BACKGROUND: The development of a novel surgical tool or technique used in mitral valve repair can be hampered by the cost, complexity, and time associated with performing animal trials. We sought to develop a dynamically pressurized model which detects and quantifies mitral regurgitation in intact porcine hearts in order to preliminarily evaluate the effectiveness of mitral valve repair methods without the need for animal trials. METHODS: A computer controlled pulse duplication system was designed to accept freshly explanted porcine hearts and replicate a wide range of physiological conditions. To test the capabilities of this system in measuring mitral regurgitation, the cardiac output of four hearts was measured under two different peak left atrial pressures (120 and 150 mmHg) before and after induced mitral valve failures. Measurements were compared with clinically standard echocardiographic images. RESULTS: For all trials, cardiac output decreased as peak left atrial pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 27%. These findings correlated well with the results from echocardiography. CONCLUSIONS: The resulting system is able to consistently and reliably detect and quantify mitral regurgitation and serves as an effective tool for the design of mitral valve repair techniques. The system is advantageous in its low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart.

Computational modeling can be used to achieve a better understanding of fluid analysis within the pulmonary circulation. Boundary conditions are used in fluid analysis to determine the pressure and flow profiles of the blood as it moves through the lung. Accurate boundary conditions are critical in providing accurate models of blood pressure and blood flow. An important consideration when determining boundary conditions for the pulmonary vasculature is the effect of respiration on the impedance of the pulmonary vasculature. An additional consideration for the pulmonary vasculature is the physiologic differences between the pulmonary circulation and that of the systemic circulation. This research determines impedance boundary conditions for the pulmonary vasculature that reflect the specific geometry of the lung and correspond to maximal inspiration and maximal expiration. The analysis was performed using an existing one-dimensional finite element analysis system. The boundary conditions were defined by a bifurcating structure tree with a number of variables that were used to change the resistance of the pulmonary vessels. The variables within the structure tree were altered to reflect the differences between the pulmonary circulation and the systemic circulation. These variables include the length to radius ratio of the vessels in the structure tree and the asymmetry as the branches. A respiration factor was used to scale the vessels of the structure tree to reflect the effects of respiration on the geometry of the lung. The compliance of the vessels was also changed to reflect the more distensible vessels found in the pulmonary system. The geometry of the lung was defined with the structured tree parameters at maximal inspiration and the respiration factor was used to scale the defined geometry and reflect maximal expiration. The parameters were determined by utilizing an optimization technique. The Levinberg-Marquardt least-squares non-linear optimization algorithm was used to find a set of non-unique optimal parameters. The computed data was validated using measured pressure and flow data collected in a previous study.

The objective of this research is to develop a series of material treatments and modifications, and, using a standardized set of tests, determine the extent of the ability of the modified material to enhance coagulation. This research focuses on materials commonly used in traditional textile based wound dressings; utilizing Streaming Potential studies, Scanning Electron Microscopy (SEM) and Thrombin Assays. The materials tested can be classified into 4 groups: control materials, modified PLA, SAMs treated glass, and TEOS treated materials. The control materials included: spun cotton and rayon yarn; continuous filament Nylon, Polypropylene (PP), and Polyethylene terephthalate (PET); heat cleaned glass (control glass); and PLA staple fibers. Contact angle measurements showed that both the control glass and the PET showed an increase in contact angle when treated with TEOS. This corresponds to a decrease and no improvement, respectively, in thrombogenicity for these materials in the thrombin assay. The remaining materials tested showed no change or a decrease in contact angle after TEOS treatment, and a corresponding increase in thrombogenicity. These results support previous studies that indicate an increase in wettability contributes to the enhancement of coagulation (16). While the streaming potential studies showed no correlation between thrombin formation or contact angle data, these tests provided an important launching platform for future studies utilizing the Streaming Potential Jar. Future work could benefit from the use of more physiologically relevant solutions, such as CaCl2, NaCl, or other blood substitutes (15). While no definitive correlations between test methods were elucidated, the results garnered from this research created a strong launching platform from which future materials research can continue.

Osteoarthritis is a severely debilitating joint disorder. It is slowly progressing chronic disease and has no precise known causes. Impact injury can lead to cellular and matrix changes in articular cartilage similar to those seen in osteoarthritis. Impact injury models are often used as models for osteoarthritis. The purpose of this study was to use an in vitro impact injury model to examine the distribution and timing of apoptosis cell death following an impact injury. In this study it was hypothesized that there will be an increase in apoptosis cells with increasing impact load; that over time in culture the number of apoptotic cells will increase due to lingering effects from the impaction; and that apoptosis will be most severe directly below the impaction. Paired porcine knees were obtained fresh and patellae were removed using sterile techniques. Controlled mechanical impactions were made on 12 patellae at 25 mm/s, using MTS load frame, to pre selected force levels of 1000N (characterized as medium) and 12 patellae were subjected to 2000N (characterized as high). The twelve non-impacted patellae were used as controls. Following impaction, the impact patellae were placed in organ culture for 0, 3, 7, or 14 days and subsequent degenerative changes over time were assessed. Apoptotic cells were quantified using terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) technique. The stained cells were quantified as a percentage of the total number of cells. Changes in percentage of apoptotic cells was analyzed with experimental factors impact level, days in culture ( 0, 3, 7, 14), distance from center of impaction, and depth in tissue. There was a significant depth and time dependent increase in the percentage of apoptotic cells for high impactions. A significant increase in percentage of apoptotic cells was observed from high impactions after 14 days culture time and a significant increase in percentage of apoptotic cells, for 0 days culture time was observed from medium impactions. In conclusion magnitude of load has significant effect on chondrocyte apoptosis throughout the depth of the cartilage tissue, but depends on culture time.

Force is required to prepare the bone and achieve the initial press fit for an uncemented hip implant during Total Hip Arthroplasty (THA) surgery. In some situations, this force may cause of an intra-operative femoral fracture resulting in an unstable implant, subsidence, and pain for the patient. Many of the less extensive fractures can be repaired with cerclage wire or cables. This study aimed to evaluate the ability of double loop cerclage wire(s) to restore the stability of the implant-bone interface after a simulated intra-operative fracture. Nine femora from euthanized canine were harvested for in vitro testing. The femora were prepared for implantation of an uncemented femoral stem (BFX⢠series, BioMedtrix, Boonton, NJ). They were then potted and mounted in a materials testing machine (MTS 858 Mini Bionix II, Eden Prairie, MN). The implant was driven to a clinically appropriate height, struck with 3 impacts (simulating seating hammer blows), and then the stem loaded to failure. Once a fracture occurred, the implant was extracted, the femur was repaired with appropriate cerclage, re-broached, and re-implanted. The repaired specimen was then tested in the same fashion as the intact bone. During loading, the displacement of the implant relative to the bone was measured using a linearly variable differential transformer LVDT. The force to initiate subsidence, the peak force at failure, and the peak subsidence distance were compared between intact (pre-fracture) and repaired (post-fracture) specimens using ANOVA with blocking by specimen. The wired specimens demonstrated a higher force to initiate subsidence than the intact specimens (2378.8N ± 656.9N c.f. 1705.1N ± 584.5N; p= 0.0019). The wired specimens also sustained a higher peak force at failure than the intact specimens (3309.0N ± 609.14N c.f. 2276.3N ± 855.6N; p=0.0022). Furthermore, the wired specimens did not subside a significantly greater amount than the intact specimens (Intact: 3.90mm, SD=2.09mm; Wired: 6.71mm, SD=3.66mm; p-value = 0.0600). Cerclage wiring of intra-operative femoral fractures was able to restore the integrity of the femur and enable a stable implant-bone interface to be achieved.

To improve the surface properties of biomaterials, the effects of changes in surface chemistry and morphology of polyethylene terephthalate (PET) films treated with atmospheric pressure plasma were investigated as a function of cellular growth, proliferation, and adhesion. PET films were subjected to helium and helium/oxygen gas plasmas. The contact angle of the treated films decreased due to plasma etching and possible scission indicating that the surfaces become more hydrophilic. Atomic force microscopy results had a large standard error, however the surface visually showed changes in surface micro and nanoscale roughness corresponding to treatment duration. Keratinocytes were plated on the day of plasma treatment and two and five days after plasma treatment and tested half a day, one, two, three, and six days after plating. The same methodology of plating and testing was also applied to hepatocytes. Cell growth, proliferation, and adhesion were characterized via a fluorescent probe based assay and were correlated with surface chemical and nanostructural features. Both the helium and helium/oxygen plasma-treated PET had little or no effect on cell behavior for both keratinocytes and hepatocytes. The nanoscale surface changes due to the plasma surface treatment are believed to be masked by the protein adherence in the media on the surface of the PET.

As a result of the growing costs of healthcare technology, there is an increasing need for medical diagnostic tools that provide accurate information in a portable, low-cost platform. A microfluidic device using on-chip passive pumping was characterized for use as a particle counter. A detection circuit interfaced with electrodes in the microfluidic chip to provide an excitation signal and to detect electrical activity. Flow occurred due to a Young-Laplace pressure gradient between a 1.2 mm diameter inlet and a 4 mm diameter reservoir when 0.5 μL fluid droplets were applied to the inlet using a micropipette. Polystyrene particles were enumerated using the resistive pulse technique, in which particles can be detected based on the difference in particle conductivity from that of the surrounding medium. Particles counted using the passive flow method demonstrated mean particle counts that were within 13% of those detected using a syringe pump, while all pumping methods displayed particle counts that were within 16% of the count obtained using a hemacytometer. Three different sample loading patterns were compared; the methods varied only in the order of sample and wash fluid administration. Zero, one, or two wash droplets were loaded after the first of two sample droplets. No statistical difference was detected in the mean particle counts for all loading patterns using the passive method (p > 0.05). This passive pumping method is easily implemented using only a micropipette, thus reducing the cost and complexity of particle enumeration, and the method can be implemented in a point-of-care (POC) device for a highly portable, cost-effective particle counter. These methods obtained particle counts that were also consistent with syringe pumping (p > 0.05).

The initial torsional stability of a cementless total hip arthroplasty (THA) is one of the key factors in determining the biological fixation of the implant. The success of a cementless hip replacement relies on the quantity and quality of bone ingrowth that occurs. This study looked at the effects of femoral neck resection level on the initial torsional stability of cementless THA in the canine population. Twenty paired cadaver femurs were collected from dogs and implanted with canine cementless hip stems. One femur from each pair was prepared with a neck cut with its medial aspect located at the proximal aspect of the lesser trochanter (low neck cut) and the other with a neck cut with its proximo-lateral aspect at the ossum collis femoris isthmus of the greater trochanter and femoral neck (high neck cut). The specimens were then subjected to cyclic torque loads in the caudal direction (Amplitude: -0.1 N-m to set torque) at four torque levels (1 N-m, 2 N-m, 4 N-m, and 6 N-m) and the torsional displacement, axial subsidence, and strain were all recorded. A paired statistical analysis was completed so that specimens from the same dogs could be compared to each other. The low neck cut group was found to have significantly less micromotion than the high neck cut group during the 1 N-m and 4 N-m torque tests (p = 0.02 for both). Because the high neck cut specimens tended to have more micromotion they may be apt to have lower quality bone ingrowth. A significant difference was not found between the torsional displacements of the two groups. The high neck cut specimens were found to have significantly (p = 0.02) more implant rotation at 1.6 N-m of torque, however the average difference was only about 0.22 degrees which most likely does not indicate a clinically significant difference. No statistical difference was found between the axial subsidence of the high and low neck cut specimens other than at the 6 N-m level (p = 0.02). At 6 N-m the stems in the low neck cut specimens had an average upward movement of 255 +/- 310 um while the stems in the high neck cuts moved in the opposite direction and had an average downward movement of 280 +/- 695 um. The low neck specimens were found to have significantly more canal fill and implant impaction than the high neck cut specimens. This suggests that surgeons need to be mindful that they may not insert stems as deeply in femurs prepared with high neck cuts as they do in femurs with low neck cuts. This study was not able to show that one neck cut level was superior to the other, however the data indicate that the low neck cut group had slightly better stability based on having less micromotion at 1 N-m and 4 N-m and less at rotation at 1.6 N-m.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on Feb. 5, 2007). PDF text: xxi, 185 p. : ill. (some col.) UMI publication number: AAT 3216412. Includes bibliographical references. Also available in microfilm and microfiche format.

Background: Clinicians use information regularly in clinical care. New electronic information resources provided in push, pull, and prompting formats have potential to improve information support but have not been designed for individualization. Physicians with differing risk status use healthcare resources differently often without an improvement in outcomes. Questions: Do physicians who are risk seeking or risk avoiding and comfortable or uncomfortable with uncertainty use or prefer electronic information resources differently when answering simulated clinical questions and can the processes be modeled with existing theoretical models? Design: Cohort study. Methods: Primary care physicians in Canada and the United States were screened for risk status. Those with high and low scores on 2 validated scales answered 23 multiple-choice questions and searched for information using their own electronic resources for 2 of these questions. They also answered 2 other questions using information from 2 electronic information sources: PIER© and Clinical Evidence© . Results: The physicians did not differ for number of correct answers according to risk status although the number of correct answers was low and not substantially higher than chance. Their searching process was consistent with 2 information-seeking models from information science (modified Wilson Problem Solving and Card/Pirolli Information Foraging/Information Scent models). Few differences were seen for any electronic searching or information use outcome based on risk status although those physicians who were comfortable with uncertainty used more searching heuristics and spent less effort on direct searching. More than 20% of answers were changed after searchingalmost the same number going from incorrect to correct and from correct to incorrect. These changes from a correct to incorrect answer indicate that some electronic information resources may not be ideal for direct clinical care or integration into electronic medical record systems. Conclusions: Risk status may not be a major factor in the design of electronic information resources for primary care physicians. More research needs to be done to determine which computerized information resources and which features of these resources are associated with obtaining and maintaining correct answers to clinical questions.