Browsing by Subject "Ischemic stroke"
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Item Chronic monitoring of cortical hemodynamics after ischemic stroke using funcional optical imaging techniques(2015-05) Schrandt, Christian John; Dunn, Andrew Kenneth, 1970-The roles of the vascular architecture and blood flow in response to neurovascular diseases are important in predicting physiological outcomes. Observing these parameters chronically with optical imaging techniques provides insight into the neurovascular recovery process. We develop and deploy optical imaging systems for monitoring the progression of vascular structure, perfusion, and functional blood response after ischemic stroke in a chronic rodent model to observe vascular dynamics of the cortex under normal and diseased pathologies. Specifically, we monitor the progression of the vascular structure and cerebral blood flow (CBF) over a chronic period in the rodent cortex after photo-thrombotic occlusion. Multi-Exposure Speckle Imaging (MESI) provides surface measurements of microvascular flow dynamics while Two-Photon Fluorescence Microscopy offers direct visualization of the microvascular structure. We observe the occurrence of vascular reorientation in the sub-surface microvascular structure over a 35 day post-occlusion period. We also correlate MESI flow estimates in the parenchyma with sub-surface microvascular volume fractions from two-photon microscopy to assess how vascular density influences the surface-integrated MESI measurements. Next, we develop and validate a MESI technique for measuring absolute changes of the functional blood flow response to forepaw stimulation in rodents, termed FA MESI. The optimal camera exposures for capturing the CBF response to forepaw stimulation are extracted from a training set of animal data and the feasibility of the technique is demonstrated in a testing animal set by comparing functional response results between new and existing techniques. We then deploy this system in a chronic study monitoring the progression of hemodynamic parameters after ischemic stroke within the functionally responding area of the cortex. The progression of the regional CBF perfusion and absolute changes in the magnitude of the functional blood flow response are monitored chronically after photo-thrombotic occlusion. We compare the differences between absolute and relative measurements of the functional blood flow responses, and validate FA MESI by comparing baseline measurements to 15-exposure MESI over the sampled flow distributions. We demonstrate the differences measured between the functional outcomes and the regional CBF perfusion over a three week post-occlusion time period.Item Quantitative cerebral blood flow measurement with Multi Exposure Speckle Imaging(2010-05) Parthasarathy, Ashwin Bharadwaj; Dunn, Andrew Kenneth, 1970-; Milner, Thomas; Tunnell, James; Emelianov, Stanislav; Fox, DouglasCerebral blood flow (CBF) measures are central to the investigation of ischemic strokes, spreading depressions, functional and neuronal activation. Laser Speckle Contrast Imaging (LSCI) is an optical imaging technique that has been used to obtain CBF measures in vivo at high spatial and temporal resolutions, by quantifying the localized spatial blurring of backscattered coherent light induced by blood flow. Despite being widely used for biomedical applications, LSCI's critical limitations such as its tendency to underestimate large flow changes and its inability to accurately estimate CBF through a thinned skull have not been overcome. This dissertation presents a new Multi Exposure Speckle Imaging (MESI) technique that combines a new instrument and mathematical model to overcome these limitations. Additionally, in a pilot clinical study, an adapted neurosurgical microscope was used to obtain intra-operative LSCI images of CBF in humans. The MESI instrument accurately estimates experimental constants by imaging backscattered speckles over a wide range of the camera's exposure durations. The MESI mathematical model helps account for light that has scattered from both static and moving particles. In controlled flow experiments using tissue simulating phantoms, the MESI technique was found to estimate large changes in flow accurately and the estimates of flow changes were found to be unaffected by the presence of static particles in these phantoms. In an in vivo experiment in which the middle cerebral artery in mice was occluded to induce ~100% reduction in CBF, not only was the reduction in CBF accurately estimated by the MESI technique but these estimates of CBF changes were found to be unaffected by the presence of a thinned skull. The validity of statistical models used to derive the MESI mathematical model was confirmed using in vivo dynamic light scattering (DLS) measurements of CBF in mice. The MESI technique's potential to estimate absolute values of CBF in vivo was demonstrated by comparing CBF estimates obtained using the MESI technique to DLS measurements. The MESI technique's ability to measure CBF changes quantitatively through a thinned skull makes it particularly useful in chronic and long term studies leading to the development of better, more accurate stroke models.Item Quantitative optical imaging platform for studying neurovascular hemodynamics during ischemic stroke(2018-08-23) Sullender, Colin Tan; Dunn, Andrew Kenneth, 1970-; Jones, Theresa A; Xie, Chong; Tunnell, James W; Ding, Ming-ChiehThe measurement of cerebral hemodynamics is vital for the study of physiological and pathophysiological conditions in the brain. Preclinical research examining the mechanisms, outcomes, and efficacies of interventions during ischemic stroke require quantitative imaging technologies. This dissertation presents the development of an optical imaging platform capable of chronic in vivo monitoring of cortical hemodynamics during ischemic stroke and the subsequent recovery. The system combines two different imaging techniques, laser speckle contrast imaging (LSCI) and oxygen-dependent quenching of phosphorescence, to measure cerebral blood flow (CBF) and dissolved oxygen tension (pO2) within cortical vasculature. Phosphorescence signal localization is achieved through the use of a spatial light modulator to selectively pattern excitation light in order to overcome the traditional limitations of the imaging modality. The spatial light modulator is also utilized to perform artery-targeted photothrombosis for the induction of highly-localized, reproducible infarcts as an extension of the photothrombotic model of ischemic stroke. The LSCI hardware implements the multi-exposure speckle imaging (MESI) technique for robust estimates of CBF that facilitate day-to-day and between-subject comparisons. The integration of an awake imaging system eliminates the confounding effects of anesthesia upon cerebral hemodynamics. The capabilities of the complete optical imaging platform are demonstrated by monitoring the acute hemodynamic response during targeted photothrombosis and the chronic recovery of the resulting ischemic infarctItem The effects of remote limb ischemic conditioning on functional motor outcome of the paretic limb after ischemic stroke(2021-01-21) Barksdale, Bryan; Jones, Theresa A.; Schnyer, David M; Monfils, Marie H; Lee, Hongjoo J; Sulzer, James SStroke is the most common cause of severe long-term adult disability in the US. Stroke survivors are often left with severe motor impairments of the arm and hand on one side, termed hemiparesis. Motor rehabilitative training (RT) can induce structural plasticity to improve functional outcome, but RT alone is usually insufficient to restore normal function. Thus, there is a critical need for treatments that can enhance the effect of rehabilitation training. Remote limb ischemic conditioning (RLIC), which consists of short repeated bouts of ischemia to a limb using a blood pressure cuff, is a non-invasive intervention known to be neuroprotective in the setting of stroke. Recently, however, RLIC was also shown in several small studies to enhance motor learning in healthy humans and thus may have the potential to enhance the adaptive plasticity induced by RT and improve functional outcome. However, this effect isn't always replicable and may be dependent on age and comorbidities. The central hypothesis of these dissertation studies is that RLIC done in conjunction with RT, can improve the functional motor outcome of the paretic limb after stroke compared to RT alone. All studies utilized the Endothelin-1 (ET-1) cortical ischemic lesion model in rats. RT was modeled using the single pellet retrieval task. RLIC was modeled by inflating a blood-pressure cuff on the hindlimb of the rat to intermittently restrict blood flow. The first study investigated RLIC+RT during the subacute phase of stroke in middle-aged rats. No beneficial effect of RLIC was found. The second study investigated RLIC+RT during the chronic phase of stroke in middle-aged rats, and no beneficial effect of RLIC was found. The third study investigated RLIC+RT during the subacute phase of stroke in adult rats and similarly found no beneficial effect of RLIC. Together these results indicate that RLIC is unlikely to enhance the effects of RT after stroke during the subacute or chronic phases. This lack of effect seen in our studies is a significant finding given the interest of the field in RLIC after the initial positive results in healthy, intact adults.Item Women's early symptom experience of stroke : a narrative study(2010-05) Beal, Claudia Calle; Stuifbergen, Alexa, 1955-; Becker, Heather; Harrison, Tracie; Pennebaker, James; Volker, DeborahThe purpose of this study was to gain understanding of the early symptom experience of ischemic stroke in women. This is the only study of which the researcher is aware in which narrative inquiry was used to examine the period of time from symptom onset until emergency department arrival in women. Data collection was achieved by in-depth interviews during which participants’ stories of stroke were elicited. Individual narrative accounts were created and analyzed using within and across case techniques. The participants were nine women ranging in age from 24-86 years (average age 53). Four participants were Caucasian, three were Hispanic, one was African American and one woman was of mixed race. The participants experienced the onset of stroke as the inability to carry out accustomed activities in usual ways. There was a tendency to objectify the body. Only two participants considered stroke as a possible cause for their symptoms, and the other women attributed symptoms everyday bodily experiences and/or other health conditions. Most participants did not perceive themselves at risk for stroke although all but one woman had risk factors. The participants displayed a variety of responses to symptoms, including trying to continue with usual activities and seeking help as well as deciding not to tell anyone about their symptoms. Symptom response was related to women’s evaluation of and emotional response to symptoms. The actions taken by the participants in response to symptoms were informed by the meaning of the symptoms, and meaning was formed within the context of each woman’s life situation. Few women made the decision to seek medical care on their own, and in every case family members or co-workers were reported to take an active role in getting the participant to the hospital. Some family members were reported to consult with one another before making the decision to call EMS or transporting the participant to the emergency department. Consistent with what was expected from extant research the majority of the participants did not arrive at the hospital in time to be offered treatment with t-PA. Recommendations for future research, stroke education and practice were discussed.