Blood pressure regulation VIII: resistance vessel tone and implications for a pro-atherogenic conduit artery endothelial cell phenotype

Acute Effects of Inorganic Nitrate Intake on Brachial and Femoral Flow-Mediated Vasodilation, and on Carotid Artery Reactivity Responses: Results of a Randomized, Double-Blinded, Placebo-Controlled Cross-Over Study in Abdominally Obese Men

Most trials on the effects of inorganic nitrate intake have focused on only one specific aspect of the endothelial cell response to a stimulus, thereby possibly missing other important effects. The aim of the present randomized, double-blinded, placebo-controlled cross-over study was therefore to investigate in eighteen healthy abdominally obese men (18–60 years, waist circumference ≥ 102 cm) acute effects of potassium nitrate on brachial and femoral flow-mediated vasodilation (FMD), and on carotid artery reactivity (CAR) to a cold pressure test. Participants received in random order a drink providing 10 mmol potassium nitrate (i.e., 625 mg of nitrate) or an iso-molar placebo drink with potassium chloride. Fasted and 4 h post-drink FMD and blood pressure measurements were performed. CAR responses were assessed at 4 h. Circulating nitrate plus nitrite concentration increased following nitrate intake (p = 0.003). Compared with placebo, potassium nitrate did not affect brachial (mean [95% confidence interval]: −0.2% [−2.5, 2.1], p = 0.86) and femoral FMD responses (−0.6% [−3.0; 1.7], p = 0.54). CAR responses were also not different (−0.8% [−2.5, 0.9], p = 0.32). Finally, changes in blood pressure and heart rate did not differ. No adverse events were observed. In conclusion, this trial did not provide evidence for effects of a single dose of inorganic nitrate on 4 h vascular endothelial function in abdominally obese men.

SGLT2 inhibition attenuates arterial dysfunction and decreases vascular F-actin content and expression of proteins associated with oxidative stress in aged mice

Aging of the vasculature is characterized by endothelial dysfunction and arterial stiffening, two key events in the pathogenesis of cardiovascular disease (CVD). Treatment with sodium glucose transporter 2 (SGLT2) inhibitors is now known to decrease cardiovascular morbidity and mortality in type 2 diabetes. However, whether SGLT2 inhibition attenuates vascular aging is unknown. We first confirmed in a cohort of adult subjects that aging is associated with impaired endothelial function and increased arterial stiffness and that these two variables are inversely correlated. Next, we investigated whether SGLT2 inhibition with empagliflozin (Empa) ameliorates endothelial dysfunction and reduces arterial stiffness in aged mice with confirmed vascular dysfunction. Specifically, we assessed mesenteric artery endothelial function and stiffness (via flow-mediated dilation and pressure myography mechanical responses, respectively) and aortic stiffness (in vivo via pulse wave velocity and ex vivo via atomic force microscopy) in Empa-treated (14 mg/kg/day for 6 weeks) and control 80-week-old C57BL/6 J male mice. We report that Empa-treated mice exhibited improved mesenteric endothelial function compared with control, in parallel with reduced mesenteric artery and aortic stiffness. Additionally, Empa-treated mice had greater vascular endothelial nitric oxide synthase activation, lower phosphorylated cofilin, and filamentous actin content, with downregulation of pathways involved in production of reactive oxygen species. Our findings demonstrate that Empa improves endothelial function and reduces arterial stiffness in a preclinical model of aging, making SGLT2 inhibition a potential therapeutic alternative to reduce the progression of CVD in older individuals.

Endothelial function and shear stress in hypobaric hypoxia: time course and impact of plasma volume expansion in men

High-altitude exposure typically reduces endothelial function, and this is modulated by hemoconcentration resulting from plasma volume contraction. However, the specific impact of hypobaric hypoxia independent of external factors (e.g., cold, varying altitudes, exercise, diet, and dehydration) on endothelial function is unknown. We examined the temporal changes in blood viscosity, shear stress, and endothelial function and the impact of plasma volume expansion (PVX) during exposure to hypobaric hypoxia while controlling for external factors. Eleven healthy men (25 ± 4 yr, mean ± SD) completed two 4-day chamber visits [normoxia (NX) and hypobaric hypoxia (HH; equivalent altitude, 3,500 m)] in a crossover design. Endothelial function was assessed via flow-mediated dilation in response to transient (reactive hyperemia; RH-FMD) and sustained (progressive handgrip exercise; SS-FMD) increases in shear stress before entering and after 1, 6, 12, 48, and 96 h in the chamber. During HH, endothelial function was also measured on the last day after PVX to preexposure levels (1,140 ± 320 mL balanced crystalloid solution). Blood viscosity and arterial shear stress increased on the first day during HH compared with NX and remained elevated at 48 and 96 h (P < 0.005). RH-FMD did not differ during HH compared with NX and was unaffected by PVX despite reductions in blood viscosity (P < 0.05). The stimulus-response slope of increases in shear stress to vasodilation during SS-FMD was preserved in HH and increased by 44 ± 73% following PVX (P = 0.023). These findings suggest that endothelial function is maintained in HH when other stressors are absent and that PVX improves endothelial function in a shear-stress stimulus-specific manner.NEW & NOTEWORTHY Using a normoxic crossover study design, we examined the impact of hypobaric hypoxia (4 days; altitude equivalent, 3,500 m) and hemoconcentration on blood viscosity, shear stress, and endothelial function. Blood viscosity increased during the hypoxic exposure and was accompanied by elevated resting and exercising arterial shear stress. Flow-mediated dilation stimulated by reactive hyperemia and handgrip exercise was preserved throughout the hypoxic exposure. Plasma volume expansion reversed the hypoxia-associated hemoconcentration and selectively increased handgrip exercise flow-mediated dilation.

Assessment of resistance vessel function in human skeletal muscle: guidelines for experimental design, Doppler ultrasound, and pharmacology

The introduction of duplex Doppler ultrasound almost half a century ago signified a revolutionary advance in the ability to assess limb blood flow in humans. It is now widely used to assess blood flow under a variety of experimental conditions to study skeletal muscle resistance vessel function. Despite its pervasive adoption, there is substantial variability between studies in relation to experimental protocols, procedures for data analysis, and interpretation of findings. This guideline results from a collegial discussion among physiologists and pharmacologists, with the goal of providing general as well as specific recommendations regarding the conduct of human studies involving Doppler ultrasound-based measures of resistance vessel function in skeletal muscle. Indeed, the focus is on methods used to assess resistance vessel function and not upstream conduit artery function (i.e., macrovasculature), which has been expertly reviewed elsewhere. In particular, we address topics related to experimental design, data collection, and signal processing as well as review common procedures used to assess resistance vessel function, including postocclusive reactive hyperemia, passive limb movement, acute single limb exercise, and pharmacological interventions.

Functional-Optical Coherence Tomography: A Non-invasive Approach to Assess the Sympathetic Nervous System and Intrinsic Vascular Regulation

Sympathetic nervous system dysregulation and vascular impairment in neuronal tissue beds are hallmarks of prominent cardiorespiratory diseases. However, an accurate and convenient method of assessing SNA and local vascular regulation is lacking, hindering routine clinical and research assessments. To address this, we investigated whether spectral domain optical coherence tomography (OCT), that allows investigation of retina and choroid vascular responsiveness, reflects sympathetic activity in order to develop a quick, easy and non-invasive sympathetic index. Here, we compare choroid and retina vascular perfusion density (VPD) acquired with OCT and heart rate variability (HRV) to microneurography. We recruited 6 healthy males (26 ± 3 years) and 5 healthy females (23 ± 1 year) and instrumented them for respiratory parameters, ECG, blood pressure and muscle sympathetic nerve microneurography. Choroid VPD decreases with the cold pressor test, inhaled hypoxia and breath-hold, and increases with hyperoxia and hyperpnea suggesting that sympathetic activity dominates choroid responses. In contrast, retina VPD was unaffected by the cold pressor test, increased with hypoxia and breath hold and decreases with hyperoxia and hyperpnea, suggesting metabolic vascular regulation dominates the retina. With regards to integrated muscle sympathetic nerve activity, HRV had low predictive power whereas choroid VPD was strongly (inversely) correlated with integrated muscle sympathetic nerve activity (R = -0.76; p < 0.0001). These data suggest that Functional-OCT may provide a novel approach to assess sympathetic activity and intrinsic vascular responsiveness (i.e., autoregulation). Given that sympathetic nervous system activity is the main determinant of autonomic function, sympathetic excitation is associated with severe cardiovascular/cardiorespiratory diseases and autoregulation is critical for brain health, we suggest that the use of our new Functional-OCT technique will be of broad interest to clinicians and researchers.

Effects of Iliac Stenosis on Abdominal Aortic Aneurysm Formation in Mice and Humans

Reduced lower-limb blood flow has been shown to lead to asymmetrical abdominal aortic aneurysms (AAAs) but the mechanism of action is not fully understood. Therefore, small animal ultrasound (Vevo2100, FUJIFILM VisualSonics) was used to longitudinally study mice that underwent standard porcine pancreatic elastase (PPE) infusion (n = 5), and PPE infusion with modified 20% iliac artery stenosis in the left (n = 4) and right (n = 5) iliac arteries. Human AAA computed tomography images were obtained from patients with normal (n = 9) or stenosed left (n = 2), right (n = 1), and bilateral (n = 1) iliac arteries. We observed rapid early growth and rightward expansion (8/9 mice) in the modified PPE groups (p < 0.05), leading to slightly larger and asymmetric AAAs compared to the standard PPE group. Further examination showed a significant increase in TGFβ1 (p < 0.05) and cellular infiltration (p < 0.05) in the modified PPE group versus standard PPE mice. Congruent, yet variable, observations were made in human AAA patients with reduced iliac outflow compared to those with normal iliac outflow. Our results suggest that arterial stenosis at the time of aneurysm induction leads to faster AAA growth with aneurysm asymmetry and increased vascular inflammation after 8 weeks, indicating that moderate iliac stenosis may have upstream effects on AAA progression.

Sympathetic Transduction in Type 2 Diabetes Mellitus

Approximately 60% of patients with type 2 diabetes mellitus (T2D) develop hypertension. Recent work also indicates greater blood pressure (BP) excursions throughout the day in T2D. Collectively, these findings suggest altered BP control in T2D. Although muscle sympathetic nerve activity (MSNA) recordings in T2D have provided equivocal results, quantification of MSNA alone does not account for ensuing vasoconstriction and BP responses elicited by MSNA. Thus, we tested the hypothesis that patients with T2D exhibit enhanced sympathetic transduction to BP. MSNA (microneurography) and beat-to-beat BP (Finometer) were measured at rest in 21 T2D and 13 age-matched and body mass index-matched control subjects and, signal-averaging was performed to quantify the mean arterial pressure and total vascular conductance responses to spontaneous bursts of MSNA. The peak mean arterial pressure and total vascular conductance responses to spontaneous MSNA were similar between T2D and control (both P>0.05). However, further analysis, separating T2D into those taking statins (n=13, T2D +statin) and not taking statins (n=8, T2D -statin), indicated that T2D -statin patients (4.2±0.6 mm Hg) exhibited greater peak mean arterial pressure responses compared with both T2D +statin patients (2.5±0.3 mm Hg, P=0.01) and control (control: 2.8±0.3 mm Hg, P=0.02). Likewise, nadir total vascular conductance responses to spontaneous MSNA bursts were greater in T2D -statin patients (T2D -statin: -3.3±0.6 mL/(min·mm Hg), T2D +statin: -1.6±0.3 mL/(min·mm Hg), P=0.03; control -2.2±0.3 mL/(min·mm Hg), P=0.08). Notably, T2D +statin patients exhibited similar peak mean arterial pressure and total vascular conductance responses to MSNA compared with control. Collectively, these findings demonstrate, for the first time, that patients with T2D exhibit augmented sympathetic transduction and this effect seems to be offset by statin therapy.

Aerobic exercise training improves insulin-induced vasorelaxation in a vessel-specific manner in rats with insulin-treated experimental diabetes

Vascular insulin resistance often precedes endothelial dysfunction in type 1 diabetes mellitus. Strategies to limit vascular dysfunction include intensive insulin therapy (4-9 mM) and aerobic training. To avoid the risk of hypoglycaemia, individuals often prescribed conventional insulin therapy (9-15 mM) and participate in resistance training. In a model of type 1 diabetes mellitus, this study examined insulin-induced vasomotor function in the aorta and femoral artery to determine (1) whether resistance training with conventional insulin therapy provides the same benefits as aerobic training with conventional insulin therapy, (2) whether aerobic training or resistance training, when paired with conventional insulin therapy, results in superior vasomotor function compared to intensive insulin therapy alone and (3) whether vessel-specific adaptations exist. Groups consisted of conventional insulin therapy, intensive insulin therapy, aerobic training with conventional insulin therapy and resistance training with conventional insulin therapy. Following multiple low doses of streptozotocin, male Sprague-Dawley rats were supplemented with insulin to maintain blood glucose concentrations (9-15 mM: conventional insulin therapy, aerobic training and resistance training; 4-9 mM: intensive insulin therapy) for 12 weeks. Aerobic training performed treadmill exercise and resistance training consisted of weighted climbing. Coinciding with increased Akt signalling, aerobic training resulted in enhanced insulin-induced vasorelaxation in the femoral artery. Intensive insulin therapy displayed increased mitogen-activated protein kinase signalling and no improvement in insulin-stimulated vasorelaxation compared to all other groups. These data suggest that aerobic training may be more beneficial for limiting the pathogenesis of vascular disease in type 1 diabetes mellitus than merely intensive insulin therapy.

Improving pregnancy outcomes in humans through studies in sheep

Experimental studies that are relevant to human pregnancy rely on the selection of appropriate animal models as an important element in experimental design. Consideration of the strengths and weaknesses of any animal model of human disease is fundamental to effective and meaningful translation of preclinical research. Studies in sheep have made significant contributions to our understanding of the normal and abnormal development of the fetus. As a model of human pregnancy, studies in sheep have enabled scientists and clinicians to answer questions about the etiology and treatment of poor maternal, placental, and fetal health and to provide an evidence base for translation of interventions to the clinic. The aim of this review is to highlight the advances in perinatal human medicine that have been achieved following translation of research using the pregnant sheep and fetus.

Vasodilator function is impaired in burn injury survivors

The effect of severe burn injury on vascular health is unknown. We tested the hypothesis that, compared with nonburn control subjects, vasodilator function would be reduced and that pulse-wave velocity (a measure of arterial stiffness) would be increased in individuals with prior burn injuries, the extent of which would be associated with the magnitude of body surface area having sustained a severe burn. Pulse-wave velocity and macrovascular (flow-mediated dilation) and microvascular (reactive hyperemia) dilator functions were assessed in 14 nonburned control subjects and 32 age-matched subjects with well-healed burn injuries. Fifteen subjects with burn injuries covering 17-40% of body surface area were assigned to a moderate burn injury group, and 17 subjects with burn injuries covering >40% of body surface area were assigned to a high burn injury group. Pulse-wave velocity [ P = 0.3 (central) and P = 0.3 (peripheral)] did not differ between the three groups. Macrovascular dilator function was reduced in the moderate ( P = 0.07) and high ( P < 0.05) burn injury groups compared with the control group. Likewise, peak vascular conductance during postocclusive reactive hyperemia differed from the moderate burn injury group ( P = 0.08 vs. control) and the high burn injury group ( P < 0.05 vs. control). These data suggest that vasodilator function is impaired in well-healed burn injury survivors, with the extent of impairment not dependent on the magnitude of body surface area having sustained a severe burn injury.

Prolonged leg bending impairs endothelial function in the popliteal artery

Uninterrupted sitting blunts vascular endothelial function in the lower extremities; however, the factors contributing to this impairment remain largely unknown. Herein, we tested the hypothesis that prolonged flexion of the hip and knee joints, as it occurs during sitting, and associated low shear stress and disturbed (i.e., turbulent) blood flow caused by arterial bending, impairs endothelial function at the popliteal artery. Bilateral measurements of popliteal artery flow‐mediated dilation (FMD) were performed in 12 healthy subjects before and after a 3‐h lying‐down period during which one leg was bent (i.e., 90‐degree angles at the hip and knee) and the contralateral leg remained straight, serving as internal control. During the 3‐h lying down period, the bent leg displayed a profound and sustained reduction in popliteal artery blood flow and mean shear rate; whereas a slight but steady decline that only became significant at 3 h was noted in the straight leg. Notably, 3 h of lying down markedly impaired popliteal artery FMD in the bent leg (pre: 6.3 ± 1.2% vs. post: 2.8 ± 0.91%; P < 0.01) but not in the straight leg (pre: 5.6 ± 1.1% vs. post: 7.1 ± 1.2%; P = 0.24). Collectively, this study provides evidence that prolonged bending of the leg causes endothelial dysfunction in the popliteal artery. This effect is likely secondary to vascular exposure to low and disturbed blood flow resulting from arterial angulation. We conclude that spending excessive time with legs bent and immobile, irrespective of whether this is in the setting of sitting or lying‐down, may be disadvantageous for leg vascular health.

Acute hypoxaemia and vascular function in healthy humans

NEW FINDINGS

What is the central question of this study? Endothelium-dependent flow-mediated dilatation (FMD) is impaired during acute (60 min) exposure to moderate hypoxia. We examined whether FMD is impaired to the same degree during exposure to milder hypoxia. Additionally, we assessed whether smooth muscle vasodilatory capacity [glyceryl trinitrate (GTN)-induced dilatation] is impaired during acute hypoxic exposure. What is the main finding and its importance? A graded impairment in FMD and GTN-induced dilatation was evident during acute (≤60 min) exposure to mild and moderate hypoxia. This study is the first to document these graded impairments, and provides rationale to examine the relationship between graded increases in sympathetic nerve activity with hypoxia on FMD and GTN-induced dilatation. Endothelium-dependent flow-mediated dilatation (FMD) and endothelium-independent dilatation [induced with glyceryl trinitrate (GTN)] are impaired at high altitude (5050 m), and FMD is impaired after acute exposure (<60 min) to normobaric hypoxia equivalent to ∼5050 m (inspired oxygen fraction ∼0.11). Whether GTN-induced dilatation is impaired acutely and whether FMD is impaired during milder hypoxia are unknown. Therefore, we assessed brachial FMD at baseline and after 30 min of mild (end-tidal PO2 74 ± 2 mmHg) and moderate (end-tidal PO2 50 ± 3 mmHg) normobaric hypoxia (n = 12) or normoxia (time-control trial; n = 10). We also assessed GTN-induced dilatation after the hypoxic FMD tests and in normoxia on a separate control day (n = 8). Compared with the normoxic baseline, reductions during mild and moderate hypoxic exposure were evident in FMD (mild versus moderate, -1.2 ± 1.1 versus -3.1 ± 1.7%; P = 0.01) and GTN-induced dilatation (-2.1 ± 1.0 versus -4.2 ± 2.0%; P = 0.01); the declines in FMD and GTN-induced dilatation were greater during moderate hypoxia (P < 0.01). When allometrically corrected for baseline diameter and FMD shear rate under the curve, FMD was attenuated in both conditions (mild versus moderate, 0.6 ± 0.9 versus 0.8 ± 0.7%; P ≤ 0.01). After 30 min of normoxic time control, FMD was reduced (-0.6 ± 0.3%; P = 0.02). In summary, there was a graded impairment in FMD during mild and moderate hypoxic exposure, which appears to be influenced by shear patterns and incremental decline in smooth muscle vasodilator capacity (impaired GTN-induced dilatation). Our findings from the normoxic control study suggest the decline in FMD in acute hypoxia also appears to be influenced by 30 min of supine rest/inactivity.

Prolonged sitting leg vasculopathy: contributing factors and clinical implications

Atherosclerotic peripheral artery disease primarily manifests in the medium- to large-sized conduit arteries of the lower extremities. However, the factors underlying this increased vulnerability of leg macrovasculature to disease are largely unidentified. On the basis of recent studies, we propose that excessive time spent in the sitting position and the ensuing reduction in leg blood flow-induced shear stress cause endothelial cell dysfunction, a key predisposing factor to peripheral artery disease. In particular, this review summarizes the findings from laboratory-based sitting studies revealing acute leg vascular dysfunction with prolonged sitting in young healthy subjects, discusses the primary physiological mechanisms and the potential long-term implications of such leg vasculopathy with repeated exposure to prolonged sitting, as well as identifies strategies that may be effective at evading it.

Vascular Adaptation to Exercise in Humans: Role of Hemodynamic Stimuli

On the 400th anniversary of Harvey's Lumleian lectures, this review focuses on "hemodynamic" forces associated with the movement of blood through arteries in humans and the functional and structural adaptations that result from repeated episodic exposure to such stimuli. The late 20th century discovery that endothelial cells modify arterial tone via paracrine transduction provoked studies exploring the direct mechanical effects of blood flow and pressure on vascular function and adaptation in vivo. In this review, we address the impact of distinct hemodynamic signals that occur in response to exercise, the interrelationships between these signals, the nature of the adaptive responses that manifest under different physiological conditions, and the implications for human health. Exercise modifies blood flow, luminal shear stress, arterial pressure, and tangential wall stress, all of which can transduce changes in arterial function, diameter, and wall thickness. There are important clinical implications of the adaptation that occurs as a consequence of repeated hemodynamic stimulation associated with exercise training in humans, including impacts on atherosclerotic risk in conduit arteries, the control of blood pressure in resistance vessels, oxygen delivery and diffusion, and microvascular health. Exercise training studies have demonstrated that direct hemodynamic impacts on the health of the artery wall contribute to the well-established decrease in cardiovascular risk attributed to physical activity.

Microvascular Dilator Function in Athletes: A Systematic Review and Meta-analysis

PURPOSE

Despite the growing research interest in vascular adaptations to exercise training over the last few decades, it remains unclear whether microvascular function in healthy subjects can be further improved by regular training. Herein, we sought to systematically review the literature and determine whether microvascular dilator function is greater in athletes compared to age-matched healthy untrained subjects.

METHODS

We conducted a systematic search of MEDLINE, Cochrane, EMBASE, and Web of Science since their inceptions until October 2013 for articles evaluating indices of primarily microvascular endothelium-dependent or endothelium-independent dilation (MVEDD and MVEID, respectively) in athletes. A meta-analysis was performed to determine the standardized mean difference (SMD) in MVEDD and MVEID between athletes and age-matched controls. Subgroup analyses were used to study potential moderating factors.

RESULTS

Thirty-six studies were selected after systematic review, comprising 521 athletes (506 endurance-trained and 15 endurance- and strength-trained) and 496 age-matched control subjects. After data pooling, athletes presented higher MVEDD (31 studies; SMD, 0.47; P < 0.00001) and MVEID (14 studies; SMD, 0.51; P < 0.00001) compared with the control subjects. Similar results were observed in young (younger than 40 yr) and master (older than 55 yr) athletes when analyzed separately.

CONCLUSION

Both young and master athletes present enhanced microvascular function compared with age-matched untrained but otherwise healthy subjects. These data provide evidence of a positive association between exercise training and microvascular function in the absence of known underlying cardiovascular disease.

Caveolae regulate vasoconstriction of conduit arteries to angiotensin II in hindlimb unweighted rats

Weightlessness induces the functional remodelling of arteries, but the changes to angiotensin II (Ang II)-elicited vasoconstriction and the underlying mechanism have never been reported. Caveolae are invaginations of the cell membrane crucial for the contraction of vascular smooth muscle cells, so we investigated the adaptation of Ang II-elicited vasoconstriction to simulated weightlessness and the role of caveolae in it. The 4 week hindlimb unweighted (HU) rat was used to simulate the effects of weightlessness. Ang II-elicited vasoconstriction was measured by isometric force recording. The morphology of caveolae was examined by transmission electron microscope. The binding of the angiotensin II type 1 receptor (AT1 ) and caveolin-1 (cav-1) was examined by coimmunoprecipitation and Western blot. We found that the maximal developing force (E(max)) of Ang II-elicited vasoconstriction was decreased in abdominal aorta by 30.6%, unchanged in thoracic aorta and increased in carotid artery by 17.9% after HU, while EC50 of the response was increased in all three arteries (P < 0.05). AT1 desensitization upon activation was significantly reduced by HU in all three arteries, as was the number of caveolae (P < 0.05). Furthermore, Ang II promoted the binding of AT1 and cav-1 significantly in control but not HU arteries. Both the number of caveolae and the binding of AT1 and cav-1 in HU arteries were restored by cholesterol pretreatment which also reinstated the change in EC50 as well as the level of AT1 desensitization. These results indicate that modified caveolae in vascular smooth muscle cells could interfere with the binding of AT1 and cav-1 mediating the adaptation of Ang II-elicited vasoconstriction to HU.

Inadequate Blood Pressure Control in Hypertensive Patients Referred for Cardiac Stress Test

The current study examined the degree of blood pressure (BP) control and incidence of myocardial ischemia in hypertensive patients (n=2039) referred for cardiac stress test. Patients were categorized into well-controlled (<140/90 mm Hg), poorly controlled (140-160/90-100 mm Hg), and very poorly controlled (>160/100 mm Hg) groups according to their resting BP. The mean age[±standard error of the mean] of the patients was 68±13 years, and 885 (43.4%) were men. The prevalence of well-controlled hypertension (HTN) was 47.2%, poorly controlled HTN was 29.5%, and very poorly controlled HTN was 23.3%. Evidence of ischemia was seen in 19.8% and 19.3% of the well-controlled and poorly controlled groups, respectively. The very poorly controlled group had the lowest incidence of ischemia (14.3%) (P<.05) compared with the other two groups. Symptoms that mimic ischemic heart disease in hypertensive patients may be partly explained by poorly controlled BP. Quality of care might be improved by optimally controlling BP in patients with angina symptoms prior to ordering diagnostic testing associated with radiation exposure and cost.

Impact of prolonged sitting on lower and upper limb micro- and macrovascular dilator function

NEW FINDINGS

What is the central question of this study? The prevalence of sedentary behaviour in the workplace and increased daily sitting time have been associated with the development of cardiovascular disease; however, studies investigating the impact of sitting on vascular function remain limited. What is the main finding and its importance? We demonstrate that there is a marked vulnerability of the vasculature in the lower and upper limbs to prolonged sitting and highlight the importance of physical activity in restoring vascular function in a limb-specific manner. Sedentary behaviour in the workplace and increased daily sitting time are on the rise; however, studies investigating the impact of sitting on vascular function remain limited. Herein, we hypothesized that 6 h of uninterrupted sitting would impair limb micro- and macrovascular dilator function and that this impairment could be improved with a bout of walking. Resting blood flow, reactive hyperaemia to 5 min cuff occlusion (microvascular reactivity) and associated flow-mediated dilatation (FMD; macrovascular reactivity) were assessed in popliteal and brachial arteries of young men at baseline (Pre Sit) and after 6 h of uninterrupted sitting (Post Sit). Measures were then repeated after a 10 min walk (~1000 steps). Sitting resulted in a marked reduction of resting popliteal artery mean blood flow and mean shear rate (6 h mean shear rate, -52 ± 8 s(-1) versus Pre Sit, P < 0.05). Interestingly, reductions were also found in the brachial artery (6 h mean shear rate, -169 ± 41 s(-1) versus Pre Sit, P < 0.05). Likewise, after 6 h of sitting, cuff-induced reactive hyperaemia was reduced in both the lower leg (-43 ± 7% versus Pre Sit, P < 0.05) and forearm (-31 ± 11% versus Pre Sit, P < 0.05). In contrast, popliteal but not brachial artery FMD was blunted with sitting. Notably, lower leg reactive hyperaemia and FMD were restored after walking. Collectively, these data suggest that prolonged sitting markedly reduces lower leg micro- and macrovascular dilator function, but these impairments can be fully normalized with a short bout of walking. In contrast, upper arm microvascular reactivity is selectively impaired with prolonged sitting, and walking does not influence this effect.

Pharmacology and therapeutic role of inorganic nitrite and nitrate in vasodilatation

Nitrite has emerged as an important bioactive molecule that can be biotransformed to nitric oxide (NO) related metabolites in normoxia and reduced to NO under hypoxic and acidic conditions to exert vasodilatory effects and confer a variety of other benefits to the cardiovascular system. Abundant research is currently underway to understand the mechanisms involved and define the role of nitrite in health and disease. In this review we discuss the impact of nitrite and dietary nitrate on vascular function and the potential therapeutic role of nitrite in acute heart failure.

Blood pressure regulation XI: overview and future research directions

While the importance of regulating arterial blood pressure within a 'normal' range is widely appreciated, the definition of 'normal' and the means by which humans and other species regulate blood pressure under various conditions remain hotly debated. The effects of diverse physiological, pathological and environmental challenges on blood pressure and the mechanisms that attempt to maintain it at an optimal level are reviewed and critically analyzed in a series of articles published in this themed issue of the European Journal of Applied Physiology. We summarize here the major points made in these reviews, with emphasis on unifying concepts of regulatory mechanisms and future directions for research.

Exercise performance and peripheral vascular insufficiency improve with AMPK activation in high-fat diet-fed mice

Intermittent claudication is a form of exercise intolerance characterized by muscle pain during walking in patients with peripheral artery disease (PAD). Endothelial cell and muscle dysfunction are thought to be important contributors to the etiology of this disease, but a lack of preclinical models that incorporate these elements and measure exercise performance as a primary end point has slowed progress in finding new treatment options for these patients. We sought to develop an animal model of peripheral vascular insufficiency in which microvascular dysfunction and exercise intolerance were defining features. We further set out to determine if pharmacological activation of 5'-AMP-activated protein kinase (AMPK) might counteract any of these functional deficits. Mice aged on a high-fat diet demonstrate many functional and molecular characteristics of PAD, including the sequential development of peripheral vascular insufficiency, increased muscle fatigability, and progressive exercise intolerance. These changes occur gradually and are associated with alterations in nitric oxide bioavailability. Treatment of animals with an AMPK activator, R118, increased voluntary wheel running activity, decreased muscle fatigability, and prevented the progressive decrease in treadmill exercise capacity. These functional performance benefits were accompanied by improved mitochondrial function, the normalization of perfusion in exercising muscle, increased nitric oxide bioavailability, and decreased circulating levels of the endogenous endothelial nitric oxide synthase inhibitor asymmetric dimethylarginine. These data suggest that aged, obese mice represent a novel model for studying exercise intolerance associated with peripheral vascular insufficiency, and pharmacological activation of AMPK may be a suitable treatment for intermittent claudication associated with PAD.

Differential regulation of adipose tissue and vascular inflammatory gene expression by chronic systemic inhibition of NOS in lean and obese rats

We tested the hypothesis that a decrease in bioavailability of nitric oxide (NO) would result in increased adipose tissue (AT) inflammation. In particular, we utilized the obese Otsuka Long Evans Tokushima Fatty rat model (n = 20) and lean Long Evans Tokushima Otsuka counterparts (n = 20) to determine the extent to which chronic inhibition of NO synthase (NOS) with N (ω) -nitro-l-arginine methyl ester (L-NAME) treatment (for 4 weeks) upregulates expression of inflammatory genes and markers of immune cell infiltration in retroperitoneal white AT, subscapular brown AT, periaortic AT as well as in its contiguous aorta free of perivascular AT. As expected, relative to lean rats (% body fat = 13.5 ± 0.7), obese rats (% body fat = 27.2 ± 0.8) were hyperlipidemic (total cholesterol 77.0 ± 2.1 vs. 101.0 ± 3.3 mg/dL), hyperleptinemic (5.3 ± 0.9 vs. 191.9 ± 59.9 pg/mL), and insulin-resistant (higher HOMA IR index [3.9 ± 0.8 vs. 25.2 ± 4.1]). Obese rats also exhibited increased expression of proinflammatory genes in perivascular, visceral, and brown ATs. L-NAME treatment produced a small but statistically significant decrease in percent body fat (24.6 ± 0.9 vs. 27.2 ± 0.8%) and HOMA IR index (16.9 ± 2.3 vs. 25.2 ± 4.1) in obese rats. Further, contrary to our hypothesis, we found that expression of inflammatory genes in all AT depots examined were generally unaltered with L-NAME treatment in both lean and obese rats. This was in contrast with the observation that L-NAME produced a significant upregulation of inflammatory and proatherogenic genes in the aorta. Collectively, these findings suggest that chronic NOS inhibition alters transcriptional regulation of proinflammatory genes to a greater extent in the aortic wall compared to its adjacent perivascular AT, or visceral white and subscapular brown AT depots.

Exploring the vascular smooth muscle receptor landscape in vivo: ultrasound Doppler versus near-infrared spectroscopy assessments

Ultrasound Doppler and near-infrared spectroscopy (NIRS) are routinely used for noninvasive monitoring of peripheral hemodynamics in both clinical and experimental settings. However, the comparative ability of these methodologies to detect changes in microvascular and whole limb hemodynamics during pharmacological manipulation of vascular smooth muscle receptors located at varied locations within the arterial tree is unknown. Thus, in 10 healthy subjects (25 ± 2 yr), changes in resting leg blood flow (ultrasound Doppler; femoral artery) and muscle oxygenation (oxyhemoglobin + oxymyoglobin; vastus lateralis) were simultaneously evaluated in response to intra-arterial infusions of phenylephrine (PE, 0.025-0.8 μg·kg(-1)·min(-1)), BHT-933 (2.5-40 μg·kg(-1)·min(-1)), and angiotensin II (ANG II, 0.5-8 ng·kg(-1)·min(-1)). All drugs elicited significant dose-dependent reductions in leg blood flow and oxyhemoglobin + oxymyoglobin. Significant relationships were found between ultrasound Doppler and NIRS changes across doses of PE (r(2) = 0.37 ± 0.08), BHT-933 (r(2) = 0.74 ± 0.06), and ANG II (r(2) = 0.68 ± 0.13), with the strongest relationships evident with agonists for receptors located preferentially "downstream" in the leg microcirculation (BHT-933 and ANG II). Analyses of drug potency revealed similar EC50 between ultrasound Doppler and NIRS measurements for PE (0.06 ± 0.02 vs. 0.10 ± 0.01), BHT-933 (5.0 ± 0.9 vs. 4.5 ± 1.3), and ANG II (1.4 ± 0.8 vs. 1.3 ± 0.3). These data provide evidence that both ultrasound Doppler and NIRS track pharmacologically induced changes in peripheral hemodynamics and are equally capable of determining drug potency. However, considerable disparity was observed between agonist infusions targeting different levels of the arterial tree, suggesting that receptor landscape is an important consideration for proper interpretation of hemodynamic monitoring with these methodologies.

Blood pressure regulation V: in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading

Recent studies are reviewed, concerning the in vivo wall stiffness of arteries and arterioles in healthy humans, and how these properties adapt to iterative increments or sustained reductions in local intravascular pressure. A novel technique was used, by which arterial and arteriolar stiffness was determined as changes in arterial diameter and flow, respectively, during graded increments in distending pressure in the blood vessels of an arm or a leg. Pressure-induced increases in diameter and flow were smaller in the lower leg than in the arm, indicating greater stiffness in the arteries/arterioles of the leg. A 5-week period of intermittent intravascular pressure elevations in one arm reduced pressure distension and pressure-induced flow in the brachial artery by about 50 %. Conversely, prolonged reduction of arterial/arteriolar pressure in the lower body by 5 weeks of sustained horizontal bedrest, induced threefold increases of the pressure-distension and pressure-flow responses in a tibial artery. Thus, the wall stiffness of arteries and arterioles are plastic properties that readily adapt to changes in the prevailing local intravascular pressure. The discussion concerns mechanisms underlying changes in local arterial/arteriolar stiffness as well as whether stiffness is altered by changes in myogenic tone and/or wall structure. As regards implications, regulation of local arterial/arteriolar stiffness may facilitate control of arterial pressure in erect posture and conditions of exaggerated intravascular pressure gradients. That increased intravascular pressure leads to increased arteriolar wall stiffness also supports the notion that local pressure loading may constitute a prime mover in the development of vascular changes in hypertension.