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Heart diseases, like any other human disorder, are complex and difficult to understand. Over the years, there is a great range of factors that have been implicated in determining the risk of heart diseases. However, a critical look at the great mass of scientific data, both old and new, together with an outline of the way in which the information is collected and interpreted, answers questions such as why do scientists never seem to agree? This therefore, reveals the complexity of the disorder and the multifarious factors associated with it.
The term heart disease is often used to describe a disease of the hearts blood vessels. These blood vessels are called coronary arteries, and their main function is to supply the heart muscles with vital oxygen and nutrients. Any restriction or block of the coronary arteries indicates coronary heart disease (CHD). In most cases, the condition that blocks the blood and oxygen supply is atherosclerosis, thickening of the artery walls due to buildup of plaque containing cholesterol, fatty material, and cellular debris. Throughout the years, coronary heart disease and its complications have reached epidemic proportions all over the world. CHD accounts for 36% of all deaths in the United States. Similar data have been accounted here in the United Kingdom, since CHD is the leading cause of death, claiming over 170,00 lives every year. A horrid, but remarkable example of the problems range is that in UK in 1989, 168,901 people died from CHD, an average of 460 people per day. That means that by the time you finish reading this essay another person could well have been added to the toll.
After several scientific investigations, researchers have identified and divided the factors relating to CHD into two categories: firstly, to some controllable factors such as: high blood pressure, high blood cholesterol, smoking, obesity, physical inactivity, diabetes and stress. Secondly, to uncontrollable factors, such as: genetics, inheritance, age, and that males are at greater risk at a younger age than women, but women who have passed through menopause have at least the same risk as a man of the same age. Until these days, these are the elements that have been distinguished to be more related to coronary heart diseases.
Over the years, scientists used a number of scientific methods to assess the numerous risk factors relating to coronary heat diseases. Some of the methods produced unambiguous and valuable results, while others projected the opposite.
Morris et al in 1953 using the job classification method assessed physical activity and the possible relation to CHD. They compared the health status of thousands of London bus drivers with that of postal workers. They found that the drivers, sitting all day in the cab, suffered far more heart attacks than the postal workers, whose job involved daily walking. More recently, Paffenbarger and Hale (1975) in San Francisco performed a similar investigation. Their research lasted 22 years, and the major objective was to assess the relationship between work activity and coronary heart mortality on 6,351 longshoremen. According to their findings, longshoremen who involved in heavy work activities had less coronary heart diseases than their workmates who were involved in lighter job activities.
The results from both researches may be significant, but the limitation of the method to assess physical activity makes them scientifically weak, therefore unreliable and inappropriate for epidemiological use. Such limitation initially includes that the variability of physical activity within a job can be large. For example, it is observable that lorry drivers and delivery truck drivers spend distinctly dissimilar amounts of time sitting and unloading. Secondly, job intensity most of the times is estimated differently by individuals. Thirdly, job requirements can change over time. For example in the 1950s the occupation of the longshoremen was hard and sufficiently unhealthy. In our days everything has been mechanized, making the specific occupation more sedentary. Fourthly, a selection bias may exist, as persons with illnesses transfer to less strenuous jobs. Finally, job classification fails to identify the importance of leisure-time physical activities performed by the unemployed or the retired. Based on these limitations it is understandable why job classification methods have not produced a clear pattern concerning the relationship of physical activity and coronary heart disease.
Consequently, since the job classification method was poor to provide reliable results, scientists started to pay more attention on the impact of leisure time of physical activity to the coronary heart disease. Scientists using survey procedures tried to identify the relationship between leisure time physical activity and risks for CHD. Morris et al (1973) using a physical activity diary survey examined 16,882 male British civil servants aged 40-64yrs. they found that 11% of the subjects who performed vigorous exercise, and 26% of the inactive subjects developed CHD. Diary survey is a very accurate method, however it suffers from cost, time, and acceptability constraints. Moreover, the participants may be unwilling to write down all the physical activity they performed throughout the day, or they may alter their normal daily plan, in order to simplify the recording process. Each of these limitations makes this procedure more inaccurate, and therefore less reliable.
Another research based on survey procedures is that performed by Paffenbarger et al in 1978. They examined 16,936 Harvards ex-students from 1916-1950 using survey procedures. They found that low activity groups had 64% higher risk of CHD than active groups. They also added, that those inactive as students, but active in middle age had lower risk than former athletes whose later physical activity level were low. The professional procedure and the extensive duration of the Harvard Alumni study revealed the important role of physical activity on the prevention of CHD. However, for once more, testing procedures was under suspicion. Beginning in 1962, alumni had been sent periodic surveys that requested information on health habits and medical history. Obviously, participants had the opportunity to provide unreal information about their health habits and medical history. Moreover, there was a problem on the assessment of physical activity. Participants had to estimate the number of city blocks walked daily and the number of flights of stairs climbed daily, as well as to list any sport activities in which they had engaged during the past week. The reliability of physical activity procedure was again under suspicion. Firstly, because it was hard to remember and estimate daily activities, and secondly it was very easy to provide just a number, which might be distant from the truth, just to save time. Obviously survey procedures are not always reliable, since reliability of the test is mostly depending on the trustfulness of the participants and lesser on the experimental procedures. The selection of the participants added another limitation factor on the experimental outcome. This selection, limited the tests range of applicability since the experiment only included participants with high educational background and excluded participants of low educated backgrounds.
Throughout the years, several researches have been carried out, assessing factors relating to CHD. Some of these provided essential results, while others presented invalid and unreliable results. For example, Fuller. H. J. et al (1993) examined the mortality from coronary heart disease and stroke in relation to degree of glycaemia. Through this study they confirmed the importance of hypertension as a cardiovascular risk factor in groups with glucose intolerance and diabetes. However the great range of the subjects age (40-64) affected negative the reliability of the test. Gibbons. W. L. et al (1983) examined the association between CHD risk factors and physical fitness in healthy women. Despite the experimental procedure, again the great range of the subjects age (18-65) affected negatively the reliability of the test. An additional factor, which influences the reliability of the experimental outcomes, is the applicability of the test, which was performed on a specific population. For example, Marti B et al (1987) examined the relationship between leisure-time physical activity and risk factors for CHD in middle-age Finnish women. The subjects were from four areas of Finland. Despite the experimental findings, once again the readers first consideration would be how representative is the population for the specific experiment.
Over the years, scientists, through scientific investigations have presented important information concerning the risk factors associated with CHD. However many experimental outcomes are based on poor scientific methods leading to the results being substantially deformed. Moreover, scientists do not only have to deal with the problem of each individual factor but they also have deal with combining of all these different theories concerning the factors of coronary heart disease and then applying them. Consequently, further consideration of old scientific methods, and developments of new assessment techniques are needed in order to obtain reliability maximization, therefore error minimizations.
REFERENCES
American heart association [No date]. Available on line from: http://www.americanheart.org [accessed: 2 December 2001].
British heart foundation (BHF), [No date]. Available on line from: http://www.bhf.org.uk [assessed: 2 December 2001].
Consumer guides (1991). Preventing Heart Disease. 5th edition. London: published by consumers association and Hodder & Stoughton.
Fuller, H. J., et al (1983). Mortality from coronary heart disease and stroke in relation to degree of glycaemia: the Whitehall study. British medical journal. 287, 867-870.
Laporte, E. R., et al (1985). Assessment of physical activity in epidemiologic research: problems and prospects. Public health reports. 100 (2), 131-146.
Marti, B., et al (1987). Relationship between leisure-time physical activity and risk factors for coronary heard disease in middle-aged Finnish women. Acta Med Scand. 222, 223-231
Morris, J. et al. (1973). Vigorous exercise in leisure time and the incidence of coronary heart disease. Lancet 17th Feb. 333-339
Paffenbarger, et al. (1975). Work activity and coronary heart mortality. N Eng J Med. 292, 545-5450.
Paffenbarger, et al. (1978). Physical activity as an index of heart attacks risk in college alumni. Am J Epidemio. 108, 161-178.
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