Browsing by Subject "Vagus Nerve Stimulation"

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    Novel therapies for hypertension and associated cardiovascular risk
    (2018-08) Annoni, Elizabeth
    This thesis is comprised of two parts. The first part investigates a novel therapy, vagus nerve stimulation, for hypertension and hypertension-induced heart disease. Hypertension impacts over 1 billion people worldwide, and clinical management is challenging. Left uncontrolled, high blood pressure can significantly increase the risk of cardiovascular events. The majority of hypertensive patients are treated with anti-hypertensive drugs to control blood pressure, but many limitations exist including resistant hypertension, inability to tolerate therapy, and non-compliance with the medication regime. For these patients, an alternative approach is needed to control blood pressure. Recently, the imbalance in the autonomic nervous system, evident in hypertension, has been the target of novel device-based therapies such as vagus nerve stimulation. The main goal of this research is to evaluate the efficacy of vagus nerve stimulation to treat hypertension and hypertension-induced heart disease. This thesis investigates the impact of vagus nerve stimulation on disease progression, survival, and cardiovascular remodeling in Dahl salt-sensitive hypertensive rats. Overall, the results of this work provide evidence for the beneficial therapeutic effects of vagus nerve stimulation in hypertension and motivate future studies to optimize therapy parameters and further understand therapeutic mechanisms. The second part of this thesis focuses on atrial fibrillation and the evaluation of new mapping techniques for improving rotor localization for ablation procedures. Currently, success rates for ablation procedures for non-paroxysmal atrial fibrillation are low and require repeat procedures or a lifetime of pharmacological agents to reduce the risk of stroke. Improved signal processing techniques for mapping electrical activity in the atrium can help further our understanding of the generation and maintenance of atrial fibrillation and ultimately improve ablation procedure success rates and terminate the arrhythmia. The main goal of this work was to validate new signal processing techniques – multiscale frequency, kurtosis, Shannon entropy, and multiscale entropy – to identify regions of abnormal electrical activity. The results of this work demonstrate improved accuracy of these novel techniques in mapping rotors in cardiac arrhythmias and motivates further studies evaluating more complex arrhythmias and human intracardiac electrograms.
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    Vagus Nerve Stimulation In Hypertensive Rats: Assessing Pathophysiology Using ECG And Pressure Data
    (2017-05) Schultz, James
    Hypertension, which is associated with an imbalanced autonomic nervous system, is becoming an increasing problem in the US and worldwide, and new therapies are needed, since not all patients respond to current medications. Vagus nerve stimulation (VNS), which aims to restore autonomic balance, has emerged as a promising new treatment for this disease. In our lab, we conducted an experimental study aimed at assessing the safety and efficacy of chronic, continuously cyclic VNS to attenuate the development of hypertension in spontaneously hypertensive rats. Hypertension was induced via a high salt diet and rats were randomized into two groups: Sham Control (n=6) and VNS Treatment (n=6). In vivo blood pressure and electrocardiogram (ECG) were monitored continuously by an implantable telemetry system. We developed and validated methods to calculate time and frequency domain metrics for heart rate variability and blood pressure variability. Additionally, the sequence method in the time domain was employed to measure baroreflex sensitivity. Artifacts and ectopic beats can cause errors in the analysis of these metrics, so we also developed and validated robust pre-processing methods to edit ECG and pressure data in order to acquire clean signals. Results show that hypertension leads to decreased heart rate variability, decreased baroreflex sensitivity, and increased blood pressure variability, all of which are indicative of pathophysiological effects of hypertension. VNS may preserve heart rate variability blood pressure variability and baroreflex sensitivity at certain frequencies.