Browsing by Author "Santa Cruz Chavez, Grace"

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    Analysis of Heart Rate Variability in Male and Female Rats
    (Office of the Vice Chancellor for Research, 2015-04-17) Ajayi, Tolulope O.; Santa Cruz Chavez, Grace; Schild, John H.
    Heart disease is the leading cause of death in the United States. Quantitative measures of cardiovascular function are often essential to effective clinical interventions. The QRS complex is one such measure widely used by cardiologists. These analyses can involve subtle changes in the magnitude and time course of the QRS complex, to differences in the timing between successive heart beats. Electrocardiograms (ECG) are continuous recordings of the QRS complex at various locations across the body surface and provide a comprehensive measurement of the electrical activity of the heart. Knowledge obtained from investigating ECG signal characteristics can help the cardiologist diagnose possible health or cardiac abnormalities such as arrhythmias and can provide objective measures of heart health following injury such as myocardial infarction. Heart rate variability (HRV) can also serve as a reliable indicator of heart health and has been shown to be a strong indicator of mortality and morbidity following myocardial infarction. Unfortunately, very little is known concerning the neurophysiological mechanisms underlying HRV beyond the broader impact of the autonomic nervous system and associated neurocirculatory reflexes. In this research project, we first implemented several established methods for quantifying HRV in male and female rats such as calculating the power spectral density of a long time series of HRV measures, and calculating the standard deviation of the averages of all beat-to-beat intervals in the recording. These measures compared well to those in the literature supporting the accuracy and reliability of the Matlab scripts created to process these data. Simultaneous recordings of the QRS complex and femoral arterial pressure (BP) provided the opportunity to determine how well BP recordings could be used to quantify HRV. In addition, HRV measurements were compared across populations of male and normal, cycling (OVI) and ovariectomized (OVX) female rats in order to determine if HRV is sexually dimorphic. Mentors: John H. Schild, Grace Santa Cruz Chavez, Department of Biomedical Engineering, Purdue School of Engineering and Technology, IUPUI, Indianapolis, IN
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    Automated Quantitative Analysis of Nerve Fiber Conduction Velocity
    (Office of the Vice Chancellor for Research, 2015-04-17) Haas, Kyle D.; Santa Cruz Chavez, Grace; Schild, John
    The baroreflex (BRX) is essential for reliable autonomic control of arterial blood pressure. Central to BRX function is a rapid, negative feedback control of heart rate. Arterial pressure sensors known as baroreceptors (BR) encode heart rate and blood pressure information into patterns of neural discharge that is conveyed to the central nervous system via a network of sensory afferent nerve fibers. These BR fibers are broadly classified as myelinated A-fibers with diameters in the range of 1-10 μm and unmyelinated Cfibers with diameters typically less than 1 μm. Fiber diameter and conduction velocity are related with the large A-fibers being much faster (> 10 m/sec) than the smaller diameter C-fibers (< 1 m/sec). Recently, our lab has documented an additional phenotype of myelinated BR afferents termed Ah-fibers that are notably present in female; but only rarely observed in male rats. In response to an electrical stimulus, the nerve fibers produce a compound action potential (CAP) that propagates away from the stimulation site. The CAP of each fiber type is observable in the evoked waveform on account of the differing conduction velocities. As Ah-fibers have conduction velocities in the range of 10 m/sec - 2 m/sec, the resulting CAP is clearly separated in time from the faster A-fibers and much slower C-fibers. Root-mean-square analysis of these distinct time segments provides a quantitative measure of the total signal energy from each of the A-, Ah-, and C-type fibers. This project sought to create MATLAB scripts that would import nerve recording files from both male and female rats and automate the energy analysis in an efficient and reliable manner. Doing so not only facilitates the analysis of these large data files, but also reduces the possibility for biases and errors that can occur during a manual measurement of nerve activity.