Non-Invasive Estimation of Skeletal Muscle Oxygen Consumption Rate and Microvascular Reactivity in Chronic Stroke Survivors using Near Infrared Spectroscopy.

BACKGROUND: Understanding post-stroke changes in skeletal muscle oxidative metabolism and microvascular reactivity could help create therapeutic targets that optimize rehabilitative interventions. Due to disuse atrophy, we hypothesized that basal muscle oxygen consumption rate and microvascular endothelial function would be impaired in the tibialis anterior (TA) muscle of the affected leg of chronic stroke survivors compared to the non-affected leg and vs. matched controls. METHODS: Fifteen chronic stroke survivors (10 female) and 15 matched controls (9 female) completed this study. A near infrared spectroscopy oximeter measured tissue oxygen saturation (StO2) of the TA in both legs of stroke survivors and the dominant leg of controls. A cuff was placed around the thigh and inflated to 225 mmHg for five minutes while StO2 was continuously measured. The rate of change in StO2 was calculated during cuff occlusion and immediately post-cuff release. RESULTS: The rate of oxygen desaturation was similar between the legs of the stroke survivors (paretic -0.12±0.04 %∙s-1 vs non-paretic -0.16±011 %∙s-1; p=0.49), but the paretic leg had a reduced desaturation rate vs. controls (-0.25±0.18%∙s-1; p=0.007 vs. paretic leg). After cuff release, there was a greater oxygen resaturation rate in the non-paretic leg compared to the paretic leg (3.13±2.08 %∙s-1 vs. 1.60±1.11 %∙s-1, respectively; p=0.01). The control leg had a similar resaturation rate vs. the non-paretic leg (control = 3.41±1.79%∙s-1; p=0.69) but was greater than the paretic leg (p=0.003). CONCLUSION: The TA in the paretic leg had an impaired muscle oxygen consumption rate and reduced microvascular endothelial function compared to controls.

5,6-diHETE lactone (EPA-L) mediates hypertensive microvascular dilation by activating the endothelial GPR-PLC-IP3 signaling pathway.

Endothelial microvascular dysfunction affects multi-organ pathologic processes that contribute to increased vascular tone and is at the base of impaired metabolic and cardiovascular diseases. The vascular dilation impaired by nitric oxide (NO) deficiency in such dysfunctional endothelium is often balanced by endothelial-derived hyperpolarizing factors (EDHFs), which play a critical role in managing vascular tone. Our latest research has uncovered a new group of lactone oxylipins produced in the polyunsaturated fatty acids (PUFAs) CYP450 epoxygenase pathway, significantly affecting vascular dilation. The lactone oxylipin, derived from arachidonic acid (5,6-diHET lactone, AA-L), has been previously shown to facilitate vasodilation dependent on the endothelium in isolated human microvessels. The administration of the lactone oxylipin derived from eicosapentaenoic acid (5,6-diHETE lactone, EPA-L) to hypertensive rats demonstrated a significant decrease in blood pressure and improvement in the relaxation of microvessels. However, the molecular signaling processes that underlie these observations were not fully understood. The current study delineates the molecular pathways through which EPA-L promotes endothelium-dependent vascular dilation. In microvessels from hypertensive individuals, it was found that EPA-L mediates endothelium-dependent vasodilation while the signaling pathway was not dependent on NO. In vitro studies on human endothelial cells showed that the hyperpolarization mediated by EPA-L relies on G-protein-coupled receptor (GPR)-phospholipase C (PLC)-IP3 signaling that further activates calcium-dependent potassium flux. The pathway was confirmed using a range of inhibitors and cells overexpressing GPR40, where a specific antagonist reduced the calcium levels and outward currents induced by EPA-L. The downstream AKT and endothelial NO synthase (eNOS) phosphorylations were non-significant. These findings show that the GPR-PLC-IP3 pathway is a key mediator in the EPA-L-triggered vasodilation of arterioles. Therefore, EPA-L is identified as a significant lactone-based PUFA metabolite that contributes to endothelial and vascular health.

Reduced oxygen desaturation in the vastus lateralis of chronic stroke survivors during graded muscle contractions.

BACKGROUND: Few studies have examined changes in skeletal muscle physiology post-stroke. This study examined changes in tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscle of stroke survivors and age-matched control participants during maximal and submaximal isometric contractions of the knee extensor muscles. OBJECTIVES: We hypothesized that tissue oxygen desaturation (ΔStO2) during knee extensor muscle contractions would be less in the VL in the paretic vs. the non-paretic and control legs. METHODS: Ten chronic stroke survivors (>6 months post-stroke) with lower extremity muscle weakness and 10 age-matched controls completed this prospective cohort study. Maximum voluntary contractions (MVCs) of the knee extensor muscles were assessed with a Biodex dynamometer and StO2 of the VL was measured using near-infrared spectroscopy. RESULTS: In the paretic leg of the stroke survivors little change in StO2 of the VL was observed during an MVC (ΔStO2 = -1.7 ± 1.8%) compared to the non-paretic (ΔStO2 = -5.1 ± 6.1%; p < 0.05) and control legs (ΔStO2 = -14.4 ± 8.8%; p < 0.05 vs. paretic and non-paretic leg). These differences remained when normalizing for strength differences between the legs. Compared to controls, both the paretic and non-paretic VL showed pronounced reductions in ΔStO2 during ramp and hold contractions equal to 20%, 40%, or 60% of the MVC (p < 0.05 vs. controls at all load levels). CONCLUSIONS: These results indicate that oxygen desaturation in response to isometric muscle contractions is impaired in both the paretic and non-paretic leg muscle of stroke survivors compared to age-matched controls, and these differences are independent of differences in muscle strength.

Addressing the decline in graduate students' mental well-being.

At the American Physiology Summit 2023 session entitled, "Mental Health for Graduate Students," numerous students expressed struggling with poor mental well-being primarily because of negative experiences during their graduate training. In fact, studies show that up to 50% of graduate students report symptoms of depression, anxiety, or burnout during their training, and poor mental well-being is a major contributor to students' decision to leave academia. Most of the current solutions focus on treatment or wellness strategies; while these are important and necessary, the training environment or culture that often contributes to worsening well-being continues to persist. In this collaborative article between trainees and mentors across various career stages, we discuss how the pace of scientific advancements and the associated competition, lack of sufficient support for students from diverse backgrounds, and mentor-mentee relationships crucially influence graduate students' mental well-being. We then offer specific solutions at the individual, institutional, and national levels that can serve as a starting point for improving graduate students' mental health and overall training experience.

Quantification of Tissue Oxygen Saturation in the Vastus Lateralis Muscle of Chronic Stroke Survivors during a Graded Exercise Test.

Purpose: This study examined tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscles of chronic stroke survivors during a graded exercise test (GXT). We hypothesized the reduction in StO2 will be blunted in the paretic vs. non-paretic VL during a maximum-effort GXT. Methods: Chronic stroke survivors performed a GXT and StO2 of the VL in each leg was measured using near infrared spectroscopy. Twenty-six stroke survivors performed a GXT. Results: At rest, there was no difference in StO2 between the paretic and non-paretic VL (65±9% vs. 68±7%, respectively, p=0.32). The maximum change in StO2 from rest during the GXT was greater in the non-paretic vs. the paretic VL (-16±14% vs. -9±10%, respectively, p<0.001). The magnitude of the oxygen resaturation response was also greater in the non-paretic vs. the paretic VL (29±23% vs. 18±15%, respectively, p<0.001). VO2 Peak was associated with the magnitude of the VL StO2 change during (r2=0.54, p<0.0001) and after (r2=0.56, p<0.001) the GXT. Conclusions: During a GXT there is a blunted oxygen desaturation response in the paretic vs. the non-paretic VL of chronic stroke survivors. In the paretic VL there was a positive correlation between the oxygen desaturation response during the GXT and VO2 Peak.

Lipid phosphate phosphatase 3 maintains NO-mediated flow-mediated dilatation in human adipose resistance arterioles.

Microvascular dysfunction predicts adverse cardiovascular events despite absence of large vessel disease. A shift in the mediator of flow-mediated dilatation (FMD) from nitric oxide (NO) to mitochondrial-derived hydrogen peroxide (H2 O2 ) occurs in arterioles from patients with coronary artery disease (CAD). The underlying mechanisms governing this shift are not completely defined. Lipid phosphate phosphatase 3 (LPP3) is a transmembrane protein that dephosphorylates lysophosphatidic acid, a bioactive lipid, causing a receptor-mediated increase in reactive oxygen species. A single nucleotide loss-of-function polymorphism in the gene coding for LPP3 (rs17114036) is associated with elevated risk for CAD, independent of traditional risk factors. LPP3 is suppressed by miR-92a, which is elevated in the circulation of patients with CAD. Repression of LPP3 increases vascular inflammation and atherosclerosis in animal models. We investigated the role of LPP3 and miR-92a as a mechanism for microvascular dysfunction in CAD. We hypothesized that modulation of LPP3 is critically involved in the disease-associated shift in mediator of FMD. LPP3 protein expression was reduced in left ventricle tissue from CAD relative to non-CAD patients (P = 0.004), with mRNA expression unchanged (P = 0.96). Reducing LPP3 expression (non-CAD) caused a shift from NO to H2 O2 (% maximal dilatation: Control 78.1 ± 11.4% vs. Peg-Cat 30.0 ± 11.2%; P < 0.0001). miR-92a is elevated in CAD arterioles (fold change: 1.9 ± 0.01 P = 0.04), while inhibition of miR-92a restored NO-mediated FMD (CAD), and enhancing miR-92a expression (non-CAD) elicited H2 O2 -mediated dilatation (P < 0.0001). Our data suggests LPP3 is crucial in the disease-associated switch in the mediator of FMD. KEY POINTS: Lipid phosphate phosphatase 3 (LPP3) expression is reduced in heart tissue patients with coronary artery disease (CAD). Loss of LPP3 in CAD is associated with an increase in the LPP3 inhibitor, miR-92a. Inhibition of LPP3 in the microvasculature of healthy patients mimics the CAD flow-mediated dilatation (FMD) phenotype. Inhibition of miR-92a restores nitric oxide-mediated FMD in the microvasculature of CAD patients.

NADPH oxidase 4 contributes to TRPV4-mediated endothelium-dependent vasodilation in human arterioles by regulating protein phosphorylation of TRPV4 channels.

Impaired endothelium-dependent vasodilation has been suggested to be a key component of coronary microvascular dysfunction (CMD). A better understanding of endothelial pathways involved in vasodilation in human arterioles may provide new insight into the mechanisms of CMD. The goal of this study is to investigate the role of TRPV4, NOX4, and their interaction in human arterioles and examine the underlying mechanisms. Arterioles were freshly isolated from adipose and heart tissues obtained from 71 patients without coronary artery disease, and vascular reactivity was studied by videomicroscopy. In human adipose arterioles (HAA), ACh-induced dilation was significantly reduced by TRPV4 inhibitor HC067047 and by NOX 1/4 inhibitor GKT137831, but GKT137831 did not further affect the dilation in the presence of TRPV4 inhibitors. GKT137831 also inhibited TRPV4 agonist GSK1016790A-induced dilation in HAA and human coronary arterioles (HCA). NOX4 transcripts and proteins were detected in endothelial cells of HAA and HCA. Using fura-2 imaging, GKT137831 significantly reduced GSK1016790A-induced Ca2+ influx in the primary culture of endothelial cells and TRPV4-WT-overexpressing human coronary artery endothelial cells (HCAEC). However, GKT137831 did not affect TRPV4-mediated Ca2+ influx in non-phosphorylatable TRPV4-S823A/S824A-overexpressing HCAEC. In addition, treatment of HCAEC with GKT137831 decreased the phosphorylation level of Ser824 in TRPV4. Finally, proximity ligation assay (PLA) revealed co-localization of NOX4 and TRPV4 proteins. In conclusion, both TRPV4 and NOX4 contribute to ACh-induced dilation in human arterioles from patients without coronary artery disease. NOX4 increases TRPV4 phosphorylation in endothelial cells, which in turn enhances TRPV4-mediated Ca2+ entry and subsequent endothelium-dependent dilation in human arterioles.

Endothelial dysfunction as a complication of anti-cancer therapy.

Recent strides in anti-cancer therapeutics have improved longevity and led to a growing population of cancer survivors, who are increasingly likely to die of other causes. Treatment-induced cardiotoxicity is a complication of several therapeutic agents with acute and long-term consequences for cancer patients. Vascular endothelial dysfunction is a precursor and hallmark of ischemic coronary disease and may play a role in anti-cancer therapy-induced cardiotoxicity. This review summarizes clinical evidence for endothelial dysfunction following anti-cancer therapy and extends the discussion to include the impact of therapeutic agents on conduit arteries and the microcirculation. We highlight the role of innate immune system activation and cross-talk between inflammation and oxidative stress as pathogenic mechanisms underlying anti-cancer therapy-induced vascular toxicity. Understanding the impact of anti-cancer agents on the vascular endothelium will inform therapeutic approaches to prevent or reverse treatment-induced cardiotoxicity and may serve as an important tool to predict, monitor, and prevent adverse cardiovascular outcomes in patients undergoing treatment.

Vascular Dysfunction in Preeclampsia.

Preeclampsia is a life-threatening pregnancy-associated cardiovascular disorder characterized by hypertension and proteinuria at 20 weeks of gestation. Though its exact underlying cause is not precisely defined and likely heterogenous, a plethora of research indicates that in some women with preeclampsia, both maternal and placental vascular dysfunction plays a role in the pathogenesis and can persist into the postpartum period. Potential abnormalities include impaired placentation, incomplete spiral artery remodeling, and endothelial damage, which are further propagated by immune factors, mitochondrial stress, and an imbalance of pro- and antiangiogenic substances. While the field has progressed, current gaps in knowledge include detailed initial molecular mechanisms and effective treatment options. Newfound evidence indicates that vasopressin is an early mediator and biomarker of the disorder, and promising future therapeutic avenues include mitigating mitochondrial dysfunction, excess oxidative stress, and the resulting inflammatory state. In this review, we provide a detailed overview of vascular defects present during preeclampsia and connect well-established notions to newer discoveries at the molecular, cellular, and whole-organism levels.

Change in out-of-hospital 12-lead ECG diagnostic classification following resuscitation from cardiac arrest.

INTRODUCTION: We evaluated the incidence of change in serial 12-lead electrocardiogram (ECG) diagnostic classifications in patients resuscitated from out-of-hospital (OH) cardiac arrest (OHCA) comparing OH to emergency department (ED) ECGs. METHODS: This retrospective case series included: 1) adults (≥ 18 years old), 2) resuscitated from OHCA, 3) ≥ 1 OH and 1 ED ECG/patient, and 4) emergency medical services (EMS) transport to the study hospital. OH and ED ECGs were classified as: 1) STEMI (ST-segment Elevation Myocardial Infarction), 2) Ischemic, and 3) Non-ischemic. Two ED physicians and one cardiologist independently classified all ECGs, then generated a consensus opinion classification for each ECG based on American Heart Association's 2018 Expert Consensus criteria. The most ischemic OH ECG classification was compared with the last ED ECG classification. RESULTS: From 7/27/12 to 7/18/19, 176 patients were entered with a mean age of 61.2 ± 16.6 years; 102/176 (58%) were male. Overall, 504 OH and ED 12-lead ECGs were acquired (2.9 ECGs/patient). ECG classification inter-rater reliability kappa score was 0.63 ± 0.02 (substantial agreement). Overall, 86/176 (49%) changed ECG classification from the OH to ED setting; 69/86 (80%) of these ECGs changed from more to less ischemic classifications. Of 49 OH STEMI ECG classifications, 33/49 (67%) changed to a less ischemic (non-STEMI) ED ECG classification. CONCLUSIONS: Change in 12-lead ECG classification from OH to ED setting in patients resuscitated from OHCA was common (49%). The OH STEMI classification changed to a less ischemic (non-STEMI) ED classification in 67% of cases.

Guidelines for the measurement of vascular function and structure in isolated arteries and veins.

The measurement of vascular function in isolated vessels has revealed important insights into the structural, functional, and biomechanical features of the normal and diseased cardiovascular system and has provided a molecular understanding of the cells that constitutes arteries and veins and their interaction. Further, this approach has allowed the discovery of vital pharmacological treatments for cardiovascular diseases. However, the expansion of the vascular physiology field has also brought new concerns over scientific rigor and reproducibility. Therefore, it is appropriate to set guidelines for the best practices of evaluating vascular function in isolated vessels. These guidelines are a comprehensive document detailing the best practices and pitfalls for the assessment of function in large and small arteries and veins. Herein, we bring together experts in the field of vascular physiology with the purpose of developing guidelines for evaluating ex vivo vascular function. By using this document, vascular physiologists will have consistency among methodological approaches, producing more reliable and reproducible results.

Hypertension preserves the magnitude of microvascular flow-mediated dilation following transient elevation in intraluminal pressure.

OBJECTIVE: The objective of this study was to measure flow-mediated dilation (FMD) prior to and following transient increases in intraluminal pressure (IILP) in resistance arterioles isolated from subjects with and without coronary artery disease (CAD) (CAD and non-CAD) and non-CAD subjects with hypertension. METHODS: Arterioles were isolated from discarded surgical tissues (adipose and atrial) from patients without coronary artery disease (non-CAD; ≤1 risk factor, excluding hypertension), with CAD, and non-CAD patients with hypertension (hypertension as the only risk factor). To simulate transient hypertension, increased IILP was generated (150 mmHg, 30 min) by gravity. Arterioles were constricted with endothelin-1, followed by FMD and endothelial-independent dilation prior to and following exposure to IILP. RESULTS: IILP reduced FMD in non-CAD and CAD arterioles relative to pre-IILP (p <.05 at 100 cmH2 O). In contrast, arterioles from non-CAD hypertensive subjects exhibited no reduction in maximal FMD following IILP (p = .84 at 100 cmH2 O). FMD was reduced by L-NAME prior to IILP in non-CAD hypertensive patients (p < .05 at 100 cmH2 O); however, following IILP, FMD was inhibited by peg-cat (p < .05 at 100 cmH2 O), indicating a switch from NO to H2 O2 as the mechanism of dilation. CONCLUSIONS: Acute exposure (30 min) to IILP (150 mmHg) attenuates the magnitude of FMD in non-CAD and CAD resistance arterioles. The presence of clinically diagnosed hypertension in non-CAD resistance arterioles preserves the magnitude of FMD following IILP as a result of a compensatory switch from NO to H2 O2 as the mechanism of dilation.

Sweat the small stuff: The human microvasculature and heart disease.

Traditionally thought of primarily as the predominant regulator of myocardial perfusion, it is becoming more accepted that the human coronary microvasculature also exerts a more direct influence on the surrounding myocardium. Coronary microvascular dysfunction (CMD) not only precedes large artery atherosclerosis, but is associated with other cardiovascular diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy. It is also highly predictive of cardiovascular events in patients with or without atherosclerotic cardiovascular disease. This review focuses on this recent paradigm shift and delves into the clinical consequences of CMD. Concepts of how resistance arterioles contribute to disease will be discussed, highlighting how the microvasculature may serve as a potential target for novel therapies and interventions. Finally, both invasive and non-invasive methods with which to assess the coronary microvasculature both for diagnostic and risk stratification purposes will be reviewed.

Critical Interaction Between Telomerase and Autophagy in Mediating Flow-Induced Human Arteriolar Vasodilation.

OBJECTIVE: Coronary artery disease (CAD) is associated with a compensatory switch in mechanism of flow-mediated dilation (FMD) from nitric oxide (NO) to H2O2. The underlying mechanism responsible for the pathological shift is not well understood, and recent reports directly implicate telomerase and indirectly support a role for autophagy. We hypothesize that autophagy is critical for shear stress-induced release of NO and is a crucial component of for the pathway by which telomerase regulates FMD. Approach and Results: Human left ventricular, atrial, and adipose resistance arterioles were collected for videomicroscopy and immunoblotting. FMD and autophagic flux were measured in arterioles treated with autophagy modulators alone, and in tandem with telomerase-activity modulators. LC3B II/I was higher in left ventricular tissue from patients with CAD compared with non-CAD (2.8±0.2 versus 1.0±0.2-fold change; P<0.05), although p62 was similar between groups. Shear stress increased Lysotracker fluorescence in non-CAD arterioles, with no effect in CAD arterioles. Inhibition of autophagy in non-CAD arterioles induced a switch from NO to H2O2, while activation of autophagy restored NO-mediated vasodilation in CAD arterioles. In the presence of an autophagy activator, telomerase inhibitor prevented the expected switch (Control: 82±4%; NG-Nitro-l-arginine methyl ester: 36±5%; polyethylene glycol catalase: 80±3). Telomerase activation was unable to restore NO-mediated FMD in the presence of autophagy inhibition in CAD arterioles (control: 72±7%; NG-Nitro-l-arginine methyl ester: 79±7%; polyethylene glycol catalase: 38±9%). CONCLUSIONS: We provide novel evidence that autophagy is responsible for the pathological switch in dilator mechanism in CAD arterioles, demonstrating that autophagy acts downstream of telomerase as a common denominator in determining the mechanism of FMD.

Two weeks of remote ischemic conditioning improves brachial artery flow mediated dilation in chronic stroke survivors.

Many stroke survivors have reduced cardiorespiratory fitness as a result of their stroke. Ischemic conditioning (IC) is a noninvasive, cost-effective, easy-to-administer intervention that can be performed at home and has been shown to improve both motor function in stroke survivors and vascular endothelial function in healthy individuals. In this study, we examined the effects of 2 wk of remote IC (RIC) on brachial artery flow mediated dilation (FMD) in chronic stroke survivors. We hypothesized that FMD would be improved following RIC compared with a sham RIC control group. This was a prospective, randomized, double-blinded, controlled study. Twenty-four chronic stroke survivors (>6 mo after stroke) were enrolled and randomized to receive either RIC or sham RIC on their affected thigh every other day for 2 wk. For the RIC group, a blood pressure cuff was inflated to 225 mmHg for 5 min, followed by 5 min of recovery, and repeated a total of five times per session. For the sham RIC group, the inflation pressure was 10 mmHg. Brachial artery FMD was assessed on the nonaffected arm at study enrollment and following the 2-wk intervention period. Nine men and fourteen women completed all study procedures. Brachial artery FMD increased from 5.4 ± 4.8 to 7.8 ± 4.4% (P = 0.030; n = 12) in the RIC group, while no significant change was observed in the sham RIC group (3.5 ± 3.9% pretreatment versus 2.4 ± 3.1% posttreatment; P = 0.281, n = 11). Two weeks of RIC increases brachial artery FMD in chronic stroke survivors.NEW & NOTEWORTHY In this study, we report that 2 wk of remote ischemic conditioning (RIC) improves brachial artery flow-mediated dilation in chronic stroke survivors. Because poor cardiovascular health puts stroke survivors at a heightened risk for recurrent stroke and other cardiovascular events, an intervention that is simple, cost-effective, and easy to perform like RIC holds promise as a means to improve cardiovascular health in this at-risk population.