Preload Stress Research Articles

Preload stress echocardiography by using dynamic postural alteration can identify high risk patients with heart failure with reduced ejection fraction

Abstract Funding Acknowledgements Type of funding sources: None. Background Haemodynamic assessment during stress testing is not commonly performed for patients with heart failure with reduced ejection fraction (HFrEF) due to its invasiveness, less feasibility, and safety concerns. Passive leg-lifting (PLL) manoeuvres have been introduced as a simple alternative for non-invasive preload stress testing; however, the haemodynamic load imposed on the cardiovascular system is unsatisfactory, which precludes the accurate assessment of the preload reserve for patients with HF. Purpose The purpose of this study was to assess the haemodynamic characteristics of patients with HFrEF in response to a preload stress during dynamic postural alterations by combining the semi-sitting position (SSP) and PLL. We also evaluated whether combined postural stress could be used for risk stratification for these patients. Methods For this study, 101 patients with HFrEF and 35 age- and sex-matched normal controls were prospectively recruited. At each postural position (i.e., baseline, SSP, and PLL), all standard echocardiographic and Doppler variables were obtained. Adverse cardiac events were prespecified as the combined endpoints of death from or hospitalisation for deteriorated HF, or sudden cardiac death. Clinical follow-up was conducted for a median of 7 months. Results During PLL stress, the stroke volume index (SVi) significantly increased in both controls (from 40 ± 6 to 43 ± 6 mL/m², P = 0.03) and HFrEF patients (from 31 ± 9 to 34 ± 10 mL/m², P = 0.03). Conversely, during SSP stress, the SVi significantly decreased for both controls (from 40 ± 6 to 37 ± 6 mL/m², P = 0.03) and HFrEF patients (31 ± 9 to 28 ± 8 mL/m², P = 0.03). During the follow-up period, 16 patients developed cardiac events. In patients without events, the Frank-Starling mechanism was well preserved (Fig. A). Namely, the SVi significantly increased from 31 ± 9 to 35 ± 10 mL/m² (P = 0.02) during PLL stress, while the SVi significantly decreased from 31 ± 8 to 28 ± 8 mL/m² (P = 0.02) during SSP stress. In contrast, for patients with cardiac events, the SVi did not change during postural alterations (n.s), which indicated that the failing heart operates on the flat portion of the Frank-Starling curve (Fig. A). When patients were divided into three equal sub-groups based on the total difference in the SVi during dynamic postural stress, patients with impaired preload reserve (third trimester, ΔSVi ≤ 3.0 mL/m²) showed significantly worse event-free survival than the other two sub-groups (Fig. B; P < 0.001). In a Cox proportional-hazard analysis, baseline LVEF (hazard ratio 0.93; P = 0.04), and ΔSVi during postural stress (hazard ratio 0.76; P = 0.004) were predictors of future cardiac events. Conclusions The combined assessment of dynamic postural stress during PLL and SPP is a simple, time-saving, and easy-to-use clinical tool for the assessment of preload reserve for patients with HFrEF. Moreover, postural stress echocardiography proved to contribute to the risk stratification for these patients. Abstract Figure.

Impaired preload reserve is an important haemodynamic characteristics that discriminates between physiological ageing and overt heart failure with preserved ejection fraction

Abstract Funding Acknowledgements Type of funding sources: None. Background Ageing process per se is a major risk factor for heart failure (HF). In fact, the incidence of HF with preserved ejection fraction (HFpEF) dramatically increases with age. Although ageing plays a central role in the development of HFpEF, not all the elderly patients develop clinical HFpEF. Multiple abnormalities in the cardiovascular system have been proposed to contribute to the development of HFpEF. However, the pathophysiology that discriminates between physiological ageing and overt HFpEF is incompletely understood. Purpose The purpose of this study was to assess the effects of ageing on the cardiac structures and haemodynamics. Moreover, we evaluated the determinant factor that discriminates between physiological ageing and overt HFpEF by non-invasive preload increasing manoeuvre using leg-positive pressure (LPP) stress echocardiography. Methods A total of 91 subjects were prospectively recruited in this study: 22 patients with HFpEF and 69 healthy controls. Normal controls were further stratified into 3 age groups: young (n = 19, 20-40 years of age), middle-aged (N = 25, 40-65 years) and elderly (n = 25, >65 years). All subjects underwent LPP stress with a continuous external pressure of 90 mmHg around both lower limbs using dedicated airbags (Fig.). Results The left ventricular mass index (LVMI; young, 68 ± 19 g/m²; middle-age, 70 ± 18 g/m²; elderly, 84 ± 21 g/m²) and also the relative wall thickness (RWT; young, 0.34 ± 0.09; middle-age, 0.41 ± 0.06; elderly 0.55 ± 0.10) increased with ageing, which was accelerated in HFpEF (LVMI: 111 ± 32 g/m², RWT; 0.63 ± 0.19, ANOVA P < 0.001, respectively). Although baseline LV ejection fraction and cardiac output were quite comparable between groups, E/e’ ratio significantly increased with with ageing (ANOVA P < 0.001, Fig.). During LPP stress, E/e’ ratio significantly increased in the middle-aged and elderly groups (from 8.8 ± 2.7 to 9.7 ± 3.3, and from 11.4 ± 2.4 to 13.0 ± 2.2, P < 0.05, respectively), which was further deteriorated in HFpEF (from 16.8 ± 5.8 to 18.0 ± 7.6, P < 0.05). On the other hand, stroke volume index (SVi) significantly increased in each healthy group during LPP stress (young; from 45 ± 10 to 50 ± 11 mL/m², middle-age; from 39 ± 7 to 44 ± 6 mL/m² and elderly; from 37 ± 7 to 43 ± 8 mL/m², all P < 0.001), while SVi failed to increase in the HFpEF group (from 45 ± 13 to 45 ± 14 mL/m², P = 0.60). In a multivariate logistic regression analysis, LVMI (hazard ratio; HR 1.055, P < 0.05), baseline E/e’ (HR 1.444; P < 0.05), and ΔSVi (HR 0.755; P < 0.05) during LPP stress were the independent parameters that characterised overt HFpEF. Conclusions Striking parallels between structure-function alterations were observed in the physiological cardiovascular ageing process, which was further accelerated in patients with HFpEF. Not only structural remodeling and impaired diastolic function, but also impaired systolic reserve during preload stress is important haemodynamic feature that characterise the pathophysiology of HFpEF. Abstract Figure.

Peri-implant bone alterations under the influence of abutment screw preload stress. A preclinical vivo study.

The study purpose was to examine peri-implant bone alternations around osseointegrated implants caused solely by abutment screw preload stress using different tightening torque values. Twenty 20- to 22-week-old Japanese white rabbits received two implants each in right and left femurs. Implants were randomly assigned to one of three tightening torque groups or the control (Cont) group. After 8weeks, 35Ncm torque was delivered to abutment screws in the recommended torque (RT) group (n=16). Other screws received 70Ncm torque as the high torque (HT) group (n=16). Temporary tightening (TT) groups (n=8) received only 70Ncm torque without preload stress as screws were untightened immediately. Cont group (n=40) remained in situ. Animals were euthanized at 4, 6, 8, and 10weeks after torque application. Micro-CT images were then taken, and undecalcified ground sections were stained with toluidine blue. Cross-sections of cortical bone showed remodeling activities adjacent to the implant in all groups. While bone marrow spaces appearance was relatively small in Cont and TT groups, RT and HT groups showed large bone marrow spaces and extensive remodeling activity. Bone-to-implant contact was significantly less in RT and HT groups compared with Cont and TT groups at different time points (p˂.05). Furthermore, RT and HT groups showed significantly less bone volume and area (p˂.05). Results suggested that preload stress without any occlusal loading might negatively affect peri-implant bone stability and initiate bone remodeling. This could alter bone mechanical properties, subsequently influencing long-term implant success.

Experimental Study and Analysis on the Durability of Concrete in Underground Engineering

The underground environment is much more complicated than the overground environment. Concrete in underground engineering bears complex environmental effects such as soil stress, water penetration stress, and soil salt erosion. The durability of concrete directly determines the service life of underground engineering. In this paper, considering the soil stress, the chloride ion, sulfate attack and permeability resistance of concrete were tested in the laboratory. The results show that fly ash has excellent resistance to sulfate attack, and when fly ash content is 20% or 30%, the concrete specimens have the best chloride ion penetration resistance and water penetration resistance. Under the effect of preload stress, when the preload stress level is less than 20%, the capacity of concrete stress cannot be reduced greatly, but when the preload stress level is greater than 20%, the concrete durability performance decreases rapidly.

Noninvasive Leg-Positive Pressure Stress Echocardiography Reveals Preload Reserve in Adult Patients after Complete Repair of Tetralogy of Fallot

Long-term sequelae such as right ventricular dysfunction and reduced hemodynamic reserve are the main determinants of cardiovascular outcomes after repair of tetralogy of Fallot (TOF). Echocardiographic parameters at rest offer only partial information on impaired hemodynamics in these patients, and data during stress testing are lacking. The leg-positive pressure (LPP) maneuver has recently been reported to be able to apply acute preload stress. The aim of this study was to test the hypothesis that preload reserve is impaired and ventricular interaction is exacerbated in patients with TOF. In this prospective cross-sectional study, we recruited 44 consecutive patients with TOF and 30 normal control subjects. Echocardiography was performed both at rest and during LPP stress, and preload reserve was defined as the change between baseline stroke volume (SV) and that obtained during LPP stress. The eccentricity index was calculated as the ratio of the left ventricular anteroposterior to septal-lateral dimensions to quantify ventricular interaction. LPP stress significantly increased SV from 73±14 to 83±16mL(P<.01) in control subjects, while the increase in SV was significantly blunted (from 75±19 to 79±18mL; P<.01 for interaction) in patients with TOF. The eccentricity index significantly changed during LPP stress in patients with TOF only from 1.07±0.13 to 1.13±0.14 (P<.01 for interaction). Patients with TOF were subdivided into two subgroups on the basis of the median value of increased response in SV (22 with sufficient and 22 with insufficient preload reserve). Multivariate analysis identified significant pulmonary regurgitation as the only independent determinant factor for insufficient preload reserve (odds ratio, 4.57; 95% CI, 1.048-19.90; P=.04). In patients after repair of TOF, ventricular interaction was exacerbated and preload reserve was impaired, especially in patients with significant pulmonary regurgitation. LPP stress testing may direct tailored treatment approaches, risk stratification, and clinical decision-making, such as more aggressive pharmacologic therapy, meticulous outpatient follow-up, or earlier reintervention.

The Mechanical Performance of V150 Drill Pipe under Combined Tension-Torsion Loading

During the drilling of deep wells and ultra-deep wells, unsuitable tension-torsion coupling results to the failure of drill pipe. Therefore, it is necessary to study the combined tension-torsion resistant loading capacity of drill pipe. The combined tension-torsion loading test methods of pre-torsion followed by tension and pre-tension followed by torsion were used to analyze the interaction laws between the tensile stress/strain and torsional stress/strain of V150 drill pipe. It was found that during the pre-torsion followed by tension, both the preload shear stress and tensile yield strength were reduced; during the pre-tension followed by torsion, both the preload tensile stress and torsional yield strength were reduced. When material yielding occured, the tensile stress and shear stress were in accordance with the tension-torsion ellipse strength criterion, and the elastic deformation safety range of this tension-torsion ellipse strength criterion was 24.5% higher than that of von Mises strength criterion. The results showed that the combined tension-torsion resistant loading capacity of drill pipe designed according to the von Mises strength criterion was conservative to some extent, while the tension-torsion ellipse strength criterion included two benchmark parameters of tensile yield strength and torsional yield strength. Such criterion perfectly aligned with the experimental data and exhibited high engineering application value.

Echocardiography during preload stress for evaluation of right ventricular contractile reserve and exercise capacity in pulmonary hypertension.

Pulmonary hypertension (PH) is characterized by marked and sustained elevation of pulmonary vascular resistance and pulmonary artery pressure, and subsequent right-sided heart failure. Right ventricular (RV) function and exercise capacity have been recognized as important prognostic factors for PH. Our aim was to investigate RV contractile reserve and exercise capacity during a leg-positive pressure (LPP) maneuver. The study population comprised 43 PH patients and 17 normal controls. All patients underwent echocardiography at rest and during LPP stress. Exercise capacity was assessed by 6-minute walk distance for PH patients. RV relative wall thickness was calculated from dividing by RV free wall thickness by basal RV linear dimensions at end-diastole. RV function was calculated by averaging peak speckle-tracking longitudinal strain from the RV free wall. RV contractile reserve was assessed as the difference in RV free wall strain at rest and during LPP stress. Changes in left ventricular stroke volume (ΔSV) during LPP stress were also calculated. ΔSV and RV contractile reserve of PH patients were significantly lower than of controls (3.6±6.0mL vs 8.5±2.3mL, and 8.2±11.9% vs 14.5±6.6%; both P<0.01). RV contractile reserve of PH patients with ΔSV <3.3mL was significantly lower than of PH patients with ΔSV >3.3mL (3.9±13.2% vs 12.3±8.9%; P=0.02). ΔSV had also significant correlation with 6-minute walk distance (r=0.42, P=0.006). Multivariate regression analysis showed that RV relative wall thickness was an independent determinant parameter of ΔSV during LPP stress for PH patients (β=3.2, P=0.003). Preload stress echocardiography in response to LPP maneuver, a noninvasive and easy-to-use procedure for routine clinical use, proved to be useful for the assessment of RV contractile reserve and exercise capacity of PH patients.

Laterally pre-compressed SiC tiles against long rod impact

Abstract A combined experimental and computational study was carried out to investigate ballistic performance of laterally preload compressed SiC tile against long rod impact. A 100 × 100 b y 20 mm thick SiC tile was pushed into a 5 mm thick steel frame at high temperature of 430 °C so that after cool down to room temperature, the lateral preload compressive stress was developed in the SiC tiles. Depth of penetration tests of the SiC tiles with and without pre-stress were performed, where tungsten alloy long rods at a nominal velocity of 1240 m/s were launched to hit the SiC tiles backed by the steel blocks. Compared with the SiC tiles without any pre-stress, the pre-compressed SiC tiles were found to reduce significantly the residual penetration in the backing block. Simulations were carried out using the LS-dyna hydrocode, taking account of preload stress. The simulations showed that the lateral preload compression strengthened the intact SiC tiles and dwell occurred in the early penetration stage, eroding the striking long rod efficiently.

A clinical application of preload stress echocardiography for predicting future hemodynamic worsening in patients with early-stage heart failure.

To improve the prognosis of patients with heart failure, risk stratification in their early stage is important. We assessed whether the change in transmitral flow (TMF) velocity pattern during preload augmentation can predict future hemodynamic worsening in early-stage heart failure patients with impaired relaxation TMF pattern. We designed a prospective cohort study that included 155 consecutive patients with impaired relaxation (IR) pattern at rest. Preload stress echocardiography was achieved using leg-positive pressure (LPP), and changes in TMF pattern during the LPP was observed during baseline echocardiographic examination. The patients whose TMF pattern developed to pseudonormal (PN) pattern throughout the study period were classified into the change to PN group, and patients whose TMF pattern stayed in IR pattern were classified into the stay in IR group. The median follow-up period was 17months. The average age was 68±11years old, and 97 patients (63%) were male. Among 155 patients, 27 were classified into the change to PN group. A Cox proportional hazard analysis confirmed that the change in the peak atrial systolic TMF velocity during the LPP (ΔA, hazard ratio=0.58 per 1SD; 95% CI=0.39-0.88, P=0.010) was the powerful independent predictor of change into PN pattern. Kaplan-Meier analysis revealed that the patients with ΔA≤-7cm/s had more likely to develop into PN pattern than patients with ΔA>-7cm/s (P=0.001). Evaluation of a response in TMF during the LPP might provide an incremental diagnostic value to detect future overt heart failure in patients with early-stage heart failure.

Right Ventricular Function and Beneficial Effects of Cardiac Rehabilitation in Patients With Systolic Chronic Heart Failure

BackgroundIt has been recognized that a comprehensive cardiac rehabilitation (CR) program improves mortality in patients with chronic heart failure. On the other hand, the magnitude of the improvement in exercise capacity after CR differs among individuals. The aim of this study was to assess the echocardiographic determinants of responders to CR using preload stress echocardiography. MethodsWe prospectively enrolled 58 chronic heart failure patients with reduced left ventricular ejection fraction (aged 62 ± 11 years; 69% male; left ventricular ejection fraction 43% ± 7%) who had received optimized medical treatment in a CR program for 5 months. We performed preload echocardiographic studies using leg positive pressure (LPP) to assess the echocardiographic parameters during preload augmentation. We defined 41 patients as a development cohort to assess the predictive value of echocardiographic variables. Next, we validated results in the remaining 17 patients as a validation cohort. ResultsIn the development cohort, significant improvement in peak oxygen uptake (VO2) (>10%) after CR was observed in 58% patients. In a multivariable logistic regression model, the significant predictor of improvement in exercise capacity was right ventricular (RV) strain during LPP (odds ratio: 3.96 per 1 standard deviation; P = 0.01). An RV strain value of −16% during LPP had a good sensitivity of 0.79 and a specificity of 0.71 to identify patients with improvement in peak VO2. In the validation cohort, an optimal cutoff value of RV strain value was the same (area under the curve: 0.77, sensitivity: 0.78, specificity: 0.65). ConclusionsRV strain during LPP may be an echocardiographic parameter for assessing beneficial effects of CR.

Noninvasive Assessment of Preload Reserve Enhances Risk Stratification of Patients With Heart Failure With Reduced Ejection Fraction.

The leg-positive pressure maneuver can safely and noninvasively apply preload stress without increase in total body fluid volume. The purpose of this study was to determine whether preload stress could be useful for risk stratification of patients with heart failure with reduced ejection fraction. For this study, 120 consecutive patients with heart failure with reduced ejection fraction were prospectively recruited. The stroke work index was estimated as product of stroke volume index and mean blood pressure, and the E/e' ratio was calculated to estimate ventricular filling pressure. The echocardiographic parameters were obtained both at rest and during leg-positive pressure stress. During the median follow-up period of 20 months, 30 patients developed adverse cardiovascular events. During preload stress, stroke work index increased significantly (from 3280±1371 to 3857±1581 mm Hg·mL/m2; P<0.001) along with minimal changes in ventricular filling pressure (E/e', from 16±10 to 17±9; P<0.05) in patients without cardiovascular events. However, patients with cardiovascular events showed impairment of Frank-Starling mechanism (stroke work index, from 2863±969 to 2903±1084 mm Hg·mL/m2; P=0.70) and a serious increase in E/e' ratio (from 19±11 to 25±14; P<0.001). Both the patients without contractile reserve and those without diastolic reserve exhibited worse event-free survival than the others (P<0.001). In a Cox proportional-hazards analysis, the changes in stroke work index (hazard ratio: 0.44 per 500 mm Hg·mL/m2 increase; P=0.001) and in E/e' (hazard ratio: 2.58 per 5-U increase; P<0.001) were predictors of cardiovascular events. Contractile reserve and diastolic reserve during leg-positive pressure stress are important determinants of cardiovascular outcomes for patients with heart failure with reduced ejection fraction.

Evaluation of the Stress Equilibrium Condition in Axially Constrained Triaxial SHPB Tests

Over the years many improvements and modifications have been made to the split Hopkinson pressure bar (SHPB). For example, the triaxial SHPB has been developed and used to study various materials. The dynamic stress equilibrium condition for conventional SHPB tests has been well studied in the literature. However, the stress equilibrium in the axially constraint triaxial SHPB tests requires careful examination because the wave propagation is affected by the axial pre-load stress. In this study, we analyzed the stress equilibrium condition in such cases using stress wave analysis and numerical simulations. Based on the study, we offer methods and suggestions for performing valid stress equilibrium assessment in axially constrained triaxial SHPB tests.

Preload Stress Echocardiography Predicts Outcomes in Patients With Preserved Ejection Fraction and Low-Gradient Aortic Stenosis.

The projected aortic valve area (AVAproj) at a normal transvalvular flow rate using dobutamine is helpful to determine the actual severity of aortic stenosis (AS) and to predict risk of adverse events in low-gradient AS cases with unclear surgical indication. Our study aimed to identify the independent and incremental value of preload stress echocardiography-derived AVAproj to predict outcomes in patients with preserved ejection fraction and low-gradient AS. We prospectively performed echocardiographic studies in 79 patients with low-gradient AS (age, 77±7 years; 30% men) with preload stress echocardiography using leg positive pressure. AVAproj was calculated using AVA and transvalvular flow rate at baseline and during leg positive pressure. The primary end point was the decision for aortic valve surgery or cardiac death. During a median period of 19 months, 23 patients had the decision for aortic valve surgery, and none died during follow-up. In a stepwise multivariable analysis, indexed AVAproj (AVAiproj; hazard ratio, 2.00 per 0.1 cm2/m2 decrease; 95% confidence interval, 1.36-2.96; P<0.001) was associated with the primary end point. Using a receiver operating characteristic curve analysis, the best cutoff value of AVAiproj for predicting cardiac events was <0.72 cm2/m2. By incorporating AVAiproj into AVAi at baseline, continuous net reclassification index for cardiac events was 0.48 (P=0.04). In patients with low-gradient AS, indexed AVAproj derived from preload stress echocardiography can be useful to predict risk of adverse events. The present article should be considered as a proof of concept study, and we think that larger multicenter studies are warranted.

Zero-Dimensional Model for Dynamic Behavior of Engineered Rubber in Automotive Applications

This paper presents a zero-dimensional model for the simulation of the mechanical behavior of automotive engineered rubber components, such as flexible couplings. The objective is to develop a real-time-capable model, able to simulate the behavior of a driveline containing elastomer components: the engineered rubber model has to correlate stretch to stress, the mechanical behavior being represented by means of a hysteresis cycle. The study presents the implementation of Maxwell and Voigt models, showing their limits in the representation of the material behavior: elastomers present a nonlinear response in the relationship stress-strain. A combination of Maxwell and Voigt models, with stiffness and damping variable according to the stress and strain rate, to represent nonlinear material responses, is coupled to a relaxation model, in order to represent the Mullins effect (the rubber mechanical behavior also depends on load history).Experimental tests have been carried out with different pre-load settings, stress amplitudes and stress frequencies. Tests results have been used to calibrate the parameters defining the simulation model, comparing the model outputs to experimental data: an optimization algorithm has been applied, with the aim of minimizing the results discrepancy with respect to experimental results. The optimization tool has been also used to reduce the number of parameters defining the model, in order to simplify the required computational power, avoiding at the same time over-parametrization.In the second section of the paper, the model is used for the simulation of a different rubber component, whose behavior is identified using quasi-static load ramps, frequency and amplitude sweeps, steps and random cycles. An alternative model formulation, minimizing the degrees of freedom is then applied to the new dataset. The model parameters are separately optimized using different tests, in order to capture the specific mechanical behavior. Finally, the identified parameters are used to simulate the elastomer response in random tests, comparing the results to experimental data, to evaluate the simulation quality in terms of RMSE.

1247The assessment of contractile reserve and diastolic reserve during non-invasive preload stress echocardiography contributes to the risk stratification for patients with heart failure

1247The assessment of contractile reserve and diastolic reserve during non-invasive preload stress echocardiography contributes to the risk stratification for patients with heart failure

Failure analysis of blots for diesel engine intercooler

In diesel generating sets, it will lead to the abominable working condition if the fault couldn’t be recovered when the bolt of intercooler cracks. This paper aims at the fault of the blots of diesel generator intercooler and completes the analysis of the static strength and fatigue strength. Static intensity is checked considering blot preload and thermal stress. In order to obtain the thermal stress of the blot, thermodynamic of intercooler is calculated according to the measured temperature. Based on the measured vibration response and the finite element model, using dynamic load identification technique, equivalent excitation force of unit was solved. In order to obtain the force of bolt, the excitation force is loaded into the finite element model. By considering the thermal stress and preload as the average stress while the mechanical stress as the wave stress, fatigue strength analysis has been accomplished. Procedure of diagnosis is proposed in this paper. Finally, according to the result of intensity verification the fatigue failure is validation. Thereby, further studies are necessary to verification the result of the intensity analysis and put forward some improvement suggestion.

Significant Prognostic Value of Acute Preload Stress Echocardiography Using Leg-Positive Pressure Maneuver for Patients With Symptomatic Severe Aortic Stenosis Awaiting Aortic Valve Intervention.

Although aortic valve intervention is recommended for virtually all symptomatic patients with aortic stenosis (AS), how urgently the intervention should be performed remains controversial. The aim of this study was thus to determine whether the preload reserve in response to leg-positive pressure (LPP) maneuver could serve for decision-making for AS patients awaiting aortic valve intervention.Methods and Results:Sixty-eight patients with symptomatic AS, who were referred for aortic valve intervention, were recruited. Stroke volume (SV) was assessed by means of pulsed-wave Doppler, and the ratio between transmitral E wave and mitral annular velocity (e') was calculated to estimate ventricular filling pressure. While waiting for intervention, 11 patients experienced preoperative cardiac events. During acute preload stress, forward SV for patients without cardiac events increased significantly (from 43±9 to 49±10 mL/m2, P<0.01) along with a minimal change in filling pressure (E/e': from 20±8 to 21±9, NS). For patients with cardiac events, the Frank-Starling mechanism was significantly impaired (SVi: from 40±9 to 38±7 mL/m2, NS), while filling pressure increased to the critical level (E/e': from 24±8 to 31±8, P<0.001). Both the patients without flow reserve (∆SVi <4.5 mL/m2) and those without diastolic reserve (∆E/e' ≥2.9) exhibited significantly worse event-free survival than the others (P<0.05, respectively). Assessment of preload reserve during LPP stress could facilitate risk stratification of patients with severe AS waiting for aortic valve intervention.

A Study on Rebound Characteristic of Sealing Ring Used in Solid Rocket Motor

Solid Rocket Motor (SRM) is a key component for the missile and space rocket. Sealing performance is an important index for SRM assembled. It is a necessary condition for study on the sealing performance of SRM to determine the residual stress of sealing ring which is difficult to be obtained by direct detection in engineering practice. This paper derives the quantitative expression of the relationship between residual stress, pressure difference and preload stress and establishes the method of determining residual stress of sealing ring by mechanical analysis. With the help of experiment, verify the correctness and applicability for expression meanwhile, analyze the influence of SRM's types and rubber sealing ring materials on residual stress changed under the effect of pressure difference. Therefore, the method of residual stress determined provides theoretical support to improve the SRM assembly process and lays a foundation for later study on the leakage rate of SRM.

Abstract 13729: Significant Prognostic Values of Acute Preload Stress Echocardiography by Using Leg-positive Pressure Maneuver in Patients With Severe Aortic Stenosis

Introduction: Recently, leg-positive pressure (LPP) maneuver, using customized air-bags inflated both lower limbs to maintain a constant loading pressure (90 mmHg for 5 minutes), is reported to be able to apply acute preload stress non-invasively without significant change in either heart rate or blood pressure. Hypothesis: We hypothesized the ability to utilize the Frank-Starling mechanism without significant increase in left ventricular (LV) filling pressure in response to LPP stress could provide additional prognostic capability for patients with aortic stenosis (AS). Methods: We prospectively recruited 48 patients with severe AS. LV stroke volume (SV) was assessed by means of pulsed-wave Doppler, and then normalized by body surface area (SVi). The ratio of transmitral E wave and mitral annular velocity (e’) was calculated to estimate LV filling pressure. These parameters were obtained both at rest and during LPP stress. Event-free survival was then tracked for 136 days. Results: Eight patients developed adverse cardiac events. During acute preload stress, forward SV increased significantly (SVi : 42±9 to 48±9 ml/m 2 , p&lt;0.001) along with minimal change in LV filling pressure (E/e’: 20±8 to 21±11, n.s.) in patients without cardiac events. On the other hand, Frank-Starling mechanism was significantly impaired (SVi: from 41±10 to 38±8 ml/m 2 ), while LV filling pressure increased to the critical level (E/e’:26±7 to 33±7, p&lt;0.01) in patients with cardiac events. When the patients were divided into two subgroups based on the response to LPP stress, patients without preload reserve (ΔSVi&lt;5ml/m 2 ) showed worse event rate than the others (p&lt;0.05). Similarly, patients without diastolic reserve (ΔE/e’ ratio &gt;3) exhibited significantly worse event-free survival (p&lt;0.05). Conclusions: Assessment of preload reserve and diastolic reserve during LPP stress can enhance the predictive capability for cardiovascular outcomes events for patients with AS.

Modeling and numerical analysis of multi-bolt elastic interaction with bolt stress relaxation

Multi-bolt joint distributed around the connecting members are generally adopted to meet the high-performance assembly requirements in aerospace, energy and power industries. However, the initial preload could be low due to non-optimized preload sequence and bolt stress relaxation, especially at elevated temperature. Thus, it is necessary to take elastic interaction and bolt stress relaxation into account before jointing. In this article, a general multi-bolt elastic interaction with bolt stress relaxation is modelled analytically. First, the multi-bolt joint is characterized by ‘spring-node’ model and elastic interaction stiffness. Second, the bolt residual preload can be estimated according to linear superposition of elastic interaction and bolt stress relaxation under the condition of node displacement equilibrium. Further, the influence of preloading sequence and bolt stress relaxation on residual preload distribution was numerically analyzed using a typical circular ring with 8-bolt joint. Two bolts’ preloading sequences were planned, star sequence and counterclockwise sequence, respectively. The bolt creep simulation time was set as 10 h using the power-model at intermediate temperature. From comparison, the predicted results using the developed model were consistent with the FE simulations both with and without bolt stress relaxation.