Researchers at the San Francisco Veterans Affairs Medical Center and UC Berkeley have found a more reliable way to measure physical and cardiopulmonary fitness in elderly people. The researchers say the test requires less running time on the treadmill, and also should serve as a reliable fitness measure for heart disease and kidney failure patients.
The conventional treadmill exercise test, the gold standard for measuring exercise performance for more than half a century, requires a person to push his or her body until it reaches its maximum rate of oxygen consumption during exercise, known as VO2 max, said Milton Hollenberg, MD, a UCSF professor of cardiology at the San Francisco VA Medical Center.
But many people over 65 either can't or don't want to push themselves hard enough to reach their maximum oxygen intake. For some, completing the test requires an extreme exertion, and it can even be dangerous for those with heart disease or other problems, Hollenberg said. Instead, some researchers simply have measured the highest oxygen consumption achieved during the test, but several studies have proven that this measure is often unreliable.
For a better alternative, Hollenberg used findings from a largely ignored 1996 study on young Japanese children with heart disease. The scientists had used a measurement called OUES (Oxygen Uptake Efficiency Slope), which employs the same treadmill exercise, but relates the rate of oxygen consumption to ventilation (the rate of air intake at any given moment during the test.)
To test OUES in adults, Hollenberg and his colleagues applied it to data he had collected for 429 elderly people from Sonoma, California, who had reached maximum effort on an exercise test. The researchers calculated OUES using data for the entire test, and compared it with the same calculation using only the first 75 percent of the data, as if the patient had quit the test earlier. The two measurements differed by less than two percent, suggesting that OUES accurately measures fitness without requiring maximum effort.
OUES has great potential to help measure the physical fitness of patients with heart disease or kidney failure who, like the elderly, often can't run a long time on a treadmill, Hollenberg said. "We now have a test for these people that is more objective and more reliable," he said. It also integrates function of the heart, lungs and working muscles into a single index.
Ira Tager, MD, MPH, a professor of public health biology and epidemiology at UC Berkeley's School of Public Health, was Hollenberg's co-author on the study, which appears in the July issue of the Journal of the American College of Cardiology.
Hollenberg and Tager are now using the OUES to study the decline of cardiopulmonary fitness with aging, as well as the relationship between OUES and other characteristics. For instance, smokers in the study group had a much lower OUES than non-smokers or ex-smokers; and heart disease patients had lower OUES than people with healthy hearts.
To confirm whether OUES can help/predict survival among heart disease patients, Hollenberg hopes to collaborate with researchers who have large numbers of these patients who have performed exercise tests. "The question is, can we use it as a more accurate predictor of mortality in heart disease?" he said.
This research was supported by a grant from the National Institute on Aging.
Journal
Journal of the American College of Cardiology