Maximum Rate Of Pressure Increase Research Articles

The Detrimental Effect of Pre-Treatment with Ivermectin on Myocardial Ischemia

Introduction: Ivermectin (IVM) is a broad-spectrum anti-parasitic agent with potential antibacterial, antiviral, and anti-cancer effects. There are limited studies on the effects of IVM on cardiovascular diseases, so the present study sought to determine the effects of pre-treatment with IVM on myocardial ischemia in both ex vivo and in vivo. Methods: In the ex vivo part, two groups of control and treated rats with IVM (0.2 mg/kg) were examined for cardiac function and arrhythmias by isolated heart perfusion. In the in vivo part, four groups, namely, control, IVM, Iso (MI), and Iso + IVM 0.2 mg/kg were used. Subcutaneous injection of isoproterenol (100 mg/kg/day) for 2 consecutive days was used for the induction of myocardial infarction (MI) in male Wistar rats. Then electrocardiogram, hemodynamic factors, cardiac hypertrophy, and malondialdehyde (MDA) levels were investigated. Results: The ex vivo results showed that administration of IVM induces cardiac arrhythmia and decreases the left ventricular maximal rate of pressure increase (contractility) and maximal rate of pressure decline (relaxation). The isoproterenol-induced MI model used as an in vivo model showed that cardiac hypertrophy were increased with no improvement in the hemodynamic and electrocardiogram pattern in the IVM-treated group in comparison to MI (Iso) group. However, the MDA level was lower in the IVM-treated group. Conclusion: IVM pre-treatment demonstrates detrimental effects in cardiac ischemia through exacerbation of cardiac arrhythmia, myocardial dysfunction, and increased cardiac hypertrophy. Therefore, the use of IVM in ischemic heart patients should be done with great caution.

On the dynamics of drifting flame front in a confined chamber with airflow disorder in a methane-air mixture

When the flame wave passes through obstacles or facilities in confined spaces, it causes airflow disorder. As the flame wave is immersed in the flow field, it can no longer sustain an ideal spherical shape but presents a constantly developing asymmetric flame wave in the flow. Although the mechanisms governing the ideal explosion process have been explored, not much is known about the complicated mechanism of drifting flame front caused by airflow disorder. The perturbation of axial jet gas is used to simulate the airflow disorder effect, and the reflected flame wave in the final stage of explosion under jet gas is reported. The results show that with the elapsing of time since ignition, the propagation behavior of drifting flame front can be identified by three categories: left-direction-propagation-flame (LPF), right-direction-propagation-flame (RPF) and right-direction-reflected-flame (RRF). The maximum rate of pressure increase is 49.26 MPa/s, compared to 20.45 MPa/s for the case without airflow disorder (φ = 1.08 and the initial pressure is 100 kPa). It is speculated that the LPF leases heat into the mixture, increasing the mixing and mass transmission between the reactant and product and promoting the explosion hazard. In addition, after its head-on collision with the chamber inner wall, the RRF is formed, and its heated flame front greatly accelerates the heat and mass transfer process. The flame speed under quiescent conditions is 3.14 m/s. Under the effect of airflow disorder, the flame speed constantly accelerates to 7.4 m/s, which benefits from the enhanced mixing effect of the jet. Under the inertia effect of flow, the speed of the LPF varies from −10 m/s to −22 m/s, and the RRF fluctuates from 6.47 m/s to 16.08 m/s, both of which are much faster than that with no airflow disorder. Our findings fill the gap in the mechanism of drifting flame front caused by airflow disorder from experimental verification, and the results may provide a new understanding of methane explosion under more realistic conditions.

Criteria of thermochemical conditions of steam gas explosions in dynamic accident modes at nuclear power units with WWER reactors

The main lessons of the major accident at the Fukushima-Daiichi NPP in 2011 for the nuclear power industry identify the need to model, analyze and develop emergency measures for relatively unlikely events with catastrophic environmental consequences, taking into account multiple failures of safety systems. Steam-gas explosions became one of the main causes of the catastrophic environmental consequences of the Chernobyl and Fukushima accidents. Criteria and conditions for the occurrence of steam-gas explosions in dynamic emergency modes in the "tight" reactor circuit of nuclear power reactor units (NPP) with water-water reactors (WWER) with failures of safety systems valves and emergency steam gas removal are determined by the rate of change of thermodynamic and physico-chemical parameters. A method for determining the criteria and conditions for the occurrence of steam-gas explosions in dynamic accident modes with a "tight" reactor circuit and failure of safety valves for modeling the initial emergency events – seismic effects, falling of massive objects, etc. is presented. The conditions for the occurrence of hydrogen explosions are determined by the maximum rate of increase in the temperature of fuel oil shells, and the conditions for steam explosions are determined by the maximum rate of pressure increase as a result of the intensification of vaporization processes. The criteria for the occurrence of steam explosions in dynamic emergency modes are determined by the maximum pressure amplitude and the propagation speed of acoustic disturbances in the steam volume. And the criteria for hydrogen detonation in dynamic emergency modes are determined by the maximum amplitude of the increase in the temperature of the fuel shells and the average flow rate of the coolant in the active zone of the reactor.

Revealing Impact Characteristics of the Cassava Dust Explosion Process: Experimental and Numerical Research

The combustion and explosion characteristics of cassava starch and the dispersive physical motion law of dust were systematically studied using a 20 L (=0.02 m3) spherical explosive test device and the numerical simulation method. The experimental results show that the explosion pressure first increases and then decreases with increasing ignition delay time, dust concentration, and spray pressure in the dust storage tank. The maximum explosion pressure was obtained with a dust concentration of 750 g/m3, while the maximum rate of pressure increase was obtained when the concentration was 250 g/m3. The calculated maximum explosion index was 22.3 MPa∙m∙s−1. The simulation results show that the physical movement law of the dust was as follows: high initial velocity → gradual decrease in diffusion velocity → upward linear movement of dust → outward diffusion motion → continuous disorder motion → free settlement → gradual reduction and disorder state → finally, complete settlement. With a powder diffusion time of 120 ms, the dust distribution in the round sphere was the most uniform, which was consistent with the experimental results. After dust ignition, the temperature first gradually increased and then decreased due to heat dissipation. The maximum pressure in the vessel was 46.7 MPa, and the turbulence was the most intense close to the ignition point.

Effect of hydrogen on explosion characteristics of liquefied petroleum gas-air mixtures

The effects of hydrogen addition on the explosion characteristics of liquefied petroleum gas (LPG)-air mixtures were experimentally investigated under initial conditions of 1 atm and 298 K. Furthermore, with reference to the detailed USC-Mech II mechanism, sensitivity and the rate of production (ROP) analyses were conducted. When the hydrogen proportion is constant, the maximum explosion pressure and the maximum rate of pressure rise first increase and then decrease, reaching peaks at an equivalence ratio of 1.3. The experimentally measured maximum explosion pressure is lower than the numerically calculated adiabatic pressure. The calculated adiabatic pressure decreases slightly with an increase in the hydrogen proportion. However, under the experimental conditions, owing to the high reactivity of hydrogen, the LPG-H2-air mixtures experience a small heat loss in the early stage of the explosion, and the maximum explosion pressure and maximum rate of pressure increase considerably, with the arrival time of the pressure peak is advanced. The addition of hydrogen promotes the sensitivity coefficient of reactants C3H8 and C4H10 and increases the maximum ROP of free radicals H, O, and OH. Meanwhile, the addition of hydrogen significantly influences the maximum ROP of the elementary reaction R2.

Effect of nitromethane on fuel/air explosion characteristics under different ambient conditions

The impact of nitromethane on the explosion characteristics of diethyl ether -aluminium powder mixed fuel in the presence of different ambient factors is studied in a 20 L sphere-shaped explosion vessel. The explosion pressure of the fuel is obtained by a series of experiments, and the mechanism of nitromethane during these experiments is deduced by analysing the maximum rate of pressure increase and the gas products. The results showed that a synergistic effect existed between nitromethane and diethyl ether at high mass concentrations. The self-decomposition reaction of nitromethane enables high mass concentration fuels to react more fully, maintaining a higher explosion pressure under a low-pressure or high-relative humidity environment.

Cardioprotective effects of memantine in myocardial ischemia: Ex vivo and in vivo studies

Myocardial infarction (MI) refers to the loss of cardiomyocytes due to inadequate coronary blood flow and subsequently a reduced oxygen supply. Activation of N-methyl-D-aspartate (NMDA) receptors has been linked to myocardial infarction. The aim of the present study was to determine the cardioprotective effects of memantine, in myocardial infarction both in ex vivo and in vivo models. Effects of memantine on the electrocardiogram (ECG) pattern, cardiodynamic parameters, infarct size and lipid peroxidation were evaluated in the isolated perfused rat heart. Moreover, in in vivo studies in rats, the protective effects of memantine on isoproterenol-induced myocardial infarction model (administration of 100 mg/kg isoproterenol subcutaneously for 2 consecutive days) was evaluated by measuring ECG pattern, mean arterial pressure, malondialdehyde (MDA) levels, myeloperoxidase (MPO) activity, cardiac tumor necrosis factor-alpha (TNF-α) level and cardiac remodeling. The results from the ex vivo isolated perfused heart showed that memantine treatment increased heart rate, left ventricular systolic pressure and left ventricular maximal rate of pressure increase, and decreased cardiac arrhythmia, MDA level and infarct size in comparison to ischemia/reperfusion (IR) group. The isoproterenol-induced MI (Iso) as used in the in vivo model demonstrated that MDA levels and MPO activity were decreased in memantine groups. Memantine treatment reduced the expression of cardiac TNF-α in comparison to Iso group. Cardiac fibrosis and hypertrophy were lower in memantine groups. In conclusion, memantine exerts cardioprotective effects in models of myocardial infarction, which may be attributed to reduction of pro-inflammatory and oxidative stress factors and subsequently a decrease in cardiac remodeling.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Adverse Drug-Induced Inotropic Effects in Early Drug Development. Part 1: General Considerations for Development of Novel Testing Platforms.

Drug-induced effects on cardiac contractility can be assessed through the measurement of the maximal rate of pressure increase in the left ventricle (LVdP/dtmax) in conscious animals, and such studies are often conducted at the late stage of preclinical drug development. Detection of such effects earlier in drug research using simpler, in vitro test systems would be a valuable addition to our strategies for identifying the best possible drug development candidates. Thus, testing platforms with reasonably high throughput, and affordable costs would be helpful for early screening purposes. There may also be utility for testing platforms that provide mechanistic information about how a given drug affects cardiac contractility. Finally, there could be in vitro testing platforms that could ultimately contribute to the regulatory safety package of a new drug. The characteristics needed for a successful cell or tissue-based testing platform for cardiac contractility will be dictated by its intended use. In this article, general considerations are presented with the intent of guiding the development of new testing platforms that will find utility in drug research and development. In the following article (part 2), specific aspects of using human-induced stem cell-derived cardiomyocytes for this purpose are addressed.

ВЛИЯНИЕ ПРОТЕЧЕК РАБОЧЕГО ТЕЛА НА КООРДИНАТУ ТОЧКИ МАКСИМАЛЬНОГО РОСТА ДАВЛЕНИЯ СЖАТИЯ

The article discusses the analysis of the parameters of the compression process, which is carried out according to the results of engine indication. The solution to this problem allows us to evaluate the technical condition of the cylinder-piston group parts. According to the requirements of most classification societies, the deviation of the compression pressure on this cylinder from the engine average should not exceed 2.5%. The dependence of the compression pressure value on the pressure of the supercharger makes it difficult to obtain correct diagnostic conclusions about the condition of the cylinder-piston group when the technical condition of the gas turbine compressor deteriorates. The existing publications investigated the position on the indicator diagram of the point at which the rate of increase in compression pressure reaches its maximum, and its position was demonstrated to be almost invariant with respect to pressure. This fact makes it possible to calculate its position relative to the top dead center of the engine even before the start of indexing and to accept the calculated value as a first approximation in the algorithmic synchronization of the display results. However, the leakage of the working medium, inevitably present in the engine, was not considered. Therefore, the problem of the displacement of the coordinate point of the maximum rate of pressure increase in the presence of leaks is legitimate. The task is solved applying a mathematical model consisting of three equations (condition, mass conservation and the first law of thermodynamics), written in a differential form and integrate at each calculated step. As an argument, the selected angle of rotation of the crankshaft of the engine. Nevertheless, to solve such systems of equations analytically considering the leaks in the full formulation is extremely difficult. Therefore the effective flow area of the piston rings was given in modeling the workflow is considered to be constant throughout the calculations. The modeling results determine the position of the point of maximum pressure rise rate on the indicator diagram, which can be used as an indirect indicator in the integral analysis of the engine technical condition

Explosion characteristics of hydrogen-air mixtures diluted with inert gases at sub-atmospheric pressures

An experimental investigation on the explosion characteristics of hydrogen-air mixtures diluted with inert gases (Ar, N2, CO2) was carried out in a cylinder chamber at room temperature (298 K) sub-atmospheric pressures (40 kPa, 60 kPa, 80 kPa, 100 kPa). Based on the pressure history recording, some explosion parameters, e.g., maximum explosion pressure (Pmax), maximum rate of pressure rise ((dp/dt)max), deflagration index (KG) and combustion duration (θ) were derived. Effects of initial pressure (P0), equivalence ratio (φ) and dilution fraction (Z%) on these explosion indices were discussed. The results show that with the increase of initial pressure, the maximum explosion pressure, maximum rate of pressure increase and deflagration index increase monotonously while the combustion duration decrease. The diluent effect on these parameters is increased in the order of Ar, N2 and CO2. Linear correlations Pmax/P0=f(Z), Pmax=f(P0) and (dp/dt)max=f(P0) were found. In addition, the heat loss to the walls during the explosion propagation was estimated on the basis of the difference between the adiabatic and experimental measured pressure. The energy loss increases with the increase of initial pressure and specific heat of the dilutions.

Titanium dioxide nanoparticle-induced dysfunction of cardiac hemodynamics is involved in cardiac inflammation in mice.

In the past two decades, titanium dioxide nanoparticles (TiO2 NPs) have been extensively used in medicine, food industry and other daily life, while their possible interactions with the their influence and human body on human health remain not well understood. Thus, the study was designed to examine whether long-term exposure to TiO2 NPs cause myocardial dysfunction which is involved in cardiac lesions and alter expression of genes and proteins involving inflammatory response in the mouse heart. The findings showed that intragastric feeding for nine consecutive months with TiO2 NPs resulted in titanium accumulation, infiltration of inflammatory cells and apoptosis of heart, reductions in net increases of body weight, cardiac indices of function (LV systolic pressure, maximal rate of pressure increase over time, maximal rate of pressure decrease over time and coronary flow), and increases in heart indices, cardiac indices of function (LV end-diastolic pressure and heart rate) in mice. TiO2 NPs also decreased ATP production in the hearts. Furthermore, TiO2 NPs increased expression of nuclear factor-κB, interleukin-lβ and tumour necrosis factor-α, and reduced expression of anti-inflammatory cytokines including suppressor of cytokine signaling (SOCS) 1 and SOCS3 in the cardiac tissue. These results suggest that TiO2 NPs may modulate the cardiac function and expression of inflammatory cytokines. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2917-2927, 2016.

Influence of turbulent flow on the explosion parameters of micro- and nano-aluminum powder–air mixtures

The environmental turbulence intensity has a significant influence on the explosion parameters of both micro- and nano-Al at the time of ignition. However, explosion research on turbulence intensity with respect to micro- and nano-Al powders is still insufficient. In this work, micro- and nano-aluminum powders were investigated via scanning electron microscopy (SEM), and their particle size distributions were measured using a laser diffraction analyzer under dispersing air pressures of 0.4, 0.6, and 0.8MPa in a 20L cylindrical, strong plexiglass vessel. The particle size distributions in three different mass ratio mixtures of micro- and nano-Al powders (micro-Al:nano-Al[massratio]=95:5, 90:10, and 85:15) were also measured. The results show that the agglomerate size of nano-Al powder is an order of magnitude larger than the nanoparticles’ actual size. Furthermore, the turbulence intensity ranges (Urms) of the Al powder-air mixtures were measured using particle image velocimetry (PIV) under dispersing air pressures of 0.4, 0.6, and 0.8MPa. The effect of turbulence intensity on the explosion characteristics of the micro- and nano-Al powders was investigated using a 20L cylindrical explosion vessel. The results of micro-Al and nano-Al powder-air mixtures with a stoichiometric concentration of 337.00g·m−3 were discussed for the maximum explosion pressure, the maximum rate of pressure increase and the maximum effective burning velocity under the different turbulence intensity.

The influence of central arterial compliance on cerebrovascular hemodynamics: insights from endurance training intervention.

Normally, central elastic arteries (e.g., aorta and common carotid artery) effectively buffer cardiac pulsation-induced flow/pressure fluctuations. With advancing age, arterial stiffening deteriorates this function and produces the greater cerebral hemodynamic pulsatility that impacts vulnerable brain tissue. It is well known that the buffering function of the central artery is improved by regular aerobic exercise, but the influence of endurance training on the pulsatile component of cerebral hemodynamics remains poorly understood. To characterize the functional role of the central artery at the heart-brain hemodynamic connection comprehensively, we assessed relations among the endurance training-induced changes in the left ventricle (LV), carotid arterial compliance, and cerebral hemodynamics. Thirteen collegiate tennis players (20 ± 1 yr) underwent a 16-wk endurance training intervention designed for improving cardiovascular function. Expectedly, maximal oxygen uptake (V̇o2peak), LV ejection velocity (via Doppler ultrasound), and the maximal rate of pressure increase of estimated aortic pressure waveform (via general transfer function) improved after the training intervention, whereas middle cerebral arterial (MCA) hemodynamics (via transcranial Doppler), such as mean and pulsatile flow velocities, remained unchanged. Carotid arterial compliance (via ultrasound and applanation tonometry) increased after the training intervention, and a larger increase in carotid arterial compliance was significantly associated with the greater attenuations of pulsatile MCA velocity (r = -0.621) normalized by mean MCA velocity. These results suggest that the training-induced improvement of carotid artery Windkessel function might offset the expected increase in the pulsatile component of cerebral perfusion induced by the enhanced LV systolic function.

Effect of pilot injection on engine noise in a single cylinder compression ignition engine

An experimental study was performed to investigate the effect of pilot injection on engine noise using a single cylinder combustion ignition engine. The engine rotary speed was fixed at 1200 RPM and a 10-mg quantity was injected at a pilot injection ratio of 1:9, 2:8, or 3:7. The engine performance parameters were calculated from the combustion pressure data acquired by a piezoelectric transducer (6057A80, Kistler), which was placed in the location of the glow plug. Engine noise was measured at a distance and height of 1 meter each from the engine for 9-10 seconds and analyzed using a commercial sound analysis program. By analyzing in-cylinder pressure and sound quality metrics, the following conclusions were obtained. The frequency analysis showed that the combustion noise was distributed at the frequency bands from 1100 Hz to 1900 Hz and from 2100 Hz to 2900 Hz. Pilot injections lowered the maximum rate of pressure increase, and the trend of the maximum pressure rise rate varied significantly according to injection pressure. The maximum pressure rise rate exhibited a linear relationship with sound level and loudness. Thus, the pilot injection strategy appeared to improve engine noise characteristics.

P 22: Omega-3 polyunsaturated fatty acids alleviates heart pump function in Type I diabetic cardiomyopathy

The term ““diabetic cardiomyopathy””, which was first proposed by Rubler in 1972 describes myocardial dysfunction in the absence of coronary heart disease, hypertension or heart valve defects. However, from 70s of previous century is known about the omega-3 polyunsaturated fatty acids (PUFAs), which are potent cardioprotectors. Despite the success of diabetology, the mechanisms of omega-3 PUFAs influence on the heart function in diabetes mellitus remains unresolved. In this study we aimed to evaluate the effects of omega-3 PUFAs on cardiac performance in rats with experimental diabetes. Experiments were fulfilled on male Wistar rats, weighing 140–270 g, who were divided into 3 groups: 1 - control, 2 - rats with streptozotocin-induced diabetes (50 mg/kg), 3 - rats with streptozotocin-induced diabetes, which received 45% of omega-3 PUFAscontaining drug Epadol during 4 weeks. Rats were anesthetized with Urethane, fixed and right carotid artery was preparated. Ultraminiature catheter 2F («Millar Instruments», USA) was injected through the right carotid artery retrograde into the left ventricle. The fatty acids composition in heart homogenates was determined by gas chromatography. We demonstrate that omega-3 fatty acid treatment of diabetic rats modifies fatty acid composition of heart by increasing omega-3 PUFAs content. Additionally, supplemented omega-3 fatty acids significantly prevent body and heart weight loss and reduce blood glucose level, induced by streptozotocin. Our data indicates the impairment of the heart pump function in animals with diabetes. We established that cardiac output declined to 36,78% (P<0,05), ejection fraction to 29,12% (P<0,05), stroke volume to 35,65% (P<0,05), stroke work to 70,13% (P<0,05). Omega-3 PUFAs under similar conditions restores pump function - increases ejection fraction at 35,37% (P<0.05), stroke volume at 40,76% (P<0,05), stroke work at 68,02% (P<0,05) and cardiac output at 15,32%. In 2 group of rats diastolic dysfunction was found - the time constants of active relaxation Tau (Weiss) reduced to 50,63% (P<0,05) and Tau (Glantz) to 59,77%, the minimum rate of myocardial relaxation dP/dtmin slightly increased. Effect omega-3 PUFAs on diastolic function is characterized by the increase of Tau (Weiss) to 64,39% (P<0,05) and Tau (Glantz) to 11,32% (P<0,05) and a slight decrease value of dP/dtmin. Omega-3 PUFAs had almost no impact on the maximum rate of pressure increase in dP/dt max under diabetes. These novel data indicate that modification of fatty acid composition of cardiac membranes by omega-3 fatty acids prevents the pump, diastolic function alterations induced by streptozotocin. It is assumed that omega-3 PUFAs treatment will lead to a decreased risk of cardiovascular complications in diabetes. These results indicate the prospects of further studies to use omega-3 PUFAs in the treatment of diabetes.

Interaction between hydrogen sulfide and nitric oxide on cardiac protection in rats with metabolic syndrome.

To investigate the interaction between hydrogen sulfide (H2S)/cystathionine gamma-lyase (CSE) system and nitric oxide (NO)/nitric oxide synthase (NOS) system on cardiac protection in metabolic syndrome (MS) rats. Forty one male Sprague-Dawley rats were randomly divided into 6 groups: control group, MS group, H2S donor group, CSE inhibitor group, NOS inhibitor group, and NO donor group. The MS rat model was established by a high-fat diet of 16 weeks. Rats in control and MS groups were subjected to normal saline and the other four groups were respectively subjected to sodium hydrosulfide (NaHS, 56 μmol/kg), D,L-propargylglycine (PPG, 37.5 mg/kg), Nψ-nitro-L-arginine methyl ester (L-NAME, 18 mg/kg), L-Arginine (500 mg/kg) every day. Four weeks later, the obesity indices, blood sugar of oral glucose tolerance test in each time point (0,30,60, and 120 minutes) and blood lipids (cholesterol, triglyceride, high density lipoprotein, low density lipoprotein) were measured. The computer-based electrophysiological recorder system was used to measure the changes of the left ventricular systolic pressure (LVSP), the left ventricular end diastolic pressure (LVEDP), the maximal rate of pressure increase in the contraction phase (+dP/dtmax), and the maximal rate of pressure decrease in the diastole phase (-dP/dtmax). H2S and NO concentration in plasma and myocardium, as well as CSE, constitutive NOS (cNOS), and inducible NOS (iNOS) activities in myocardium were measured with colorimetric method. Reverse transcription-polymerase chain reaction was used to assess the gene expression of CSE and endothelial NOS (eNOS) mRNAs. Compared with control group, the obesity indices, blood sugar at each time point, and blood lipids significantly increased in MS group (P<0.05). H2S and NO concentration in plasma and myocardium, CSE and cNOS activities in myocardium, the expressions of CSE mRNA and eNOS mRNA, and the myocardial function significantly decreased in MS group (P<0.05). Compared with MS group, NO concentration in plasma and myocardium, cNOS and iNOS activities in myocardium, and the expression of eNOS mRNA significantly increased in CSE inhibitor group (P<0.05). However, activities of cNOS and iNOS in myocardium and the expression of eNOS mRNA were significantly decreased in H2S donor group (P<0.01), while the myocardial function significantly increased (P<0.05). H2S concentration in plasma and myocardium, and the expression of CSE mRNA significantly increased in NOS inhibitor group (P<0.05). However, in NO donor group, the CSE activity in myocardium and the expression of CSE mRNA significantly decreased (P<0.05). And the myocardial function was improved significantly (P<0.05). Both the H2S/CSE and NO/NOS systems appear to have a mutual down-regulation effect on myocardium in MS rats. Meanwhile, exogenous H2S and NO supplement is cardioprotective in rat model of MS.

Inotropic, Vasodilating and Preconditioning Actions of Levosimendan in the Heart

Levosimendan improves ventricular function, induces vasodilation and induces myocardial preconditioning. We determined the external efficiency and assessed the effects on arrhythmias. In isolated, blood-perfused rabbit hearts, levosimendan (0.75 micromol) or placebo was administered, while hemodynamics were recorded. After no-flow ischemia and reperfusion, data were recorded again. Placebo in normoxic hearts did not affect measurements, while levosimendan increased heart rate (+ 18 %) and improved coronary output (+ 52 %), stroke volume (+ 28 %), maximal left ventricular pressure (+ 30 %), maximal rate of pressure increase (+ 36 %), work (+ 68 %), minimal rate of pressure increase (+ 53 %), coronary blood flow (+ 41 %), coronary resistance (- 19 %) and external efficiency (33 %; P < 0.05). During reperfusion, hemodynamics in the levosimendan group were significantly better preserved compared with the placebo group. Early reperfusion arrhythmias were decreased (levosimendan group: 7 +/- 3 % vs. placebo group: 25 +/- 17 %; P < 0.05). Levosimendan does not impair diastole, dilates coronary vessels, induces pharmacological preconditioning, improves external efficiency and exerts antiarrhythmic properties during reperfusion. As this drug protects the heart from reperfusion injury, it seems well suited for treating dysfunctional hearts after cardiac surgery.

Effects of Sustained Length-Dependent Activation on In Situ Cross-Bridge Dynamics in Rat Hearts

The cellular basis of the length-dependent increases in contractile force in the beating heart has remained unclear. Our aim was to investigate whether length-dependent mediated increases in contractile force are correlated with myosin head proximity to actin filaments, and presumably the number of cross-bridges activated during a contraction. We therefore employed x-ray diffraction analyses of beat-to-beat contractions in spontaneously beating rat hearts under open-chest conditions simultaneous with recordings of left ventricle (LV) pressure-volume. Regional x-ray diffraction patterns were recorded from the anterior LV free wall under steady-state contractions and during acute volume loading (intravenous lactate Ringers infusion at 60 ml/h, <5 min duration) to determine the change in intensity ratio ( I 1,0/ I 1,1) and myosin interfilament spacing ( d 1,0). We found no significant change in end-diastolic (ED) intensity ratio, indicating that the proportion of myosin heads in proximity to actin was unchanged by fiber stretching. Intensity ratio decreased significantly more during the isovolumetric contraction phase during volume loading than under baseline contractions. A significant systolic increase in myosin head proximity to actin filaments correlated with the maximum rate of pressure increase. Hence, a reduction in interfilament spacing at end-diastole (∼0.5 nm) during stretch increased the proportion of cross-bridges activated. Furthermore, our recordings suggest that d 1,0 expansion was inversely related to LV volume but was restricted during contraction and sarcomere shortening to values smaller than the maximum during isovolumetric relaxation. Since ventricular volume, and presumably sarcomere length, was found to be directly related to interfilament spacing, these findings support a role for interfilament spacing in modulating cross-bridge formation and force developed before shortening.

Implantation of an Elastic Ring at Equator of the Left Ventricle Influences Cardiac Mechanics in Experimental Acute Ventricular Dysfunction

We hypothesize that the implantation of an endoventricular elastic ring at the left ventricle (LV) equatorial site will positively affect the cardiac mechanics in an experimental model of acute LV dysfunction. Changes in the elastic properties of LV occur in the dilated and failing heart, contributing to overall cardiac mechanical dysfunction. No interventions are as yet specifically designed to improve LV elasticity in failing hearts. Acute LV enlargement and dysfunction was induced in 13 healthy sheep via the insertion of a large Dacron patch into the lateral wall. In 6 of these sheep, a customized elastic ring was implanted at the inner surface of the LV equator (ring group), and the remaining 7 served as control subjects (dysfunction group). Systolic and diastolic function was evaluated using echocardiography and pressure-volume (P-V) analysis. In the ring group, both the maximum rate of pressure increase and the slope of end-systolic P-V relationship were significantly different from those without ring (1,718 +/- 726 vs. 1,049 +/- 269 and 1.25 +/- 0.30 vs. 0.88 +/- 0.19; both p < 0.05). Preload recruitable stroke work changed even more prominently (33 +/- 11 vs. 17 +/- 5; p = 0.005), along with stroke volume, ejection fraction, and stroke work. Although ring implantation had no effect on end-diastolic P-V relationship, it positively affected the active component of diastole: the maximum rate of pressure decrease declined significantly (p = 0.037). The time constant of relaxation tended to decrease (37 +/- 8 vs. 44 +/- 6; p = 0.088). Improving the elastic component of the LV at its equatorial site substantially augments contractility and early relaxation in acute systodiastolic LV dysfunction.

Effects of halothane, sevoflurane and desflurane on the force-frequency relation in the dog heart in vivo.

Frequency potentiation is the increase in force of contraction induced by an increased heart rate (HR). This positive staircase phenomenon has been attributed to changes in Ca2+ entry and loading of intracellular Ca2+ stores. Volatile anesthetics interfere with Ca2+ homeostasis of cardiomyocytes. We hypothesized that frequency potentiation is altered by volatile anesthetics and investigated the influence of halothane (H), sevoflurane (S) and desflurane (D) on the positive staircase phenomenon in dogsin vivo. Dogs were chronically instrumented for measurement of left ventricular (LV) pressure and cardiac output. Heart rate was increased by atrial pacing from 120 to 220 beats·min-1 and the LV maximal rate of pressure increase (dP/ dtmax) was determined as an index of myocardial performance. Measurements were performed in conscious dogs and during anesthesia with 1.0 minimal alveolar concentrations of each of the three inhaled anesthetics. Increasing HR from 120 to 220 beats·min-1 increased dP/dtmax from 3394 ± 786 (mean ± SD) to 3798 ± 810 mmHg sec-1 in conscious dogs. All anesthetics reduced dP/dtmax during baseline (at 120 beatss·min-1: H, 1745 ± 340 mmHgs·sec-1; S, 1882 ± 418; D, 1928 ± 454, allP < 0.05vs awake) but did not influence the frequency potentiation of dP/dtmax (at 220 beatss·min-1: H, 1981 ± 587 mmHgs·sec-1; S, 2187 ± 787; D, 2307 ± 691). The slope of the regression line correlating dP/dtmax and HR was not different between awake and anesetized dogs. Increasing HR did not influence cardiac output in awake or anesthetized dogs. These results indicate that volatile anesthetics do not alter the force-frequency relation in dogs in vivo.