Browsing by Author "Schild, John"

Now showing 1 - 7 of 7
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    Analysis of Heart Rate Variability During Focal Parasympathetic Drive of the Rat Baroreflex
    (2020-05) Bustamante, David J.; Schild, John; Yoshida, Ken; Salama, Paul
    Autonomic control of the heart results in variations in the intervals between heart beats, known as heart rate variability. One of the defining components of autonomic control is the baroreflex, a negative feedback controller that balances heart rate and blood pressure. The baroreflex is under constant command from the branches of the autonomic nervous system. To better understand how the autonomic nervous system commands the baroreflex, a baroreflex reflexogenic animal protocol was carried out. Heart rate variability analysis and baroreflex sensitivity were used to quantify the neural control of the heart. This thesis reconfirmed the existence of sexually dimorphic properties in the baroreflex through the use of heart rate variability analysis and baroreflex sensitivity. It was discovered that there are many caveats to utilizing heart rate variability analysis, which have to be addressed both in the experimental protocol and the signal processing technique. Furthermore, it was suggested that the slope method for quantifying baroreflex sensitivity also has many caveats, and that other baroreflex sensitivity methods are likely more optimal for quantifying sustained activation of the baroreflex. By utilizing various heart rate variability signal processing algorithms to assess autonomic tone in Sprague-Dawley rats during rest and sustained electrical activation of the baroreflex, the null hypothesis was rejected.
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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.
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    CONTINUOUS MONITORING OF THE GALVANIC SKIN RESPONSE
    (Office of the Vice Chancellor for Research, 2012-04-13) Teach, Heather; Igega, Christele; Schild, John; Carpenter, Janet
    Galvanic Skin Response (GSR) is an objective measurement of the electrical conductance of the skin. GSR is tightly correlated with peripheral sweat rate, which in turn is associated with many clinical conditions. These conditions include, but are not limited to, menopausal “hot flashes”, diabetic hypoglycemic and hyperglycemic episodes, and various cancers. The objective quantification of GSR can be a valuable clinical tool in evaluating the effectiveness of clinical interventions for these and other conditions. Current methods of monitoring GSR are not well suited to implementation outside of the clinical setting. The goal of this research is to develop a reliable portable device for real-time ambulatory monitoring of GSR. In order to get accurate and consistent readings, electrodes must be attached to the patient with a lasting and non-irritating electrically conductive gel with suitable impedance characteristics. Development of such a device requires consideration of many physiological factors. The distribution and density of sweat glands must be considered to determine a location for the device on the body that will yield measurable GSR without interfering with the patient’s daily activities. We are in the process of evaluating the electrical impedance of electrode and gel combinations presently used in the Carpenter lab. Quantification of the frequency dependent loading profile of the electrode-gel interface will improve the measurement accuracy of the GSR. The ionic composition of sweat and the sweat rate must be evaluated to ensure that the integrity of the interface between the body and the device is maintained throughout the monitoring period. 1Department of Biomedical Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University Indianapolis, IN 46204 2Center for Enhancing Quality of Life, Indiana University School of Nursing, IUPUI, Indianapolis, IN 46204
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    Propagation of mechanical strain in peripheral nerve trunks and their interaction with epineural structures
    (2017-08) Cox, T.G. Hunter; Yoshida, Ken; Wallace, Joseph; Schild, John
    Advances in peripheral nerve electrode technology have outpaced the advances in chronic implantation reliability of the electrodes. An observable trend is the increased deposition of fibrotic encapsulation tissue around the electrode to shift its position away from the implantation site and subsequently reducing performance. A finite element model (FEM) is developed in conjunction with tensile testing and digital image correlation of strain to understand the relationship between cuff electrode attachment and the strain environment of the nerve. A laminar and bulk nerve model are both developed with material properties found in literature and geometry found from performing histology. The introduction of a cuff electrode to an axially stretched nerve indicates a significant behavior deviation from the expected response of the axial strain environment. When implemented in ex-vivo tensile testing, results indicate that the reduction of strain is statistically significant but becomes much more apparent when paired with a digital image correlation system to compare predicted and measured effects. A robust FEM is developed and tested to emphasize the effect that the boundary conditions and attachment methodology significantly effects the strain environment. By coupling digital image correlation with FEM, predictive models can be made to the strain environment to better design around the long term chronic health of the implant.
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    Reversible Nerve Conduction Block Using Low Frequency Alternating Currents
    (2020-08) Muzquiz, Maria I.; Yoshida, Ken; Schild, John; Berbari, Ed
    This thesis describes a novel method to reversibly and safely block nerve conduction using a low frequency alternating current (LFAC) waveform at 1 Hz applied through a bipolar extrafascicular electrode. This work follows up on observations made on excised mammalian peripheral nerves and earthworm nerve cords. An in-situ electrophysiology setup was used to assess the LFAC waveform on propagating action potentials (APs) within the cervical vagus nerve in anaesthetized Sprague-Dawley rats (n = 12). Two sets of bipolar cuff or hook electrodes were applied unilaterally to the cervical vagus nerve, which was crushed rostral to the electrodes to exclude reflex effects on the animal. Pulse stimulation was applied to the rostral electrode, while the LFAC conditioning waveform was applied to the caudal electrode. The efferent volley, if unblocked, elicits acute bradycardia and hypotension. The degree of block of the vagal stimulation induced bradycardia was used as a biomarker. Block was assessed by the ability to reduce the bradycardic drive by monitoring the heart rate (HR) and blood pressure (BP) during LFAC alone, LFAC with vagal stimulation, and vagal stimulation alone. LFAC applied via a hook electrode (n = 7) achieved 86.6 +/- 11% block at current levels 95 +/- 38 uAp (current to peak). When applied via a cuff electrode (n = 5) 85.3 +/- 4.60% block was achieved using current levels of 110+/-65 uAp. Furthermore, LFAC was explored on larger vagal afferent fibers in larger human sized nerve bundles projecting to effects mediated by a reflex. The effectiveness of LFAC was assessed in an in-situ electrophysiological setup on the left cervical vagus in anaesthetized domestic swine (n = 5). Two bipolar cuff electrodes were applied unilaterally to the cervical vagus nerve, which was crushed caudal to the electrodes to eliminate cardiac effects. A tripolar extrafascicular cuff electrode was placed most rostral on the nerve for recording of propagating APs induced by electrical stimulation and blocked via the LFAC waveform. Standard pulse stimulation was applied to the left cervical vagus to induce the Hering-Breuer reflex. If unblocked, the activation of the Hering-Breuer reflex would cause breathing to slow down and potentially cease. Block was quantified by the ability to reduce the effect of the Hering-Breuer reflex by monitoring the breathing rate during LFAC alone, LFAC and vagal stimulation, and vagal stimulation alone. LFAC achieved 87.2 +/- 8.8% (n = 5) block at current levels of 0.8 +/- 0.3 mAp. Compound nerve action potentials (CNAP) were monitored directly. They show changes in nerve activity during LFAC, which manifests itself as the slowing and amplitude reduction of components of the CNAPs. Since the waveform is balanced, all forward reactions are reversed, leading to a blocking method that is similar in nature to DC block without the potential issues of toxic byproduct production. These results suggest that LFAC can achieve a high degree of nerve block in both small and large nerve bundles, resulting in the change in behavior of a biomarker, in-vivo in the mammalian nervous system at low amplitudes of electrical stimulation that are within the water window of the electrode.
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    ROLE OF SWEAT GLAND PHYSIOLOGY IN OBJECTIVE GALVANIC SKIN RE-SPONSE MEASUREMENT
    (Office of the Vice Chancellor for Research, 2012-04-13) Igega, Christele M.; Schild, John; Teach, Heather; Carpenter, Janet S.
    For the purpose of studying sweat in response to hot flashes, a type of thermal sweating, the process of extensive literature review performed in this particular project focused primarily on the eccrine sweat glands. Of the three categories of sweat glands, eccrine sweat glands account for the ma-jority of the sweat glands on the human body, existing over almost the en-tire body surface, and contributing to thermal sweating. Thermal sweating occurs as a means for the human body to regulate temperature (Johnson 1996). There are approximately 1.6 to 5 million eccrine sweat glands dis-tributed over the surface of the human body. Sweat gland density varies across different regions of the body, with the highest density on the palms of hands and soles of feet, while the lowest sweat gland density of 64 sweat glands per square centimeter is found on the back (Wilke et al., 2007). Wa-ter comprises approximately 99% of eccrine sweat, with the remaining com-pounds consisting mostly of varying amounts of sodium, potassium, calcium, and magnesium (Groscurth, 2002). The Galvanic Skin Response is an objec-tive measure of skin conductance that has been linked with the peripheral sweat rate (Carpenter et al., 2005). Importance has been put upon the po-tential clinical significance of using the Galvanic Skin Response to objectively enumerate the influence and effectiveness of interventions for health related issues in which sweating is a substantial symptom (Tataryn et al., 1981). One of the objectives of this research is to determine the effect that various sweat gland physiological factors, such as density, ionic composition, and sweat rate, may have on the accuracy of different Galvanic Skin Response measurement techniques and devices. 1Center for Enhancing Quality of Life, Indiana University School of Nursing, IUPUI, Indian-apolis, IN 46202
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    Sustained Stimulus Paradigms and Sexual Dimorphism of the Aortic Baroreflex in Rat
    (2019-05) Mintch, Landan M.; Schild, John; Yoshida, Ken; Mirro, Michael
    The neurophysiological pathways associated with beat-to-beat regulation of mean arterial pressure are well known. Less known are the control dynamics associated with short term maintained of arterial blood pressure about a homeostatic set point. The barorefex (BRx), the most rapid and robust of neural refexes within the autonomic nervous system, is a negative feedback controller that monitors and regulates heart rate and blood pressure. By leveraging the parasympathetic and sympathetic divisions of the autonomic nervous system, the BRx can change blood pressure within a single heart beat. To better understand these controller dynamics, a classic BRx refexogenic experimental preparation was carried out. This thesis recon rmed previous observations of an electrically-evoked sexually-dimorphic peak depressor response in the BRx of Sprague-Dawley rats and veri ed that these functional refexogenic differences carry over to sustained electrical paradigms. Further, it uncovered interesting recovery dynamics in both blood pressure and heart rate. The rat aortic depressor nerve was used as an experimental target for electrical activation of the parasympathetic-mediated reduction in mean arterial pressure. The duration, frequency, and patterning of stimulation were explored, with emphasis on differences between sexes. By measuring the normalized percent decrease in mean arterial pressure as well as the differences in beats per minute during rest and during stimulation, the null hypothesis was rejected.