Thursday, October 31, 2019

Feliz Navidad Essay Example | Topics and Well Written Essays - 750 words

Feliz Navidad - Essay Example The performance consists of simple singing or chanting of religious songs and all the homes are set up as a "Nativity scene" where the home owners pose as inn keepers. The interesting part is that the procession carries candles and statues of Jesus and Mary as the re-enactors ask for lodging at three houses and only the third house lets them inside in accordance with the Christmas story. The guests then enter the chosen house and sing traditional Christmas and religious songs for the Virgin Mary which concludes into a famous piata party for the children. Of course the ever famous Piata (which originates from Italian tradition) is the main object of interest for the children at these parties .This is a clay pot decorated with paper, and is filled with hard candy, peanuts sugar cane and fruit. The children are blindfolded and take turns at hitting it with a stick until it breaks so they can all have the sweet treats inside. The traditional Christmas piata is shaped like a star and has seven peaks, which symbolizes the seven deadly sins. The stick with which it is broken is a symbol of faith and therefore the destruction of the Piata is a symbol of the destruction of these deadly sins with faith. The Mexicans also have a very unique tradition of exchanging presents at New Years Eve rather than on Christmas .This gift exchanging is known as Misa de Gallo (Rooster's Mass). Some families might even wait as late as the Wise Mens Day which is on January the 6th to exchange gifts because on this day the Magi brought gifts to the baby Jesus. Instead of stockings (like in the American culture) the children traditionally place their shoes near the window so the Magi can fill the shoes with gifts .The children also look forward to the Merienda, ( a tea time with hot chocolate) and La Meridenda, (an festive dinner) in celebration of this day. This is a two week national holiday for the Mexicans .The US influence is ever present as in the recent decades there has been an adaptation of Santa Claus and many other American traditions. However the strong and unique Mexican culture continues to dominate these very family oriented traditions. The Holiday festivities end on the Noche Buena (Christmas Eve) with the celebration of a late-night Misa de Gallo (Rooster's Mass).This is followed by a festive dinner of traditional cuisines and sweet meats. The Christmas celebration hardly ends there as on December 28, Day of the Holy Innocents there is a commemoration of King Herod's attempt to slaughter all the new born male infants including baby Jesus. The Mexicans add a comic twist to the day as they play pranks on each other just like the April fool's day. The Christmas season continues merrily into the Three Kings Day which symbolises the arrival in Bethlehem of The Wise Men bringing gifts for baby Jesus. Reyes Magos is the Mexican version of the Santa Claus and on every January the 6th the native Mexican children hope to receive toys and gifts from this mythical figure. The Mexicans with their merry culture and strong family ties make the Christmas festivities a treat for the eyes and the soul. The final Candlemas is on February the 2nd officially marking the end of

Tuesday, October 29, 2019

The Role of Women, Family, and State according to Aristotle Essay

The Role of Women, Family, and State according to Aristotle - Essay Example According to the views of Aristotle, every State has the intention of doing good for its people. It does not matter in what ways the goodness is achieved, at the end of the day every State has the intention of providing the best for its people and giving them a comfortable and justiciable lifestyle so that they can develop as human beings and usher into the new era with more confidence and passion.Mankind always acts in the order of good. Every society is formed with a view of having a positive impact and influence on the people who comprise the society and this circle flows in existence. The human existence is marked by positivism as well as optimism for the greater good.He then follows by saying that the definition of the leader to be the manager of a few people and for the Statesman to be the manager of a large number of people is sometimes misconstrued to display a false picture which does not exist in reality. Government is very different to the system which is run in the househ olds and from that understanding it would be foolish to say that the qualification required is the same for both the parties.Aristotle then goes on to say that in a family the men is the master and the woman is a slave to the master who has to take care of the house as the man would be out in the fields to get food and money for the family. He works and earns for the family while the woman is there to take care of the children and the men of the family. This is a very narrow definition of the family and Aristotle has gone on a very negative tangent to define the functions and characteristics of the family.

Sunday, October 27, 2019

Human Resource Managements Distinctive Employment Approach Commerce Essay

Human Resource Managements Distinctive Employment Approach Commerce Essay Human resource management is a distinctive approach to employment management which seeks to obtain competitive advantage through the strategic deployment of a highly committed and skilled workforce, using an array of cultural, structural and personnel techniques. (Storey, 1995). Thus, HRM is mainly a set of policies that are created aiming to obtain the organizational goal through the successful implementation of corporate strategy considering the human resource of the company as the driving force that can make the difference or in other words give the company its most needed competitive advantage. Company needs to balance the aspirations of its people as well as its strategic demands towards making HRM policies. There have been many models to explain the concept Human Resource Management. One of the important models is Harvard model. The Harvard Framework preferred to see the whole process of HRM from the General Managers point of view (Armstrong, 2003). How they want to see the consequences of every step recognizing the importance of trade-offs between owners, employees and various interest groups (Armstrong, 2003). Here, the HR gets some outcomes as the direct affect of its policy choices and those outcomes brings the consequences that meet the stakeholders interests. It suggests that the general managers should develop a viewpoint, as they provide the strategic vision, of how they wish to see the employee involvement in achieving the goals. Another important model is Warwick model. As Harvard model is developed in the American context it reflects the American style and way of managing HR but Warwick model reflects the European style (Loosemore et al., 2003). Unlike Harvard model it focuses on external and internal both context and explores how both the internal and external environment influence the HR decisions (Bratton and Gold, 1999). From Personnel to HRM: The concept of HRM started getting shape in the early stage of industrial revolution (Bratton and Gold, 2001). Emerging concern of employee rights and the growth of trade union, changing reactions of the workforce and employers towards the public policy, implementation of strict health and safety regulations, increased demands of specialised personnel in the work force along with the technological innovations, scientific and sophisticated approach to managing employees and the ever ending competition in the market played vital role in the emergence of the concept Human Resource Management (Bratton and Gold, 2001). Though the concept is old but the title HRM was given to it only couple of decades back. Before that it was known as Personnel Management. Some scholars say that there is no actual difference between Personnel Management and HRM except the two different names (Storey, 2007; Armstrong, 2003; Torrington et al., 2008). Along with the emergence of the new economic order in 80s and 90s of last century the approach towards people management changed and the preference of treating personnel moved to individual rather then collective in order to ensure that the highly skilled and loyal employees will give the organization a competitive advantage (Bratton and Gold, 2001). Thus, changing the title is also an approach to give the people management a new image to fit to the changing environment. Torrington and Hall (1991, cited in Armstrong, 2003) sees the distinction as, Personnel Management is workforce centred and therefore directs itself to employees, on the other hand HRM is resource centred concerns itself with the overall human resource needs of the organization. Storey (2007) shows the detailed differences between Personal Management and HRM in his twenty seven points of differences where he categorized the elements into four-part basic outlines. These are; Beliefs and assumptions, Strategic Aspects, Line Management and Key levers (Storey, 2007). Miller (1998) integrated Storeys twenty seven points into six main points that focuses on the major points of distinction between Personnel Management and Human Resource Management. Dimension Personnel HRM Nature of relations Pluralist Unitarist Speed of decision Slow Fast Key managers Personnel General/line Pay Job evaluation Performance related Job categories Many Few Communication Restricted Increased Table: Personnel Management vs Human Resource Management (Miller, 1998) So, the distinction between personnel and HR is clear. The biggest change probably is focus. The focus has now shifted from overall performance to individuals. Employee involvement through personal development is now not only highly encouraged but also to ensure it the companies are undertaking different training and development programmes. An early example of this change was set by Ford when it announced its change initiatives that contain statement like employee involvement is our way of life (Storey, 2007). The Characteristics of HRM: The attempt of HRM is to manage the people, the most valuable asset of a company, to achieve its goals and objectives. Thus, the typical characteristics of HRM include both the welfare of the company and the welfare of its employee. Armstrong (2003) pointed out some characteristics of HRM, these are; It integrates the HR and business strategies and emphasizes the need for all strategic fit. It is commitment oriented as it emphasizes on gaining the committed goals and mission of the organisation. It attaches diversified cultures and values together and brings harmony in the workplace. It identifies the potentials of the employee and appoints the task accordingly to ensure the maximum benefits. It manages and harnesses the potentials of the personnel and brings the best out of them. It ensures both the happiness of the personnel and happiness of the stakeholders. The Functions HRM: The basic HR functions according to Armstrong (2003) and Torrington et al (1991) are: Human Resource Planning The management determines the types and the number of human resources it needs to accomplish a task or reach the goal. In this case the management has to consider the financial support available to it. Recruitment and selection; Proper recruitment and selection procedure needs to be followed in order to meet the demand of required skills. In this case the necessary skills can be tested through written or oral test or a combination of both. Reward systems; Reward systems are structured and measured by the company to keep the employee motivated. It may include direct, indirect or psychological reward. Employment legislation; Terms and conditions, policies and opportunities for both parties should be open and written in order to avoid confusion. The HR department has to clearly mention the company policies in the employment contract. Management of diversity; As the business is now global the companies need to ensure an environment where employees from different cultural, religious and ethnic groups are treated equal. Again, Fords early realisation prompted them apply policies such as our doors are open to men and women alike without discrimination and without regard to ethnic origin or personal beliefs (Storey, 2007). Training and development; To make the employees more efficient and prepare them for higher level of responsibilities the HRM department needs to have a continuous training and development process. Along with the routine process the companies also train their employees during a sudden demand such as an addition of new software or hardware. Grievance and discipline; To ensure time keeping, good employee relations, proper behaviour and professional attitudes the HR department formulate company procedures. Termination of employment relation; As part of disciplinary action, end of the contract, the part of an employment cut or the relocation of the employee the HRM takes all the necessary actions. Strategic HRM: Human resource management is no more limited to managing people, recruiting, selecting, training and all other conventional administrative duties. As the people are the core competitive advantage in todays business, they are evaluated as the brainpower of the company rather than manpower. The way of business competition has become knowledge based (storey et al, 2009). Thus, the human resource department plays a more strategic role today. Apart from all the administrative works Strategic HR participates on planning corporate strategy. It plans out the necessary skills and required effort needed for a particular task to be carried out in future. SHRM also indicates a planned HR policy that integrates the business goal and may encompasses a number of HR strategies to improve the individual, thus business, performance to make the reward system more effective (CIPD , 2010). Miller (1998) says if a company be able to establish an appropriate fit between strategy and HRM it can be considered as practising strategic HRM. The business strategy and the strategic human resource management run in parallel, both are informative and communicative. Information available to SHRM about how people are motivated deployed and the availability of skills and knowledge might determine the business strategy, on the other hand when business strategy requires the improvement of customer service this will probably shape the training plans and performance improvement plans (CIPD, 2010). Approaches to SHRM: Strategic HRM is mainly a resource based philosophy and this encompasses three possible approaches (Armstrong, 2003). These are explained bellow: Resource based SHRM: Resource based HRM strategy focuses on the performance of the employee and compare the productivity of its people with the competitors. In this approach learning is highly encouraged and the intellectual capital is developed and nurtured. High-performance management approach: By developing the skills of the employees and improving the self management capacity and team performance the HR department can actually enhance the overall productivity and ensure customer satisfaction. Here, the quality leadership, vision, benchmarking and decentralization are suggested in order to have greater success (Stevens, 1998; cited in Armstrong, 2003). High performance approach also require to have a rigorous recruitment and selection procedure, a proper learning and development process and merit pay and profit sharing to encourage high performance (Armstrong, 2003). High involvement management: This approach says employees are to be treated as partners, their interests should be respected and their equal involvement in decision making should be encouraged. A very good communication between the managers and the employees that gives clear understanding of organizational vision, values and the expectation of both parties can achieve the organization its expected productivity. Characteristics of SHRM: There are some characteristics of SHRM can be drawn from the writing of Salaman et al (2005) and Armstrong (2003). These are discussed below: It connects the whole process to the business strategy and plays a proactive role rather than reactive. Instead of waiting for the instruction and complaints strategic HR managers take proactive steps and plans out the future outcome. SHRM is output driven. It takes all strategic steps to improve the performance of the employees and achieve the overall competitive advantage. It is more preventive than corrective and thus it value employees who are multi-skilled, cross-functional and team players. It expects people to do the things write the first attempt. It provides the guidance to other sections of the organization on what to measure, how to measure and how to report the outcomes of the measurement CIPD (2010) Dave Ulrich (1997) suggested four strategic roles in order to be able to create real value to the business. These are: Strategic partner: Here, the HR manger help the company turn the strategy into result. He will evaluate the existing strategy and figure out whether there is any strategic change needed. Change agent: HRM helps the change happen and it happens faster. Also make sure human resource understand and cope up with the change. Employee champion: managing and evaluating talents or the intellectual capital and Administrative expert: Ensuring the all the human resource related jobs are done and they are done in a way that helps the business. Effect of Globalization: Globalization is shortening the trade barriers, making the market more open and thus more competitive. It is a very influencing source that fuelling the changes faster. Toyota, one of the largest car producers in the world, was the hundredth Japanese company when it decided to locate their first UK based manufacturing facility in Derby (Storey, 2007). But it took fifteen years, from 1972-87, for the first fifty Japanese companies to arrive in UK and the next fifty companies arrived in following two years time (Storey, 1992, p. 12). The challenges that globalization has brought to Human Resource Management and the they should be faced are: Restructuring: Business is expanding in one way or other. Either two or more firms of same industry are merging together or one is acquiring the other. As a direct result of this the company eliminate layers of managers, closes facilities and cut jobs. HR managers are facing challenges in managing people who worked in different company cultures and some whom withdraw their loyalty. Even sometimes when the companies from different countries of different time zones merge than language and cultures become the main concern (CIPD, 2011). In this regard the HR professionals need work in co-operation with other organizational sections. Need to understand different organizational management policy and take the professional through smooth transition process. Management of diversity: As an effect of globalisation people from different cultures, ethnic groups and religion come in one place and work together and they require a mutual understanding that make the way to productivity smooth. Here, the HR department needs to ensure a working environment that offers equal opportunity and respect to the people from all background (CIPD, 2010). They need to understand different cultural and religious values. Technological innovation: Continuous innovation of new technology put pressure on HR department of the company to ensure a continuous training and development programme. Also, the technologies are reducing HR tasks that create the chance of HR job cuts. HR professionals need to make themselves equipped with latest technological knowledge. They need to diversify themselves and be useful in participating other organizational tasks. Outsourcing: Outsourcing concept has come up along with the globalization. Organizations are now outsourcing some of their task to other companies that may be located some other part of the world. Thus, some of the HR functions now to be done by the line managers (Kumar, 2011). Along with other qualifications the line managers need to have the proper understanding of Human Resource Management. On the other hand the HR managers need to outline and monitor the HR task of the line managers. Economic and political change: Economic changes such as global recession, change in government policy as a result of the shift in political power force the companies to close facilities and decrease production cost. As a direct result of this organizations decrease the size of HR body and put pressure on the remaining to be more productive (Kumar, 2011). Through the effective training and development process the HR managers need to ensure top level productivity of the human capital that will reduce production cost and make the organization more sustainable. Conclusion: Human Resource Management has come through different changes and challenges over the recent years. Though, the innovation of technologies is reducing some of the HR tasks but these affecting the HR roles very less. Also, outsourcing is also happening in a number of cases thus it is not affecting HR roles significantly (CIPD, 2006). Yet outsourcing may reduce the HR task of an organization but it is shifting those tasks to some other companies. The cost of running a HR department may go up and down but at the end it repay with the improved productivity it brings to the human resource of the company. The human resource still remains the competitive advantage factor and it will remain so in the future. Different market boundaries are falling apart and forming one single global market. In this marketplace different companies of an industry are experimenting all possible and available resources to achieve the competitive advantage. But it is human resource that can offer additional featur es to a business through a continuous development process. Thus, the task of people management is not limiting rather its expanding. A dynamic human resource management body can attract the best bunches of talent by designing and offering exceptional reward and career opportunity package and at the same time it can improve the productivity of its existing resource to the highest level by planning, developing and implementing an effective training and development programme. For instance, Microsoft and Google both have search engines. The number of users using a search engine determines its business success. Now, people will use the search engine that consists of highest number of resources and that offer additional features that carry the better value then the others. The human resources are bringing all the features and widening business opportunities in these both cases. And it is the HRM department that recruits those professionals through an effective selection and recruitment pr ocess, offering them their dream package of reward and compensation, and later on it brings those professionals to this level through a proper training and development. Thus, the Human Resource Management is crucial for organizational survival in todays marketplace.

Friday, October 25, 2019

Factors Contributing to Americas War With Mexico :: American America History

Factors Contributing to America's War With Mexico In 1825 President John Quincy Adams appointed Joel Poinsett as the first U.S. minister to Mexico. His first assignment was to persuade the Mexican government to sell the U.S. the province of Texas, thus continuing the rapid expansion of the American democracy. The United States continued to pursue Texas with little success for the next 20 years. It was not until December 1845 when the U.S. finally annexed Texas by a joint resolution (and thus simple majority) . Immediately following the Texas acquisition, and with U.S.-Mexico relations swiftly deteriorating, the U.S. wanted the Mexican province of California, mainly for her harbours San Frasisco and San Diego. The American policy towards Mexico which ensued in the following years was governed almost exclusively by President James Polk's personal opinions and actions, as well as Nicholas Trist's defiant behavior; a manifestation of the state-centric theory in which key individual decision makers govern policy. In addition, Polk's policies were secondarily influenced by the consideration of relative power, American mass ideology, and Public opinion. In 1845 President Polk began, cofidentially from the public, considering the annexation of California. Polk's initial desire was to simply purchase California, attempting to maintain peace. He soon learned this would be impossible. When Polk ordered General Taylor to cross the Nueces River and eventually to fortify on the Rio Grande, he fully understood the possilble consequences of these actions. In fact, by deploying Taylor and his troops, Polk putting a slow squeeze on the Mexicans which would leave them with no other option than to strike back. Polk waited for the initial attack to be made by the Mexicans and then struck back. Polk claimed that American blood had been spilled on American soil, thus garnering enough public and congressional support to declare war on Mexico safe from domestic unrest. Norman Graebner states that, " Polk was too astute a politician to favor any cause until public opinion had crystallized "1 Although the war decleration contained no reference to the territorial conquest, Polk's persaonal diary conveys his clandestine intentions of acquiring the much coveted California as well as New Mexico. The intentions of the President to occupy Mexico undoubtedly took into consideration public opinion, but the most prominent reason for the decleration of war was Polk's belief that california was a strong economic and militarily strategic addition to the U.S. Secretary of Navy George Bancraft noted that the acquisition of California was among Polk's top four priorities from the outset of his administration, however, Polk had kept this under wraps. Glenn Price also points out that, ". Factors Contributing to America's War With Mexico :: American America History Factors Contributing to America's War With Mexico In 1825 President John Quincy Adams appointed Joel Poinsett as the first U.S. minister to Mexico. His first assignment was to persuade the Mexican government to sell the U.S. the province of Texas, thus continuing the rapid expansion of the American democracy. The United States continued to pursue Texas with little success for the next 20 years. It was not until December 1845 when the U.S. finally annexed Texas by a joint resolution (and thus simple majority) . Immediately following the Texas acquisition, and with U.S.-Mexico relations swiftly deteriorating, the U.S. wanted the Mexican province of California, mainly for her harbours San Frasisco and San Diego. The American policy towards Mexico which ensued in the following years was governed almost exclusively by President James Polk's personal opinions and actions, as well as Nicholas Trist's defiant behavior; a manifestation of the state-centric theory in which key individual decision makers govern policy. In addition, Polk's policies were secondarily influenced by the consideration of relative power, American mass ideology, and Public opinion. In 1845 President Polk began, cofidentially from the public, considering the annexation of California. Polk's initial desire was to simply purchase California, attempting to maintain peace. He soon learned this would be impossible. When Polk ordered General Taylor to cross the Nueces River and eventually to fortify on the Rio Grande, he fully understood the possilble consequences of these actions. In fact, by deploying Taylor and his troops, Polk putting a slow squeeze on the Mexicans which would leave them with no other option than to strike back. Polk waited for the initial attack to be made by the Mexicans and then struck back. Polk claimed that American blood had been spilled on American soil, thus garnering enough public and congressional support to declare war on Mexico safe from domestic unrest. Norman Graebner states that, " Polk was too astute a politician to favor any cause until public opinion had crystallized "1 Although the war decleration contained no reference to the territorial conquest, Polk's persaonal diary conveys his clandestine intentions of acquiring the much coveted California as well as New Mexico. The intentions of the President to occupy Mexico undoubtedly took into consideration public opinion, but the most prominent reason for the decleration of war was Polk's belief that california was a strong economic and militarily strategic addition to the U.S. Secretary of Navy George Bancraft noted that the acquisition of California was among Polk's top four priorities from the outset of his administration, however, Polk had kept this under wraps. Glenn Price also points out that, ".

Thursday, October 24, 2019

Development of English Weapons Essay

Back in history, human beings used hunting by products such as craws, horns and animal teeth as weapon. As human being developed, he started to use axes made of stone as a weapon both for personal protection and for hunting. More development and civilization led to the development of weapons such as the wooden clubs, unshaped stones for throwing at the enemies and spears for both hunting and fighting. By then, human beings used to make wooden spears for hunting and for attacking any possible human enemy. With time the fire hardened spear points were replaced with stone sharp ones which were more effective than they precedents. Further development and civilization saw the development of bows and arrows to hunt and to counter attack an enemy (Davies, 1990, 67). By 400 B. C, evolution of what can be termed as earlier technology had enabled humans to develop a four wheeled ballista which was drawn by armored horses and more effective while it came to making attacks or counter attacking an enemy than the primitive weapons previously used. However, ancient weapons to be used by human being in their activities were qualitative improvement of the primitive weapons. In this context, revolution in military technology arose as a result of improvement in techniques and materials used in creating prehistoric weapons. As technology began to improve, weapons used in wars also started to improve. For example, with the discovery of the spooked wheel chariots drawn by horses became possible and useful for transporting soldiers to and fro the battle field. Around 1300BC, use of spoke wheel chariots had heightened but ceased later in the 4th century BC as humans began breeding horses that supported human weight and as cavalry replaced the military force that was used in fighting from chariots. In western world, the medieval period was highly characterized by knights and rudimentary siege artillery with their purpose inclusive of negating the increased use of castles which proliferated most of Europe and the neighboring East. The knights made use of various weapons such as the knifes, the bow and the sword. First, the knife which came in various designs was used highly by the knights to thrust into the weak sports of an enemy’s armor, to slit their throats when using stealth or to slash those enemies that came to the battle field un-armored. In essence, the knife could be single edged but many of them were usually double edged and unserrated. Today, knifes continue to be a major weapon used by soldiers both for fighting and other purposes. However, as opposed to knifes in the earlier times, most of knifes used by soldiers today are serrated. In particular, a knife forms one of the basic equipments for soldiers during any warfare. Secondly, the knights made use of swords which like knifes were designed either single edged or double edged. They also came in different sizes with some built heavy enough to be carried by only the strong men in the army. They were used in slashing the enemy or even killing them (http://atschool. eduweb. co. uk/sirrobhitch. suffolk/Portland%20State%20University%20Greek%20Civilization%20Home%20Page%20v2/DOCS/10/seanh1. htm. The design with which swords were supplied depended on the way in which they were intended to counter and kill the enemy. Some were long and others short while others were broad enough to accommodate both hands and could penetrate virtually any type of armor. For example, the bastard was a long or broad sword with normal types of blades but with a heavy pommel or ball at the bottom that was helpful for balancing purposes and as a mace for bashing the head of an enemy. Further, the saber was useful for slashing and employed by cavalry to kill the enemy and in this case could penetrate the armor of an enemy while riding a horse at a high speed. Other weapons commonly used by the knights and the cavalry include the pole arms, spears and lances, axe and other blunt objects such as a hammer and a mace. For one, the mace came as a metal or wood stick about twelve inches long and with a leather loop to prevent it from frying of the wrist while being used. The part used in striking the enemy was usually a sphere with spikes or angled blades designed to inflict injury on the enemy. Spears were simple weapons used for piercing the enemy both at close range or long range. They could have metal or wood heads and was useful while aiming at the weaker spots of the armor. It could also penetrate through the shields or mail given its length and sharpness (Boardman, 1998, 45). Further, the handle of the spear was commonly designed to break off once it hit the target to prevent the enemy from throwing it back. Pole arms came in different sizes and designs. They were used in piercing the armor of the enemy besides slicing or chopping through the enemy given its sharp and curved edges. It was useful while in a cavalry battle field due to the fact that it could be used in chopping off the feet of a horse rode by an enemy thus temporary incapacitating him. While many of this weapons such as the mace and the hammer did not see the light of modern usage, they still presented a good and viable starting point for the development of more sophisticated weapons used by armies all over the world. In regard to the armor used during the medieval times, leather formed the first form of armor to be worn and used by human beings in the battle field. As weapons developed and with the discovery of metal, leather started to become obsolete and was replaced by plate and mail. These two were worn on various parts of the body to prevent a soldier from being slashed by the enemy in the battle field (http://www. angelfire. com/wy/svenskildbiter/siege. html). As enlightenment hit the world, armors began to be worn together with undergarments and actually to be tailored like suits so that a knight could be hit but be on his feet within seconds having sustained no injury. Today, the plates and the mails have been discarded paving way for bullet proof armors and other forms of discovery. For example, the tanks used by armies around the world and in Europe in particular are heavily armored vehicles used for transporting weapons and soldiers to the battle field as well as launching missiles from the safety of highly armored walls. Despite this, the same metals used in designing and producing plates and mails are the ones used in producing today’s armored vehicles (U. S. Congress, 1995, 35). The knights developed from the earlier Calvary. On the other hand, siege artillery which were by then been used to breach the walls of the castles led to many revolutionary advances including the use of gun powder and cannon use. It was not until the Renaissance period that the western world and most parts of the rest of the world started to use firearms in warfare. Human powered weapons were finally exiting battle fields and being replaced with more powerful mechanically powered weapons. This is commonly referred to as the age of riffles as riffles begun to be commonly used in the battle fields. Firearms were developed in large numbers and cannons to support them. Motor vehicles replaced the use of horses in the battlefield and escalation technology which involves the use of armed aircrafts and armored vehicles developed. Firearms and cannons were designed to be fitted on these vehicles and aircrafts and were useful in attacking using long range missiles as is the case today. This saw the introduction of guns and rockets for use in the battle field. Guns and rockets were more efficient than their predecessors by the virtue of their design to store energy in a combustible propellant like gun powder as opposed to springs and weight. They increasingly started to be used in 16th century and with progressive ignition mechanisms remain in use to date. Based on these new developments, new technologies have such as machine guns have risen over the years (http://www. angelfire. com/wy/svenskildbiter/siege. html). Later in the 19th century, fossil fuel powered steam engines replaced sail power warship propulsion. In earlier times, bayonets were developed and which were used both as a pole-arm and as a knife but were later discarded with the discovery of rifled artillery which was by then being used in destroying masonry fortress. In essence, this discovery caused a huge revolution in the field of military and continues to affect today’s weaponry development and war strategies (Blair, 1997, 56). Further, the era of World War II marked a major revolution in military technology with more sophisticated weapons been developed in line with the emerging technologies. New concepts and designs of weapons were developed in massive numbers and the existing technology improved to march with the military needs. For example, atomic bomb was developed around this period. In essence, the end of World War II saw the institutionalization of weapons development as institutions and countries competed to develop unique weapons and counter weapons. In the western world, this constant development of weapons still continues to date (Collins, 1997, 87). In conclusion, despite the fact that weapons used during the medieval times have changed increasingly as compared to those used in recent times, these weapons formed the basis for developments of today world. The strategies employed during the medieval times were highly dependent on the kind of weapons in use. For example, the use of anchors to attack the enemy was dependent on the use of bows and arrows. Still, with the discovery of gunpowder, use of cannons became prominent in blasting the walls of castles and in sinking the ships of the enemy. Today’s weapons and strategies have their roots in the weapons and strategies employed during the earlier times with technology improvements and discoveries increasing the effectiveness of weapons being produced.For example, computer guided weaponry and nuclear weapons have developed over recent years though the later is useless for small wars. Work Cited: Blair Claude. European Armor c1066 to c1700. London: Batsford Publishers, 1997, pp. 56 Boardman Andrew. The Medieval Soldier in the Wars of the Roses. London: Alan Sutton,1998, pp, 45 Collins McNamee. The Wars of the Bruces: Scotland, England and Irelan. , London: East Linton, 1997, pp. 87 Davies R. Domination and Conquest: The Experience of Ireland, Scotland and Wales. New York: Cambridge University Press, 1990, pp. 67 Organized Infantry. Retrieved on 2nd January 2009 from http://atschool. eduweb. co. uk/sirrobhitch. suffolk/Portland%20State%20University%20Greek%20Civilization%20Home%20Page%20v2/DOCS/10/seanh1. htm U. S. Congress, Office of Technology Assessment. Improving the prospects for future international peace operations: workshop proceedings, Washington DC, US Government Printing Office, 1995, pp. 35 Wyley Stephen, Siege Warfare. The Art of Offense and Defense, 1989. Retrieved on 2nd January 2009 from http://www. angelfire. com/wy/svenskildbiter/siege. html

Wednesday, October 23, 2019

Blood pressure Essay

Blood pressure (BP), sometimes referred to as arterial blood pressure, is the pressureexerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, â€Å"blood pressure† usually refers to thearterial pressure of the systemic circulation. During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure.[1] The blood pressure in the circulation is principally due to the pumping action of the heart.[2] Differences in mean blood pressure are responsible for blood flow from one location to another in the circulation. The rate of mean blood flow depends on the resistance to flow presented by the blood vessels. Mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles.[3] Gravity affects blood pressure via hydrostatic forces (e.g., during standing) and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins.[2] The measurement blood pressure without further specification usually refers to the systemic arterial pressure measured at a person’s upper arm and is a measure of the pressure in the brachial artery, major artery in the upper arm. A person’s blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure and is measured in millimetres of mercury (mmHg), for example 120/80. The table on the right shows the classification of blood pressure adopted by the American Heart Association for adults who are 18 years and older.[4] It assumes the values are a result of averaging blood pressure readings measured at two or more visits to the doctor.[6][7] In the UK, blood pressures are usually categorised into three groups: low (90/60 or lower), high (140/90 or higher), and normal (values above 90/60 and below 130/80).[8][9] Normal range of blood pressure While average values for arterial pressure could be computed for any given population, there is often a large variation from person to person; arterial pressure also varies in individuals from moment to moment. Additionally, the average of any given population may have a questionable correlation with its general health; thus the relevance of such average values is equally questionable. However, in a study of 100 human subjects with no known history of hypertension, an average blood pressure of 112/64 mmHg was found,[10] which are currently classified as desirable or â€Å"normal† values. Normal values fluctuate through the 24-hour cycle, with highest readings in the afternoons and lowest readings at night.[11][12] Various factors, such as age and sex influence average values, influence a person’s average blood pressure and variations. In children, the normal ranges are lower than for adults and depend on height.[13] As adults age, systolic pressure tends to rise and diastolic tends to fall.[14] In the elderly, blood pressure tends to be above the normal adult range,[15] largely because of reduced flexibility of the arteries. Also, an individual’s blood pressure varies with exercise, emotional reactions, sleep, digestion and time of day. Differences between left and right arm blood pressure measurements tend to be random and average to nearly zero if enough measurements are taken. However, in a small percentage of cases there is a consistent difference greater than 10 mmHg which may need further investigation, e.g. for obstructive arterial disease.[16][17] The risk of cardiovascular disease increases progressively above 115/75 mmHg.[18] In the past, hypertension was only diagnosed if secondary signs of high arterial pressure were present, along with a prolonged high systolic pressure reading over several visits. Regarding hypotension, in practice blood pressure is considered too low only if noticeable symptoms are present.[5] Clinical trials demonstrate that people who maintain arterial pressures at the low end of these pressure ranges have much better long term cardiovascular health. The principal medical debate concerns the aggressiveness and relative value of methods used to lower pressures into this range for those who do not maintain such pressure on their own. Elevations, more commonly seen in older people, though often considered normal, are associated with increased morbidity and mortality. Physiology There are many physical factors that influence arterial pressure. Each of these may in turn be influenced by physiological factors, such as diet, exercise, disease, drugs or alcohol, stress, obesity, and so-forth.[20] Some physical factors are: †¢ Volume of fluid or blood volume, the amount of blood that is present in the body. The more blood present in the body, the higher the rate of blood return to the heart and the resulting cardiac output. There is some relationship between dietary salt intake and increased blood volume, potentially resulting in higher arterial pressure, though this varies with the individual and is highly dependent on autonomic nervous system response and the renin-angiotensin system.[21][22][23] †¢ Resistance. In the circulatory system, this is the resistance of the blood vessels. The higher the resistance, the higher the arterial pressure upstream from the resistance to blood flow. Resistance is related to vessel radius (the larger the radius, the lower the resistance), vessel length (the longer the vessel, the higher the resistance), blood viscosity, as well as the smoothness of the blood vessel walls. Smoothness is reduced by the build up of fatty deposits on the arterial walls. Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the size of blood vessels, thereby decreasing arterial pressure. Resistance, and its relation to volumetric flow rate (Q) and pressure difference between the two ends of a vessel are described by Poiseuille’s Law. †¢ Viscosity, or thickness of the fluid. If the blood gets thicker, the result is an increase in arterial pressure. Certain medical conditionscan change the viscosity of the blood. For instance, anemia (low red blood cell concentration), reduces viscosity, whereas increased red blood cell concentration increases viscosity. It had been thought that aspirin and related â€Å"blood thinner† drugs decreased the viscosity of blood, but instead studies found[24] that they act by reducing the tendency of the blood to clot. In practice, each individual’s autonomic nervous system responds to and regulates all these interacting factors so that, although the above issues are important, the actual arterial pressure response of a given individual varies widely because of both split-second and slow-moving responses of the nervous system and end organs. These responses are very effective in changing the variables and resulting blood pressure from moment to moment. Moreover, blood pressure is the result of cardiac output increased by peripheral resistance: blood pressure = cardiac output Xperipheral resistance. As a result, an abnormal change in blood pressure is often an indication of a problem affecting the heart’s output, the blood vessels’ resistance, or both. Thus, knowing the patient’s blood pressure is critical to assess any pathology related to output and resistance. Mean arterial pressure The mean arterial pressure (MAP) is the average over a cardiac cycle and is determined by the cardiac output (CO), systemic vascular resistance (SVR), and central venous pressure (CVP),[25] Curve of the arterial pressure during one cardiac cycle The up and down fluctuation of the arterial pressure results from the pulsatile nature of thecardiac output, i.e. the heartbeat. The pulse pressure is determined by the interaction of thestroke volume of the heart, compliance (ability to expand) of the aorta, and the resistance to flow in the arterial tree. By expanding under pressure, the aorta absorbs some of the force of the blood surge from the heart during a heartbeat. In this way, the pulse pressure is reduced from what it would be if the aorta wasn’t compliant.[26] The loss of arterial compliance that occurs with aging explains the elevated pulse pressures found in elderly patients. The pulse pressure can be simply calculated from the difference of the measured systolic and diastolic pressures,[26] Arm–leg gradient The arm–leg (blood pressure) gradient is the difference between the blood pressure measured in the arms and that measured in the legs. It is normally less than 10 mmHg,[27] but may be increased in e.g. coarctation of the aorta.[27] Vascular resistance The larger arteries, including all large enough to see without magnification, are conduits with low vascular resistance (assuming no advanced atherosclerotic changes) with high flow rates that generate only small drops in pressure. The smaller arteries and arterioles have higher resistance, and confer the main drop in blood pressure along the circulatory system. Vascular pressure wave Modern physiology developed the concept of the vascular pressure wave (VPW). This wave is created by the heart during the systoleand originates in the ascending aorta. Much faster than the stream of blood itself, it is then transported through the vessel walls to the peripheral arteries. There the pressure wave can be palpated as the peripheral pulse. As the wave is reflected at the peripheral veins, it runs back in a centripetal fashion. When the reflected wave meets the next outbound pressure wave, the pressure inside the vessel rises higher than the pressure in the aorta. This concept explains why the arterial pressure inside the peripheral arteries of the legs and arms is higher than the arterial pressure in the aorta,[28][29][30] and in turn for the higher pressures seen at the ankle compared to the arm with normal ankle brachial pressure index values. Regulation The endogenous regulation of arterial pressure is not completely understood, but the following mechanisms of regulating arterial pressure have been well-characterized: †¢ Baroreceptor reflex: Baroreceptors in the high pressure receptor zones detect changes in arterial pressure. These baroreceptors send signals ultimately to the medulla of the brain stem, specifically to the Rostral ventrolateral medulla (RVLM). The medulla, by way of the autonomic nervous system, adjusts the mean arterial pressure by altering both the force and speed of the heart’s contractions, as well as the total peripheral resistance. The most important arterial baroreceptors are located in the left and rightcarotid sinuses and in the aortic arch.[31] †¢ Renin-angiotensin system (RAS): This system is generally known for its long-term adjustment of arterial pressure. This system allows the kidney to compensate for loss in blood volume or drops in arterial pressure by activating an endogenous vasoconstrictorknown as angiotensin II. †¢ Aldosterone release: This steroid hormone is released from the adrenal cortex in response to angiotensin II or high serum potassiumlevels. Aldosterone stimulates sodium retention and potassium excretion by the kidneys. Since sodium is the main ion that determines the amount of fluid in the blood vessels by osmosis, aldosterone will increase fluid retention, and indirectly, arterial pressure. †¢ Baroreceptors in low pressure receptor zones (mainly in the venae cavae and the pulmonary veins, and in the atria) result in feedback by regulating the secretion of antidiuretic hormone (ADH/Vasopressin), renin and aldosterone. The resultant increase inblood volume results an increased cardiac output by the Frank–Starling law of the heart, in turn increasing arterial blood pressure. These different mechanisms are not necessarily independent of each other, as indicated by the link between the RAS and aldosterone release. Currently, the RAS is targeted pharmacologically by ACE inhibitors and angiotensin II receptor antagonists. The aldosterone system is directly targeted by spironolactone, an aldosterone antagonist. The fluid retention may be targeted by diuretics; the antihypertensive effect of diuretics is due to its effect on blood volume. Generally, the baroreceptor reflex is not targeted in hypertensionbecause if blocked, individuals may suffer from orthostatic hypotension and fainting. Measurement A medical student checking blood pressure using a sphygmomanometer and stethoscope. Arterial pressure is most commonly measured via a sphygmomanometer, which historically used the height of a column of mercury to reflect the circulating pressure.[32] Blood pressure values are generally reported in millimetres of mercury (mmHg), though aneroid and electronic devices do not use mercury. For each heartbeat, blood pressure varies between systolic and diastolic pressures. Systolic pressure is peak pressure in the arteries, which occurs near the end of the cardiac cyclewhen the ventricles are contracting. Diastolic pressure is minimum pressure in the arteries, which occurs near the beginning of the cardiac cycle when the ventricles are filled with blood. An example of normal measured values for a resting, healthy adult human is 120 mmHgsystolic and 80 mmHg diastolic (written as 120/80 mmHg, and spoken [in the US and UK] as â€Å"one-twenty over eighty†). Systolic and diastolic arterial blood pressures are not static but undergo natural variations from one heartbeat to another and throughout the day (in a circadian rhythm). They also change in response to stress, nutritional factors, drugs, disease, exercise, and momentarily from standing up. Sometimes the variations are large. Hypertension refers to arterial pressure being abnormally high, as opposed to hypotension, when it is abnormally low. Along with body temperature, respiratory rate, and pulse rate, blood pressure is one of the four main vital signs routinely monitored by medical professionals and healthcare providers.[33] Measuring pressure invasively, by penetrating the arterial wall to take the measurement, is much less common and usually restricted to a hospital setting. Noninvasive The noninvasive auscultatory and oscillometric measurements are simpler and quicker than invasive measurements, require less expertise, have virtually no complications, are less unpleasant and less painful for the patient. However, noninvasive methods may yield somewhat lower accuracy and small systematic differences in numerical results. Noninvasive measurement methods are more commonly used for routine examinations and monitoring. [edit]Palpation A minimum systolic value can be roughly estimated by palpation, most often used in emergency situations, but should be used with caution.[34] It has been estimated that, using 50% percentiles, carotid, femoral and radial pulses are present in patients with a systolic blood pressure > 70 mmHg, carotid and femoral pulses alone in patients with systolic blood pressure of > 50 mmHg, and only a carotid pulse in patients with a systolic blood pressure of > 40 mmHg.[34] A more accurate value of systolic blood pressure can be obtained with a sphygmomanometer and palpating the radial pulse.[35] The diastolic blood pressure cannot be estimated by this method.[36] The American Heart Association recommends that palpation be used to get an estimate before using the auscultatory method. Auscultatory Auscultatory method aneroid sphygmomanometer with stethoscope Mercury manometer The auscultatory method (from the Latin word for â€Å"listening†) uses a stethoscope and asphygmomanometer. This comprises an inflatable (Riva-Rocci) cuff placed around the upperarm at roughly the same vertical height as the heart, attached to a mercury or aneroidmanometer. The mercury manometer, considered the gold standard, measures the height of a column of mercury, giving an absolute result without need for calibration and, consequently, not subject to the errors and drift of calibration which affect other methods. The use of mercury manometers is often required in clinical trials and for the clinical measurement of hypertension in high-risk patients, such as pregnant women. A cuff of appropriate size is fitted smoothly and snugly, then inflated manually by repeatedly squeezing a rubber bulb until the artery is completely occluded. Listening with the stethoscope to the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. When blood just starts to flow in the artery, the turbulent flow creates a â€Å"whooshing† or pounding (first Korotkoff sound). The pressure at which this sound is first heard is the systolic blood pressure. The cuff pressure is further released until no sound can be heard (fifth Korotkoff sound), at the diastolic arterial pressure. The auscultatory method is the predominant method of clinical measurement.[37] Oscillometric The oscillometric method was first demonstrated in 1876 and involves the observation of oscillations in the sphygmomanometer cuff pressure[38] which are caused by the oscillations of blood flow, i.e., the pulse.[39] The electronic version of this method is sometimes used in long-term measurements and general practice. It uses a sphygmomanometer cuff, like the auscultatory method, but with an electronic pressure sensor (transducer) to observe cuff pressure oscillations, electronics to automatically interpret them, and automatic inflation and deflation of the cuff. The pressure sensor should be calibrated periodically to maintain accuracy. Oscillometric measurement requires less skill than the auscultatory technique and may be suitable for use by untrained staff and for automated patient home monitoring. The cuff is inflated to a pressure initially in excess of the systolic arterial pressure and then reduced to below diastolic pressure over a period of about 30 seconds. When blood flow is nil (cuff pressure exceeding systolic pressure) or unimpeded (cuff pressure below diastolic pressure), cuff pressure will be essentially constant. It is essential that the cuff size is correct: undersized cuffs may yield too high a pressure; oversized cuffs yield too low a pressure. When blood flow is present, but restricted, the cuff pressure, which is monitored by the pressure sensor, will vary periodically in synchrony with the cyclic expansion and contraction of the brachial artery, i.e., it will oscillate. The values of systolic and diastolic pressure are computed, not actually measured from the raw data, using an algorithm; the computed results are displayed. Oscillometric monitors may produce inaccurate readings in patients with heart and circulation problems, which include arterial sclerosis, arrhythmia, preeclampsia, pulsus alternans, and pulsus paradoxus. In practice the different methods do not give identical results; an algorithm and experimentally obtained coefficients are used to adjust the oscillometric results to give readings which match the auscultatory results as well as possible. Some equipment uses computer-aided analysis of the instantaneous arterial pressure waveform to determine the systolic, mean, and diastolic points. Since many oscillometric devices have not been validated, caution must be given as most are not suitable in clinical and acute care settings. The term NIBP, for non-invasive blood pressure, is often used to describe oscillometric monitoring equipment. Continuous noninvasive techniques (CNAP) Continuous Noninvasive Arterial Pressure (CNAP) is the method of measuring arterial blood pressure in real-time without any interruptions and without cannulating the human body. CNAP combines the advantages of the following two clinical â€Å"gold standards†: it measures blood pressure continuously in real-time like the invasive arterial catheter system and it is noninvasive like the standard upper arm sphygmomanometer. Latest developments in this field show promising results in terms of accuracy, ease of use and clinical acceptance. Non-occlusive techniques: the Pulse Wave Velocity (PWV) principle Since the 90s a novel family of techniques based on the so-called Pulse wave velocity (PWV) principle have been developed. These techniques rely on the fact that the velocity at which an arterial pressure pulse travels along the arterial tree depends, among others, on the underlying blood pressure.[40] Accordingly, after a calibration maneuver, these techniques provide indirect estimates of blood pressure by translating PWV values into blood pressure values.[41] The main advantage of these techniques is that it is possible to measure PWV values of a subject continuously (beat-by-beat), without medical supervision, and without the need of inflating brachial cuffs. PWV-based techniques are still in the research domain and are not adapted to clinical settings. White-coat hypertension For some patients, blood pressure measurements taken in a doctor’s office may not correctly characterize their typical blood pressure.[42] In up to 25% of patients, the office measurement is higher than their typical blood pressure. This type of error is calledwhite-coat hypertension (WCH) and can result from anxiety related to an examination by a health care professional.[43] The misdiagnosis of hypertension for these patients can result in needless and possibly harmful medication. WCH can be reduced (but not eliminated) with automated blood pressure measurements over 15 to 20 minutes in a quiet part of the office or clinic.[44] Debate continues regarding the significance of this effect.[citation needed] Some reactive patients will react to many other stimuli throughout their daily lives and require treatment. In some cases a lower blood pressure reading occurs at the doctor’s office.[45] Home monitoring Ambulatory blood pressure devices that take readings every half hour throughout the day and night have been used for identifying and mitigating measurement problems like white-coat hypertension. Except for sleep, home monitoring could be used for these purposes instead of ambulatory blood pressure monitoring.[46] Home monitoring may be used to improve hypertension management and to monitor the effects of lifestyle changes and medication related to blood pressure.[6] Compared to ambulatory blood pressure measurements, home monitoring has been found to be an effective and lower cost alternative,[46][47][48] but ambulatory monitoring is more accurate than both clinic and home monitoring in diagnosing hypertension. Ambulatory monitoring is recommended for most patients before the start of antihypertensive drugs.[49] Aside from the white-coat effect, blood pressure readings outside of a clinical setting are usually slightly lower in the majority of people. The studies that looked into the risks from hypertension and the benefits of lowering blood pressure in affected patients were based on readings in a clinical environment. When measuring blood pressure, an accurate reading requires that one not drink coffee, smoke cigarettes, or engage in strenuous exercise for 30 minutes before taking the reading. A full bladder may have a small effect on blood pressure readings; if the urge to urinate arises, one should do so before the reading. For 5 minutes before the reading, one should sit upright in a chair with one’s feet flat on the floor and with limbs uncrossed. The blood pressure cuff should always be against bare skin, as readings taken over a shirt sleeve are less accurate. During the reading, the arm that is used should be relaxed and kept at heart level, for example by resting it on a table.[50] Since blood pressure varies throughout the day, measurements intended to monitor changes over longer time frames should be taken at the same time of day to ensure that the readings are comparable. Suitable times are: †¢ immediately after awakening (before washing/dressing and taking breakfast/drink), while the body is still resting, †¢ immediately after finishing work. Automatic self-contained blood pressure monitors are available at reasonable prices, some of which are capable of Korotkoff’s measurement in addition to oscillometric methods, enabling irregular heartbeat patients to accurately measure their blood pressure at home. Invasive Arterial blood pressure (BP) is most accurately measured invasively through an arterial line. Invasive arterial pressure measurement with intravascular cannulae involves direct measurement of arterial pressure by placing a cannula needle in an artery (usually radial, femoral,dorsalis pedis or brachial). The cannula must be connected to a sterile, fluid-filled system, which is connected to an electronic pressure transducer. The advantage of this system is that pressure is constantly monitored beat-by-beat, and a waveform (a graph of pressure against time) can be displayed. This invasive technique is regularly employed in human and veterinary intensive care medicine, anesthesiology, and for research purposes. Cannulation for invasive vascular pressure monitoring is infrequently associated with complications such as thrombosis, infection, andbleeding. Patients with invasive arterial monitoring require very close supervision, as there is a danger of severe bleeding if the line becomes disconnected. It is generally reserved for patients where rapid variations in arterial pressure are anticipated. Invasive vascular pressure monitors are pressure monitoring systems designed to acquire pressure information for display and processing. There are a variety of invasive vascular pressure monitors for trauma, critical care, and operating room applications. These include single pressure, dual pressure, and multi-parameter (i.e. pressure / temperature). The monitors can be used for measurement and follow-up of arterial, central venous, pulmonary arterial, left atrial, right atrial, femoral arterial, umbilical venous, umbilical arterial, and intracranial pressures. Fetal blood pressure Further information: Fetal circulation#Blood pressure In pregnancy, it is the fetal heart and not the mother’s heart that builds up the fetal blood pressure to drive its blood through the fetal circulation. The blood pressure in the fetal aorta is approximately 30 mmHg at 20 weeks of gestation, and increases to approximately 45 mmHg at 40 weeks of gestation.[51] The average blood pressure for full-term infants: Systolic 65–95 mm Hg Diastolic 30–60 mm Hg[52] Blood pressure is the measurement of force that is applied to the walls of the blood vessels as the heart pumps blood throughout the body.[53] The human circulatory system is 400,000 miles long, and the magnitude of blood pressure is not uniform in all the blood vessels in the human body. The blood pressure is determined by the diameter, flexibility and the amount of blood being pumped through the blood vessel.[53] Blood pressure is also affected by other factors including exercise, stress level, diet and sleep. The average normal blood pressure in the brachial artery, which is the next direct artery from the aorta after the subclavian artery, is 120mmHg/80mmHg. Blood pressure readings are measured in millimeters of mercury (mmHg) using sphygmomanometer. Two pressures are measured and recorded namely as systolic and diastolic pressures. Systolic pressure reading is the first reading, which represents the maximum exerted pressure on the vessels when the heart contracts, while the diastolic pressure, the second reading, represents the minimum pressure in the vessels when the heart relaxes.[54] Other major arteries have similar levels of blood pressure recordings indicating very low disparities among major arteries. The innominate artery, the average reading is 110/70mmHg, the right subclavian artery averages 120/80 and the abdominal aorta is 110/70mmHg.[55] The relatively uniform pressure in the arteries indicate that these blood vessels act as a pressure reservoir for fluids that are transported within them. Pressure drops gradually as blood flows from the major arteries, through the arterioles, the capillaries until blood is pushed up back into the heart via the venules, the veins through the vena cava with the help of the muscles. At any given pressure drop, the flow rate is determined by the resistance to the blood flow. In the arteries, with the absence of diseases, there is very little or no resistance to blood. The vessel diameter is the most principal determinant to control resistance. Compared to other smaller vessels in the body, the artery has a much bigger diameter (4mm), therefore the resistance is low.[55] In addition, flow rate (Q) is also the product of the cross-sectional area of the vessel and the average velocity (Q = AV). Flow rate is directly proportional to the pressure drop in a tube or in this case a vessel. ∆P ÃŽ ± Q. The relationship is further described by Poisseulle’s equation ∆P = 8 µlQ/Ï€r4.[56] As evident in the Poisseulle’s equation, although flow rate is proportional to the pressure drop, there are other factors of blood vessels that contribute towards the difference in pressure drop in bifurcations of blood vessels. These include viscosity, length of the vessel, and radius of the vessel. Factors that determine the flow’s resistance as described by Poiseuille’s relationship: †¢ ∆P: pressure drop/gradient †¢  µ: viscosity †¢ l: length of tube. In the case of vessels with infinitely long lengths, l is replaced with diameter of the vessel. †¢ Q: flow rate of the blood in the vessel †¢ r: radius of the vessel Assuming steady, laminar flow in the vessel, the blood vessels behavior is similar to that of a pipe. For instance if p1 and p2 are pressures are at the ends of the tube, the pressure drop/gradient is:[57] In the arterioles blood pressure is lower than in the major arteries. This is due to bifurcations, which cause a drop in pressure. The more bifurcations, the higher the total cross-sectional area, therefore the pressure across the surface drops. This is why the arterioles have the highest pressure-drop. The pressure drop of the arterioles is the product of flow rate and resistance: ∆P=Q xresistance. The high resistance observed in the arterioles, which factor largely in the ∆P is a result of a smaller radius of about 30  µm.[58] The smaller the radius of a tube, the larger the resistance to fluid flow. Immediately following the arterioles are the capillaries. Following the logic obvserved in the arterioles, we expect the blood pressure to be lower in the capillaries compared to the arterioles. Since pressure is a function of force per unit area, (P = F/A), the larger the surface area, the lesser the pressure when an external force acts on it. Though the radii of the capillaries are very small, the network of capillaries have the largest surface area in the vascular network. They are known to have the largest surface area (485mm) in the human vascular network. The larger the total cross-sectional area, the lower the mean velocity as well as the pressure.[55] Reynold’s number also affects the blood flow in capillaries. Due to its smaller radius and lowest velocity compared to other vessels, the Reynold’s number at the capillaries is very low, resulting in laminar instead of turbulent flow.[59] The Reynold’s number (denoted NR or Re) is a relationship that helps determine the behavior of a fluid in a tube, in this case blood in the vessel. The equation for this dimensionless relationship is written as:[56] †¢ Ï : density of the blood †¢ v: mean velocity of the blood †¢ L: characteristic dimension of the vessel, in this case diameter †¢ ÃŽ ¼: viscosity of blood The Reynold’s number is directly proportional to the velocity and diameter of the tube. Note that NR is directly proportional to the mean velocity as well as the diameter. A Reynold’s number of less than 2300 is laminar fluid flow, which is characterized by constant flow motion, whereas a value of over 4000, is represented as turbulent flow. Turbulent flow is characterized as chaotic and irregular flow.[56] Disorders Disregulation disorders of blood pressure control include high blood pressure, blood pressure that is too low, and blood pressure that shows excessive or maladaptive fluctuation. High Main article: Hypertension Overview of main complications of persistent high blood pressure. Arterial hypertension can be an indicator of other problems and may have long-term adverse effects. Sometimes it can be an acute problem, for examplehypertensive emergency. All levels of arterial pressure put mechanical stress on the arterial walls. Higher pressures increase heart workload and progression of unhealthy tissue growth (atheroma) that develops within the walls of arteries. The higher the pressure, the more stress that is present and the more atheroma tend to progress and the heart muscle tends to thicken, enlarge and become weaker over time. Persistent hypertension is one of the risk factors for strokes, heart attacks,heart failure and arterial aneurysms, and is the leading cause of chronic renal failure. Even moderate elevation of arterial pressure leads to shortened life expectancy. At severely high pressures, mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.[60] In the past, most attention was paid to diastolic pressure; but nowadays it is recognised that both high systolic pressure and high pulse pressure (the numerical difference between systolic and diastolic pressures) are also risk factors. In some cases, it appears that a decrease in excessive diastolic pressure can actually increase risk, due probably to the increased difference between systolic and diastolic pressures (see the article on pulse pressure). If systolic blood pressure is elevated (>140) with a normal diastolic blood pressure (