A number of physiological changes occur in the body as we age, including a decrease in heart's ability to pump blood. New findings show that blood vessels in the legs adapt to reduced cardiac output by regulating the flow of blood to the leg muscles during exercise.

In the study, older and younger men were able to maintain normal blood pressure levels as they participated in a study of the body's response to stress, but the two groups had different mechanisms for doing so.

"It appears that the control of blood vessels in working muscles may be altered by aging," Dr. David Proctor of Pennsylvania State University stated.

"In order to maintain a physically active lifestyle you need to maintain healthy blood vessel function," he said. "The ability to sustain exercise is critically dependent on adequate blood flow to the legs," he added. "Walking, climbing the stairs (and) mowing the lawn all require adequate blood flow and oxygen."

During exercise, the body must balance the need to dilate blood vessels in the legs so that more oxygenated blood can be delivered to the muscle cells, with the need to constrict in response to the resulting temporary drop in blood pressure. Whether this balancing act is affected by the aging process has been unknown, until now.

Proctor and his colleagues measured the changes in blood flow that occurred in response to a sudden stress among a group of older and younger men while cycling on a stationary bicycle. The stress was produced by plunging the participants' hands into a bucket of ice, a standard means of triggering blood vessel constriction.

Thus, the researchers created a situation in which the subjects' blood vessels needed to both dilate in response to the cycling activity and constrict in response to the stressor.

Based on previous studies in older animals and humans, Proctor and his team expected to see less constriction in the older men's blood vessels in comparison to the younger men. Yet, the opposite happened.

Blood vessel constriction was greater among the older men, so that they maintained adequate blood pressure. This could be "a compensatory mechanism for their reduced level of cardiac output during exercise," the researchers speculate.

Still, the older men were able "to meet the demands of whole body exercise, (although they) used slightly different means to achieve that," Proctor said.

He added that "it's important we understand normal healthy aging and physiology to better understand the disease processes that accompany aging" such as hypertension and diabetes.

The study findings were presented last week during the American Physiological Society's 2004 Intersociety Meeting in Austin, Texas.

Reference Source 89
October 11, 2004

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