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As stress can make blood vessels constrict and blood pressure rise, it may also reduce the heart's ability to relax and fill with blood, researchers says.
If they are right, this may be one of the earliest changes that eventually lead to congestive heart failure, a disabling, sometimes lethal condition affecting nearly 5 million Americans.
"What we are saying is that long before the pumping chamber of the heart becomes enlarged and dysfunctional – a classic sign of congestive heart failure – you have early changes in the way the heart is functioning," says Dr. Gaston Kakota Kapuku, cardiovascular researcher at the Medical College of Georgia. "If we can identify those changes, we may be able to stop the progression before the heart becomes dysfunctional."
Dr. Kapuku recently received a four-year Scientific Development Grant from the American Heart Association to look for the first time at the impact of mental stress on filling the left ventricle in hearts of young, healthy individuals.
He's recruiting 160 15-18-year-olds over the next four years. Study participants will be put on a diet for three days to regulate their sodium intake, then come to MCG's Georgia Prevention Institute to play challenging video games. In addition to measuring how stress affects heart rate and blood pressure, researchers will use painless ultrasound to study how the heart relaxes and fills with blood in stressful and normal conditions.
"By stimulating them with the video games, we increase their blood pressure," says Dr. Kapuku. "We are going to see when their blood pressure increases if their diastolic function also is immediately impacted. I am hoping we will be able to identify factors that trigger this diastolic dysfunction."
Systolic function is the heart contracting and pumping blood to the body; diastolic function is when it relaxes and fills with blood. In congestive heart failure the heart – for reasons such as years of working against elevated pressures inside blood vessels – becomes oversized, inflexible and incapable of properly pumping blood to the body.
But pumping is not the real, or at least not the first problem, Dr. Kapuku says. Like loosening the belt to eat a big meal, the heart must relax to fill with blood. In fact, the heart is relaxed two-thirds of the time and a healthy left ventricle – which pumps blood to the body – should fill with blood during the early stage of relaxation. Scientists such as Dr. Kapuku say the true dysfunction of congestive heart failure occurs when that begins to change. When the heart muscle relaxes, differences in pressure between the upper and lower chambers should move the blood into the lower chamber, the left ventricle. The atrium, the upper, collecting chamber, then contracts. In very early heart failure, the heart also begins to rely on the contraction of the atrium to finish filling the left ventricle. Dr. Kapuku was among the first to demonstrate this abnormal filling is one of the earliest expressions of heart malfunction and that this phenomenon may occur behind the façade of normal pump function and cardiac structure.
Many risk factors for cardiovascular disease, such as high blood pressure, obesity and inactivity, contribute to the decline of heart tissue, turning strong, flexible muscle stiff and fibrous. "When you have a mild increase in blood pressure, the pump function is still good, sometimes even exaggerated, but at that time, you can already figure out the heart is starting to depend more on the atrial contribution than the early filling. So how do you reverse that? By lowering blood pressure," says Dr. Kapuku. That may mean taking antihypertensive medications at these early signs of trouble. Measures such as weight loss and exercise also may help stop the cascade that ultimately leads to a failing heart.
He's focusing his studies on adolescents because of mounting evidence, from centers such as the Georgia Prevention Institute, that cardiovascular disease and related conditions such as high blood pressure begin in youth.
Using a hypertension model developed by the institute's associate director, Dr. Gregory Harshfield, Dr. Kapuku is first looking at those who might be most at risk: people with a genetic tendency to retain sodium and an elevated blood pressure following stress, such as a competitive video game.
The body naturally responds to stress by increasing blood vessel constriction and fluid volume inside vessels. The kidneys help with volume by retaining sodium. Natriuresis is the body's way of eliminating sodium so pressures can return to pre-stress levels. Dr. Harshfield's studies have shown certain populations, including young black males and overweight males, have a problem with pressure returning to normal because of reduced ability to eliminate sodium.
Dr. Kapuku wants to know if this impaired ability to regulate sodium also increases the risk for the early changes in the heart's ability to fill. He'll look at a cross- section of teens to determine the contribution of race and gender as well. "The purpose of this study is to tell you that before you have difficulty breathing, you show some signs that we could modify earlier and prevent you from going on to that," says Dr. Kapuku.
The many unknowns about heart disease prompted Dr. Kapuku to leave his practice in the Congo, complete training in clinical cardiology and cardiovascular physiology in Japan and three research fellowships, including one in interventional cardiology at the Montreal Heart Institute and two at MCG. He joined the MCG faculty in 2001.