Evaluation of microvascular structure in humans: a ‘state-of-the-art’ document of the Working Group on Macrovascular and Microvascular Alterations of the Italian Society of Arterial Hypertension

Prognostic significance of the wall to lumen ratio of retinal arterioles evaluated by adaptive optics

OBJECTIVE

Microvascular structural alterations may be considered an important form of hypertension-mediated organ damage. An increased media-to-lumen ratio of subcutaneous small arteries evaluated with locally invasive techniques (micromyography) predicts the development of cardiovascular (CV) events. However, it is not known whether retinal arteriole structural alterations evaluated with a noninvasive approach (Adaptive Optics) may have a prognostic significance.

DESIGN AND METHODS

Two-hundred and thirty-seven subjects (mean age 58.7 ± 16.1 years, age range 13-89 years; 116 males) were included in the study: 65 normotensive subjects (27.4 %) and 172 patients with essential hypertension or primary aldosteronism (72.6 %). All subjects underwent a non-invasive evaluation of retinal arteriolar wall-to-lumen ratio (WLR) by Adaptive Optics. Subjects were re-evaluated after an average follow-up time of 4.55 years in order to assess the occurrence of clinical events (non CV and/or CV death or events).

RESULTS

Fifty-four events occurred in the study population:26 were cardio-cerebrovascular events (ischemic or hemorragic stroke, atrial fibrillation, heart failure, coronary artery disease, peripheral artery disease, cardiac valvular disease) while the remaining were deaths for any cause, or neoplastic diseases. Subjects with events were older and had a WLR of retinal arterioles significantly greater than those without events. The event-free survival was significantly worse in those with a baseline WLR above the median value of the population (0.28) according to Kaplan-Mayer survival curves and multivariate analysis (Cox's proportional hazard model). The evidence was confirmed after restricting the analysis to CV events.

CONCLUSIONS

Structural alterations of retinal arterioles evaluated by Adaptive Optics may predict total and CV events.

Microcirculation in Hypertension: A Therapeutic Target to Prevent Cardiovascular Disease?

Arterial hypertension is a common condition worldwide and an important risk factor for cardio- and cerebrovascular events, renal diseases, as well as microvascular eye diseases. Established hypertension leads to the chronic vasoconstriction of small arteries as well as to a decreased lumen diameter and the thickening of the arterial media or wall with a consequent increased media-to-lumen ratio (MLR) or wall-to-lumen ratio (WLR). This process, defined as vascular remodeling, was firstly demonstrated in small resistance arteries isolated from subcutaneous biopsies and measured by micromyography, and this is still considered the gold-standard method for the assessment of structural alterations in small resistance arteries; however, microvascular remodeling seems to represent a generalized phenomenon. An increased MLR may impair the organ flow reserve, playing a crucial role in the maintenance and, probably, also in the progressive worsening of hypertensive disease, as well as in the development of hypertension-mediated organ damage and related cardiovascular events, thus possessing a relevant prognostic relevance. New non-invasive techniques, such as scanning laser Doppler flowmetry or adaptive optics, are presently under development, focusing mainly on the evaluation of WLR in retinal arterioles; recently, also retinal microvascular WLR was demonstrated to have a prognostic impact in terms of cardio- and cerebrovascular events. A rarefaction of the capillary network has also been reported in hypertension, which may contribute to flow reduction in and impairment of oxygen delivery to different tissues. These microvascular alterations seem to represent an early step in hypertension-mediated organ damage since they might contribute to microvascular angina, stroke, and renal dysfunction. In addition, they can be markers useful in monitoring the beneficial effects of antihypertensive treatment. Additionally, conductance arteries may be affected by a remodeling process in hypertension, and an interrelationship is present in the structural changes in small and large conductance arteries. The review addresses the possible relations between structural microvascular alterations and hypertension-mediated organ damage, and their potential improvement with antihypertensive treatment.

Evaluation of inter-rater and test-retest reliability for near-infrared spectroscopy reactive hyperemia measures

BACKGROUND

Near-infrared spectroscopy (NIRS) is a non-invasive tool used to measure blood flow in peripheral tissues. More information on inter-rater agreement and test-retest reliability of NIRS-based reperfusion assessments is needed.

PURPOSE

To assess inter-rater agreement for NIRS based data analysis, and evaluate the measurement's reliability across days.

METHODS

On three separate days (average days between visits 1 and 3: 19.4 ± 6.9 days), participants' (N = 15 males, 22 ± 2 yr.) post-occlusion reactive hyperemia (PORH) was measured in the left gastrocnemius muscle using Continuous-Wave NIRS (CW-NIRS). A blood pressure cuff was placed proximal to the knee and inflated to occlude lower leg blood flow for 5 min. The following CW-NIRS parameters were selected: (1) percent saturation in HbO₂ (StO₂%) at baseline; (2) the O₂Hb range used to normalize the NIRS signal; (3) the time for the O₂Hb signal to reach 50 % peak post-occlusion hyperemia (T_1/2), and (4) the post peak hyperemic O₂Hb recovery slope (O₂REC-SLP). Absolute agreement between the two analysts was calculated using two-way random effects Intraclass Correlation Coefficients (ICC_2,1). Consistency between analysts and across days was calculated using two-way mixed models (ICC_3,1). Mean and 95 % confidence intervals (CI) of ICCs are reported. Coefficient of variation (CV) and standard error of the measurement (SEM) are reported.

RESULTS

The ICC_2,1 data indicated "adequate" to "excellent" absolute agreement between the two NIRS analysts. ICC_2,3 data indicated "adequate" to "good" reliability across visits. The CV and SEM for rater 1 and rater 2 across visit were StO₂ (CV: 3.79 % ± 2.71 % and 4.50 % ± 2.37 %; SEM: 3.42 and 3.82), O₂Hb range (CV: 10.50 ± 5.93 and 12.79 ± 12.41; SEM: 3.26 and 4.71), T_1/2 (CV: 11.15 % ± 5.52 % and 10.96 % ± 4.50; SEM: 1.22 and 1.11), and O₂REC-SLP (CV: 19.49 % ± 9.99 % and 18.45 % ± 9.48 %; SEM: 0.04 and 0.04).

CONCLUSION

It is concluded that NIRS parameters assessed show adequate reliability between analysts and across three visits. It is recommended, when feasible and because of the absence of 100 % reliability, that investigators employ more than one rater for scoring at least a portion of the data across each trial in a study's control condition in order to have the ability to estimate the magnitude of error attributable to imperfect reliability.

State of the Art Review: Vascular Remodeling in Hypertension

Although the gold-standard method for the assessment of structural alteration in small resistance arteries is the evaluation of the MLR by micromyography in bioptic tissues, new, noninvasive techniques are presently under development, focusing mainly on the evaluation of WLR in retinal arterioles. These approaches represent a promising and interesting future perspective. Appropriate antihypertensive treatment is able to prevent the development of microvascular alterations or to induce their regression. Also, conductance arteries may be affected by a remodeling process in hypertension, and a cross-talk may exist between structural changes in the small and large arteries. In conclusion, the evaluation of microvascular structure is ready for clinical prime time, and it could, in the future, represent an evaluation to be performed in the majority of hypertensive patients, to better stratify cardiovascular risk and better evaluate the effects of antihypertensive therapy. However, for this purpose, we need a clear demonstration of the prognostic relevance of noninvasive measures of microvascular structure, in basal conditions and during treatment. Vascular remodeling may be frequently observed in hypertension, as well as in obesity and diabetes mellitus. An increased media to lumen ratio (MLR) or wall to lumen ratio (WLR) in microvessels is the hallmark of hypertension, and may impair organ flow reserve, being relevant in the maintenance and, probably, also in the progressive worsening of hypertensive disease, as well as in the development of hypertension-mediated organ damage/cardiovascular events. The molecular mechanisms underlying the development of vascular remodeling are only partly understood.

Skin capillary alterations in patients with acute SarsCoV2 infection

BACKGROUND

Acute SarsCov2 infection is associated with endothelial dysfunction and 'endothelitis', which might explain systemic microvascular impairment. The presence of endothelial damage may promote vasoconstriction with organ ischemia, inflammation, tissue oedema and a procoagulant state resulting in an increase in the incidence of cardiovascular and cerebrovascular events. Microvascular thrombosis has been demonstrated in postmortem autopsy of COVID-19 patients; however, few data are available about skin capillary alterations in these patients.

MATERIALS AND METHODS

We evaluated skin microvascular alteration in 22 patients admitted to our hospital with SarsCov2 infection. Capillary density was evaluated by capillaroscopy in the nailfold and the dorsum of the finger in the acute phase of the disease. Capillaroscopy was repeated after 3 months (recovery phase). In addition, blood chemistry parameters and inflammatory markers were obtained during acute infection and at the recovery after 3 months.

RESULTS

Patients with COVID-19 showed skin microvascular complications, such as thrombosis, microhaemorrhages and neoangiogenesis, which were not detected after 3 months from the discharge. A significant reduction of capillary density in the dorsum was observed after 3 months from the acute infection (97.2 ± 5.3 vs. 75.81 ± 3.9 n/mm 2P  < 0.05). A significant inverse correlation between C-reactive protein and capillary density was observed in patients with acute SarsCov2 infection ( r  = 0.44, P  < 0.05). Conversely a direct correlation between capillary density during the acute phase and lymphocyte number was detected ( r  = 0.49, P  < 0.05).

CONCLUSION

This is the first in-vivo evidence of skin capillary thrombosis, microhaemorrhages and angiogenesis in patients with acute SarsCov2 infection, which disappeared after 3 months, supporting the presence of endothelial dysfunction and inflammation. Capillary alterations might reflect systemic vascular effects of viral infection.

Unattended versus Attended Blood Pressure Measurement: Relationship with Retinal Microcirculation

Though the relationship between both “attended” and “unattended” BP and several forms of target organ damage have been evaluated, data on retinal arteriolar alterations are lacking. The aim of our study was to evaluate the relationship between “attended” or “unattended” BP values and retinal arteriolar changes in consecutive individuals undergoing a clinical evaluation and assessment of retinal fundus at an ESH Excellence Centre. An oscillometric device programmed to perform 3 BP measurements, at 1 min intervals and after 5 min of rest was used on all individuals to measure BP with the patient alone in the room (“unattended”) or in the presence of the physician (“attended”) in the same day in a random order. The retinal arteriole’s wall thickness (WT) was measured automatically by a localization algorithm as the difference between external (ED) and internal diameter (ID) by adaptive optics (RTX-1, Imagine Eyes, Orsay, Francia). Media-to-lumen ratio (WLR) of the retinal arterioles and cross-sectional area (WCSA) of the vascular wall were calculated. Results: One-hundred-forty-two patients were examined (mean age 57 ± 12 yrs, 48% female, mean BMI 26 ± 4). Among them, 60% had hypertension (84% treated) and 11% had type 2 diabetes mellitus. Unattended systolic BP (SBP) was lower as compared to attended SBP (129 ± 14.8. vs. 122.1 ± 13.6 mmHg, p < 0.0001). WLR was similarly correlated with unattended and attended SBP (r = 0.281, p < 0.0001 and r = 0.382, p < 0.0001) and with unattended and attended diastolic BP (r = 0.34, p < 0.001 and r = 0.29, p < 0.0001). The differences between correlations were not statistically significant (Steiger’s Z test). Conclusion: The measurement of “unattended” or “attended” BP provides different values, and unattended BP is lower as compared to attended BP. In this study a similar correlation was observed between attended and unattended BP values and structural changes of retinal arterioles.

New Noninvasive Methods to Evaluate Microvascular Structure and Function

The structural and functional alterations of microvessels are detected because of physiological aging and in several cardiometabolic diseases, including hypertension, diabetes, and obesity. The small resistance arteries of these patients show an increase in the media or total wall thickness to internal lumen diameter ratio (MLR or WLR), often accompanied by endothelial dysfunction. For decades, micromyography has been considered as a gold standard method for evaluating microvascular structural alterations through the measurement of MLR or WLR of subcutaneous small vessels dissected from tissue biopsies. Micromyography is the most common and reliable method for assessing microcirculatory endothelial function ex vivo, while strain-gauge venous plethysmography is considered the reference technique for in vivo studies. Recently, several noninvasive methods have been proposed to extend the microvasculature evaluation to a broader range of patients and clinical settings. Scanning laser Doppler flowmetry and adaptive optics are increasingly used to estimate the WLR of retinal arterioles. Microvascular endothelial function may be evaluated in the retina by flicker light stimulus, in the finger by tonometric approaches, or in the cutaneous or sublingual tissues by laser Doppler flowmetry or intravital microscopy. The main limitation of these techniques is the lack of robust evidence on their prognostic value, which currently reduces their widespread use in daily clinical practice. Ongoing and future studies will overcome this issue, hopefully moving the noninvasive assessment of the microvascular function and structure from bench to bedside.

Etiopathogenic features of severe epistaxis in histological samples from individuals with or without arterial hypertension

There is a consensus that arterial hypertension (AH) is associated with stroke. Therefore, this study aimed to evaluate the histology of the microvasculature associated with the mucosa of the posterior nasal cavity to identify possible factors related to vascular weakening and rupture. Histological sections were obtained from hypertensive and normotensive individuals, regardless of epistaxis. Our results showed that the group with AH had: (a) smaller median diameter of the lumen of arteries and arterioles; (b) increased thickness of the intimal arteries and arterioles, slight inflammatory infiltrate, and rupture of internal elastic lamina; (c) greater thickness of the middle tunica in arterioles; (d) lower percentage of histological sections with non-injured intimal layers in capillaries, arterioles, and small arteries; (e) lower percentage of histological sections with intact media tunic and/or myocytes juxtaposed in arteries and arterioles; (f) no difference between the diameters of small arteries or arterioles. The intima was thicker in individuals with severe epistaxis than in the normotensive group, but it did not differ from the AH group. Thus, hypertension may cause structural lesions in the vascular layers, and in the absence of tissue repair and the persistence of AH, these lesions may favour vascular rupture, especially during hypertensive peaks.

Microstructural Characterization of Resistance Artery Remodelling in Diabetes Mellitus

INTRODUCTION

Microvascular remodelling is a symptom of cardiovascular disease. Despite the mechanical environment being recognized as a major contributor to the remodelling process, it is currently only understood in a rudimentary way.

OBJECTIVE

A morphological and mechanical evaluation of the resistance vasculature in health and diabetes mellitus.

METHODS

The cells and extracellular matrix of human subcutaneous resistance arteries from abdominal fat biopsies were imaged using two-photon fluorescence and second harmonic generation at varying transmural pressure. The results informed a two-layer mechanical model.

RESULTS

Diabetic resistance arteries reduced in wall area as pressure was increased. This was attributed to the presence of thick, straight collagen fibre bundles that braced the outer wall. The abnormal mechanical environment caused the internal elastic lamina and endothelial and vascular smooth muscle cell arrangements to twist.

CONCLUSIONS

Our results suggest diabetic microvascular remodelling is likely to be stress-driven, comprising at least 2 stages: (1) Laying down of adventitial bracing fibres that limit outward distension, and (2) Deposition of additional collagen in the media, likely due to the significantly altered mechanical environment. This work represents a step towards elucidating the local stress environment of cells, which is crucial to build accurate models of mechanotransduction in disease.

Assessment and pathophysiology of microvascular disease: recent progress and clinical implications

The development of novel, non-invasive techniques and standardization of protocols to assess microvascular dysfunction have elucidated the key role of microvascular changes in the evolution of cardiovascular (CV) damage, and their capacity to predict an increased risk of adverse events. These technical advances parallel with the development of novel biological assays that enabled the ex vivo identification of pathways promoting microvascular dysfunction, providing novel potential treatment targets for preventing cerebral-CV disease. In this article, we provide an update of diagnostic testing strategies to detect and characterize microvascular dysfunction and suggestions on how to standardize and maximize the information obtained from each microvascular assay. We examine emerging data highlighting the significance of microvascular dysfunction in the development CV disease manifestations. Finally, we summarize the pathophysiology of microvascular dysfunction emphasizing the role of oxidative stress and its regulation by epigenetic mechanisms, which might represent potential targets for novel interventions beyond conventional approaches, representing a new frontier in CV disease reduction.

Microvascular Structural Alterations in Cancer Patients Treated With Antiangiogenic Drugs

Objective: Antiangiogenic therapies (tyrosine kinase inhibitors-TKI and direct anti-VEGF monoclonal antibodies) are being increasingly used in the treatment of solid tumors; hypertension represents a common side effect of these agents. Several mechanisms are involved in the development of hypertension, including microvascular rarefaction and other microvascular alterations. Therefore, the aim of our study was to evaluate whether TKI and direct anti-VEGF agents may affect the structure of retinal arterioles or capillary density.

Design and Methods: We investigated 20 patients with a diagnosis of cancer who underwent a treatment with either a TKI or an anti-VEGF antibody. Patients were submitted to ambulatory monitoring blood pressure for blood pressure evaluation. Basal and total capillary density were assessed by capillaroscopy whereas, retinal arteriole morphology was measured by Adaptive Optics. Patients were evaluated before starting the antiangiogenic therapy (T0) and re-evaluated after 3 (T3) and 6 (T6) months after treatment. Fourteen patients completed the study.

Results: Systolic and diastolic blood pressure values were similar in all patients at T3 and T6 compared to T0. However, during the study antihypertensive treatment was optimized (increased dose and/or addition of drugs) in 57% of patients (n = 8). No differences were observed in retinal arteriole structural parameters and in large artery stiffness. Basal capillary density was reduced by antiangiogenic drugs after 3 or 6 months.

Conclusions: Our data suggest that an increase of antihypertensive treatment is necessary in patients treated with a TKI or a direct VEGF inhibitor, confirming pro-hypertensive effects of these drugs. However, under adequate blood pressure control, microvascular structure seem to be partially preserved, since a worsening of basal capillary density but no changes in retinal arteriole morphology were observed.

Reference values of retinal microcirculation parameters derived from a population random sample

Retinal microcirculation reflects retinal perfusion abnormalities and retinal arterial structural changes at relatively early stages of various cardiovascular diseases. Our objective has been to establish reference values for major functional and structural parameters of retinal microcirculation in a randomly selected urban population sample. A total of 398 randomly selected individuals from an urban population aged 25 to 65 years, resident in Pilsen, Czech Republic, were screened for major cardiovascular risk factors. Retinal microcirculation was assessed using scanning laser Doppler flowmetry (SLDF), with data evaluable in 343 patients. Of this number, complete data were available for 256 individuals free from manifest cardiovascular disease, diabetes and drug treatment for hypertension and/or dyslipidemia, constituting the reference value population. Juxtapapillary retinal capillary blood flow has increased significantly with age whereas vessel and luminal diameters have decreased. No sex differences in retinal microcirculation parameters have been found. Therefore, reference values for retinal microcirculation parameters have been established by age groups. Unattended automated office systolic BP, after adjusting for age, correlated significantly with wall-to-lumen ratio (WLR) and wall thickness (WT). Moreover, after adjusting for age and mean BP, a positive relationship has been found between carotid femoral pulse wave velocity and WT, WLR and wall cross-sectional area, indicating the interaction between micro- and macro-vasculature. In conclusion, our study is the first to provide reference values of retinal microcirculation parameters in a random Caucasian population sample. Our results have shown that, at the population level, the first structural changes in retinal microcirculation are those in lumen diameters. Of note, a close relationship between BP and vascular remodeling of retinal arterioles and between aortic stiffness and WLR of retinal arterioles suggests an interaction between micro- and macro-vasculature.

The value of coronary computed tomography angiography in assessing the cardiac circulation of an outpatient-based population

To evaluate the perfusion of coronary circulation and its related factors and the difference in the peak filling times in aortic sinus and coronary sinus by coronary computed tomography angiography (CCTA).From January 1 to August 1, 2018, 61 outpatients with angina pectoris were recruited, completed a questionnaire about risk factors and underwent CCTA, which was also used to assess the stenosis of different coronary artery segments.The duration of circulation was 9.50 ± 2.43 seconds in patients with flat T wave, which was shorter than the duration in normal subjects (P = .021). However, other cardiovascular risk factors showed no effect on the duration of circulation. In addition, the duration of circulation was closely related to the peak filling time of coronary sinus [r(s) = 0.681]. We further divided the circulation time difference (delta) values into 3 levels (<6, 6-12, and ≥12 seconds).It showed that the circulation duration (Y) was associated with:Therefore, the cardiac circulation duration was negatively related to the degree of stenosis in the 1 diagonal and proximal LCA.It compensates for the inability of CCTA to assess circulation at rest simply by determining the peak filling time in the aortic sinus and the coronary sinus. Moderate cardiac microcirculation duration was related to a low incidence of clinical symptoms and electrocardiogram disorders, which was determined mainly by the diagonal and left circumflex branch 1 of LCA.

Mas Receptor Activation Contributes to the Improvement of Nitric Oxide Bioavailability and Vascular Remodeling During Chronic AT1R (Angiotensin Type-1 Receptor) Blockade in Experimental Hypertension

Angiotensin (1-7) production increases during AT1R (angiotensin type-1 receptor) blockade. The contribution of Ang (1-7) (angiotensin [1-7]) and its receptor (MasR) to the favorable effect of angiotensin receptor blockers on remodeling and function of resistance arteries remains unclear. We sought to determine whether MasR contributes to the improvement of vascular structure and function during chronic AT1R blockade. Spontaneously hypertensive rats were treated with Ang (1-7) or olmesartan ± MasR antagonist A-779, or vehicle, for 14 days. Blood pressure was measured by tail cuff methodology. Mesenteric arteries were dissected and mounted on a pressurized micromyograph to evaluate media-to-lumen ratio (M/L) and endothelial function. Expression of MasR and eNOS (endothelial nitric oxide synthase) was evaluated by immunoblotting, plasma nitrate by colorimetric assay, and reactive oxygen species production by dihydroethidium staining. Independently of blood pressure, olmesartan significantly reduced M/L and improved NO bioavailability, A-779 prevented these effects. Likewise, Ang (1-7) significantly reduced M/L and NO bioavailability. MasR expression was significantly increased by Ang (1-7) as well as by olmesartan, and it was blunted in the presence of A-779. Both Ang (1-7) and olmesartan increased eNOS expression and plasma nitrite which were reduced by A-779. Superoxide generation was attenuated by olmesartan and Ang (1-7) and was blunted in the presence of A-779. These MasR-mediated actions were independent of AT2R activation since olmesartan and Ang (1-7) increased MasR expression and reduced M/L in Ang II (angiotensin II)-infused AT2R knockout mice, independently of blood pressure control. A-779 prevented these effects. Hence, MasR activation may contribute to the favorable effects of AT1R antagonism on NO bioavailability and microvascular remodeling, independently of AT2R activation and blood pressure control.

Microvascular disease in chronic kidney disease: the base of the iceberg in cardiovascular comorbidity

Chronic kidney disease (CKD) is a relentlessly progressive disease with a very high mortality mainly due to cardiovascular complications. Endothelial dysfunction is well documented in CKD and permanent loss of endothelial homeostasis leads to progressive organ damage. Most of the vast endothelial surface area is part of the microcirculation, but most research in CKD-related cardiovascular disease (CVD) has been devoted to macrovascular complications. We have reviewed all publications evaluating structure and function of the microcirculation in humans with CKD and animals with experimental CKD. Microvascular rarefaction, defined as a loss of perfused microvessels resulting in a significant decrease in microvascular density, is a quintessential finding in these studies. The median microvascular density was reduced by 29% in skeletal muscle and 24% in the heart in animal models of CKD and by 32% in human biopsy, autopsy and imaging studies. CKD induces rarefaction due to the loss of coherent vessel systems distal to the level of smaller arterioles, generating a typical heterogeneous pattern with avascular patches, resulting in a dysfunctional endothelium with diminished perfusion, shunting and tissue hypoxia. Endothelial cell apoptosis, hypertension, multiple metabolic, endocrine and immune disturbances of the uremic milieu and specifically, a dysregulated angiogenesis, all contribute to the multifactorial pathogenesis. By setting the stage for the development of tissue fibrosis and end organ failure, microvascular rarefaction is a principal pathogenic factor in the development of severe organ dysfunction in CKD patients, especially CVD, cerebrovascular dysfunction, muscular atrophy, cachexia, and progression of kidney disease. Treatment strategies for microvascular disease are urgently needed.

The importance of endothelial dysfunction in resistance artery remodelling and cardiovascular risk

AIMS

The relationship between resistance artery remodelling and endothelial function remains unknown. In this study, we assessed (i) the capacity of endothelial function and nitric oxide (NO) availability to provide more information on the severity of resistance artery remodelling than common cardiovascular risk factors in subjects at low or high cardiovascular risk; and (ii) differences between patterns of resistance artery remodelling associated with deficit of NO availability and with exposure to cardiovascular risk factors.

METHODS AND RESULTS

All analyses were conducted on the microvascular data set of the Italian Society for Arterial Hypertension (SIIA) that includes 356 patients with measures of small resistance arteries remodelling acquired with pressure or wire myography. Information on endothelial function and NO availability were also available in 116 patients. The European Heart Score (HS) was used to define the total cardiovascular risk of each patient. Endothelial function was inversely related with the severity of the resistance artery remodelling, and this association remained significant after adjustment for the HS. By contrast, the HS lost its significant association with the media-to-lumen (M/L) ratio and the media cross-sectional area after adjustment for endothelial function. The strength of these associations was similar in subjects at high and low cardiovascular risk. The addition of endothelial function and NO availability to the HS significantly improved the identification of subjects at more and less severe resistance artery remodelling. A severe deficit of NO availability was associated with hypertrophic remodelling, while a higher HS was more clearly associated with eutrophic remodelling.

CONCLUSION

Resistance artery endothelial function and NO availability might represent important factors involved in resistance artery remodelling, independently from cardiovascular risk factor exposure.

Effect of direct renin inhibition on vascular function after long-term treatment with aliskiren in hypertensive and diabetic patients

OBJECTIVE

We tested the hypothesis that chronic treatment with the direct renin inhibitor aliskiren improves vascular function in resistance and conduit arteries of type two diabetic and hypertensive patients.

METHOD

Sixteen patients with mild essential hypertension and with a previous diagnosis of noninsulin-dependent diabetes mellitus were included in the study. Patients were then randomized to aliskiren (150 mg once daily, n = 9), or ramipril (5 mg once daily, n = 7). Each patient underwent a biopsy of the subcutaneous tissue and small arteries were dissected and mounted on a pressurized micromyograph to evaluate endothelium dependent vasorelaxation in response to acetylcholine ± N omega-nitro-L-arginine methyl ester hydrochloride in vessels precontracted with norepinephrine. Endothelial function has been quantified also in large conduit arteries by flow-mediated dilation.

RESULTS

A similar office blood pressure-lowering effect was observed with the two drugs, although changes in DBP were not statistically significant in the ramipril group. Aliskiren significantly improved endothelium-dependent relaxation in subcutaneous resistance arteries, as well as increased flow-mediated dilation in conduit arteries, whereas the effects induced by ramipril did not reach statistical significance. Only aliskiren significantly increased the expression of p1177-endothelial nitric oxide synthase in the endothelium. Both aliskiren and ramipril had a negligible effect on markers of oxidative stress.

CONCLUSION

Aliskiren restored endothelial function and induced a more prompt peripheral vasodilation in hypertensive and diabetic patients possibly through the increased production of nitric oxide via the enhanced expression and function of the active phosphorylated form of endothelial nitric oxide synthase.

Involvement of microcirculation in critical ischemia: how to identify it?

Critical limb ischemia represents the most severe pattern of peripheral arterial disease (PAD) associated with the high risk of major amputation, cardiovascular events and death. The diagnosis and management of critical limb ischemia (CLI) is often challenging. Systolic ankle and toe pressure measurements are considered to be the basic techniques for the identification of PAD. However, they provide rough insight into the dependent local tissue perfusion. Furthermore, those techniques do not enable investigation of microcirculation which has crucial role in the pathogenesis of CLI. Some patients with mild deterioration of macrocirculation develop CLI if microcirculation is affected. Investigation of perfusion on macro- and local microcirculatory level enables more effective treatment: revascularization of the angiosome-related artery. The technologies capable of assessing limb tissue oxygenation or perfusion on microcirculatory level enable direct assessment of distant tissue oxygenation. Transcutaneous oxygen tension (TcPO2) measurement which was introduced in clinical practice represents one of the objective criteria for the diagnosis of CLI. Main weakness of this technique as well as laser Doppler flow measurement is low penetrance from the skin surface. Measurement of tissue blood flow on microcirculatory level can be performed with indocyanine green fluorescent imaging (ICG), contrast-enhanced magnetic resonance and vital microscopy. ICG is promising method which provides excellent informative image of tissue perfusion. However, it offers little quantitative information. Investigation of microcirculation in patients with CLI is of outmost importance because it enables insight in local tissue perfusion and oxygenation, which represents the basis of identification of most ischemic regions and provide more successful angiosome related revascularization of an affected artery.

Vascular Aging and Central Aortic Blood Pressure: From Pathophysiology to Treatment

Large conductive arteries undergo to structural modifications by aging, eventually leading to increased vascular stiffness. As consequence, cardiovascular hemodynamic changes by increasing central blood pressure which may be also associated to the remodelling of peripheral resistance arteries that contribute to increase further the central vascular stiffness and blood pressure. These modifications resemble the ones that has been shown in essential hypertension, thus a condition of "early vascular aging" has been described in hypertensive patients. Since hypertension related target organs, particularly the heart, face aortic blood pressure rather than brachial blood pressure, it has been recently suggested that central blood pressure and other parameters of large arteries' stiffness, including pulse wave velocity (PWV), may better correlate with subclinical organ damage and might be useful to assess the cardiovascular risk of patients beyond the traditional risk factors. Different devices have been validated to measure central blood pressure and PWV, and are currently available for clinical use. The increasing application of these tools in clinical practice could improve the management of hypertensive patients by better defining the cardiovascular risk and address the antihypertensive therapy.

Morphological remodeling of the intramural coronary resistance artery network geometry in chronically Angiotensin II infused hypertensive female rats

Segmental remodeling of resistance arteries, inhibition of angiogenetic processes, their rarefaction by AngiotensinII and hypertension are accepted facts. Less is known about alterations in resistance artery network geometry potentially induced by them. Female rats were infused with 100 ng/kg/min AngiotensinII with osmotic minipumps for four weeks that raised mean arterial blood pressure from 98 ± 3 to 125 ± 7 mmHg. Geometry of the left coronary artery system was studied on plastic casts and on in situ microsurgically prepared, saline infused video-microscoped networks (n = 13 and 11 controls and hypertensives, respectively). Parallel running branches, broken course of larger branches, multiple branchings and branch crossings have been identified (13 and 74 such deformities, in control and hypertensive networks, respectively, p < 0.01). Bifurcation angles increased with increasing asymmetry of daughter branches but not in hypertensives. Dividing the whole network (theoretically) into several hundreds of 50μm long ring units, ring frequency peaked at 200μm diameter in normal networks. This peak diminished and was replaced by a peak at 300μm in hypertensives (p < 0.01). In controls, diameter of vascular units decreased at a fairly even rate with flow distance from the orifice. The 350, 200, 150μm diameter units were found with highest frequencies at flow distances around 2.5, 5.5 and 7.5mm, respectively. This regular pattern disintegrated in hypertensives. Higher blood flow routes were needed to cover the same distance from the orifice (p < 0.01). Shrinkage and diminishment of many parallel connected 200μm segments, concomitant enlargement of many larger segments accompanied with morphological deformities can be expected to contribute to elevated vascular resistance.

Aortic stiffness is not only associated with structural but also functional parameters of retinal microcirculation

OBJECTIVE

The aim of the study was to test the hypothesis that alterations in large arteries are associated with microvascular remodelling and decreased retinal capillary blood flow.

METHODS

The study group comprised of 88 patients with essential hypertension and 32 healthy controls. Retinal microcirculation was evaluated by scanning laser Doppler flowmetry. Macrovascular changes were assessed on the basis of arterial stiffness measurement (carotid-femoral pulse wave velocity), its hemodynamic consequences (central pulse pressure, augmentation pressure, augmentation index) and intima media thickness of common carotid artery.

RESULTS

Pulse wave velocity was inversely correlated to mean retinal capillary blood flow in hypertensive patients (R = -0.32, p < 0.01). This relationship remained significant in multivariate regression analysis after adjustment for age, sex, central systolic blood pressure (BP) and body mass index (β = -31.27, p < 0.001). Lumen diameter (LD) of retinal arterioles was significantly smaller in hypertensive then normotensive subjects (79.4 vs. 83.8, p = 0.03). Central and brachial systolic, diastolic and mean BPs were significantly correlated with LD and outer diameter of retinal arterioles. The relationship between LD and central BPs remained significant in multivariate analysis (β = -0.15, p = 0.03 for cSBP; β = -0.22, p = 0.04 for cDBP; β = -0.21, p = 0.03 for cMBP). Moreover, in a subgroup with cardiac damage central and brachial pulse pressure were positively associated with retinal wall thickness, wall cross sectional area, and wall to lumen ratio.

CONCLUSION

In conclusion, the study provides a strong evidence that microcirculation is coupled with macrocirculation not only in terms of structural but also functional parameters.

Pheochromocytoma as a Clinical Model of Peripheral Sympathetic Overdrive: Old and New Findings

PURPOSE OF REVIEW

The present paper will review the results of experimental and clinical studies aimed at defining the functional behavior of the central and peripheral nervous system in adrenal pheochromocytoma.

RECENT FINDINGS

The contribution of sympathetic neural influences to the development of high blood pressure values in pheochromocytoma is complex. Studies performed in experimental animal models have shown that hypertension and the concomitant high circulating levels of catecholamines can lead to inhibition of central sympathetic neural outflow by reflex mechanisms and direct stimulation of central adrenergic receptors, respectively. However, these studies have also shown that high circulating levels of catecholamines favor a downregulation of alpha- and beta-adrenergic receptors, lessening their response to endogenous and exogenous adrenergic stimulation. The present paper reviews results of human studies performed by our group and others on the behavior of the central and peripheral nervous system in human pheochromocytoma. We discuss data collected in patients with different levels of peripheral sympathetic drive, i.e., before and after surgical removal of the adrenal pheochromocytoma. In the presence of elevated plasma catecholamine level, such as that characterizing adrenal pheochromocytoma, microneurography shows that central sympathetic neural activity is normal or even inhibited. At the peripheral vascular level, pheochromocytoma is characterized by a reduced vascular reactivity to exogenous sympathetic stimulation but a normal response by the vessels to endogenous adrenergic stimulation.

Comparison between invasive and noninvasive techniques of evaluation of microvascular structural alterations

BACKGROUND

The evaluation of the morphological characteristics of small resistance arteries in humans is challenging. The gold standard method is generally considered to be the measurement by wire or pressure micromyography of the media-to-lumen ratio of subcutaneous small vessels obtained by local biopsies. However, noninvasive techniques for the evaluation of retinal arterioles were recently proposed; in particular, two approaches, scanning laser Doppler flowmetry (SLDF) and adaptive optics, seem to provide useful information; both of them provide an estimation of the wall-to-lumen ratio (WLR) of retinal arterioles. Moreover, a noninvasive measurement of basal and total capillary density may be obtained by videomicroscopy/capillaroscopy. No direct comparison of these three noninvasive techniques in the same population was previously performed; in particular, adaptive optics was never validated against micromyography.

METHODS

In the current study, we enrolled 41 controls and patients: 12 normotensive lean controls, 12 essential hypertensive lean patients, nine normotensive obese patients and eight hypertensive obese patients undergoing elective surgery. All patients underwent a biopsy of subcutaneous fat during surgery. Subcutaneous small resistance artery structure was assessed by wire micromyography and the media-to-lumen ratio was calculated. WLR of retinal arterioles was obtained by SLDF and adaptive optics. Functional (basal) and structural (total) microvascular density was evaluated by capillaroscopy before and after venous congestion.

RESULTS AND CONCLUSION

Our data suggest that adaptive optics has a substantial advantage over SLDF in terms of evaluation of microvascular morphology, as WLR measured with adaptive optics is more closely correlated with the M/L of subcutaneous small arteries (r = 0.84, P < 0.001 vs. r = 0.52, P < 0.05, slopes of the relations: P < 0.01 adaptive optics vs. SLDF). In addition, the reproducibility of the evaluation of the WLR with adaptive optics is far better, as compared with SLDF, as intraobserver and interobserver variation coefficients are clearly smaller. This may be important in terms of clinical evaluation of microvascular morphology in a clinical setting, as micromyography has substantial limitations in its clinical application due to the local invasiveness of the procedure.

Angiotensin II and vascular damage in hypertension: Role of oxidative stress and sympathetic activation

Reactive oxygen species (ROS) are oxygen derivates and play an active role in vascular biology. These compounds are generated within the vascular wall, at the level of endothelial and vascular smooth muscle cells, as well as by adventitial fibroblasts. Physiologically, ROS generation is counteracted effectively by the rate of elimination. In hypertension, a ROS excess occurs, which is not counterbalanced by the endogenous antioxidant mechanisms, leading to a state of oxidative stress. Angiotensin II, the active peptide of the renin-angiotensin-system (RAS), is a significant stimulus for ROS generation within the vasculature. It was also documented that at the level of subfornical cerebral regions an inappropriate RAS stimulation may lead to an increased vascular sympathetic activity. More recently, in conditions of fetal undernutrition, it was also proposed an increased vascular sympathetic activity secondary to inappropriate RAS activation, leading to the development of hypertension in adult life. The present review will discuss the complex interaction between RAS activation, vascular ROS generation and increased sympathetic outflow in hypertension.

Age- and Sex-Specific Reference Values for Media/Lumen Ratio in Small Arteries and Relationship With Risk Factors

Small-artery remodeling is an early feature of target organ damage in hypertension and retains a negative prognostic value. The aim of the study is to establish age- and sex-specific reference values for media/lumen in small arteries obtained in humans by biopsy. Data from 91 healthy individuals and 200 individuals with cardiovascular risk factors in primary prevention from 4 Italian centers were pooled. Sex-specific equations for media/lumen in the healthy subpopulation, with age as dependent variable, were calculated. These equations were used to calculate predicted media/lumen values in individuals with risk factors and Z scores. The association between classical risk factors and Z scores was then explored by multiple regression analysis. A second-degree polynomial equation model was chosen to obtain sex-specific equations for media/lumen, with age as dependent variable. In the population with risk factors (111 men, age 50.5±14.0 years, hypertension 80.5%), media/lumen Z scores were independently associated with body mass index (standardized β=0.293, P=0.0001), total cholesterol (β=0.191, P=0.031), current smoking (β=0.238, P=0.0005), fasting blood glucose (β=0.204, P=0.003), systolic blood pressure (β=0.233, P=0.023), and female sex (β=0.799, P=0.038). A significant interaction between female sex and total cholesterol was found (β=-0.979, P=0.014). Results were substantially similar in the hypertensive subgroup. A method to calculate individual values of remodeling and growth index based on reference values was also presented. Age- and sex-specific percentiles of media/lumen in a healthy population were estimated. In a predominantly hypertensive population, media/lumen Z scores were associated with major cardiovascular risk factors, including body mass index, cholesterol, smoking, glucose, and systolic blood pressure. Significant sex differences were observed.

The role of noninvasive cardiovascular testing, applied clinical nutrition and nutritional supplements in the prevention and treatment of coronary heart disease

Numerous clinical trials suggest that we have reached a limit in our ability to decrease the incidence of coronary heart disease (CHD) and cardiovascular disease (CVD) utilizing the traditional diagnostic evaluation, prevention and treatment strategies for the top five cardiovascular risk factors of hypertension, diabetes mellitus, dyslipidemia, obesity and smoking. About 80% of heart disease (heart attacks, angina, coronary heart disease and congestive heart failure) can be prevented by optimal nutrition, optimal exercise, optimal weight and body composition, mild alcohol intake and avoiding smoking. Statistics show that approximately 50% of patients continue to have CHD or myocardial infarction (MI) despite presently defined 'normal' levels of the five risk factors listed above. This is often referred to as the 'CHD gap'. Novel and more accurate definitions and evaluations of these top five risk factors are required, such as 24 h ambulatory blood pressure (ABM) results, advanced lipid profiles, redefined fasting and 2 h dysglycemia parameters, a focus on visceral obesity and body composition and the effects of adipokines on cardiovascular risk. There are numerous traumatic insults from the environment that damage the cardiovascular system but there are only three finite vascular endothelial responses, which are inflammation, oxidative stress and immune vascular dysfunction. In addition, the concept of translational cardiovascular medicine is mandatory in order to correlate the myriad of CHD risk factors to the presence or absence of functional or structural damage to the vascular system, preclinical and clinical CHD. This can be accomplished by utilizing advanced and updated CV risk scoring systems, new and redefined CV risk factors and biomarkers, micronutrient testing, cardiovascular genetics, nutrigenomics, metabolomics, genetic expression testing and noninvasive cardiovascular testing.

New Methods to Study the Microcirculation

Essential hypertension is associated with structural alterations in the microvessels; in particular, an increase in the media thickness to internal lumen ratio of small resistance arteries (MLR) and a reduction in capillary density have been observed. The evaluation of the morphological characteristics of small resistance arteries in humans is challenging. The gold-standard method is generally considered to be the measurement by wire or pressure micromyography of MLR of subcutaneous small vessels obtained by local biopsies. However, noninvasive techniques for the evaluation of retinal arterioles were recently proposed; in particular, 2 approaches, scanning laser Doppler flowmetry (SLDF) and adaptive optics (AO), seem to provide useful information. Both of them provide an estimation of the wall to lumen ratio (WLR) of retinal arterioles. Moreover, a noninvasive measurement of basal and total capillary density may be obtained by videomicroscopy/capillaroscopy. It has been recently demonstrated that AO has a substantial advantage over SLDF in terms of evaluation of microvascular morphology, since WLR measured with AO is more closely correlated with the M/L of subcutaneous small arteries. The possibility to noninvasively assess in a reliable way, microvascular morphology in a clinical setting may represent a major advancement, since micromyography has substantial limitations in its application due to the local invasiveness of the procedure.

Coherence and Coupling Functions Reveal Microvascular Impairment in Treated Hypertension

The complex interactions that give rise to heart rate variability (HRV) involve coupled physiological oscillators operating over a wide range of different frequencies and length-scales. Based on the premise that interactions are key to the functioning of complex systems, the time-dependent deterministic coupling parameters underlying cardiac, respiratory and vascular regulation have been investigated at both the central and microvascular levels. Hypertension was considered as an example of a globally altered state of the complex dynamics of the cardiovascular system. Its effects were established through analysis of simultaneous recordings of the electrocardiogram (ECG), respiratory effort, and microvascular blood flow [by laser Doppler flowmetry (LDF)]. The signals were analyzed by methods developed to capture time-dependent dynamics, including the wavelet transform, wavelet-based phase coherence, non-linear mode decomposition, and dynamical Bayesian inference, all of which can encompass the inherent frequency and coupling variability of living systems. Phases of oscillatory modes corresponding to the cardiac (around 1.0 Hz), respiratory (around 0.25 Hz), and vascular myogenic activities (around 0.1 Hz) were extracted and combined into two coupled networks describing the central and peripheral systems, respectively. The corresponding spectral powers and coupling functions were computed. The same measurements and analyses were performed for three groups of subjects: healthy young (Y group, 24.4 ± 3.4 y), healthy aged (A group, 71.1 ± 6.6 y), and aged treated hypertensive patients (ATH group, 70.3 ± 6.7 y). It was established that the degree of coherence between low-frequency oscillations near 0.1 Hz in blood flow and in HRV time series differs markedly between the groups, declining with age and nearly disappearing in treated hypertension. Comparing the two healthy groups it was found that the couplings to the cardiac rhythm from both respiration and vascular myogenic activity decrease significantly in aging. Comparing the data from A and ATH groups it was found that the coupling from the vascular myogenic activity is significantly weaker in treated hypertension subjects, implying that the mechanisms of microcirculation are not completely restored by current anti-hypertension medications.

Hemodynamic Consequences of Changes in Microvascular Structure

In hypertension, an increased media-to-lumen ratio of small resistance arteries might play an important role in the increase of vascular resistance, and may also be an adaptive response to the increased hemodynamic load. The presence of morphological alteration in the microvasculature may be associated to an impaired tissue perfusion and/or to the development of target organ damage. Structural alterations in the microcirculation might represent a predictor of the onset of cardio-cerebrovascular events and hypertension complications. A cross-talk between the small and large artery may exaggerate arterial damage, following a vicious circle. Therefore, in the present review, possible hemodynamic consequences of the presence of microvascular structural alterations will be considered, in terms of their time of onset, role in the development and/or maintenance of high blood pressure values, and interrelationships with structural/mechanical alterations of large conductance arteries.

Comparison of lercanidipine plus hydrochlorothiazide vs. lercanidipine plus enalapril on micro and macrocirculation in patients with mild essential hypertension

Dihydropyridine calcium channel blockers may possess antioxidant properties, and might improve micro and macrovascular structure and function. Combination treatment with an ACE inhibitor may have additional advantages, compared with a thiazide diuretic. The aim of the present study is to investigate the effects of a short-term treatment with lercanidipine, and to compare two combination treatments: lercanidipine + enalapril vs. lercanidipine + hydrochlorothiazide on structural alterations in retinal arterioles, on skin capillary density and on large artery distensibility. Thirty essential hypertension patients are included in the study, and treated for 4 weeks with lercanidipine 20 mg per day orally. Then, they were treated for 6 months with lercanidipine + enalapril (n = 15) or lercanidipine + hydrochlorothiazide (n = 15) combinations. Investigations were performed on basal condition, after appropriate wash out of previous treatments, after 4 weeks of lercanidipine monotherapy treatment, and at the end of the combination treatment. Non-invasive measurements of wall-to-lumen ratio (WLR) and other morphological parameters of retinal arterioles were performed using either scanning laser Doppler flowmetry or adaptive optics. Capillary density was evaluated by capillaroscopy, while pulse wave velocity was measured, and central blood pressures were assessed by pressure waveform analysis. A significant improvement of WLR and other indices of retinal artery structure is observed with both technical approaches after treatment with lercanidipine alone, with a further improvement after treatment with lercanidipine + enalapril, while after treatment with lercanidipine + hydrochlorothiazide, the improvement is partially blunted. Central systolic and diastolic blood pressures are similarly reduced by both therapeutic strategies. Capillary density is increased only after treatment with lercanidipine + enalapril. In conclusion, lercanidipine both in monotherapy and in combination with enalapril but not with hydrochlorothiazide is able to improve microvascular structure; on the other hand, a decrease in central blood pressure is observed with both therapeutic combinations.

Microvascular structure as a prognostically relevant endpoint

Remodelling of subcutaneous small resistance arteries, as indicated by an increased media-to-lumen ratio, is frequently present in hypertensive, obese, or diabetic patients. The increased media-to-lumen ratio may impair organ flow reserve. This may be important in the maintenance and, probably, also in the progressive worsening of hypertensive disease. The presence of structural alterations represents a prognostically relevant factor, in terms of development of target organ damage or cardiovascular events, thus allowing us a prediction of complications in hypertension. In fact, media-to-lumen ratio of small arteries at baseline, and possibly their changes during treatment may have a strong prognostic significance. However, new, non-invasive techniques are needed before suggesting extensive application of the evaluation of remodelling of small arteries for the cardiovascular risk stratification in hypertensive patients. Some new techniques for the evaluation of microvascular morphology in the retina, currently under clinical investigation, seem to represent a promising and interesting future perspective. The evaluation of microvascular structure is progressively moving from bench to bedside, and it could represent, in the near future, an evaluation to be performed in all hypertensive patients, to obtain a better stratification of cardiovascular risk, and, possibly, it might be considered as an intermediate endpoint in the evaluation of the effects of antihypertensive therapy, provided that a demonstration of a prognostic value of non-invasive measures of microvascular structure is made available.

Impaired Muscle Oxygenation and Elevated Exercise Blood Pressure in Hypertensive Patients: Links With Vascular Stiffness

This study examined in vivo (1) skeletal muscle oxygenation and microvascular function, at rest and during handgrip exercise, and (2) their association with macrovascular function and exercise blood pressure (BP), in newly diagnosed, never-treated patients with hypertension and normotensive individuals. Ninety-one individuals (51 hypertensives and 40 normotensives) underwent office and 24-hour ambulatory BP, arterial stiffness, and central aortic BP assessment, followed by a 5-minute arterial occlusion and a 3-minute submaximal handgrip exercise. Changes in muscle oxygenated and deoxygenated hemoglobin and tissue oxygen saturation were continuously monitored by near-infrared spectroscopy and beat-by-beat BP by Finapres. Hypertensives had higher (P<0.001) central aortic BP and pulse wave velocity versus normotensives and exhibited (1) a blunted tissue oxygen saturation response during occlusion, with slower (P=0.006) deoxygenation rate, suggesting reduced muscle oxidative capacity, and (2) a slower reoxygenation rate and blunted hyperemic response (P<0.05), showing reduced microvascular reactivity. Muscle oxygenation responses were correlated with aortic systolic and pulse pressure and augmentation index (P<0.05; age and body mass index (BMI) adjusted). When exercising at the same submaximal intensity, hypertensives required a significantly greater (P<0.001) increase in BP for achieving similar muscle oxygenation levels as normotensives. This response was correlated with the magnitude of microvascular hyperemia and aortic BP. In conclusion, nontreated patients with hypertension exhibit prominent reductions in in vivo indices of skeletal muscle oxidative capacity, suggestive of mitochondrial dysfunction, and blunted muscle microvascular reactivity. These dysfunctions were associated with higher aortic systolic BP and arterial stiffness. Dysregulations in muscle oxygen delivery/utilization and microvascular stiffness, in hypertensive patients, partially contribute to their exaggerated BP during exercise.

Obesity and hypertension

Obesity and in particular the excessive visceral fat distribution is accompanied by several alterations at hormonal, inflammatory and endothelial level. These alterations induce a stimulation of several other mechanisms that contribute to the hypertensive state and on the other side to increase the cardiovascular morbidity. In these chapter we will examine the main mechanisms of obesity and obesity-related hypertension and in particular the role of sympathetic nervous system, the alterations of the renal function and at the microvascular level. We will also depict the role of insulin resistance as factor stimulating and potentiating the other mechanisms. The second part will be focalized on the major target organ damage linked with obesity and obesity-related hypertension. We will finally describe the management and treatment of obesity and the antihypertensive drug therapies more effective in hypertensive obeses.

Relationship between different subpopulations of circulating CD4+ T lymphocytes and microvascular or systemic oxidative stress in humans

BACKGROUND AND OBJECTIVE

Different components of the immune system, including innate and adaptive immunity (T effector lymphocytes and T regulatory lymphocytes - TREGs) may be involved in the development of hypertension, vascular injury and inflammation. However, no data are presently available in humans about possible relationships between T-lymphocyte subtypes and microvascular oxidative stress. Our objective was to investigate possible relationships between T-lymphocyte subtypes and systemic and microvascular oxidative stress in a population of normotensive subjects and hypertensive patients.

PATIENTS AND METHODS

In the present study we enrolled 24 normotensive subjects and 12 hypertensive patients undergoing an elective surgical intervention. No sign of local or systemic inflammation was present. All patients underwent a biopsy of subcutaneous fat during surgery. A peripheral blood sample was obtained before surgery for assessment of T lymphocyte subpopulations by flow cytometry and circulating indices of oxidative stress.

RESULTS

A significant direct correlation was observed between Th1 lymphocytes and reactive oxygen species (ROS) production (mainly in microvessels). Additionally, significant inverse correlations were observed between ROS and total TREGs, or TREGs subtypes. Significant correlations were detected between circulating indices of oxidative stress/inflammation and indices of microvascular morphology/Th1 and Th17 lymphocytes. In addition, a significant inverse correlation was detected between TREGs in subcutaneous small vessels and C reactive protein.

CONCLUSIONS

Our data suggest that TREG lymphocytes may be protective against microvascular damage, probably because of their anti-oxidant properties, while Th1-Th17 lymphocytes seem to exert an opposite effect, confirming an involvement of adaptive immune system in microvascular damage.

The association between retinal vasculature changes and stroke: a literature review and Meta-analysis

AIM

To determine the association between retinal vasculature changes and stroke.

METHODS

MEDLINE and EMBASE were searched for relevant human studies to September 2015 that investigated the association between retinal vasculature changes and the prevalence or incidence of stroke; the studies were independently examined for their qualities. Data on clinical characteristics and calculated summary odds ratios (ORs) were extracted for associations between retinal microvascular abnormalities and stroke, including stroke subtypes where possible, and adjusted for key variables.

RESULTS

Nine cases were included in the study comprising 20 659 patients, 1178 of whom were stroke patients. The retinal microvascular morphological markers used were hemorrhage, microaneurysm, vessel caliber, arteriovenous nicking, and fractal dimension. OR of retinal arteriole narrowing and retinal arteriovenous nicking and stroke was 1.42 and 1.91, respectively, indicating that a small-caliber retinal arteriole and retinal arteriovenous nicking were associated with stroke. OR of retinal hemorrhage and retinal microaneurysm and stroke was 3.21 and 3.83, respectively, indicating that retinal microvascular lesions were highly associated with stroke. Results also showed that retinal fractal dimension reduction was associated with stroke (OR: 2.28 for arteriole network, OR: 1.80 for venular network).

CONCLUSION

Retinal vasculature changes have a specific relationship to stroke, which is promising evidence for the prediction of stroke using computerized retinal vessel analysis.

Different Impact of Essential Hypertension on Structural and Functional Age-Related Vascular Changes

We evaluated whether vascular remodeling is present in physiological aging and whether hypertension accelerates the aging process for vascular function and structure. Small arteries from 42 essential hypertensive patients (HT) and 41 normotensive individuals (NT) were dissected after subcutaneous biopsy. Endothelium-dependent vasodilation (pressurized myograph) was assessed by acetylcholine, repeated under the nitric oxide synthase inhibitor N -nitro- l -arginine methylester or the antioxidant tempol. Structure was evaluated by media–lumen ratio (M/L). Intravascular oxidative generation and collagen deposition were assessed. Inhibition by N -nitro- l -arginine methylester on ACh was inversely related to age in both groups ( P <0.0001) and blunted in HT versus NT for each age range. In NT, tempol enhanced endothelial function in the oldest subgroup; in HT, the potentiating effect started earlier. HT showed an increased M/L ( P <0.001) versus control. In both groups, M/L was directly related to age ( P <0.0001). M/L was greater in HT, starting from 31 to 45 years range. A significant age–hypertension interaction occurred ( P =0.0009). In NT, intravascular superoxide emerged in the oldest subgroup, whereas it appeared earlier among HT. Among NT, aged group displayed an increment of collagen fibers versus young group. In HT, collagen deposition was already evident in youngest, with a further enhancement in the aged group. In small arteries, ageing shows a eutrophic vascular remodeling and a reduced nitric oxide availability. Oxidative stress and fibrosis emerge in advanced age. In HT, nitric oxide availability is early reduced, but the progression rate with age is similar. Structural alterations include wide collagen deposition and intravascular reactive oxygen species, and the progression rate with age is steeper.

Relationship Between Different Subpopulations of Circulating CD4+ T-lymphocytes and Microvascular Structural Alterations in Humans

BACKGROUND

Different components of the immune system, including innate and adaptive immunity (T-effector lymphocytes and T-regulatory lymphocytes-TREGs) may be involved in the development of hypertension. In addition, it was demonstrated in animal models that TREGs may prevent angiotensin II-induced hypertension and vascular injury/inflammation. However, no data are presently available in humans about possible relationships between T-lymphocyte subtypes and microvascular structural alterations.

METHODS

For this purpose, in the present study, we enrolled 24 normotensive subjects and 12 hypertensive patients undergoing an elective surgical intervention. No sign of local or systemic inflammation was present. All patients underwent a biopsy of subcutaneous fat during surgery. Subcutaneous small resistance arteries were dissected and mounted on a wire myograph and the media to lumen ratio (M/L) was calculated. In addition, retinal arteriolar structure was evaluated noninvasively by scanning laser Doppler flowmetry. Capillary density in the nailfold, dorsum of the finger, and forearm were evaluated by videomicroscopy. A peripheral blood sample was obtained before surgery for assessment of T-lymphocyte subpopulations by flow cytometry.

RESULTS

Significant negative correlations were observed between indices of microvascular structure (M/L of subcutaneous small arteries and wall to lumen ratio of retinal arterioles) and circulating TREG lymphocytes. A direct correlation was observed between M/L of subcutaneous small arteries and circulating Th17 lymphocytes. In addition, total capillary density was correlated with a TREG effector memory subpopulation.

CONCLUSION

Our data suggest that some lymphocyte subpopulations may be related to microvascular remodeling, confirming previous animal data, and opening therapeutic possibilities.

Forearm Resistance-Vessel Dilatation Function During Reactive Hyperemia in Patients With Resistant Hypertension

BACKGROUND

Forearm blood flow (FBF) measured during reactive hyperemia by venous-occlusion plethysmography assesses resistance-vessel dilatation function but has never been investigated in resistant hypertension. The aim was to evaluate the independent correlates of forearm resistance-vessel function parameters in resistant hypertensives.

METHODS

In a cross-sectional study, 274 resistant hypertensives performed 24-hour ambulatory blood pressure (BP) monitoring, 2D-echocardiography, aortic pulse wave velocity, and venous-occlusion plethysmography with baseline and hyperemic FBF and vascular resistance measurements. A subsample of 103 patients also performed ultrasonographic brachial artery endothelial function examination. Independent correlates of baseline and hyperemic vascular parameters were assessed by multiple linear regressions.

RESULTS

Median (interquartile range) baseline FBF was 3.1 (2.4-4.0) ml/min/100ml of tissue, and during hyperemia mean FBF rose to 7.0 (5.2-9.4) ml/min/100ml of tissue. Baseline FBF and resistance were independently associated with left ventricular mass index (partial correlations -0.14 and 0.13, respectively), whereas hyperemic parameters were independently associated with body mass index (BMI) (inversely for FBF, partial correlation: -0.18 to -0.21) and with the nocturnal BP fall (directly for FBF, partial correlation: 0.12-0.15), after adjustments for age, sex, mean arterial pressure, and baseline vascular parameters. In a separate analysis, a larger brachial artery diameter was associated with higher hyperemic FBF, but there were no associations between resistance-vessel and conduit-vessel dilatation function parameters.

CONCLUSION

In patients with resistant hypertension, left ventricular mass was the only correlate of baseline FBF and resistance, whereas higher BMI and lower nocturnal BP fall were independently associated with lower FBF and higher resistance during reactive hyperemia.

Impact of apocynin on vascular disease in hypertension

Reactive oxygen species (ROS) are generated by cell metabolism of oxygen and represent signaling molecules playing an active role in vascular biology. In pathological conditions, including hypertension, a ROS excess, together with reduced endogenous antioxidant defenses, occurs, determining a state of oxidative stress. NAD(P)H oxidase (Nox) is a major ROS source within the vasculature. A large body of literature has demonstrated that hypertension-associated vascular functional and structural changes are attributable to Nox-driven intravascular ROS generation. Apocynin is a methoxy-catechol discovered as an inhibitor of superoxide. It has been utilized in several laboratories and in different models of hypertension as an inhibitor of Nox. Recent evidence proposes that apocynin predominantly acts as an antioxidant. The present review will discuss the role of ROS in vascular disease in hypertension and the impact of apocynin on these vascular changes.