Browsing by Subject "Cats"
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Item Open Access Analyzing Euthyroid & Hyperthyroid Indoor Cat Exposure to Flame Retardants(2020-04-23) Osteen, Mary-CatherineHyperthyroidism in cats has increased since its original description in the 1970s. Environmental exposures are suggested as a potential contributing factor. This research investigated pet cats’ exposure to flame retardant chemicals in the home environment and associations with hyperthyroidism. Silicone collar tags were used as indicators of exposure to two classes of flame retardants: polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs). Though previous studies have documented PBDE exposure among house cats, less is known about exposure to OPEs. Thus, we first evaluated silicone tags as measures of internal exposure to OPEs. Cats wore silicone collar tags for 7 days in their home environment, after which tags were analyzed for flame retardants. Urine samples were collected from 9 cats and analyzed for OPE metabolites. Tris(2-chloroisopropyl) phosphate (TCIPP), was significantly and positively correlated with its urinary metabolites (r≥0.73; p<0.05), and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) was significantly and positively correlated with its urinary metabolite (r=0.77; p<0.05). Several other OPEs from tags were correlated with their metabolites in urine, suggesting that tags capture information about cats’ internal exposure; however, correlations were not statistically significant. To evaluate exposure differences by thyroid status, 12 hyperthyroid and 12 euthyroid cats (matched by age and sex) wore tags for 7 days. Tags were analyzed for PBDEs and OPEs. Two PBDEs, BDE-47 and BDE-99, were higher on tags worn by hyperthyroid compared to euthyroid cats (p<0.05). Associations with thyroid status were not significant for OPEs; however, we caution against over-interpretation of these results given our limited sample size. Potential confounders, including diet and activity level, were evaluated; however, no significant differences were found between hyperthyroid and euthyroid cats (p>0.20), suggesting these factors are not likely to confound associations with flame retardant exposures. Cumulatively, results suggest that exposure to PBDE flame retardants is higher among hyperthyroid cats, which is in agreement with previous studies that have reported differences in serum PBDE levels of hyperthyroid and euthyroid cats.Item Open Access Cerebral oxygenation and optimal vascular brain organization.(J R Soc Interface, 2015-06-06) Hadjistassou, Constantinos; Bejan, Adrian; Ventikos, YiannisThe cerebral vascular network has evolved in such a way so as to minimize transport time and energy expenditure. This is accomplished by a subtle combination of the optimal arrangement of arteries, arterioles and capillaries and the transport mechanisms of convection and diffusion. Elucidating the interaction between cerebral vascular architectonics and the latter physical mechanisms can catalyse progress in treating cerebral pathologies such as stroke, brain tumours, dementia and targeted drug delivery. Here, we show that brain microvascular organization is predicated on commensurate intracapillary oxygen convection and parenchymal diffusion times. Cross-species grey matter results for the rat, cat, rabbit and human reveal very good correlation between the cerebral capillary and tissue mean axial oxygen convective and diffusion time intervals. These findings agree with the constructal principle.Item Open Access Design and in vivo evaluation of more efficient and selective deep brain stimulation electrodes.(Journal of neural engineering, 2015-08) Howell, Bryan; Huynh, Brian; Grill, Warren MObjective
Deep brain stimulation (DBS) is an effective treatment for movement disorders and a promising therapy for treating epilepsy and psychiatric disorders. Despite its clinical success, the efficiency and selectivity of DBS can be improved. Our objective was to design electrode geometries that increased the efficiency and selectivity of DBS.Approach
We coupled computational models of electrodes in brain tissue with cable models of axons of passage (AOPs), terminating axons (TAs), and local neurons (LNs); we used engineering optimization to design electrodes for stimulating these neural elements; and the model predictions were tested in vivo.Main results
Compared with the standard electrode used in the Medtronic Model 3387 and 3389 arrays, model-optimized electrodes consumed 45-84% less power. Similar gains in selectivity were evident with the optimized electrodes: 50% of parallel AOPs could be activated while reducing activation of perpendicular AOPs from 44 to 48% with the standard electrode to 0-14% with bipolar designs; 50% of perpendicular AOPs could be activated while reducing activation of parallel AOPs from 53 to 55% with the standard electrode to 1-5% with an array of cathodes; and, 50% of TAs could be activated while reducing activation of AOPs from 43 to 100% with the standard electrode to 2-15% with a distal anode. In vivo, both the geometry and polarity of the electrode had a profound impact on the efficiency and selectivity of stimulation.Significance
Model-based design is a powerful tool that can be used to improve the efficiency and selectivity of DBS electrodes.Item Open Access Evaluation of high-perimeter electrode designs for deep brain stimulation.(Journal of neural engineering, 2014-08) Howell, Bryan; Grill, Warren MObjective
Deep brain stimulation (DBS) is an effective treatment for movement disorders and a promising therapy for treating epilepsy and psychiatric disorders. Despite its clinical success, complications including infections and mis-programing following surgical replacement of the battery-powered implantable pulse generator adversely impact the safety profile of this therapy. We sought to decrease power consumption and extend battery life by modifying the electrode geometry to increase stimulation efficiency. The specific goal of this study was to determine whether electrode contact perimeter or area had a greater effect on increasing stimulation efficiency.Approach
Finite-element method (FEM) models of eight prototype electrode designs were used to calculate the electrode access resistance, and the FEM models were coupled with cable models of passing axons to quantify stimulation efficiency. We also measured in vitro the electrical properties of the prototype electrode designs and measured in vivo the stimulation efficiency following acute implantation in anesthetized cats.Main results
Area had a greater effect than perimeter on altering the electrode access resistance; electrode (access or dynamic) resistance alone did not predict stimulation efficiency because efficiency was dependent on the shape of the potential distribution in the tissue; and, quantitative assessment of stimulation efficiency required consideration of the effects of the electrode-tissue interface impedance.Significance
These results advance understanding of the features of electrode geometry that are important for designing the next generation of efficient DBS electrodes.Item Open Access Stimulation Efficiency With Decaying Exponential Waveforms in a Wirelessly Powered Switched-Capacitor Discharge Stimulation System.(IEEE transactions on bio-medical engineering, 2018-05) Lee, Hyung-Min; Howell, Bryan; Grill, Warren M; Ghovanloo, MaysamThe purpose of this study was to test the feasibility of using a switched-capacitor discharge stimulation (SCDS) system for electrical stimulation, and, subsequently, determine the overall energy saved compared to a conventional stimulator. We have constructed a computational model by pairing an image-based volume conductor model of the cat head with cable models of corticospinal tract (CST) axons and quantified the theoretical stimulation efficiency of rectangular and decaying exponential waveforms, produced by conventional and SCDS systems, respectively. Subsequently, the model predictions were tested in vivo by activating axons in the posterior internal capsule and recording evoked electromyography (EMG) in the contralateral upper arm muscles. Compared to rectangular waveforms, decaying exponential waveforms with time constants >500 μs were predicted to require 2%-4% less stimulus energy to activate directly models of CST axons and 0.4%-2% less stimulus energy to evoke EMG activity in vivo. Using the calculated wireless input energy of the stimulation system and the measured stimulus energies required to evoke EMG activity, we predict that an SCDS implantable pulse generator (IPG) will require 40% less input energy than a conventional IPG to activate target neural elements. A wireless SCDS IPG that is more energy efficient than a conventional IPG will reduce the size of an implant, require that less wireless energy be transmitted through the skin, and extend the lifetime of the battery in the external power transmitter.Item Open Access Transmission of MRSA between companion animals and infected human patients presenting to outpatient medical care facilities.(PLoS One, 2011) Ferreira, Jorge Pinto; Anderson, Kevin L; Correa, Maria T; Lyman, Roberta; Ruffin, Felicia; Reller, L Barth; Fowler, Vance GMethicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in both human and veterinary medicine. The importance of companion animals as reservoirs of human infections is currently unknown. The companion animals of 49 MRSA-infected outpatients (cases) were screened for MRSA carriage, and their bacterial isolates were compared with those of the infected patients using Pulsed-Field Gel Electrophoresis (PFGE). Rates of MRSA among the companion animals of MRSA-infected patients were compared to rates of MRSA among companion animals of pet guardians attending a "veterinary wellness clinic" (controls). MRSA was isolated from at least one companion animal in 4/49 (8.2%) households of MRSA-infected outpatients vs. none of the pets of the 50 uninfected human controls. Using PFGE, patient-pets MRSA isolates were identical for three pairs and discordant for one pair (suggested MRSA inter-specie transmission p-value = 0.1175). These results suggest that companion animals of MRSA-infected patients can be culture-positive for MRSA, representing a potential source of infection or re-infection for humans. Further studies are required to better understand the epidemiology of MRSA human-animal inter-specie transmission.Item Restricted Whole body mechanics of stealthy walking in cats.(PLoS One, 2008) Bishop, Kristin L; Pai, Anita K; Schmitt, DanielThe metabolic cost associated with locomotion represents a significant part of an animal's metabolic energy budget. Therefore understanding the ways in which animals manage the energy required for locomotion by controlling muscular effort is critical to understanding limb design and the evolution of locomotor behavior. The assumption that energetic economy is the most important target of natural selection underlies many analyses of steady animal locomotion, leading to the prediction that animals will choose gaits and postures that maximize energetic efficiency. Many quadrupedal animals, particularly those that specialize in long distance steady locomotion, do in fact reduce the muscular contribution required for walking by adopting pendulum-like center of mass movements that facilitate exchange between kinetic energy (KE) and potential energy (PE). However, animals that are not specialized for long distance steady locomotion may face a more complex set of requirements, some of which may conflict with the efficient exchange of mechanical energy. For example, the "stealthy" walking style of cats may demand slow movements performed with the center of mass close to the ground. Force plate and video data show that domestic cats (Felis catus, Linnaeus, 1758) have lower mechanical energy recovery than mammals specialized for distance. A strong negative correlation was found between mechanical energy recovery and diagonality in the footfalls and there was also a negative correlation between limb compression and diagonality of footfalls such that more crouched postures tended to have greater diagonality. These data show a previously unrecognized mechanical relationship in which crouched postures are associated with changes in footfall pattern which are in turn related to reduced mechanical energy recovery. Low energy recovery was not associated with decreased vertical oscillations of the center of mass as theoretically predicted, but rather with posture and footfall pattern on the phase relationship between potential and kinetic energy. An important implication of these results is the possibility of a tradeoff between stealthy walking and economy of locomotion. This potential tradeoff highlights the complex and conflicting pressures that may govern the locomotor choices that animals make.