Stijn Vandenberghe

Universität Bern, Berna, Bern, Switzerland

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Publications (55)112.65 Total impact

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    Dataset: AO
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    Dataset: EJCTS
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    Dataset: JTCVS
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    Dataset: EJCTS
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    ABSTRACT: Functional tricuspid regurgitation (TR) is recognized as a significant cause of morbidity and mortality in cardiothoracic surgery. We hypothesized that a variably expandable, transvalvular balloon mounted on a catheter could be percutaneously inserted and fixed to the right ventricle apex. This novel approach could provide a minimally invasive way to eliminate clinically relevant TR caused by annular dilatation. This study was performed to test the ex vivo hemodynamic effects and the feasibility of the "balloon plug concept." Twenty harvested calf tricuspid valves were placed in a mechanical simulator. Tricuspid regurgitation was created by annular stretching and displacement of the papillary muscles so as to create central TR. A flexible catheter with a 4-cm-long, soft, fusiform balloon was positioned across the valve so that the balloon was suspended centrally across the valve annular plane. After activating the mechanical ventricle, data were collected with balloon inflation volumes of saline from 5 to 20 mL. Transvalvular pressure gradients and leaflet mechanics were evaluated with incremental inflation. In all cases, 5-mL inflation did not significantly reduce TR and 20-mL inflation caused obstruction to antegrade flow (mean transvalvular gradient > 4 mm Hg). Inflation between 10 and 15 mL caused significant reduction in TR with acceptable transvalvular gradients (<3 mm Hg). The balloon plug concept showed promising ex vivo hemodynamic results. In vivo investigations are warranted to evaluate percutaneous techniques, thrombogenicity, and effects of repeated balloon-leaflet contact on valve integrity.
    Innovations Technology and Techniques in Cardiothoracic and Vascular Surgery 01/2015; 10(1):27-32. DOI:10.1097/IMI.0000000000000124
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    ABSTRACT: Arterial waves are seen as possible independent mediators of cardiovascular risks, and the wave intensity analysis (WIA) has therefore been proposed as a method for patient selection for ventricular assist device (VAD) implantation. Interpreting measured wave intensity (WI) is challenging, and complexity is increased by the implantation of a VAD. The waves generated by the VAD interact with the waves generated by the native heart, and this interaction varies with changing VAD settings. Eight sheep were implanted with a pulsatile VAD (PVAD) through ventriculoaortic cannulation. The start of PVAD ejection was synchronized to the native R wave and delayed between 0 and 90% of the cardiac cycle in 10% steps or phase shifts (PS). Pressure and velocity signals were registered, with the use of a combined Doppler and pressure wire positioned in the abdominal aorta, and used to calculate the WI. Depending on the PS, different wave interference phenomena occurred. Maximum unloading of the left ventricle (LV) coincided with constructive interference and maximum blood flow pulsatility, and maximum loading of the LV coincided with destructive interference and minimum blood flow pulsatility. We believe that noninvasive WIA could potentially be used clinically to assess the mechanical load of the LV and to monitor the peripheral hemodynamics such as blood flow pulsatility and risk of intestinal bleeding.
    AJP Heart and Circulatory Physiology 10/2014; 307(8):H1243-51. DOI:10.1152/ajpheart.00085.2014 · 4.01 Impact Factor
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    ABSTRACT: Lumped parameter models have been employed for decades to simulate important hemodynamic couplings between a left ventricular assist device (LVAD) and the native circulation. However, these studies seldom consider the pathological descending limb of the Frank-Starling response of the overloaded ventricle. This study introduces a dilated heart failure model featuring a unimodal end systolic pressure-volume relationship (ESPVR) to address this critical shortcoming. The resulting hemodynamic response to mechanical circulatory support are illustrated through numerical simulations of a rotodynamic, continuous flow ventricular assist device (cfVAD) coupled to systemic and pulmonary circulations with baroreflex control. The model further incorporated septal interaction to capture the influence of left ventricular (LV) unloading on right ventricular function. Four heart failure conditions were simulated (LV and bi-ventricular failure with/without pulmonary hypertension) in addition to normal baseline. Several metrics of LV function, including cardiac output and stroke work, exhibited a unimodal response whereby initial unloading improved function, and further unloading depleted preload reserve thereby reducing ventricular output. The concept of extremal loading was introduced to reflect the loading condition in which the intrinsic LV stroke work is maximized. Simulation of bi-ventricular failure with pulmonary hypertension revealed inadequacy of LV support alone. These simulations motivate the implementation of an extremum tracking feedback controller to potentially optimize ventricular recovery.
    PLoS ONE 01/2014; 9(1):e85234. DOI:10.1371/journal.pone.0085234 · 3.53 Impact Factor
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    ABSTRACT: The current article presents a novel physiological control algorithm for ventricular assist devices (VADs), which is inspired by the preload recruitable stroke work. This controller adapts the hydraulic power output of the VAD to the end-diastolic volume of the left ventricle. We tested this controller on a hybrid mock circulation where the left ventricular volume (LVV) is known, i.e., the problem of measuring the LVV is not addressed in the current article. Experiments were conducted to compare the response of the controller with the physiological and with the pathological circulation, with and without VAD support. A sensitivity analysis was performed to analyze the influence of the controller parameters and the influence of the quality of the LVV signal on the performance of the control algorithm. The results show that the controller induces a response similar to the physiological circulation and effectively prevents over- and underpumping, i.e., ventricular suction and backflow from the aorta to the left ventricle, respectively. The same results are obtained in the case of a disturbed LVV signal. The results presented in the current article motivate the development of a robust, long-term stable sensor to measure the LVV.
    Artificial Organs 11/2013; DOI:10.1111/aor.12225 · 1.87 Impact Factor
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    ABSTRACT: A lumped parameter model of the cardiovascular system has been developed and optimized using experimental data obtained from 13 healthy subjects during graded head-up tilt (HUT) from the supine position to [Formula: see text]. The model includes descriptions of the left and right heart, direct ventricular interaction through the septum and pericardium, the systemic and pulmonary circulations, nonlinear pressure volume relationship of the lower body compartment, arterial and cardiopulmonary baroreceptors, as well as autoregulatory mechanisms. A number of important features, including the separate effects of arterial and cardiopulmonary baroreflexes, and autoregulation in the lower body, as well as diastolic ventricular interaction through the pericardium have been included and tested for their significance. Furthermore, the individual effect of parameter associated with heart failure, including LV and RV contractility, baseline systemic vascular resistance, pulmonary vascular resistance, total blood volume, LV diastolic stiffness and reflex gain on HUT response have also been investigated. Our fitted model compares favorably with our experimental measurements and published literature at a range of tilt angles, in terms of both global and regional hemodynamic variables. Compared to the normal condition, a simulated congestive heart failure condition produced a blunted response to HUT with regards to the percentage changes in cardiac output, stroke volume, end diastolic volume and effector response (i.e., heart contractility, venous unstressed volume, systemic vascular resistance and heart rate) with progressive tilting.
    PLoS ONE 10/2013; 8(10):e77357. DOI:10.1371/journal.pone.0077357 · 3.53 Impact Factor
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    ABSTRACT: The clinical importance of pulsatility is a recurring topic of debate in mechanical circulatory support. Lack of pulsatility has been identified as a possible factor responsible for adverse events and has also demonstrated a role in myocardial perfusion and cardiac recovery. A commonly used method for restoring pulsatility with rotodynamic blood pumps (RBPs) is to modulate the speed profile, synchronized to the cardiac cycle. This introduces additional parameters that influence the (un)loading of the heart, including the timing (phase shift) between the native cardiac cycle and the pump pulses, and the amplitude of speed modulation. In this study, the impact of these parameters upon the heart-RBP interaction was examined in terms of the pressure head-flow (HQ) diagram. The measurements were conducted using a rotodynamic Deltastream DP2 pump in a validated hybrid mock circulation with baroreflex function. The pump was operated with a sinusoidal speed profile, synchronized to the native cardiac cycle. The simulated ventriculo-aortic cannulation showed that the level of (un)loading and the shape of the HQ loops strongly depend on the phase shift. The HQ loops displayed characteristic shapes depending on the phase shift. Increased contribution of native contraction (increased ventricular stroke work [WS ]) resulted in a broadening of the loops. It was found that the previously described linear relationship between WS and the area of the HQ loop for constant pump speeds becomes a family of linear relationships, whose slope depends on the phase shift.
    Artificial Organs 07/2013; 38(4). DOI:10.1111/aor.12139 · 1.87 Impact Factor
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    ABSTRACT: Aims: To investigate a pressure-controlled intermittent coronary sinus occlusion (PICSO) system in an ischaemia/reperfusion model. Methods and results: We randomly assigned 18 pigs subjected to 60 minutes ischaemia by left anterior descending (LAD) coronary artery balloon occlusion to PICSO (n=12, groups A and B) or to controls (n=6, group C). PICSO started 10 minutes before (group A), or 10 minutes after (group B) reperfusion and was maintained for 180 minutes. A continuous drop of distal LAD pressure was observed in group C. At 180 minutes of reperfusion, LAD diastolic pressure was significantly lower in group C compared to groups A and B (p=0.02). LAD mean pressure was significantly less than the systemic arterial mean pressure in group C (p=0.02), and the diastolic flow slope was flat, compared to groups A and B (p=0.03). IgG and IgM antibody deposition was significantly higher in ischaemic compared to non-ischaemic tissue in group C (p<0.05). Significantly more haemorrhagic lesions were seen in the ischaemic myocardium of group C, compared to groups A and B (p=0.002). The necrotic area differed non-significantly among groups. Conclusions: PICSO was safe and effective in improving coronary perfusion pressure and reducing antibody deposition consistent with reduced microvascular obstruction and ischaemia/reperfusion injury.
    EuroIntervention: journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology 07/2013; 9(3):398-406. DOI:10.4244/EIJV9I3A63 · 3.76 Impact Factor
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    ABSTRACT: /st>Cardiac output (CO) measurement with lithium dilution (COLD) has not been fully validated in sheep using precise ultrasonic flow probe technology (COUFP). Sheep generate important cardiovascular research models and the use of COLD has become more popular in experimental settings. /st>Ultrasonic transit-time perivascular flow probes were surgically implanted on the pulmonary artery of 13 sheep. Paired COLD readings were taken at six time points, before and after implantation of a left ventricular assist device (LVAD) and compared with COUFP recorded just after lithium injection. /st>The mean COLD was 5.7 litre min(-1) (range 3.8-9.6 litre min(-1)) and mean COUFP 5.9 litre min(-1) (range 4.0-9.2 litre min(-1)). The bias (standard deviation) was 0.3 (1.0) litre min(-1) [5.1 (16.9)%] and limits of agreement (LOA) were -1.7 to 2.3 litre min(-1) (-28.8 to 39.0%) with a percentage error (PE) of 34.4%. Data to assess trending [rate (95% confidence intervals)] included a 78 (62-93)% concordance rate in the four-quadrant plot (n=27). In the half moon polar plot (n=19), the mean polar angle was +5°, the radial LOA were -49 to +35° and 68 (47-89)% of data points fell within 22.5° of the mean polar angle. Both tests indicated moderate to poor trending ability. /st>COLD is not precise when evaluated against COUFP in sheep based on the statistical criteria set, but the results are comparable with previously published animal studies.
    BJA British Journal of Anaesthesia 07/2013; 111(5). DOI:10.1093/bja/aet220 · 4.35 Impact Factor
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    ABSTRACT: BACKGROUND AND PURPOSE:Conventional platinum coils cause imaging artifacts that reduce imaging quality and therefore impair imaging interpretation on intraprocedural or noninvasive follow-up imaging. The purpose of this study was to evaluate imaging characteristics and artifact production of polymeric coils compared with standard platinum coils in vitro and in vivo.MATERIALS AND METHODS:Polymeric coils and standard platinum coils were evaluated in vitro with the use of 2 identical silicon aneurysm models coiled with a packing attenuation of 20% each. DSA, flat panel CT, CT, and MR imaging were performed. In vivo evaluation of imaging characteristics of polymeric coils was performed in experimentally created rabbit carotid bifurcation aneurysms. DSA, CT/CTA, and MR imaging were performed after endovascular treatment of the aneurysms. Images were evaluated regarding visibility of individual coils, coil mass, artifact production, and visibility of residual flow within the aneurysm.RESULTS:Overall, in vitro and in vivo imaging showed relevantly reduced artifact production of polymeric coils in all imaging modalities compared with standard platinum coils. Image quality of CT and MR imaging was improved with the use of polymeric coils, which permitted enhanced depiction of individual coil loops and residual aneurysm lumen as well as the peri-aneurysmal area. Remarkably, CT images demonstrated considerably improved image quality with only minor artifacts compared with standard coils. On DSA, polymeric coils showed transparency and allowed visualization of superimposed vessel structures.CONCLUSIONS:This initial experimental study showed improved imaging quality with the use of polymeric coils compared with standard platinum coils in all imaging modalities. This might be advantageous for improved intraprocedural imaging for the detection of complications and posttreatment noninvasive follow-up imaging.
    American Journal of Neuroradiology 05/2013; 34(11). DOI:10.3174/ajnr.A3589 · 3.68 Impact Factor
  • The Journal of thoracic and cardiovascular surgery 04/2013; 145(4):1145-6. DOI:10.1016/j.jtcvs.2012.12.075 · 3.99 Impact Factor
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    ABSTRACT: Ventricular assist devices are blood pumps that offer an option to support the circulation of patients with severe heart failure. Since a failing heart has a remaining pump function, its interaction with the ventricular assist device influences the hemodynamics. Ideally, the hearts action is taken into account for actuating the device such that the device is synchronized to the natural cardiac cycle. To realize this in practice, a reliable real-time algorithm for the automatic synchronization of the ventricular assist device to the heart rate is required. This paper defines the tasks such an algorithm needs to fulfill: the automatic detection of irregular heart beats and the feedback control of the phase shift between the systolic phases of the heart and the assist device. We demonstrate a possible solution to these problems and analyze its performance in two steps. First, the algorithm is tested using the MIT-BIH arrhythmia database. Second, the algorithm is implemented in a controller for a pulsatile and a continuousflow ventricular assist device. These devices are connected to a hybrid mock circulation where three test scenarios are evaluated. The proposed algorithm ensures a reliable synchronization of the ventricular assist device to the heart cycle, while being insensitive to irregularities in the heart rate.
    IEEE transactions on bio-medical engineering 03/2013; 60(8). DOI:10.1109/TBME.2013.2251634 · 2.23 Impact Factor
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    ABSTRACT: OBJECTIVE: Current pulsatile ventricular assist devices operate asynchronous with the left ventricle in fixed-rate or fill-to-empty modes because electrocardiogram-triggered modes have been abandoned. We hypothesize that varying the ejection delay in the synchronized mode yields more precise control of hemodynamics and left ventricular loading. This allows for a refined management that may be clinically beneficial. METHODS: Eight sheep received a Thoratec paracorporeal ventricular assist device (Thoratec Corp, Pleasanton, Calif) via ventriculo-aortic cannulation. Left ventricular pressure and volume, aortic pressure, pulmonary flow, pump chamber pressure, and pump inflow and outflow were recorded. The pump was driven by a clinical pneumatic drive unit (Medos Medizintechnik AG, Stolberg, Germany) synchronously with the native R-wave. The start of pump ejection was delayed between 0% and 100% of the cardiac period in 10% increments. For each of these delays, hemodynamic variables were compared with baseline data using paired t tests. RESULTS: The location of the minimum of stroke work was observed at a delay of 10% (soon after aortic valve opening), resulting in a median of 43% reduction in stroke work compared with baseline. Maximum stroke work occurred at a median delay of 70% with a median stroke work increase of 11% above baseline. Left ventricular volume unloading expressed by end-diastolic volume was most pronounced for copulsation (delay 0%). CONCLUSIONS: The timing of pump ejection in synchronized mode yields control over left ventricular energetics and can be a method to achieve gradual reloading of a recoverable left ventricle. The traditionally suggested counterpulsation is not optimal in ventriculo-aortic cannulation when maximum unloading is desired.
    The Journal of thoracic and cardiovascular surgery 01/2013; 146(3). DOI:10.1016/j.jtcvs.2012.12.048 · 3.99 Impact Factor
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    ABSTRACT: This paper presents a novel mock circulation for the evaluation of ventricular assist devices (VADs), which is based on a hardware-in-the-loop concept. A numerical model of the human blood circulation runs in real-time and computes instantaneous pressure, volume, and flow rate values. The VAD to be tested is connected to a numerical-hydraulic interface, which allows the interaction between the VAD and the numerical model of the circulation. The numerical-hydraulic interface consists of two pressure-controlled reservoirs, which apply the computed pressure values from the model to the VAD, and a flow probe to feed the resulting VAD flow rate back to the model. Experimental results are provided to show the proper interaction between a numerical model of the circulation and a mixed-flow blood pump.
    IEEE transactions on bio-medical engineering 11/2012; DOI:10.1109/TBME.2012.2230000 · 2.23 Impact Factor
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    ABSTRACT: Energy-harvesting devices attract wide interest as power supplies of today's medical implants. Their long lifetime will spare patients from repeated surgical interventions. They also offer the opportunity to further miniaturize existing implants such as pacemakers, defibrillators or recorders of bio signals. A mass imbalance oscillation generator, which consists of a clockwork from a commercially available automatic wrist watch, was used as energy harvesting device to convert the kinetic energy from the cardiac wall motion to electrical energy. An MRI-based motion analysis of the left ventricle revealed basal regions to be energetically most favorable for the rotating unbalance of our harvester. A mathematical model was developed as a tool for optimizing the device's configuration. The model was validated by an in vitro experiment where an arm robot accelerated the harvesting device by reproducing the cardiac motion. Furthermore, in an in vivo experiment, the device was affixed onto a sheep heart for 1 h. The generated power in both experiments-in vitro (30 μW) and in vivo (16.7 μW)-is sufficient to power modern pacemakers.
    Annals of Biomedical Engineering 07/2012; DOI:10.1007/s10439-012-0623-3 · 3.23 Impact Factor
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    ABSTRACT: OBJECTIVES: Rotary blood pumps (RBPs) running at a constant speed are routinely used for the mechanical support of the heart in various clinical applications, from short-term use in heart-lung machines to long-term support of a failing heart. Their operating range is delineated by suction and regurgitation events, leaving limited control on the cardiac workload. This study investigates whether different ratios of systolic/diastolic support are advantageous over a constant-speed operation. METHODS: In order to effectively control the load on the heart, this study aimed at developing a pulsatile control algorithm for rotary pumps to investigate the impact of pump speed modulation during systole and diastole on the left ventricle unloading. The CentriMag(TM) RBP with a modified controller was implanted in four sheep via a left thoracotomy and cannulated from the ventricular apex to the descending aorta. To modulate the pump speed synchronized with the heartbeat, custom-made real-time software detected the QRS complex of the electrocardiogram and controlled the pump speed during systole and diastole. Four different speed modulations with the same average speed but different systolic and diastolic speeds were compared with the baseline and the constant speed support. Left ventricular (LV) pressure and volume, coronary flow and pump flow were analysed to examine the influence of the pump speed modulation. RESULTS: Pulsatile setting reduces the cardiac workload to 64% of the baseline and 72% of the constant speed value. Maximum unloading is obtained with the highest speed during diastole and high-pulse amplitude. End-diastolic volume in the pulsatile modes varied from 85 to 94% of the baseline and 96 to 107% of the constant speed value. Consequently, the mechanical load on the heart can be adjusted to provide assuagement, which may lead to myocardial recovery. The higher pump speed during systole results in an increase in the pulse pressure up to 140% compared with the constant speed. CONCLUSIONS: The present study is an initial step to more accurate speed modulation of RBPs to optimize the cardiac load control. To develop future control algorithms, the concept of high speed during diastole having a maximal unloading effect on the LV and high speed during systole increasing the pulse pressure is worth considering.
    European journal of cardio-thoracic surgery: official journal of the European Association for Cardio-thoracic Surgery 06/2012; 43(2). DOI:10.1093/ejcts/ezs299 · 2.81 Impact Factor

Publication Stats

425 Citations
112.65 Total Impact Points

Institutions

  • 2009–2015
    • Universität Bern
      Berna, Bern, Switzerland
  • 2006–2011
    • Carnegie Mellon University
      • Department of Biomedical Engineering
      Pittsburgh, Pennsylvania, United States
    • Leiden University
      Leyden, South Holland, Netherlands
  • 2008–2009
    • University of Pittsburgh
      • Division of Cardiac Surgery
      Pittsburgh, Pennsylvania, United States
  • 2001–2005
    • Ghent University
      • Institute of Biomedical Technology
      Gent, VLG, Belgium