"When you are young, your veins are nice and elastic--like rubber bands," William Farquhar, a cardiovascular physiologist in UD's College of Health Sciences, said. "But as you grow older, we've found that your veins become more like lead pipes."
And that physiological change may be an important factor in the development of high blood pressure, or hypertension, which currently affects an estimated 65 million Americans, most of them older adults, according to Farquhar.
The study, which was conducted over the past two years, was led by Farquhar and Colin Young from the University of Delaware and Michael Stillabower and Angela Disabatino at Christiana Care Health System. The results are published in the November issue of the Journal of Applied Physiology.
Young recently completed his bachelor's and master's degrees at UD, with Farquhar as his adviser, and is now pursuing a doctorate in physiology and pharmacology at the University of Missouri. Stillabower is a cardiologist and director of cardiovascular research at Christiana Care Health System, as well as a clinical associate professor of medicine at Jefferson Medical College in Philadelphia. DiSabatino is the nurse manager at Christiana Care's cardiovascular research office.
While the arterial side of the human circulatory system has been studied extensively, Farquhar said much less research has been conducted on the venous system. Yet the veins contain approximately 70 percent of your body's total blood volume when you are at rest, and the flexibility of these blood vessels is a major factor in how much blood gets returned to your heart during the vital fluid's journey through your circulatory system.
Every minute, the steady beating of that am azing living pump--your heart--sends about five quarts of blood through the 60,000-mile network of arteries, capillaries and veins in your body. The muscular arteries carry blood away from the heart and out to your organs and limbs. Microscopic capillaries connect the arteries to the veins. The veins then transport the blood back to the heart.
The veins are equipped with valves to prevent any backflow of blood caused by gravity as blood is returned to the heart from the lower extremities. The walls of the veins are made of collagen and elastin, two proteins that give the tube-like blood vessels flexibility and help them to maintain your blood pressure.
To determine if there are age-related differences in how our veins work, the research team recruited 24 people for their study--12 healthy young adults between the ages of 18 and 30, and 12 healthy older adults between 60 and 70 years old. Each individual underwent medical screening at Christiana Hospital, which included a lipid profile, blood pressure monitoring, electrocardiogram and several other tests to ensure overall good health.
Then each participant was involved in a series of research trials at UD's Human Performance Lab on the Newark campus. While each subject lay resting on a gurney, various gauges, connected to computers, were placed on their arms and legs. An arterial cuff was attached to an upper arm to monitor blood pressure, and venous cuffs were placed around the upper thigh and upper arm to measure the blood flow to the limbs.
As the cuffs were inflated over an eight-minute period, and then slowly deflated to let blood escape from the limbs, the blood volume was measured, recorded, and graphed. The consistently lower blood volume under pressure pointed to the less springy veins of the older participants.
Graphic courtesy of the American Medical Association "
Based on previous research, we suspected that the veins of the older adults would be less f lexible than those of the younger adults," Farquhar said. "But we didn't know if that might be due to a functional process, such as a chronic constriction of the muscles around the veins, or if this decreased flexibility was due to some change in the structure of the veins themselves."
To find the answer, the researchers monitored the blood flow through each participant's veins in different scenarios that might constrict the veins, such as having one foot immersed in cold water, or while squeezing a handgrip. They also administered a nitroglycerin pill under the tongue of each participant to relax the veins. In each case, they found that the tests had no effect on the response of the veins in either age group.
"Thus, we think that the stiffening of our veins as we age is probably due to structural changes, such as a thickening of the vein walls," Farquhar said. "Hardening of the arteries is a good analogy for what is happening in our veins as we grow older."
So can we do anything to keep our veins limber as time marches on?
"While there have been no longitudinal studies of this yet, it's possible that regular exercise training may blunt age-related increases in vein stiffness," Farquhar notes.
In the second phase of the UD study, now under way, the research team wants to find out if the veins of people with high pressure are stiffer than the veins of people with normal blood pressure. Two doctoral students, Erin Delaney and Megan Wenner, are assisting with this portion of the research, which will examine both young and older adults with high blood pressure.
While high blood pressure is all too common among older adults, Farquhar said it can be harder to find young adults who already have the disease. However, several individuals already have been identified for the study, and the team hopes to have data to report in the next six months.
This research is both literally and figuratively "close to the heart " for Farquhar. He said he has always had an interest in cardiology and helping people.
Before his UD career, he worked with cardiac patients in a rehabilitation setting, where he provided patients with information about the risk factors affecting heart disease and the benefits of exercise. Then, during his postdoctoral training at Boston's Beth Israel Deaconess Medical Center, he worked with patients who were unable to stand without getting dizzy. And that began his research on veins.
Today, he's busy working to find out what role these less-studied blood vessels may play in high blood pressure.
"Lots of people have high blood pressure, but we still don't know the underlying cause of this disease," Farquhar said. "That's why we're pushing forward with these studies."