Nikolaos Stergiopoulos

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In this paper, we present a method for estimating local pulse wave velocity (PWV) solely from ultrasound measurements: the area-flow (QA) method. With the QA method, PWV is estimated as the ratio between change in flow and change in cross-sectional area (PWV = dQ/dA) during the reflection-free period of the cardiac cycle. In four anaesthetized dogs and 21 human subjects (age 23-74) we measured the carotid flow and cross-sectional area non-invasively by ultrasound. As a reference method we used the Bramwell-

Background Transcatheter aortic valve implantation (TAVI) abruptly relieves aortic stenosis. The consequences for the peripheral vascular network, organ perfusion and postoperative organ dysfunction remain unclear. This study assessed hemodynamic and microcirculatory changes after TAVI, and their association with postoperative organ dysfunction. Methods This prospective, single‐center physiological study included 20 patients with severe aortic stenosis undergoing transfemoral TAVI at Geneva University Hospi

We developed a mathematical model describing the interaction between the heart and the arterial system. The model was constructed and tested on basis of invasive hemodynamic data in six sheep. Data from a first group of three animals (49 cardiac cycles) were used to assess a template time-varying elastance curve for the left ventricle, while the baseline steady-state data of a second group of three animals were used to assess reference cardiac and arterial parameters in sheep. The model is fully characteriz

Spontaneous low frequency diameter oscillations have been observed in vivo in some muscular arteries. The aim of this paper is to propose a possible mechanism for their appearance. A lumped parameter mathematical model for the mechanical response of an artery perfused with constant flow is proposed, which takes into account the active behavior of the vascular smooth muscle. The system of governing equations is reduced into two nonlinear autonomous differential equations for the arterial circumferential stre

Most previous studies of arterial wall elasticity and rheology have assumed that the properties of the wall are uniform across the thickness of the media and, therefore, that the relationship between stress and strain may be described by a constitutive equation based on a single strain energy function. The few studies where this assumption has been questioned, focussed on differences between the adventitia and the media rather than on differences within the media itself. Here, we report in vitro elasticity

In earlier studies we found that the three-element windkessel, although an almost perfect load for isolated heart studies, does not lead to accurate estimates of total arterial compliance. To overcome this problem, we introduce an inertial term in parallel with the characteristic impedance. In seven dogs we found that ascending aortic pressure could be predicted better from aortic flow by using the four-element windkessel than by using the three-element windkessel: the root-mean-square errors and the Akaike

We propose a new method to derive aortic pressure from peripheral pressure and velocity by using a time domain approach. Peripheral pressure is separated into its forward and backward components, and these components are then shifted with a delay time, which is the ratio of wave speed and distance, and added again to reconstruct aortic pressure. We tested the method on a distributed model of the human systemic arterial tree. From carotid and brachial artery pressure and velocity, aortic systolic and diastol

The product of resistance, R, and compliance, C (RC time), of the entire pulmonary circulation is constant. It is unknown if this constancy holds for individual lungs. We determined R and C in individual lungs in chronic thromboembolic pulmonary hypertensi ...

Left ventricular end-systolic elastance (Ees) is a major determinant of cardiac systolic function and ventricular-arterial interaction. Previous methods for the Ees estimation require the use of the echocardiographic ejection fraction (EF). However, given ...

Determination of left ventricular (LV) end-systolic elastance (E- es ) is of utmost importance for assessing the cardiac systolic function and hemodynamical state in humans. Yet, the clinical use of E- es is not established due to the invasive nature and h ...

Introduction: Glaucoma, the leading cause of irreversible blindness globally, affects more than 70 million people across the world. When initial treatments prove ineffective, especially for cases with high intraocular pressure (IOP), the preferred approach ...

Recent data support the idea that the effects of RAS are not restricted to the cardiovascular and renal systems. Importantly, RAS modulates free radical production and the cellular synthesis of several molecules such as cytokines, chemokines and transcription factors. These functions reflect directly the RAS ability to modulate the cell growth, senescence and migration. Activation of the classic RAS, ACE/Ang II/AT(1)R, has been strictly related to down regulation of pro-survival genes (Nampt and Sirt3), inc

During fetal circulatory compromise, velocity pulsations in the precordial veins increase and are commonly transmitted through the ductus venosus into the umbilical vein, indicating a serious prognosis. The nature of the pulsations and their transmission into the periphery, specifically the umbilical vein, is poorly understood. We present information on the mechanical properties of fetal veins as a basis for describing the pulse wave propagation. Five fetal sheep livers with connecting veins (gestational ag

We studied the changes in vascular smooth muscle (VSM) cell tone during the adaptation of rat common carotids to induced hypertension. Hypertension was induced in 8 week old male Wistar rats by total ligation of the aorta between the two kidneys. Mean blood pressure increased abruptly from 92 +/- 2mm Hg (mean +/- SE) to 145 +/- 4 mm Hg and remained constant thereafter. Rats were sacrificed 2, 4, 8, and 56 days after surgery and the left common carotid artery was excised for analysis. Pressure-diameter curve

The effects of flow and flow changes on arterial diameter were investigated in vitro on isolated rat femoral arteries. Segments of femoral arteries were excised, mounted on microcannulas, and perfused with Tyrode's solution (37 degrees C). Perfusion pressure was kept constant at 90 mm Hg. The mean external diameter after equilibration at a transmural pressure of 90 mm Hg was 720 +/- 50 microm (n = 12). Vessels were then constricted with norepinephrine (1 microM in the superfusion solution) to 77% +/- 13% of

Arterial vasomotion and its relation to intraluminal pressure were investigated in vitro in isolated rat arteries. Femoral arteries (mean diameter = 768.2 +/- 25 microns, n = 5) and mesenteric arteries (mean diameter = 393.4 +/- 32 microns, n = 5) were used in this study. Arterial segments were excised, mounted on microcannulas and perfused with Tyrode's solution at a constant flow (100 microliters/min). After equilibration, intraluminal pressure was stepwise changed from 0 to 120 mm Hg. The changes in the

The biomechanical adaptation of the arterial wall to hypertension has been studied extensively in recent years; however, the exact biomechanical contribution of vascular smooth muscle cells (VSMCs) during the adaptation process in conduit vessels is not known. We induced hypertension in 8 wk old Wistar rats by total ligation of the aorta between the two kidneys. Mean blood pressure increased from 92 +/- 2 (mean +/- SE) mm Hg to approximately 150 mmHg. Rats were sacrificed 2, 4, and 8 d after surgery and the

We investigated the patterns of vasomotion in various conduit arteries of the human arm. The internal diameter of the brachial, radial, ulnar, and digital artery was measured noninvasively in 17 healthy volunteers (aged 24-40 yr), using a high-precision ultrasonic echotracking device. Under resting conditions, the radial, ulnar, and digital internal diameter exhibited spontaneous oscillations (vasomotion) with a relative amplitude ranging from 1 to 5% of the mean diameter and a fundamental frequency ranging

Systems and methods for monitoring penile tumescence are provided that overcome the drawbacks of previously known systems by providing a wearable formed of a flexible and elastic tube having a plurality of sensors disposed on or embedded within it, the wea ...

In this study, an image-based morphometry toolset quantifying geometric descriptors of the left ventricle, aorta and their coupling is applied to investigate whether morphological information can differentiate between subjects affected by diastolic dysfunc ...

Nikolaos Stergiopoulos

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An ultrasound-based method for determining pulse wave velocity in superficial arteries

Hemodynamic and microcirculatory early adaptations following transcatheter aortic valve implantation ( TAVI ): A physiological pilot study

Predicting systolic and diastolic aortic blood pressure and stroke volume in the intact sheep

A theoretical investigation of low frequency diameter oscillations of muscular arteries

Assessing the homogeneity of the elastic properties and composition of the pig aortic media

Total arterial inertance as the fourth element of the windkessel model

Physical basis of pressure transfer from periphery to aorta: a model-based study

RC time constant of single lung equals that of both lungs together: a study in chronic thromboembolic pulmonary hypertension

AI-Based Estimation of End-Systolic Elastance From Arm-Pressure and Systolic Time Intervals

Estimation of Left Ventricular End-Systolic Elastance From Brachial Pressure Waveform via Deep Learning

A new self-adjustable glaucoma valve

Role of Renin-Angiotensin System in Inflammation, Immunity and Aging

Mechanical properties of the fetal ductus venosus and umbilical vein

Adaptation of conduit artery vascular smooth muscle tone to induced hypertension

Flow-driven diameter response in rat femoral arteries perfused in vitro

Intraluminal pressure modulates the magnitude and the frequency of induced vasomotion in rat arteries

Short-Term biomechanical adaptation of the rat carotid to acute hypertension: contribution of smooth muscle

Simultaneous ipsilateral and contralateral measurements of vasomotion in conduit arteries of human upper limbs

Tumescense monitoring system for diagnosing erectile dysfunction and methods of use

Cardiovascular morphometry with high-resolution 3D magnetic resonance: First application to left ventricle diastolic dysfunction