Current Hypertension Reviews - Volume 14, Issue 2, 2018

This paper illustrates the evolution of our knowledge of arterial mechanics from our initial research works up to the present time. Several techniques focusing on this topic in terms of our experience are discussed. An interdisciplinary team composed by different institutions from Argentina, Uruguay, France and Spain was created to conduct research, to train human resources and to fulfill the inevitable social role of gaining access to technological innovation to improve public health.

To enhance the efficiency of patient-specific risk stratification and diagnosis, an assessment of arterial structural and functional changes associated to a vascular disease in both early and advanced stages have been proposed, with the objective of limiting the progression or revert vascular alterations. In this connection, an interdisciplinary international partnership made up by research institutions from France, Argentina, Uruguay and Spain was established, with the objective of contributing to the evaluation and follow-up of factors involved in the physiopathology of cardiometabolic diseases and human aging. Several studies, such as the effect of hypertension in large arteries, alterations in arterial wall viscosity, stiffness and inertia, endothelial function and vascular reactivity, cardiovascular risk improvement, vascular age assessment and cryografts vascular response evaluation were carried out as a result of this international collaboration during the last twenty-five years.

Adaptive identification systems focus on dynamical approaches based on the observed data from an experiment and/or clinical data. These systems establish a relationship between an input (arterial or vein instantaneous pressure) and an output (instantaneous arterial or vein diameter). Several dynamics relationships and applications can be established because of this adaptive identification as an arterial dynamic range (frequency response), biomechanical behavior of cryopreserved arteries, regional differences in veins as artery substitution, role of vascular smooth muscle in human hypertension and time invariance in the biomechanics of wall arteries. The aim of this review is to summarize some of those relevant results obtained from adaptive filter identification in cardiovascular dynamics research and clinical evaluation.

Vascular research in end-stage renal diseases is an interesting field in which the characterization of arterial stiffness proved to be valuable to predict morbidity and mortality. Particularly, patients on renal replacement therapy have been reported to have significant increases in arterial stiffness and cardiovascular mortality. The clinical relevance of the measurement of arterial stiffness is linked to therapeutical and preventive interventions. The purpose of this work is to analyze the results of the scientific research in the field of arterial stiffness, in which hemodialyzed patients were involved, emphasizing on clinical and in-vitro research carried out by our group compared to contributions previously reported in the specialized literature. These investigations are necessary to improve diagnostic strategies and monitor the arterial response to therapeutical interventions in chronic kidney disease.

Vascular assessment is becoming increasingly important in the diagnosis of cardiovascular diseases. In particular, clinical assessment of arterial stiffness, as measured by pulse wave velocity (PWV), is gaining increased interest due to the recognition of PWV as an influential factor on the prognosis of hypertension as well as being an independent predictor of cardiovascular and all-cause mortality. Whilst age and blood pressure are established as the two major determinants of PWV, the influence of heart rate on PWV measurements remains controversial with conflicting results being observed in both acute and epidemiological studies. In a majority of studies investigating the acute effects of heart rate on PWV, results were confounded by concomitant changes in blood pressure. Observations from epidemiological studies have also failed to converge, with approximately just half of such studies reporting a significant blood-pressure-independent association between heart rate and PWV. Further to the lack of consensus on the effects of heart rate on PWV, the possible mechanisms contributing to observed PWV changes with heart rate have yet to be fully elucidated, although many investigators have attributed heart-rate related changes in arterial stiffness to the viscoelasticity of the arterial wall. With elevated heart rate being an independent prognostic factor of cardiovascular disease and its association with hypertension, the interaction between heart rate and PWV continues to be relevant in assessing cardiovascular risk.

The vascular endothelium plays an important role to maintain the functional integrity of the cardiovascular system. The synthesis and secretion of substances with biological activity such as prostacyclin and NO give endothelium the vasodilator, antithrombotic, and antiatherosclerotic properties. Endothelial dysfunction participates in the genesis of HTA, but also hypertension produces endothelial damage. The major class of antihypertensive drugs has beneficial effects in the recuperation of the endothelial function, actions that are contributing to explain the impact of the adequate control of HTA in the reduction of CV events.

Background: Pulse wave velocity ratio (PWV-ratio), a measure of central-to-peripheral arterial stiffness gradient, is calculated as a quotient between carotid-femoral and carotid-radial PWV (cf-PWV/cr-PWV). This new index has been reported to be significantly associated with increased mortality in hemodialyzed patients. Since several reports showed differences in arterial stiffness regarding the pathway where the vascular access (VA) is, the purpose of this research was: a) to compare arterial stiffness values obtained in the left and right sides of the body in hemodialyzed and non-hemodialyzed patients, and b) to analyze PWV-ratio values obtained on the side of the body where the VA was placed and compare them to its contralateral intact side. Since it is difficult to adequately measure cr-PWV in patients with a VA in the forearm, we measured the carotid- brachial PWV (cb-PWV) and used it to calculate PWV-ratio (cf-PWV/cb-PWV). Methods: A Pearson's correlation and Bland & Altman analysis were performed in hemodialyzed (n=135) and non-hemodialyzed (n=77) patients, to quantify the equivalence between arterial stiffness parameters (cf-PWV, cb-PWV, PWV-ratio) obtained on each side of the body with respect to its contralateral side. Results: We conclude that PWV-ratio values measured on the side where the VA is placed were significantly higher than those obtained in its contralateral side, in hemodialyzed patients included in this research. Moreover, cf-PWV, cb-PWV and PWV-ratio values obtained on one side of the body were always highly correlated with its contralateral side. Conclusion: According to this research, any research involving PWV-ratio should always consider the observed territory.

Background: High blood pressure states (HBP) would differ in wave components and reflections indexes, which could associate clinical and prognostic implications. The study aims: 1) to characterize the association of aortic wave components and reflection parameters (backward [Pb], forward [Pf], Pb/Pf ratio and augmentation index [AIx]) with demographic, anthropometric, hemodynamic and arterial parameters in healthy children and adolescents; 2) to generate multivariate prediction models for the associations, to contribute to understand the main determinants of Pf, Pb, Pb/Pf and AIx; 3) to identify if differences in wave reflection indexes observed in HBP could be explained by differences in the analyzed parameters. Methods: Healthy children and adolescents (n=816, females: 386; Age: 3-20 years) were studied. Evaluations: central aortic pressure and wave components (Pb, Pf, Pb/Pf and AIx determination with SphygmoCor [SCOR] and Mobil-o-Graph [MOG]); anthropometric assessment; regional arterial stiffness (carotid-femoral, carotid-radial pulse wave velocity [PWV] and PWV ratio); carotid intima-media thickness; carotid and femoral distensbility; cardiac output; systemic vascular resistances (SVR). Simple and multiple regression models were constructed to determine aortic wave parameters; the main explanatory variables. Normotensive and HBP groups were compared. Differences in wave reflection indexes were analyzed before and after controlling for explanatory variables. Equivalences between SphygmoCor and Mobil-O-Graph data were assessed (correlation and Bland-Altman analyses). Results and Conclusion: There were systematic and proportional differences between the data obtained with SphygmoCor and Mobil-O-Graph devices. Heart rate (HR), peripheral pulse pressure, height and weight were the variables that isolated (simple associations) or combined (multiple associations), showed the major capability to explain interindividual differences in Pf, Pb, Pb/Pf and AIx. Arterial stiffness also showed explanatory capacity, being the carotid the artery with the major contribution. HBP associated higher Pf, Pb, AIx and lower Pb/Pf ratio. Those findings were observed together with higher weight, arterial stiffness and HR. After adjusting for anthropometric characteristics, HR, cardiac output and SVR, the HBP group showed greater Pf and Pb. Then, Pf and Pb characteristics associated with HBP would not be explained by anthropometric or hemodynamic factors. Evaluating wave components and reflection parameters could contribute to improve the comprehension and management of HBP states.

Introduction: Chronic serum uric acid elevation (SUA) is known to be induced by dyslipidemia, hypertension, inflammation, and insulin resistance. Therefore, it has been associated with higher risk for coronary artery disease and cardiovascular mortality. Also, increased levels of SUA have been associated with regional arterial stiffness, assessed by pulse wave velocity (PWV). Aims: To evaluate the relationships of PWV, SUA and different metabolic parameters in essential hypertensive patients. Material and Methods: We evaluated 445 essential hypertensive patients, by measuring office blood pressure (BP), weight, height, and waist circumference. In each patient, blood samples were drawn for biochemical evaluations and 24h urine collection. Body Mass Index (BMI) and Glomerular Filtration Rate (GFR) were calculated. Carotid-Femoral PWV and Left Ventricular Mass Index (LVMI) were measured in all patients. Results: All subjects (n=402), 242 males (55±0.9 yrs.; BMI: 28.9±0.3 Kg/m2) and 160 females (58±1 yrs.; BMI: 28.1±0.4 Kg/m2) had normal renal function. PWV values showed a significant association with SUA (p<0.001), Systolic BP (p<0.025) and LVMI (p<0.05). SUA showed a significant association, p&;lt;0.025: with BMI, Waist Circumference, and HDL-C; p<0.05: with Glycaemia at 120 min, Insulin at 120 min, TG, and LVMI; and p<0.001: with serum Creatinine. Backward Stepwise Regression showed that PWV could be predicted from SUA (p<0.001) and Systolic BP (p<0.05). BMI, Waist Circumference, DBP and HR did not significantly add to the ability of the equation to predict PWV. Conclusions: In this population of essential hypertensive patients, SUA was associated to increased arterial stiffness and to components of the Metabolic Syndrome. These results raise the possibility that a new approach to the role of SUA, linked to cardiovascular stratification, and a most appropriate treatment might be considered.

Background: Hypertension (HTN) is the main cause of cardiovascular diseases accounting for one-third of global mortality. Physical exercise reduces the incidence and prevalence of HTN and cardiovascular morbidity and mortality. Exercises recommended for hypertensive patients include supervised cardiac rehabilitation, which occurs in rehabilitation centers, and partly supervised rehabilitation, with the individual prescription of exercises conducted at patients' residences. Objective: Compare clinical and functional parameters of hypertensive patients subjected to two cardiac rehabilitation protocols: supervised and partly supervised. Method: Hypertensive patients stage I or II were randomly divided into group one (G1) (partly supervised cardiac rehabilitation) and group two (G2) (supervised cardiac rehabilitation). All patients performed a warm-up, aerobic exercise, strength training and cool-down. Participants' assessments conducted before and after intervention included: physical examination, six-minute walk test, cardiac stress test, metabolic tests, and central and peripheral blood pressure measurements. Results: A total of 61 patients (mean age 60.3±11.3 years, 78.7% women) were randomized (30 in G1 and 31 in G2). At the end of the intervention, G1 increased 30.6 meters (p=0.004) and G2 increased 55.0 meters (p>0.001) the distance covered in the six-minute walk test. G2 showed an increase in the maximum oxygen consumption from 24.7±8.6 mlO2/Kg/min to 28.4±7.5 mlO2/Kg/min (p=0.003). Compliance with the intervention was similar in G1 and G2 (77.5±11% x 82±10%; p=0.654). Conclusion: Participants from both groups improved their physical fitness and showed satisfactory compliance and tolerability to the interventions. The supervised exercise was more effective in improving muscle strength and some physical fitness parameters.

Background: Arterial changes associated with children and adolescents high blood pressure (HBP) states would vary depending on the arterial type, arterial indexes considered and/or on blood pressure (BP) levels. Aims: To determine in children and adolescents: 1) if there is gradual structural-functional arterial impairment associated with gradual peripheral (brachial) systolic BP (pSBP) level or z-score increases, and 2) whether subjects with HBP levels and those with normal BP differ in the profiles of arterial changes associated with pSBP deviations. Methods: 1005 asymptomatic children and adolescents were included. Clinical, anthropometric and arterial non-invasive evaluations were performed. Heart rate, brachial BP, aortic BP and wavederived parameters (i.e. augmentation index), carotid and femoral diameters, blood velocities and elastic modulus, carotid intima-media thickness and aortic pulse wave velocity, were obtained. Two groups were assembled: Reference (without cardiovascular risk factors (CVRFs); n=379) and HBP (n=175). Additionally, subjects were ascribed to groups according to their pSBP z-scores (z-score ≤ 0, 0< z-score < 1 or z-score ≥ 1). Age and sex-related mean and standard deviation equations were obtained for each variable (Reference group). Using those equations, data (entire population) were converted into z-scores. Groups were compared (absolute and z-scored variables) before and after adjusting for cofactors (ANOVA/ANCOVA). Linear regression analyses were done considering: pSBP and z-pSBP (independent) and absolute levels and z-scores for hemodynamic and arterial indexes (dependent variables). Differences in hemodynamic and arterial levels and z-scores variations (dependent) associated with variations in pSBP and z-pSBP (independent variable) were assessed. The slopes of the models for Reference and HBP groups were compared. Conclusion: HBP states associate hemodynamic and arterial changes not explained by exposure to other CVRFs, anthropometric or demographic factors. The higher the pSBP deviations from ageand sex-expected mean value in the Reference group, the higher the hemodynamic and arterial indexes deviation. The pSBP-related variations in hemodynamic and arterial indexes would not differ depending on whether HBP states are present or not.