Browsing by Subject "Heart rate variability"

Now showing 1 - 4 of 4
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    Eigenvalue based alternans prediction and the effects of heart rate variability on alternans formation
    (2013-06) Kakade, Virendra Vilas
    Ventricular fibrillation, a leading cause of death in the US, is an instability observed at the whole heart level which may result from the alternation of action potential viz. alternans at the cellular level. Previous approaches to predict alternans formation are based on the slope of the restitution curve which is the relation between the action potential duration (APD) and the duration of the preceding diastolic interval (DI). These approaches propose that alternans exists when the slope of this curve is greater than one and ceases to exist otherwise. However restitution based approaches have not been successful in all cases. One of the shortcomings of restitution approach is the non-uniqueness of the restitution curve which results from the variety of pacing protocols used to construct it. This has lead to observations in which alternans existed when the slope was less than one and vice a versa. Moreover restitution approaches use just one measurement from each action potential(AP). Another shortcoming of these approaches is periodic pacing, which is employed to attain the responses (APD and DI) at different basic cycle lengths (BCL) to construct the restitution curve. Upon analysis of electrocardiograms, it is evident that natural pacing is not periodic and exhibits rate variability which can be seen from measurement of RR intervals (which are analogous to BCL) over time. It would be beneficial to develop a method which is not very related to the restitution approach to predict alternans formation and which would not necessitate the generation of a curve and thus reduce errors introduced due to slope calculation. Such a method could also use multiple measurements from each AP to characterize it. Also, it would be beneficial to study the effects of introducing variability in pacing, on alternans formation. Analysis of such data would give us some valuable insight into the complex phenomenon of alternans. With these two shortcomings in sight two studies were conducted with specific aims as follows:Aim1: Apply a dominant eigenvalue method to predict alternans formation in the rabbit heart. A dominant eigenvalue based alternans prediction was recently developed and tested on data obtained from single cell numerical simulation data. I applied this technique at whole heart level to test whether alternans formation could be predicted using a eigenvalue calculated at each BCL from AP response data. I found that the eigenvalue showed decreasing trend towards the value of -1 as BCL was decreased and approached alternans onset. Aim2: Study the effect of introducing rate variability in pacing on a ionic model of a single cell. Ionic model of a single cell was paced using two protocols which introduced variability in the pacing rate by either varying the BCL or DI to test the effects on alternans formation. It was found that introducing variability using first method (varying BCL) lead to alternans formation over wider range of BCL than without variability. The second method (varying DI) however did not give rise to alternans in the model with or without variability.
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    Time series analysis of cardiometabolic parameters: reliability and energy drink response
    (2013-12) Nelson, Michael T.
    Cardiometabolic data is currently analyzed primarily by the use of averages. While this method can provide some data, further analysis by time series (variability) methods can provide more physiologic insights. Historically, time series analysis has been performed primarily using heart rate data in the form of heart rate variability (HRV) analysis. This was done to determine the status of the autonomic nervous system via changes in parasympathetic and sympathetic output. Researchers have used different methods of analysis, but a lack of reproducibility studies raises questions about the validity of these methods when applied to heart rate (HR) data. Currently in the literature, these methods have not applied to metabolic data such as the respiratory exchange ratio (RER). This dissertation will investigate the reliability of time series assessments of caridiometaoblic parameters. We hypothesize that in healthy individuals, HRV analysis performed on the same RR intervals but by two different measurement systems, are indeed interchangeable. We further hypothesize that the time series analysis of metabolic data such as the RER will be stable and repeatable over two trials conducted under the same conditions. Lastly, we hypothesize that under conditions of physical stress (e.g. ride time-to-exhaustion) and biochemical stress (e.g. energy drink), resting HR and HR variability preexercise will be altered and the ride time-to-exhaustion will be increased after subjects consume an energy drink (standardized to 2.0mg/kg caffeine) compared to a taste-matched placebo. The results of this dissertation will provide further insight into the repeatability of these time series analyses, which could be utilized for future research to determine metabolic flexibility.
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    Time series analysis of cardiometabolic parameters: reliability and energy drink response
    (2013-12) Nelson, Michael Thomas
    Cardiometabolic data is currently analyzed primarily by the use of averages. While this method can provide some data, further analysis by time series (variability) methods can provide more physiologic insights. Historically, time series analysis has been performed primarily using heart rate data in the form of heart rate variability (HRV) analysis. This was done to determine the status of the autonomic nervous system via changes in parasympathetic and sympathetic output. Researchers have used different methods of analysis, but a lack of reproducibility studies raises questions about the validity of these methods when applied to heart rate (HR) data. Currently in the literature, these methods have not applied to metabolic data such as the respiratory exchange ratio (RER). This dissertation will investigate the reliability of time series assessments of caridiometaoblic parameters. We hypothesize that in healthy individuals, HRV analysis performed on the same RR intervals but by two different measurement systems, are indeed interchangeable. We further hypothesize that the time series analysis of metabolic data such as the RER will be stable and repeatable over two trials conducted under the same conditions. Lastly, we hypothesize that under conditions of physical stress (e.g. ride time-to-exhaustion) and biochemical stress (e.g. energy drink), resting HR and HR variability preexercise will be altered and the ride time-to-exhaustion will be increased after subjects consume an energy drink (standardized to 2.0mg/kg caffeine) compared to a taste-matched placebo. The results of this dissertation will provide further insight into the repeatability of these time series analyses, which could be utilized for future research to determine metabolic flexibility.
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    Vagal flexibility and parenting behaviors in post-deployed military fathers
    (2018-05) Zhang, Na
    The lives of about two million American children have been affected by the military deployment of a parent. A parent's deployment influences children's adjustment through compromised parenting. While an emerging body of literature suggests that effective parenting requires parental emotion regulation, few studies have focused on fathers. In addition, limited knowledge exists about whether or how fathers' emotion regulation might affect their responsivity to a parent training program. With a focus on military fathers who had been deployed since 2001, the current research consisted of two studies that investigated vagal flexibility as an index of physiological emotion regulation and social engagement in relation to observed parenting behaviors. The first study, entitled "Military fathers' nurturing parenting: Psychological and physiological flexibility both matter", demonstrated that vagal flexibility buffers against the negative effects of psychological inflexibility (i.e. self-reported experiential avoidance) on observed emotion-related parenting. The second study, entitled "Adapting to 'ADAPT': Vagal flexibility predicts military fathers' changes in parenting following a parent training program", tested the effect of vagal flexibility in predicting the degree of changes in observed parenting skills at 1-year follow-up in a randomized controlled trial of the After Deployment Adaptive Parenting Tools/ADAPT program. These two studies provided evidence for the role of cardiac vagal tone as a correlate of emotion-related parenting and a tailoring variable to inform precision-based parenting programming for military fathers.