A Penn State study has found that, although both the healthy young and old may report similar discomfort, tolerate similar temperature levels and endure similar exposure times, their cardiovascular responses are very different. Even at rest, healthy men over age 64 had a decreased ability to pump and redistribute blood to the skin to cool their body core in extreme heat. The older men's hearts also had to work harder compared to a group of men 18 to 27 years old.
Christopher T. Minson, doctoral candidate in kinesiology at Penn State, and his adviser, Dr. W. Larry Kenney, professor of physiology and kinesiology, conducted the study. Minson presented the findings Wednesday, April 9, at the Experimental Biology '97 conference in New Orleans, La.
Minson says the results indicate that "During heat waves, older individuals who don't have air conditioning -- particularly if they have heart disease -- need to be in cooler surroundings since the chance of them having cardiovascular problems is significantly increased. Even the average healthy older person should be careful and get into cooler conditions to minimize the strain on their heart."
The study was specifically designed to examine the heat stress sedentary older people experience during serious heat waves like the one in Chicago in 1995 during which 733 people died. Kenney says, "When older people die during a heat wave, they usually are not exercising. They are typically sitting in a very hot room without air conditioning. And they seldom die of heat stroke; rather there is almost always an underlying cardiovascular cause."
In the Penn State experiments, eight men 64 to 81 years old and eight 18 to 27 years old donned special body suits that rapidly raised their skin temperature to just below the pain threshold, about 108 degrees F. The suits have a system of tubing through which the experimenters piped water kept at 122 degrees F.
Catheters in each arm and one threaded through a vein to a position just above the heart, were used to measure the men's blood flow to the skin, the liver and the kidneys as well as the filling pressure of the heart. The heart's pumping capacity was also monitored. The men were asked to rest quietly in the heat until they couldn't take it anymore.
Minson says the older men's outward appearance wasn't different from the younger ones during heating and their reports of how they felt didn't differ either. Their tolerance to the heat stress was also similar. The shortest exposure time, 45 minutes, was recorded by an older man but so was the longest exposure time, 85 minutes.
However, their skin blood flow was markedly different as was the energy expended by the heart to pump blood. The younger men experienced increased skin blood flow 2.5 times greater than that observed in the older men.
Minson says, " The hearts of the older men were just not doing the job that the younger ones' were doing. The older individuals' left ventricles were stressed much more by the heating than the younger ones'."
The Penn State study, which was supported in part by grants from the American College of Sports Medicine and the National Institutes of Health, is the first to examine a very high level of heat stress in old and young people at rest.
EDITORS: Minson can be reached at Penn State at (814) 865-1236 or at firstname.lastname@example.org by e-mail. Dr. Kenney is at (814) 863-1672 or at email@example.com by e-mail.