Detection of cardiac arrhythmia patterns in ECG through H × C plane.

The aim of this study is to formulate a new methodology based upon informational tools to detect patients with cardiac arrhythmias. As it is known, sudden death is the consequence of a final arrhythmia, and here lies the relevance of the efforts aimed at the early detection of arrhythmias. The information content in the time series from an electrocardiogram (ECG) signal is conveyed in the form of a probability distribution function, to compute the permutation entropy proposed by Bandt and Pompe. This selection was made seeking its remarkable conceptual simplicity, computational speed, and robustness to noise. In this work, two well-known databases were used, one containing normal sinus rhythms and another one containing arrhythmias, both from the MIT medical databank. For different values of embedding time delay τ, normalized permutation entropy and statistical complexity measure are computed to finally represent them on the horizontal and vertical axes, respectively, which define the causal plane H×C. To improve the results obtained in previous works, a feature set composed by these two magnitudes is built to train the following supervised machine learning algorithms: random forest (RF), support vector machine (SVM), and k nearest neighbors (kNN). To evaluate the performance of each classification technique, a 10-fold cross-validation scheme repeated 10 times was implemented. Finally, to select the best model, three quality parameters were computed, namely, accuracy, the area under the receiver operative characteristic (ROC) curve (AUC), and the F1-score. The results obtained show that the best classification model to detect the ECG coming from arrhythmic patients is RF. The values of the quality parameters were at the same levels reported in the available literature using a larger data set, thus supporting this proposal that uses a very small-sized feature space to train the model later used to classify. Summarizing, the attained results show the possibility to discriminate both groups of patients, with normal sinus rhythm or arrhythmic ECG, showing a promising efficiency in the definition of new markers for the detection of cardiovascular pathologies.

Are biopsy specimens predictive of HER2 status in gastric cancer patients?

BACKGROUND: Trastuzumab has been recently proposed as a treatment for patients with HER2-positive advanced/metastatic gastric cancer (GC). Since most patients have inoperable disease at diagnosis, accurate assessment of HER2 status on biopsy specimens is essential to select the patients who may benefit from therapy. AIM: The aim of this study is to establish whether HER2 status assessed on biopsy material could be reliable for treatment decisions using anti-HER2 agents. METHODS: The HER2 status was evaluated in 61 consecutive pairs of biopsy and surgical GCs samples by immunohistochemistry and chromogenic in situ hybridization. RESULTS: The overall concordance of HER2 status between biopsy and surgical specimens was 91.8 % with a predictive positive value of 71.4 % and a negative predictive value of 94.4 %. Of five discordant cases, there were three negative and two positive false biopsy results. All the false negative cases showed heterogeneous expression of HER2 protein in surgical samples. Two cases displayed overexpression of the receptors without corresponding gene amplification. CONCLUSIONS: HER2 status as evaluated on biopsy samples is a fairly good predictor of HER2 status of surgically-excised GCs. The most important influence for discordant results is tumor heterogeneity. However, HER2 overexpression, especially without coexisting gene amplification, may only be a temporary change in a tumor population. This may explain those cases with positive HER2 evaluation on biopsy material and a negative result on corresponding surgical specimen.

Stroke Work Damping Ratio is Increased in Trained Athletes.

INTRODUCTION: Athletes training is often associated with morphological changes in the heart. In this sense, the ventricular pressure-volume (PV) relation provides a complete characterization of cardiac pump performance. Regarding the arterial system (AS), arterial wall viscosity is a source of energy dissipation, that takes place during mechanical transduction. Left ventricular stroke work (SW) constitutes the useful fraction of ventricular energy that is delivered to the AS. OBJECTIVE: Left ventricular PV-loops were evaluated in terms of AS viscous property, by means of the interaction of two SW components (Stroke Work Damping Ratio, SWDR), both in untrained and trained subjects. MATERIAL AND METHODS: Fourteen healthy individuals (seven trained) were noninvasively evaluated in terms of echocardiographic and aortic pressure measurements. RESULTS: SWDR was observed to be increased in trained subjects. CONCLUSION: SWDR was evaluated in trained individuals, being increased in comparison with the non-trained group. This effect is a consequence of a significant increase of SWD, which could be related with the viscous mechanical property of AS.

Arterial-Ventricular Coupling Impairment is Evidenced in Both Normal and Ischemic Subjects by Applying Cluster Analysis.

INTRODUCTION: Left ventricular (LV) interaction with the arterial system (arterial-ventricular coupling, AVC) is a central determinant of cardiovascular performance and cardiac energetics. Stress Echocardiography (SE) constitutes a valuable clinical tool in both diagnosis and risk stratification of patients with suspected and established coronary artery disease. Cluster Analysis (CA), an unsupervised Machine Learning technique, defines an exploratory statistical method which can be used to uncover natural groups within data. OBJECTIVE: To evaluate the capacity of CA to identify uncoupled groups with ischemic condition based on SE baseline information. MATERIAL AND METHODS: CA was applied to SE data acquired at baseline and peak exercise (PE) conditions. Obtained clusters were evaluated in terms of coupling conditions and LV wall motility alterations. RESULTS: Inter cluster significant AVC differences were obtained in terms of baseline data and changes in wall motility, confirmed by CA applied to PE data. CONCLUSION: AVC impairment was evidenced in both normal and ischemic subjects by applying CA.

Arterial-Ventricular Coupling Evaluation in Individuals with Stress-Evidenced Diastolic Dysfunction: A Pilot Study.

INTRODUCTION: Arterial-ventricular coupling (AVC) has been recognized as a key determinant of global cardiovascular performance. Diastolic dysfunction (DD) occurs when inadequate filling of the ventricles is related to an abnormal elevation of intracardiac filling pressures. In some cases, DD is evidenced during cardiac stress, provoked by exercise. OBJECTIVE: To evaluate AVC in individuals with stress evidenced DD, in relation to controls. MATERIALS AND METHODS: Stress echocardiography was applied to assess cardiac function during exercise. Arterial-ventricular coupling was evaluated, based on the assessment of left ventricular and arterial elastances. RESULTS: AVC showed a significant difference at peak exercise compared to controls, basically due to a loss of cardiac contractility. CONCLUSION: The manifestation of AVC coupling imbalance could act as a complementary parameter to support the diagnosis of DD.

Beat to Beat Modulation of Arterial Pulse Wave Velocity Induced by Vascular Smooth Muscle Tone.

INTRODUCTION: The level of smooth muscle activation or `tone' (VSMT) can be defined as an intrinsic spontaneous level of vasoconstriction that may change in response to biomechanical stimuli such as flow, pressure, hormonal stimuli, neural stimuli, and drugs. Arteries can actively modify arterial pressure pulse wave velocity (PWV) by changing smooth muscle tone and diameter with little change in the mean arterial blood pressure. OBJECTIVE: To evaluate the influence of aortic VSMT in terms of beat to beat PWV variations. METHODS: Aortic pressure-diameter (P-D) relationships were invasively evaluated in five conscious animals. An `incremental' PWV was directly derived from the P-D loops, both in purely elastic conditions as well as in the presence of VSMT. RESULTS: Beat to beat PWV waveform variations showed different behavior, where mean PWV values were higher when VSMT was included in the P-D evaluation. CONCLUSION: Changes in incremental beat to beat PWV could be attributed to the influence of VSMT.

A Soliton-Based Model Mimics the Arterial Pulse Propagation as Much as a Widely Used 1D Model.

INTRODUCTION: A comparison among two blood pressure pulse propagation models has made in this work. One of them is a traditional model based upon the Navier Stockes equations in one spatial dimension, the one along the direction of the arteries (from here NS1D), the other is based the concept of soliton propagation using the Korteweg De Vries equation (named KdV). METHODS: The arterial three is assumed a long successive connection of serial segments of arteries, at the inlet of the network (close up to the aorta), an acquired pulse, in vivo, wave is imposed. The computed of the peripheral blood pressure at the outlet of the final segment constitutes the output of the model (near the radial artery). RESULTS: Both models reproduced main characteristics of the measured radial wave pressure for the same input. CONCLUSION: The results show that the model KdV have many conceptual and computer benefits than the usual model NS1D that constitutes an interesting pathway for the scientific research.

Characterization of Microvascular Post Occlusive Hyperemia Using Laser Doppler Flowmetry Technique in Subjects With Cardiometabolic Disorders.

INTRODUCTION: Laser Doppler flowmetry (LDF) provides a noninvasive real-time quantification of relative changes in cutaneous perfusion. Assessment of the microvascular function can provide information on the development of various cardiometabolic disorders. In recent years, non-invasive measurements have gain attention, due to the potential complications associated to invasive procedures. OBJECTIVE: To differentiate the microvascular function between subjects with cardiometabolic disorders and healthy controls. METHODS: Evaluation through LDF during post-occlusive reactive hyperemia (PORH) in patients with or without history of cardiometabolic disorders. RESULTS: Peak values of microvascular flow during post-occlusive reactive hyperemia and both upload and recovery slopes were lesser in the pathological group. CONCLUSION: A novel approach to characterize LDF during PORH was useful to differentiate patients with cardiometabolic disorders from healthy subjects.

Cryografts implantation in human circulation would ensure a physiological transition in the arterial wall energetics, damping and wave reflection.

Each artery conduces blood (conduit function, CF) and smoothes out the pulsatility (buffering function, BF), while keeping its wall protected against the high oscillations of the pulse waves (damping function, xi). These functions depend on each segment viscoelasticity and capability to store and dissipate energy. When a graft/prosthesis is implanted, the physiological gradual transition in the viscoelasticity and functionality of adjacent arterial segments is disrupted. It remains to be elucidated if the cryografts would allow keeping the physiological biomechanical transition. The aim of this study was to evaluate the cryografts capability to reproduce the functional, energetic and reflection properties of patients' arteries and fresh homografts. Common carotid's pressure, diameter and wall-thickness were recorded in vivo (15 patients) and in vitro (15 cryografts and 15 fresh homografts from donors). Calculus: elastic (Epd) and viscous (Vpd) indexes, CF, BF, dissipated (WD) and stored (WPS) energy and xi. The graft-patient's artery matching was evaluated using the reflection coefficient (Gamma) and reflected power (WGamma). Cryografts did not show differences in Epd, Vpd, BF, CF, WD, WPS, and xi, in respect to fresh homografts and patients' arteries, ensuring a reduced Gamma and WGamma. Cryografts could be considered as alternatives in arterial reconstructions since they ensure the gradual transition of patients' arteries biomechanical and functional behavior.

Modeling Cardiac Hemodynamic Response During Exercise in Health and Hypertrophic Cardiomyopathy.

INTRODUCTION: Hypertrophic cardiomyopathy (HCM) is associated with altered hemodynamics in the left ventricular outflow tract and tissue abnormalities. Exercise testing has become an integral and powerful tool for the noninvasive evaluation of HCM and, in some patients, it could define a treatment strategy. Obiective: To model the hemodynamic alterations during exercise in healthy and HCM patients, obtained by noninvasive methods. METHODS: Cardiac output (CO), heart rate (HR), arterial blood pressure (ABP) and Total Peripheral Resistance (TPR) were assessed during exercise. The evaluation included a curve-fitting approach (sigmoidal model) that allowed a quantitative comparison of CO profiles. RESULTS: When compared to controls, patients with HCM showed reduced peak exercise cardiac output and demonstrated high peripheral resistance during exercise. Analysis of modeled it CO curves revealed a higher maximum rate of recovery in healthy individuals than in HCM patients. CONCLUSION: The application of the sigmoidal model showed to be efficient in the characterization of CO dynamics for the different studied groups.

Flow Mediated Dilation in Cirrhosis: A Pilot Study in Different Stages of the Disease.

INTRODUCTION: Cirrhosis is associated with changes in the cardiovascular system, where the circulatory dysfunction is compensated by the development of a hyperdynamic circulation. Endothelial function can be understood as the endothelium capability to release Nitric Oxide (NO) where an impairment in the normal development of this process constitutes a main step in the genesis and progression of atherosclerosis, a major cause of cardiovascular events. In recent years, non-invasive measurements have gained attention, due to the potential complications associated to invasive procedures. OBJECTIVE: To evaluate endothelial function (EF) in patients with cirrhosis, in different stages of the disease, complemented with hemodynamic measurements. METHODS: Individuals were divided in three age groups, according to the severity of their disease. EF was assessed by using the flow mediated dilation technique (FMD), jointly with noninvasive determination of cardiac output (CO), total peripheral resistance (TPR) and arterial compliance (AC). RESULTS: TPR showed a decrease in advanced severity while AC had an increase. Particularly, EF was found to be higher in CHC group, decreasing in CHB and more pronounceably in CHA. Concomitantly, an inverse behavior was observed regarding CO evolution. CONCLUSION: EF was noninvasively evaluated in cirrhosis, in terms of the progression of the disease. Hyperdynamic states in the more advanced condition were accompanied by a higher vascular reactivity, probably associated with higher peripheral NO release and increased AC.

Modeling young and adult patients with cirrhosis through a three element windkessel (WK3e).

INTRODUCTION: Measurement of hemodynamic parameters constitutes an important tool in the management of patients with cirrhosis. In recent years, non-invasive measurements have gain attention, due to the potential complications associated to invasive procedures. OBJECTIVE: To characterize the hemodynamic alterations of cirrhosis in young and adult subjects, through a three element windkessel (WK3e). METHODS: Individuals were divided in three age groups: Young Healthy group (control, CG), Young Cirrhotic Group (YCG) and Adult Cirrhotic Group (ACG). A Finapres® Nova device was used to obtain cardiac output (CO), heart rate and arterial blood pressure. Systemic arterial compliance (C), peripheral resistance (R) and characteristic impedance (Zc) were also provided. Effective arterial elastance (Ea), left ventricular work (LVW), input impedance, efficiency and model cutoff frequency (WKCF) were assessed based on the provided data. RESULTS: CO resulted to be higher in ACG than in CG and YGC. LVW, C and WKcf showed an increase, while R and Ea showed a decrease. However, this behavior was not observed in YCG. CONCLUSION: Cirrhosis was properly modeled in young and adult subjects in terms of non-invasive measurements and a WK3e.

[Vascular access for haemodyalisis. Comparative analysis of the mechanical behaviour of native vessels and prosthesis]. / Accesos vasculares para hemodialisis: analisis comparativo del comportamiento mecanico de vasos nati.

INTRODUCTION: The prosthesis nowadays used in the vascular access for haemodialysis have low patency rates, mainly due to the luminal obstruction, determined by the intimal hyperplasia. Several factors have been related to de development of intimal hyperplasia and graft failure. Among them are the differences in the biomechanical properties between the prosthesis and the native vessels. In the searching for vascular prosthesis that overcomes the limitations of the currently used, the cryopreserved vessels (cryografts) appear as an alternative of growing interest. However, it is unknown if the mechanical differences or mismatch between prosthesis and native vessels are lesser when using cryografts. OBJECTIVE: To characterize and compare the biomechanical behaviour of native vessels used in vascular access and cryografts. Additionally, segments of expanded polytetrafluoroethylene (ePTFE) were also evaluated, so as to evaluate the potential biomechanical advantages of the cryografts respect to synthetic prosthesis used in vascular access. METHODS: Segments from human humeral (n = 12), carotid (n = 12) and femoral (n = 12) arteries, and saphenous vein (n = 12), were obtained from 6 multiorgan donors. The humeral arteries were studied in fresh state. The other segments were divided into two groups, and 6 segments from each vessel were studied in fresh state, while the remaining 6 segments were evaluated after 30 days of criopreservation. For the mechanical evaluation the vascular segments and 6 segments of ePTFE were mounted in a circulation mock and submitted to haemodynamic conditions similar to those of the in vivo. Instantaneous pressure (Konigsberg) and diameter (Sonomicrometry) were measured and used to calculate the viscous and elastic indexes, the compliance, distensibility and characteristic impedance. For each mechanical parameter studied, the mismatch between the prosthesis and the native vessel was evaluated. RESULTS: The ePTFE was the prosthesis with the higher mechanical mismatch (p < 0.05). The venous and arterial cryografts showed the least mismatch with native veins and arteries, respectively. The prosthesis with the least mechanical mismatch was different, depending on the native vessel evaluated, and for a native vessel, on the parameter considered. CONCLUSION: The mechanical mismatch between the native vessel and the vascular prosthesis used in a vascular access could be reduced using cryografts.

Arterial pressure beat to beat characterization during post-occlusive reactive hyperemia.

INTRODUCTION: In recent years, peripheral arterial tonometry (PAT, a non-invasive and reproducible technique) has gained considerable interest. In this sense, arterial capacity to react to vasoactive stimulus (induced by reactive hyperemia) is known as vascular reactivity (VR). OBJECTIVE: Post ischemic beat to beat VR characterization was performed based on PAT measurements. METHODS: Systolic Blood Pressure (SBP) and Augmentation index (AIx) variations were modeled, as a response to flow stimulus. RESULTS: Obtained R2 values were around 70% for VR while, to a lesser degree, AIx fit was about 50% Conclusion: Beat to Beat VR was described in terms of SBP and AIx behavior. Further studies are needed to determine the clinical usefulness of the proposed indicators.

Evaluation of the impact of arterial wall viscosity in pressure morphology by means of a simplified 1D model.

INTRODUCTION: The interest on computational simulations of biomedical models has increased in the last years. Nevertheless, the viscous properties of vessel all are usually neglected. MATERIALS AND METHODS: A 1D model of blood flow and its interaction with the arterial wall was implemented. Non-viscous modeling and the addition of a wall-viscosity term were considered. The goodness of fit in each case was evaluated. RESULTS: Simulated radial blood pressure was generated using central blood pressure as the input of the proposed 1D tapered model. Results obtained showed an improvement as a consequence of introducing wall viscosity into the model calculations. DISCUSSION: The effect of viscoelasticity has a great significance in the implementation of computational models, since a better fit between simulated and experimental data is achieved.

Gender differences in wall shear-mediated brachial artery vasoconstriction and vasodilation.

OBJECTIVES: We sought to investigate wall shear rate (WSR) and brachial artery diameter (BAD) changes simultaneously and to determine whether any gender differences exist in arterial reactivity. BACKGROUND: Wall shear rate/stress and arterial reactivity are rarely assessed at the same time. Furthermore, flow-mediated vasoconstriction has received less attention than flow-mediated vasodilation in humans. METHODS: A new noninvasive evaluation of WSR in the brachial artery, using multigated, pulsed Doppler velocimeter and a double-transducer probe moved and fixed by a robotic system, was developed. RESULTS: The validity of the system was tested in vitro with calibrated tubes and showed a high correlation (r = 0.98, p < 0.001). In 10 men and 10 women of similar age, induction of low and high shear rates by forearm occlusion produced significant vasoconstriction and vasodilation, respectively. The time lag for maximal BAD changes was 3 min for vasoconstriction and 1 min for vasodilation. A greater half-time for vasodilation (96 +/- 6 for men and 86 +/- 12 s for women) than for shear rate (31 +/- 5 s for men and 34 +/- 4 s for women) was observed after discontinuation of occlusion. Relative BAD was correlated with WSR changes, showing a significantly higher slope in women than in men (p < 0.01). Moreover, a larger normalized arterial diameter per shear rate was observed for vasoconstriction (p < 0.01) and vasodilation (p < 0.01) in women than in men. CONCLUSIONS: Shear-mediated arterial vasodilation and vasoconstriction were more pronounced in women than in men, suggesting different gender-related sensitivity in the regulation of large-artery vascular tone.

Immunohistochemical and serological 90K/Mac-2BP detection in hepatocellular carcinoma patients: different behaviour of two monoclonal antibodies.

To clarify the biological role of the 90K/Mac-2BP glycoprotein, we evaluated the ability of two MAbs SP-2 and 1A4.22, to reveal this glycoprotein in both serum and tissue from hepatocellular carcinoma (HCC) patients. Tissue expression of 90K was detected by the immunohistochemical method in 20 HCC patients, while the 90K serum level was assessed by the ELISA assay in 13 HCC patients. MAb SP-2 was reactive only in serum, with a mean value of 12.8+/- 6.7 microg/ml . On the contrary, MAb 1A4.22 revealed immunoreactivity both in 92% of sera and in 60% of neoplastic samples. Positive staining was seen only in the epithelial cells and was cytoplasmic and granular in all instances. The mean 90K serum level assayed with MAb 1A4.22 was 29.4 +/- 13.7 microg/ml. Patients with a 90K serum level 30 microg/ml. Moreover, a possible poor prognostic role was observed for negative 90K in tissue. Our results suggest that only MAb 1A4.22 could demonstrate 90K glycoprotein expression in paraffin-embedded tissue and that this MAb could have a diagnostic and prognostic role in both sera and tissues from HCC patients.

Preventive effect of chronic converting enzyme inhibition on aortic stiffening induced by renovascular hypertension in conscious dogs.

OBJECTIVE: The aim was to assess the influence of the renin-angiotensin system on the geometrical and elastic properties of the aorta in conscious dogs, using a model of renovascular hypertension, and to examine the effects of inhibition of the system by the angiotensin converting enzyme inhibitor spirapril. METHODS: The aortic elastic behaviour in response to renovascular hypertension was studied in 15 conscious dogs instrumented with a pressure microtransducer and a pair of ultrasonic diameter dimension gauges in the upper descending thoracic aorta. Renovascular hypertension was induced by surgical occlusion of one renal artery and stenosis of the other. One day after renal surgery, dogs were randomly assigned to two groups receiving for two months either the new angiotensin converting enzyme inhibitor spirapril (n = 8) or a placebo capsule (n = 7). The two groups of dogs were compared to a control group of normotensive dogs (n = 7). After two months of treatment the elastic properties of the aorta were studied by computation of the beat to beat pressure-diameter hysteresis loops obtained during transient increase of pressure induced by bolus doses of angiotensin. The aortic pressure-diameter (P-D) relationship, obtained over a wide range, was fitted by an exponential fit (P = alpha.e beta D), where beta is the stiffness index. A decomposition of the P-D curve according to a biphasic model of the parallel arrangement of elastin and collagen enabled two pressure-diameter elastic moduli to be obtained, one representing the resistance to stretch at low pressure levels (elastic fibres and smooth muscle), and the other representing the resistance to stretch at the highest pressures (collagen fibres). RESULTS: The pressure-diameter curve of the placebo group was shifted to the left compared to the curves of the control and spirapril groups, showing that renovascular hypertension was associated with isobaric reduction of aortic diameter. The stiffness index beta was higher (p < 0.05) in the placebo group [0.605(SD 0.304) mm-1] than in either the control group [0.362(0.126) mm-1] or the spirapril group [0.348(0.083) mm-1], suggesting that renovascular hypertension was associated with aortic stiffening. The biphasic analysis showed that the collagen pressure-diameter elastic modulus was unaffected by spirapril, whereas the elastin pressure-diameter elastic modulus was significantly reduced by converting enzyme inhibitor with respect to the placebo (p < 0.05). CONCLUSIONS: Chronic converting enzyme inhibition by spirapril prevents the isobaric aortic diameter reduction induced by renovascular hypertension in conscious dogs and decreases aortic stiffness, in particular by changing the elastic behaviour of the elastin fibres rather than of the collagen fibres.

Constricting and stiffening action of atropine on aortic response to angiotensin in dogs.

The elasticity of the thoracic aorta was studied in nine dogs instrumented with a pressure microtransducer and two ultrasonic crystals diametrically fixed in the adventitia. Systolic and diastolic changes in pressure and diameter were used to calculate Peterson and incremental elastic moduli. Acute hypertension was induced by infusions of angiotensin performed 1) during the control period, 2) after propranolol (1.5 mg/kg), 3) after atropine (0.2 mg/kg), and 4) after propranolol plus atropine. Absolute and percent variations of mean diameter were correlated to pressure in the control period and after autonomic blockade (p less than 0.01). The slopes of these correlations were not different between propranolol and control groups, but were lower with atropine (p less than 0.01) and with atropine plus propranolol (p less than 0.001) than in the control period. Correlations were also found between Peterson and incremental elastic moduli and mean pressure in the control period and after blockade (p less than 0.001). No differences of slopes existed between propranolol and control groups, but the slope of the correlation relative to the incremental elastic modulus was higher with atropine than in the control period (p less than 0.05), and the slopes of the correlations relative to the Peterson and the incremental elastic moduli were respectively higher with atropine plus propranolol than in the control period (p less than 0.05, p less than 0.05). Thus, atropine decreased the distention and increased the stiffness of the aorta in response to acute angiotensin-mediated hypertension.

Mechanical pressure versus intrinsic effects of hypertension on large arteries in humans.

Brachial artery diameter and compliance were measured in 23 normotensive control subjects and 49 hypertensive patients. The results were compared in isobaric conditions by a modeling analysis extrapolating from the measured data a short segment of the pressure-diameter and pressure-compliance curves in the artery. A logarithmic diameter-pressure function was used as well as measurements of brachial artery blood pressure and lumen diameter (by pulsed Doppler), and of brachial-to-radial pulse wave velocity (by mechanography). The measured values of diameter and compliance in the hypertensive patients were 109% and 63%, respectively, of the control group values. By extrapolating the data via the model at the same pressure level in all subjects (the average level of mean blood pressure of the two groups), the isobaric values of diameter and compliance in the hypertensive patients were 107% and 81%, respectively, of the control group values. Overall, measured isobaric diameters and measured compliance correlated with systolic, diastolic, and mean blood pressure values (p less than 0.001), whereas isobaric compliance correlated only with systolic (p less than 0.05) and pulse (p less than 0.01) pressure values. Thus, the increased diameter and reduced compliance of the brachial artery observed in hypertensive humans cannot be attributed solely to the stretching effect of elevated blood pressure, but also to intrinsic alteration of the arterial walls. These could represent either adaptative structural or functional changes secondary to the chronic increase in arterial pressure, or primary abnormalities of the vessel wall.