UNDER PRESSURE
When the Bogalusa Heart Study began, in 1972, Berenson and his colleagues were interested in identifying risk factors that contribute to heart disease, specifically in kids. Other studies had identified risk factors in adulthood, but not in children. Moreover, no other study had ever looked at risk factors among blacks as well as whites (at the time, all major heart disease studies had an exclusively white study population). And that's important, because different populations can have different patterns of risk.
One of the main risk factors the researchers were interested in was elevated blood pressure. Blood pressure is expressed as two separate numbers that relate to the action of the heart muscle as it pumps. With every heartbeat, the ventricles contract and blood is forced out of the heart into arteries. This relatively high pressure is the systolic pressure. The force of the blood entering the arteries can be felt as the pulse—as, for example, in your neck or your wrist. When the ventricles relax, the pressure in the arteries drops; this lower pressure during ventricular relaxation is the diastolic pressure. Blood pressure is expressed as systolic pressure over diastolic pressure. The normal measure for blood pressure is systolic pressure less than 120 and diastolic pressure less than 80 (120/80). Chronic elevation of either number increases the risk of cardiovascular disease, including atherosclerosis, heart attack, and stroke.
High blood pressure, or hypertension, is dangerous because it can put stress on the walls of arteries, damaging them. If the damage is great enough, the blood vessels can burst. Even if they don't burst, the damaged areas can develop scar tissue. The scar tissue provides a site for the buildup of fatty deposits, contributing further to atherosclerosis (INFOGRAPHIC 27.7).
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The fatty deposits of atherosclerosis can also promote the formation of blood clots. When plaques rupture, blood clots can form on the surface of the plaque. These clots obstruct blood flow where they form, and can break off and clog other vessels. If blood vessels in the brain are damaged or obstructed, the supply of oxygen to the brain is disrupted, causing a stroke.
Hypertension is particularly dangerous because, while it can have deadly consequences, there are typically no symptoms associated with it. This means that people have no way of knowing they are hypertensive unless they have their blood pressure checked and monitored.
What causes hypertension? Researchers are not entirely sure. However, they do know what factors predispose people to it. Some factors are controllable, some aren't. Uncontrollable ones include family history, older age, being African American, and being male; controllable ones include low physical activity, eating a high-salt diet, being overweight or obese, drinking too much alcohol, and stress.
Obviously, when the bodies of the young people arrived at the funeral home in Bogalusa, they no longer had any vital signs, so it was not possible to take their blood pressure. However, because nearly every child in the town had been followed as part of the heart study, researchers were able to correlate the victims' blood pressure when alive with the autopsy results. They found that having had high blood pressure correlated closely with the extent of atherosclerosis found in the arteries of the victims.
High blood pressure wasn't the only risk factor that researchers were able to link with the autopsy results. Other strong links were high body mass index (BMI), high cholesterol levels, and smoking cigarettes. When all the known risk factors were considered, a clear pattern emerged: the amount and extent of atherosclerosis increased with age and was strongly correlated with the known risk factors for heart disease. In fact, the young people with the most risk factors when alive were the ones with the most evidence of heart disease at the time of death. For example, those with no risk factors had approximately 20% of their aorta covered with fatty streaks, while those with two risk factors had about 38% of their aorta covered with fatty streaks; those with no risk factors had less than 1% of their coronary arteries covered with fibrous plaques, whereas those with three or four risk factors had more than 7% of their coronary arteries covered with fibrous plaques. The relationship between number of risk factors and extent of heart disease was statistically significant (INFOGRAPHIC 27.8).
“The autopsy studies were really landmark studies,” says Peter Katzmarzyk, an epidemiologist at the Pennington Biomedical Research Center in Baton Rouge. Before them, he says, scientists didn't really understand that things like heart attack and stroke have their genesis in childhood. “The Bogalusa Heart Study really put that on the map,” he says. And, it made a strong case that averting severe consequences of heart disease later in life would mean addressing the lifestyle choices we make when we are young.
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