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Aging Blood Vessels Adapt to Exercise
Lab studies healthy aging and exercise to maintain
lifestyle, cut health costs
Oct. 6, 2004 – Researchers have found that blood
vessels in the legs of older people restrict more than younger men
during exercise, suggesting the body makes adjustments for lower cardiac
output.
The "fight or flight" mechanism is one of the
best-known physiological responses. It increases our ability to respond
to stressful situations. One way to look at exercise – physiologically
-- is as a non-life-threatening example of a stressful situation.
When we exercise, our heart and breathing rates
rise rapidly and blood vessels in our limbs dilate in order to deliver
more oxygenated blood to our working muscle cells. The rapid rise in
blood flow to the periphery -- especially to the legs -- can create a
"heady" feeling, which reflects a temporary drop in blood pressure. This
stimulates sympathetic nerves throughout the body to release substances
that constrict blood vessels, even those vessels that feed working
muscles.
Blood vessels in our leg muscles must respond to
both dilating and constricting substances to meet the competing demands
of muscle oxygen delivery and maintenance of bodily blood pressure, so
we don't faint! It's a balancing act that could change with advancing
age.
David Proctor and Urs Leuenberger and physiology
student Dennis Koch, researchers at Pennsylvania State University and
Hershey Medical Center, studied this possibility by manipulating the
activity of the sympathetic nervous system in healthy older and younger
men undergoing a moderate level of leg (cycling) exercise. They used a
simple, but powerful sympathetic stimulus -- plunging a hand into a
bucket of ice while still cycling -- and compared the blood vessel
reactions in the legs of both age groups.
Leg blood supply in old age important to
maintain lifestyle
Results of the Proctor-Leuenberger-Koch study
suggest that the mechanisms controlling blood vessel "tone" in
exercising muscles may be altered by age in humans. "The augmented
constrictor response seen in legs of older men could be a compensatory
mechanism for their reduced level of cardiac output during exercise,"
they reported. In other words, older adults may require a higher level
of vascular "restraint" to preserve systemic blood pressure during
exercise, Proctor said.
"We expected the blood vessels in the older men to
constrict less (relative to younger men) during cold stimulation, based
on previous research in older animals and humans under resting
conditions," Proctor said. But leg vessels of the older men constricted
more, perhaps as a compensation for their reduced level of cardiac
output. This indicates that the balance between vasodilation and
vasoconstriction in exercising muscle may change with age.
Proctor noted that his laboratory group "is one of
the first to systematically study the impact of aging on blood flow to
exercising muscle in healthy humans." It's important to study how
healthy people age, he noted, "because keeping our rapidly expanding
older population healthy will reduce the burden on our health-care
system" as well as contribute to enhanced independence and quality of
life in these individuals. Understanding the mechanisms by which blood
flow to exercising muscles is altered with advancing age will also help
us target interventions aimed at improving exercise tolerance in older
adults, he said.
Next steps and funding: The researchers will be
conducting similar experiments in women (both on estrogen replacement
and not). They plan to study the mechanisms underlying age-related
changes in vascular responsiveness to sympathetic stimulation; and to
examine the importance of sympathetic outflow in regulating vascular
tone and oxygen delivery to exercising muscles. Research is supported by
the National Institute on Aging.
Copyright: SeniorJournal.com |
