15 November 2014

Effects of Physical Activity on Cerebrovascular Disease

Effects of Physical Activity on Cerebrovascular Disease

Introduction
Cerebrovascular disease, or stroke, is a devastating illness. A stroke is a type of cardiovascular disease affecting the arteries leading to and within the brain. It occurs when a blood vessel that carries oxygen and nutrients to the brain bursts or is blocked by a blood clot. The result is a loss or impairment of bodily function resulting from the injury or death of brain cells after insufficient blood supply.

There are two types of stroke, ischemic or hemorrhagic. An ischemic stroke accounts for 83% of all cases in the United States (American Heart Association, 2006). This occurs as the result of an obstruction in a blood vessel supplying blood to the brain. The principle condition for an ischemic stroke is atherosclerosis, the development of fatty deposits lining the vessel walls. The fatty deposits themselves can cause two types of obstructions, cerebral thrombosis or cerebral embolism. Cerebral thrombosis refers to the blood clot that develops at the clogged part of the vessel. Cerebral embolism refers to a clot that has formed at a different part of the circulatory system. A portion of the clot breaks loose and travels towards the brain through the bloodstream until the blood vessels become so small that the clot becomes lodged, thus obstructing the flow of blood.

A hemorrhagic stroke is where the blood vessel ruptures, causing blood to leak into the brain. This type of stroke accounts for 17% percent of all stroke cases (AHA, 2006). When the vessel ruptures and leaks into the brain the blood accumulates and compresses the surrounding brain tissue. The rupture is a result of either an aneurysm, a ballooning of a weakened blood vessel, or an arteriovenous malformation, a cluster of abnormally formed blood vessels.

Over 273,000 people died from a stroke in the United States in 2003 (AHA, 2006). Cerebrovascular disease kills about 4.4 million people worldwide (Dishman, Washburn, and Heath, 2004). A greater number of women than men die from stroke accounting for 61% of all United States stroke deaths in 2003 (AHA, 2006). Stroke is the leading cause of serious, long-term disability in the United States (AHA, 2006). The estimated cost of stroke for 2006 is $57.9 billion (AHA, 2006).

Stroke has a destructive impact in the United States due to loss of life, loss or impairment of function, and a national economic loss. Identifying risk factors for stroke and taking action to reduce the prevalence of those risk factors in the population will save many lives and the financial savings could be in the billions.

Review of Literature
Surgeon General’s Report: Physical Activity and Health, 1996
In 1996 the Office of the Surgeon General addressed physical activity and health. The main message of the report was that Americans can greatly improve their health and quality of life by including moderate amounts of physical activity in their daily lives. As it relates to cardiovascular disease the report found that regular physical activity or cardiorespiratory fitness decreases the risk of cardiovascular disease mortality. However, the report found inconclusive data regarding a relationship between physical activity and stroke. It indirectly reported that physical activity reduces some of the risk factors for stroke, such as hypertension and atherosclerosis. At the time, stroke was the third leading cause of death in the United States (US Department of Health and Human Services, 1996). The report identified stroke as a major cardiovascular problem in developed countries.

The report found atherosclerosis of the extracranial and intracranial arteries to be the underlying basis of ischemic stroke, hypertension to be a major risk factor for ischemic stroke, and hypertension to be a major determinant of hemorrhagic stroke. The report wrote that physical activity may not affect ischemic and hemorrhagic stroke in the same way because of different pathophysiologies (US DHHS, 1996). In one study cited, inactive men were more likely than active men to have a hemorrhagic stroke and physical activity was associated with a lower risk of ischemic stroke in smokers but not in nonsmokers.

As it relates to hypertension, a risk factor for stroke, it is estimated that those least physically active have a 30 percent greater risk of developing hypertension than their most active counterparts (US DHHS, 1996). Endurance training reduces thrombosis by enhancing the enzymatic breakdown of blood clots and by decreasing platelet adhesiveness and aggregation (US DHHS, 1996). Despite the evidence that an increase in physical activity reduced hypertension and thrombosis, the Surgeon General’s report found no conclusive evidence that physical activity plays a protective role against stroke.

Risk Factors and Mortality in Men and Women in Scotland
The aim of the study was to relate risk factors in middle-aged men and women to stroke mortality over a long follow-up period. This study found that women’s stroke mortality rates were similar to men’s. The study concluded that control of risk factors for reduction of stroke mortality should be targeted at men and women in a similar fashion, particularly with blood pressure control (Hart, Hole, and Smith, 1999).

The study identified hypertension, cardiac disease, age, smoking, and diabetes as major risk factors for stroke. The study population contained men and women, aged 45 to 64 years, in west Scotland. The study found a positive relationship between systolic blood pressure and stroke mortality in both men and women. The stroke mortality rate was approximately 3 times that for men and women in the highest quintile of blood pressure than in the lowest (Hart, et al. 1999).

The study concluded that elevated systolic and diastolic blood pressure were both highly significantly associated with stroke mortality. The study found no relationship between cholesterol and stroke mortality. The study found diabetics had 3 times the risk for stroke than non diabetics (Hart, et al. 1999).

Physical activity is known to reduce blood pressure and could thus reduce the risk for stroke by lowering blood pressure (US DHHS, 1996). Physical activity also reduces the risk for diabetes and therefore contributes to the reduction in risk for stroke (US DHHS, 1996).

Leisure-Time Physical Activity and Risk for Stroke in Men
The objective of this study was to examine the association of leisure time physical activity and pulmonary function with the risk for stroke. The participants in this stuffy were 4484 men aged 45 to 80 years followed for a mean of 10.6 years (Agnarsson, Thorgeirsson, Sigvaldason, and Sigfusson, 1999). The principle findings of the study is that regular continued leisure-time physical activity in middle-aged men offers an apparent protective effect on diminished pulmonary function and on the risk for ischemic stroke. The greatest benefit seemed to be associated with low intensity sports, such as walking or swimming (Agnarsson, et al. 1999). The important factor associated with the protective effect seems to be regular physical activity maintained into ages at which the risk for stroke increases.

The study indicated that physical activity has complex physiologic effects. The study implies that physical activity causes favorable changes in the lipoprotein profile and may reduce potential for thrombosis through enhanced fibrinolytic activity and reduced platelet adhesiveness. The study reports that physical inactivity may be a reason for the increase in stroke mortality in the United States. The study acknowledges a limitation in the specific nature of the inquiry about the level of physical activity in its participants. The study concludes that in men, regular leisure-time physical activity maintained after 40 years age may protect against ischemic stroke.

Physical Activity and Stroke Mortality in Women
This study was conducted to examine the association between different levels of leisure-time physical activity and stroke mortality in women aged greater than or equal to 50 years. The study looked at 14,101 women that participated in the Nord-Trondelag Health Survey in Norway during 1984 – 1986. The study concluded that physical activity was associated with reduced risk of death from stroke in middle aged and elderly women. The study recommends that physical activity should be the primary prevention strategy against stroke in women.

The information was obtained by questionnaires and clinical measurements included in a screening program. Activity among women that exercised less than once per week was classified as low activity; once or several times per week at a moderate intensity was classified as medium activity; and several times per week at a higher intensity was classified as high activity.

The study found that women with a high level of physical activity tended to be younger, leaner, and had lower systolic blood pressure than less active women. The prevalence of coronary heart disease, diabetes, and use of antihypertensive medication decreased with increasing physical activity. In groups aged 50 to 69 and 70 to 79 years, the most active women had an adjusted relative risk of 0.39 and 0.48, respectively (Ellekjær, Holmen, Ellekjær, and Vatten, 2000). In the group aged 80 to 101 years, the most active women had an adjusted relative risk of 0.50 but the study found that it was not statistically significant (Ellekjær, et al. 2000). The overall multivariate-adjusted relative risk was 0.54 (Ellekjær, et al. 2000).

The study also found that women in the least active category were more likely to report ill health and prevalent disease. The study demonstrated a consistent, negative association between levels of physical activity and stroke mortality in women. When compared with inactive women, the most active had almost a 50% lower risk of stroke. The study reported that the negative association between physical activity and stroke mortality may be mediated by decelerating the atherosclerotic process, modifying the structure of arteries, reducing vasospasm, enhancing myocardial electrical stability, or increasing fibrinolysis (Ellekjær, et al. 2000).

This study found evidence to strongly suggest that higher intensity leisure-time activity is a protective measure against stroke in women aged 50 years and greater.

Incidence of Ischemic Stroke in African American and White Men and Women
The purpose of this study was to find an association between white blood cell, WBC, count and incidence of ischemic stroke and mortality in 13,555 African American and White men and women (Lee, Folsom, Nieto, Chambless, Shahar, and Wolfe, 2001). An elevated WBC count is a risk factor for atherosclerotic vascular disease. WBC – derived macrophages and other phagocytes are believed to contribute to vascular injury and atherosclerotic progression. According to the study WBC count is inversely associated with physical activity, high density lipoprotein cholesterol, and family income. The major finding of the study is that elevated WBC count is directly associated with risk of coronary heart disease and stroke incidence and mortality from cardiovascular disease in African Americans.

Since elevated WBC count is a risk factor for ischemic stroke and WBC count is inversely associated with physical activity this study possibly shows that physical activity has an indirect effect on the prevention of ischemic stroke by lowering WBC count.

Physical Activity and Stroke, A Meta-Analysis
The purpose of this study was to examine the overall association between physical activity or cardiorespiratory fitness and stroke incidence of mortality. This study maintains that hypertension and cardiac disease are the primary risk factors for stroke and that physical activity may modify these risk factors and may have more direct effects to lower stroke risk. The study reported that overall, highly active individuals had a 27% lower risk of stroke incidence or mortality than did low active individuals (Lee, Folsom, and Blair, 2003). The study also reported that overall, moderately active individuals had a 20% lower risk of stroke incidence or mortality than did low active individuals (Lee, et al. 2003).

The study concluded, stating that the major finding was that moderately or highly active individuals had a lower risk of stroke incidence or mortality than did low active individuals. Moderately or highly active individuals reduced their risk by 20% and 27%, respectively. The study maintained that physical activity probably reduced stroke risk. The study said that since physical activity questionnaires tend to be imprecise it was possible to have a large measurement error and therefore the relative risk estimates may not be accurate because definitions of low, moderate, and high intensity activity varied widely among the studies reviewed in the analysis.

The study continues by discussing the plausibility that physical activity may decrease stroke risk by reducing hypertension, atherosclerosis, improving blood lipid profiles, and reduces blood viscosity, fibrinogen levels, and platelet aggregability and by enhancing fibrinolysis (Lee, et al. 2003). The study found a distinctive risk reduction caused by physical activity but due to possible errors in physical activity reporting could not claim with supreme confidence that physical activity reduces stroke risk.

Risk of Stroke in Elderly Men
The study examined the relation between high density lipoprotein cholesterol levels and the risk of thromboembolic and hemorrhagic stroke in elderly men. The study found that low concentrations of HDL cholesterol, less than 40 milligrams per deciliter, were more likely to be associated with a future risk of thromboembolic stroke than were high concentrations, greater than or equal to 60 milligrams per deciliter (Curb, Abbot, Rodriguez, Masaki, Chen, Popper, Petrovich, Ross, Schatz, Belleau, and Yano, 2004). The study suggests that stroke risk increases with each unit decline in HDL cholesterol level.

The study identified low concentrations of HDL cholesterol to be a risk factor for stroke. Exercise raises HDL levels (US DHHS, 1996). It is therefore possible that physical activity reduces the risk for stroke indirectly by raising HDL levels in elderly men.

Risk Factors for Stroke
This study compared different risk factors for coronary heart disease, stroke, and venous thromboembolism. The results of the study indicated that those that exercised had a relative risk of 0.94 for stroke (Glynn and Rosner, 2005). The study reported that more frequent exercise was associated with decreased risk of coronary heart disease and stroke. The study was limited by its reliance on self reported information for physical activity. The results that this study published indicated a weak correlation with physical activity and risk for stroke.

Metabolic Syndrome and Risk of Stroke
This study examined the relationship of metabolic syndrome with the risk of stroke. The metabolic syndrome is a clustering of disturbed glucose and insulin metabolism, obesity and abdominal fat distribution, dyslipidemia, and hypertension. The study found that metabolic syndrome is a risk factor for stroke through other risk factors, such as hypertension and atherosclerosis. The study urges that early identification, treatment, and ultimately prevention of the metabolic syndrome present a major challenge for health care professionals. Physical activity reduces hypertension, obesity, dyslipidemia, and abdominal fat distribution. This study suggests that physical activity indirectly reduces the risk for metabolic syndrome by reducing the risk and therefore reduces the risk for stroke.

Conclusion
After reviewing some of the literature pertaining to stroke the evidence strongly suggests that physical activity is a preventative measure against stroke. This is biologically plausible. Physical activity reduces blood pressure, reduces atherosclerosis, reduces the risk for diabetes, and increases HDL cholesterol; elevated blood pressure, atherosclerosis, diabetes, and low HDL cholesterol levels are all risk factors for stroke.

Four of the nine articles reviewed did not find sufficient evidence to claim that physical activity is a preventative tool against stroke. One article found that physical activity reduces stroke risk by reducing blood pressure. One article found that physical activity reduces stroke risk by reducing the risk of diabetes. Two articles reviewed strongly recommended physical activity as a preventative measure against stroke. One article suggested that physical activity reduced the risk for stroke by reducing WBC count. One article suggested that physical activity reduced the risk for stroke by raising HDL cholesterol levels.

All of the articles did not conclusively suggest that physical activity can be used as a tool to reduce the risk for stroke; however, all of the articles did show that physical activity could reduce the risk for stroke directly or indirectly by limiting the risk factors associated with stroke. Ultimately, this review will conclude that physical activity does have some preventive effect on the risk for cerebrovascular disease by reducing several of the major risk factors for stroke.

References
Agnarsson, U., Thorgeirsson, G., Sigvaldason, H., and Sigfusson, N. (1999). Effects of Leisure-Time Physical Activity and Ventilatory Function on Risk for Stroke in Men: The Reykjavík Study. Annals of Internal Medicine. Volume 130. 987 – 990.

American Heart Association. (2006). Heart Disease and Stroke Statistics – 2006 Update. Retrieved April 9, 2006 from American Heart Association Web site: http://circ.ahajournals.org/cgi/content/short/113/6/e85#SEC5

Curb, J. D., Abbott, R. D., Rodriguez, B. L., Masaki, K. H., Chen, R., Popper, J. S., Petrovich, H., Ross, G. W., Schatz, I. J., Belleau, G. C., Yano, K. (2004). High Density Lipoprotein Cholesterol and the Risk of Stroke in Elderly Men: The Honolulu Heart Program. American Journal of Epidemiology. Volume 160. 150 – 157.

Dishman, R. K., Washburn, R. A., & Heath, G. W. (2004). Physical Activity Epidemiology. Champaign, IL: Human Kinetics

Ellekjær, H., Holmen, J., Ellekjær, E., Vatten, L. (2000). Physical Activity and Stroke Mortality Women: Ten-Year Follow-Up of the NordTrondelag Health Survey, 1984 – 1986. Stroke. Volume 31. 14

Glynn, R. J., Rosner, B. (2005). Comparison of Risk Factors for the Competing Risks of Coronary Heart Disease, Stroke, and Venous Thromboembolism. American Journal of Epidemiology. Volume 162. 975 – 982.

Hart, C. L., Hole, D. J., and Smith, G. D. (1999). Risk Factors and 20-Year Stroke Mortality in Men and Women in the Renfrew/Paisley Study in Scotland. Stroke. Volume 30. 1999-2007.

Kurl, S., Laukkanen, J. A., Niskanen, L., Laaksonen, D., Sivenius, J., Nyyssönen, K., Salonen, J. T. (2006). Metabolic Syndrome and the Risk of Stroke in Middle-Aged Men. Stroke. Volume 37. 806 – 811.

Lee, C. D., Folsom, A. R., Blair, S. N. (2003). Physical Activity and Stroke: A Meta-Analysis. Stroke. Volume 34. 2475 - 2482

Lee, C. D., Folsom, A. R., Nieto, F. J., Chambless, L. E., Shahar, E., Wolfe, D. A. (2001). White Blood Cell Count and Incidence of Coronary Heart Disease and Ischemic Stroke and Mortality from Cardiovascular Disease in African American and White Men and Women. American Journal of Epidemiology. Volume 154. 758 – 764.

US Department of Health and Human Services. (1996). Physical Activity and Health: A Report of the Surgeon General. US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion. Atlanta, GA.

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