As if creaking joints and hardening of the arteries weren’t bad enough, a research team from the University and the Christiana Care Health System now has confirmed that even our veins stiffen as we age.

“When you are young, your veins are nice and elastic—like rubber bands,” according to William Farquhar, a cardiovascular physiologist and assistant professor in the College of Health Sciences’ Department of Health, Nutrition and Exercise Sciences. “But, as you grow older, we’ve found that your veins become more like lead pipes.”

That physiological change may be an important factor in the development of high blood pressure, or hypertension, which affects an estimated 65 million Americans, most of them older adults, Farquhar says.

The study, which was conducted over the past two years, was led by Farquhar and graduate assistant Colin Young, CHS ’03, ’05M, at UD and Michael Stillabower and Angela Disabatino at Christiana Care. The results were published in the Journal of Applied Physiology.

While the arterial side of the human circulatory system has been studied extensively, Farquhar says much less research has been conducted on the venous system. Yet the veins contain about 70 percent of the body’s total blood volume at rest, and the flexibility of these blood vessels is a major factor in how much blood gets returned to the heart during the vital fluid’s journey through the circulatory system.

Every minute, the steady beating of that amazing living pump that is the heart sends about five quarts of blood through the 60,000-mile network of arteries, capillaries and veins in the body. The muscular arteries carry blood away from the heart and out to the organs and limbs. Microscopic capillaries connect the arteries to the veins, which then transport the blood back to the heart.

The veins are equipped with valves to prevent any backflow 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 vessels flexibility and help them to maintain blood pressure.
To determine if there are age-related differences in how veins work, the research team recruited 24 healthy people for the study—half ages 18-30 and half ages 60-70. Each individual underwent medical screening at Christiana Hospital, including 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. While subjects lay resting on a gurney, various gauges, connected to computers, were placed on their arms and legs. An arterial cuff was attached to the 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.
“Based on previous research, we suspected that the veins of the older adults would be less flexible than those of the younger adults,” Farquhar says. “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 immersing one foot in cold water or having the participant squeeze 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 says. “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 says.

In the second phase of the UD study, now under way, the research team wants to find out if the veins of people with hypertension are stiffer than those 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.

“Lots of people have high blood pressure, but we still don’t know the underlying cause of this disease,” Farquhar says. “That’s why we’re pushing forward with these studies.”

The UD research is supported by a $151,000 grant from the National Institute on Aging, which is one of 27 institutes and centers that compose the National Institutes of Health.

—Tracey Bryant