Investigation of changing geometry parameters of nickel-titanium shape memory alloys wire stent in cardiovascular implants.

The purpose of this investigation was to assess the effects of changing the Nitinol stent's geometrical characteristics on the superelastic behavior of the stent using the finite element method. Four different geometrical parameters were considered and analyzed in sixteen stents. These geometrical parameters consisted of stent length, number of stent's meanders, inside diameter of the stent and wire diameter. Results showed that decreasing either stent length or the number of stent meanders and increasing either the inside diameter of the stent or wire diameter generally result in more sensible superelastic behavior exposure. The effect of changing stent length is independent of the inside diameter and number of the stent's meanders. Effects of changing inside diameter and number of stent's meanders were exactly dependent together. In addition, increasing wire diameter has a great effect on the maximum force. In conclusion, the results of this study may serve as guidelines for future stent design.

Three-dimensional modeling of Marfan syndrome with elastic and hyperelastic materials assumptions using fluid-structure interaction.

BACKGROUND: Marfan syndrome (MFS) is a genetic disorder of the connective tissue. It most prominently influences the skeletal, cardiovascular, and ocular systems, but all fibrous connective tissue throughout the body can be affected as well. OBJECTIVE: This study aims to investigate a realistic three-dimensional model of an aorta of a specific patient suffering from MFS by considering elastic and hyperelastic materials for the tissue using fluid-structure interaction (FSI). METHODS: Isotropic linear elastic and Mooney-Rivlin hyperelastic assumptions are implemented. Linear and nonlinear mechanical properties of the aneurysmal MFS aortic tissue are derived from an uniaxial experimental test. RESULTS: Vortex generation in the vicinity of the aneurysm region in both elastic and hyperelastic models and the maximum blood velocity at peak flow time is calculated as 0.517 and 0.533 m/s for the two materials, respectively. The blood pressure is not significantly different between the two models (±8 Pa) and the blood pressure difference between the points in the horizontal plane of the aneurysm region is obtained as ±10 Pa for both models. The maximum von Mises stress for the hyperelastic model (2.19 MPa) is 27% more than the elastic one (1.72 MPa) and takes place at the inner curvature and upper part of the aorta and somehow far from the aneurysm region. The wall shear stress (WSS) is also considered for the elastic and hyperelastic assumptions, which is 36.7 Pa for both elastic and hyperelastic models. CONCLUSION: The aneurysm region in the MFS affects the blood flow and causes the vortex to be generated which consequently affects the blood flow in the downstream by adding some perturbations to the blood flow. The WSS is obtained to be lower in the aneurysm region compared to other regions which indicated vascular remodeling.

A preliminary evaluation of serum level of testosterone, LH, and FSH in patients with varicocele after varicocelectomy as a kidney-related disease.

INTRODUCTION: Varicocele is a common problem with a high prevalence in population with primary and secondary infertilities. The adverse effects of varicocele on spermatogenesis and fertility are known, but the association between clinical varicocele and testosterone is not clear. Hence, we decided to evaluate the serum levels of testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in patients with varicocele after varicocelectomy. METHODS: In this study, 100 patients with varicocele were divided into two groups: hypogonadal patients with testosterone level <280 ng/dL and eugonadal patients with testosterone level >280 ng/dL. The serum levels of testosterone, FSH, and LH were measured before surgery and 3 months after surgery, and the results were analyzed using the SPSS software. P-value <0.05 was considered statistically significant. RESULTS: Patients with varicocele after puberty till 50 years were divided into two groups: hypogonadal (testosterone <280 ng/dL) and eugonadal (testosterone >280 ng/dL) patients who required varicocelectomy. The mean testosterone level before surgery in hypogonadal patients was 215.22±83.31 ng/dL, which reached 326.95±35.125 ng/dL after surgery (P<0.0001), which was significant. There was no significant decrease in the mean FSH level, but there was a significant decrease in the mean LH level after varicocelectomy. In eugonadal group, testosterone level before surgery was 471.90±145.71 ng/dL, which reached 469.57±145.61 ng/dL after surgery, which was not significant. CONCLUSION: In our study, patients who underwent varicocelectomy had improved testosterone levels, so that this increase was more significant in hypogonadal patients than in eugonadal patients. Decrease in LH and FSH levels in all patients was seen after varicocelectomy, which can be due to increase in testosterone levels.

Investigating the performance of four specific types of material grafts and their effects on hemodynamic patterns as well as on von Mises stresses in a grafted three-layer aortic model using fluid-structure interaction analysis.

One of the important parts of the cardiac system is aorta which is the fundamental channel and supply of oxygenated blood in the body. Diseases of the aorta represent critical cardiovascular bleakness and mortality around the world. This study aims at investigation of hemodynamic parameters in a two-dimensional axisymmetric model of three-layer grafted aorta using fluid-structure interaction (FSI). It assumes that a damaged part of aorta, which may happen as a result of some diseases like aneurysm, dissection and post-stenotic dilatation, is replaced with a biomaterial graft. Four types of grafts materials so-called Polyurethane, Silicone rubber, Polytetrafluoroethylene (PTFE) and Dacron are considered in the present study. The assumption of linear elastic and isotropic material is set for the both aorta's wall and aforementioned grafts. Blood is considered as an incompressible and Newtonian fluid. The results indicate higher displacement in Polyurethane and silicone rubber in comparison with other two. Furthermore, results reveal that blood flow velocity has slightly higher values in PTFE and Dacron grafted models compared to Polyurethane and Silicone rubber ones. Even though there are some differences in hemodynamic patterns in these grafted models, they are not considerable as much as von Mises stresses across the graft-aorta intersections are. This study shows that the types of material grafts play an important role in the amount of stresses particularly at intersections of aorta and graft.

Concurrent Oncocytoma and Two Angiomyolipomas in a Diabetic Kidney: A Very Rare Condition.

Angiomyolipoma (AML) and oncocytoma are uncommon benign neoplasms of the kidney which their simultaneous occurrence in the same kidney is extremely rare. This study reports a 60-year-old diabetic woman with the rare simultaneous occurrence of three renal masses. Histologic evaluation revealed two angiomyolipomas and one oncocytoma within the same kidney, in a background of histologic features of diabetic nephropathy. Renal angiomyolipoma and oncocytoma are uncommon neoplasms, and their simultaneous occurrence in the same kidney is extremely rare.

Analysis of Interleukin-17 mRNA Level in the Urinary Cells of Kidney Transplant Recipients with Stable Function.

OBJECTIVES: Kidney transplantation supports patients with end-stage kidney diseases. Many factors control the allograft function in kidney transplant recipients. Interleukin-17 (IL-17) can be used as a non-invasive diagnostic biomarker of rejection. The aim of this study was to evaluate the expression of IL-17 mRNA in urinary cells of kidney transplant recipients with stable function. MATERIAL AND METHODS: A total of 40 renal transplant recipients who were admitted for surgery and 30 healthy controls were enrolled in the study. From each patient, 30 mL urine samples were collected in 50 mL tubes on days 3 and 5 after renal transplantation; also, 30 mL urine samples were obtained from controls. Quantitative Real-Time PCR (qRT-PCR) technique was used for analysis of IL-17 mRNA level in the tested groups; 2-ÄÄCT method was performed for determining the relative gene expression between tested groups. RESULTS: The mRNA expression mean ± SE of fold in patients and controls were 3.58±1.61 fold and 2.85±1.37 fold, respectively. The mRNA expression mean of IL-17 (fold) was not statistically different in tested groups (P-value = 0.63). CONCLUSIONS: In kidney transplant recipients, urinary IL-17 expression provides informative data in relation to the allograft function regardless of allograft pathology.

Outcome of Kidney Transplantation From Living Donors With Multiple Renal Arteries Versus Single Renal Artery.

INTRODUCTION: Receiving a kidney transplant from donors with multiple renal arteries (MRAs) is suggested to be associated with higher risk of vascular and urologic complications and poor allograft outcomes compared to the donors with single renal artery (SRA). We evaluated survival rates in the recipients from donors with MRAs compared to those from donors with SRA. MATERIALS AND METHODS: In a retrospective study on 115 kidney allograft recipients, demographic characteristics and the outcomes of kidney transplantation were compared between the recipients from donors with MRAs compared to those from donors with SRA. These included acute tubular necrosis, acute allograft rejection, hypertension, vascular complications, urologic complications, kidney function indicators, and allograft survival at 1 year. RESULTS: There was no significant difference in the recipients' age, sex distribution, and weight, donors' age, donor-recipient familial relation, urologic complications, and duration of hospitalization between the two groups. However, MRA was significantly associated with a higher likelihood of right-side kidney donation, longer warm and cold ischemia times, and lower glomerular filtration rate and higher serum creatinine concentrations at discharge and 12 months after transplantation, as compared to SRA transplants. No significant difference was seen in late complications including hypertension and renal artery stenosis. One-year graft survival was slightly poorer in the MRA group than the SRA group. CONCLUSIONS: Our results demonstrate that kidney allografts with MRAs are associated with risks but have acceptable outcomes during the 1st year after transplantation, as compared to SRA kidney allografts.

Wall stress in media layer of stented three-layered aortic aneurysm at different intraluminal thrombus locations with pulsatile heart cycle.

At the point when the aorta ruptures suddenly, as opposed to as the after-effect of injury, it is for the most part in aortic aneurysm. Aortic aneurysm rupture happens when the wall stress surpasses the strength of the vascular tissue. Intraluminal thrombus (ILT) may have advantages as it can absorb tension and decrease aortic aneurysm wall stress. This study aims to investigate the presence and growth effects of ILT on the wall stress in a stented aneurysm in one heart cycle. A virtual stented aneurysm model with ILT was made to study the flow and wall dynamics using fluid-structure interaction (FSI) analysis. Wall stresses at the center line of media layer of aorta thickness were calculated by two-dimensional axisymmetric finite element analysis. Calculations were executed as thrombus elastic modulus increased from 0.1 to 2 MPa and calculations were repeated as thrombus depth was increased in 10% increment until thrombus filled the whole aneurysm cavity. The von Mises stresses were compared in three sections, namely proximal, aneurysm and distal sections in the abdominal aorta. The wall stress showed its maximum value during a peak flow and pressure and gradually decreased as the pressure and velocity of blood reduced in all three aforementioned sections. As the intraluminal thrombus depth increased from 10% to 100%, the wall stress in distal, proximal and centre of aneurysm during one heart cycle was decreased. Furthermore, increasing the elastic modulus of thrombus from 10% to 100% triggered a reduction in wall stress in proximal, centre of intraluminal thrombus and distal regions during one heart cycle. The achievements of this study may have implications not only for understanding the wall stress in ILT, but also for providing more detailed information about aortic aneurysm with intraluminal thrombus and can help surgeons to do their best.

A depth dependent transversely isotropic micromechanic model of articular cartilage.

Articular cartilage owing to the variation of collagen fibers orientation through its zones has been indicated to have depth dependent mechanical properties. The aim of this study was to present an innovative micromechanics model to predict the depth dependent mechanical properties of articular cartilage as a function of collagen fibers and proteoglycan matrix mechanical properties, collagen fibers volume fraction as well as angle toward cartilage surface. The variation of collagen fibers angle toward the cartilage surface as a function of cartilage depth was computed using the micromechanics model. This function showed that the collagen fibers parallel to the cartilage surface in the superficial zone have a nonlinear angle variation in the transition zone and become perpendicular to cartilage surface in the deep zone. Depth dependent elastic modulus in perpendicular to cartilage surface plane direction was calculated using presented micromechanics model and variation function of the collagen fibers' angle. The results revealed a suitable agreement with that of the experimental measurements in different samples at different ages and races (R2=0.944). The results also showed that the elastic and aggregate modules perpendicular to the cartilage surface plane in the deep zone were 25.8 and 26.3 times higher than that of the superficial zone, respectively. These findings have implications not only for computing the depth dependent mechanical properties of any type of articular cartilage at different ages and races, but also of potential ability for developing a depth dependent transversely isotropic biphasic model to predict the accurate mechanical behavior of articular cartilage.

Hemodynamic simulation of blood flow in a new type of cardiac assist device named AVICENA.

The purpose of this study is to investigate the hemodynamic parameters of blood flow in a balloon as a part of a new type of cardiac assist device named AVICENA, which is implanted into the descending aorta to improve the strength of pumping blood flow in a poor-performing left ventricle. Balloon is inflated and deflated during diastole and systole, respectively. The longitudinal velocity of blood flow during balloon inflation and deflation has been considered. Through these investigations, the result reveals that the balloon inflation causes the blood flow to accelerate through the balloon and compensates the blood flow velocity required for the normal circulation system. When the balloon deflates, a reverse flow is generated and improves the perfusion of coronary arteries. Furthermore, the inlet pressure and acting force on the aortic valve for the healthy, unhealthy, and assisted heart have been compared. Result indicates that the force acting on the aortic valve has been considerably reduced for the assisted heart compare to the unhealthy or unassisted heart.

Effects of hydrochlorothiazide on kidney stone therapy with extracorporeal shock wave lithotripsy.

OBJECTIVE: The aim of this investigation was to assess the efficacy of hydrochlorothiazide as a hypocalciuric diuretic on stone-free rate of renal pelvic calculi after extracorporeal shock wave lithotripsy (ESWL). MATERIALS AND METHODS: A double-blind, placebo-controlled randomized clinical trial was conducted and 52 patients with renal pelvic calculi (diameter ≤2 cm) were enrolled from February 2010 to September 2010. ESWL protocol was performed by 2,500 shocks per session. The patients were randomized into two groups: (1) 26 patients who were given 25 mg hydrochlorothiazide twice daily; and (2) 26 patients who received placebo. The stone-free rate was defined as residual calculus size ≤4 mm in controlled ultrasound on 2(nd) week, 1 month and 3 months after ESWL. RESULTS: 19 (78%) of the first group and 9 (42.9%) of the second group were stone-free after one session of ESWL (P = 0.02). 88% of the group 1 and 47.8% of the group 2 were stone-free on 1 month after ESWL (P = 0.003); however, this effect of hydrochlorothiazide was not related to the patients' body mass index, age and gender. The accessory treatment procedures were applied in 24% of the group 1 compared with 19% of the group 2 during 3 months (P = 0.68). All patients in both groups were stone-free on 3 months following lithotripsy. CONCLUSIONS: Hydrochlorothiazide did not impact on the stone-free rate and using accessory procedure within 3 months; however, it decreased duration of stone-free status and number of ESWL sessions.

A comparative study on the elastic modulus of polyvinyl alcohol sponge using different stress-strain definitions.

There have been different stress-strain definitions to measure the elastic modulus of spongy materials, especially polyvinyl alcohol (PVA) sponge. However, there is no agreement as to which stress-strain definition should be implemented. This study was aimed to show how different results are given by the various definitions of stress-strain used, and to recommend a specific definition when testing spongy materials. A fabricated PVA sponge was subjected to a series of tensile tests in order to measure its mechanical properties. Three stress definitions (second Piola-Kichhoff stress, engineering stress, and true stress) and four strain definitions (Almansi-Hamel strain, Green-St. Venant strain, engineering strain, and true strain) were used to determine the elastic modulus. The results revealed that the Almansi-Hamel strain definition exhibited the highest non-linear stress-strain relation and, as a result, may overestimate the elastic modulus at different stress definitions (second Piola-Kichhoff stress, engineering stress, and true stress). The Green-St. Venant strain definition failed to address the non-linear stress-strain relation using different definitions of stress and invoked an underestimation of the elastic modulus values. Engineering stress and strain definitions were only valid for small strains and displacements, which make them impractical when analyzing spongy materials. The results showed that the effect of varying the stress definition on the maximum stress measurements was significant but not when calculating the elastic modulus. It is important to consider which stress-strain definition is employed when characterizing the mechanical properties of spongy materials. Although the true stress-true strain definition exhibits a non-linear relation, we favor it in spongy materials mechanics as it gives more accurate measurements of the material's response using the instantaneous values.

Comparative study of color Doppler voiding urosonography without contrast enhancement and direct radionuclide voiding cystography for diagnosis of vesicoureteric reflux in children.

OBJECTIVES: Most available studies investigating the diagnostic accuracy of color Doppler voiding urosonography in the detection of vesicoureteric reflux used an echo contrast agent. It is unknown whether echo contrast agents are necessary for diagnosis or follow-up of vesicoureteric reflux. We compared color Doppler voiding urosonography without contrast enhancement and direct radionuclide voiding cystography in the detection and grading of vesicoureteric reflux with respect to the sex and age of patients as well as the severity of reflux. METHODS: In the 66 patients enrolled (56 girls and 10 boys), 132 renoureteral units were investigated. All patients under went Doppler voiding urosonography and direct radionuclide voiding cystography within 3 hours. Direct radionuclide voiding cystography was used as the reference standard. RESULTS: Our results indicate good overall sensitivity (83%) and specificity (77%) for color Doppler voiding urosonography without contrast enhancement in comparison with direct radionuclide voiding cystography. As the age of the patients decreased, the sensitivity of urosonography increased, reaching 100% among patients younger than 1 year. In the comparison of different grades of reflux severity, we found that the sensitivity and specificity were elevated as the grade increased (both parameters reaching 100% in the most severe cases). Severity grading was equal between the two methods. CONCLUSIONS: We have shown that Doppler voiding urosonography without contrast enhancement is a comparably reliable method versus direct radionuclide voiding cystography in the detection and grading of vesicoureteric reflux, especially at higher grades of reflux and in children younger than 1 year.

Megacystis secondary to congenital urethral stricture.

Functional bladder capacity at a certain age can be accurately estimated and expressed as a function of age. We present a 13-year-old boy with abdominal distention who was presumed to have ascites. Abdominal ultrasound revealed that the bladder was severely distended, and cystoscopy showed a short stricture in the bulbar urethra followed by a large bladder without obvious borders. Under general anesthesia, bladder capacity was 9250 cc. Reduction cystoplasty was performed. At the 2-year follow-up, he voided spontaneously with 20 cc post-void residual urine.