Pascal Verdonck - Academia.edu (original) (raw)

Papers by Pascal Verdonck

WIT Transactions on Biomedicine and Health, 1970

With the advent of transesophageal echocardiography, pulmonary venous flow is easily obtained in ... more With the advent of transesophageal echocardiography, pulmonary venous flow is easily obtained in all patients by pulsed-wave Doppler echocardiography. Therefore it has become a current topic of clinical investigation as a part of an assessment of left ventricular filling dynamics. In order to understand the relation between left ventricular function and Doppler indices, a lumped parameter model of the flow through the left heart is developed. The model predicts the time course of pressure and flow in the pulmonary veins and the left heart chambers given pulmonary venous compliance, inertance and resistance, left atrial and ventricular stiffness and mitral valve impedance. A case study is presented.

Abaqus Benelux Users’ Meeting 2009 Realistic virtual radial strength testing of stents M. De Beul... more Abaqus Benelux Users’ Meeting 2009 Realistic virtual radial strength testing of stents M. De Beule, P. Mortier, P. Verdonck, P. Segers, B. Verhegghe, F. Bakczewitz and N. Gotzen Biofluid, Tissue and Solid Mechanics for Medical Applications (bioMMeda) Institute Biomedical Technology (IBiTech), Ghent University, Belgium Cortronik GmbH, Rostock-Waremunde, Germany The most important task of a stent is to reopen the artery and support or scaffold the stenosed lesion in a target vessel. To that extent, the stent requires a sufficient radial strength. Experimental evidence has shown that, in addition to the material properties, this radial strength is also strongly design dependent (Rieu et al., Catheter Cardiovasc Interv, 1999). Its assessment, especially in the case of balloonexpandable stents, requires a sophisticated and accurate test set-up and dedicated experimental protocol. Complementary to such experimental methods, we developed a virtual testing procedure which allows to gain val...

American Journal of Physiology-Heart and Circulatory Physiology, 2000

We fitted a three-segment transmission line model for the radial-carotid/aorta pressure transfer ... more We fitted a three-segment transmission line model for the radial-carotid/aorta pressure transfer function (TFF) in 31 controls and 30 patients with coronary artery disease using noninvasively measured (tonometry) radial and carotid artery pressures (Pcar). Except for the distal reflection coefficient (0.85 ± 0.21 in patients vs. 0.71 ± 0.25 in controls; P < 0.05), model parameters were not different between patients or controls. Parameters were not related to blood pressure, age, or heart rate. We further assessed a point-to-point averaged TFF (TFFavg) as well as upper (TFFmax) and lower (TFFmin) enveloping TFF. Pulse pressure (PP) and augmentation index (AIx) were derived on original and reconstructed Pcar (Pcar,r). TFFavg yielded closest morphological agreement between Pcar and Pcar,r (root mean square = 4.3 ± 2.3 mmHg), and TTFavg best predicted PP (41.5 ± 11.8 vs. 41.1 ± 10.0 mmHg measured) and AIx (−0.02 ± 0.19 vs. 0.01 ± 0.19). PP and AIx, calculated from Pcar or Pcar,r, we...

European Journal of Echocardiography, 2006

vided as a surrogate marker for LV-EF. Unfortunately, there are only few data on the relation bet... more vided as a surrogate marker for LV-EF. Unfortunately, there are only few data on the relation between the WMSI and LV-EF. In addition, poor non-contrast enhanced echo windows can make the WMSI (and LV-EF) unreliable. The value of contrast imaging for WMSI assessment was not investigated before. Aim of the study: To compare segmental wall motion and WMSI interobserver agreement in patients who underwent both two-dimensional second harmonic (SH) and contrast left ventricular opacification (LVO) echocardiography. Methods: The study comprised 100 consecutive patients (mean age 57±13 years, 85% males) who underwent both SH and SonoVue LVO echocardiography for clinical evaluation of LV function. Two independent physicians assessed segmental quality and wall motion for both the SH and LVO studies according to a 17-segment model. Systolic wall motion was defined as (1) normokinesia, (2) hypokinesia (systolic inward endocardial motion <7 mm), (3) akinesia, and (4) dyskinesia. LV-EF was assessed from the LVO images according to the biplane modified Simpson's method by a third blinded physician. Results: Of the 1,700 analyzed segments, 453 (26.6%) were poorly visualized with SH imaging, and 173 (10,2%) with LVO imaging (p<0.0001). The two independent observers agreed on segmental wall motion score in 1,299 of the 1,700 segments (agreement 76%, Kappa 0.60) with SH imaging and in 1,491 of the 1,700 segments (agreement 88%, Kappa 0.78) with LVO imaging. Interobserver correlation (R 2) was 0.86 for the SH-imaged WMSI and 0.93 for the LVO-imaged WMSI. The limits of agreement for interobserver LVO-imaged WMSI (mean relative difference-1.0%±6.8%, agreement-14.6%, 12.6%) were lower than those for SH-imaged WMSI (mean relative difference-2.3%±10.1%, agreement-22.5, 17.9). The LVO-imaged WMSI correlated well with LVO-imaged LV-EF (R 2=0.71). LV-EF could be estimated according to the formula 1.01-0.32xWMSI. Conclusion: Echo contrast improves interobserver agreement for wall motion and WMSI scoring. The LVO-imaged WMSI correlates well with LVOimaged LV-EF.

Artery research, 2017

This paper aims to summarize and map contemporary views on some contentious aspects of arterial h... more This paper aims to summarize and map contemporary views on some contentious aspects of arterial hemodynamics that have remained unresolved despite years of research. These were discussed during a workshop entitled Arterial hemodynamics: past, present and future held in London on June 14 and 15, 2016. To do this we formulated a list of potential consensus statements informed by discussion at the meeting in London and quantified the degree of agreement and invited comments from the participants of the workshop. Overall the responses and comments show a high measure of quantitative agreement with the various proposed 'consensus' statements. Taken together, these statements seem a useful basis for proceeding with a more detailed and comprehensive consensus document on the current understanding and approaches to analysis of the pulse waveform. Future efforts should be directed at identifying remaining areas of dispute and future topics for research.

2002 IEEE Ultrasonics Symposium, 2002. Proceedings.

In 16 subjects (age 26-74) we recorded radio-frequency (RF) data of the Carotid artery with a Viv... more In 16 subjects (age 26-74) we recorded radio-frequency (RF) data of the Carotid artery with a Vivid7 scanner (GE Vingmed Ultrasound, Horten, Norway) and Carotid diameters with WallTrack (Pie Medical, Maastricht, The Netherlands). The RF data were stored as complex demodulated radio-frequency data (IQ data) and transferred to a PC for estimation of diameter curves. For the prototype system, diameter

The International Journal of Artificial Organs, 2014

Purpose Carotid artery stenting (CAS) is an alternative procedure for the treatment of severely s... more Purpose Carotid artery stenting (CAS) is an alternative procedure for the treatment of severely stenosed carotid artery lesions in high-risk patients. Appropriate patient selection and stent design are paramount to achieve a low stroke and death rate in these complex high-risk procedures. This study introduces and evaluates a novel virtual, patient-specific, pre-operative environment to quantify scaffolding parameters based on routine imaging techniques. Methods Two patients who underwent CAS with two different sizes of the Acculink stent (Abbott Vascular, Santa Clara, CA, USA) were studied. Pre-operative data were used to build the numerical models for the virtual procedure. Numerical results were validated with post-operative angiography. Using novel virtual geometrical tools, incomplete stent apposition, free cell area and largest fitting sphere in the stent cell were evaluated in situ as quantitative measures of successful stent placement and to assess potential risk factors for...

Key Engineering Materials, 2007

In Western countries, cardiovascular disease is the most common cause of death, often related to ... more In Western countries, cardiovascular disease is the most common cause of death, often related to atherosclerosis which can lead to a narrowing of the arteries. To restore perfusion of downstream tissues, an intravascular stent (i.e. a small tube-like structure) can be deployed in the obstructed vessel. The vast majority of stents are balloon expandable and crimped on a folded balloon to obtain a low profile for deliverability and lesion access. Several studies have exploited the finite element method to gain insight in their mechanical behaviour or to study the vascular reaction to stent deployment. However, to date – to the best of our knowledge – none of them include the balloon itself in its actual folded shape. Furthermore, literature on the effect of the crimping process on the expansion behaviour of the stent is even scarcer. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with data provided by the manufacturer and consequently our approach could be the basis for new realistic computational models of angioplasty procedures. The plastic deformation, prior to the stent expansion and induced by the crimping procedure, has a minor influence on the overall expansion behaviour of the stent but nevertheless influences the maximum von Mises stress and nominal strain. The maximum von Mises stress drops from 440 N/mm² to 426 N/mm² and the maximum nominal strain value lowers from 0.23 to 0.22 at the end of the expansion phase when neglecting the presence of the residual stresses. Depending on the context in which to use the developed mathematical models, the crimping phase can be discarded from the simulations in order to speed up the analyses.

Nuclear Medicine Communications, 2004

Journal of Hypertension, 2004

Objectives Absolute (ΔD) and relative (ΔD/D) arterial diameter distension, parameters related to ... more Objectives Absolute (ΔD) and relative (ΔD/D) arterial diameter distension, parameters related to the elasticity of the vessel, can be measured in superficial arteries using ultrasound-based vessel ‘wall tracking’ techniques. Currently available systems (e.g. the Wall Track System; WTS) measure the displacement of the media-adventitia transition (outer wall). We hypothesize that, given volume incompressibility of the vessel wall, ΔD and ΔD/D measured at the outer wall, significantly underestimate vessel distension at the lumen–intima interface (inner wall). Methods We measured ΔD and ΔD/D at both the inner and outer wall of the common carotid artery in 39 subjects (aged 18–83 years) using a new prototype ‘wall tracking’ system based on the Vivid-7 scanner (GE Vingmed Ultrasound, Horten, Norway). In addition, ΔD and ΔD/D were also measured using WTS. Results As anticipated, tracking the inner wall yielded lower diastolic diameters than when tracking the outer wall (Ddia = 5.70 ± 0.80 and 6.91 ± 0.98 mm, respectively, P < 0.0001). ΔD (0.54 ± 0.16 versus 0.49 ± 0.16 mm; P < 0.0001) and ΔD/D (0.096 ± 0.030 versus 0.071 ± 0.026, P < 0.0001) were indeed larger at the inner than at the outer wall. For WTS, Ddia, ΔD and ΔD/D were 7.04 ± 1.02 mm, 0.45 ± 0.14 mm and 0.066 ± 0.022, respectively. Conclusions On average, ΔD and ΔD/D are 10 and 25% higher on the inner than on the outer wall, respectively. Follow-up studies in larger cohort trials are mandatory to assess whether tracking the inner wall yields arterial function parameters with a higher cardiovascular prognostic potential.

Journal of Biomechanics, 2006

From the numerical simulation point of view, the very small windows of the stent (about 100 micro... more From the numerical simulation point of view, the very small windows of the stent (about 100 microns) make it very difficult to build a computational mesh including all the geometrical details. Besides the technological difficulties, it would induce prohibitive computational costs and a bad numerical conditioning. Moreover, it would be questionable to model the blood as an homogeneous fluid while solving the scale of 100 microns. These reasons motivate us to model the stent using mathematical homogenization techniques: instead of solving the fluid mechanics equations in an intricated geometry, we replace the stent by an immersed surface and modify the equations to take into account the presence of the stent. The parameters introduced in this model can be determined either with the homogenization theory or experimentally. Another major difficulty is the numerical simulation of the fluid-structure interaction. We propose an original algorithm based on a projection method in order to couple in a robust and efficient way the incompressible Navier-Stokes equations in ALE formulation and nonlinear shell equations in large displacement. We will discuss the relevance of the fluid-structure simulation to evaluate the influence of the stent on the hemodynamics in the aneurysm. We will show results on 3D real geometries obtained from medical imaging. Comparisons with experimental results will also be presented.

Journal of Biomechanics, 2012

Huberts (1), Koen van Canneyt (2), Pascal Verdonck (2), Patrick Segers (2), Jan Tordoir (3), Fran... more Huberts (1), Koen van Canneyt (2), Pascal Verdonck (2), Patrick Segers (2), Jan Tordoir (3), Frans van de Vosse (1), Marielle Bosboom (3)

Heart and Vessels, 1999

ponent traveling from the left atrium to the pulmonary bed and a reflected component propagating ... more ponent traveling from the left atrium to the pulmonary bed and a reflected component propagating from the pulmonary bed to the left atrium. The peak of the reflected pressure wave corresponded well with the positive peak in wave intensity in systole. We conclude that the gross features of the pressure and flow waves in the pulmonary vein can be explained in the following manner: the waves originate in the LA and travel towards the pulmonary bed, where reflections give rise to waves traveling back to the LA. Although the gross features of the measured pressure were captured well by the model predicted pressure, there was still some discrepancy between the two. Thus, other factors initiating or influencing waves traveling towards the LA cannot be excluded.

Echocardiography, 2006

Rationale and Objectives: In experimental models of the left heart, the mitral valve (MV) is comm... more Rationale and Objectives: In experimental models of the left heart, the mitral valve (MV) is commonly implanted perpendicular to a central axis of the apex/MV. To adapt this to a more correct anatomical model, as well as for further studies of the left ventricle, we created a database of implantation angles of the MV and annulus during three main phases of the heart cycle, based on standard cardiac ultrasound measurements. Materials and Methods: Twenty-eight patients were studied with the standard cardiac ultrasound equipment. From the apical echo window, an anteroposterior (AP) plane and a perpendicular commisure-commisure (CC) plane were generated during three critical moments in the heart cycle: systole (S); diastole early filling (E); and diastole late filling (A). In both planes, the angles between the annular plane and each mitral leaflet, as well as the angle between a theoretical longitudinal axis through the apex and center of the MV orifice and the mitral annulus plane, were measured with a custom-made application of Matlab R14. Results: We observed an inclination of the angle mitral annulus/central left ventricle axis, with its lowest point in the direction of the aortic valve (AP plane) of 85 • ± 7 • in systole (S), 88 • ± 8 • in early diastole (E), and 88 • ± 7 • in late diastole (A). In the CC plane, we observed an almost horizontal implantation of 91 • ± 5 • in systole (S), 91 • ± 8 • in early diastole (E), and 91 • ± 7 • in late diastole (A).

ASAIO Journal, 2005

Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation... more Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation, Pleasanton, CA) are small, nonpulsatile pumps designed for long-term use. However, its capability for providing full cardiac decompression and circulatory support has been questioned and indeed some have felt that the only safe way rotary pumps can be used is in an assistive mode. Methods: Three patients (Ischemic cardiomyopathy: 2, Post-partum cardiomyopathy: 1, ejection fraction: 10-20%) implanted the HeartMate II LVAD were followed using regular transthoracic echocardiography (TTE). Pump rpm, aortic valve opening (AVO), and left ventricular end-diastolic diameter (LVDd) were measured while changing pump rpm. Results: Full cardiac decompression and circulatory support were observed in all three patients. With the increasing of pump rpm, LVDd and the frequency of AVO decreased in inverse proportion. At an appropriate pump rpm setting, the aortic valve closed completely and LVDd decreased to 60-70% of preoperative LVDd without causing suction by the apical cannula. Longterm renal and circulatory function was normal without heart failure symptoms. Considerations: The Heartmate II provides sufficient circulatory support at an appropriate pump rpm setting in patients with severe congestive heart failure. Long-term full circulatory support can be achieved which is a requirement for destination therapy.

ASAIO Journal, 2005

Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation... more Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation, Pleasanton, CA) are small, nonpulsatile pumps designed for long-term use. However, its capability for providing full cardiac decompression and circulatory support has been questioned and indeed some have felt that the only safe way rotary pumps can be used is in an assistive mode. Methods: Three patients (Ischemic cardiomyopathy: 2, Post-partum cardiomyopathy: 1, ejection fraction: 10-20%) implanted the HeartMate II LVAD were followed using regular transthoracic echocardiography (TTE). Pump rpm, aortic valve opening (AVO), and left ventricular end-diastolic diameter (LVDd) were measured while changing pump rpm. Results: Full cardiac decompression and circulatory support were observed in all three patients. With the increasing of pump rpm, LVDd and the frequency of AVO decreased in inverse proportion. At an appropriate pump rpm setting, the aortic valve closed completely and LVDd decreased to 60-70% of preoperative LVDd without causing suction by the apical cannula. Longterm renal and circulatory function was normal without heart failure symptoms. Considerations: The Heartmate II provides sufficient circulatory support at an appropriate pump rpm setting in patients with severe congestive heart failure. Long-term full circulatory support can be achieved which is a requirement for destination therapy.

Artificial Organs, 2002

In this study, we used a mathematical model to study the influence of backflow through a failing ... more In this study, we used a mathematical model to study the influence of backflow through a failing rotary blood pump. We performed simulations based on animal experiments that were published earlier by Nishida et al., who used the Medos Microdiagonal pump to assess the acute effect of sudden pump failure. The mathematical model consists of validated cardiac and arterial modules and a pump module. We could evaluate the influence of pump failure with mechanoenergetic parameters and wall stress obtained from model output. Simulations were performed at baseline and after 15 min of backflow in a control group and a heart failure group. Simulation results agreed well with the experiment. Stroke volume, aortic flow, and stress time integral increased significantly because of pump failure. However, total systemic flow and arterial pressure were not altered by backflow, and a lifethreatening situation did not appear.

WIT Transactions on Biomedicine and Health, 1970

With the advent of transesophageal echocardiography, pulmonary venous flow is easily obtained in ... more With the advent of transesophageal echocardiography, pulmonary venous flow is easily obtained in all patients by pulsed-wave Doppler echocardiography. Therefore it has become a current topic of clinical investigation as a part of an assessment of left ventricular filling dynamics. In order to understand the relation between left ventricular function and Doppler indices, a lumped parameter model of the flow through the left heart is developed. The model predicts the time course of pressure and flow in the pulmonary veins and the left heart chambers given pulmonary venous compliance, inertance and resistance, left atrial and ventricular stiffness and mitral valve impedance. A case study is presented.

Abaqus Benelux Users’ Meeting 2009 Realistic virtual radial strength testing of stents M. De Beul... more Abaqus Benelux Users’ Meeting 2009 Realistic virtual radial strength testing of stents M. De Beule, P. Mortier, P. Verdonck, P. Segers, B. Verhegghe, F. Bakczewitz and N. Gotzen Biofluid, Tissue and Solid Mechanics for Medical Applications (bioMMeda) Institute Biomedical Technology (IBiTech), Ghent University, Belgium Cortronik GmbH, Rostock-Waremunde, Germany The most important task of a stent is to reopen the artery and support or scaffold the stenosed lesion in a target vessel. To that extent, the stent requires a sufficient radial strength. Experimental evidence has shown that, in addition to the material properties, this radial strength is also strongly design dependent (Rieu et al., Catheter Cardiovasc Interv, 1999). Its assessment, especially in the case of balloonexpandable stents, requires a sophisticated and accurate test set-up and dedicated experimental protocol. Complementary to such experimental methods, we developed a virtual testing procedure which allows to gain val...

American Journal of Physiology-Heart and Circulatory Physiology, 2000

We fitted a three-segment transmission line model for the radial-carotid/aorta pressure transfer ... more We fitted a three-segment transmission line model for the radial-carotid/aorta pressure transfer function (TFF) in 31 controls and 30 patients with coronary artery disease using noninvasively measured (tonometry) radial and carotid artery pressures (Pcar). Except for the distal reflection coefficient (0.85 ± 0.21 in patients vs. 0.71 ± 0.25 in controls; P < 0.05), model parameters were not different between patients or controls. Parameters were not related to blood pressure, age, or heart rate. We further assessed a point-to-point averaged TFF (TFFavg) as well as upper (TFFmax) and lower (TFFmin) enveloping TFF. Pulse pressure (PP) and augmentation index (AIx) were derived on original and reconstructed Pcar (Pcar,r). TFFavg yielded closest morphological agreement between Pcar and Pcar,r (root mean square = 4.3 ± 2.3 mmHg), and TTFavg best predicted PP (41.5 ± 11.8 vs. 41.1 ± 10.0 mmHg measured) and AIx (−0.02 ± 0.19 vs. 0.01 ± 0.19). PP and AIx, calculated from Pcar or Pcar,r, we...

European Journal of Echocardiography, 2006

vided as a surrogate marker for LV-EF. Unfortunately, there are only few data on the relation bet... more vided as a surrogate marker for LV-EF. Unfortunately, there are only few data on the relation between the WMSI and LV-EF. In addition, poor non-contrast enhanced echo windows can make the WMSI (and LV-EF) unreliable. The value of contrast imaging for WMSI assessment was not investigated before. Aim of the study: To compare segmental wall motion and WMSI interobserver agreement in patients who underwent both two-dimensional second harmonic (SH) and contrast left ventricular opacification (LVO) echocardiography. Methods: The study comprised 100 consecutive patients (mean age 57±13 years, 85% males) who underwent both SH and SonoVue LVO echocardiography for clinical evaluation of LV function. Two independent physicians assessed segmental quality and wall motion for both the SH and LVO studies according to a 17-segment model. Systolic wall motion was defined as (1) normokinesia, (2) hypokinesia (systolic inward endocardial motion <7 mm), (3) akinesia, and (4) dyskinesia. LV-EF was assessed from the LVO images according to the biplane modified Simpson's method by a third blinded physician. Results: Of the 1,700 analyzed segments, 453 (26.6%) were poorly visualized with SH imaging, and 173 (10,2%) with LVO imaging (p<0.0001). The two independent observers agreed on segmental wall motion score in 1,299 of the 1,700 segments (agreement 76%, Kappa 0.60) with SH imaging and in 1,491 of the 1,700 segments (agreement 88%, Kappa 0.78) with LVO imaging. Interobserver correlation (R 2) was 0.86 for the SH-imaged WMSI and 0.93 for the LVO-imaged WMSI. The limits of agreement for interobserver LVO-imaged WMSI (mean relative difference-1.0%±6.8%, agreement-14.6%, 12.6%) were lower than those for SH-imaged WMSI (mean relative difference-2.3%±10.1%, agreement-22.5, 17.9). The LVO-imaged WMSI correlated well with LVO-imaged LV-EF (R 2=0.71). LV-EF could be estimated according to the formula 1.01-0.32xWMSI. Conclusion: Echo contrast improves interobserver agreement for wall motion and WMSI scoring. The LVO-imaged WMSI correlates well with LVOimaged LV-EF.

Artery research, 2017

This paper aims to summarize and map contemporary views on some contentious aspects of arterial h... more This paper aims to summarize and map contemporary views on some contentious aspects of arterial hemodynamics that have remained unresolved despite years of research. These were discussed during a workshop entitled Arterial hemodynamics: past, present and future held in London on June 14 and 15, 2016. To do this we formulated a list of potential consensus statements informed by discussion at the meeting in London and quantified the degree of agreement and invited comments from the participants of the workshop. Overall the responses and comments show a high measure of quantitative agreement with the various proposed 'consensus' statements. Taken together, these statements seem a useful basis for proceeding with a more detailed and comprehensive consensus document on the current understanding and approaches to analysis of the pulse waveform. Future efforts should be directed at identifying remaining areas of dispute and future topics for research.

2002 IEEE Ultrasonics Symposium, 2002. Proceedings.

In 16 subjects (age 26-74) we recorded radio-frequency (RF) data of the Carotid artery with a Viv... more In 16 subjects (age 26-74) we recorded radio-frequency (RF) data of the Carotid artery with a Vivid7 scanner (GE Vingmed Ultrasound, Horten, Norway) and Carotid diameters with WallTrack (Pie Medical, Maastricht, The Netherlands). The RF data were stored as complex demodulated radio-frequency data (IQ data) and transferred to a PC for estimation of diameter curves. For the prototype system, diameter

The International Journal of Artificial Organs, 2014

Purpose Carotid artery stenting (CAS) is an alternative procedure for the treatment of severely s... more Purpose Carotid artery stenting (CAS) is an alternative procedure for the treatment of severely stenosed carotid artery lesions in high-risk patients. Appropriate patient selection and stent design are paramount to achieve a low stroke and death rate in these complex high-risk procedures. This study introduces and evaluates a novel virtual, patient-specific, pre-operative environment to quantify scaffolding parameters based on routine imaging techniques. Methods Two patients who underwent CAS with two different sizes of the Acculink stent (Abbott Vascular, Santa Clara, CA, USA) were studied. Pre-operative data were used to build the numerical models for the virtual procedure. Numerical results were validated with post-operative angiography. Using novel virtual geometrical tools, incomplete stent apposition, free cell area and largest fitting sphere in the stent cell were evaluated in situ as quantitative measures of successful stent placement and to assess potential risk factors for...

Key Engineering Materials, 2007

In Western countries, cardiovascular disease is the most common cause of death, often related to ... more In Western countries, cardiovascular disease is the most common cause of death, often related to atherosclerosis which can lead to a narrowing of the arteries. To restore perfusion of downstream tissues, an intravascular stent (i.e. a small tube-like structure) can be deployed in the obstructed vessel. The vast majority of stents are balloon expandable and crimped on a folded balloon to obtain a low profile for deliverability and lesion access. Several studies have exploited the finite element method to gain insight in their mechanical behaviour or to study the vascular reaction to stent deployment. However, to date – to the best of our knowledge – none of them include the balloon itself in its actual folded shape. Furthermore, literature on the effect of the crimping process on the expansion behaviour of the stent is even scarcer. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with data provided by the manufacturer and consequently our approach could be the basis for new realistic computational models of angioplasty procedures. The plastic deformation, prior to the stent expansion and induced by the crimping procedure, has a minor influence on the overall expansion behaviour of the stent but nevertheless influences the maximum von Mises stress and nominal strain. The maximum von Mises stress drops from 440 N/mm² to 426 N/mm² and the maximum nominal strain value lowers from 0.23 to 0.22 at the end of the expansion phase when neglecting the presence of the residual stresses. Depending on the context in which to use the developed mathematical models, the crimping phase can be discarded from the simulations in order to speed up the analyses.

Nuclear Medicine Communications, 2004

Journal of Hypertension, 2004

Objectives Absolute (ΔD) and relative (ΔD/D) arterial diameter distension, parameters related to ... more Objectives Absolute (ΔD) and relative (ΔD/D) arterial diameter distension, parameters related to the elasticity of the vessel, can be measured in superficial arteries using ultrasound-based vessel ‘wall tracking’ techniques. Currently available systems (e.g. the Wall Track System; WTS) measure the displacement of the media-adventitia transition (outer wall). We hypothesize that, given volume incompressibility of the vessel wall, ΔD and ΔD/D measured at the outer wall, significantly underestimate vessel distension at the lumen–intima interface (inner wall). Methods We measured ΔD and ΔD/D at both the inner and outer wall of the common carotid artery in 39 subjects (aged 18–83 years) using a new prototype ‘wall tracking’ system based on the Vivid-7 scanner (GE Vingmed Ultrasound, Horten, Norway). In addition, ΔD and ΔD/D were also measured using WTS. Results As anticipated, tracking the inner wall yielded lower diastolic diameters than when tracking the outer wall (Ddia = 5.70 ± 0.80 and 6.91 ± 0.98 mm, respectively, P < 0.0001). ΔD (0.54 ± 0.16 versus 0.49 ± 0.16 mm; P < 0.0001) and ΔD/D (0.096 ± 0.030 versus 0.071 ± 0.026, P < 0.0001) were indeed larger at the inner than at the outer wall. For WTS, Ddia, ΔD and ΔD/D were 7.04 ± 1.02 mm, 0.45 ± 0.14 mm and 0.066 ± 0.022, respectively. Conclusions On average, ΔD and ΔD/D are 10 and 25% higher on the inner than on the outer wall, respectively. Follow-up studies in larger cohort trials are mandatory to assess whether tracking the inner wall yields arterial function parameters with a higher cardiovascular prognostic potential.

Journal of Biomechanics, 2006

From the numerical simulation point of view, the very small windows of the stent (about 100 micro... more From the numerical simulation point of view, the very small windows of the stent (about 100 microns) make it very difficult to build a computational mesh including all the geometrical details. Besides the technological difficulties, it would induce prohibitive computational costs and a bad numerical conditioning. Moreover, it would be questionable to model the blood as an homogeneous fluid while solving the scale of 100 microns. These reasons motivate us to model the stent using mathematical homogenization techniques: instead of solving the fluid mechanics equations in an intricated geometry, we replace the stent by an immersed surface and modify the equations to take into account the presence of the stent. The parameters introduced in this model can be determined either with the homogenization theory or experimentally. Another major difficulty is the numerical simulation of the fluid-structure interaction. We propose an original algorithm based on a projection method in order to couple in a robust and efficient way the incompressible Navier-Stokes equations in ALE formulation and nonlinear shell equations in large displacement. We will discuss the relevance of the fluid-structure simulation to evaluate the influence of the stent on the hemodynamics in the aneurysm. We will show results on 3D real geometries obtained from medical imaging. Comparisons with experimental results will also be presented.

Journal of Biomechanics, 2012

Huberts (1), Koen van Canneyt (2), Pascal Verdonck (2), Patrick Segers (2), Jan Tordoir (3), Fran... more Huberts (1), Koen van Canneyt (2), Pascal Verdonck (2), Patrick Segers (2), Jan Tordoir (3), Frans van de Vosse (1), Marielle Bosboom (3)

Heart and Vessels, 1999

ponent traveling from the left atrium to the pulmonary bed and a reflected component propagating ... more ponent traveling from the left atrium to the pulmonary bed and a reflected component propagating from the pulmonary bed to the left atrium. The peak of the reflected pressure wave corresponded well with the positive peak in wave intensity in systole. We conclude that the gross features of the pressure and flow waves in the pulmonary vein can be explained in the following manner: the waves originate in the LA and travel towards the pulmonary bed, where reflections give rise to waves traveling back to the LA. Although the gross features of the measured pressure were captured well by the model predicted pressure, there was still some discrepancy between the two. Thus, other factors initiating or influencing waves traveling towards the LA cannot be excluded.

Echocardiography, 2006

Rationale and Objectives: In experimental models of the left heart, the mitral valve (MV) is comm... more Rationale and Objectives: In experimental models of the left heart, the mitral valve (MV) is commonly implanted perpendicular to a central axis of the apex/MV. To adapt this to a more correct anatomical model, as well as for further studies of the left ventricle, we created a database of implantation angles of the MV and annulus during three main phases of the heart cycle, based on standard cardiac ultrasound measurements. Materials and Methods: Twenty-eight patients were studied with the standard cardiac ultrasound equipment. From the apical echo window, an anteroposterior (AP) plane and a perpendicular commisure-commisure (CC) plane were generated during three critical moments in the heart cycle: systole (S); diastole early filling (E); and diastole late filling (A). In both planes, the angles between the annular plane and each mitral leaflet, as well as the angle between a theoretical longitudinal axis through the apex and center of the MV orifice and the mitral annulus plane, were measured with a custom-made application of Matlab R14. Results: We observed an inclination of the angle mitral annulus/central left ventricle axis, with its lowest point in the direction of the aortic valve (AP plane) of 85 • ± 7 • in systole (S), 88 • ± 8 • in early diastole (E), and 88 • ± 7 • in late diastole (A). In the CC plane, we observed an almost horizontal implantation of 91 • ± 5 • in systole (S), 91 • ± 8 • in early diastole (E), and 91 • ± 7 • in late diastole (A).

ASAIO Journal, 2005

Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation... more Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation, Pleasanton, CA) are small, nonpulsatile pumps designed for long-term use. However, its capability for providing full cardiac decompression and circulatory support has been questioned and indeed some have felt that the only safe way rotary pumps can be used is in an assistive mode. Methods: Three patients (Ischemic cardiomyopathy: 2, Post-partum cardiomyopathy: 1, ejection fraction: 10-20%) implanted the HeartMate II LVAD were followed using regular transthoracic echocardiography (TTE). Pump rpm, aortic valve opening (AVO), and left ventricular end-diastolic diameter (LVDd) were measured while changing pump rpm. Results: Full cardiac decompression and circulatory support were observed in all three patients. With the increasing of pump rpm, LVDd and the frequency of AVO decreased in inverse proportion. At an appropriate pump rpm setting, the aortic valve closed completely and LVDd decreased to 60-70% of preoperative LVDd without causing suction by the apical cannula. Longterm renal and circulatory function was normal without heart failure symptoms. Considerations: The Heartmate II provides sufficient circulatory support at an appropriate pump rpm setting in patients with severe congestive heart failure. Long-term full circulatory support can be achieved which is a requirement for destination therapy.

ASAIO Journal, 2005

Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation... more Rotary pumps such as the Heartmate II left ventricular assist device (LVAD) (Thoratec Corporation, Pleasanton, CA) are small, nonpulsatile pumps designed for long-term use. However, its capability for providing full cardiac decompression and circulatory support has been questioned and indeed some have felt that the only safe way rotary pumps can be used is in an assistive mode. Methods: Three patients (Ischemic cardiomyopathy: 2, Post-partum cardiomyopathy: 1, ejection fraction: 10-20%) implanted the HeartMate II LVAD were followed using regular transthoracic echocardiography (TTE). Pump rpm, aortic valve opening (AVO), and left ventricular end-diastolic diameter (LVDd) were measured while changing pump rpm. Results: Full cardiac decompression and circulatory support were observed in all three patients. With the increasing of pump rpm, LVDd and the frequency of AVO decreased in inverse proportion. At an appropriate pump rpm setting, the aortic valve closed completely and LVDd decreased to 60-70% of preoperative LVDd without causing suction by the apical cannula. Longterm renal and circulatory function was normal without heart failure symptoms. Considerations: The Heartmate II provides sufficient circulatory support at an appropriate pump rpm setting in patients with severe congestive heart failure. Long-term full circulatory support can be achieved which is a requirement for destination therapy.

Artificial Organs, 2002

In this study, we used a mathematical model to study the influence of backflow through a failing ... more In this study, we used a mathematical model to study the influence of backflow through a failing rotary blood pump. We performed simulations based on animal experiments that were published earlier by Nishida et al., who used the Medos Microdiagonal pump to assess the acute effect of sudden pump failure. The mathematical model consists of validated cardiac and arterial modules and a pump module. We could evaluate the influence of pump failure with mechanoenergetic parameters and wall stress obtained from model output. Simulations were performed at baseline and after 15 min of backflow in a control group and a heart failure group. Simulation results agreed well with the experiment. Stroke volume, aortic flow, and stress time integral increased significantly because of pump failure. However, total systemic flow and arterial pressure were not altered by backflow, and a lifethreatening situation did not appear.