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Papers by Nicholas Greatrex

Research paper thumbnail of A compact mock circulation loop for the in vitro testing of cardiovascular devices

Faculty of Built Environment and Engineering Institute of Health and Biomedical Innovation School of Engineering Systems, Sep 1, 2010

Research paper thumbnail of Self-learning fuzzy physiological control of rotary artificial hearts

Research paper thumbnail of Timing of RBP pulsations in relation to the cardiac cycle to improve RBP physiological interaction

Objective: Alterations of impeller speed to induce pulsatility in RBP applications may be physiol... more Objective: Alterations of impeller speed to induce pulsatility in RBP applications may be physiologically beneficial to the patient by improving end organ perfusion. However, the timing of these pulsations in relation to the native cardiac cycle could also influence both ventricle volumes and ...

Research paper thumbnail of Do RBP's have sufficient inherent Frank-Starling like characteristics?: A study of the preload sensitivity of RBPs

Objective: The preload sensitivity of a RBP is an important feature for a device to alter outflow... more Objective: The preload sensitivity of a RBP is an important feature for a device to alter outflow in response to changing patient physiologic conditions, as per the Frank-Starling response of the natural heart. Since RBP's are pre/afterload dependant, a constant afterload and RPM ...

Research paper thumbnail of Monitoring system development for driving condition of a Ventricular assist device by using mobile phone

Procedia - Social and Behavioral Sciences, 2010

ABSTRACT

Research paper thumbnail of Pulsatile operation of the BiVACOR TAH - Motor design, control and hemodynamics

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Although there is limited consensus about the strict requirement to deliver pulsatile perfusion t... more Although there is limited consensus about the strict requirement to deliver pulsatile perfusion to the human circulatory system, speed modulation of rotary blood pumps is an approach that may capture the benefits of both positive displacement and continuous flow blood pumps. In the current stage of development of the BiVACOR Total Artificial Heart emphasis is placed on providing pulsatile outflow from the pump. Multiple pulsatile speed profiles have been applied in preliminary in-vivo operation in order to assess the capability of the TAH to recreate a physiologic pulse. This paper provides an overview about recent research towards pulsatile BiVACOR operation with special emphasis on motor and control requirements and developments.

Research paper thumbnail of Effect of Inflow Cannula Tip Design on Potential Parameters of Blood Compatibility and Thrombosis

Artificial Organs, 2014

During ventricular assist device support, a cannula acts as a bridge between the native cardiovas... more During ventricular assist device support, a cannula acts as a bridge between the native cardiovascular system and a foreign mechanical device. Cannula tip design strongly affects the function of the cannula and its potential for blood trauma. In this study, the flow fields of five different tip geometries within the ventricle were evaluated using stereo particle image velocimetry. Inflow cannulae with conventional tip geometries (blunt, blunt with four side ports, beveled with three side ports, and cage) and a custom-designed crown tip were interposed between a mixed-flow rotary blood pump and a compressible, translucent silicone left ventricle. The contractile function of the failing ventricle and hemodynamics were reproduced in a mock circulation loop. The rotary blood pump was interfaced with the ventricle and aorta and used to fully support the failing ventricle. Among these five tip geometries, high-shear volume ( γ ˙ ≥ 2778 / s , potential parameter of platelet activation) was found to be the greatest in the blunt tip. The cage tip was observed to have the highest low-shear volume and recirculation volume ( γ ˙ ≤ 100 / s and Vz > 0, respectively; potential parameters of thrombus formation). The crown tip, together with conventional tip geometries with side ports (blunt with four side ports and beveled with three side ports) showed no significant difference in either high-shear volume or low-shear volume. However, recirculation volume was reduced significantly in the crown tip. Despite limited generalizability to clinical situations, these transient-state measurements supported the potential mitigation of complications by changing the design of conventional cannula tip geometries.

Research paper thumbnail of Effect of rotary blood pump pulsatility on potential parameters of blood compatibility and thrombosis in inflow cannula tips

The International Journal of Artificial Organs, 2014

Rotary Blood Pump (RBP) pulsatile strategies relative to the native cardiac cycle have been widel... more Rotary Blood Pump (RBP) pulsatile strategies relative to the native cardiac cycle have been widely studied because of their benefits to hemodynamics. However, the effects that inducing pulses has on the blood compatibility of ventricular assist device (VAD) support have not yet been understood. Inflow cannulae have been found to be associated with thrombosis under conventional constant speed support of RBPs. To prevent further risks to blood compatibility, it is necessary to understand the relationship between cannula tip design and the induced pulsatility. The purpose of this study was to evaluate the flow field of 5 different tip geometries under RBP pulsatile support using stereo-particle image velocimetry (PIV). Inflow cannulae with conventional tip geometries (blunt, blunt with 4 side ports, beveled with 3 side ports, and cage) and a custom designed crown tip were studied. All cannulae were interposed between a mixed-flow RBP and a silicone left ventricle. The contractile function and hemodynamics were reproduced in a mock circulation loop (MCL). The RBP was configured to induce synchronous and counter-synchronous pulses relative to cardiac cycles while supporting the failing ventricle. Between both pulsing strategies, low shear volume (γ̇≤100/s, potential parameter of thrombus formation) showed no significant difference. However, counter-synchronous pulsatile mode induced less increase of both high shear volume (γ̇≥2778/s, potential parameter of platelet activation) and recirculation volume (V(z)>0, potential parameter of thrombus formation). Although the clinical relationship cannot be inferred from this measurement, when considering the inflow tips only, a necessary trade-off should be made between adverse effects on blood compatibility and benefits for hemodynamics during RBP pulsatile mode.

Research paper thumbnail of Design and basic characteristics of permanent magnet hybrid type axial magnetic bearings

Digests of the 2010 14th Biennial IEEE Conference on Electromagnetic Field Computation, 2010

In order to improve rotor-impeller suspension performance of the developing ventricular assist de... more In order to improve rotor-impeller suspension performance of the developing ventricular assist device, axial magnetic bearing with various permanent magnet arrangements are designed and fabricated. Separate permanent magnets type stator shows wide linear range and improved force characteristics.

Research paper thumbnail of Axial Magnetic Bearing Development for the BiVACOR Rotary BiVAD/TAH

IEEE Transactions on Biomedical Engineering, 2000

Research paper thumbnail of A Compact Mock Circulation Loop for the In Vitro Testing of Cardiovascular Devices

Research paper thumbnail of Assessment of Right Pump Outflow Banding and Speed Changes on Pulmonary Hemodynamics During Biventricular Support With Two Rotary Left Ventricular Assist Devices

Research paper thumbnail of Simulation and enhancement of a cardiovascular device test rig

Journal of Simulation, a publication of the OR Society, comprised of articles and technical notes... more Journal of Simulation, a publication of the OR Society, comprised of articles and technical notes from researchers and practioners in the field of simulation.

Research paper thumbnail of Rapid Speed Modulation of a Rotary Total Artificial Heart Impeller

Artificial organs, 2016

Unlike the earlier reciprocating volume displacement-type pumps, rotary blood pumps (RBPs) typica... more Unlike the earlier reciprocating volume displacement-type pumps, rotary blood pumps (RBPs) typically operate at a constant rotational speed and produce continuous outflow. When RBP technology is used in constructing a total artificial heart (TAH), the pressure waveform that the TAH produces is flat, without the rise and fall associated with a normal arterial pulse. Several studies have suggested that pulseless circulation may impair microcirculatory perfusion and the autoregulatory response and may contribute to adverse events such as gastrointestinal bleeding, arteriovenous malformations, and pump thrombosis. It may therefore be beneficial to attempt to reproduce pulsatile output, similar to that generated by the native heart, by rapidly modulating the speed of an RBP impeller. The choice of an appropriate speed profile and control strategy to generate physiologic waveforms while minimizing power consumption and blood trauma becomes a challenge. In this study, pump operation modes ...

Research paper thumbnail of A compact mock circulation loop for the in vitro testing of cardiovascular devices

Faculty of Built Environment and Engineering Institute of Health and Biomedical Innovation School of Engineering Systems, Sep 1, 2010

Research paper thumbnail of Self-learning fuzzy physiological control of rotary artificial hearts

Research paper thumbnail of Timing of RBP pulsations in relation to the cardiac cycle to improve RBP physiological interaction

Objective: Alterations of impeller speed to induce pulsatility in RBP applications may be physiol... more Objective: Alterations of impeller speed to induce pulsatility in RBP applications may be physiologically beneficial to the patient by improving end organ perfusion. However, the timing of these pulsations in relation to the native cardiac cycle could also influence both ventricle volumes and ...

Research paper thumbnail of Do RBP's have sufficient inherent Frank-Starling like characteristics?: A study of the preload sensitivity of RBPs

Objective: The preload sensitivity of a RBP is an important feature for a device to alter outflow... more Objective: The preload sensitivity of a RBP is an important feature for a device to alter outflow in response to changing patient physiologic conditions, as per the Frank-Starling response of the natural heart. Since RBP's are pre/afterload dependant, a constant afterload and RPM ...

Research paper thumbnail of Monitoring system development for driving condition of a Ventricular assist device by using mobile phone

Procedia - Social and Behavioral Sciences, 2010

ABSTRACT

Research paper thumbnail of Pulsatile operation of the BiVACOR TAH - Motor design, control and hemodynamics

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Although there is limited consensus about the strict requirement to deliver pulsatile perfusion t... more Although there is limited consensus about the strict requirement to deliver pulsatile perfusion to the human circulatory system, speed modulation of rotary blood pumps is an approach that may capture the benefits of both positive displacement and continuous flow blood pumps. In the current stage of development of the BiVACOR Total Artificial Heart emphasis is placed on providing pulsatile outflow from the pump. Multiple pulsatile speed profiles have been applied in preliminary in-vivo operation in order to assess the capability of the TAH to recreate a physiologic pulse. This paper provides an overview about recent research towards pulsatile BiVACOR operation with special emphasis on motor and control requirements and developments.

Research paper thumbnail of Effect of Inflow Cannula Tip Design on Potential Parameters of Blood Compatibility and Thrombosis

Artificial Organs, 2014

During ventricular assist device support, a cannula acts as a bridge between the native cardiovas... more During ventricular assist device support, a cannula acts as a bridge between the native cardiovascular system and a foreign mechanical device. Cannula tip design strongly affects the function of the cannula and its potential for blood trauma. In this study, the flow fields of five different tip geometries within the ventricle were evaluated using stereo particle image velocimetry. Inflow cannulae with conventional tip geometries (blunt, blunt with four side ports, beveled with three side ports, and cage) and a custom-designed crown tip were interposed between a mixed-flow rotary blood pump and a compressible, translucent silicone left ventricle. The contractile function of the failing ventricle and hemodynamics were reproduced in a mock circulation loop. The rotary blood pump was interfaced with the ventricle and aorta and used to fully support the failing ventricle. Among these five tip geometries, high-shear volume ( γ ˙ ≥ 2778 / s , potential parameter of platelet activation) was found to be the greatest in the blunt tip. The cage tip was observed to have the highest low-shear volume and recirculation volume ( γ ˙ ≤ 100 / s and Vz > 0, respectively; potential parameters of thrombus formation). The crown tip, together with conventional tip geometries with side ports (blunt with four side ports and beveled with three side ports) showed no significant difference in either high-shear volume or low-shear volume. However, recirculation volume was reduced significantly in the crown tip. Despite limited generalizability to clinical situations, these transient-state measurements supported the potential mitigation of complications by changing the design of conventional cannula tip geometries.

Research paper thumbnail of Effect of rotary blood pump pulsatility on potential parameters of blood compatibility and thrombosis in inflow cannula tips

The International Journal of Artificial Organs, 2014

Rotary Blood Pump (RBP) pulsatile strategies relative to the native cardiac cycle have been widel... more Rotary Blood Pump (RBP) pulsatile strategies relative to the native cardiac cycle have been widely studied because of their benefits to hemodynamics. However, the effects that inducing pulses has on the blood compatibility of ventricular assist device (VAD) support have not yet been understood. Inflow cannulae have been found to be associated with thrombosis under conventional constant speed support of RBPs. To prevent further risks to blood compatibility, it is necessary to understand the relationship between cannula tip design and the induced pulsatility. The purpose of this study was to evaluate the flow field of 5 different tip geometries under RBP pulsatile support using stereo-particle image velocimetry (PIV). Inflow cannulae with conventional tip geometries (blunt, blunt with 4 side ports, beveled with 3 side ports, and cage) and a custom designed crown tip were studied. All cannulae were interposed between a mixed-flow RBP and a silicone left ventricle. The contractile function and hemodynamics were reproduced in a mock circulation loop (MCL). The RBP was configured to induce synchronous and counter-synchronous pulses relative to cardiac cycles while supporting the failing ventricle. Between both pulsing strategies, low shear volume (γ̇≤100/s, potential parameter of thrombus formation) showed no significant difference. However, counter-synchronous pulsatile mode induced less increase of both high shear volume (γ̇≥2778/s, potential parameter of platelet activation) and recirculation volume (V(z)>0, potential parameter of thrombus formation). Although the clinical relationship cannot be inferred from this measurement, when considering the inflow tips only, a necessary trade-off should be made between adverse effects on blood compatibility and benefits for hemodynamics during RBP pulsatile mode.

Research paper thumbnail of Design and basic characteristics of permanent magnet hybrid type axial magnetic bearings

Digests of the 2010 14th Biennial IEEE Conference on Electromagnetic Field Computation, 2010

In order to improve rotor-impeller suspension performance of the developing ventricular assist de... more In order to improve rotor-impeller suspension performance of the developing ventricular assist device, axial magnetic bearing with various permanent magnet arrangements are designed and fabricated. Separate permanent magnets type stator shows wide linear range and improved force characteristics.

Research paper thumbnail of Axial Magnetic Bearing Development for the BiVACOR Rotary BiVAD/TAH

IEEE Transactions on Biomedical Engineering, 2000

Research paper thumbnail of A Compact Mock Circulation Loop for the In Vitro Testing of Cardiovascular Devices

Research paper thumbnail of Assessment of Right Pump Outflow Banding and Speed Changes on Pulmonary Hemodynamics During Biventricular Support With Two Rotary Left Ventricular Assist Devices

Research paper thumbnail of Simulation and enhancement of a cardiovascular device test rig

Journal of Simulation, a publication of the OR Society, comprised of articles and technical notes... more Journal of Simulation, a publication of the OR Society, comprised of articles and technical notes from researchers and practioners in the field of simulation.

Research paper thumbnail of Rapid Speed Modulation of a Rotary Total Artificial Heart Impeller

Artificial organs, 2016

Unlike the earlier reciprocating volume displacement-type pumps, rotary blood pumps (RBPs) typica... more Unlike the earlier reciprocating volume displacement-type pumps, rotary blood pumps (RBPs) typically operate at a constant rotational speed and produce continuous outflow. When RBP technology is used in constructing a total artificial heart (TAH), the pressure waveform that the TAH produces is flat, without the rise and fall associated with a normal arterial pulse. Several studies have suggested that pulseless circulation may impair microcirculatory perfusion and the autoregulatory response and may contribute to adverse events such as gastrointestinal bleeding, arteriovenous malformations, and pump thrombosis. It may therefore be beneficial to attempt to reproduce pulsatile output, similar to that generated by the native heart, by rapidly modulating the speed of an RBP impeller. The choice of an appropriate speed profile and control strategy to generate physiologic waveforms while minimizing power consumption and blood trauma becomes a challenge. In this study, pump operation modes ...