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.

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.

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.

Carotid wall viscosity increase is related to intima-media thickening in hypertensive patients.

Increases in arterial wall viscosity and intima-media thickness (IMT) were found in hypertensive patients. Because smooth muscle cells are responsible for the viscous behavior of the arterial wall and they are involved in the process of thickening of the intima-media complex, this study evaluates the relationship between carotid thickness and wall viscosity. The simultaneous and noninvasive assessment of the intima-media complex and arterial diameter waveform was performed using high-resolution ultrasonography. This technique was contrasted against sonomicrometry in sheep, showing that the waveforms obtained by both methods were similar. The common carotid arteries of 11 normotensive subjects (NTA) and 11 patients with mild to moderate essential hypertension (HTA) were measured noninvasively by using tonometry and an automatic densitometric analysis of B-mode images to obtain IMT and instantaneous pressure and diameter loops. A viscoelastic model was used to derive the wall viscosity index (eta) using the hysteresis loop elimination criteria. In NTA, eta was 2.73+/-1.66 (mm Hg x s/mm) and IMT was 0.58+/-0.08 (mm), whereas in HTA, eta was 5.91+/-2.34 (P<.025) and IMT was 0.70+/-0.12 (P<.025), respectively. When all data of eta versus IMT of NTA and HTA were pooled in a linear regression analysis, a correlation coefficient of r=.71 (P<.05) was obtained. Partial correlation between eta and IMT holding constant pressure was r=.59 (P<.05). In conclusion, wall viscosity increase was associated with a higher IMT even maintaining blood pressure fixed, suggesting that the intima-media thickening might be related to smooth muscle alterations manifested as an increase in viscous behavior.

Experimental acute right ventricular failure and right ventricular assist in the dog.

We describe a technique for the production of acute progressive right ventricular failure in experimental animals that mimics the hemodynamic characteristics of right ventricular failure found in some patients being weaned from extracorporeal circulation after surgical repair of left ventricular abnormalities. The technique combines three alterations of right ventricular state: excision of the tricuspid valve, ventriculotomy, and ligation of the right coronary artery. Seven control dogs died within 3 hours after this intervention. Death was due to low cardiac output as a result of low left atrial and pulmonary arterial pressures. Right atrial pressure was high. Use of a right ventricular assist device in an additional seven dogs to pump blood from the right atrium to the pulmonary artery confirmed good preservation of left ventricular function by reestablishing adequate left ventricular filling pressure. All seven dogs survived for more than 3 hours. The validity of the technique in restricting failure principally to the right ventricle was thus demonstrated.

Experimental and clinical validation of arterial diameter waveform and intimal media thickness obtained from B-mode ultrasound image processing.

A new automated computerized system (IôTEC) that assesses concomitantly the instantaneous temporal arterial diameter and intimal media thickness (IMT) obtained from B-mode ultrasound (US) images was validated by sonomicrometry in sheep, by an echo-tracking system in humans, and by a Lucite phantom in vitro. Differences between methods for diameter measurements did not vary in any systematic way, with no significant differences in the lower frequency range. Ultrasonic measurements of the true phantom gap sizes showed high correlation (r2 = 0.98,p < 0.001) with no systematic errors. Carotid and femoral arteries in humans were strongly related between IôTEC and echo-tracking device (r2 = 0.94 carotid; R2 = 0.88 femoral, p < 0.001), with a Gaussian distribution of the errors. This new method showed high intra- and interobserver repeatability of arterial diameter and IMT, allowing consistent characterization of arterial dynamics in humans.

Mechanical vs intrinsic components in the improvement of brachial arterial compliance. Comparison of the effects of atenolol versus ramipril in hypertensive patients.

The aim of this study was to compare the mechanical and intrinsic effects of an angiotensin converting enzyme inhibitor, vs a beta-blocker, on brachial arterial compliance. In a double blind study, 34 essential hypertensive patients were treated for 3 months with either ramipril 2.5-5.0 mg daily (n = 17, age 57 +/- 7 y, 11 males) or atenolol 50-100 mg daily (n = 17, age 53 +/- 8 y, 11 males). Blood pressure (BP), brachial artery diameter (D), brachial-radial pulse wave velocity (PWV) and effective compliance (Ceff), were measured before and at the end of the study. Isobaric evaluation (Ciso) was performed in the entire population studied at an average mean BP of 110 mmHg. Ramipril significantly reduced BP from 155 +/- 16/94 +/- 6 mmHg to 140 +/- 15/85 +/- 7 mmHg (p < 0.001) without affecting heart rate (HR; 74 +/- 10 vs. 75 +/- 12 bpm). In addition, it significantly improved both PWV (18%; p < 0.001) and arterial compliance (45%; p < 0.001), from which 35% was related to a pressure independent effect (p < 0.01). Atenolol also induced a reduction in both BP (159 +/- 17/96 +/- 10 to 133 +/- 13/81 +/- 8 mmHg; p < 0.001) and HR (76 +/- 10 to 57 +/- 7 bpm; p < 0.001). In a similar way, PWV (11%; p < 0.05) and Ceff (30%; p < 0.05) were significantly improved without significant change in Ciso. This suggests that blood pressure reduction was responsible for compliance improvement. In conclusion, it is suggested that atenolol induces only hemodynamic changes, mediated mainly by BP reduction. In contrast, the improved brachial buffering function observed after ramipril involves not only hemodynamic changes, but also changes mediated by other mechanisms, such as modification of wall structures.

Elasticity assessment of electrospun nanofibrous vascular grafts: a comparison with femoral ovine arteries.

Development of successful small-diameter vascular grafts constitutes a real challenge to biomaterial engineering. In most cases these grafts fail in-vivo due to the presence of a mechanical mismatch between the native vessel and the vascular graft. Biomechanical characterization of real native vessels provides significant information for synthetic graft development. Electrospun nanofibrous vascular grafts emerge as a potential tailor made solution to this problem. PLLA-electrospun nanofibrous tubular structures were prepared and selected as model bioresorbable grafts. An experimental setup, using gold standard and high resolution ultrasound techniques, was adapted to characterize in vitro the poly(L-lactic acid) (PLLA) electrospun structures. The grafts were subjected to near physiologic pulsated pressure conditions, following the pressure-diameter loop approach and the criteria stated in the international standard for cardiovascular implants-tubular vascular prostheses. Additionally, ovine femoral arteries were subjected to a similar evaluation. Measurements of pressure and diameter variations allowed the estimation of dynamical compliance (%C, 10(-2) mmHg) and the pressure-strain elastic modulus (E(Pε), 10(6) dyn cm(-2)) of the abovementioned vessels (grafts and arteries). Nanofibrous PLLA showed a decrease in %C (1.38±0.21, 0.93±0.13 and 0.76±0.15) concomitant to an increase in EPε (10.57±0.97, 14.31±1.47 and 17.63±2.61) corresponding to pressure ranges of 50 to 90 mmHg, 80 to 120 mmHg and 100 to 150 mmHg, respectively. Furthermore, femoral arteries exhibited a decrease in %C (8.52±1.15 and 0.79±0.20) and an increase in E(Pε) (1.66±0.30 and 15.76±4.78) corresponding to pressure ranges of 50-90 mmHg (elastin zone) and 100-130 mmHg (collagen zone). Arterial mechanics framework, extensively applied in our previous works, was successfully used to characterize PLLA vascular grafts in vitro, although its application can be directly extended to in vivo experiences, in conscious and chronically instrumented animals. The specific design and construction of the electrospun nanofibrous PLLA vascular grafts assessed in this work, showed similar mechanical properties as the ones observed in femoral arteries, at the collagen pressure range.

An hemodynamic work bench for in-vitro measurements in arterial bifurcations: experimental results and comparison with the output of a simplified CFD model.

To quantify fluid-structure interactions in arterial walls, from a biomechanical standpoint, a complete characterization of blood flow, shear stress in the interface between blood and endothelium, wall elasticity and wall stresses distribution are needed.

Fractal dimension as an index of left ventricular ischaemia: a pilot study.

Myocardial perfusion is performed by the left and the right coronary arteries, which deliver blood to the left and right ventricles, respectively. The impairment of arterial flow supply to the cardiac muscle by disease denotes a phenomenon known as ischaemia. Previous studies have demonstrated the ability of fractal dimension (FD) value of a physiological parameter in differentiating healthy/pathological behaviours. The aim of this study consisted in quantifying the loss of ventricular thickness fractal complexity in order to determine if FD is an intrinsic marker of acute coronary ischaemia. Five mongrel dogs weighing 18.8-26.5 kg (24.4 ± 3.3, mean ± SD) were submitted to this studio. A left ventricular pressure transducer and a fluid-filled catheter for later calibration of the pressure transducer were introduced through a stab wound near the apex. Two pairs of ultrasonic microcrystals (5 MHz) for continuous wall thickness measurements were implanted at the anterior and posterior walls of the left ventricle following a previously described technique. During coronary occlusion, the ischemic wall started to thin at the very onset of relaxation (showing abnormal motility), while the normoperfused wall displayed postejective thickening. Concomitantly, posterior ventricular wall thickness and anterior wall ventricular thickness showed a significant decrease in its FD value (P <0.05). In conclusion, loss of time series fractal complexity (waveform fine structure diminution or 'unwrinkling') constitutes a marker of the presence of an ischemic process. As a result, a single scalar value is sufficient to characterize the entire behaviour of the time series. This value manifested a similar trend compared to the most well-known clinical indices of myocardial ischaemia.