ORCID Profile
0000-0002-5448-1917
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Design Practice and Management | Design Innovation | Digital and Interaction Design
Computer Hardware and Electronic Equipment not elsewhere classified | Expanding Knowledge in Engineering |
Publisher: Elsevier
Date: 2018
Publisher: Springer Science and Business Media LLC
Date: 07-03-2015
DOI: 10.1007/S10877-015-9685-8
Abstract: Non-invasive cardiac output monitoring techniques provide high yield, low risk mechanisms to identify and in idually treat shock in the emergency setting. The non-invasive ultrasonic cardiac output monitoring (USCOM) device uses an ultrasound probe applied externally to the chest however limitations exist with previous validation strategies. This study presents the in vitro validation of the USCOM device against calibrated flow sensors and compares user variability in simulated healthy and septic conditions. A validated mock circulation loop was used to simulate each condition with a range of cardiac outputs (2-10 l/min) and heart rates (50-95 bpm). Three users with varying degrees of experience using the USCOM device measured cardiac output and heart rate by placing the ultrasound probe on the mock aorta. Users were blinded to the condition, heart rate and cardiac output which were randomly generated. Results were reported as linear regression slope (β). All users estimated heart rate in both conditions with reasonable accuracy (β = 0.86-1.01), while cardiac output in the sepsis condition was estimated with great precision (β = 1.03-1.04). Users generally overestimated the cardiac output in the healthy simulation (β = 1.07-1.26) and reported greater difficulty estimating reduced cardiac output compared with higher values. Although there was some variability between users, particularly in the healthy condition (P < 0.01), all estimations were within a clinically acceptable range. In this study the USCOM provided a suitable measurement of cardiac output and heart rate when compared with our in vitro system. It is a promising technique to assist with the identification and treatment of shock.
Publisher: Wiley
Date: 25-05-2012
DOI: 10.1111/J.1525-1594.2012.01457.X
Abstract: A clinically intuitive physiologic controller is desired to improve the interaction between implantable rotary blood pumps and the cardiovascular system. This controller should restore the Starling mechanism of the heart, thus preventing overpumping and underpumping scenarios plaguing their implementation. A linear Starling-like controller for pump flow which emulated the response of the natural left ventricle (LV) to changes in preload was then derived using pump flow pulsatility as the feedback variable. The controller could also adapt the control line gradient to accommodate longer-term changes in cardiovascular parameters, most importantly LV contractility which caused flow pulsatility to move outside predefined limits. To justify the choice of flow pulsatility, four different pulsatility measures (pump flow, speed, current, and pump head pressure) were investigated as possible surrogates for LV stroke work. Simulations using a validated numerical model were used to examine the relationships between LV stroke work and these measures. All were approximately linear (r(2) (mean ± SD) = 0.989 ± 0.013, n = 30) between the limits of ventricular suction and opening of the aortic valve. After aortic valve opening, the four measures differed greatly in sensitivity to further increases in LV stroke work. Pump flow pulsatility showed more correspondence with changes in LV stroke work before and after opening of the aortic valve and was least affected by changes in the LV and right ventricular (RV) contractility, blood volume, peripheral vascular resistance, and heart rate. The system (flow pulsatility) response to primary changes in pump flow was then demonstrated to be appropriate for stable control of the circulation. As medical practitioners have an instinctive understanding of the Starling curve, which is central to the synchronization of LV and RV outputs, the intuitiveness of the proposed Starling-like controller will promote acceptance and enable rational integration into patterns of hemodynamic management.
Publisher: Elsevier BV
Date: 08-2019
Publisher: Informa UK Limited
Date: 03-2010
DOI: 10.1057/JOS.2009.15
Publisher: Springer Science and Business Media LLC
Date: 23-07-2019
DOI: 10.1007/S10439-019-02303-3
Abstract: Ventricular Assist Devices (VADs) provide continuous mechanical circulatory support during in- and out-of-hospital care. However, limitations of the external wearable components influence patient quality of life. There is insufficient understanding of the issues with such components that combines a holistic viewpoint from both human factors and user (including patient and caregiver) experience perspectives. This paper comprehensively details the issues with VAD wearable systems and proposes a way for human-centered design to bridge the gap, addressing such issues synergistically. Through the review the authors investigated: the user issues caused by wearable components of VADs, and how human factors issues correlate to the VAD user experience. A Boolean search ("ventricular assist" AND "human factors" AND "experience") for peer-reviewed studies published between 2008 and 2018 returned 338 titles, with 35 relevant studies selected using a PRISMA process for inclusion in cross-study analysis and synthesis. This paper provides design recommendations for the issues found in the literature. Four key focus areas to inform the future design of VAD wearable components were identified-'Power Supply', 'Wearability and Travel Freedom', 'The Female Experience' and 'Intuitive Handling'. Using design to drive innovation could result in VAD wearable components which better meet or exceed users' quality of life goals.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2018
Publisher: Wiley
Date: 16-06-2017
DOI: 10.1111/AOR.12919
Abstract: Rotary blood pumps (RBPs) are used for mechanical circulatory support in heart failure patients but exhibit a reduced response to preload changes, which can lead to ventricular suction events. A passive control system, in the form of a compliant inflow cannula (IC), has been developed to mitigate suction, although this device may cause significant hemolysis. This study compared the incidence of mechanically induced hemolysis of two compliant IC designs (strutted and nonstrutted) with a rigid IC (control) in a blood circulation loop over 90 min. The nonstrutted compliant IC introduced high frequency and high litude oscillations in RBP inlet pressure and RBP IC resistance. These oscillations were correlated with a significant increase in plasma-free hemoglobin (pfHb) and hemolysis: pfHb increased to 2.005 ± 0.665 g/L, while normalized index of hemolysis (NIH) and modified index of hemolysis (MIH) increased to 0.04945 ± 0.01276 g/100 L and 4.0505 ± 0.6589 after 90 min (P < 0.05). In contrast, the strutted compliant IC performed similar to the clinically utilized rigid IC and did not increase pfHb (0.300 ± 0.090 and 0.320 ± 0.171 g/L, respectively) and rate of hemolysis (NIH 0.00435 ± 0.00155 and 0.00543 ± 0.00371 g/100 L MIH 0.3896 ± 0.1749 and 0.4261 ± 0.2792, respectively) within the RBP circuit. These data indicated that strutted, compliant ICs meet the hemocompatibility of clinically used rigid ICs while also offering a potential solution to prevent ventricular suction events.
Publisher: Springer Science and Business Media LLC
Date: 15-07-2015
DOI: 10.1007/S10439-015-1388-2
Abstract: As a left ventricular assist device is designed to pump against the systemic vascular resistance (SVR), pulmonary congestion may occur when using such device for right ventricular support. The present study evaluates the efficacy of using a fixed right outflow banding in patients receiving biventricular assist device support under various circulatory conditions, including variations in the SVR, pulmonary vascular resistance (PVR), total blood volume (BV), as well as ventricular contractility. Effect of speed variation on the hemodynamics was also evaluated at varying degrees of PVR. Pulmonary congestion was observed at high SVR and BV. A reduction in right ventricular assist device (RVAD) speed was required to restore pulmonary pressures. Meanwhile, at a high PVR, the risk of ventricular suction was prevalent during systemic hypotension due to low SVR and BV. This could be compensated by increasing RVAD speed. Isolated right heart recovery may aggravate pulmonary congestion, as the failing left ventricle cannot accommodate the resultant increase in the right-sided flow. Compared to partial assistance, the sensitivity of the hemodynamics to changes in VAD speed increased during full assistance. In conclusion, our results demonstrated that the introduction of a banding graft with a 5 mm diameter guaranteed sufficient reserve of the pump speed spectrum for the regulation of acceptable hemodynamics over different clinical scenarios, except under critical conditions where drug administration or volume management is required.
Publisher: IEEE
Date: 12-2017
Publisher: Wiley
Date: 10-2018
DOI: 10.1111/AOR.13361
Publisher: Springer Science and Business Media LLC
Date: 08-07-2011
DOI: 10.1007/S10439-011-0348-8
Abstract: The optimal treatment option for end stage heart failure is transplantation however, the shortage of donor organs necessitates alternative treatment strategies such as mechanical circulatory assistance. Ventricular assist devices (VADs) are employed to support these cases while awaiting cardiac recovery or transplantation, or in some cases as destination therapy. While left ventricular assist device (LVAD) therapy alone is effective in many instances, up to 50% of LVAD recipients demonstrate clinically significant postoperative right ventricular failure and potentially need a biventricular assist device (BiVAD). In these cases, the BiVAD can effectively support both sides of the failing heart. This article presents a technical review of BiVADs, both clinically applied and under development. The BiVADs which have been used clinically are predominantly first generation, pulsatile, and paracorporeal systems that are bulky and prone to device failure, thrombus formation, and infection. While they have saved many lives, they generally necessitate a large external pneumatic driver which inhibits normal movement and quality of life for many patients. In an attempt to alleviate these issues, several smaller, implantable second and third generation devices that use either immersed mechanical blood bearings or hydrodynamic/magnetic levitation systems to support a rotating impeller are under development or in the early stages of clinical use. Although these rotary devices may offer a longer term, completely implantable option for patients with biventricular failure, their control strategies need to be refined to compete with the inherent volume balancing ability of the first generation devices. The BiVAD systems potentially offer an improved quality of life to patients with total heart failure, and thus a viable alternative to heart transplantation is anticipated with continued development.
Publisher: Wiley
Date: 06-06-2019
DOI: 10.1002/JBM.B.34428
Abstract: The interface between synthetic percutaneous devices and skin is a common area for bacterial infection, which may ultimately result in failure of the device. Better integration of percutaneous devices with skin may help reduce infection rates due to the creation of a dermal seal. However, the mismatch in material and chemical properties of devices and skin presents a challenge for closing the dermal gap at the skin-device interface. Here, we have used a tissue engineering approach to tissue integration by creating a highly fibrous poly(ε-caprolactone) scaffold using melt electrowriting and seeding this with dermal fibroblasts, followed by maturation and insertion into a full-thickness defect made in an ex vivo skin model. The integration of seeded scaffolds was compared with controls including a non-seeded scaffold and a polymer tube with a smooth surface. Dermal fibroblast inclusion in the scaffold and epidermal upgrowth versus downgrowth/marsupialization around the device were used as measures of integration. Based on these measures, almost all pre-seeded scaffolds performed better than both the non-seeded scaffolds and smooth tubes. The hypothesis is that the fibroblasts act as a barrier to epithelial downward migration, and provide healthy tissue for nascent epidermal development.
Publisher: Wiley
Date: 03-02-2022
DOI: 10.1111/AOR.14179
Abstract: Venoarterial extracorporeal membrane oxygenation (ECMO) provides mechanical support for critically ill patients with cardiogenic shock. Typically, the size of the arterial return cannula is chosen to maximize flow. However, smaller arterial cannulae may reduce cannula‐related complications and be easier to insert. This in vitro study quantified the hemodynamic effect of different arterial return cannula sizes in a simulated acute heart failure patient. Baseline support levels were simulated with a 17 Fr arterial cannula in an ECMO circuit attached to a cardiovascular simulator with targeted partial (2.0 L/min ECMO flow, 60–65 mm Hg mean aortic pressure—MAP) and targeted full ECMO support (3.5 L/min ECMO flow and 70–75 mm Hg MAP). Return cannula size was varied (13–21 Fr), and hemodynamics were recorded while keeping ECMO pump speed constant and adjusting pump speed to restore desired support levels. Minimal differences in hemodynamics were found between cannula sizes in partial support mode. A maximum pump speed change of +600 rpm was required to reach the support target, and arterial cannula inlet pressure varied from 79 (21 Fr) to 224 mm Hg (13 Fr). The 15 Fr arterial cannula could provide the target full ECMO support at the targeted hemodynamics however, the 13 Fr cannula could not due to the high resistance associated with the small diameter. A 15 Fr arterial return cannula provided targeted partial and full ECMO support to a simulated acute heart failure patient. Balancing reduced cannula size and ECMO support level may improve patient outcomes by reducing cannula‐related adverse events.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 07-2022
DOI: 10.1097/MAT.0000000000001593
Abstract: Tissue-mimicking materials (TMMs) have been investigated and used for decades as imaging phantoms in various medical applications. They are designed and fabricated to replicate certain biological tissue characteristics, a process often dictated by the target application. Moreover, TMMs have been utilized in some medical procedural training requiring the use of imaging modalities. One potential application for TMMs is ultrasound-guided cannulation training. Cannulation is a procedure that requires a level of dexterity to gain vascular access using ultrasound guidance while avoiding complications like vessel laceration and bleeding. However, an ideal phantom for this application is yet to be developed. This work investigates the development and characterization of high-fidelity phantoms for cannulation training. The mechanical (shore hardness, elastic modulus, and needle-interaction forces) and acoustic (B-mode ultrasound scans) properties of candidate materials were quantitatively compared with biological tissue. The evaluated materials included ballistic gel, plasticized polyvinyl chloride (PVC), silicone, gelatin, agar, and polyvinyl alcohol (PVA)- cryogel. Mechanical testing demonstrated that each material could replicate the Shore hardness and elasticity characteristics of different biological tissues (skin, fat, and muscle), with PVA and PVC showing tunability by varying composition or fabrication processes. Shore hardness (OO-range) for PVA ranged between 6.3 ± 1.0 to 59.3 ± 2.6 and PVC from 4.8 ± 0.7 to 14.6 ± 0.8. Ultrasound scans of PVA were the closest to human scans, both qualitatively (based on experts’ opinion) and quantitatively (based on pixel intensity measurements). Modified mixtures of PVA are found to best serve as high-fidelity cannulation phantoms. Alternatively, PVC can be used to avoid troublesome fabrication processes of PVA.
Publisher: Wiley
Date: 09-2014
DOI: 10.1111/AOR.12395
Abstract: It has been shown that left ventricular assist devices (LVADs) increase the survival rate in end-stage heart failure patients. However, there is an ongoing demand for an increased quality of life, fewer adverse events, and more physiological devices. These challenges necessitate new approaches during the design process. In this study, computational fluid dynamics (CFD), lumped parameter (LP) modeling, mock circulatory loops (MCLs), and particle image velocimetry (PIV) are combined to develop a numerical Pump Testing Framework (nPTF) capable of analyzing local flow patterns and the systemic response of LVADs. The nPTF was created by connecting a CFD model of the aortic arch, including an LVAD outflow graft to an LP model of the circulatory system. Based on the same geometry, a three-dimensional silicone model was crafted using rapid prototyping and connected to an MCL. PIV studies of this setup were performed to validate the local flow fields (PIV) and the systemic response (MCL) of the nPTF. After validation, different outflow graft positions were compared using the nPTF. Both the numerical and the experimental setup were able to generate physiological responses by adjusting resistances and systemic compliance, with mean aortic pressures of 72.2-132.6 mm Hg for rotational speeds of 2200-3050 rpm. During LVAD support, an average flow to the distal branches (cerebral and subclavian) of 24% was found in the experiments and the nPTF. The flow fields from PIV and CFD were in good agreement. Numerical and experimental tools were combined to develop and validate the nPTF, which can be used to analyze local flow fields and the systemic response of LVADs during the design process. This allows analysis of physiological control parameters at early development stages and may, therefore, help to improve patient outcomes.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2016
Publisher: IEEE
Date: 08-2011
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 15-02-2022
DOI: 10.1097/MAT.0000000000001669
Abstract: Veno-venous extracorporeal membrane oxygenation (VV-ECMO) supports patients with severe respiratory failure not responding to conventional treatments. Single-site jugular venous cannulation with dual-lumen cannulas (DLC) have several advantages over traditional single-lumen cannulas, however, bleeding and thrombosis are common, limiting their clinical utility. This study numerically investigated the effects of DLC side holes on blood flow dynamics since the maximum wall shear stress (WSS) occurs around the side holes. A DLC based on the Avalon Elite 27Fr model was implanted into an idealized 3D model of the vena cava and right atrium (RA). Eight DLCs were developed by changing the number, diameter, and spacing of side holes through an iterative design process. Physiologic flow at the inferior vena cava (IVC) and superior vena cava (SVC) were applied along with a partial ECMO support of 2 L/min. The SST k-ω turbulent model was solved for 6.4 seconds. WSS, washout, stagnation volume, and recirculation were compared. For all DLCs, no stasis region lasted more than one cardiac cycle and a complete washout was obtained in less than 4 seconds. Due to the IVC and SVC backflows, maximum WSS occurred around the DLC side holes at late systole and late diastole. A DLC with 16 and three side holes within the IVC and SVC, respectively, reduced the maximum WSS by up to 67% over the Avalon Elite 27Fr. Improved DLCs provided a more uniform WSS distribution with lower WSS around the side holes, potentially reducing the chance of thrombosis and bleeding.
Publisher: Hindawi Limited
Date: 2017
DOI: 10.1155/2017/4907898
Abstract: Objectives . Transthoracic echocardiography (TTE) is fundamental in managing patients supported with ventricular assist devices (VAD). However imaging can be difficult in these patients. Contrast improves image quality but they are hydrodynamically fragile agents. The aim was to assess contrast concentration following passage through a VAD utilising a mock circulation loop (MCL). Methods . Heartware continuous flow (CF) VAD was incorporated into a MCL. Definity® contrast was infused into the MCL with imaging before and after CF-VAD. 5 mm 2 regions of interest were used to obtain signal intensity (decibels), as a surrogate of contrast concentration. Results . Four pump speeds revealed significant reduction in contrast signal intensity after CF-VAD compared to before CF-VAD (all p 0.0001 ). Combined pre- and postpump data at all speeds showed a 22.2% absolute reduction in contrast signal intensity across the CF-VAD (14.8 ± 0.8 dB prepump versus 11.6 ± 1.4 dB postpump p 0.0001 ). Mean signal intensity reduction at each speed showed an inverse relationship between speed and relative reduction in signal intensity. Conclusion . Contrast microsphere transit through a CF-VAD within a MCL resulted in significant reduction in signal intensity, consistent with destruction within the pump. This was evident at all CF-VAD pump speeds but relative signal drop was inversely proportional to pump speed.
Publisher: Springer Science and Business Media LLC
Date: 12-2016
Publisher: ASME International
Date: 17-01-2018
DOI: 10.1115/1.4038429
Abstract: Rotary blood pumps (RBPs) used for mechanical circulatory support of heart failure patients cannot passively change pump flow sufficiently in response to frequent variations in preload induced by active postural changes. A physiological control system that mimics the response of the healthy heart is needed to adjust pump flow according to patient demand. Thus, baseline data are required on how the healthy heart and circulatory system (i.e., heart rate (HR) and cardiac output (CO)) respond. This study investigated the response times of the healthy heart during active postural changes (supine-standing-supine) in 50 healthy subjects (27 male/23 female). Early response times (te) and settling times (ts) were calculated for HR and CO from data continuously collected with impedance cardiography. The initial circulatory response of HR and CO resulted in te of 9.0–11.7 s when standing up and te of 4.7–5.7 s when lying back down. Heart rate and CO settled in ts of 50.0–53.6 s and 46.3–58.2 s when standing up and lying down, respectively. In conclusion, when compared to active stand up, HR and CO responded significant faster initially when subjects were lying down (p 0.05) there were no significant differences in response times between male and female subjects. These data will be used during evaluation of physiological control systems for RBPs, which may improve patient outcomes for end-stage heart failure patients.
Publisher: IEEE
Date: 08-2014
Publisher: Wiley
Date: 25-07-2019
DOI: 10.1111/AOR.13510
Abstract: Rotary ventricular assist devices (VADs) operated clinically under constant speed control (CSC) cannot respond adequately to changes in patient cardiac demand, resulting in sub-optimal VAD flow regulation. Starling-like control (SLC) of VADs mimics the healthy ventricular flow regulation and automatically adjusts VAD speed to meet varying patient cardiac demand. The use of a fixed control line (CL - the relationship between ventricular preload and VAD flow) limits the flow regulating capability of the controller, especially in the case of exercise. Adaptive SLC (ASLC) overcomes this limitation by allowing the controller to adapt the CL to meet a erse range of circulatory conditions. This study evaluated ASLC, SLC and CSC in a biventricular supported mock circulation loop under the simulated conditions of exercise, sleep, fluid loading and systemic hypertension. Each controller was evaluated on its ability to remain within predefined limits of VAD flow, preload, and afterload. The ASLC produced superior cardiac output (CO) during exercise (10.1 L/min) compared to SLC (7.3 L/min) and CSC (6.3 L/min). The ASLC produced favourable haemodynamics during sleep, fluid loading and systemic hypertension and could remain within a predefined haemodynamic range in three out of four simulations, suggesting improved haemodynamic performance over SLC and CSC.
Publisher: Elsevier
Date: 2018
Publisher: Wiley
Date: 03-02-2020
DOI: 10.1111/AOR.13636
Abstract: Controlled and repeatable in vitro evaluation of cardiovascular devices using a mock circulation loop (MCL) is essential prior to in vivo or clinical trials. MCLs often consist of only a systemic circulation with no autoregulatory responses and limited validation. This study aimed to develop, and validate against human data, an advanced MCL with systemic, pulmonary, cerebral, and coronary circulations with autoregulatory responses. The biventricular MCL was constructed with pneumatically controlled hydraulic circulations with Starling responsive ventricles and autoregulatory cerebral and coronary circulations. Hemodynamic repeatability was assessed and complemented by validation using impedance cardiography data from 50 healthy humans. The MCL successfully simulated patient scenarios including rest, exercise, and left heart failure with and without cardiovascular device support. End-systolic pressure-volume relationships for respective healthy and heart failure conditions had slopes of 1.27 and 0.54 mm Hg mL
Publisher: Public Library of Science (PLoS)
Date: 17-02-2017
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 21-02-2023
Abstract: In patients with aortic stenosis (AS), the presence of mitral regurgitation (MR) can lead to underestimation of AS severity and worse clinical outcomes. The objective of this study was to characterize the magnitude of the effects of concomitant MR on hemodynamic indicators of AS severity using clinical data and a computational cardiovascular simulation. Echocardiographic data from 1427 patients with severe AS were used to inform a computational cardiovascular system model, and varying degrees of MR and AS were simulated. Hemodynamic data, including left ventricular and aortic pressure waveforms, were generated for all simulations. Simulated reduction in mean transaortic pressure gradient (MPG) associated with MR was then used to calculate the adjusted MPG in the clinical cohort. MR was present in 861 (60%) patients. Compared with patients without MR, patients with MR had a lower aortic‐valve area (0.83±0.2 cm 2 versus 0.75±0.2 P .001) and were more likely to have a low‐gradient pattern (MPG mm Hg) (45% versus 54% P .001). Simulations showed that the presence of concomitant mild, moderate, and severe MR with AS was accompanied by a mean reduction in MPG of 10%, 29%, and 40%, respectively. For patients with MR, their calculated adjusted MPG was on average 24% higher than their MPG (52±22 versus 42±16 mm Hg). Of the 467 patients with low‐gradient AS and MR, 240 (51%) would reclassify as high gradient based on their adjusted MPG. Concomitant MR results in lower MPG and reduced forward flow compared with isolated AS. Careful quantitation of MR should be factored into the assessment of AS severity to mitigate for potential underestimation.
Publisher: Wiley
Date: 08-2013
DOI: 10.1111/AOR.12143
Abstract: Aortic insufficiency (AI) is usually repaired prior to rotary blood pump (RBP) implantation but can develop during support due, in part, to the sustained RBP-induced high pressure gradient across the aortic valve. Repair of the aortic valve before or during RBP support predisposes these critically ill patients to even higher risks. This study used an in vitro mock circulation loop to identify the severity of AI and/or left heart failure (LHF) that might benefit from valve repair while investigating RBP operating strategies to reduce the hemodynamic influence of AI. Reproduction of AI with RBP-supported LHF reduced device efficiency, particularly in the more severe cases of AI and LHF. The requirement for repair or closure of the aortic valve was demonstrated in all conditions other than those with only mild AI. When a sinusoidal RBP speed pulse was induced, small changes in systemic flow rate and regurgitant volume were observed with all degrees of AI. Variation of the pulse phase delay only resulted in minor changes to systemic flow rate, with a maximum difference of 0.17 L/min. Although the clinical implications of these small changes may be insignificant, changes in systemic flow rate and transvalvular pressure were shown when the sinusoidal RBP speed pulse was applied with no AI. In these cases, transvalvular pressure was reduced by up to 8% through sinusoidal copulsation of the RBP, which may prevent or delay the onset of AI. This in vitro study suggests that surgical intervention is required with moderate or worse AI and that RBP operating strategies should be further explored to delay the onset and reduce the harmful effects of AI.
Publisher: Informa UK Limited
Date: 2009
DOI: 10.1080/03091900802184072
Abstract: Mock circulation loops are used to evaluate the performance of cardiac assist devices prior to animal and clinical testing. A compressible, translucent silicone ventricle chamber that mimics the exact size, shape and motion of a failing heart is desired to assist in flow visualization studies around inflow cannulae during VAD support. The aim of this study was therefore to design and construct a naturally shaped flexible left ventricle and evaluate its performance in a mock circulation loop. The ventricle shape was constructed by the use of CT images taken from a patient experiencing cardiomyopathic heart failure and used to create a 3D image and subsequent mould to produce a silicone ventricle. Different cardiac conditions were successfully simulated to validate the ventricle performance, including rest, left heart failure and VAD support.
Publisher: Hindawi Limited
Date: 2014
DOI: 10.1155/2014/468309
Abstract: Animal models of critical illness are vital in biomedical research. They provide possibilities for the investigation of pathophysiological processes that may not otherwise be possible in humans. In order to be clinically applicable, the model should simulate the critical care situation realistically, including anaesthesia, monitoring, s ling, utilising appropriate personnel skill mix, and therapeutic interventions. There are limited data documenting the constitution of ideal technologically advanced large animal critical care practices and all the processes of the animal model. In this paper, we describe the procedure of animal preparation, anaesthesia induction and maintenance, physiologic monitoring, data capture, point-of-care technology, and animal aftercare that has been successfully used to study several novel ovine models of critical illness. The relevant investigations are on respiratory failure due to smoke inhalation, transfusion related acute lung injury, endotoxin-induced proteogenomic alterations, haemorrhagic shock, septic shock, brain death, cerebral microcirculation, and artificial heart studies. We have demonstrated the functionality of monitoring practices during anaesthesia required to provide a platform for undertaking systematic investigations in complex ovine models of critical illness.
Publisher: Wiley
Date: 29-04-2013
DOI: 10.1111/AOR.12067
Abstract: Right heart dysfunction is one of the most serious complications following implantation of a left ventricular assist device, often leading to the requirement for short- or long-term right ventricular assist device (RVAD) support. The inflow cannulation site induces major hemodynamic changes and so there is a need to optimize the site used depending on the patient's condition. Therefore, this study evaluated and compared the hemodynamic influence of right atrial cannulation (RAC) and right ventricular cannulation (RVC) inflow sites. An in vitro variable heart failure mock circulation loop was used to compare RAC and RVC in mild and severe biventricular heart failure (BHF) conditions. In the severe BHF condition, higher ventricular ejection fraction (RAC: 13.6%, RVC: 32.7%) and thus improved heart chamber and RVAD washout were observed with RVC, which suggested this strategy might be preferable for long-term support (i.e., bridge-to-transplant or destination therapy) to reduce the risk of thrombus formation. In the mild BHF condition, higher pulmonary valve flow (RAC: 3.33 L/min, RVC: 1.97 L/min) and lower right ventricular stroke work (RAC: 0.10 W, RVC: 0.13 W) and volumes were recorded with RAC. These results indicate an improved potential for myocardial recovery, thus RAC should be chosen in this condition. This in vitro study suggests that RVAD inflow cannulation site should be chosen on a patient-specific basis with a view to the support strategy to promote myocardial recovery or reduce the risk of long-term complications.
Publisher: IEEE
Date: 07-2018
Publisher: Wiley
Date: 05-03-2013
DOI: 10.1111/AOR.12060
Abstract: Successful anatomic fitting of a total artificial heart (TAH) is vital to achieve optimal pump hemodynamics after device implantation. Although many anatomic fitting studies have been completed in humans prior to clinical trials, few reports exist that detail the experience in animals for in vivo device evaluation. Optimal hemodynamics are crucial throughout the in vivo phase to direct design iterations and ultimately validate device performance prior to pivotal human trials. In vivo evaluation in a sheep model allows a realistically sized representation of a smaller patient, for which smaller third-generation TAHs have the potential to treat. Our study aimed to assess the anatomic fit of a single device rotary TAH in sheep prior to animal trials and to use the data to develop a three-dimensional, computer-aided design (CAD)-operated anatomic fitting tool for future TAH development. Following excision of the native ventricles above the atrio-ventricular groove, a prototype TAH was inserted within the chest cavity of six sheep (28-40 kg). Adjustable rods representing inlet and outlet conduits were oriented toward the center of each atrial chamber and the great vessels, with conduit lengths and angles recorded for future analysis. A three-dimensional, CAD-operated anatomic fitting tool was then developed, based on the results of this study, and used to determine the inflow and outflow conduit orientation of the TAH. The mean diameters of the sheep left atrium, right atrium, aorta, and pulmonary artery were 39, 33, 12, and 11 mm, respectively. The center-to-center distance and outer-edge-to-outer-edge distance between the atria, found to be 39 ± 9 mm and 72 ± 17 mm in this study, were identified as the most critical geometries for successful TAH connection. This geometric constraint restricts the maximum separation allowable between left and right inlet ports of a TAH to ensure successful alignment within the available atrial circumference.
Publisher: Springer Science and Business Media LLC
Date: 03-2016
DOI: 10.1007/S10439-016-1579-5
Abstract: Mitral valve regurgitation (MVR) is common in patients receiving left ventricular assist device (LVAD) support, however the haemodynamic effect of MVR is not entirely clear. This study evaluated the haemodynamic effect of MVR with LVAD support and the influence of inflow cannulation site and LVAD speed modulation. Left atrial (LAC) and ventricular (LVC) cannulation was evaluated in a mock circulation loop with no, mild, moderate and severe MVR with constant speed and speed modulation (±600 RPM) modes. The use of an LVAD relieved pulmonary congestion during severe MVR, by reducing left atrial pressure from 20.5 to 10.8 (LAC) and 11.5 (LVC) mmHg. However, LAC resulted in decreased left ventricular stroke work (-0.08 J), ejection fraction (-7.9%) and higher MVR volume (+12.7 mL) and pump speed (+100 RPM) compared to LVC. This suggests that LVC, in addition to reducing MVR severity, also improves ventricular washout over LAC. LVAD speed modulation in synchrony with ventricular systole reduced MVR volume and increased ejection fraction with LAC and LVC, thus demonstrating the potential benefits of this mode, despite a reduction in cardiac output.
Publisher: Walter de Gruyter GmbH
Date: 2016
Abstract: Direct write melt electrospinning is an additive manufacturing technique used to produce 3D polymer scaffolds for tissue engineering applications. It is similar to conventional 3D printing by layering 2D patterns to build up an object, but uses a high-electric potential to draw out fibres into micron-scale diameters with great precision. Direct write melt electrospinning is related to a well-established fabrication technique, solution electrospinning, but extrudes a melted polymer in a controlled manner rather than a polymer solution. The effect of environmental conditions such as humidity has been extensively studied in the context of solution electrospinning however, there is a lack of similar studies for direct write melt electrospinning. In this study, melt electrospun polycaprolactone scaffolds were produced with 90 degree cross-hatch architecture at three specific humidity [
Publisher: Wiley
Date: 08-01-2016
DOI: 10.1111/AOR.12654
Abstract: Preventing ventricular suction and venous congestion through balancing flow rates and circulatory volumes with dual rotary ventricular assist devices (VADs) configured for biventricular support is clinically challenging due to their low preload and high afterload sensitivities relative to the natural heart. This study presents the in vivo evaluation of several physiological control systems, which aim to prevent ventricular suction and venous congestion. The control systems included a sensor-based, master/slave (MS) controller that altered left and right VAD speed based on pressure and flow a sensor-less compliant inflow cannula (IC), which altered inlet resistance and, therefore, pump flow based on preload a sensor-less compliant outflow cannula (OC) on the right VAD, which altered outlet resistance and thus pump flow based on afterload and a combined controller, which incorporated the MS controller, compliant IC, and compliant OC. Each control system was evaluated in vivo under step increases in systemic (SVR ∼1400-2400 dyne/s/cm(5) ) and pulmonary (PVR ∼200-1000 dyne/s/cm(5) ) vascular resistances in four sheep supported by dual rotary VADs in a biventricular assist configuration. Constant speed support was also evaluated for comparison and resulted in suction events during all resistance increases and pulmonary congestion during SVR increases. The MS controller reduced suction events and prevented congestion through an initial sharp reduction in pump flow followed by a gradual return to baseline (5.0 L/min). The compliant IC prevented suction events however, reduced pump flows and pulmonary congestion were noted during the SVR increase. The compliant OC maintained pump flow close to baseline (5.0 L/min) and prevented suction and congestion during PVR increases. The combined controller responded similarly to the MS controller to prevent suction and congestion events in all cases while providing a backup system in the event of single controller failure.
Publisher: Wiley
Date: 09-07-2015
DOI: 10.1111/AOR.12338
Abstract: Biventricular support with dual rotary ventricular assist devices (VADs) has been implemented clinically with restriction of the right VAD (RVAD) outflow cannula to artificially increase afterload and, therefore, operate within recommended design speed ranges. However, the low preload and high afterload sensitivity of these devices increase the susceptibility of suction events. Active control systems are prone to sensor drift or inaccurate inferred (sensor-less) data, therefore an alternative solution may be of benefit. This study presents the in vitro evaluation of a compliant outflow cannula designed to passively decrease the afterload sensitivity of rotary RVADs and minimize left-sided suction events. A one-way fluid-structure interaction model was initially used to produce a design with suitable flow dynamics and radial deformation. The resultant geometry was cast with different initial cross-sectional restrictions and concentrations of a softening diluent before evaluation in a mock circulation loop. Pulmonary vascular resistance (PVR) was increased from 50 dyne s/cm(5) until left-sided suction events occurred with each compliant cannula and a rigid, 4.5 mm diameter outflow cannula for comparison. Early suction events (PVR ∼ 300 dyne s/cm(5) ) were observed with the rigid outflow cannula. Addition of the compliant section with an initial 3 mm diameter restriction and 10% diluent expanded the outflow restriction as PVR increased, thus increasing RVAD flow rate and preventing left-sided suction events at PVR levels beyond 1000 dyne s/cm(5) . Therefore, the compliant, restricted outflow cannula provided a passive control system to assist in the prevention of suction events with rotary biventricular support while maintaining pump speeds within normal ranges of operation.
Publisher: Wiley
Date: 08-2011
DOI: 10.1111/J.1525-1594.2011.01311.X
Abstract: Limited preload sensitivity of rotary left ventricular assist devices (LVADs) renders patients susceptible to harmful atrial or ventricular suction events. Active control systems may be used to rectify this problem however, they usually depend on unreliable sensors or potentially inaccurate inferred data from, for ex le, motor current. This study aimed to characterize the performance of a collapsible inflow cannula reservoir as a passive control system to eliminate suction events in extracorporeal, rotary LVAD support. The reservoir was evaluated in a mock circulation loop against a rigid cannula under conditions of reduced preload and increased LVAD speed in both atrial and ventricular cannulation scenarios. Both cases demonstrated the ease with which chamber suction events can occur with a rigid cannula and confirm that the addition of the reservoir maintained positive chamber volumes with reduced preload and high LVAD speeds. Reservoir performance was dependent on height with respect to the cannulated chamber, with lower placement required in atrial cannulation due to reduced filling pressures. This study concluded that a collapsible inflow cannula is capable of minimizing suction events in extracorporeal, rotary LVAD support.
Publisher: Wiley
Date: 03-05-2018
DOI: 10.1111/AOR.13142
Abstract: Although rotary blood pumps (RBPs) sustain life, blood exposure to continuous supra-physiological shear stress induces adverse effects (e.g., thromboembolism) thus, pulsatile flow in RBPs represents a potential solution. The present study introduced pulsatile flow to the HeartWare HVAD using a custom-built controller and compared hemocompatibility biomarkers (i.e., platelet aggregation, concentrations for ADAMTS13, von Willebrand factor (vWf), and free-hemoglobin in plasma (pfHb), red blood cell (RBC) deformability, and RBC-nitric oxide synthase (NOS) activity) between continuous and pulsatile flow in a blood circulation loop over 5 h. The HeartWare HVAD was operated using a custom-built controller, at continuous speed (3282 rev/min) or in a pulsatile mode (mean speed = 3273 rev/min, litude = 430 rev/min, frequency = 1 Hz) to generate a blood flow rate of 5.0 L/min, HVAD differential pressure of 90 mm Hg for continuous flow and 92 mm Hg for pulsatile flow, and systolic and diastolic pressures of 121/80 mm Hg. For both flow regimes, the current study found (i) ADP- and collagen-induced platelet aggregation, and ADAMTS13 concentration significantly decreased after 5 h (P < 0.01 P < 0.05), (ii) ristocetin-induced platelet aggregation significantly increased after 45 min (P < 0.05), (iii) vWf concentration did not significantly differ at any time point, (iv) pfHb significantly increased after 5 h (P < 0.01), (v) RBC deformability improved during the continuous flow regime (P < 0.05) but not during pulsatile flow, and (vi) RBC-NOS activity significantly increased during continuous flow (15 min), and pulsatile flow (5 h P < 0.05). The current study demonstrated: (i) speed modulation does not improve hemocompatibility of the HeartWare HVAD based on no observable differences being detected for routine biomarkers, and (ii) the time-course for increased RBC-NOS activity observed during continuous flow may have improved RBC deformability.
Publisher: Wiley
Date: 09-2010
DOI: 10.1111/J.1525-1594.2010.01093.X
Abstract: The ventricular assist device inflow cannulation site is the primary interface between the device and the patient. Connecting these cannulae to either atria or ventricles induces major changes in flow dynamics however, there are little data available on precise quantification of these changes. The objective of this investigation was to quantify the difference in ventricular/vascular hemodynamics during a range of left heart failure conditions with either atrial (AC) or ventricular (VC) inflow cannulation in a mock circulation loop with a rotary left VAD. Ventricular ejection fraction (EF), stroke work, and pump flow rates were found to be consistently lower with AC compared with VC over all simulated heart failure conditions. Adequate ventricular ejection remained with AC under low levels of mechanical support however, the reduced EF in cases of severe heart failure may increase the risk of thromboembolic events. AC is therefore more suitable for class III, bridge to recovery patients, while VC is appropriate for class IV, bridge to transplant/destination patients.
Publisher: Elsevier BV
Date: 2018
Publisher: AIP Publishing
Date: 02-2023
DOI: 10.1063/5.0137907
Abstract: Venoarterial extracorporeal membrane oxygenation is a form of artificial heart–lung therapy able to support patients undergoing refractory cardio-respiratory failure. Drainage cannulae are responsible for extracting venous blood from the body via a negative pressure gradient induced by the pump downstream. However, the unique designs of single- and multi-stage cannulae, such as the presence of small inlets on the walls of the cannula (side holes), result in complex flow dynamics. This study evaluated flow features of both cannula designs using a stress blended eddy simulation turbulence model, within a patient-specific geometry of the venous system. The wall-adapted local eddy viscosity subgrid-scale model was used to resolve the large eddies directly in the free stream region, while small eddies were modeled using the k–ω shear stress transport model in the near-wall region. Flow within both cannulae was dominated by turbulent structures, such as counter-rotating vortex pairs, followed by a region of flow separation created by the entering jet. This phenomenon was synonymous with a jet in a crossflow, but involved multiple tandem and opposing jets in an internal tubular environment. The single-stage cannula drained 38% of the total flow via the most proximal holes compared to the multi-stage cannula (52.8%). The single-stage cannula allowed for larger tip velocities and was able to extract more flow from the upper body. Overall, this study demonstrated notable differences in blood flow dynamics between single- and multi-stage cannulae, which can be applied in clinical selection and cannula design.
Publisher: Elsevier BV
Date: 04-2018
DOI: 10.1016/J.JBIOMECH.2018.02.038
Abstract: Left ventricular assist devices are associated with thromboembolic events, which are potentially caused by altered intraventricular flow. Due to patient variability, differences in apical wall thickness affects cannula insertion lengths, potentially promoting unfavourable intraventricular flow patterns which are thought to be correlated to the risk of thrombosis. This study aimed to present a 3D multiscale computational fluid dynamic model of the left ventricle (LV) developed using a commercial software, Ansys, and evaluate the risk of thrombosis with varying inflow cannula insertion lengths in a severely dilated LV. Based on a HeartWare HVAD inflow cannula, insertion lengths of 5, 19, 24 and 50 mm represented cases of apical hypertrophy, typical ranges of apical thicknesses and an experimental length, respectively. The risk of thrombosis was evaluated based on blood washout, residence time, instantaneous blood stagnation and a pulsatility index. By introducing fresh blood to displace pre-existing blood in the LV, after 5 cardiac cycles, 46.7%, 45.7%, 45.1% and 41.8% of pre-existing blood remained for insertion lengths of 5, 19, 24 and 50 mm, respectively. Compared to the 50 mm insertion, blood residence time was at least 9%, 7% and 6% higher with the 5, 19 and 24 mm insertion lengths, respectively. No instantaneous stagnation at the apex was observed directly after the E-wave. Pulsatility indices adjacent to the cannula increased with shorter insertion lengths. For the specific scenario studied, a longer insertion length, relative to LV size, may be advantageous to minimise thrombosis by increasing LV washout and reducing blood residence time.
Publisher: Springer Science and Business Media LLC
Date: 02-2016
DOI: 10.1007/S10439-016-1552-3
Abstract: Rotary left ventricular assist devices (LVADs) show weaker response to preload and greater response to afterload than the native heart. This may lead to ventricular suction or pulmonary congestion, which can be deleterious to the patient's recovery. A physiological control system which optimizes responsiveness of LVADs may reduce adverse events. This study compared eight physiological control systems for LVAD support against constant speed mode. Pulmonary (PVR) and systemic (SVR) vascular resistance changes, a passive postural change and exercise were simulated in a mock circulation loop to evaluate the controller's ability to prevent suction and congestion and to increase exercise capacity. Three active and one passive control systems prevented ventricular suction at high PVR (500 dyne s cm(-5)) and low SVR (600 dyne s cm(-5)) by decreasing LVAD speed (by 200-515 rpm) and by increasing LVAD inflow cannula resistance (up to 1000 dyne s cm(-5)) respectively. These controllers increased LVAD preload sensitivity (to 0.196-2.415 L min(-1) mmHg(-1)) compared to the other control systems and constant speed mode (0.039-0.069 L min(-1) mmHg(-1)). The same three active controllers increased pump speed (600-800 rpm) and thus LVAD flow by 4.5 L min(-1) during exercise which increased exercise capacity. Physiological control systems that prevent adverse events and/or increase exercise capacity may help improve LVAD patient conditions.
Publisher: Wiley
Date: 21-05-2015
DOI: 10.1111/AOR.12497
Abstract: Implantable left ventricular assist devices (LVADs) have been adapted clinically for right-sided mechanical circulatory support (RVAD). Previous studies on RVAD support have established the benefits of outflow cannula restriction and rotational speed reduction, and recent literature has focused on assessing either the degree of outflow cannula restriction required to simulate left-sided afterload, or the limitation of RVAD rotational speeds. Anecdotally, the utility of outflow cannula restriction has been questioned, with suggestion that banding may be unnecessary and may be replaced simply by varying the outflow conduit length. Furthermore, many patients have a high pulmonary vascular resistance (PVR) at the time of ventricular assist device (VAD) insertion that reduces with pulmonary vascular bed remodeling. It is therefore important to assess the potential changes in flow through an RVAD as PVR changes. In this in vitro study, we observed the use of dual HeartWare HVAD devices (HeartWare Inc., Framingham, MA, USA) in biventricular support (BiVAD) configuration. We assessed the pumps' ability to maintain hemodynamic stability with and without banding and with varying outflow cannulae length (20, 40, and 60 cm). Increased length of the outflow conduit was found to produce significantly increased afterload to the device, but this was not found to be necessary to maintain the device within the manufacturer's recommended operational parameters under a simulated normal physiological setting of mild and severe right ventricular (RV) failure. We hypothesize that 40 cm of outflow conduit, laid down along the diaphragm and then up over the RV to reach the pulmonary trunk, will generate sufficient resistance to maintain normal pump function.
Publisher: Wiley
Date: 09-11-2018
DOI: 10.1111/AOR.13342
Abstract: Rotary ventricular assist devices (VADs) are less sensitive to preload than the healthy heart, resulting in inadequate flow regulation in response to changes in patient cardiac demand. Starling-like physiological controllers (SLCs) have been developed to automatically regulate VAD flow based on ventricular preload. An SLC consists of a cardiac response curve (CRC) which imposes a nonlinear relationship between VAD flow and ventricular preload, and a venous return line (VRL) which determines the return path of the controller. This study investigates the importance of a physiological VRL in SLC of dual rotary blood pumps for biventricular support. Two experiments were conducted on a physical mock circulation loop (MCL) the first compared an SLC with an angled physiological VRL (SLC-P) against an SLC with a vertical VRL (SLC-V). The second experiment quantified the benefit of a dynamic VRL, represented by a series of specific VRLs, which could adapt to different circulatory states including changes in pulmonary (PVR) and systemic (SVR) vascular resistance versus a fixed physiological VRL which was calculated at rest. In both sets of experiments, the transient controller responses were evaluated through reductions in preload caused by the removal of fluid from the MCL. The SLC-P produced no overshoot or oscillations following step changes in preload, whereas SLC-V produced 0.4 L/min (12.5%) overshoot for both left and right VADs. Additionally, the SLC-V had increased settling time and reduced controller stability as evidenced by transient controller oscillations. The transient results comparing the specific and standard VRLs demonstrated that specific VRL rise times were improved by between 1.2 and 4.7 s (
Publisher: Wiley
Date: 08-2012
DOI: 10.1111/J.1525-1594.2012.01504.X
Abstract: Rotary ventricular assist device (VAD) support of the cardiovascular system is susceptible to suction events due to the limited preload sensitivity of these devices. This may be of particular concern with rotary biventricular support (BiVAD) where the native, flow balancing Starling response is diminished in both ventricles. The reliability of sensor and sensorless-based control systems which aim to control VAD flow based on preload has limitations, and, thus, an alternative solution is desired. This study introduces a compliant inflow cannula (CIC) which could improve the preload sensitivity of a rotary VAD by passively altering VAD flow depending on preload. To evaluate the design, both the CIC and a standard rigid inflow cannula were inserted into a mock circulation loop to enable biventricular heart failure support using configurations of atrial and ventricular inflow, and arterial outflow cannulation. A range of left (LVAD) and right VAD (RVAD) rotational speeds were tested as well as step changes in systemic ulmonary vascular resistance to alter relative preloads, with resulting flow rates recorded. Simulated suction events were observed, particularly at higher VAD speeds, during support with the rigid inflow cannula, while the CIC prevented suction events under all circumstances. The compliant section passively restricted its internal diameter as preload was reduced, which increased the VAD circuit resistance and thus reduced VAD flow. Therefore, a CIC could potentially be used as a passive control system to prevent suction events in rotary left, right, and biventricular support.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 20-04-2021
DOI: 10.1097/MAT.0000000000001440
Abstract: Thrombosis is a potentially life-threatening complication in veno-arterial extracorporeal membrane oxygenation (ECMO) circuits, which may originate from the drainage cannula due to unfavorable blood flow dynamics. This study aims to numerically investigate the effect of cannula design parameters on local fluid dynamics, and thus thrombosis potential, within ECMO drainage cannulas. A control cannula based on the geometry of a 17 Fr Medtronic drainage cannula concentrically placed in an idealized, rigid-walled geometry of the right atrium and superior and inferior vena cava was numerically modeled. Simulated flow dynamics in the control cannula were systematically compared with 10 unique cannula designs which incorporated changes to side hole diameter, the spacing between side holes, and side hole angles. Local blood velocities, maximum wall shear stress (WSS), and blood residence time were used to predict the risk of thrombosis. Numerical results were experimentally validated using particle image velocimetry. The control cannula exhibited low blood velocities (59 mm/s) at the cannula tip, which may promote thrombosis. Through a reduction in the side hole diameter (2 mm), the spacing between the side holes (3 mm) and alteration in the side hole angle (30° relative to the flow direction), WSS was reduced by 52%, and cannula tip blood velocity was increased by 560% compared to the control cannula. This study suggests that simple geometrical changes can significantly alter the risk of thrombosis in ECMO drainage cannulas.
Publisher: IEEE
Date: 08-2011
Publisher: Wiley
Date: 30-09-2010
DOI: 10.1111/J.1525-1594.2010.01088.X
Abstract: In vitro cardiovascular device performance evaluation in a mock circulation loop (MCL) is a necessary step prior to in vivo testing. A MCL that accurately represents the physiology of the cardiovascular system accelerates the assessment of the device's ability to treat pathological conditions. To serve this purpose, a compact MCL measuring 600 × 600 × 600 mm (L × W × H) was constructed in conjunction with a computer mathematical simulation. This approach allowed the effective selection of physical loop characteristics, such as pneumatic drive parameters, to create pressure and flow, and pipe dimensions to replicate the resistance, compliance, and fluid inertia of the native cardiovascular system. The resulting five-element MCL reproduced the physiological hemodynamics of a healthy and failing heart by altering ventricle contractility, vascular resistance/compliance, heart rate, and vascular volume. The effects of interpatient anatomical variability, such as septal defects and valvular disease, were also assessed. Cardiovascular hemodynamic pressures (arterial, venous, atrial, ventricular), flows (systemic, bronchial, pulmonary), and volumes (ventricular, stroke) were analyzed in real time. The objective of this study is to describe the developmental stages of the compact MCL and demonstrate its value as a research tool for the accelerated development of cardiovascular devices.
Publisher: Elsevier BV
Date: 11-2019
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 15-07-2020
Publisher: Springer Science and Business Media LLC
Date: 18-08-2016
DOI: 10.1007/S10439-015-1425-1
Abstract: The low preload and high afterload sensitivities of rotary ventricular assist devices (VADs) may cause ventricular suction events or venous congestion. This is particularly problematic with rotary biventricular support (BiVAD), where the Starling response is diminished in both ventricles. Therefore, VADs may benefit from physiological control systems to prevent adverse events. This study compares active, passive and combined physiological controllers for rotary BiVAD support with constant speed mode. Systemic (SVR) and pulmonary (PVR) vascular resistance changes and exercise were simulated in a mock circulation loop to evaluate the capacity of each controller to prevent suction and congestion and increase exercise capacity. All controllers prevented suction and congestion at high levels of PVR (900 dynes s cm(-5)) and SVR (3000 dynes s cm(-5)), however these events occurred in constant speed mode. The controllers increased preload sensitivity (0.198-0.34 L min(-1) mmHg(-1)) and reduced afterload sensitivity (0.0001-0.008 L min(-1) mmHg(-1)) of the VADs when compared to constant speed mode (0.091 and 0.072 L min(-1) mmHg(-1) respectively). The active controller increased pump speeds (400-800 rpm) and pump flow by 2.8 L min(-1) during exercise, thus increasing exercise capacity. By reducing suction and congestion and by increasing exercise capacity, the control systems presented in this study may help increase quality of life of VAD patients.
Publisher: Wiley
Date: 13-12-2017
DOI: 10.1111/AOR.13018
Abstract: Implantation of left ventricular assist devices typically requires cardiopulmonary bypass support, which is associated with postoperative complications. A novel suture-less inflow cannula, which can be implanted without bypass, uses mild myocardial compression to seal the interface, however, this may lead to necrosis of the myocardium. To circumvent this issue, a bilayered scaffold has been developed to promote tissue growth at the interface between cannula and myocardium. The bilayered scaffold consists of a silicone base layer, which mimics the seal, and a melt electrospun polycaprolactone scaffold to serve as a tissue integration layer. Biocompatibility of the bilayered scaffolds was assessed by analyzing cell viability, morphology, and metabolic activity of human foreskin fibroblasts cultured on the scaffolds for up to 14 days. There was no evidence of cytotoxicity and the cells adhered readily to the bilayered scaffolds, revealing a cell morphology characteristic of fibroblasts, in contrast to the low cell adhesion observed on flat silicone sheets. The rate of cell proliferation on the bilayered scaffolds rose over the 14-day period and was significantly greater than cells seeded on the silicone sheets. This study suggests that melt electrospun bilayered scaffolds have the potential to support tissue integration of a suture-less inflow cannula for cardiovascular applications. Furthermore, the method of fabrication described here and the application of bilayered scaffolds could also have potential uses in a erse range of biomedical applications.
Publisher: Wiley
Date: 24-03-2014
DOI: 10.1111/AOR.12289
Abstract: Dual rotary left ventricular assist devices (LVADs) have been used clinically to support patients with biventricular failure. However, due to the lower vascular resistance in the pulmonary circulation compared with its systemic counterpart, excessively high pulmonary flow rates are expected if the right ventricular assist device (RVAD) is operated at its design LVAD speed. Three possible approaches are available to match the LVAD to the pulmonary circulation: operating the RVAD at a lower speed than the LVAD (mode 1), operating both pumps at their design speeds (mode 2) while relying on the cardiovascular system to adapt, and operating both pumps at their design speeds while restricting the diameter of the RVAD outflow graft (mode 3). In this study, each mode was characterized using in vitro and in vivo models of biventricular heart failure supported with two VentrAssist LVADs. The effect of each mode on arterial and atrial pressures and flow rates for low, medium, and high vascular resistances and three different contractility levels were evaluated. The amount of speed/diameter adjustment required to accommodate elevated pulmonary vascular resistance (PVR) during support with mode 3 was then investigated. Mode 1 required relatively low systemic vascular resistance to achieve arterial pressures less than 100 mm Hg in vitro, resulting in flow rates greater than 6 L/min. Mode 2 resulted in left atrial pressures above 25 mm Hg, unless left heart contractility was near-normal. In vitro, mode 3 resulted in expected arterial pressures and flow rates with an RVAD outflow diameter of 6.5 mm. In contrast, all modes were achievable in vivo, primarily due to higher RVAD outflow graft resistance (more than 500 dyn·s/cm(5)), caused by longer cannula. Flow rates could be maintained during instances of elevated PVR by increasing the RVAD speed or expanding the outflow graft diameter using an externally applied variable graft occlusion device. In conclusion, suitable hemodynamics could be produced by either restricting or not restricting the right outflow graft diameter however, the latter required an operation of the RVAD at lower than design speed. Adjustments in outflow restriction and/or RVAD speed are recommended to accommodate varying PVR.
Publisher: Wiley
Date: 25-07-2017
DOI: 10.1111/AOR.12962
Abstract: Rotary ventricular assist devices (VADs) are used to provide mechanical circulatory support. However, their lack of preload sensitivity in constant speed control mode (CSC) may result in ventricular suction or venous congestion. This is particularly true of biventricular support, where the native flow-balancing Starling response of both ventricles is diminished. It is possible to model the Starling response of the ventricles using cardiac output and venous return curves. With this model, we can create a Starling-like physiological controller (SLC) for VADs which can automatically balance cardiac output in the presence of perturbations to the circulation. The comparison between CSC and SLC of dual HeartWare HVADs using a mock circulation loop to simulate biventricular heart failure has been reported. Four changes in cardiovascular state were simulated to test the controller, including a 700 mL reduction in circulating fluid volume, a total loss of left and right ventricular contractility, reduction in systemic vascular resistance ( SVR) from 1300 to 600 dyne s/cm5, and an elevation in pulmonary vascular resistance ( PVR) from 100 to 300 dyne s/cm5. SLC maintained the left and right ventricular volumes between 69-214 mL and 29-182 mL, respectively, for all tests, preventing ventricular suction (ventricular volume = 0 mL) and venous congestion (atrial pressures > 20 mm Hg). Cardiac output was maintained at sufficient levels by the SLC, with systemic and pulmonary flow rates maintained above 3.14 L/min for all tests. With the CSC, left ventricular suction occurred during reductions in SVR, elevations in PVR, and reduction in circulating fluid simulations. These results demonstrate a need for a physiological control system and provide adequate in vitro validation of the immediate response of a SLC for biventricular support.
Publisher: Wiley
Date: 25-07-2018
DOI: 10.1111/AOR.12967
Publisher: Wiley
Date: 20-10-2019
DOI: 10.1111/AOR.13570
Abstract: Due to improved durability and survival rates, rotary blood pumps (RBPs) are the preferred left ventricular assist device when compared to volume displacement pumps. However, when operated at constant speed, RBPs lack a volume balancing mechanism which may result in left ventricular suction and suboptimal ventricular unloading. Starling-like controllers have previously been developed to balance circulatory volumes however, they do not consider ventricular workload as a feedback and may have limited sensitivity to adjust RBP workload when ventricular function deteriorates or improves. To address this, we aimed to develop a Starling-like total work controller (SL-TWC) that matched the energy output of a healthy heart by adjusting RBP hydraulic work based on measured left ventricular stroke work and ventricular preload. In a mock circulatory loop, the SL-TWC was evaluated using a HeartWare HVAD in a range of simulated patient conditions. These conditions included changes in systemic hypertension and hypotension, pulmonary hypertension, blood circulatory volume, exercise, and improvement and deterioration of ventricular function by increasing and decreasing ventricular contractility. The SL-TWC was compared to constant speed control where RBP speed was set to restore cardiac output to 5.0 L/min at rest. Left ventricular suction occurred with constant speed control during pulmonary hypertension but was prevented with the SL-TWC. During simulated exercise, the SL-TWC demonstrated reduced LVSW (0.51 J) and greater RBP flow (9.2 L/min) compared to constant speed control (LVSW: 0.74 J and RBP flow: 6.4 L/min). In instances of increased ventricular contractility, the SL-TWC reduced RBP hydraulic work while maintaining cardiac output similar to the rest condition. In comparison, constant speed overworked and increased cardiac output. The SL-TWC balanced circulatory volumes by mimicking the Starling mechanism, while also considering changes in ventricular workload. Compared to constant speed control, the SL-TWC may reduce complications associated with volume imbalances, adapt to changes in ventricular function and improve patient quality of life.
Publisher: Wiley
Date: 11-04-2019
DOI: 10.1111/AOR.13454
Abstract: The high cost of ventricular assist devices results in poor cost-effectiveness when used as a short-term bridging solution, thus a low-cost alternative is desirable. The present study aimed to develop an intraventricular balloon pump (IVBP) for short-term circulatory support, and to evaluate the effect of balloon actuation timing on the degree of cardiac support provided to a simulated in vitro severe heart failure (SHF) patient. A silicone IVBP was designed to avoid contact with internal left ventricular (LV) features (ie, papillary muscles, chordae, aortic, and mitral valves) based on LV computed tomography data of 10 SHF patients with dilated cardiomyopathy. The hemodynamic effects of varying balloon inflation and deflation timing parameters (inflation duty [D] and end-inflation point [σ]) were evaluated in a purpose-built systemic mock circulatory loop. Three IVBP actuation timing categories were defined: co-, transitional, and counterpulsation. Compared to the SHF baseline, co-pulsation increased aortic flow from 3.5 to 5.2 L/min, mean arterial pressure from 72.1 to 94.8 mmHg and ejection fraction from 14.4% to 21.5%, while mean left atrial pressure decreased from 14.6 to 10 mmHg. Transitional and counterpulsation resulted in a double ventricular pulse and extended the duration of increased ventricular pressure, potentially impeding diastolic filling and coronary perfusion. This in vitro study showed the IVBP could restore the hemodynamic balance of a simulated SHF patient with dilated cardiomyopathy to healthy levels.
Publisher: Wiley
Date: 27-09-2018
DOI: 10.1111/AOR.13330
Abstract: Rotary left ventricular assist devices (LVADs) are commonly operated at a constant speed, attenuating blood flow pulsatility. Speed modulation of rotary LVADs has been demonstrated to improve vascular pulsatility and pump washout. The effect of LVAD speed modulation on intraventricular flow dynamics is not well understood, which may have an influence on thromboembolic events. This study aimed to numerically evaluate intraventricular flow characteristics with a speed modulated LVAD. A severely dilated anatomical left ventricle was supported by a HeartWare HVAD in a three-dimensional multiscale computational fluid dynamics model. Three LVAD operating scenarios were evaluated: constant speed and sinusoidal co- and counter-pulsation. In all operating scenarios, the mean pump speed was set to restore the cardiac output to 5.0 L/min. Co- and counter-pulsation was speed modulated with an litude of 750 rpm. The risk of thrombosis was evaluated based on blood residence time, ventricular washout, kinetic energy densities, and a pulsatility index map. Blood residence time for co-pulsation was on average 1.8 and 3.7% lower than constant speed and counter-pulsation mode, respectively. After introducing fresh blood to displace preexisting blood for 10 cardiac cycles, co-pulsation had 1.5% less old blood in comparison to counter-pulsation. Apical energy densities were 84 and 27% higher for co-pulsation in comparison to counter-pulsation and constant speed mode, respectively. Co-pulsation had an increased pulsatility index around the left ventricular outflow tract and mid-ventricle. Improved flow dynamics with co-pulsation was caused by increased E-wave velocities which minimized blood stasis. In the studied scenario and from the perspective of intraventricular flow dynamics, co-pulsation of rotary LVADs could minimize the risk of intraventricular thrombosis.
No related organisations have been discovered for Shaun Gregory.
Start Date: 12-2021
End Date: 12-2024
Amount: $274,933.00
Funder: Australian Research Council
View Funded Activity