Partial vs. full support of the heart with a continuous-flow left ventricular assist device : implications for myocardial recovery.

INTRODUCTION: Heart failure is a major and growing public health concern. Although heart failure has been considered an inexorable and progressive disorder, emerging evidence suggests that some patients may have reversible left ventricular dysfunction. Indeed, recent reports have documented the potential for myocardial recovery in humans in response to prolonged mechanical circulatory support with a left ventricular assist device (LVAD). However, myocardial recovery remains uncommon, and a strategy of unloading the failing left ventricle with a continuous-flow (non-pulsatile) LVAD has not been specifically developed to promote favorable myocardial remodeling. As a preliminary investigation, we developed a bovine model of chronic, ischemic heart failure and quantified the effects of different levels of support with a continuous-flow LVAD on myocardial mechanoenergetics. METHODS: Normal cows (n=8) and cows with chronic, ischemic heart failure (n=9) were studied. To induce heart failure, 90 µm micro spheres were percutaneously injected into the left main coronary artery. Heart failure developed over 60 days. In an acute surgery, a continuous-flow LVAD was implanted and operated at Low Partial Support (~1.5 L/min support, aortic valve opening every beat), High Partial Support (~3 L/min support, aortic valve opening every beat) and Full Support (~5 L/min, aortic valve maintained closed, left ventricle maximally unloaded). Cardiac and systemic arterial hemodynamics were measured with flow probes and pressure catheters. Myocardial blood flow was mapped with 15 µm fluorescent-labeled microspheres. After termination, molecular and histological markers of heart failure were quantified. RESUL TS: In normal animals, increasing levels of non-pulsatile support deranged the profile of cardiac and arterial hemodynamics. As cardiac workload decreased, myocardial vascular resistance increased, and myocardial blood flow decreased. The ratio between blood supply and demand did not change and indicated appropriate coronary autoregulation and the presence of an intact coronary reserve. Animals with chronic, ischemic heart failure exhibited hallmark signs of severe left ventricular systolic dysfunction that included a 50% reduction in ejection fraction, left ventricular dilatation, decreased cardiac output and arterial pressures, decreased end-organ blood flow, severe myocardial fibrosis, myocyte hypertrophy, and increased myocardial apoptosis. In animals with chronic heart failure, increasing levels of non-pulsatile support similarly deranged the profile of cardiac and arterial hemodynamics. As cardiac workload decreased, myocardial vascular resistance increased. However myocardial blood flow did not change and indicated a lack of a coronary reserve. Importantly, during full but not partial support, the ratio between blood supply and demand improved significantly to levels observed in normal control animals. CONCLUSIONS: After the implantation of an LVAD, full but not partial support of the failing left ventricle with an LVAD normalizes the myocardial blood supply/demand relationship. In the immediate postoperative period, the left ventricle should be completely unloaded. Chronic studies are necessary to determine whether a transition to partial support may prevent myocardial atrophy and fibrosis that is seen with prolonged full support. Our bovine model of chronic, ischemic heart failure is appropriate for such a study

HEAT TRANSFER ENHANCEMENT FROM A WIRE TO AN IMPINGING UPWARD SUBMERGED SLOT JET OF WATER IN SUBCOOLED AND SATURATED BOILING CONDITIONS

Experimental data about the heat transfer from a heated 0.25 mm in diameter nickel wire to a submerged upward flow slot jet of distilled water are reported. The tests are carried on in forced convection regime, in sub-cooled and saturated boiling conditions. The influence on the heat transfer rate of different parameters is investigated, such as the jet exit velocity, the distance between the slot exit and the wire and the heat transfer regime, in particular the sub-cooling degree. The choice of the nickel is due to the opportunity to operate in a wide range of the jet exit velocity, thanks to its mechanical and thermometric characteristics. The main aim of this research was to find out the optimal conditions, in order to maximize the heat transfer coefficient enhancement, and moreover, to make a comparison between other results obtained in the 1990s by the same authors on horizontal circular cylinders, with the diameter one size order bigger than the present wire

Free convection coefficient enhancement between inclined wall and air in presence of expired jets

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.This paper aims to determine the heat transfer enhancement in natural convection between a downward-facing inclined wall, heated by Joule effect, and air in the presence of small air pulsating expired jets, in conditions of medium temperature difference between wall and air, namely 40K. Experimental measurements have been taken both with and without pulsating expired jets. The wall is kept in condition of uniform temperature. The expired jets blow out perpendicularly from the wall surface. An infrared thermo-camera was used to check the wall temperature uniformity. Hot-wire anemometer and visualization with smoke were used to find information on the air velocity field. The wall inclination angle which maximizes the convective heat exchange near the leading edge has been investigated too.vk201

Heat transfer enhancement between vertical wall and air in presence of expired or aspired jets : comparison between free and mixed convection conditions

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This keynote lecture aims to determine the heat transfer enhancement in natural and in mixed convection between a vertical wall, heated by Joule effect, and air in the presence of small air pulsating aspirated and expired jets, in conditions of medium and large temperature differences between wall and air, namely from 25 to 70K. Experimental measurements have been taken both with and without pulsating and continuous expired and aspirated jets. The expired jets blow out perpendicularly from the wall surface. A thermo camera was used to ensure the wall temperature uniformity. A hot wire anemometer and visualization with smoke were used to found information about the air velocity field. The parameters which maximize the convective heat exchange have been computed. The present research represents a first step of a basic study to optimize the turbine behavior cooled by pulsating jets.cs201

Biochar based silicon composites for sensors applications

Nowadays, the development of innovative sensors represents a field of great interest in the scientific community because of their ever increasing application in everyday life. Piezoresistive transducers are among the most interesting not only as sensors but also as actuators. They are of interest for a number of applicative fields ranging from pressure sensors to applications in nanomanipulation. Please click Additional Files below to see the full abstract

Experimental utilization of interferometric radar techniques for structural monitoring

SUMMARY This paper presents a new surveying technique that can be employed with hardly reachable structures or extensive structures. The technique is based on an interferometric radar device, which can be positioned up to 2 km away from the structure to be examined and can record displacement measurements with a sampling frequency of up to 100 Hz and an accuracy of 0.1 mm. The results given by the radar are compared with those given by a set of three accelerometers on a test structure (namely, a steel cable-stayed footbridge) for three different loads: a symmetric dynamic load, an eccentric dynamic load and a symmetric quasi-static load. Copyright # 2008 John Wiley & Sons, Ltd

Influence of Commercial Biochar Fillers on Brittleness/Ductility of Epoxy Resin Composites

Production of versatile composites is a very attractive field. Carbon containing epoxy resins are one of the most relevant reinforced plastics used for a wide number of applications. In this research, we studied the influence of five different commercial biochar samples for the selective enhancement of brittleness and ductility of an epoxy based composite. We proved the relationship between biochar morphology and composites mechanical properties with the aid of FT-IR and FE-SEM analysis. We were able to improve the neat resin mechanical properties by doubling its Young’s modulus and ultimate tensile strength using a wheat straw derived material, and to increase its elongation by 40%, we used a Miscanthus derived biochar

Efficacy and safety of two different tolvaptan doses in the treatment of hyponatremia in the Emergency Department

Hyponatremia (plasma sodium concentration or P[Na(+)] <136 mEq/L) is the most common electrolyte unbalance in clinical practice. Although it constitutes a negative prognostic factor, it frequently remains underdiagnosed and undertreated. Tolvaptan is an oral V2-receptor antagonist which produces aquaresis. Given its emerging role in the treatment of dilutional hyponatremia, we aimed to compare the efficacy and safety of two different doses of this drug in an Emergency Department (ED) setting. Consecutive patients with moderate-severe euvolemic or hypervolemic hyponatremia were sequentially assigned to the 15 mg Group and to the 7.5 mg Group, and were revaluated at 6, 12 and 24 h. Further evaluations and administrations were scheduled daily until P[Na(+)] correction was achieved or the maximum period of 72 h was exceeded. A 1-month follow-up was performed. Twenty-three patients were enrolled: 12 were included in the 15 mg Group, 11 in the 7.5 mg Group. Both doses significantly elevated the P[Na(+)] over 24 h, although the 15 mg Group showed faster corrections than the 7.5 mg Group (12 vs 6 mEq/L/24 h; P = 0.025). An optimal correction rate (within 4-8 mEq/L/24 h) was observed in 45.4 % of the 7.5 mg Group against 25.0 % (P n.s.). The standard dose led to dangerous overcorrections (>12 mEq/L/24 h) in 41.7 % of the patients, while the low dose did not cause any (P = 0.037). No osmotic demyelination syndrome was observed. A 7.5 mg tolvaptan dose can be considered both effective and safe in treating hyponatremia in the ED, while a 15 mg dose implicates too high risk of overcorrection

Synergistic and Interdisciplinary Approaches for the Conservation of Monumental Heritage: Cupola of Santa Maria del Fiore in Florence, Italy

This paper presents the results of an interdisciplinary study carried out on Brunelleschi’s Cupola of Santa Maria del Fiore in Florence, Italy, one of the most emblematic masonry domes in the world. The cupola has been affected since the beginning of its construction by a widespread cracking phenomenon, and several studies were done over the centuries to clarify its safety conditions. To have a direct and indirect record of the cracks opening or closing, a complex monitoring system was installed on the monument during the last century. An accurate analysis of crack widths and global displacements, performed considering both historical and recent monitoring data, has allowed for the identification of the movements developed in the monument, evaluating their relationship with environmental and seismic events. In line with the interdisciplinary approach strongly recommended in the field of assessment and conservation of monumental heritage, this paper reconsiders some issues concerning the causes of the actual damage to the cupola. In particular, in light of the obtained results, the famous seventeenth century Viviani’s conclusions about the cupola’s damage, confirmed by Chiarugi in the 1980s, are compared with other hypotheses, such as the differential settlement of pillars (Cecchini in 1698 and Ximenes in 1757) and the influence of temperature variations (Nervi in 1934). The large amount of measured data and the results of the last numerical models of the cupola, combined with recent dynamic measurements, allowed the updating of some previous conclusions on damage causes and trends. Starting from these conclusions, a more reliable forecasting model of the monument can be set up that could be useful in identifying effective conservation strategy for this outstanding monument