Browsing by Subject "Pressure"
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Item Open Access Design and Implementation of High Pressure Systems(2014) Shoop, Logan ThomasHydrogen is arising as a potential fuel source due to its high mass-specific energy and wide applicability. However, hydrogen must first be pressurized before being implemented, causing a loss in efficiency and larger issues in implementation. Current processes produce hydrogen at low pressure and then pressurize the gaseous hydrogen with a compressor. Thermodynamic studies have shown that producing hydrogen in pressurized chambers could reduce the energy losses due to compression, raising generation efficiency. These projected gains are purely theoretical, however, and ignore practical limitations. The goal of this thesis is to design and construct a safe high-pressure hydrogen producing system at 5000 psi and to show the steps and considerations during this process.
Item Open Access Effect of lithotripter focal width on stone comminution in shock wave lithotripsy.(J Acoust Soc Am, 2010-04) Qin, Jun; Simmons, W Neal; Sankin, Georgy; Zhong, PeiUsing a reflector insert, the original HM-3 lithotripter field at 20 kV was altered significantly with the peak positive pressure (p(+)) in the focal plane increased from 49 to 87 MPa while the -6 dB focal width decreased concomitantly from 11 to 4 mm. Using the original reflector, p(+) of 33 MPa with a -6 dB focal width of 18 mm were measured in a pre-focal plane 15-mm proximal to the lithotripter focus. However, the acoustic pulse energy delivered to a 28-mm diameter area around the lithotripter axis was comparable ( approximately 120 mJ). For all three exposure conditions, similar stone comminution ( approximately 70%) was produced in a mesh holder of 15 mm after 250 shocks. In contrast, stone comminution produced by the modified reflector either in a 15-mm finger cot (45%) or in a 30-mm membrane holder (14%) was significantly reduced from the corresponding values (56% and 26%) produced by the original reflector (no statistically significant differences were observed between the focal and pre-focal planes). These observations suggest that a low-pressure/broad focal width lithotripter field will produce better stone comminution than its counterpart with high-pressure/narrow focal width under clinically relevant in vitro comminution conditions.Item Open Access Effect of Prone Positional Apparatus on the Occurrence of Acute Kidney Injury After Spine Surgery.(World neurosurgery, 2019-08) Jin, Seok-Joon; Park, Yong-Seok; Kim, Sung-Hoon; Kim, Dongseop; Shim, Woo-Hyun; Jang, Dong-Min; Shaffrey, Christopher I; Naik, Bhiken IBackground and objective
Increased intra-abdominal pressure with prone positioning for spinal surgery is associated with intraoperative hemodynamic alterations and the potential for postoperative complications. This study investigated the incidence of postoperative acute kidney injury (AKI) in patients undergoing spine surgery on a Jackson spinal table or a Wilson frame.Methods
A total of 1374 patients who underwent spine surgery were divided into 2 groups: Jackson spinal table (n = 598) and Wilson frame group (n = 776). After 1:1 propensity score matching, a final analysis was performed on 970 patients. The primary endpoint was a comparison of the incidence of AKI in the 2 groups.Results
After propensity score matching analysis, the mean ± standard deviations of spine surgery invasiveness index were 4.7 ± 3.5 and 2.1 ± 1.4 in patients with the Jackson spinal table and the Wilson frame, respectively (P < 0.001). Considering the differences in surgical invasiveness, operative time, estimated blood loss, and administration of packed red blood cells were higher in the Jackson spinal table group than in the Wilson frame group (P < 0.001). However, the incidence of AKI was less with the Jackson spinal table than with the Wilson frame (1.7% vs. 3.7%, 2.25 [0.978-5.175], P = 0.056), not reaching statistical significance.Conclusion
This analysis showed that postoperative AKI in patients undergoing spine surgery in the prone position was not different with the Wilson frame than in the Jackson spinal table despite higher surgical severity, longer operative times, and more blood loss in the latter group. In spine surgery, the appropriate selection of prone positioning apparatus can potentially be an important consideration in reducing the risk of AKI.Item Open Access In vitro fluid dynamics of the Ahmed glaucoma valve modified with expanded polytetrafluoroethylene.(Curr Eye Res, 2011-02) DeCroos, Francis Char; Kondo, Yuji; Mordes, Daniel; Lee, Maria Regina; Ahmad, Sameer; Asrani, Sanjay; Allingham, R Rand; Olbrich, Kevin C; Klitzman, BrucePURPOSE: Long-term intraocular pressure reduction by glaucoma drainage devices (GDDs) is often limited by the fibrotic capsule that forms around them. Prior work demonstrates that modifying a GDD with a porous membrane promotes a vascularized and more permeable capsule. This work examines the in vitro fluid dynamics of the Ahmed valve after enclosing the outflow tract with a porous membrane of expanded polytetrafluoroethylene (ePTFE). MATERIALS AND METHODS: The control and modified Ahmed implants (termed porous retrofitted implant with modified enclosure or PRIME-Ahmed) were submerged in saline and gelatin and perfused in a system that monitored flow (Q) and pressure (P). Flow rates of 1-50 μl/min were applied and steady state pressure recorded. Resistance was calculated by dividing pressure by flow. RESULTS: Modifying the Ahmed valve implant outflow with expanded ePTFE increased pressure and resistance. Pressure at a flow of 2 μl/min was increased in the PRIME-Ahmed (11.6 ± 1.5 mm Hg) relative to the control implant (6.5 ± 1.2 mm Hg). Resistance at a flow of 2 μl/min was increased in the PRIME-Ahmed (5.8 ± 0.8 mm Hg/μl/min) when compared to the control implant (3.2 ± 0.6 mm Hg/μl/min). CONCLUSIONS: Modifying the outflow tract of the Ahmed valve with a porous membrane adds resistance that decreases with increasing flow. The Ahmed valve implant behaves as a variable resistor. It is partially open at low pressures and provides reduced resistance at physiologic flow rates.Item Open Access Level of beta-adrenergic receptor kinase 1 inhibition determines degree of cardiac dysfunction after chronic pressure overload-induced heart failure.(Circulation, 2005-02-08) Tachibana, Hideo; Naga Prasad, Sathyamangla V; Lefkowitz, Robert J; Koch, Walter J; Rockman, Howard ABACKGROUND: Heart failure is characterized by abnormalities in beta-adrenergic receptor (betaAR) signaling, including increased level of myocardial betaAR kinase 1 (betaARK1). Our previous studies have shown that inhibition of betaARK1 with the use of the Gbetagamma sequestering peptide of betaARK1 (betaARKct) can prevent cardiac dysfunction in models of heart failure. Because inhibition of betaARK activity is pivotal for amelioration of cardiac dysfunction, we investigated whether the level of betaARK1 inhibition correlates with the degree of heart failure. METHODS AND RESULTS: Transgenic (TG) mice with varying degrees of cardiac-specific expression of betaARKct peptide underwent transverse aortic constriction (TAC) for 12 weeks. Cardiac function was assessed by serial echocardiography in conscious mice, and the level of myocardial betaARKct protein was quantified at termination of the study. TG mice showed a positive linear relationship between the level of betaARKct protein expression and fractional shortening at 12 weeks after TAC. TG mice with low betaARKct expression developed severe heart failure, whereas mice with high betaARKct expression showed significantly less cardiac deterioration than wild-type (WT) mice. Importantly, mice with a high level of betaARKct expression had preserved isoproterenol-stimulated adenylyl cyclase activity and normal betaAR densities in the cardiac membranes. In contrast, mice with low expression of the transgene had marked abnormalities in betaAR function, similar to the WT mice. CONCLUSIONS: These data show that the level of betaARK1 inhibition determines the degree to which cardiac function can be preserved in response to pressure overload and has important therapeutic implications when betaARK1 inhibition is considered as a molecular target.Item Open Access Modification of pH and pressure in a microfluidic cell culture device.(2012) Gatti, John WIlliamA three-dimensional tissue culture device previously described by Elliott et al. 1 is tested for its capacity to mimic cancer interstitial fluid pressure and interstitial pH. The device described by Elliott et al. is a three-channel system; a central channel that contains cells, and two side channels that act as model capillaries. The potential for variation of the interstitial fluid pressure was determined by measuring the resistances with respect to the various channels. It was determined that the unmodified device is incapable of mimicking physiological tumor pressures. The ability to vary pH was performed by using a pH sensitive florescent and by infusing a pH 5.9 solution into the side channels, before checking if the device could maintain this pressure for a long time period during constant perfusion of media into the device. It was observed that the florescence of the pH sensitive molecule decreased upon infusion of an acidic solution, as it should upon exposure to acid. However, no conclusions can be drawn from these tests, as the florescent molecule was no longer viable after the 12 hour perfusion of media. Further experiments are needed before any conclusions can be reached about the device's potential.
Item Open Access Numerical detection of the Gardner transition in a mean-field glass former.(Phys Rev E Stat Nonlin Soft Matter Phys, 2015-07) Charbonneau, Patrick; Jin, Yuliang; Parisi, Giorgio; Rainone, Corrado; Seoane, Beatriz; Zamponi, FrancescoRecent theoretical advances predict the existence, deep into the glass phase, of a novel phase transition, the so-called Gardner transition. This transition is associated with the emergence of a complex free energy landscape composed of many marginally stable sub-basins within a glass metabasin. In this study, we explore several methods to detect numerically the Gardner transition in a simple structural glass former, the infinite-range Mari-Kurchan model. The transition point is robustly located from three independent approaches: (i) the divergence of the characteristic relaxation time, (ii) the divergence of the caging susceptibility, and (iii) the abnormal tail in the probability distribution function of cage order parameters. We show that the numerical results are fully consistent with the theoretical expectation. The methods we propose may also be generalized to more realistic numerical models as well as to experimental systems.Item Open Access Scaffold-free, Human Mesenchymal Stem Cell-Based Tissue Engineered Blood Vessels.(Sci Rep, 2015-10-12) Jung, Y; Ji, H; Chen, Z; Fai Chan, H; Atchison, L; Klitzman, B; Truskey, G; Leong, KWTissue-engineered blood vessels (TEBV) can serve as vascular grafts and may also play an important role in the development of organs-on-a-chip. Most TEBV construction involves scaffolding with biomaterials such as collagen gel or electrospun fibrous mesh. Hypothesizing that a scaffold-free TEBV may be advantageous, we constructed a tubular structure (1 mm i.d.) from aligned human mesenchymal cell sheets (hMSC) as the wall and human endothelial progenitor cell (hEPC) coating as the lumen. The burst pressure of the scaffold-free TEBV was above 200 mmHg after three weeks of sequential culture in a rotating wall bioreactor and perfusion at 6.8 dynes/cm(2). The interwoven organization of the cell layers and extensive extracellular matrix (ECM) formation of the hMSC-based TEBV resembled that of native blood vessels. The TEBV exhibited flow-mediated vasodilation, vasoconstriction after exposure to 1 μM phenylephrine and released nitric oxide in a manner similar to that of porcine femoral vein. HL-60 cells attached to the TEBV lumen after TNF-α activation to suggest a functional endothelium. This study demonstrates the potential of a hEPC endothelialized hMSC-based TEBV for drug screening.Item Open Access Supercritical water oxidation of a model fecal sludge without the use of a co-fuel.(Chemosphere, 2015-12) Miller, A; Espanani, R; Junker, A; Hendry, D; Wilkinson, N; Bollinger, D; Abelleira-Pereira, JM; Deshusses, MA; Inniss, E; Jacoby, WA continuous supercritical water oxidation reactor was designed and constructed to investigate the conversion of a feces simulant without the use of a co-fuel. The maximum reactor temperature and waste conversion was determined as a function of stoichiometric excess of oxygen in order to determine factor levels for subsequent investigation. 48% oxygen excess showed the highest temperature with full conversion. Factorial analysis was then used to determine the effects of feed concentration, oxygen excess, inlet temperature, and operating pressure on the increase in the temperature of the reacting fluid as well as a newly defined non-dimensional number, NJa representing heat transfer efficiency. Operating pressure and stoichiometric excess oxygen were found to have the most significant impacts on NJa. Feed concentration had a significant impact on fluid temperature increase showing an average difference of 46.4°C between the factorial levels.Item Open Access The effect of posterior polyester tethers on the biomechanics of proximal junctional kyphosis: a finite element analysis.(Journal of neurosurgery. Spine, 2017-01) Bess, Shay; Harris, Jeffrey E; Turner, Alexander WL; LaFage, Virginie; Smith, Justin S; Shaffrey, Christopher I; Schwab, Frank J; Haid, Regis WOBJECTIVE Proximal junctional kyphosis (PJK) remains problematic following multilevel instrumented spine surgery. Previous biomechanical studies indicate that providing less rigid fixation at the cranial aspect of a long posterior instrumented construct, via transition rods or hooks at the upper instrumented vertebra (UIV), may provide a gradual transition to normal motion and prevent PJK. The purpose of this study was to evaluate the ability of posterior anchored polyethylene tethers to distribute proximal motion segment stiffness in long instrumented spine constructs. METHODS A finite element model of a T7-L5 spine segment was created to evaluate range of motion (ROM), intradiscal pressure, pedicle screw loads, and forces in the posterior ligament complex within and adjacent to the proximal terminus of an instrumented spine construct. Six models were tested: 1) intact spine; 2) bilateral, segmental pedicle screws (PS) at all levels from T-11 through L-5; 3) bilateral pedicle screws from T-12 to L-5 and transverse process hooks (TPH) at T-11 (the UIV); 4) pedicle screws from T-11 to L5 and 1-level tethers from T-10 to T-11 (TE-UIV+1); 5) pedicle screws from T-11 to L-5 and 2-level tethers from T-9 to T-11 (TE-UIV+2); and 6) pedicle screws and 3-level tethers from T-8 to T-11 (TE-UIV+3). RESULTS Proximal-segment range of motion (ROM) for the PS construct increased from 16% at UIV-1 to 91% at UIV. Proximal-segment ROM for the TPH construct increased from 27% at UIV-1 to 92% at UIV. Posterior tether constructs distributed ROM at the UIV and cranial adjacent segments most effectively; ROM for TE-UIV+1 was 14% of the intact model at UIV-1, 76% at UIV, and 98% at UIV+1. ROM for TE-UIV+2 was 10% at UIV-1, 51% at UIV, 69% at UIV+1, and 97% at UIV+2. ROM for TE-UIV+3 was 7% at UIV-1, 33% at UIV, 45% at UIV+1, and 64% at UIV+2. Proximal segment intradiscal pressures, pedicle screw loads, and ligament forces in the posterior ligament complex were progressively reduced with increasing number of posterior tethers used. CONCLUSIONS Finite element analysis of long instrumented spine constructs demonstrated that posterior tethers created a more gradual transition in ROM and adjacent-segment stress from the instrumented to the noninstrumented spine compared with all PS and TPH constructs. Posterior tethers may limit the biomechanical risk factor for PJK; however, further clinical research is needed to evaluate clinical efficacy.Item Open Access Towards a field-compatible optical spectroscopic device for cervical cancer screening in resource-limited settings: effects of calibration and pressure.(Opt Express, 2011-09-12) Chang, Vivide Tuan-Chyan; Merisier, Delson; Yu, Bing; Walmer, David K; Ramanujam, NirmalaQuantitative optical spectroscopy has the potential to provide an effective low cost, and portable solution for cervical pre-cancer screening in resource-limited communities. However, clinical studies to validate the use of this technology in resource-limited settings require low power consumption and good quality control that is minimally influenced by the operator or variable environmental conditions in the field. The goal of this study was to evaluate the effects of two sources of potential error: calibration and pressure on the extraction of absorption and scattering properties of normal cervical tissues in a resource-limited setting in Leogane, Haiti. Our results show that self-calibrated measurements improved scattering measurements through real-time correction of system drift, in addition to minimizing the time required for post-calibration. Variations in pressure (tested without the potential confounding effects of calibration error) caused local changes in vasculature and scatterer density that significantly impacted the tissue absorption and scattering properties Future spectroscopic systems intended for clinical use, particularly where operator training is not viable and environmental conditions unpredictable, should incorporate a real-time self-calibration channel and collect diffuse reflectance spectra at a consistent pressure to maximize data integrity.Item Open Access Treatment with Imatinib in NSCLC is associated with decrease of phosphorylated PDGFR-beta and VEGF expression, decrease in interstitial fluid pressure and improvement of oxygenation.(Br J Cancer, 2006-10-23) Vlahovic, G; Rabbani, ZN; Herndon, JE; Dewhirst, MW; Vujaskovic, ZElevated intratumoral interstitial fluid pressure (IFP) and tumour hypoxia are independent predictive factors for poor survival and poor treatment response in cancer patients. However, the relationship between IFP and tumour hypoxia has not yet been clearly established. Preclinical studies have shown that lowering IFP improves treatment response to cytotoxic therapy. Interstitial fluid pressure can be reduced by inhibition of phosphorylated platelet-derived growth factor receptor-beta (p-PDGFR-beta), a tyrosine kinase receptor frequently overexpressed in cancer stroma, and/or by inhibition of VEGF, a growth factor commonly overexpressed in tumours overexpressing p-PDGFR-beta. We hypothesised that Imatinib, a specific PDGFR-beta inhibitor will, in addition to p-PDGFR-beta inhibition, downregulate VEGF, decrease IFP and improve tumour oxygenation. A549 human lung adenocarcinoma xenografts overexpressing PDGFR-beta were grown in nude mice. Tumour-bearing animals were randomised to control and treatment groups (Imatinib 50 mg kg(-1) via gavage for 4 days). Interstitial fluid pressure was measured in both groups before and after treatment. EF5, a hypoxia marker, was administered 3 h before being killed. Tumours were sectioned and stained for p-PDGFR-beta, VEGF and EF5 binding. Stained sections were viewed with a fluorescence microscope and image analysis was performed. Imatinib treatment resulted in significant reduction of p-PDGFR-beta, VEGF and IFP. Tumour oxygenation was also significantly improved. This study shows that p-PDGFR-beta-overexpressing tumours can be effectively treated with Imatinib to decrease tumour IFP. Importantly, this is the first study demonstrating that Imatinib treatment improves tumour oxygenation and downregulates tumour VEGF expression.