Characterization of the Ejector Pump Performance for the Assisted Bidirectional Glenn Procedure

This study introduces an algebraic model informed by computational fluid dynamics (CFD) simulations to investigate the performance of the assisted bidirectional Glenn (ABG) operation on a broad range of conditions. The performance of this operation, as measured by the superior vena cava (SVC) pressure, depends on the nozzle area in its ejector pump and the patient’s pulmonary vascular resistance (PVR). Using the developed algebraic model to explore this two-dimensional parameter space shows that the ejector pump can create a pressure difference between the pulmonary artery and the SVC as high as 5 mmHg. The lowest SVC pressure is produced at a nozzle area that decreases linearly with the PVR such that, at PVR =4.2 (Wood units-m2), there is no added benefit in utilizing the ejector pump effect (optimal nozzle area is zero, corresponding to the bidirectional Glenn circulation). At PVR =2 (Wood units-m2), the SVC pressure can be lowered to less than 4 mmHg by using an optimal nozzle area of ≈2.5 mm2. Regardless of the PVR, adding a 2 mm2 nozzle to the baseline bidirectional Glenn boosts the oxygen saturation and delivery by at least 15%. The SVC pressure for that 2 mm2 nozzle remains below 14 mmHg for all PVRs less than 7 Wood units-m2. The mechanical efficiency of the optimal designs consistently remains below 30%, indicating the potential for improvement in the future. A good agreement is observed between the algebraic model and high-fidelity CFD simulations.

Overexpression of NOX2 Exacerbates AngII-Mediated Cardiac Dysfunction and Metabolic Remodelling

The present study aimed to examine the effects of low doses of angiotensin II (AngII) on cardiac function, myocardial substrate utilization, energetics, and mitochondrial function in C57Bl/6J mice and in a transgenic mouse model with cardiomyocyte specific upregulation of NOX2 (csNOX2 TG). Mice were treated with saline (sham), 50 or 400 ng/kg/min of AngII (AngII50 and AngII400) for two weeks. In vivo blood pressure and cardiac function were measured using plethysmography and echocardiography, respectively. Ex vivo cardiac function, mechanical efficiency, and myocardial substrate utilization were assessed in isolated perfused working hearts, and mitochondrial function was measured in left ventricular homogenates. AngII50 caused reduced mechanical efficiency despite having no effect on cardiac hypertrophy, function, or substrate utilization. AngII400 slightly increased systemic blood pressure and induced cardiac hypertrophy with no effect on cardiac function, efficiency, or substrate utilization. In csNOX2 TG mice, AngII400 induced cardiac hypertrophy and in vivo cardiac dysfunction. This was associated with a switch towards increased myocardial glucose oxidation and impaired mitochondrial oxygen consumption rates. Low doses of AngII may transiently impair cardiac efficiency, preceding the development of hypertrophy induced at higher doses. NOX2 overexpression exacerbates the AngII -induced pathology, with cardiac dysfunction and myocardial metabolic remodelling.

Work and oxygen consumption of isolated right ventricular papillary muscle in experimental pulmonary hypertension

Right-sided myocardial mechanical efficiency (work output/metabolic energy input) in pulmonary hypertension can be severely reduced. We determined the contribution of intrinsic myocardial determinants of efficiency using papillary muscle preparations from monocrotaline-induced pulmonary hypertensive (MCT-PH) rats. The hypothesis was tested that efficiency is reduced by mitochondrial dysfunction in addition to increased activation heat reported previously. Right ventricular (RV) muscle preparations were subjected to 5 Hz sinusoidal length changes at 37°C. Work and suprabasal oxygen consumption (VO2) were measured before and after cross-bridge inhibition by blebbistatin. Cytosolic cytochrome c concentration, myocyte cross-sectional area, proton permeability of the inner mitochondrial membrane (PP IMM), and monoamine oxidase (MAO)-A and glucose 6-phosphate dehydrogenase (G-6-PDH) activities and phosphatidylglycerol (PG) and cardiolipin (CL) contents were determined. Mechanical efficiency ranged from 23 to 11% in control (n = 6) and from 22 to 1% in MCT-PH (n = 15) and correlated with work (r2 = 0.68, P < 0.0001) but not with VO2 (r2 = 0.004, P = 0.7919). VO2 for cross-bridge cycling was proportional to work (r2 = 0.56, P = 0.0005). Blebbistatin-resistant VO2 (r2 = 0.32, P = 0.0167) and IMM PP (r2 = 0.36, P = 0.0110) correlated inversely with efficiency. Together, these variables explained the variance of efficiency (coefficient of multiple determination R2 = 0.79, P = 0.0001). Cytosolic cytochrome c correlated inversely with work (r2 = 0.28, P = 0.0391), but not with efficiency (r2 = 0.20, P = 0.0867). G-6-PDH, MAO-A and PG/CL increased in the RV wall of MCT-PH but did not correlate with efficiency. Reduced myocardial efficiency in MCT-PH is due to activation processes and mitochondrial dysfunction. The variance of work and the ratio of activation heat reported previously and blebbistatin-resistant VO2 are discussed.

Design and research of 2D piston pumps with a stacked cone roller set

A new type of two-dimensional (2D) piston pump with a stacked cone roller set was introduced to eliminate the influence of the gap between the guiding rail and the cone roller. First, the structure and working principle of the 2D piston pump were studied; then, a corresponding mathematical model which considered the oil viscosity and oil churning loss caused by the rotation of the guiding rail in the enclosed chamber was established to examine the volumetric and mechanical efficiency of the 2D piston pump. The effects of different speeds, load pressures, and rolling friction coefficients between the guiding rail and the cone rollers on the efficiency were considered. During the test, when the speed was 6000 r/min and the load pressure was 6 MPa and 8 MPa, the volumetric efficiency reached 98.3% and 96.8%, respectively, basically consistent with the theoretical analysis. Because the temperature rise of the tested pump caused the oil viscosity and the eccentricity of the piston and piston rings increased the leakage, the test result was slightly lower than that of the theoretical analysis. When the speed was 1000 r/min and the load pressure was 5 MPa, the mechanical efficiency was 69.3%, and the mechanical efficiency model was consistent with the test results. However, with the increase in speed and load pressure, the difference between the test results and theoretical analysis results increased because the supporting force of the cone roller on the guiding rail increased, increasing the rolling frictional losses.

Gearbox Mechanical Efficiency Determination by Strain Gauges Direct Application

This article describes a unique method of measuring the efficiency of gearboxes using foil strain gauges, which allows maintaining the current configuration of the gearbox within the overall assembly of the machine and its functional condition. The presented method is applicable to gearboxes located in the original equipment assembly without the need to use a test rig. Using foil strain gauges, the torque at the input and output of the gearbox is detected. Therefore, the accuracy of torque measurement is key. The crucial step is the calibration of the instrumentation to the given application conditions, which, in this case, is ensured by a virtual calibration using a very accurate FEM analysis. The accuracy of the position of strain gauges and virtual calibration of measurements generate inaccuracies affecting the resulting uncertainty of the determined efficiency. The present article shows, on the example of several measurements, that when using 24-bit converters, after processing the obtained data, mechanical stress with a sensitivity better than hundredths of an MPa can be reliably detected even without signal amplification from strain gauges. It follows that the efficiency is determined with an accuracy of better than low units of tenths.

The mitochondrial signaling peptide MOTS-c improves myocardial performance during exercise training in rats

Cardiac remodeling is a physiological adaptation to aerobic exercise and which is characterized by increases in ventricular volume and the number of cardiomyocytes. The mitochondrial derived peptide MOTS-c functions as an important regulator in physical capacity and performance. Exercise elevates levels of endogenous MOTS-c in circulation and in myocardium, while MOTS-c can significantly enhance exercise capacity. However, the effects of aerobic exercise combined with MOTS-c on cardiac structure and function are unclear. We used pressure–volume conductance catheter technique to examine cardiac function in exercised rats with and without treatment with MOTS-c. Surprisingly, MOTS-c improved myocardial mechanical efficiency, enhanced cardiac systolic function, and had a tendency to improve the diastolic function. The findings suggest that using exercise supplements could be used to modulate the cardiovascular benefits of athletic training.

Aberrant Mechanical Efficiency during Exercise Relates to Metabolic Health and Exercise Intolerance in Adolescents with Obesity

Background. Mechanical efficiency (ME) might be an important parameter evaluating cardiometabolic health and the effectiveness of physical activity interventions in individuals with obesity. However, whether these cardiometabolic risk factors may relate to ME in adolescents with obesity is not known yet. Therefore, this study aims to compare the mechanical efficiency during maximal exercise testing between adolescents with obesity and lean adolescents, and to examine associations with exercise tolerance and metabolic health. Methods. Twenty-nine adolescents with obesity (BMI SDS: 2.11 ± 0.32, age: 13.4 ± 1.1 years, male/female: 15/14) and 29 lean (BMI SDS: −0.16 ± 0.84, age: 14.0 ± 1.5 years, male/female: 16/13) adolescents performed a maximal cardiopulmonary exercise test from which the net mechanical efficiency (MEnet) and substrate oxidation (carbohydrates and lipids) were calculated. Indicators for peak performance were collected. Biochemistry (lipid profile, glycaemic control, inflammation, leptin) was studied in fasted blood samples. Regression analyses were applied to examine relations between MEnet and exercise tolerance or blood variables in the total group. Results. Peak work rate (WRpeak), oxygen uptake (V̇O2peak)/WRpeak, ME, and MEnet were significantly lower (p < 0.05) in adolescents with obesity compared to their lean counterparts (p < 0.05). Furthermore, a reduced MEnet was independently related to a lower WRpeak (SC β = 2.447; p < 0.001) and elevated carbohydrate oxidation during exercise (SC β = −0.497; p < 0.001), as well as to elevated blood low-density lipoprotein cholesterol (SC β = −0.275; p = 0.034) and fasting glucose (SC β = −0.256; p = 0.049) concentration. Conclusion. In adolescents with obesity, the mechanical efficiency is lowered during exercise and this relates to exercise intolerance and a worse metabolic health.

Effect of clearance on volumetric efficiency in 2D piston pumps

In order to solve the limitations of the friction pairs in axial piston pumps on rotational speed and mechanical efficiency, a 2D piston pump whose 2D piston has two-degree-of-freedom motions of rotation and reciprocating motion was proposed by the author team. The volumetric efficiency of 2D pumps predicted by the original volumetric efficiency model is higher than the experimental results. A new mathematical model of the volumetric efficiency is researched by considering effect of clearance between the cone roller and the guiding rail. In previous studies, the volumetric losses of the 2D pump were considered to be composed of leakage and compressibility loss. However, it is found that the effect of the clearance on the volumetric efficiency in 2D pumps is greater than that of leakage and compressibility loss. The experimental results show that the difference between the prediction of the new model and the volumetric efficiency of the tested pump with 0.19 mm clearance is reduced from 8% to 1.5% comparing with the original model. The volumetric efficiency of the tested pump without the clearance is 96.5% at 5000 rpm rotational speed and 8 MPa load pressure.

Dynamic Analysis of a Single-Rotor Wind Turbine with Counter-Rotating Electric Generator under Variable Wind Speed

This paper presents a theoretical study of the dynamic behaviour of a wind turbine consisting of a wind rotor, a speed increaser with fixed axes, and a counter-rotating electric generator, operating in variable wind conditions. In the first part, the dynamic analytical model of the wind turbine mechanical system is elaborated based on the dynamic equations associated with the component rigid bodies and the linear mechanical characteristics associated with the direct current (DC) generator and wind rotor. The paper proposes a method for identifying the coefficients of the wind rotor mechanical characteristics depending on the wind speed. The numerical simulations performed in Simulink-MATLAB by MathWorks on a case study of a 10 kW wind turbine highlight the variation with the time of the kinematic parameters (angular speeds and accelerations), torques and powers for wind system shafts, as well as the mechanical efficiency, both in transient and steady-state regimes, considering variable wind speed. The analytical and numerical results are helpful for researchers, designers, developers, and practitioners of wind turbines aiming to optimise their construction and functionality through virtual prototyping.