Dr. Tony Babb and Dr. Rebecca MacDougall, a physician and research assistant in Dr. Babb's laboratory, presented the findings on April 4 at Experimental Biology 2006 in San Francisco. The presentation was part of the scientific program of The American Physiological Society.
More than half of Americans are classified as overweight and more than 22 percent are obese; obesity contributes to diabetes and metabolic syndrome; heart disease, hypertension, and stroke; and some forms of cancer. Last year, approximately 300,000 deaths in the United States were attributed to obesity, and the annual healthcare cost related to obesity now runs at $117 billion. Physical activity and exercise are among the most important components in the prevention and treatment of obesity, but many obese adults do not participate in regular physical activity because they simply can't get enough breath while exerting themselves.
But it's not only their weight per se that's too blame, say the researchers. In earlier studies in the Babb laboratory, researchers had measured the oxygen cost of breathing - a unique measurement of how much oxygen is utilized for breathing -- in mild to moderately obese women. The oxygen cost was markedly increased in some but not all of the women, even when their overall body fat was similar. In the study reported at Experimental Biology, the researchers tested eight mild-to-moderately obese women to see what caused this difference.
Age, height, weight, body mass index (BMI), percentage of overall body fat (as determined by hydrostatic or underwater weighing), and pulmonary function at rest all were similar among all the women. But multiple MRI scans of the upper body found significant differences in fat distribution between the four women who had exertional dyspnea or shortness of breath on exertion and the four women who did not have such shortness of breath. There was a significant correlation between the amount of abdominal fat (fat under the skin of the abdomen as opposed to visceral fat or fat actually inside the abdominal cavity where the stomach and other organs are located) and the oxygen cost of breathing.
It is not yet clear whether increased shortness of breath in these women is simply the result of increased weight and forces on the lungs, or if increased fat on the surface of the abdominal area decreases lung volume, causing the sensation of shortness of breath, say the researchers. But what is clear, they continue, is that sending the women to the gym with orders to soldier on through and get in better condition may not help.
Dr. Babb says these preliminary data show that some obese patients with breathlessness during exertion do not appear to be deconditioned as conventionally thought, but rather suffer from respiratory limitations. Thus the recommendations for these patients may need to focus on weight loss and use special considerations for the type of exercise they are prescribed. He adds that it is important that we obtain more information as to the cause of breathlessness on exertion in people with high amounts of abdominal fat. -more-
Co-authors of the Experimental Biology study with Dr. Babb and Dr. MacDougall are Rebecca McGehee, who is the recipient of the APS 2005 Frontiers in Physiology Professional Development Fellowship and will be in attendance at Experimental Biology; Trisha Semon, an exercise physiologist and pulmonary technologist; Laurie Comeau, respiratory therapist; and medical student Belinda Schwartz.
Support for the research came from the American Heart Association Texas Affiliate, King Charitable Foundation Trust, and Cain Foundation.