Wearable Baxter-Novacor mechanical ventricular assistance

Progressive technological developments have permitted clinical use of the wearable Baxter-Novacor left ventricular assist system. The system allows total bypass of the left ventricular function, and recovery of and adequate circulation in patients in cardiogenic shock. Since the first clinical use, in March 1993, eight patients about to die have been supported with a cardiac transplantation. This experience suggests that an an acceptable answer to the problem of organ shortage is now available.     

Right ventricular failure in patients requiring left ventricular assistance

Right ventricular failure may complicate isolated left ventricular assistance. In a series of 8 patients undergoing left ventricular assistance in postcardiotomy cardiogenic shock, right ventricular failure developed in 5, directly contributing to death in all cases despite initially satisfactory support. Difficulty in grafting a dominant right coronary artery was a common factor in all cases. Early consideration should be given to biventricular support under these circumstances.     

Orthodontic wire: a continuing evolution

Previous studies have shown that large doses of vitamin A potentiate chemical-induced liver injury and that the Kupffer cell is directly involved in this potentiation. Therefore, these studies were designed to determine if Kupffer cells isolated from vitamin A treated male Sprague-Dawley rats (75 mg/kg/day for 3-7 days as all- trans-retinol) had altered activity and function. Respiratory activity of Kupffer cells isolated from rats treated with vitamin A for 3 to 7 days markedly increased. Similarly, phagocytic activity was significantly elevated (up to 9-fold) after exposure to vitamin A for 3 to 7 days. Production of reactive oxygen species, measured by luminol-enhanced chemiluminescence of Kupffer cells isolated after 7 days of vitamin A exposure, was significantly higher than that of control cells when stimulated with opsonized zymosan. Also, the release of superoxide anion by individual Kupffer cells isolated from vitamin A treated rats was nearly three times greater than that of control cells. Basal production of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2) production were significantly elevated in Kupffer cells isolated from rats treated with vitamin A. Lastly, peripheral blood monocytes (PBMC) isolated from rats treated with vitamin A for 7 days had a significantly greater respiratory activity, as well as TNF-alpha and PGE2 production, than PBMC isolated from control rats. Our data suggest that large doses of vitamin A enhance both Kupffer cell and PBMC function. Upregulation of the activity by these phagocytic cells may play a role in the vitamin A potentiation of chemical-induced liver injury.     

Influence of inhaled nitric oxide on systemic flow and ventricular filling pressure in patients receiving mechanical circulatory assistance

BACKGROUND: In patients with left ventricular (LV) dysfunction, inhaled nitric oxide (NO) decreases pulmonary vascular resistance (PVR) but causes a potentially clinically significant increase in left atrial pressure (LAP). This has led to the suggestion that inhaled NO may reach the coronary circulation and have a negative inotropic effect. This study tested an alternative hypothesis that LAP increases because of volume shifts to the pulmonary venous compartment caused by NO-induced selective pulmonary vasodilation. METHODS AND RESULTS: The Thermo Cardiosystems Heartmate is an LV assist device (LVAD) that can be set (by controlling pump rate) to deliver fixed or variable systemic blood flow. Eight patients (between 1 and 11 days after LVAD implantation) were administered inhaled NO (20 and 40 ppm for 10 minutes), and LAP, systemic flow, and pulmonary arterial pressure were measured in both fixed and variable pump flow modes. In both modes, inhaled NO lowered PVR (by 25 +/- 6% in the fixed mode, P < .001, and by 21 +/- 5% in the variable mode, P < .003). With fixed pump flow, LAP rose from 12.5 +/- 1.2 to 15.1 +/- 1.4 mm Hg (P < .008). In the variable flow mode, LAP did not increase and the assist device output rose from 5.3 +/- 0.3 to 5.7 +/- 0.3 L/min (P < .008). CONCLUSIONS: A selective reduction in PVR by inhaled NO can increase LAP if systemic flow cannot increase. These data support the hypothesis that with LV failure, inhaled NO increases LAP by increasing pulmonary venous volume and demonstrate that inhaled NO has beneficial hemodynamic effects in LVAD patients.     

Mechanical assistance of the pulmonary circulation after right ventricular exclusion

The Fontan procedure is often associated with elevated right-sided pressures and low cardiac output during the early postoperative period. A dog model was established to test the effect of pulmonary artery counterpulsation after atriopulmonary anastomosis. After exclusion of the right ventricle by a purse-string suture at the right AV orifice, placed during inflow occlusion, a valved conduit was inserted between the right atrial appendage and the pulmonary artery. This created a circulatory pattern comparable to a Fontan procedure. Counterpulsation was achieved by inserting a cannula into the conduit distal to the valve in eight dogs; alternatively, in four, counterpulsation could be achieved through a 10 mm side-arm graft connected to the conduit distal to the valve. Twenty-four observations were made. Without counterpulsation the circulatory status of the dog deteriorated rapidly. Counterpulsation resulted in a mean increase in cardiac output of 48% (p less than 0.0001). Right atrial pressure fell significantly with a mean drop of 4 mm Hg (p less than 0.003). This allowed for a further increase in right-sided filling pressure by transfusion, with a subsequent further increase in cardiac output. Left atrial pressure did not change significantly unless altered by transfusion. Counterpulsation instituted through the 10 mm side-arm graft gave similar results. Pulmonary vascular resistance decreased with counterpulsation (mean decrease 35%; p less than 0.002). The use of a side-arm graft connected to the conduit after a Fontan procedure affords a clinical method of circulatory support without the need for additional surgical intervention for decannulation. These data suggest that mechanical assistance of the failing right atrium after atriopulmonary anastomosis is both feasible and effective.     

The evolution of solutions: A thermodynamic analysis of mechanical alloying

Normal thermodynamic theory for solutions begins with the mixing of component atoms. Many solutions are, however, prepared by mixing together lumps of the components, each of which might contain millions of identical atoms. We examine here the way in which a solution evolves from these large clusters of components, from a purely thermodynamic point of view. There are some interesting results, including the prediction that solution formation by the mechanical alloying of solid components cannot occur unless there is a gain in coherency as the particles become small. The nature of the barrier to mechanical alloying is discovered. There is also the possibility of a metastable state prior to the achievement of full solution, when the component atoms prefer like-neighbors.     

Atrial cannulation for left ventricular assistance: superiority of the dome approach

Successful left ventricular support is dependent on adequate inflow drainage. We describe atrial cannulation using the dome of the left atrium, which in our experience has resulted in excellent inflow drainage.     

Modeling of particle size evolution during mechanical milling

The process of mechanical alloying (MA) involves the repeated deformation, welding, and fracture of powder materials during grinding in high-energy mills. During MA, the size and size distribution of the particles change as a result of the particles’ different fracture and welding rates. The evolution of particle volume distributions during such a combined “fission-fusion” process can be describedvia a differential-integral equation. While analytical solutions are known for systems in which only fusion takes place, there is apparently no such solution for the fission-fusion problem. In this article, we describe a discretized form of the fission-fusion equation and apply it to modeling of particle size distributions during milling of elemental powders using previously determined fracture and welding rates appropriate to the global system of particles. Predicted particle size distributions mimic well those determined experimentally. Formerly Graduate Student, Department of Formerly Graduate Student, Department of Formerly Graduate Student, Department of Formerly Professor, Department of Materials Formerly Professor, Department of Materials     

Microstructural evolution and mechanical properties of Cr-Ru alloys

In an effort to enhance ductility and strength of Cr-base alloys, a series of Cr-Ru alloys with Ru contents ranging from 3 to 30 at. pct were made to study their microstructure evolution and mechanical properties. The microstructure of the alloys with 6 to 20 at. pct Ru showed signs of a eutectic structure. However, no corresponding eutectic reaction is indicated in the published Cr-Ru phase diagram. The yield strength of the Cr-Ru alloys increased with increasing Ru content at both room temperature and 1200 °C. The tensile ductility of Cr-3 at. pct Ru is about 1.5 pct at room temperature, while the alloys containing 6 at. pct or more Ru showed zero tensile elongation. The deformation mechanisms of the Cr-Ru alloys are discussed in terms of the microstructure and fracture behavior. This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

The concept of "direct mechanical ventricular assistance" in the treatment of left-ventricular failure. Part 2. Results of the new intrathoracic implantable multi-chamber pump system (IMPS) in an animal study

An assist device was developed which is able to support the pumping function of the heart by direct application of pressure to the left ventricle. The goal of this animal study in pigs was to determine whether it is possible to maintain sufficient blood circulation with the aid of the new system when the heart is fibrillating or its capacity has been greatly reduced. Following sternotomy complete invasive monitoring was installed. The intrathoracic implantable mechanical multi-chamber pump system (IMPS) was placed around the left ventricle. By means of the beta-blocker carazolol, systolic left-ventricular pressure (LVPsys), cardiac output, heart rate, and left-ventricular dp/dtmax (LVdp/dtmax) were gradually lowered and the pump system was tested intermittently. Then the heart was fibrillated and the system was tested again. When cardiac output, LVdp/dtmax, and systolic blood pressure were reduced by approximately 50% IMPS was able to increase LVPsys by 83% (IMPS) on: 96 +/- 9 mmHg vs. IMPS off: 63 +/- 6 mmHg), and the blood pressure in the carotid artery by 86% (IMPS on: 95/40 +/-15 mmHg vs. IMPS off: 69/38 +/- 9 mmHg). The mean cardiac output was 64% (IMPS on: 4.3 L/min vs. IMPS off: 3.9L/min); in most cases a great variability could be observed depending on the preload, the heart rate, and the mode of pressure application. When the heart was fibrillating, IMPS was able to maintain adequate circulatory conditions with LVPsys = 88%, blood pressure in the carotid artery = 85%, and LVdp/dtmax = 57% of the control values measured before fibrillation and beta-blockade. The system presented here is able to support the impaired left ventricle and to replace its pumping function. The advantages of the system are its efficiency and the lack of contact of the circulating blood with foreign surfaces. Whether the system is suited for bridging and recovery support shall be clarified in further studies.     

Prolonged total circulatory support using direct mechanical ventricular actuation

Direct mechanical ventricular actuation (DMVA) is a unique, non blood contacting method for biventricular cardiac assist. Although DMVA has successfully provided cardiac assist for more than 7 days in humans, with long-term survival, its potential for long-term circulatory support has not been adequately investigated. DMVA has not been studied in the large ruminants commonly used to evaluate support devices. To develop a large animal experimental model of prolonged total circulatory support using DMVA, Suffolk sheep (n = 10) underwent sterile instrumentation for hemodynamic and chemistry monitoring. After baseline values were obtained, a left lateral thoracotomy and pericardotomy were performed. Upon electrical ventricular fibrillation (VF), DMVA was begun and the thoracotomy closed. Total circulatory support was continued until mean arterial pressure (MAP) persisted below 50% of the baseline value for more than 1 hr, with a goal of 7 days' support. Mean duration (plus or minus the standard deviation [SD]) of circulatory support was 65.9 +/- 56.8 hr (range, 10-168 hr). Pressors were not used during DMVA support. The subject supported for the maximal time (7 days) was defibrillated into sinus rhythm. No CK-MB fraction was greater than 1%, suggesting that DMVA, even with prolonged application during VF, does not result in myocardial injury. Blood urea nitrogen and creatinine levels indicate renal function was preserved. The model described represents the longest period any animal has been supported in VF using DMVA. This new model will be useful in determining what limitations, if any, exist to the prolonged use of DMVA for circulatory support.     

The continuing challenge of cardiac transplant arteriosclerosis

Coronary arteriosclerosis of the graft, a manifestation of CAV, continues to limit the long-term success of cardiac transplantation. It is characterized by vascular injury induced by a variety of noxious stimuli, including the humoral and cellular immune system response to the allograft, ischemia-reperfusion injury, viral infection, immunosuppressive drugs, and classical risk factors. The proliferative and obstructive vascular lesions are thought to develop through repetitive endothelial injury followed by repair response. T lymphocytes, macrophages and neutrophils migrate to the subendothelial area via the activity of endothelial adhesion molecules, and, in turn, produce various cytokines and growth factors which cause progression of the process. Development of anti-endothelial antibodies may progress CAV in specific settings. Intravascular ultrasound studies reveal a dual morphology with donor-transmitted or de novo focal, noncircumferential plaques in proximal segments and/or a diffuse, concentric pattern of intimal proliferation observed in distal segments. In addition to the morphological alterations, functional endothelial and smooth muscle cell alterations may occur independently and transiently. The use of cyclosporine A levels > 3 mg/kg/day, HMG-CoA-reductase inhibitors and calcium antagonists has been shown to decrease the progression of CAV. Strategies for blocking T-cell costimulation and expression of adhesion molecules, cytokines and antiendothelial antibodies, as well as, antiproliferative drugs, methods to augment endogenous nitric oxide bioavailability and newer immunosuppressive regimens may be protective to endothelial injury and subsequent development of CAV. Revascularization procedures have an established, but very limited role in the setting of significant focal lesions. The ethical dilemma surrounding retransplantation, however, is considerable because of the scarcity of donor hearts.     

The continuing mischaracterization of radical behaviorism.

Contrary to R. W. Sperry's (see record 1989-00022-001) characterization, radical behaviorism (RB) is not reductive or atomistic. RB's central concept of the response class in antiatomistic, and its emphasis on the experimental analysis of behavior is not reductive. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phase transformation,structural evolution and mechanical property of nanostructured FeAl as a result of mechanical alloying

Objective of the work was to synthesize nanostructured FeAl alloy powder by mechanical alloying (MEA). The work concentrated on synthesis, characterization, structural and mechanical properties of the alloy. Nanostructured FeAl intermetallics were prepared directly by MEA in a high energy rate ball mill. Milling was performed under toluene solution to avoid contamination from the milling media and atmosphere. Mixtures of elemental Fe and Al were progressively transformed into a partially disordered solid solution with an average composition of Fe—50 at % Al. Phase transformation, structural changes, morphology, particle size measurement and chemical composition during MEA were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS) respectively. Vickers micro hardness (VMH) indentation tests were performed on the powders. XRD and SEM studies revealed the alloying of elemental powders as well as transition to nanostructured alloy, crystallite size of 18 nm was obtained after 28 hours of milling. Expansion/contraction in lattice parameter accompanied by reduction in crystallite size occurs during transition to nanostructured alloy. Longer milling duration introduces ordering in the alloyed powders as proved by the presence of superlattice reflection. Elemental and alloyed phase coexist while hardness increased during MEA.     

Effect of exercise on left ventricular mechanical efficiency in conscious dogs

BACKGROUND: We studied the effect of exercise (7.2 to 8.0 km/h) on the efficiency of the conversion of metabolic energy to external work or stroke work (SW) by the left ventricle (LV). METHODS AND RESULTS: Energy use was calculated from LV myocardial oxygen consumption per beat (MVO2). LV volume was calculated from orthogonal dimensions and coronary flow measured with ultrasonic flow probes. The total mechanical energy of the LV was calculated as the pressure-volume area (PVA). At rest, the MVO2-PVA point fell on the MVO2-PVA relation determined by steady-state changes in arterial pressure produced by graded infusions of phenylephrine. Exercise increased the slope (Ees) of LV end-systolic pressure-volume (PV) relation by 29%. During exercise, the MVO2-PVA point shifted to the right only slightly above the control MVO2-PVA relation by 0.007 +/- 0.005 mL O2.beat-1.100 g LV-1. Despite the increase in ventricular contractility with exercise, the PVA/MVO2 ratio was unchanged because of the marked increase in PVA. During exercise, the transmission of total mechanical energy to external work (SW/PVA) increased from 65 +/- 5% to 72 +/- 4% (P < .01) as the ratio of the arterial end-systolic elastance to Ees decreased from 1.1 +/- 0.2 to 0.8 +/- 0.1 (P < .05). Thus, LV mechanical efficiency (SW/MVO2 = SW/PVA.PVA/MVO2) improved from 12.9 +/- 1.5% to 14.3 +/- 1.1% (P < .05) during exercise. CONCLUSIONS: Exercise increases the efficiency of conversion of metabolic energy to external work by the LV due to alteration in LV arterial coupling resulting in increased production of mechanical energy and enhanced transmission of mechanical energy to external work, which more than offsets any increased metabolic cost of the enhanced contractility.     

The continuing ethical dilemma of the do-not-resuscitate order

The continued use of the do-not-resuscitate (DNR) order remains very confusing to health care workers, especially when surgical intervention is undertaken either by choice or necessity. Although ethics committees can aid in clarification, and the use of advance directives can further define patient wishes, patient and family member education is necessary to ascertain what a surgical patient really desires. As technology advances, perioperative nurses will continue to be bombarded with ethical issues surrounding the DNR order. This article addresses how nurses can be proactive in obtaining answers to these difficult questions and learn how to deal with this dilemma.