Blood pressure and cardiovascular disease: Tracing the steps from Framingham
This study examines the risk of cardiovascular disease associated with incremental increases in blood pressure, elucidates the key markers of cardiovascular risk, and refutes several existing misconceptions about the effects of high blood pressure...
Title: Blood pressure and cardiovascular disease: Tracing the steps from Framingham
Authors: F Turnbull, A Kengne, S MacMahon
Reference: Progress in Cardiovascular Diseases 2010; 53: 39-44 (open access on ProCor)
http://www.procor.org/news/news_show.htm?doc_id=1305731
Location of study: Camperdown, Australia
Summarized by: Vikram Rangan, third year medical student, Duke University School of Medicine, Durham, North Carolina, USA
Summary: This article discusses the key findings and implications of the Framingham Study, a landmark cohort study of cardiovascular risk performed during the 1960s. Launched in 1949, this study followed 5209 subjects initially aged 30-59 years. Blood pressure readings for each subject were taken at two year intervals for a period of 14 years. Incidence of cardiovascular disease in this population was tracked during this time, and an association between elevated blood pressure and cardiovascular disease was probed. The Framingham study offered several improvements over similar prior studies, such as standardized protocols for measuring blood pressure, regular follow-up at two year intervals (after a full decade, only 2% of subjects in the study were reported as being "lost to follow-up"), and recruitment of female subjects. The study played an important role in quantifying the risk of cardiovascular disease associated with incremental increases in blood pressure, and also helped dispel several existing misconceptions about the effects of high blood pressure.
The first key finding from the study was that both systolic blood pressure (SBP) and diastolic blood pressure (DBP) are key markers of cardiovascular risk. Both were significantly elevated in patients who died over the course of the study, and elevations in SBP and DBP were also associated with physical manifestations of coronary heart disease, such as angina (chest pain resulting from insufficient blood perfusing the myocardium), myocardial infarction, and sudden death. The authors found that systolic, rather than diastolic blood pressure was more strongly associated with these manifestations. This set of findings refuted the existing consensus view that DBP was a more important risk factor than SBP for cardiovascular disease, and that elevated SBP was not a concerning finding in patients with normal DBP. A similar relationship between elevated blood pressure and increased stroke risk was also elucidated by the Framingham study. The authors note a recent collaboration of 61 studies indicating that a 10 mmHg reduction in SBP or a 5 mmHg reduction DBP is associated with a 40% reduced risk of stroke death, and a 30% reduced risk of ischemic heart disease death.
A second landmark finding was that the increase in cardiovascular risk with increased blood pressure was present in several groups of individuals to whom this relationship was previously thought not to apply. First, decreased blood pressure was associated with lower cardiovascular risk throughout the continuum of recorded blood pressure values. Even for subjects whose blood pressures did not qualify as "hypertensive," elevated blood pressures were still associated with increased cardiovascular risk. This finding indicated that superior blood pressure control would benefit not only individuals with elevated blood pressure, but also individuals with normal (or nearly normal) blood pressure at baseline. Second, the inclusion of women in the study allowed researchers to discover that the association between high blood pressure and cardiovascular risk was present in both men and women. This finding refuted the existing consensus that high blood pressure was less harmful in women. Finally, this relationship remained constant in different age groups as well. This once again refuted the existing consensus that elevated blood pressure was an innocuous finding in elderly individuals.
The authors also note that during the 1980s, data from this study was used to theorize that very low diastolic blood pressures may be associated with an increased risk of coronary events, in effect creating a "U shaped" or "J-shaped" relationship between DBP and cardiovascular risk (i.e., increased cardiovascular risk at very low and very high DBPs). They note, however, that no evidence of a "U-shaped" relationship was found after a combined dataset of 420,000 individuals (consisting of subjects from the Framingham study and eight others) was built and analyzed. The authors suggest that the initial findings of a "U-shaped" relationship in the Framingham data was a result of blood pressure lowering therapy being used more frequently in individuals with known cardiovascular risk factors. Thus, these individuals were found to have lower average DBP, though there was no causative relationship between their low DBP values and cardiovascular disease. Indeed, the authors note a study demonstrating that in low-risk subjects without cardiovascular risk factors, lower DBPs were associated with lower cardiovascular risk, as the initial findings from the Framingham study suggested.
The authors highlight the worldwide impact of high blood pressure, noting that it is associated with 54% of all cases of stroke and 47% of all cases of ischemic heart disease, leading to 7.6 million premature deaths each year. The number of individuals worldwide with high blood pressure is also expected to rise from one quarter currently to 29% by 2025. The authors conclude, however, by noting that other risk factors play a major role in mediating cardiovascular risk as well. Among hypertensive men and women, the vast majority of coronary events occur in those with other risk factors (such as diabetes and dyslipidemia) compounding the risk already present due to high blood pressure. Thus, patients requiring blood pressure therapy should not be identified based solely on their blood pressure, but rather based on their overall cardiovascular risk profile.
Title: Blood pressure and cardiovascular disease: Tracing the steps from Framingham
Authors: F Turnbull, A Kengne, S MacMahon
Reference: Progress in Cardiovascular Diseases 2010; 53: 39-44 (open access on ProCor)
http://www.procor.org/news/news_show.htm?doc_id=1305731
Location of study: Camperdown, Australia
Summarized by: Vikram Rangan, third year medical student, Duke University School of Medicine, Durham, North Carolina, USA
Summary: This article discusses the key findings and implications of the Framingham Study, a landmark cohort study of cardiovascular risk performed during the 1960s. Launched in 1949, this study followed 5209 subjects initially aged 30-59 years. Blood pressure readings for each subject were taken at two year intervals for a period of 14 years. Incidence of cardiovascular disease in this population was tracked during this time, and an association between elevated blood pressure and cardiovascular disease was probed. The Framingham study offered several improvements over similar prior studies, such as standardized protocols for measuring blood pressure, regular follow-up at two year intervals (after a full decade, only 2% of subjects in the study were reported as being "lost to follow-up"), and recruitment of female subjects. The study played an important role in quantifying the risk of cardiovascular disease associated with incremental increases in blood pressure, and also helped dispel several existing misconceptions about the effects of high blood pressure.
The first key finding from the study was that both systolic blood pressure (SBP) and diastolic blood pressure (DBP) are key markers of cardiovascular risk. Both were significantly elevated in patients who died over the course of the study, and elevations in SBP and DBP were also associated with physical manifestations of coronary heart disease, such as angina (chest pain resulting from insufficient blood perfusing the myocardium), myocardial infarction, and sudden death. The authors found that systolic, rather than diastolic blood pressure was more strongly associated with these manifestations. This set of findings refuted the existing consensus view that DBP was a more important risk factor than SBP for cardiovascular disease, and that elevated SBP was not a concerning finding in patients with normal DBP. A similar relationship between elevated blood pressure and increased stroke risk was also elucidated by the Framingham study. The authors note a recent collaboration of 61 studies indicating that a 10 mmHg reduction in SBP or a 5 mmHg reduction DBP is associated with a 40% reduced risk of stroke death, and a 30% reduced risk of ischemic heart disease death.
A second landmark finding was that the increase in cardiovascular risk with increased blood pressure was present in several groups of individuals to whom this relationship was previously thought not to apply. First, decreased blood pressure was associated with lower cardiovascular risk throughout the continuum of recorded blood pressure values. Even for subjects whose blood pressures did not qualify as "hypertensive," elevated blood pressures were still associated with increased cardiovascular risk. This finding indicated that superior blood pressure control would benefit not only individuals with elevated blood pressure, but also individuals with normal (or nearly normal) blood pressure at baseline. Second, the inclusion of women in the study allowed researchers to discover that the association between high blood pressure and cardiovascular risk was present in both men and women. This finding refuted the existing consensus that high blood pressure was less harmful in women. Finally, this relationship remained constant in different age groups as well. This once again refuted the existing consensus that elevated blood pressure was an innocuous finding in elderly individuals.
The authors also note that during the 1980s, data from this study was used to theorize that very low diastolic blood pressures may be associated with an increased risk of coronary events, in effect creating a "U shaped" or "J-shaped" relationship between DBP and cardiovascular risk (i.e., increased cardiovascular risk at very low and very high DBPs). They note, however, that no evidence of a "U-shaped" relationship was found after a combined dataset of 420,000 individuals (consisting of subjects from the Framingham study and eight others) was built and analyzed. The authors suggest that the initial findings of a "U-shaped" relationship in the Framingham data was a result of blood pressure lowering therapy being used more frequently in individuals with known cardiovascular risk factors. Thus, these individuals were found to have lower average DBP, though there was no causative relationship between their low DBP values and cardiovascular disease. Indeed, the authors note a study demonstrating that in low-risk subjects without cardiovascular risk factors, lower DBPs were associated with lower cardiovascular risk, as the initial findings from the Framingham study suggested.
The authors highlight the worldwide impact of high blood pressure, noting that it is associated with 54% of all cases of stroke and 47% of all cases of ischemic heart disease, leading to 7.6 million premature deaths each year. The number of individuals worldwide with high blood pressure is also expected to rise from one quarter currently to 29% by 2025. The authors conclude, however, by noting that other risk factors play a major role in mediating cardiovascular risk as well. Among hypertensive men and women, the vast majority of coronary events occur in those with other risk factors (such as diabetes and dyslipidemia) compounding the risk already present due to high blood pressure. Thus, patients requiring blood pressure therapy should not be identified based solely on their blood pressure, but rather based on their overall cardiovascular risk profile.
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