909 research outputs found

    Echocardiography and Hemodynamic Monitoring Tools for Clinical Assessment of Patients on Mechanical Circulatory Support

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    Recent developments in ventricular assist devices have been quite remarkable. Rapid advances have been made particularly in terms of smaller size and more durable material and design. As a result, ventricular assist devices are increasingly being implanted in children and they are increasingly being used as a means of destination therapy for elderly patients with heart failure who are not eligible for heart transplantation. New issues have arisen as a result of these expanded indications. This book focuses on recent advances in ventricular assist devices itself and related issues

    Treatment-Specific Approaches for Analysis and Control of Left Ventricular Assist Devices

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    A Left Ventricular Assist Device (LVAD) is a mechanical pump that helps patients with heart failure conditions. This rotary pump works in parallel to the ailing heart and provides an alternative path for blood flow from the weak left ventricle to the aorta. The LVAD is controlled by the power supplied to the pump motor. An increase in the pump motor power increases the pump speed and the pump flow. The LVAD is typically controlled at a fixed setting of pump power. This basically means that the controller does not react to any change in the activity level of the patient. An important engineering challenge is to develop an LVAD feedback controller that can automatically adjusts its pump motor power so that the resulting pump flow matches the physiological demand of the patient. To this end, the development of a mathematical model that can be used to accurately simulate the interaction between the cardiovascular system of the patient and the LVAD is essential for the controller design. The use of such a dynamic model helps engineers and physicians in testing their theories, assessing the effectiveness of prescribed treatments, and understanding in depth the characteristics of this coupled bio-mechanical system. The first contribution of this dissertation is the development of a pump power-based model for the cardiovascular-LVAD system. Previously, the mathematical models in the literature assume availability of the pump speed as an independent control variable. In reality, however, the device is controlled by pump motor power which, in turn, produces the rotational pump speed. The nonlinear relationship between the supplied power and the speed is derived, and interesting observations about the pump speed signal are documented. The second contribution is the development of a feedback controller for patients using an LVAD as either a destination therapy or a bridge to transplant device. The main objective of designing this controller is to provide a physiological demand of the patient equivalent of that of a healthy individual. Since the device is implanted for a long period of time, this objective is chosen to allow the patient to live a life as close to normal as possible. The third contribution is an analysis of the aortic valve dynamics under the support of an LVAD. The aortic valve may experiences a permanent closure when the LVAD pump power is increased too much. The permanent closure of the aortic valve can be very harmful to the patients using the device as a bridge to recovery treatments. The analysis illustrates the various changes in the hemodynamic variables of the patient as a result of aortic valve closing. The results establish the relationship between the activity level and the heart failure severity with respect to the duration of the aortic valve opening

    Rotary pump speed modulation to produce pulsatile flow and ventricular volume unloading.

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    Background: Continuous-flow (CF) left ventricular assist devices (LVADs) have gained widespread clinical acceptance as a treatment option for advanced heart failure (HF); however, they have also been associated with an increased risk of adverse events, including gastrointestinal bleeding, aortic insufficiency, and hemorrhagic stroke. It has been hypothesized that the increase in adverse event incidence may be due in part to diminished vascular pulsatility and high shear stress when CF-LVADs are operated at fixed speeds. Previous studies have shown that pump speed modulation generates greater levels of pulsatility in rotary pumps than when operated at fixed speeds. The objective of this study was to characterize the hemodynamic and pump performance of LVADs operated with a low-frequency asynchronous pump speed modulation algorithm in a chronic healthy bovine model with partial VAD support. Materials and Methods: Clinical-grade LVAD with aortic (HeartWare HVAD, n=3) or transaortic (proprietary VADx, n=4) outflow were implanted into chronic (30-day) healthy male Jersey calves (60-110 kg). An asynchronous pump speed modulation algorithm (frequency = 20 bpm, amplitude = 2500-4000 RPM for HVAD or 11000-19000 RPM for VADx) was implemented by controlling pump current. Hemodynamic measurements (pressures, flows) were recorded throughout the study duration (30s epochs collected hourly at 400Hz), echocardiographic data was recorded during the implant, weekly, and at terminal, and blood laboratory measurements were regularly collected throughout the study. All data were analyzed to characterize aortic pulsatility, LV unloading, blood damage, and device power usage. Statistical analysis was performed to determine significance between fixed and pump speed modulation operating conditions. Results and Discussion: Two HVAD and four VADx animals achieved the 30-day study endpoint. Due to surgical complications, one animal died intraoperatively. Both HVAD devices maintained asynchronous modulation for the full study duration with mean high and low speeds of 4000 RPM and 2500 RPM, respectively. Two of the four VADx devices maintained asynchronous modulation at average high and low speeds of 17238 RPM and 11333 RPM over the 30-day study; however, the other two VADx devices operated at fixed pump speed for 1 and 2 days, respectively, due to unforeseen controller malfunctions, which were corrected to restore asynchronous modulation. Near-physiologic aortic pulse pressure for HVAD (45±4 mmHg) and VADx (46±9 mmHg) was demonstrated. HVAD and VADx with asynchronous modulation reduced stroke volume by 27% and 23%, respectively. HVAD (n=2) and VADx (n=3) maintained plasma free hemoglobin (pfHb) less than 40 mg/dL for the entire study duration while one VADx had pfHb \u3e 40 mg/dL for a period of 3 days, which resolved. Asynchronous modulation increased power consumption with HVAD (25%) and VADx (6%) compared to fixed speed operation. Conclusion: This study demonstrated asynchronous modulation of HVAD and VADx maintained near-physiologic pulsatility and LV unloading at the expense of minimal hemolysis and increased power consumption in the partial VAD support model. Future studies in clinically-relevant heart failure models warrant further investigation

    Mechanical Circulatory Support in End-Stage Heart Failure

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    LVAD Occlusion Condition Monitoring Using Boost Classification Trees

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    Cardiac related diseases are a serious health risk for adults. Consequently, therapies exist to treat these aliments such as heart transplant and medication. Heart transplant remains the gold standard for treating severe heart failure, however left ventricular assistive devices, a cardiac blood pump, are become a viable long term treatment. Unfortunately, with the benefits of these devices come risks of clot formation. These occlusions can cause strokes, further cardiac damage, or even death. Therefore, it is critical that these occlusions be detected as early as possible. This work presents an expanded method to non-invasively monitor the condition of a Thoratec HeartMate II ventricular assist device through the application of a boosted classification tree. In addition, both inflow and outflow blockages measured at aorta and pump locations were experimentally tested on a cardiac phantom. The proposed method presents a potential outpatient diagnostic method that may assist experienced cardiologists in their treatment of LVAD patients

    Remote monitoring for better management of LVAD patients: the potential benefits of CardioMEMS

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    Left ventricular assist devices (LVAD) are frequently used in the treatment of end-stage heart failure (HF), and due to the shortage of heart donors and destination programs, it is likely to keep on growing. Still, LVAD therapy is not without complications and morbidity and rehospitalization rates are high. New ways to improve LVAD care both from the side of the patient and the physician are warranted. Remote monitoring could be a tool to tailor treatment in these patients, as no feedback exists at all about patient functioning on top of the static pump parameters. We aim to provide an overview and evaluation of the novel remote monitoring strategies to optimize LVAD management and elaborate on the opportunities of remote hemodynamic monitoring with CardioMEMS, at home in these patients as the next step to improve care
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