INTRODUCTION: As populations are adopting a Western lifestyle, with high intake of dietary sugar and fat and low physical activity, the risk of developing Type 2 Diabetes is only increasing dramatically. Diabetes leads to drastic alterations within the body, primarily leading to neuropathies, nephropathies and retinopathies. As the prevalence of diabetes increases, it is important to understand the threat that it poses to the retina, and ultimately, vision. OBJECTIVE: We plan to compare the retina of diabetic patients with retinopathies to normal, healthy patients to understand the differences between them. We will be using a novel imaging technique, called Laser Speckle Flowgraphy, which provides the Mean Blur Rate, a value directly related to the blood flow velocity within the retina, specifically the optic nerve head. Using the calculated Mean Blur Rate, this study will quantify baseline blood flows in patients with diabetic retinopathies. This project aims to understand and differentiate the Mean Blur Rate of healthy patients and diabetic patients, including inter-patient and intra-patient comparisons, as well as changes in the Mean Blur Rate over time. The potential influence of treatment factors, such as intravitreal injection treatment or laser treatment, or demographic factors, such as age and race, on the Mean Blur Rate of diabetic retinopathy patients will also be evaluated. By understanding the difference in the retinas of diabetic patients and healthy patients, we can work towards preventing the loss of vision and function. METHODS: A total of 25 Type 2 diabetic patients with a diabetic retinopathy equaling 46 eyes were compared to 20 healthy patients, equaling 40 eyes. We collected the Mean Blur Rate for comparison between the two populations. Data was compared with correlation, t-test and ANOVA studies to find whether demographic or treatment variables influenced the Mean Blur Rate of diabetic retinopathy patients. RESULTS: We found a difference between the Mean Blur Rate, and thus blood flow, between the retina of diabetic and healthy patients. Diabetic patients tended to have a lower flow, presumably attributable the effects of hyperglycemia on blood circulation. Diabetic patients also have a significant difference in the Mean Blur Rate between both of their eyes, indicating that their hyperglycemia may affect both eyes differently (p<0). There was significant variability within both diabetic retinopathy patients and normal, healthy patients (p<0 for healthy patients and p<0.001 for diabetic patients). This is expected as blood circulation can be affected by a variety of factors other than disease status. We also found that the MBR of diabetics who were treated with intravitreal injections was on average higher than those who had not received intravitreal treatment. (p<0.05) CONCLUSION: Our study highlights how diabetic retinopathy impacts retinal blood flow, as well as showcases how Laser Speckle Flowgraphy can be used as a reliable method to measure and compare retinal blood velocities. Further studies are needed to understand how exactly diabetes affects blood circulation, although several theories are currently available. We also found a relation between previous intravitreal injection history and the blood flow velocity, but other studies have had mixed results on how exactly these injections alter the blood flow within the retina. Future studies can be conducted to better understand this relationship and uncover whether the effect on blood flow velocity is related to the drug used for the intravitreal injection or some other factor.

Neurons and the underlying vascular structure that maintains the nutrients necessary for their normal function are intrinsically linked. The relationship between neural activity and its accompanying blood flow is called neurovascular coupling. Our understanding of the intricacies of this relationship has evolved over the years from one of pure supply and demand to one that is highly complex and involves various cell types. While the exact mechanisms underlying neurovascular coupling still remains unresolved, altered coupling has been implicated in a variety of pathological conditions. The overall motivation of this thesis was to uncover how specific perturbations to either the neural or vascular system affect the resulting interplay between them. Our hope is that the results could act as a framework for guiding more specific mechanistic dissections in the future.Until recently, technological constraints have precluded the ability to comprehensively characterize neurovascular coupling on a large scale. Much of our understanding of the coupling relationship on a circuit level has been inferred from individual measurements of either neuronal firing or blood flow dynamics. Our lab has the ability to study coupling more directly through simultaneous imaging of both neural and hemodynamic activity. In this thesis, I set out to characterize how coupling could be differentially altered at a mesoscopic level by specifically perturbing either blood flow or cortical circuit organization. Thus, this work is split into two projects. The first investigates the downstream effects of an acute ischemic injury and the second focuses on how a developmental change in neuronal circuit structure alters function. My work in the acute ischemia model allowed us to capture a curious phenomenon called cortical spreading depolarization (CSD). CSDs have been implicated in a range of acute brain injuries, including ischemia. Despite being a neural event, CSDs have a profound impact on the cerebrovascular. Unfortunately, existing work in this field has been discordant and the results have been difficult to interpret. We used wide-field optical mapping to characterize the dynamics and impact of ischemia-triggered CSDs. Our imaging technique revealed that CSDs had a spatially heterogeneous impact on tissue depending on factors such as baseline metabolic condition and spatiotemporal properties of the CSDs themselves. Furthermore, we observed that CSDs were not isolated events and that multiple could occur in succession in a short period of time. By tracking each and every CSD, we were able to characterize the cumulative effects of CSDs on tissue oxygenation. Our results provide a contextual framework that reconciles some of the observed experimental variabilities. We conclude that an ischemic insult triggers a CSD and consequently, a combination of CSD dynamics and the tissue’s metabolic condition begets more CSDs. This pushes the brain deeper into a feedback loop of exacerbating damage. The second study was done in collaboration with Dr. Ewoud Schmidt and Dr. Franck Polleux, and looks at the functional changes mediated by expression of a human-specific gene duplication, SRGAP2C. The human brain exhibits unique features that enable its enhanced cognitive abilities. The Polleux lab found that humanized SRGAP2C mice showed similar features that characterize the human brain, such as increased synaptic density and delayed synaptic maturation. This ultimately led to increased local and long-range cortico-cortical connectivity and even improved the behavioral performance in a texture discrimination task. Thus, we were motivated to investigate the functional underpinnings that may explain and link these structural and behavioral differences. We used two-photon imaging to determine whether SRGAP2C expression changed neuronal firing dynamics and found that it increased response reliability and selectivity to whisker inputs, thus improving accuracy of sensory coding. This improvement may help to explain why SRGAP2C mice performed better in a cortex-dependent task that actively relies on engagement of multiple cortical regions. Moreover, by using a humanized SRGAP2C mouse model, our results provide a small step towards better understanding how experimental studies can be interpreted for and translated to humans.

A PC based waveform acquisition and analysis system has been developed for use in aorta-iliac arterial assessment. A Motorola DSP56001 based system containing dual Analog to Digital converters is used to sample phase quadrature demodulated signals from a commercially available continuous wave Doppler unit. The Power Spectral Density is calculated using an autoregressive model from which the mean velocity waveform is calculated. This waveform is used to calculate the damping factor, vessel compliance and runoff resistance of a simple electrical model of the lower limb arterial circulation using a non-linear regression technique of curve fitting in the time domain. A pilot study using the system shows a significant separation (p < 0.001 Mann Whitney U-test) between the damping factors of a normal control group (quartile range = 0. 15 - 0.25 ; median = 0. 19) and a patient group with angiographically determined aorta-iliac arterial disease (quartile range = 0.45 - 0.89 ; median= 0.49).

Gulf War Illness (GWI) is a medically unexplained illness that is classified by two common case criteria including the CDC chronic multisymptom illness definition and Kansas GWI criteria. It occurred among veterans who served in the Persian Gulf War from August, 1990 to February, 1991. Because of its complex chronic symptoms and multiple potential causes the neuropathological mechanisms and/or successfully clinical treatments for it remain elusive. Those in the theater of this war experienced exposures to many neurotoxicants, suggesting an association between GWI and neurologic dysfunction. In order to better understand the underlying cause of GWI, we have chosen to explore cerebral blood flow. Our hypothesis is that abnormal cerebral blood flow is associated with GWI and ultimately neurological dysfunction. By conducting a comprehensive evaluation of cerebral blood flow we will be able to determine if it has a role in Gulf War Illness. Historically, several techniques have been used to measure cerebral blood flow. Arterial spin labeling (ASL) has been widely used in research as a non-invasive and non-ionizing technique, which has the least adverse effects on the participants. An ASL subtype called pseudo-continuous arterial spin labeling (PCASL) has become a favorable technique in ASL research because it combines the advantages of continuous arterial spin labeling (CASL) and pulsed arterial spin labeling (PASL). PCASL can quantify the absolute cerebral blood flow without the exogenous contrast agents. The cost of PCASL is relatively low as most scanner can run this sequence without additional hardware. It provides higher label efficiency (to CASL) and greater signal-to-noise ratio (to PASL). We utilized the data from an ongoing study with 114 GW veterans study participants aged from 42 to 80. Their regional cerebral blood flow was scanned using a 3T Philips Achieva MRI scanner. Asltoolbox (Wang et al., 2016) was used to calculate the cerebral blood flow, and Freesurfer v6.0 was used to do the co-registration and quantification. The analysis of demographic data suggested that the presence of hypertension was the only variables that made differences between control and GWI case groups (p = 0.02). General linear models indicated that alternations of cerebral blood flow were not a component of GWI at least using CMI definition. Whether cerebral blood flow associates with GWI is still pending on further studies with utilizing a more refined case definition.

Passive hallux adduction has been shown to decrease blood flow in the lateral plantar artery (LPA) in a non-weight-bearing condition. Further research in weight-bearing and shod conditions is necessary to explore relationships between altered blood flow and injury or tissue healing. However, measuring blood flow in a shod foot would require an alternate measurement location to accommodate footwear, such as the more proximal posterior tibial artery (PTA). PURPOSE: To determine changes in blood flow in the PTA and LPA subsequent to passive hallux adduction and to compare the observed changes between the two arteries. Second, to determine if measurement at the PTA is a viable surrogate for measurement at the LPA. METHODS: Forty-one subjects (21 males, 20 females) participated in this study (age 23.5 ± 4.5 years, body mass 72.6 ± 13.7 kg, and height 173.1 ± 10.2 cm). PTA and LPA vessel diameter and velocity were measured via doppler ultrasound (L8-18i transducer GE Logiq S8). LPA was imaged distal to the abductor hallucis and the PTA posterior to the medial malleolus. Each artery was measured for 120 s: 60 s at rest followed by 60 s of passive hallux adduction. PTA and LPA metrics were log transformed and compared using a two-way repeated measures ANOVA, then the log transformed data was assessed with paired t-tests and Bland-Altman plots (alpha = 0.05). RESULTS: There was an expected decrease in blood flow within each artery after passive hallux adduction (p < 0.001). The volume of blood flow differed between the arteries (p < .0001), but the change between baseline to first 5 cardiac cycles after hallux adduction was similar in each artery (p = 0.419). Bland-Altman analysis showed large spread limits of agreement, indicating the PTA underestimated or overestimated measurements at the LPA. CONCLUSIONS: These data suggest that PTA blood flow behaves in a similar manner as LPA blood flow in consequence to passive hallux adduction. There is no significant difference in the absolute change of blood flow during hallux adduction between the LPA and PTA. However, Bland-Altman analysis suggests that the PTA is not a direct surrogate for the LPA due to the large variance in flow between the arteries. Despite this, the PTA can still be a beneficial location of measurement for plantar blood flow. Some reasons are that the PTA has a larger diameter making it an easier artery to image and allows for further research implications due to its ease of access in more applicable circumstances, such as in a shod condition.

Vascular risk factors affect cerebral blood flow (CBF) and cerebral vascular reactivity, contributing to cognitive decline. Hippocampus is vulnerable to both Alzheimer's disease (AD) pathology and ischemia; nonetheless, the information about the impact of vascular risk on hippocampal perfusion is minimal. Cognitively, healthy elderly (NL18, 69.96.7 years) and subjects with mild cognitive impairment (MCI15, 74.98.1 years) were evaluated for the Framingham cardiovascular risk profile (FCRP). All underwent structural imaging and resting CBF assessment with arterial spin labeling (ASL) at 3T magnetic resonance imaging (MRI). In 24 subjects (NL17, MCI7), CBF was measured after a carbon dioxide rebreathing challenge. Across all subjects, FCRP negatively correlated with hippocampal (0.41, P0.049) and global cortical (0.46, P0.02) vasoreactivity to hypercapnia (VRh). The FCRP-VRh relationships were most pronounced in the MCI group: hippocampus (0.77, P=0.04); global cortex (0.83, P=0.02). The FCRP did not correlate with either volume or resting CBF. The hippocampal VR h was lower in MCI than in NL subjects (Z2.0, P=0.047). This difference persisted after age and FCRP correction (F 3,20 4.6, P0.05). An elevated risk for vascular pathology is associated with a reduced response to hypercapnia in both hippocampal and cortical tissue. The VR h is more sensitive to vascular burden than either resting CBF or brain volume.

Objectives. Electrical stimulation of the dorsal aspect of the upper thoracic spinal cord is used increasingly to treat patients with angina pectoris refractory to conventional therapeutic strategies. The purpose of this study was to determine whether spinal cord stimulation (SCS) in dogs affects regional myocardial blood flow and left-ventricular (LV) function before and during transient obstruction of the left anterior descending coronary artery (LAD). Methods. In anesthetized dogs, regional myocardial blood flow distribution was determined using radiolabeled microspheres and left-ventricular function was measured by impedance-derived pressure-volume loops. SCS was accomplished by stimulating the dorsal T1-T2 segments of the spinal cord using epidural bipolar electrodes at 90% of motor threshold (MT) (50 Hz, 0.2-ms duration). Effects of 5-min SCS were assessed under basal conditions and during 4-min occlusion of the LAD. Results. SCS alone evoked no change in regional myocardial blood flow or cardiovascular indices. Transient LAD occlusion significantly diminished blood flow within ischemic, but not in non-ischemic myocardial tissue. Left ventricular pressure-volume loops were shifted rightward during LAD occlusion. Cardiac indices were altered similarly during LAD occlusion and concurrent SCS. Conclusions. SCS does not influence the distribution of blood flow within the non-ischemic or ischemic myocardium. Nor does it modify LV pressure-volume dynamics in the anesthetized experimental preparation.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaf 186. / by Thomas James Miller, Jr. / M.S.

Bakgrund: Styrka är en viktig faktor i självständighet och säkerhet, i synnerlighet hos äldre. Evidensen idag säger att högintensiv styrketräning är att föredra över lågintensiv i syfte att maximera styrkeökning. BFR-träning är en metod där blodflödet stryps åt för att snabbare åstadkomma en metabolisk stress vilket innebär att styrketräning kan utföras lågintensivt men sägs producera resultat jämförbara med högintensiv styrketräning. Syfte: Syftet med denna studie var att mäta effekt avseende styrka och hypertrofi av lågintensiv BFR-träning samt smärta och upplevd ansträngning hos två friska unga män. Metod: Två personer rekryterades till studien. De fick utföra en intervention med lågintensiv BFR-träning tre pass i veckan under fem veckor. Utfallsmåtten för studien är maxstyrka mätt i 1RM, peak torque mätt i Biodex Isokinetic Dynamometer, hypertrofi mätt med måttband runt låren, samt upplevelse av ansträngningsgrad samt smärta utifrån Borg-RPE och NRS. Resultat: Deltagare 1 visade en förändring av muskelstyrka i peak torque (-7,2% H., -2,4% V.), -9,4% i benpress (1RM), +35,4% i knäextension (1RM). Omkrets uppmättes till -0,5cm H. (-0,79%), +1cm V. (+1,61%). Borg-RPE var jämn under hela interventionen medan NRS värdena sjönk successivt. Deltagare 2 visade en förändring av muskelstyrka i peak torque (-3,1% H., -3,2% V.), +11,5% i benpress (1RM), +9,3% i knäextension (1RM). Omkrets uppmättes till -0,5cm H. (-0,86%), -0,5cm V. (-0,88%). Borg-RPE och NRS visade båda en successivt stigande trend. Slutsats: 5 veckors lågintensiv BFR-träning visar en potential för styrkeökning i 1RM. Ingen styrkeökning i peak torque observerades och ingen påtaglig skillnad uppmättes i omkrets. BFR-träning som metod bör således vara en lägre prioriterad träningsmetod och bör endast användas efter noggrann övervägelse och uppsyn, med tanke på de kontraindikationer som finns. Denna studie undersökte endast unga friska individer vilket också då gör denna metod särskild applicerbar på denna målgrupp.

Chapter 1: Molecular Mechanism of Mitochondrial Fragmentation and Glucose Metabolism under Disturbed Flow in Endothelial Cells: Focus on the Role of Dynamin-Related Protein 1. The luminal surface of the endothelium is continually exposed to dynamic blood flow patterns that is known to alter immunometabolic phenotypes of the endothelial cells (ECs). Recent literature reported that inhibition of the metabolic reprogramming to glycolysis or enhancement of oxidative phosphorylation (OXPHOS) is considered as an effective strategy to prevent EC proinflammatory activation and eventually the progression of vascular diseases. Endothelial mitochondria are highly dynamic organelles playing versatile roles in maintaining endothelial cell homeostasis working as bioenergetic, biosynthetic, and signaling organelles. The balance between fusion and fission processes modulates mitochondrial network, which is essential for maintaining mitochondrial homeostasis. Disruption of the orchestrated balance, especially toward excessive fission resulting in fragmented and dysfunctional mitochondria, has been shown to be associated with atheroprone phenotypes of ECs. However, there is a key knowledge gap with respect to morphology of EC mitochondria under different flow conditions and its role on EC immunometabolic phenotypes.In chapter 1, the purpose of this study was to investigate the effect of different flow patterns on mitochondrial morphology in ECs and its implication in immunometabolic endothelial phenotype. The overarching hypothesis of the Chapter 1 was that disturbed flow (DF) will increase mitochondrial fragmentation, which will facilitate glycolysis and inflammatory activation in ECs. In the study, mitochondrial morphology was analyzed in ECs at multiple segments of the aorta and arteries in EC-specific photo-activatable mitochondria (EC-PhAM) mice. Increased mitochondrial fragmentation was observed at atheroprone regions (e.g., lesser curvature of the aortic arch, LC) with increased dynamin-related protein 1 (Drp1) activity, compared with the atheroprotective regions (e.g., thoracic aorta, TA). The atheroprone regions also showed a higher level of endothelial activation and glycolysis. Carotid artery partial ligation surgery, as a surgical model of DF, significantly induced mitochondrial fragmentation with elevated Drp1 activity and increased EC activation. in vitro experiments recapitulated in vivo observations. Inhibition of Drp1 activity by mdivi-1 attenuated the DF-induced atheroprone EC phenotypes, showing the close relationship between mitochondrial morphology and atheroprone phenotypes of ECs. As for the molecular mechanism, hypoxia-inducible factor 1 α (HIF-1α) stabilization and its nuclear translocation was significantly increased under DF, which was attenuated by mdivi-1 treatment. Mitochondrial reactive oxygen species (mtROS) and succinate, which are known to reduce prolyl hydroxylase domain 2 (PHD2) activity thereby increasing HIF-1α stabilization, were significantly elevated under DF, but those were attenuated by mdivi-1 treatment. Finally, a 7-week voluntary wheel-running exercise training significantly decreased mitochondrial fragmentation with a down-regulation of VCAM-1 expression at the LC. In conclusion, our data suggest that DF induces mitochondrial fragmentation with increased Drp1 activity, which is associated with an atheroprone EC phenotype. In addition, regular practice of aerobic exercise reduces mitochondrial fragmentation and prevents ECs from an atheroprone endothelial phenotype at the atheroprone regions. Chapter 2: Molecular Mechanisms for Unidirectional Flow (UF)/Exercise-Induced improvement of Mitochondrial Integrity: Focus on phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) /PARKIN-Dependent Mitochondrial Autophagy (Mitophagy) Phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) is an essential molecule in the mitophagy process and known to act as a cytoprotective protein involved in several cellular mechanisms in mammalian cells. It has been documented that the loss of PINK1 expression in mice and various cell types enhance susceptibility to stress-induced cell damage, while the overexpression of PINK1 significantly attenuates stress-induced mitochondrial and cellular dysfunction.In chapter 2, the purpose of this study was to investigate PINK1 expression and its subcellular localization under an exercise-mimic laminar shear stress (LSS) condition in human primary endothelial cells and in exercizing mice, and its implications on endothelial homeostasis and cardiovascular disease (CVD) prevention. The overarching hypothesis of the Chapter 2 was that unidirectional flow (UF) will increase cytosolic PINK1 expression through which UF-preconditioned ECs will be more protective against an accumulation of dysfunctional mitochondria via a greater mitophagy induction. In this study, we measured the full-length PINK1 (FL-PINK1) mRNA and protein expression levels in ECs under unidirectional laminar shear stress (LSS). LSS significantly elevated both FL-PINK1 mRNA and protein expressions in ECs. Mitochondrial fractionation assays showed a decrease in FL-PINK1 accumulation in the mitochondria with an increase in the cytosolic FL-PINK1 level under LSS. Confocal microscopic analysis confirmed these subcellular localization patterns suggesting downregulation of mitophagy induction. Indeed, mitophagy flux was decreased under LSS, determined by a mtKeima probe. Mitochondrial morphometric analysis and mitochondrial membrane potential determined by tetraethylbenzimidazolylcarbocyanine iodide (JC-1) showed mitochondrial elongation and increased mitochondrial membrane potential under LSS respectively, suggesting that an elevation of cytosolic PINK1 is not related to an immediate induction of mitophagy. However, increased cytosolic PINK1 elevated mitophagic sensitivity toward dysfunctional mitochondria in pathological conditions. Preconditioned ECs with LSS showed lower mtDNA lesions under angiotensin II stimulation. Moreover, LSS-preconditioned ECs showed rapid Parkin recruitment and mitophagy induction in response to mitochondrial toxin (i.e., carbonyl cyanide chlorophenylhydrazone, CCCP) treatment compared to the control. We measured PINK1 expression at ECs of the thoracic aorta in exercised mice, a physiological LSS-enhanced model, which was significantly elevated compared to sedentary animals. In addition, exercise-preconditioned mice were more protective to angiotensin II-induced mtDNA lesion formation in the mouse abdominal aorta than sedentary mice, suggesting a potential protective mechanism of exercise in a PINK1-dependent manner. In conclusion, LSS increases a cytosolic pool of FL-PINK1, which may elevate the mitophagic sensitivity toward dysfunctional mitochondria or activate other cytoprotective mechanisms in ECs. Our data suggest that exercise may support mitochondrial homeostasis in vascular ECs by enhancing PINK1-dependent cell protection mechanisms. / Kinesiology