Evaluation of the porcine model to teach various ancillary procedures to gynecologic oncology fellows.

OBJECTIVE: The purpose of this study was to subjectively evaluate the adequacy of the porcine model for training gynecologic oncology fellows. STUDY DESIGN: Following a defined surgical curriculum, fellow-attending pairs operated on female hogs. A predetermined dataset was collected for each procedure. RESULTS: Twenty pigs were operated on. The porcine model was determined to be a good model for laparoscopic lymphadenectomy (11), ureteroneocystostomy (7), repair of vascular injury (11), bowel anastamoses (21), distal pancreatectomy (5), nephrectomy (6), partial hepatectomy (5), diaphram stripping (5), and diaphragmatic resection (4). Two attendings and 1 fellow judged the porcine model to be fair (remaining 11 good) for ileocolonic urinary diversion, mainly due to significant differences in anatomy. Liver mobilization (5) and splenectomy (11) were determined to be fair or poor models by all participants due to the limited attachments in the pig. CONCLUSION: The porcine model is adequate for teaching some ancillary gynecologic oncology surgical procedures and is inadequate for others.

Age-related changes in the aortic valve affect leaflet stress distributions: implications for aortic valve degeneration.

BACKGROUND AND AIM OF THE STUDY: The degeneration of aortic valve leaflets occurs primarily due to high mechanical stresses in zones of leaflet flexion. Aging, which has been identified as a risk factor for degenerative aortic stenosis, is associated with reductions in stretch and in compliance, and an increase in tissue thickness of the leaflet and root. The study aim was to investigate the effects of age-related tissue changes on valve opening dynamics and leaflet stress patterns, and its implications for valve degeneration. METHODS: A three-dimensional finite element model of the aortic valve and root was developed in Ansys. A transient, non-linear analysis was carried out of the valve opening phase. Three age groups were identified based on leaflet and root tissue properties: group I age <35 years; group II aged 33-55 years; and group III aged >55 years. The valve opening dynamics was studied and von Mises stresses in various regions of the leaflet were computed. RESULTS: Maximum leaflet stresses occurred along the leaflet-root attachment, analogous to the spatial distribution of calcific deposits in the aortic valve. With increasing age, the rate of valve opening decreased, and the magnitude of leaflet tip displacement in both radial and axial directions reduced progressively. At the leaflet-root attachment, groups II and III showed 19% and 32.7% increases in average stress over group I, respectively. At the free edge, the stresses in group III increased 2.7% over group I; however, the average stress at the free edge in group II decreased 3.5% over group I. In the leaflet belly, groups II and III showed 27.6% and 60.9% increases in stresses over group I, respectively. CONCLUSION: Changes in leaflet and root tissue properties lead to altered leaflet dynamics and increased stresses. This not only emphasizes the role of aging on the development and progression of degenerative aortic valve disease, but also has implications in the design of bioprosthetic heart valves.

Human umbilical cord blood progenitor cells are attracted to infarcted myocardium and significantly reduce myocardial infarction size.

We are investigating the effects of human umbilical cord blood mononuclear progenitor cells (HUCBC) for the treatment of acute myocardial infarction because human cord blood is a readily available and an abundant source of primitive cells that may be beneficial in myocardial repair. However, there is currently no scientific consensus on precisely when to inject stem/progenitor cells for the optimal treatment of acute myocardial infarction. We used an in vitro assay to determine the attraction of infarcted rat myocardium at 1, 2, 2.5, 3, 6, 12, 24, 48, and 96 h after left anterior descending coronary artery (LAD) occlusion from 45 rats for HUCBC in order to determine the optimal time to transplant HUCBC after myocardial infarction. Our assay is based on the migration of fluorescent DAPI-labeled HUCBC from wells in an upper chamber of a modified Boyden apparatus through a semiporous polycarbonate membrane into wells in a lower chamber that contain either normal or infarcted myocardium. DAPI-labeled HUCBC (100,000) were placed in each of the separate wells above the membrane that corresponded to normal or infarct homogenate in the lower wells. The greatest HUCBC migration to infarcted myocardium occurred at 2 h and 24 h after LAD occlusion in comparison with normal controls. A total of 76,331 +/- 3384 HUCBC migrated to infarcted myocardium at 2 h and 69,911 +/- 2732 at 24 h after LAD occlusion (both p < 0.001) and significantly exceeded HUCBC migration to normal heart homogenate. The HUCBC migration remained greatest at 2 and 24 h after LAD occlusion when the number of migrated cells was adjusted for the size of each myocardial infarction. Injection of 106 HUCBC in saline into infarcted myocardium of non immunosuppressed rats within 2 h (n=10) or at 24 h (n=5) after LAD occlusion resulted in infarction sizes 1 month later of 6.4 +/- 0.01% and 8.4 +/- 0.02% of the total left ventricular muscle area, respectively, in comparison with infarction sizes of 24.5 +/- 0.02% (n=10) in infarcted rat hearts treated with only saline (p < 0.005). Acute myocardial infarction in rats treated with only saline increased the myocardial concentration of tumor necrosis factor-alpha (TNF-alpha) from 6.9 +/- 0.8% to 51.3 +/- 4.6%, monocyte/macrophage chemoattractant protein (MCP-1) from 10.5 +/- 1.1% to 39.2 +/- 2.0%, monocyte inflammatory protein (MIP) from 10.6 +/- 1.6% to 23.1 +/- 1.5%, and interferon-gamma (INF-gamma) from 8.9 +/- 0.3% to 25.0 +/- 1.7% between 2 and 12 h after coronary occlusion in comparison with known controls (all p < 0.001). In contrast, the myocardial concentrations of these cytokines in rat hearts treated with HUCBC did not significantly change from the controls at 2, 6, 12, and 24 h after coronary occlusion. The present investigations suggest that infarcted myocardium significantly attracts HUCBC, that HUCBC can substantially reduce myocardial infarction size, and that HUCBC can limit the expression of TNF-alpha, MCP-1, MIP, and INF-gamma in acutely infarcted myocardium.

Mechanical and sensory testing of overfilled breast implants.

BACKGROUND: To obtain an ideal outcome in breast augmentation procedures, breast implants may be overfilled to reduce wrinkles and improve longevity. Determination of the optimal volume for saline-filled breast implants remains problematic for plastic surgeons. OBJECTIVE: We sought to evaluate the effect of overfilling or underfilling implants on sensory response and on implant shell mechanical properties. METHODS: Fifty-three Mentor Style 1600 smooth saline-filled mammary implants (275-cc base volume) were examined. Saline fill volumes ranged from 230 cc to 1650 cc. Implants were incubated at 37 degrees C and 100% humidity for 6 weeks. Before destructive testing to determine strength, elasticity, and toughness, 22 women ranging in age from 18 to 55 years graded the implants for firmness to palpation. Objective indices of firmness were measured by durometer. RESULTS: Implants filled 50% above manufacturer's recommended volume were considered firm, whereas implants 50% below manufacturer's recommended volume were considered natural or soft. A linear relationship was observed between sensory response and durometer hardness data. Fill volume did not affect shell mechanical properties: shell strength, toughness, and elasticity remained unchanged (P > .05). CONCLUSIONS: Saline-filled breast implants can be safely filled far beyond manufacturer's recommendations with regard to the mechanical properties of the Silastic polymer implant shell. Clinical judgment is required to avoid hardness due to overfill. Repeating this study using an in vivo incubation method is required to determine how overfill will affect implant shells over time in the harsh milieu of a biologic environment.

Blood rheological characterization using the thickness-shear mode resonator.

Thickness-shear mode (TSM) resonators have been used to characterize static rheological properties of plasma and whole blood samples. We demonstrated simple and rapid techniques for determining plasma viscosity without cell separation, for measuring erythrocyte sedimentation rate, and for tracking blood coagulation throughout the entire process. Additionally, mathematical models, previously developed to characterize surface-loaded resonators, were used to extract non-Newtonian and viscoelastic material properties of blood layers during sedimentation and coagulation experiments. These studies indicate the utility of the TSM resonator for several clinical applications. Because the resonators can be miniaturized, potential exists for extending the techniques for use inside the body or blood stream (in vivo).

Stability of tuberosity reattachment in proximal humeral hemiarthroplasty.

Hemiarthroplasty can be an effective treatment for 4-part fractures of the proximal humerus; however, results are often unpredictable. Proper surgical technique is critical for success. Reconstruction of the displaced tuberosities should attempt to impart maximal interfragmentary stability. To our knowledge, a comparison of different tuberosity reconstruction methods has not been reported. We evaluated 5 techniques of tuberosity reattachment on 8 humeri. Four-part fractures were simulated by an oscillating saw in fresh-frozen cadaveric shoulders. In the control construct, the greater and lesser tuberosities were attached to the humeral shaft with nylon strap ties (2.4 x l mm) applied at 9.1 N with closure of the rotator interval. Five anatomic reconstructions were then performed:(1) the control tuberosities were attached to each other with strap ties, and (2) the control tuberosities were attached to each other with strap ties, incorporating the anterior fin of the prosthesis. To each of these 3 constructs, a circumferential cerclage (4.8 x 1.25-mm strap tie) applied at 39.2 N was placed around the tuberosities and incorporated into the medial hole of the prosthesis (techniques 3, 4, and 5). Through use of a robot articulator at a rate of 10 degrees /s, passive external rotation from 0 degrees to 60 degrees was performed on the control and the 5 test constructs of each specimen. Interfragmentary displacement of the bony fragments was measured with mercury strain gauges and strain calculated. This strain was minimal and statistically less (P <.05) in those constructs in which a cerclage was used. Incorporation of the nylon strap into the fin of the prosthesis did not enhance stability. In those constructs in which a cerclage was used, maximal displacement was 0.14 +/- 0.7 mm (38% +/- 19% strain), as compared with 0.72 +/- 0.5 mm (204% +/- 133% strain) without it. Reconstruction of 4-part proximal humerus fractures with hemiarthroplasty should incorporate a circumferential medial cerclage. This will decrease interfragmentary motion and strain, maximize fracture stability, and facilitate postoperative rehabilitation.