Psychologists Seek A Behavioral Approach To Lowering Blood Pressure
DURHAM, N.C. – Duke University Medical Center psychologists James Blumenthal, PhD and Andrew Sherwood, PhD, are on a mission to discover a non-pharmacologic behavioral approach to lowering blood pressure, one of the key risk factors for cardiovascular disease and stroke.
Finding such a behavioral-based strategy of diet and exercise for treating hypertension is important, Blumenthal argues, since commonly-used medications used to treat the disorder are not always successful, can be costly, and in some cases the drugs can cause unwanted side effects and actually exacerbate other medical conditions common to patients with hypertension.
"We have shown in earlier studies that exercise combined with a behavioral weight loss program can result in significant blood pressure reductions," Blumenthal said. "Other studies have shown that certain diets can also have a positive effect on lowering blood pressure. We hope that combining both dietary and weight loss approaches will lead to even greater blood pressure reductions."
The results of the latest large diet study, dubbed PREMIER, were published earlier in the April 23, 2003, edition of the Journal of the American Medical Association. PREMIER showed a small blood pressure benefit for those patients who ate according to the DASH diet, which is high in low-fat dairy products, fruits and vegetables.
Believing PREMIER did not go far enough in demonstrating the benefits of the diet in reducing blood pressure, Blumenthal organized a 120-patient clinical trial that is being supported by a four-year, $3 million grant from the National Institutes of Health. The study, known as ENCORE (Exercise and Nutrition interventions for Cardiovascular Health), is a follow-up to PREMIER and several other diet and exercise studies conducted by the Duke team.
The DASH (Dietary Approaches to Stop Hypertension) diet is a reduced-fat regimen that includes four to five daily servings of fruits and vegetables, and three daily servings of low-fat dairy foods. It has been shown to reduce blood pressure in the absence of weight loss, but has not been critically evaluated in free-living situations.
"The DASH diet is widely regarded as the 'anti-hypertension' diet, and is recommended by the latest blood pressure guidelines (Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure), so we wanted to see if we combined it with exercise and a weight loss program, could we achieve even greater blood pressure reductions?" Blumenthal said.
He explained that previous DASH studies, like PREMIER, have limitations that the current trial hopes to address.
"The DASH studies were conducted in controlled settings," Blumenthal said. "We'd like to see how it performs in a more real-world setting, where the participants have to shop for the food, prepare it and eat it in their own homes. Also, the earlier studies were short-term, and they found that the bulk of the benefits accrued during the first two weeks of the being on the diet. We plan to follow participants for one year to measure the long-term effects.
"Additionally, most experts agree that blood pressure may be considered an imprecise measure of cardiovascular risk," Blumenthal continued. "ENCORE will provide more precise estimates of risk by measuring important aspects of cardiovascular function and structure."
For the trial, the team will recruit adults with high blood pressure and randomize them to one of three groups -- the DASH diet alone, the DASH diet combined with a behavioral weight-loss program that includes exercise, or a usual care control group.
In addition to studying the effects of the different strategies on blood pressure, the researchers also plan to take detailed physiological measurements of vascular stiffness and endothelial function, both of which are important in the development of cardiovascular disease.
"Vascular stiffness can play a very important role in the actual pumping of the heart," Sherwood explained. "Each time the heart beats and pumps blood into the circulation, the arteries stretch to buffer the sudden surge in pressure. While the heart relaxes between beats, the arteries recoil, which helps facilitate the flow of blood throughout the body."
Physicians measure two components when they take a patient's blood pressure. The first is the systolic pressure, which occurs when the heart contracts. The second reading is the diastolic pressure, which occurs as the heart rests between beats.
"If the arterial walls are not as elastic as they should be, the heart must squeeze harder to pump blood into the arterial system" Sherwood continued. "Over time, the heart's main chamber, the left ventricle, grows thicker and less efficient, a condition known as left ventricle hypertrophy."
The researchers will determine vascular stiffness by measuring how fast the pulse of blood travels through the body's major arteries. The stiffer the vessel, the faster the pulse will pass though, he said. The measurement technique is non-invasive and simply involves precise measurement of the time of arrival of the pulse at different points in the body, like at the wrist.
"We hope to be able to see if diet and exercise can have a positive effect by reducing vascular stiffness," Sherwood said.
The team will also employ non-invasive vascular ultrasound technology to measure the health of the endothelial lining of the artery. The endothelium helps regulate blood flow through its release of nitric oxide, which causes the artery to relax.
The focus of the endothelium measurements will be the brachial artery, the major artery of the arm. The researchers will first occlude the artery with a tourniquet, and then release it after five minutes. The ultrasound machine will record the minute changes that indicate how much the artery is relaxing.
"When the tourniquet is released, healthy arteries will release greater amounts of nitric oxide to help the vessel expand to accommodate the need for additional blood flow to the forearm and hand," Sherwood explained. "By measuring these changes, we can gauge the health of the artery, and also see if the interventions have a beneficial effect on the endothelium."
The researchers will also measure the effects of the interventions on body composition, insulin resistance and left ventricular structure and function.
Other members of the Duke team include Michael Babyak, PhD, Simon Bacon, PhD, Mark Feinglos, MD, Tanya Goyal, PhD, Pao-Hwa Lin, PhD, Jennifer Norten, Eugene Oddone, MD, David Madden, PhD, and Lana Watkins, PhD, Alan Hinderliter, MD, University of North Carolina-Chapel Hill, is also a member of the team.
An orientation session for the study will be held at 7 p.m., Tuesday, Oct. 28, at the Stedman Auditorium on the campus of the Duke University Center for Living. For more information about participating in the trial, contact Bacon, the study coordinator, at (919) 681-4280.