KEYSTONE, COLO. – Regular physical activity is a cornerstone of the treatment of type 2 diabetes, yet patients with the disease often have an impaired ability to exercise even in the absence of clinically evident coronary heart disease.
It’s a catch-22 situation. Recent studies suggest a couple of explanations for this impaired ability to exercise, compared to that of equally sedentary nondiabetic controls. One, subclinical cardiac dysfunction during exercise is already present quite early in the course of type 2 diabetes. And two, patients with type 2 diabetes perceive even a very low exercise workload as requiring much more effort than do matched controls, Judith G. Regensteiner, Ph.D., said at a the conference, on practical ways to achieve targets in diabetes care sponsored by the University of Colorado and the Children’s Diabetes Foundation at Denver.
Dr. Judith Regensteiner
She and her coworkers studied 10 premenopausal women with type 2 diabetes and 10 healthy but equally sedentary controls in the cardiac catheterization lab. Their purpose was to learn why the disease is associated with reduced peak exercise capacity as expressed via peak oxygen uptake. The diabetic subjects had been diagnosed an average of 3.6 years earlier, and all were free of clinical cardiovascular disease.
Resting measurements of cardiac hemodynamics assessed via an indwelling pulmonary artery catheter were similar in diabetic subjects and controls. However, during a peak cardiopulmonary exercise test one glaring difference between the two groups became evident: All 10 diabetic subjects demonstrated a significantly greater increase in pulmonary capillary wedge pressure than controls. The mean increase was 23.6 mm Hg in the diabetic subjects compared to 16.7 mm Hg in controls.
"This was a most startling result. It showed evidence of a stiff heart suggestive of diastolic dysfunction in people who’d been diagnosed with diabetes only 3.6 years earlier. It’s a scary finding," observed Dr. Regensteiner, professor of medicine and director of the Center for Women’s Health at the University of Colorado.
On another day the investigators performed myocardial perfusion imaging using technetium-99m sestamibi in seven subjects in each group during peak exercise. The normalized myocardial perfusion index was significantly diminished in the diabetic patients: a mean of 11.0 compared to 17.5 x e-9 in controls. This is indicative of significantly less blood flow to the heart in the diabetic group. The myocardial perfusion index was inversely related to pulmonary capillary wedge pressure during peak exercise.
The investigators restricted this study to women because the gap in exercise tolerance between diabetic women and men is greater than between nondiabetic women and men.
Dr. Regensteiner and coworkers are now studying leg muscle blood flow to learn if abnormalities in peripheral circulation also contribute to exercise intolerance in patients with type 2 diabetes.
Another barrier to physical activity on the part of patients with type 2 diabetes may be mental. In a separate study, she and her coinvestigators utilized a standardized rate-of-perceived-exertion scale to study 13 women with type 2 diabetes and a mean body mass index of 34.2 kg/m2 along with 13 sedentary overweight controls and 13 equally sedentary but normal-weight controls. All subjects performed three 7-minute bicycle exercise tests at workloads of 20 W and 30 W.
These are very modest workloads. Indeed, the two groups of nondiabetic controls barely perceived them as workloads at all. The diabetic subjects perceived the physical effort as being much greater than did either control group.
"Is it all in the head? I don’t know. We’re looking now to see if there are things about having diabetes that may make patients perceive low-intensity exercise as being more difficult physiologically," Dr. Regensteiner said.
Dr. Regensteiner declared having no financial conflicts.