Cardiac Pacemakers Essays (2606 words) - Cardiac Arrhythmia

Cardiac Pacemakers The heart is bestowed with a specialized system that automatically generates rhythmic control via the sinus node, located in the superior lateral wall of the right atrium near the opening of the superior vena cava. The specialized pacemaker cells dictate control of the rest of the heart through regular electrical impulses that propagate from the right atria to the lower ventricles. The rapid conduction of these impulses cause the muscle cells of the atria to contract and squeeze blood into the ventricles, which contract and force blood into the aorta and pulmonary arteries. Abnormalities of the heart rhythm, called arrhythmias, can disrupt this normal cardiac control making it necessary to use some artificial means to regulate the rhythm of the heart. Today, some half a million men and women, most of them over the age of sixty, carry implanted cardiac pacemakers that take over the duties of the natural conduction system. Tens of thousands of these devices are implanted each year in this country alone. Over the past thirty years cardiac pacemakers have evolved from simple devices only capable of fixed-rate stimulation of a single chamber of the heart to more sophisticated "implanted computers" that medical personnel can interrogate and reprogram from outside the patient's body. These refinements have allowed for more physiologic pacing with maintenance of atrioventricular synchrony and cardiac output. There are various types of cardiac pacemakers available today that can be surgically implanted to treat specific arryhythmic disorders in the heart. Abnormal rhythms in the heart are one of the most frequent causes of heart malfunction, and in most cases necessitate some type of cardiac pacing unit. Cardiac arrhythmias are common in the elderly, in whom age-related physiologic changes often alter the conduction system of the heart. Such changes may remain asymptomatic, or they may progress to syncope, or possibly sudden death. In the event of acute myocardial infarction, arrhythmias are no more frequent in the elderly than in younger subjects; in fact, ventricular premature beats are seen less commonly in patients aged seventy years and older. Age is also not a factor in determining the success of resuscitation from cardiac arrest, although it may be a predictor of six-month survival. In general, there is nothing unique about arrhythmias in the elderly. All of the commonly encountered arrhythmias may be seen in older patients. Arrhythmias may occur in otherwise normal hearts, but with increasing age, associated cardiac disease becomes more likely. A possible exception is atrial flutter; in younger patients, its presence almost always indicates a serious cardiac disorder. There are two indications for antiarrhythmic therapy: relief of symptoms and prevention of more malignant arrhythmias. In elderly patients, pacemakers are the preferred treatment for bradyarrhythmias. Most arrhythmias occur in response to the aging heart. In the sinoatrial node, the number of pacemaker cells decreases, until often less than 10% of the normal complement remain after age 75. Beginning at age 60, there is a detectable loss of fiber from the fascicles of the left bundle branch. Commonly, less than one-half the original number remain, the others having been replaced by fibrous tissue. Microcalcification is often found in this region, and can be related to both age-associated change and pathologic processes. There is also some fibrous tissue replacement of conduction fibers in the distal conduction system, as well as occurrences of fibrosis and hyalinization in the media of the blood vessels supplying the conduction tissue. Any of these age related processes can lead to a disrupted rhythmic and conduction system of the heart. One type of arrhythmia, bradycardia, normally necessitates the surgical implantation of a pacemaker device. Bradycardia is a circulatory condition in which the myocardium contracts steadily but at a rate of less than sixty contractions a minute. This condition may be normal in some physically fit people, where their pulse may be quite slow. This is because an athlete's heart is considerably stronger and is capable of pumping a larger volume of blood per heart beat than someone who is less physically active. However, in other people, cardiac output is decreased which can cause faintness, dizziness, chest pain, and eventually syncope and circulatory collapse. The cause of bradycardia can be an increase in the parasympathetic nervous system. As the vagus nerve applies more acetylcholine on the heart, the overall output of the heart decreases which means that there is less stroke volume. In addition, severe episodic bradycardia may occur in patients with a hypersensitive carotid sinus reflex. In these patients, their carotid sinus region of the carotid artery becomes extremely sensitive to the pressure receptors within the arterial wall.

Dark Energy (Definition)

Dark Energy (Definition) Dark energy is a hypothetical form of energy that permeates space and exerts a negative pressure, which would have gravitational effects to account for the differences between the theoretical and observational results of gravitational effects on visible matter. Dark energy is not directly observed, but rather inferred from observations of gravitational interactions between astronomical objects. The term dark energy was coined by the theoretical cosmologist Michael S. Turner. Dark Energys Predecessor Before physicists knew about dark energy, a cosmological constant  was a feature of Einsteins original general relativity equations that caused the universe to be static. When it was realized the universe was expanding, the assumption was that the cosmological constant had a value of zeroan assumption that remained dominant among physicists and cosmologists for many years. Discovery of Dark Energy In 1998, two different teamsthe Supernova Cosmology Project and the High-z Supernova Search Teamboth failed at their goal of measuring the deceleration of the universes expansion. In fact, they measured not only a deceleration, but a totally unexpected acceleration  (Well, almost totally unexpected: Stephen Weinberg had once made such a prediction). Further evidence since 1998 has continued to support this finding, that distant regions of the universe are actually speeding up with respect to each other. Instead of a steady expansion, or a slowing expansion, the expansion rate is getting faster, which means that Einsteins original cosmological constant prediction manifests in todays theories in the form of dark energy. The latest findings indicate that over 70% of the universe is composed of dark energy. In fact, only about 4% is believed to be made up of ordinary, visible matter. Figuring out more details about the physical nature of dark energy is one of the major theoretical and observational goals of modern cosmologists. Also Known As: vacuum energy, vacuum pressure, negative pressure, cosmological constant

What are the similarities and differences in the operations management Essay

What are the similarities and differences in the operations management of bmibaby and in the case of Fuller, Smith & Turner PLC (Brewery) - Essay Example It was founded in 1845 in Chiswick as the Griffins brewery. The logo for the Fuller, Smith and Turners brewery states that quality, service and pride are provided in equal measures by them. The main product of the company is beer and it also operates pubs. The geographical area that Fuller, Smith and Turner and Bmibaby cater to is the same. Both of them are located in England but there is a huge difference in the market they cater to. There is a huge difference in the history and background of both companies. The brewery is well known because of its ancient roots and traditional methods whereas Bmibaby is a company which hasn’t even completed a decade of existence. Smith, Fuller and Turner currently own 363 pubs and supply their products to them. The range of products is very wide and includes Chiswick Bitter, London pride and ESB. A major factor of their success is the companys recent acquisition of the Gale group which added another 111 pubs to its empire. This move ensured the elimination of a major competitor from the scene. Besides that Smith, Fuller and Turner are well known because of the quality of their products. The Chiswick Bitter has been known as the Champion beer of Britain and the record has been unmatched. The brewery also operated by adding more and newer beers to its portfolio thereby reducing monotony of products. Michael Turner, the CEO of the company once said that We have a long-term strategy, strong balance sheet, excellent cash flow generation and an experienced management team and are well placed to meet the challenges ahead. (Review) In contrast Bmibaby works by providing its services at the lowest cost possible. They provide services which are already there in the market but its core competency lies in the fact that it custom provides those, thus charging the customer for what it wants. As compared to the brewerys 363 locations, it operates from four