The effect of underwater explosion on a mine countermeasures vessel: structural response and material design

In the modern geo-strategic scenario, characterized by the presence of sophisticated mines as well as rudimental and cheaper ones, the Italian Navy decided to design a New Generation Mine Countermeasures Vessel, in which the historical capabilities of minesweepers must be enhanced, considering the necessity of holding unmanned systems. In particular, they must survive in case of an underwater explosion event, according to some design criteria and corresponding limit states. Nowadays, the continuous increase of using modern numerical methods, such as Finite Element (FE) methods, allowed by the evolution of the computational capabilities of computers, has strongly influenced the shock design against underwater explosions. However, the complete numerical simulation of the phenomena in issue is even nowadays a matter of research, and it requests the comparison of numerical results with experimental data and theoretical formulations for validation. The main target of the thesis is to provide suitable methodologies for the ship design phase to assess the strength of naval structures in composite material against non-contact underwater explosions, thus reducing the vulnerability of the New Generation Mine Countermeasures Vessel. The experiments realized for this purpose were conducted in the Naval Support and Experimentation Centre’s (CSSN) laboratory in La Spezia and allowed validation of a set of increasingly complex numerical models. At first, the shock phenomenon involving ship structures only is analysed. Some reliable guidelines to perform a dynamic calculation using the finite element method, not yet available in the literature, are provided. Then, the dynamic response of New Generation Mine Countermeasures Vessel composite structure is studied. An experimental and numerical method to characterize the shock transient response of naval E-glass biaxial laminates is presented. This procedure opens for relatively straightforward material characterization, limiting the need for complex experimental shock trials to a few selected laminates. It can be applied in the design of minesweepers’ structures to select the proper stacking sequences of laminates and to design adequate composite materials. Finally, the effectiveness of different numerical approaches to predict the effects of Fluid-Structure Interaction caused by non-contact underwater explosions on minesweepers hull structures is verified. In particular, a numerical methodology, in which the Volume of Fluid approach is pursued, provides the most realistic results when comparing analytical theory, numerical models and experiments. This modelling strategy includes the simulation of the complete phenomenon, in which structures, water and vapor of cavitation are included. Eventually, it can be considered a valuable and cost-effective tool for the design of composite structures subject to non-contact underwater explosions

Aortic stenosis and aortic regurgitation express different titin isoforms: Differences and relationships with functional and geometric characteristics

Background-Titin represents an important biomechanical sensor which determines compliance and diastolic/ systolic function of the left ventricle (LV). To assess the different titin-isoform expression and the relationships with functional and geometric patterns, we analyzed titin-isoform expression and cardiomyocytes contractile functioninmyocardialbiopsysamplesofpatientsundergoingaorticvalvereplacement(AVR)foraorticstenosis (AS)and for aorticregurgitation (AR). Method-Specimens,collectedfromtheLVof35withASand35withARundergoingAVRwereanalyzedfortitinisoform expression and cardiomyocytes force measurement. Ten donor hearts were analyzed as controls for normal values. Results were implemented with preoperative geometry and function assessed by Doppler echocardiography. Results-Comparedtocontrols,N2BA/N2Btitin-isoformsratiowasreducedto0.24inAS(p b 0.001)butincreased to 0.51 in AR (p b 0.001). N2BA/N2B titin-isoforms ratio was further reduced in 8 patients with severe (restrictive) diastolic dysfunction (0.17 ± 0.03, p b 0.001) but was increased in patients with severe systolic dysfunction (0.58 ± 0.07, p b 0.001). As compared to controls, Fpasive was higher in AS (6.7 ± 0.2 vs 4.4 ± 0.4kN/m2,p b 0.001)butwaslowerinAR(3.7±0.2vs4.4±0.4kN/m2,p b 0.001).Totalforcewascomparable. FpassivewassignificantlyhigherinAS patientswithseverethanwithmoderateLVdiastolicdysfunction(7.1± 0.5 vs 6.6.±0.6,p=0.004). Conclusions-titin-isoform expression differs in AS and AR as adaptive response to different pathophysiologic scenarios. Co-expressing isoforms at varying ratios results in modulation of the passive mechanical behavior of the LV at different degree of dysfunction and allows for compensative adjustment of the diastolic/systolic properties of the myocardium

Continuative statin therapy after percutaneous coronary intervention improves outcome in coronary bypass surgery: A propensity score analysis of 2501 patients

ObjectivesA history of percutaneous coronary intervention increases the risk of death and complications of coronary artery bypass grafting. This retrospective multicenter study evaluated the impact of continuative use of statin on postoperative outcomes when subsequent elective coronary artery bypass grafting is required after percutaneous coronary intervention.MethodsAmong 14,575 patients who underwent isolated first-time coronary artery bypass grafting between January 2000 and December 2010, 2501 who had previous percutaneous coronary intervention with stenting and fulfilled inclusion criteria were enrolled. Continuative statin therapy was used in 1528 patients and not used in 973 patients. Logistic multiple regression and propensity score analyses were used to assess the risk-adjusted impact of statin therapy on in-hospital mortality and major adverse cardiac events. The Cox proportional hazards model was constructed to assess the effect of continuative statin therapy on 24-month outcome.ResultsAt multivariate analysis, age more than 70 years, 3-vessel or 2-vessel plus left main coronary disease, multivessel percutaneous coronary intervention, ejection fraction 0.40 or less, diabetes mellitus, and logistic European System for Cardiac Operative Risk Evaluation 5 or greater were independent predictors of hospital mortality and major adverse cardiac events. After propensity score matching, conditional logistic regression analysis demonstrated that continuative statin therapy before coronary artery bypass grafting reduced the risk for hospital and 2-year mortality (odds ratio [OR], 0.27; 95% confidence interval [CI], 0.12-0. 57; P = .004 and OR, 0.6; 95% CI, 0.36-0.96; P = .04, respectively) and major adverse cardiac events (OR, 0.31; 95% CI, 0.18-0.78; P = .003 and OR, 0.5; 95% CI, 0.34-0.76; P = .006, respectively).ConclusionsLong-term statin treatment after percutaneous coronary intervention improves early and midterm outcome when surgical revascularization will be required

Influence of prosthesis-patient mismatch on exercise-induced arrhythmias: a further aspect after aortic valve replacement.

Objectives: The influence of prosthesis–patient mismatch on outcome after aortic valve replacement is controversial. This study analyzed the impact of prosthesis–patient mismatch on survival, the extent of left ventricular mass, and physical capacity after replacement with a small-size prosthesis. Patients and Methods: A total of 157 patients who underwent valve replacement for pure aortic stenosis were reviewed. Late mortality, morbidity, left ventricular mass regression, transprosthetic gradient at rest and after exercise, exercise capacity, and occurrence of arrhythmias were evaluated. Results: Prosthesis–patient mismatch, defined as an indexed effective orifice area of 0.75 cm2/m2 or more, occurred in 96 (61.1%) patients and had no significant impact on early and late mortality. The only independent predictor of mortality was age greater than 65 years. At follow-up, multivariate analysis of prosthetic gradient at rest of 35 mm Hg end exercise capacity or more revealed that both these evidences were associated with high left ventricular mass (P<.001), female gender (P<.001), and follow-up time (P<.001). Arrhythmias occurred during exercise in 34.1% of patients (40/117). Multivariate analysis of occurrence of arrhythmias revealed that they were associated with high mean transprosthetic gradients: values of 50 mm Hg or more during exercise had 95% sensitivity and 72% specificity for predicting arrhythmias. Conclusion: Prosthesis–patient mismatch failed to demonstrate any significant impact on early and late mortality and morbidity and in left ventricular mass regression. High transprosthetic gradients influence exercise capacity and occurrence of arrhythmias

Effect of rosuvastatin pretreatment on myocardial damage after coronary surgery: a randomized trial.

Objective: Myocardial disease without evidence of myocardial infarction is a frequent complication after cardiac surgery during cardiopulmonary bypass. Statins might be protective, but their efficacy has not been established in randomized trials. Methods: Two hundred patients undergoing coronary surgery were enrolled. They were randomized to rosuvastatin (20 mg/d, n ¼ 100) or placebo (n ¼ 100) starting 1 week before the operation. Troponin I, myoglobin, creatine kinase–MB mass, and high-sensitivity C-reactive protein were used as markers of myocardial injury, and their values were determined at baseline and at regular intervals after the operation. Electrocardiography and echocardiography were performed before and after the operation. Results: Myocardial disease was diagnosed when troponin I, myoglobin, and creatine kinase–MB mass values were above the upper normal limit without evidence of electrocardiographic changes, echocardiographic changes, or both. The percentages of marker level increase indicative of myocardial disease were determined in the placebo versus statin groups and were as follows: troponin I, 35%versus 65%(P<.0001); myoglobin, 39%versus 72% (P<.0001); creatine kinase–MB mass, 22% versus 40% (P ¼ .0002). Peak postoperative values of troponin I (0.16 0.15 vs 0.32 0.26 ng/mL, P ¼ .0008), myoglobin (72.25 25 vs 98.31 31 ng/mL, P<.0001), and creatine kinase–MB mass (3.9 3.3 vs 9.3 8.1 ng/mL, P<.0001) were significantly higher in the placebo group. High-sensitivity C-reactive protein values were increased in 58%of pretreated versus 88%of the control patients (15.4 2.5 vs 17.2 3.4 mg/L, P<.0001). In high-risk patients myocardial disease was observed more frequently but significantly less in statin-pretreated patients. Conclusions: Statin pretreatment reduces myocardial damage after coronary surgery and could improve both short- and long-term results