A new University of Colorado at Boulder study involving laboratory rats that indicates low-intensity exercise may significantly delay the onset of congestive heart failure appears to have some promising implications for humans.
According to Professor Russell Moore of CU-Boulder's integrative physiology department who led the study, lab rats carrying the genetic characteristics for spontaneously developing heart failure were shown to live significantly longer if they exercised moderately on a treadmill. The exercise protocol, the equivalent of daily, leisurely strolls in humans, extended the life expectancy of the rat study group by at least 10 percent to 15 percent, according to the study.
"Assuming the results are applicable to humans, low-intensity exercise is likely to have benefits to humans in early stages of congestive heart failure," he said.
The study was published in the November 2005 issue of the American Journal of Physiology -- Heart and Circulatory Physiology. The study was co-authored by CU-Boulder doctoral student Craig Emter, Associate Professor Sylvia McCune, Research Associate Genevieve Sparagna and Ohio State University Professor Judith Radin.
"Our study, coupled with several human studies conducted elsewhere, shows a definite trend indicating that moderate intensity exercise has a potential role in stemming the downward spiral in heart failure," he said.
Moore said a unique feature of the CU-Boulder study was that the delay in the onset of CHF in the rats through moderate exercise was accomplished without reducing hypertension, or high blood pressure, in the animals. Most people in the early stages of development of heart failure also have hypertension, which is regularly treated to help improve the prognosis of CHF sufferers, said Moore.
Although several human studies in the last 10 to 20 years have shown that moderate exercise does not appear to harm CHF sufferers, the positive benefits of such exercise have not been found to be statistically significant, he said. Such studies are difficult to evaluate because participants often are taking a number of different medications, he said.
The intensity of exercise in the study was a crucial factor affecting longevity in the rats used in the study, said Moore. Early in the study, several of the rats that began exercising at nine months of age died after the locomotion speed was increased from 10 meters per minute to 17.5 meters per minute, he said. The speed was subsequently reduced to 14 meters per minute for the duration of the study, and no additional rat deaths occurred, he said.
"The bottom line is if the animals are exercised too hard, they will die," he said. "But when exercised moderately, in this case at barely more than a walk, the results were striking."
According to the American Heart Association, about 65 million Americans are afflicted with hypertension and nearly five million suffer from CHF. In addition, about 75 percent of patients diagnosed with CHF die within eight years. "This is the most costly health problem in the United States to manage and treat," Moore said.
Low-intensity exercise for patients diagnosed early with CHF could preclude the use of expensive drug therapies and their side effects until later in life, he said.
The rats used in the study were bred over generations to carry a genetic blueprint causing spontaneously hypertensive heart failure, or SHHF. Rats and humans share a large number of common genes and proteins, including many thought to be involved in heart disease, he said.
"The biggest issue still looming out there is which molecular switches govern healthy growth of hearts at the cellular level," said Moore. "The question is whether there are therapeutic ways to positive, as opposed to pathological, growth of the heart."
The study involved the work of four undergraduates, three of whom were participating in CU-Boulder's Undergraduate Research Opportunities Program, which has provided more than $5 million to almost 6,000 students since 1986.
The study was funded by the National Heart, Blood and Lung Institute of the National Institutes of Health and by the American Heart Association.
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