celiac artery blood flow was recorded by Doppler ultrasonography. RESULTS: MAP increased progressively and was higher (P < 0.05) in the resistance trial (100.5 ± 4.4 mmHg) than in the non-resistance trial (92.8 ± 2.0 mmHg) at the end of trial. Celiac artery blood flow decreased gradually from baseline value in the resistance trial (469.3 ± 47.6 mL/min), whereas did not change in the non-resistance trial (605.7 ± 56.2 mL/min). Celiac artery vascular conductance was lower in the resistance trial (4.8 ± 0.6 mL/min/mmHg) than in the non-resistance trial (6.6 ± 0.6 mL/min/mmHg, P < 0.05). CONCLUSIONS: These results suggest that increasing work of breathing affects the splanchnic circulation, via respiratory muscle-induced metaboreflex.

Effects of nociceptive and mechanosensitive afferents sensitization on central and peripheral hemodynamics following exercise-induced muscle damage.

This study aims to test the separated and combined effects of mechanoreflex activation and nociception through exercise-induced muscle damage (EIMD) on central and peripheral hemodynamics before and during single passive leg movement (sPLM). Eight healthy young males undertook four experimental sessions, in which a sPLM was performed on the dominant limb while in each specific session the contralateral was: 1) in a resting condition (CTRL), 2) stretched (ST), 3) resting after EIMD called delayed onset muscle soreness (DOMS) condition, or 4) stretched after EIMD (DOMS + ST). EIMD was used to induce DOMS in the following 24-48 h. Femoral blood flow (FBF) was assessed using Doppler ultrasound whereas central hemodynamics were assessed via finger photoplethysmography. Leg vascular conductance (LVC) was calculated as FBF/mean arterial pressure (MAP). RR-intervals were analyzed in the time (root mean squared of successive intervals; RMSSD) and frequency domain [low frequency (LF)/high frequency (HF)]. Blood samples were collected before each condition and gene expression analysis showed increased fold changes for P2X4 and IL1β in DOMS and DOMS + ST compared with baseline. Resting FBF and LVC were decreased only in the DOMS + ST condition (-26 mL/min and -50 mL/mmHg/min respectively) with decreased RMSSD and increased LF/HF ratio. MAP, HR, CO, and SV were increased in ST and DOMS + ST compared with CTRL. Marked decreases of Δpeaks and AUC were observed for FBF (Δ: -146 mL/min and -265 mL respectively) and LVC (Δ: -8.66 mL/mmHg/min and ±1.7 mL/mmHg/min respectively) all P < 0.05. These results suggest that the combination of mechanoreflex and nociception resulted in decreased vagal tone and concomitant rise in sympathetic drive that led to increases in resting central hemodynamics with reduced limb blood flow before and during sPLM.NEW & NOTEWORTHY Exercise-induced muscle damage (EIMD) is a well-known model to study mechanical hyperalgesia and muscle peripheral nerve sensitizations. The combination of static stretching protocol on the damaged limb extensively increases resting central hemodynamics with reduction in resting limb blood flow and passive leg movement-induced hyperemia. The mechanism underlining these results may be linked to reduction of vagal tone with concomitant increase in sympathetic activity following mechano- and nociceptive activation.

Ruan Jian Qing Mai Recipe Inhibits the Inflammatory Response in Acute Lower Limb Ischemic Mice through the JAK2/STAT3 Pathway.

Ruan jian qing mai recipe (RJQM) is an empirical prescription for treating arteriosclerosis obliterans (ASO). However, the mechanism of RJQM recipe-mediated ASO attenuation has not yet been elucidated. Therefore, this study aimed to explore the mechanism by which the RJQM recipe relieves ASO in a mouse model of lower limb ischemia, which was established by ligating and breaking the femoral artery of the left lower limb. The surgical groups were divided into the ischemic group, beraprost sodium group, low-dose RJQM group, medium-dose RJQM group, and high-dose RJQM group. Normal mice were set as the control group. The blood flow of the lower limb was examined on days 7 and 14. At the end of animal procedures, blood samples were collected, and the rectus femoris of the left lower limb were harvested. Results revealed that mice in the ischemic group demonstrated low blood flow. Additionally, hematoxylin and eosin, and Masson staining results showed that inflammation of the rectus femoris was obvious in the ischemia group, and the level of fibrosis was increased. Blood flow was recovered in all treatment groups compared to the ischemic group, and the inflammatory infiltration and fibrosis of the rectus femoris were relieved after RJQM treatment. The serum levels of interleukin (IL)-17A and IL-21 were decreased, and the expression of JAK2/STAT3 proteins was inhibited in all RJQM treatment groups compared to the ischemia group. Furthermore, the improvement of IL-17A, IL-21, and rectus femoris fibrosis was more obvious with increasing treatment time. In conclusion, RJQM can effectively alleviate ASO and promote the recovery of lower limb blood flow by regulating the JAK2/STAT3 signaling pathway to reduce the inflammatory response.

Differences in the limb blood flow between two types of blood flow restriction cuffs: A pilot study.

Introduction: The determination of the optimal occlusion level is a key parameter in blood flow restriction (BFR). This study aimed to compare the effects of elastic (BStrong) vs. nylon (Hokanson) BFR cuffs on blood flow in the lower and upper limbs. Methods: Eleven healthy participants undertook several BFR sessions with 2 different cuffs of similar width on their lower and upper limbs at different pressures [200, 250, 300, 350, and 400 mmHg for BStrong and 0, 40, and 60% of the arterial occlusion pressure (AOP) for Hokanson]. Doppler ultrasound recorded blood flows through the brachial and femoral artery at rest. Results: With BStrong, only 350 and 400 mmHg pressures were significantly different from resting values (0% AOP). With Hokanson, both 40% and 60% of the AOP were significantly different from resting values (p < 0.05). Discussion: While both cuffs elicited BFR, they failed to accurately modulate blood flow. Hokanson is appropriate for research settings while BStrong appears to be a convenient tool for practitioners due to its safety (i.e., the impossibility of completely occluding arteries) and the possibility of exercising freely detached from the pump.

Single Leg Cycling Offsets Reduced Muscle Oxygenation in Hypoxic Environments.

The intensity of large muscle mass exercise declines at altitude due to reduced oxygen delivery to active muscles. The purpose of this investigation was to determine if the greater limb blood flow during single-leg cycling prevents the reduction in tissue oxygenation observed during traditional double-leg cycling in hypoxic conditions. Ten healthy individuals performed bouts of double and single-leg cycling (4, four-minute stages at 50–80% of their peak oxygen consumption) in hypoxic (15% inspired O2) and normoxic conditions. Heart rate, mean arterial pressure, femoral blood flow, lactate, oxygenated hemoglobin, total hemoglobin, and tissue saturation index in the vastus lateralis were recorded during cycling tests. Femoral blood flow (2846 ± 912 mL/min) and oxygenated hemoglobin (−2.98 ± 3.56 au) during single-leg cycling in hypoxia were greater than double-leg cycling in hypoxia (2429 ± 835 mL/min and −6.78 ± 3.22 au respectively, p ≤ 0.01). In addition, tissue saturation index was also reduced in the double-leg hypoxic condition (60.2 ± 3.1%) compared to double-leg normoxic (66.0 ± 2.4%, p = 0.008) and single-leg hypoxic (63.3 ± 3.2, p < 0.001) conditions. These data indicate that while at altitude, use of reduced muscle mass exercise can help offset the reduction in tissue oxygenation observed during larger muscle mass activities allowing athletes to exercise at greater limb/muscle specific intensities.

Dietary nitrate supplementation and small muscle mass exercise hemodynamics in patients with essential hypertension.

Exaggerated blood pressure and diminished limb hemodynamics during exercise in patients with hypertension often are not resolved by antihypertensive medications. We hypothesized that, independent of antihypertensive medication status, dietary nitrate supplementation would increase limb blood flow, decrease mean arterial pressure (MAP), and increase limb vascular conductance during exercise in patients with hypertension. Patients with hypertension either abstained from (n = 14, Off-Meds) or continued (n = 12, On-Meds) antihypertensive medications. Within each group, patients consumed (crossover design) nitrate-rich or nitrate-depleted (placebo) beetroot juice for 3 days before performing handgrip (HG) and knee-extensor exercise (KE). Blood flow and MAP were measured using Doppler ultrasound and an automated monitor, respectively. Dietary nitrate increased plasma-[nitrite] Off-Meds and On-Meds. There were no significant effects of dietary nitrate on blood flow, MAP, or vascular conductance during HG in Off-Meds or On-Meds. For KE, dietary nitrate decreased MAP (means ± SD across all 3 exercise intensities, 118 ± 14 vs. 122 ± 14 mmHg, P = 0.024) and increased vascular conductance (26.2 ± 6.1 vs. 24.7 ± 7.0 mL/min/mmHg, P = 0.024), but did not affect blood flow for Off-Meds, with no effects On-Meds. Dietary nitrate-induced changes in blood flow (r = -0.67, P < 0.001), MAP (r = -0.43, P = 0.009), and vascular conductance (r = -0.64, P < 0.001) during KE, but only vascular conductance (r = -0.35, P = 0.039) during HG, were significantly related to the magnitude of placebo values, with no differentiation between groups. Thus, the effects of dietary nitrate on limb hemodynamics and MAP during exercise in patients with hypertension are dependent on the values at baseline, independent of antihypertensive medication status, and dependent on whether exercise was performed by the forearm or quadriceps.NEW & NOTEWORTHY Adverse hemodynamic responses to exercise in patients with hypertension, despite antihypertensive medication, indicate a sustained cardiovascular risk. The efficacy of dietary nitrate to improve limb vascular conductance during exercise was inversely dependent on the magnitude of exercising limb vascular conductance at baseline, rather than antihypertensive medication status. The effects of dietary nitrate on hemodynamics during exercise in patients with hypertension are dependent on the values at baseline and independent of antihypertensive medication status.

The Use of Limb Blood Flow Occlusion for Rehabilitation and Performance

Apply it! • Gain a better understanding of the purpose of occlusion training, how to properly utilize it, and when to use it with your clients. • Understand the contraindications to occlusion training and know some of the possible health risks associated with it.

N-Acetylcysteine Enhances the Recovery of Ischemic Limb in Type-2 Diabetic Mice

Critical limb ischemia (CLI) is a severe complication of diabetes mellitus that occurs without effective therapy. Excessive reactive oxygen species (ROS) production and oxidative stress play critical roles in the development of diabetic cardiovascular complications. N-acetylcysteine (NAC) reduces ischemia-induced ROS production. The present study aimed to investigate the effect of NAC on the recovery of ischemic limb in an experimental model of type-2 diabetes. TALLYHO/JngJ diabetic and SWR/J non-diabetic mice were used for developing a CLI model. For NAC treatment, mice received NAC (1 mg/mL) in their drinking water for 24 h before initiating CLI, and continuously for the duration of the experiment. Blood flow, mechanical function, histology, expression of antioxidant enzymes including superoxide dismutase (SOD)-1, SOD-3, glutathione peroxidase (Gpx)-1, catalase, and phosphorylated insulin receptor substrate (IRS)-1, Akt, and eNOS in ischemic limb were evaluated in vivo or ex vivo. Body weight, blood glucose, plasma advanced glycation end-products (AGEs), plasma insulin, insulin resistance index, and plasma TNF-a were also evaluated during the experiment. NAC treatment effectively attenuated ROS production with preserved expressions of SOD-1, Gpx-1, catalase, phosphorylated Akt, and eNOS, and enhanced the recovery of blood flow and function of the diabetic ischemic limb. NAC treatment also significantly decreased the levels of phosphorylated IRS-1 (Ser307) expression and plasma TNF-α in diabetic mice without significant changes in blood glucose and AGEs levels. In conclusion, NAC treatment enhanced the recovery of blood flow and mechanical function in ischemic limbs in T2D mice in association with improved tissue redox/inflammatory status and insulin resistance.

Cardiac Adjustments During a Very Hot and Dry Heatwave Simulation in Older Adults

Heatwaves are the leading cause of death among natural disasters in the United States and are predicted to increase in frequency, duration, and severity. During heatwaves, older adults (over 65 years old) have disproportionally greater morbidity and mortality, primarily from cardiovascular complications. However, it is unknown whether a very hot and dry heat wave simulation would impair cardiac function in older adults.PurposeWe tested the hypothesis that three hours of exposure to a very hot and dry heat wave simulation would increase left‐ventricular contractility (s’) in older adults.MethodsWe assessed internal body temperature (ingestible telemetric pill and/or rectal thermistor), mean skin temperature (thermocouples), cardiac function (echocardiography), limb blood flow (brachial artery sonography) in eight healthy older adults (5 Female/3 Male; 70 ± 4 years; 26 ± 3 kg•m‐2) while they were exposed to a simulation of the 2018 Los Angeles heatwave for three hours. We measured hemodynamics in a temperate environment (~23 ºC) before repeating these measures after three hours of heat exposure in an environmental chamber (46 ± 1 ºC, 17 ± 1 % relative humidity). For ecological validity, participants performed seven bouts of exercise (3 METS for 5 minutes) dispersed across the three‐hour‐long heat exposure to simulate activities of daily living. Additionally, participants consumed 9 mL of 15 ºC (tap‐temperature) water per kilogram of body mass dispersed throughout the trial. We compared values before (BASE) or at the start (START) of heating with values obtained at the end of heating (END) using a Wilcoxon test for propagation velocity, limb blood flow and vascular conductance, and paired, two‐tailed t‐tests for all other variables.ResultsInternal body temperature (START: 36.8 ± 0.4, END: 38.2 ± 0.5 ºC, p&lt;0.01) and mean skin temperature (START: 35.5 ± 1.3, END: 37.3 ± 0.7 ºC, p=0.02) increased during heating. Heart rate increased (BASE: 73 ± 19, END: 99 ± 40 bpm, p=0.04) and mean arterial pressure decreased (BASE: 90 ± 14, END: 77 ± 11 mmHg, p=0.03) during heating. Combined [septal &amp; lateral] s’ (BASE: 8.2 ± 1.4, END: 11.3 ± 1.5 cm/s, p&lt;0.01) increased during heating, for which changes from BASE to END were moderately, but non‐significantly, related to Δ internal body temperature (R2= 0.25, p= 0.21). Indices of left ventricular diastolic function did not change during heating (p&gt;0.24 for E, A, E/A, combined e’, E/combined e’, propagation velocity, &amp; iso‐volumetric relaxation time). Limb blood flow and vascular conductance increased ~four‐fold during heating (p&lt;0.02 for both).ConclusionThese preliminary data suggest that older adults increase left‐ventricular contractility to maintain stroke volume, potentially to compensate for increased limb vascular conductance, during three hours of exposure to a very hot and dry heatwave simulation.

Limb Hemodynamic Responses to a Single Bout of Inspiratory Muscle Strength Training

BackgroundInspiratory muscle strength training (IMST) has been shown to bring about improvements in respiratory muscle strength and reductions in blood pressure after 6 weeks of daily high intensity training. However, there has been little investigation into the effects of IMST on limb blood flow, and it is unclear how hemodynamics are altered within a single bout of training.PurposeTo investigate the acute effects of one session of either low or high intensity IMST on blood flow in the upper and lower limbs.MethodsParticipants (n=7, 57% female) aged 20 to 47 years completed two randomized laboratory visits wherein resting blood flow was measured via duplex Doppler ultrasound at the left brachial and popliteal arteries. Following baseline measures, participants' maximal inspiratory pressure (PImax) was measured using a PowerBreathe K3 device. Participants performed one session (30 breaths) of IMST at either 15% or 75% of their PImax, and blood flow was measured again at each artery for five breaths during the final ten breaths of the training. At their second visit, subjects performed whichever training level had yet to be completed and blood flow was assessed as described above.ResultsMean blood flow at the brachial artery appeared reduced during both 15% (p=0.070) and 75% training (p=0.078), which may be attributed to a significant increase in retrograde blood flow in both cases (p=0.014 and p=0.037, respectively). This increase in retrograde blood flow tended to be greater during the 75% training (p=0.066). Popliteal artery blood flow showed similar trends to brachial artery blood flow.ConclusionsWhile IMST appears to reduce brachial artery mean blood flow during a single training session, this may be due to alterations in retrograde blood flow, which tended to increase in an intensity‐dependent manner. Further investigation into the chronic hemodynamic effects of IMST is warranted.