Joshua Cysyk

Changes in the functional status measures of heart failure patients with mechanical assist devices.

Continuous-flow left ventricular assist devices (cfLVADs) have been proven safe and effective for bridge-to-transplant and destination therapy (DT) in patients with advanced heart failure. However, the fixed pump speed of these devices may lack response to activity and oxygen demand, thereby limiting exercise tolerance. The objective of this observational study was to describe exercise capacity as measured by peak oxygen consumption (peak VO2) that may be expected during support with a cfLVAD. Peak VO2 was measured in patients (mean age: 58.3 ± 11.7 years; 66.7% ischemic and 33.3% DT) before cfLVAD support (11.2 ± 3.0 ml/kg/min, n = 25), between 3 and 6 months (12.7 ± 3.5 ml/kg/min, n = 31), at 1 year (10.7 ± 2.6 ml/kg/min, n = 16), and longer than 1 year (11.2 ± 1.7 ml/kg/min, n = 10). There was no statistical improvement in peak VO2 at any time point after implantation. In addition, ventilatory efficiency remained poor after LVAD implantation at all time points. Although studies have shown an increase in survival and patient’s quality of life, exercise capacity as measured by cardiopulmonary exercise testing remains low during cfLVAD support.

Development of an inlet pressure sensor for control in a left ventricular assist device.

A Tesla type continuous flow left ventricular assist device (VAD) has been designed by Penn State and Advanced Bionics, Inc. (ABI). When a continuous flow device is used, care must be taken to limit low pressures in the ventricle, which can produce an obstruction to the inlet cannula or trigger arrhythmias. Design of an inexpensive, semiconductor strain gauge inlet pressure sensor to detect suction has been completed. The research and design analysis included finite element modeling of the sensing region. Sensitivity, step-response, temperature dependence, and hysteresis tests have been performed on prototype units. All sensors were able to withstand the maximum expected strain of 82 &mgr;m/in at 500 mm Hg internal pressure. Average sensitivity was 0.52 ± 0.24 &mgr;V/mm Hg with 0.5 V excitation (n = 5 units). Step-response time for a 0- to 90-mm Hg step change averaged 22 msec. Hysteresis was measured by applying and holding 75 mm Hg internal pressure for 4 hours, followed by a zero pressure measurement, and ranged from −15 to 4.1 mm Hg (n = 3 units). Offset drift varied between 180 and −140 mm Hg over a 4-week period (n = 2 units). Span temperature sensitivity ranged from 18 to −21 &mgr;V/°C (n = 5 units). Gain temperature sensitivity ranged from −7.4 to 4.9 &mgr;V/°C (n = 5 units). With the inherent drift, it is currently not possible to use the transducer to measure actual pressures, but it can easily be used to measure pressure changes throughout the cardiac cycle. This signal can then be used in the control system to avoid ventricular suction events.

An implantable Fabry-Pérot pressure sensor fabricated on left ventricular assist device for heart failure

Continuous flow left ventricular assist devices (LVADs) are commonly used as bridge-to-transplantation or destination therapy for heart failure patients. However, non-optimal pumping speeds can reduce the efficacy of circulatory support or cause dangerous ventricular arrhythmias. Optimal flow control for continuous flow LVADs has not been defined and calls for an implantable pressure sensor integrated with the LVAD for real-time feedback control of pump speed based on ventricular pressure. A MEMS pressure sensor prototype is designed, fabricated and seamlessly integrated with LVAD to enable real-time control, optimize its performance and reduce its risks. The pressure sensing mechanism is based on Fabry-Pérot interferometer principle. A biocompatible parylene diaphragm with a silicon mirror at the center is fabricated directly on the inlet shell of the LVAD to sense pressure changes. The sensitivity, range and response time of the pressure sensor are measured and validated to meet the requirements of LVAD pressure sensing.

A Passively-Suspended Tesla Pump Left Ventricular Assist Device

The design and initial test results of a new passively suspended Tesla type left ventricular assist device blood pump are described. Computational fluid dynamics (CFD) analysis was used in the design of the pump. Overall size of the prototype device is 50 mm in diameter and 75 mm in length. The pump rotor has a density lower than that of blood and when spinning inside the stator in blood it creates a buoyant centering force that suspends the rotor in the radial direction. The axial magnetic force between the rotor and stator restrain the rotor in the axial direction. The pump is capable of pumping up to 10 L/min at a 70 mm Hg head rise at 8,000 revolutions per minute (RPM). The pump has demonstrated a normalized index of hemolysis level below 0.02 mg/dL for flows between 2 and 9.7 L/min. An inlet pressure sensor has also been incorporated into the inlet cannula wall and will be used for control purposes. One initial in vivo study showed an encouraging result. Further CFD modeling refinements are planned and endurance testing of the device.

Effective ventricular unloading by left ventricular assist device varies with stage of heart failure: cardiac simulator study.

Although the use of left ventricular assist devices (LVADs) as a bridge-to-recovery (BTR) has shown promise, clinical success has been limited due to the lack of understanding the timing of implantation, acute/chronic device setting, and explantation. This study investigated the effective ventricular unloading at different heart conditions by using a mock circulatory system (MCS) to provide a tool for pump parameter adjustments. We tested the hypothesis that effective unloading by LVAD at a given speed varies with the stage of heart failure. By using a MCS, systematic depression of cardiac performance was obtained. Five different stages of heart failure from control were achieved by adjusting the pneumatic systolic/diastolic pressure, filling pressure, and systemic resistance. The Heart Mate II® (Thoratec Corp., Pleasanton, CA) was used for volumetric and pressure unloading at different heart conditions over a given LVAD speed. The effective unloading at a given LVAD speed was greater in more depressed heart condition. The rate of unloading over LVAD speed was also greater in more depressed heart condition. In conclusion, to get continuous and optimal cardiac recovery, timely increase in LVAD speed over a period of support is needed while avoiding the akinesis of aortic valve.

Chronic In Vivo Testing of the Penn State Infant Ventricular Assist Device

The Penn State Infant Ventricular Assist Device (VAD) is a 12–14 ml stroke volume pneumatically actuated pump, with custom Björk-Shiley monostrut valves, developed under the National Heart, Lung, and Blood Institute Pediatric Circulatory Support program. In this report, we describe the seven most recent chronic animal studies of the Infant VAD in the juvenile ovine model, with a mean body weight of 23.5 ± 4.1 kg. The goal of 4–6 weeks survival was achieved in five of seven studies, with support duration ranging from 5 to 41 days; mean 26.1 days. Anticoagulation was accomplished using unfractionated heparin, and study animals were divided into two protocol groups: the first based on a target activated partial thromboplastin time of 1.5–2 times normal, and a second group using a target thromboelastography R-time of two times normal. The second group required significantly less heparin, which was verified by barely detectable heparin activity (anti-Xa). In both groups, there was no evidence of thromboembolism except in one animal with a chronic infection and fever. Device thrombi were minimal and were further reduced by introduction of the custom valve. These results are consistent with results of adult VAD testing in animals and are encouraging given the extremely low levels of anticoagulation in the second group.

Tesla-Based Blood Pump and Its Applications

A continuous flow left ventricular assist device (LVAD) that the Penn State University has developed utilizes Tesla turbomachinery technology. Tesla pumping technology patented by Nikola Tesla in the early 20th century has multiple intriguing characteristics such as simpler manufacturing process, reduced turbulent-related stress, less cavitation due to viscous flow distribution over larger surface areas, and less hemolysis by smooth transition of fluid energy. We successfully tested the 1st version of the Penn State Tesla LVAD [1, 2]. We recently tested the 2nd version of the Tesla pump; to make the pump usable in a wide range of patients, the size of the pump was significantly reduced while trying to avoid any degradation of hemodynamic and hemolytic characteristics.Copyright

Ventricular contractility and compliance measured during axial flow blood pump support: in vitro study.

End-systolic elastance and end-diastolic compliance have been used to quantify systolic and diastolic function of the left ventricle (LV). In this study, the effective end-systolic elastance, (EES )eff , end-systolic volume intercept, (V0 )eff , and end-diastolic compliance of the LV were assessed at various levels of left ventricular assist device (LVAD) support. We tested the hypothesis that (EES )eff and (V0 )eff vary as a function of LVAD speed, while compliance does not change. The Penn State in vitro cardiac simulator was used in two heart conditions (control and heart failure [HF]) with the HeartMate II axial flow LVAD. The LVAD speed was linearly increased from 6000 to 11 000 rpm, with 500-rpm increments. The end-systolic and end-diastolic pressure-volume relationships were estimated at each LVAD speed. Acute LVAD support itself showed pseudo-improvement of ventricular contractility. The (EES )eff and (V0 )eff in HF were found to be dependent on the LVAD speed. The effective compliance for both control and HF was independent of the LVAD speed. Therefore, when examining the time-course cardiac recovery induced by the LVAD support, LV performance should be measured immediately before and after LVAD support while keeping LVAD speed consistent to avoid potential overestimation of long-term cardiac recovery.

Rotary blood pump control using integrated inlet pressure sensor

Due to improved reliability and reduced risk of thromboembolic events, continuous flow left ventricular assist devices are being used more commonly as a long term treatment for end-stage heart failure. As more and more patients with these devices are leaving the hospital, a reliable control system is needed that can adjust pump support in response to changes in physiologic demand. An inlet pressure sensor has been developed that can be integrated with existing assist devices. A control system has been designed to adjust pump speed based on peak-to-peak changes in inlet pressure. The inlet pressure sensor and control system have been tested with the HeartMate II axial flow blood pump using a mock circulatory loop and an active left ventricle model. The closed loop control system increased total systemic flow and reduced ventricular load following a change in preload as compared to fixed speed control. The increase in systemic flow occurred under all operating conditions, and maximum unloading occurred in the case of reduced ventricular contractility.

A Fabry-Pérot pressure sensor fabricated on left ventricular assist device for heart failure implant

An implantable Fabry-Pérot interferometer based pressure sensor is developed. The pressure sensor could be integrated directly onto the inlet shell of a left ventricular assist device (LVAD) to monitor blood pressure in real-time and provide a feedback control signal to achieve the optimal operation of LVAD. The diaphragm of the pressure sensor is made out of biocompatible polymer parylene-C.