Diastolic Heart Failure and Exercise Intolerance

Researchers at Wake Forest University Baptist Medical Center have found people with diastolic heart failure have relatively normal blood flow to the legs. This means there are other potential causes of their inability to do everyday activities.

“Reduced tolerance for physical activity is the primary symptom of diastolic heart failure, and it greatly affects quality of life,” said Dalane Kitzman, M.D., Professor of Cardiology and senior researcher on the study. “This condition will increase as our population ages, so it’s important to pinpoint the reasons for their symptoms and to develop effective treatments.”

Nearly half of the estimated five million heart failure patients in the US suffer from diastolic heart failure. Such patients have stiff heart muscle which doesn’t take in enough blood with each beat. On the other hand, patients with systolic heart failure have heart muscle that is too weak to effectively pump blood into the body. Elderly patients are more prone to diastolic heart failure and with the population age increasing, this condition is expected to rise.

The only common point between both types of heart failures is patients’ bodies are not getting enough oxygenated blood. This restricts their ability to perform daily activities. Even after the heart is treated and function improves, many patients still have symptoms of exercise intolerance.

“This is a complex puzzle and we need to understand whether part of the picture is the blood vessels that deliver flow or perhaps how the muscles are using the oxygenated blood,” said Greg Hundley, M.D., lead author and an Associate Professor of Cardiology.

Research has already shown exercise performance in healthy subject as well as patients with systolic heart failure depends largely on the amount of blood flow to the legs. It has long been suspected diastolic heart failure patients also face the same issues; however research had not confirmed the hypothesis.

30 participants over the age of 60 were studied for the research. Researchers examined blood flow in the femoral artery, which is the major blood supply route to the leg. Eleven of the 30 participants were healthy; nine had diastolic heart failure while the remaining 10 had systolic heart failure.

The volume of oxygen consumed during exhaustive exercise was tested and measured for all participants. A magnetic resonance imaging (MRI) test was also conducted before and after the exercise to check the blood flow through their femoral artery. Flow was temporarily stopped with a blood pressure cuff. The MRI test measures minute changes in the interior size of the vessel and in blood flow velocity.

Reduced exercise tolerance was confirmed by the severely reduced peak oxygen consumption observed in patients with both types of heart failure. However researchers were surprised to find almost similar blood flow to the legs in healthy participants and diastolic heart failure patients after the occlusion cuff was released. Patients with systolic heart failure had 75% lower blood flow.

“This is important because exercise intolerance is the primary symptom of patients with diastolic failure,” said Dr. Hundley. “It suggests that factors other than leg blood flow may be responsible for the severely reduced exercise tolerance in this increasingly important disorder.”

The researchers carried out tests and made adjustments to negate the effect of other variables like tobacco use, diabetes, or certain other medications. This actually increased the gap in the leg blood flow between the two types of heart failure.

“If these results are confirmed, they could help us turn our attention to evaluating other factors that may contribute to reduced exercise tolerance in diastolic heart failure,” said Dr. Kitzman. “This might include, in addition to other parts of the cardiovascular system, the leg muscles themselves. Such information should help guide treatment of the severe physical disability experienced by the increasing number of patients with this newly recognized form of heart failure.”

Results of the study are published online in American Journal of Physiology – Heart Circulation Physiology.

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