Search Results (72)

Cardiopulmonary exercise testing (CPET) is recommended as part of routine care in people with congenital heart disease. A significant difference has been observed in many CPET parameters, depending on the ergometer and exercise protocol used. The aim of this study is to investigate such differences in Fontan patients. All Fontan patients (<40 years old, NYHA class I/I–II) underwent two consecutive CPETs on different ergometers (treadmill with ramped Bruce protocol versus cycle ergometer with ramp protocol) within less than 12 months. The exclusion criterion was the presence of significant clinical/anthropometric changes between the two tests. Anthropometric, surgical, clinical, electrocardiogram (ECG) and CPET data were collected. 47 subjects were enrolled (25 males, mean age 16.4 at first test). Peak heart rate (HR) tended to be higher on the treadmill (p = 0.05 as % of predicted, p = 0.062 in absolute value). Peak oxygen consumption (VO₂) (mL/min, mL/kg/min, and % of predicted) was significantly higher on the treadmill (p < 0.01), as well the VO₂ at the ventilatory anaerobic threshold (VAT) and the peak oxygen pulse. A different kinetics of the oxygen pulse wave was observed in the same patient comparing the two testing modalities. Maximal respiratory-exchange-ratio values (>1.1) were reached more frequently on the cycle ergometer (p < 0.001). The minute ventilation–carbon dioxide output slope (VE/VCO₂ slope) was not different between the two tests (p = 0.400). Many parameters of CPET may differ depending on the ergometer used. These should be considered in clinical evaluation of Fontan patients and when exercise is to be prescribed. Full article

Background: In exercise testing, the ventilatory threshold 1 (VT1) and ventilatory threshold 2 (VT2) are used in lifestyle-related diseases, cardiac rehabilitation, and athletic training. We investigated a VT2 measuring method using a pulse oximeter. Methods: Thirty-four adults (men: 15; women: 19) performed a bicycle ergometer Ramp Test. VT1 values were determined using expiratory gas data. The bifurcation of the curve obtained by designating the pulse rate (PR) as an independent variable and SpO₂/PR as a dependent variable was calculated using the residual sum of squares and defined as the SpO₂ threshold (ST) (SpO₂-Slope method). A second bifurcation with ST as the origin was further defined (ST2). ST2 validity was assessed by comparing and analyzing the differences and correlations with each VT2 obtained by expiratory gas analysis. Results: The correlation between ST2 determined by the SpO₂-Slope method using PR as an index and VT2 obtained from respiratory gas analysis was significant, showing a positive correlation (r = 0.74~0.92; p < 0.01), with most data points falling within the 1.96 ± SD in the Bland–Altman analysis. Conclusions: ST2 values derived from SpO₂ and pulse rate measurements by pulse oximeter may be a valuable VT2 measuring method. Full article

This study is aimed at evaluating the combined influence of running conditions that affect frost morphology and defrost strategies on the thermal-fluid-dynamic performance of tube-fin ‘no-frost’ evaporators. To this end, two purpose-built experimental apparatuses were designed and constructed, one based upon a fully instrumented two-door bottom-mount ‘combi’ refrigerator with independent temperature and humidity control in both compartments, and another devised specifically for testing evaporator–heater assemblies under controlled frosting and defrosting cycles. Frost accumulation was studied for different surface temperatures and air humidity levels, revealing that higher humidity and lower surface temperatures led to lower frost density and thermal conductivity. Defrosting operations were analyzed for two different psychrometric conditions using three control strategies: step, ramp and pulse-width modulation (PWM). The ramp strategy yielded the highest defrost efficiency, reaching 36.7% in milder frost conditions, while the step strategy led to lower defrosting times. Such findings support the optimization of evaporator design and defrost strategies to improve energy efficiency in household refrigerating appliances. Full article

Background: Anderson–Fabry disease (AFD) is a progressive lysosomal storage disorder characterized by systemic glycosphingolipid accumulation. While cardiac imaging plays a central role in disease monitoring, the relationship between structural myocardial changes and exercise capacity remains incompletely defined. This study aimed to evaluate functional impairment in AFD patients using cardiopulmonary exercise testing (CPET) and to determine whether limitations are primarily cardiac or extracardiac in origin. Methods: Thirty-one patients with genetically confirmed AFD were retrospectively enrolled from two tertiary centers. All underwent baseline clinical assessment, resting transthoracic echocardiography (TTE), spirometry, and symptom-limited CPET using a cycle ergometer and a 10 W/min ramp protocol. Echocardiographic parameters included the LVEF, global longitudinal strain (GLS), E/e′ ratio, TAPSE, and PASP. CPET measurements included the peak VO₂, anaerobic threshold (AT), VE/VCO₂ slope, oxygen pulse (VO₂/HR), and VO₂/watt ratio. Results: The mean age was 48.4 ± 17.6 years, with most patients classified as NYHA I. LVEF was preserved (62.3 ± 8.6%), and diastolic indices were within normal limits (E/e′ 7.1 ± 2.4), but GLS was impaired (11.3 ± 10.5%). CPET showed reduced peak VO₂ (18.6 ± 6.1 mL/kg/min; 71.4% predicted) and early AT (40.8%), with preserved ventilatory efficiency and oxygen pulse. VO₂/watt was mildly reduced, suggesting peripheral limitations despite intact central hemodynamics. Conclusions: Functional impairment is common in AFD patients, even with mild cardiac involvement. CPET reveals early systemic limitations not captured by standard imaging, supporting its role in phenotypic characterization and therapeutic decision-making. Full article

Background: ESC sports classification in 2020, based on cardiac morphological adaptations, may not fully reflect also the variations in functional parameters of athletes. This study aims to characterize CPET-derived physiological parameters in elite athletes according to the ESC classification and evaluate whether this morphological classification also corresponds to a functional categorization. Methods: Elite athletes underwent pre-participation screening before the 2023 European Games and 2024 Olympic Games. Athletes were classified into four categories (skill, power, mixed and endurance). CPET was performed on a cycle ergometer using a ramp protocol, with measurements of VO₂ max, heart rate, power output and ventilatory efficiency. Results: We enrolled 1033 athletes (46.8% females; mean 25.6 ± 5.2 years old) engaged in skill (14.1%), power (33.2%), mixed (33.3%) and endurance (19.4%) disciplines. O₂ pulse showed an incremental significant increase (p < 0.0001) among sport categories (skill 14.9 ± 3.8 mL/beat; power 17.5 ± 4.6 mL/beat, mixed 19 ± 4.3 mL/beat and endurance 22.7 ± 5.8 mL/beat). The lowest ${\dot{\mathrm{V}}\mathrm{O}}_2$max was observed in skill disciplines (36.3 ± 7.9 mL/min/kg) whilst endurance ones showed the highest values (52.4 ± 9.7 mL/min/kg) (p < 0.0001). ${\dot{\mathrm{V}}\mathrm{O}}_2$max was higher in power compared to mixed (42 ± 7.7 mL/min/kg vs. 40.5 ± 5.8 mL/min/kg, p = 0.005) disciplines with an overlapping amount between some mixed and power disciplines. No differences were found for VE max (p = 0.075). Conclusions: Our study provided values of CPET parameters in elite athletes. Significant differences in CPET parameters were observed among different sports disciplines, with endurance athletes showing the highest absolute and relative values in all parameters. An overlap amount was noted between mixed and power categories, especially for relative maximal oxygen consumption. Full article

Ultrafast laser processing is a critical technology for micro- and nano-fabrication due to its ability to minimize heat-affected zones. The effects of intensity variation on the ultrafast laser ablation of fused silica were investigated to gain fundamental insights into the dynamic modulation of pulse intensity. This study revealed significant enhancement in ablation efficiency for downward ramp intensity modulation compared to the upward ramp. This effect was independent of the repetition rate ranging from 100 Hz to 1 MHz, which suggested that it originates from persistent residual effects of preceding pulses. Photoluminescence experiments indicated that the observed effect is primarily attributed to the dynamic reduction in the ablation threshold caused by the formation of defects such as non-bridging oxygen hole centers. The correlation between the sequence of intensity-modulated pulses and defect formation has been clarified. The knowledge of these correlations, combined with machine learning-based optimization methods, is useful for the optimization of the throughput and quality of ultrafast laser processing. Full article

The core subunits of the K_V7.2, K_V7.3, and K_V7.5 channels, encoded by the KCNQ2, KCNQ3, and KCNQ5 genes, are expressed across various cell types and play a key role in generating the M-type K⁺ current (I_K(M)). This current is characterized by an activation threshold at low voltages and displays slow activation and deactivation kinetics. Variations in the amplitude and gating kinetics of I_K(M) can significantly influence membrane excitability. Notably, I_K(M) demonstrates distinct voltage-dependent hysteresis when subjected to prolonged isosceles-triangular ramp pulses. In this review, we explore various small-molecule modulators that can either inhibit or enhance the amplitude of I_K(M), along with their perturbations on its gating kinetics and voltage-dependent hysteresis. The inhibitors of I_K(M) highlighted here include bisoprolol, brivaracetam, cannabidiol, nalbuphine, phenobarbital, and remdesivir. Conversely, compounds such as flupirtine, kynurenic acid, naringenin, QO-58, and solifenacin have been shown to enhance I_K(M). These modulators show potential as pharmacological or therapeutic strategies for treating certain disorders linked to gain-of-function or loss-of-function mutations in M-type K⁺ (K_V7x or KCNQx) channels. Full article

This paper introduces a voltage-mode DC-DC buck converter designed to address the challenges of high-frequency operation. The proposed comparator-less Reactive Ramp Generator (RRG) topology mitigates the issues associated with comparator delays, achieving a fast load transient response. By eliminating all comparators from the buck converter’s control circuit, we prevent potential delay-induced malfunctions, thereby enhancing overall operational reliability. The rapid response of the RRG, enabled by a short feedback loop, allows for swift output voltage regulation during load transients. Replacing comparators in the PWM controller with inverters effectively removes delay issues without adding complexity. Since the proposed design retains the conventional voltage-mode transfer function, standard type-3 compensation is readily applicable. Operating with a 3.3 V input, the buck converter provides an output range from 0.65 V to 3.0 V, achieving a settling time of 0.802 µs for load changes from 200 mA to 1 A, and 1.27 µs for load changes from 1 A to 200 mA. The proposed architecture achieves a peak efficiency of 92.78% at 2.4 V and 600 mA. Full article

Corneal biomechanical properties are closely related to the cornea’s physiological and pathological conditions, primarily determined by the stromal layer. However, little is known about the influence of corneal cell interaction on the viscoelasticity of the stromal extracellular matrix (ECM). In this study, collagen-based hydrogels incorporated with keratocytes were reconstructed as corneal stromal models. Air-pulse optical coherence elastography (OCE) was used to characterize the viscoelastic properties of the corneal models. Plate compression, ramp–hold relaxation testing was performed on the initial corneal models. The findings demonstrated that the elastic modulus increased 5.27, 2.65 and 1.42 kPa, and viscosity increased 0.22, 0.06 and 0.09 Pa·s in the stromal models with initial collagen concentrations of 3, 5, and 7 mg/mL over 7 days. The elastic modulus and viscosity exhibited high correlation coefficients between air-pulse OCE and ramp–hold relaxation testing, with 92.25% and 98.67%, respectively. This study enhances the understanding of the influence of cell–matrix interactions on the corneal viscoelastic properties and validates air-pulse OCE as an accurate method for the mechanical characterization of tissue-engineered materials. Full article

Nickel (Ni) single-layer coatings were electrodeposited under varying pulse periods (T), duty cycles (θ), and average current densities (i_av) using four distinct pulse current waveforms: rectangular (Rec), triangular (Tri), ramp-up triangular (Rup), and ramp-down triangular (Rdn). This study demonstrated, through dynamic polarization curves and surface morphology analysis, that single-layer coatings showed relatively good corrosion resistance when deposited at shorter pulse periods, larger duty cycles, and higher average current densities. Moreover, compared with other pulse current waveforms, single-layer coatings electrodeposited at T = 10 ms, θ = 0.5, and i_av = 10 mA/cm², 20 mA/cm², and 40 mA/cm² with Rdn had similar dynamic polarization curves and relatively good corrosion resistance. Consequently, two pulse current combinations, the descending gradient and convex gradient, were introduced for electrodepositing Ni multilayer coatings. Analysis revealed that the corrosion resistance of coatings deposited with the convex gradient current was further enhanced. Full article

The inherent instability of laser welding, particularly keyhole instability, poses significant challenges in industrial applications, leading to defects such as porosities that compromise weld quality. Various forces act on the keyhole and molten pool during laser welding, influencing process stability. These forces are categorized into those promoting keyhole opening and penetration (e.g., recoil pressure) and those promoting keyhole collapse (e.g., surface tension, Darcy’s damping forces), increasing instability and defect likelihood. This paper provides a comprehensive instability analysis to uncover key factors affecting keyhole and process instability, presenting future avenues for improving laser welding stability. Using a novel numerical method for simulating laser spot welding on aluminum with COMSOL Multiphysics 5.6, we investigated the effect of laser pulse shaping on keyhole and process instability. Our analysis focused on keyhole morphology, fluid flow behaviour, and force analysis. The results indicated that the curvature effect, Marangoni effect, and Darcy’s damping force are primary contributors to instability, with the curvature effect and Darcy’s damping force being the most dominant. Additionally, erratic and high-velocity magnitudes induce intense fluid flow behaviour, exacerbating keyhole instability. Moreover, single/quadruple peak triangular and variant rectangular ramp-down pulse shapes produced the least instability, while multi-pulse rectangular shapes exhibited intense instability. It was found that combining triangular/rectangular pulse shapes can reduce force and keyhole instability by smoothing spontaneous force spikes, resulting in a more stabilized welding process. Controlling fluid flow and abrupt force changes with appropriate pulse shaping is key to defect-free welded products. Full article

In this study, sulfamethoxazole (SMX) was applied as the model pollutant to assess the performance of pulsed current (PC) waveforms in the decontamination efficiency of the PC/peroxymonosulfate (PMS)/Fe(III) process and to investigate underlying oxidation mechanisms. Among the various waveforms tested, the sinusoidal wave (SIN), combined with the Dimensionally Stable Anode (DSA) electrode, demonstrated superior degradation performance, with the order being SIN > ramp > square > direct current (DC). The operational conditions for the SIN/PMS/Fe(III) system were optimized to an initial pH of 3, a voltage of 6 V, 0.6 mmol/L of Fe³⁺, 1.0 mmol/L of PMS, and a frequency of 1 kHz. The results of quenching and probe experiments confirmed the generation of abundant reactive radicals such as ^•OH, SO₄^•−, O₂^•−, Fe(IV), and ¹O₂ in the SIN/PMS/Fe(III) process, which collectively enhanced the degradation of SMX. Additionally, results of high-resolution mass spectrometry analysis were employed to identify the SMX oxidation byproducts, and the toxicity of SMX byproducts was evaluated. Overall, the SIN/PMS/Fe(III) process exhibits effective degradation capacity with high energy efficiency, establishing itself as an effective strategy for the practical treatment of medical wastewater. Full article

Background/Objectives: The aim of this study was to investigate the feasibility and safety of neuromuscular electrical stimulation (NMES) in patients on extracorporeal membrane oxygenation (ECMO) and thoroughly assess any potential adverse events. Methods: We conducted a prospective observational study assessing safety and feasibility, including 16 ICU patients on ECMO support who were admitted to the cardiac surgery ICU from January 2022 to December 2023. The majority of patients were females (63%) on veno-arterial (VA)-ECMO (81%), while the main cause was cardiogenic shock (81%) compared to respiratory failure. Patients underwent a 45 min NMES session while on ECMO support that included a warm-up phase of 5 min, a main phase of 35 min, and a recovery phase of 5 min. NMES was implemented on vastus lateralis, vastus medialis, gastrocnemius, and peroneus longus muscles of both lower extremities. Two stimulators delivered biphasic, symmetric impulses of 75 Hz, with a 400 μsec pulse duration, 5 sec on (1.6 sec ramp up and 0.8 sec ramp down) and 21 sec off. The intensity levels aimed to cause visible contractions and be well tolerated. Primary outcomes of this study were feasibility and safety, evaluated by whether NMES sessions were successfully achieved, and by any adverse events and complications. Secondary outcomes included indices of rhabdomyolysis from biochemical blood tests 24 h after the application of NMES. Results: All patients successfully completed their NMES session, with no adverse events or complications. The majority of patients achieved type 4 and 5 qualities of muscle contraction. Conclusions: NMES is a safe and feasible exercise methodology for patients supported with ECMO. Full article

This paper proposes the development of an active control system to control the power output of a low-power horizontal-axis wind turbine (HAWT) when operating at wind speeds above the rated wind speed. The system is composed of an active articulated vane (AAV) in charge of the orientation of the wind turbine, which is driven by an electric actuator that changes the angle of the AAV to maintain a constant power output. Compared with the passive power regulation systems most often used in low-power HAWTs, active systems allow for better control and, therefore, greater stability of the delivered power, which reduces the structural stresses and allows for controlled braking in any wind condition or during system failures. The control system was designed and simulated using MATLAB R2022b software, and then built and evaluated under laboratory conditions. For the control design, the transfer function (TF) between the pulse width modulation (PWM) and the AAV angle ($\theta$) was determined via laboratory tests using MATLAB’s PIDTurner tool. For the simulation, the relationship between the power output and the AAV angle was determined using the vector decomposition of the wind speed and wind rotor area. Wind speed step and ramp response tests were performed for proportional–integral–derivative (PID) control. The results obtained demonstrate the technical feasibility of this type of control, obtaining settling times (ts) of 6.7 s in the step response and 2.8 s in the ramp response. Full article

Background: Despite a successful repair of tetralogy of Fallot (rToF) in childhood, residual lesions are common and can contribute to impaired exercise capacity. Although both cycle ergometer and treadmill protocols are often used interchangeably these approaches have not been directly compared. In this study we examined cardiopulmonary exercise test (CPET) measurements in rToF. Methods: Inclusion criteria were clinically stable rToF patients able to perform a cardiac magnetic resonance imaging (CMR) and two CPET studies, one on the treadmill (incremental Bruce protocol) and one on the cycle ergometer (ramped protocol), within 12 months. Demographic, surgical and clinical data; functional class; QRS duration; CMR measures; CPET data and international physical activity questionnaire (IPAQ) scores of patients were collected. Results: Fifty-seven patients were enrolled (53% male, 20.5 ± 7.8 years at CPET). CMR measurements included a right ventricle (RV) end-diastolic volume index of 119 ± 22 mL/m², a RV ejection fraction (EF) of 55 ± 6% and a left ventricular (LV) EF of 56 ± 5%. Peak oxygen consumption (VO₂)/Kg (25.5 ± 5.5 vs. 31.7 ± 6.9; p < 0.0001), VO₂ at anaerobic threshold (AT) (15.3 ± 3.9 vs. 22.0 ± 4.5; p < 0.0001), peak O₂ pulse (10.6 ± 3.0 vs. 12.1± 3.4; p = 0.0061) and oxygen uptake efficiency slope (OUES) (1932.2 ± 623.6 vs. 2292.0 ± 639.4; p < 0.001) were significantly lower on the cycle ergometer compared with the treadmill, differently from ventilatory efficiency (VE/VCO₂) max which was significantly higher on the cycle ergometer (32.2 ± 4.5 vs. 30.4 ± 5.4; p < 0.001). Only the VE/VCO₂ slope at the respiratory compensation point (RCP) was similar between the two methodologies (p = 0.150). Conclusions: The majority of CPET measurements differed according to the modality of testing, with the exception being the VE/VCO₂ slope at RCP. Our data suggest that CPET parameters should be interpreted according to test type; however, these findings should be validated in larger populations and in a variety of institutions. Full article