Examining the Relationship of Cardiovascular Disease and Activity Levels - Coursework Example

Cardiovascular disease is the main cause of morbidity and mortality in the western world today. It is a complex disease with a multi factorial etiology and wide effect on other aspects of health. Of the many risk factors for cardiovascular disease which include genetic predisposition, diet, contributory habits such as smoking,hypertension, activity level is one of the most touted because much current evidence indicates that increasing activity levels will reduce the risk of cardiovascular disease. This paper will review some of the avenues of research that have been pursued examining the relationship of cardiovascular disease and activity levels. In particular it will focus on 8 studies that examine the question of the relationship between activity levels and cardiovascular disease from a variety of perspectives in order to present the multi factorial nature of this relationship. The first study is a good study in which to first approach the subject of cardiovascular disease and its relationship with activity. This study, was a large prospective observational study of 72,488 nurses who ranged in age from 40 to 65 years of age over an 8 year period between 1986 and 1994. This was a most useful study because at the time of its inception there was little research addressing this question. This study established some key groundwork with its size and sophisticated statistical accounting of possible confounding variables. This study selected subjects on the basis of exclusion of other confounding co morbidities. Levels of activity were assessed through self evaluations of how much physical activity was performed per week. This study relied heavily on self evaluations filled out by the subjects over the trial period and therefore suffered from the inherent weaknesses of subjectivity that comes with such assesments. The weakness of self-evaluations were offset by the size of the study and the use of meta-analysis to account for all the possible confounder s. The endpoint was in keeping with the broad nature of the study not a discrete variable but on the basis of admission to hospital for CHD. The results of this study were supportive of the positive relation that increased activity level has on the improvement of cardiovascular disease. As the authors stated “These prospective data from a large cohort of women indicate that both walking and vigorous activity are associated with substantial reductions in the incidence of coronary events.”( p.656 Manson). As well as laying the groundwork for much subsequent research this study also raised the other question on whether the intensity of exercise has any bearing on the the prevention of Coronary Heart Disease(CHD). The results were supportive of all exercise having benefits providing it was of equal energy units, as the authors state “We observed in this cohort, the magnitudes of risk reduction associated with brisk walking and vigorous exercise were similar when total energy expenditures were similar.”(p.656 Manson) This study was a suitable starting point to sponsor new lines of research in the relationship between activity levels and exercise but clearly more work needed to follow to deal with some of the finer points of the relationship. The question was more sharply defined in the next study. This second paper Changes in Cardiorespiratory fitness and Coronary heart disease risk factors following 24 weeks of moderate or high-intensity exercise of equal energy cost by Gary Donovan et al raises the question of whether the intensity level of the exercise has any effect on improving the markers for cardiovascular disease. This study took 64 subjects between the ages of 30 -45 who were screened on the basis of a self evaluation on the basis of abstinence of smoking for at least 2 years and a sedentary lifestyle. These subjects were then assigned to the trial groups or to controls on a random basis as per the randomly controlled trial nature of the experiment. Two groups of 22 received exercise of equal caloric value for 24 weeks and the same in other ways except the intensity level. One group received exercise at a V02 maximum, of 40 % and the other at 80 % of V02 max. The V02 max measures the maximum flow of oxygen that can be used by the subject and it is a good measure of exercise tolerance. Twenty individuals were assigned to the control group Other measures were monitored by physicians as risk factors for cardiovascular studies, notably non HDL cholesterol levels and fibringogen . This study challenged the current assertion of the American College of sports Medicine that activity of any lower intensity was as beneficial in reducing cardiovascular disease risk as higher intensity activity. The results of this study showed a significant difference in non-HDL cholesterol and V02 max between the high intensity exercise group and controls but not in the moderate intensity exercise group and controls. This study appears to be good start to investigation of the question of intensity of exercise and CHD. It was elegantly designed to restrict the question to intensity by keeping the caloric use in both groups the same. Limitations of the study and the reason it should be considered a first foray into the question is that it regarded a small sample of individuals. A larger prospective randomized control trial with a similar design would do much to clarify this area and further challenge the conventional wisdom that intensity of exercise is independent of cardiovascular benefit. Another study approached the question of the relationship between cardiovascular disease and activity levels from a more long term basis. The long-term effect of physical activity on the incidence of coronary heart disease: A 12 year follow-up study by Kristina Sundquist et al. This was a 12 year follow-up study of 7090 individuals starting from 1988 to the year 2000. The cohort of individuals chosen for this study were admitted into the study on the basis of interviews with researchers that screened and eliminated those individuals with bad health that would confound the research question . Subjects ranged in age from 35 to 74 and were stratified according to age and also classified on smoking status ( ex-smokers, present smokers) and Body Mass Index ( three groups, from underweight, normal weight to overweight) and activity levels, that described a range from little activity to very physically active. Measurement of cardiovascular disease was clearly defined as the first time of admission to hospital for any type of problem related to CHD. This study used a Cox Regression model of hazard analysis and showed some significant findings in support of the relationship between cardiovascular disease and inactivity. As the study showed when the analysis corrected for age and sex “There was an apparent link between leisure-time physical activity and CHD risk; when the amount of physical activity was increased, the risk of CHD decreased sharply.” ( p. 4 Sundquist ) This risk was as much as a “54% decrease “from those who did no activity. This was another useful study that confirmed the positive benefits of activity in preventing CHD. The sample was large and the duration of the study was sufficient as to allow the tracking of potential complications of CHD which do not present typically in an acute fashion. The authors of the study admit to the weakness of the use of evaluations in choosing subjects but since this cannot be avoided it was perhaps a moot point. This study unlike the previous study had only coarse definition of the outcome in terms of an event worthy of admission to hospital. Such criteria is not necessarily informative about the potential problems of CHD as they develop. A fourth study examined the question of how activity levels effect an aspect of cardiovascular disease that is is less studied: the relationship of activity levels and the the progress of peripheral arterial disease, P.A.D. Peripheral Arterial Disease occurs through the same mechanism as coronary heart disease but manifests with pain and claudication of distal limbs because of the atherosclerotic process. The study , Physical Performance in Peripheral Arterial Disease: A Slower Rate of Decline in Patients Who Walk More by Mary McGrae McDermot et al was intended as initial foray into the question to provoke further stronger Randomized Control Studies in the field. This was a 36 month observational cohort study of 417 patients with established P.A.D who were evaluated by means of the the number of experiences of blocks that they had in a week. Patients were observed in terms of three categories: those that exercised three times a week; those that exercise less than three times a week and those that did not exercise at all. This found that when all the confounding variables were accounted for, those patients that walked three times or more per week showed a slower progression of P.A.D than those patients that exercised at less than that intensity, or not at all. Of all the studies examined so far this was the weakest in terms of design since it relied a good deal on self reporting of symptoms, did not have well established controls; but it was intended as a prelude to further studies and therefore it served its purpose by suggesting that there was some evidence of a relationship between the progression of P.A.D and lack of activity. In fact, this study did seem to recommend that those patients that did not undertake any activity stood to gain the most from an increased pattern of physical activity. The fifth study examined the defects of activity on a different but equally contributory factor cardiovascular disease: Hypertension. The study, The Beneficial Effect of Regular Endurance Training on Blood Pressure and Quality of Life in Patients with Hypertension Jen-Chen Tsai et al was a randomized control trial where 120 subjects with moderate hypertension ( defined as a systolic reading over 140 and up to 180 or a diastolic reading over 90 and up to 110 mm Hg) were randomly assigned to either an exercise group that participated in an exercise regimen of 3 moderate aerobic exercise sessions per week for 10 weeks or were placed in a control group that did not participate in any regular exercise program. Subjects ranged in age from 20 to 60 and were screened so that there were not other co morbidities that would confound the area of study. This study built on previous research that indicates that cardiovascular exercise produces a significant reduction in hypertension levels. This study did not refute those earlier studies. The outcomes of the study were achieved by using repeated measures of the blood pressure over the course of the 10 week trial and with a survey known as the Health Related Quality of Life Survey (HRQOL). The results were significant:”The present data showed that endurance exercise training improved exercise capacity, HQORL and induced a significant reduction in blood pressure of hypertensive patients.”( p.62 Tsai) This study had some clear flaws that the researcher's openly admitted. The sample size was small and it was further skewed by the withdrawal of 18 subjects which reduced the sample further to 102. Errors of measurement were discussed such as the possibility of the “white coat effect” of the observed phenomena of subjects blood pressures being effected by the interaction with a medical professional. This particular study did not push the area of inquiry further but it did add some validity to the contention that cardiovascular exercise had a definite benefit in reducing blood pressure in patients with moderate hypertension. While the previous study reaffirmed previous work on the relationship between hypertension and activity levels the next study addressed the change in a very specific marker in hypertensive patients that engaged in higher activity levels. The study, Daily Aerobic Exercise Improves Reactive Hyperemia in Patients with Essential Hypertension by Yukihito Higashi et al examined hyperemia in the forearm of test subject because this was directly proportional to the activity of Endothelial Relaxing Factor and therefore a useful measure of this substance. This was an ingenious study since it looked at subjects with essential hypertension which is elevated blood pressure( over systolic 160or diastolic 95) without a primary cause and therefore any increase in this substance with a trial of exercise would be also be related in theory to a reduction of blood pressure. This study looked at one group that underwent a 12 week trial of exercise 5 to 7 times a week of 30 minute walks compared with another control group that did not undergo any systematic form of activity. The groups were randomly assigned from a subject pool of 27 and there were also 17 normotensive subject that also served as controls ( normotensive defined as below systolic blood pressure of 140 and diastolic of 90). This study followed research with animal subjects that showed that lack of Endothelial Releasing Factor played a role in in essential hypertension. The results of the study showed that there was indeed a statistically significant increase in Reactive Hyperemia ( measured by increased forearm blood flow (FBF) ) in the subjects that had undergone the the 12 week exercise trial but no change was noted in either the hypertensive or normotensive controls. Other variables were also measured during this experiment and it was noted there was a association between increased FBF and decreased LDL cholesterol levels. The conclusions of the study suggest a multi factorial cause to the the increased Reactive Hyperemia brought on by exercise and perhaps related to the reduction of LDL cholesterol which therefore removes the block on formation of Nitrous Oxide (NO) which is thought to be the causative factor in the changes. This study was flawed by the small sample size and the the uneven division of the hypertensive subjects ( 20) and the hypertensive controls ( 7). The exercise was not as precisely defined as in the earlier study described in this paper. This trial was the first to follow the test s of a similar nature done with animals and it did start the field of inquiry. In all it was otherwise an excellent experiment that broached the subject of cardiovascular disease and activity levels in a novel way. An often overlooked but vitally important aspect of the activity and cardiovascular disease question was raised by the paper, Relationship between Adolescent Fitness and Fatness and Cardiovascular Disease Risk Factors in Adulthood: The Aerobics Center Longitudinal Study ( ACLS) by Joey C. Eisenmann et al. This is a small study that grew out of a very large prospective study going on since 1970 involving 65, 000 subjects. This was the first study branched of that large study that looked at the question of how adolescent fatness levels manifested in adult presentations of cardiovascular disease. Despite the large size of the parent study this was a small study involving 48 subjects that were seen in the ACLS as adolescents with mean age of 15.8 and then again followed up as adults with a mean age of 26.6. Objective measurements were made of percentage body fat, waist circumference, Body Mass Index, a treadmill test of fitness and the the typical serum markers for cardiovascular disease such as Lipids fractions and blood glucose. The results did show that adolescent obesity levels were predictors of adult obesity but they were equivocal about the effects of adolescent obesity and adult cardiovascular disease. This study was weakened significantly by its small sample size and lack of stratification of data in terms of sex. Cardiovascular disease is a problem that develops over large time intervals which could not be demonstrated in this study were the subjects were measured in young adulthood when the problems of cardiovascular disease are less likely to to be symptomatic. Again this study was intended by its authors to be a starting point as they too recommended more research in this area, especially as the problem of childhood obesity is on the rise. The last study to be examined addresses the question of activity level and cardiovascular disease among women in China. The study, Physical Activity, Diet and Cardiovascular Disease Risks in Chinese Women by Jing Ma et al looked at subject pool of 720 Chinese women who were typically screened to rule out other comorbidity and ranging in age from 35 to 65. This was a prospective study that relied on a self evaluation questionare of activity levels and along with measurement of anthropometric details also on the the traditional markers for cardiovascular disease such as serum lipid fractions but with the addition of the Apo B levels and certain antioxidants. The measurements of Apo B levels and antioxidant levels distinguishes this study from some of the others that have been examined since it these factors give a more precise measurement of the progression of cardiovascular disease. This more precise measurement also entails a more immediate assessment of the the benefits of activity levels by measuring the changes in these same markers. This study interestingly found that moderate exercise had the greatest benefit by increasing beneficial antioxidant levels, improving blood lipid levels, notably Apo B and HDL cholesterol as well as increasing insulin sensitivity. This study used an excellent set of end outcome variable but it was hampered by the errors of measurement that can occur from self assessments of activity levels. This study would be an excellent prelude to randomized controlled trials that used similarly sensitive end outcome factors. These eight studies provide an interesting picture of the complexity of the relationship between cardiovascular disease and activity levels. The difficulties in designing studies to examine the question in a focused way are presented here but also a sense of the evolving and cooperative nature of research as each study adds to our understanding of the relationship between activity levels and cardiovascular disease. References Changes in Cardiorespiratory fitness and Coronary heart disease risk factors following 24 weeks of moderate or high-intensity exercise of equal energy cost by Gary Donovan et al Relationship between Adolescent Fitness and Fatness and Cardiovascular Disease Risk Factors in Adulthood: The Aerobics Center Longitudinal Study ( ACLS) by Joey C. Eisenmann et al. Daily Aerobic Exercise Improves Reactive Hyperemia in Patients with Essential Hypertension by Yukihito Higashi et al A Prospective Study of Walking as Compared with Vigorous Exercise in the Prevention of Coronary Heart Disease in Women by JoAnn E. Manson et al Physical Performance in Peripheral Arterial Disease: A Slower Rate of Decline in Patients Who Walk More by Mary McGrae McDermot et al The long-term effect of physical activity on the incidence of coronary heart disease: A 12 year follow-up study by Kristina Sundquist et al. The Beneficial Effect of Regular Endurance Training on Blood Pressure and Quality of Life in Patients with Hypertension Jen-Chen Tsai et al Physical Activity, Diet and Cardiovascular Disease Risks in Chinese Women by Jing Ma et al Read More