Optimal aerobic exercise training may benefit patients with pulmonary arterial hypertension

A physical therapy researcher with the IU School of Health and Rehabilitation Services at Indiana University-Purdue University Indianapolis has been awarded a $465,000 National Institutes of Health grant to optimize aerobic exercise training for patients with pulmonary arterial hypertension, a goal data suggests could reduce morbidity and mortality among those with the disease.

Traditionally, it had been thought that these patients, who often struggle to walk across a room or climb a flight of stairs, shouldn't exercise, said Mary Beth Brown, an assistant professor in the Department of Physical Therapy.

"It's only in the last decade that the first evidence came out that exercise may be okay and may even be beneficial", Brown said. "Because it is such a relatively new potential therapy there is a lot of work that needs to be done to optimize it, just like with any other new therapy."

Pulmonary hypertension is high blood pressure that occurs in the arteries in the lungs. Blood vessels that carry blood from the heart to the lungs become narrow, forcing the heart to work harder to pump the blood through.

As the pressure builds, the heart's right ventricle must work harder to pump blood through the lungs, eventually causing the heart muscle to weaken and eventually fail.

While researchers believe exercise is beneficial, the best approach to maximizing those benefits and minimizing risks has yet to be discovered, Brown said.

"Patients with pulmonary hypertension can get extremely high pulmonary pressures during exercise," she said. "So you have to wonder what the implications of that are."

One thing that happens with pulmonary hypertension is that tolerance for exercise, even walking short distances, worsens over time, Brown said. Researchers believe that is due in part to skeletal muscle and heart muscle metabolism failing to generate energy as efficiently as they had before the onset of the disease.

Regular exercise is expected to help with the exercise intolerance in pulmonary hypertension because exercise is known to reverse or at least ameliorate the inefficient energy metabolism of other diseases, Brown said.

"If we can find an exercise protocol that will improve blood pressure in the lungs, and thus the load on the right heart, in addition to promoting improvement in skeletal muscle and heart metabolism, we could actually slow the progression of the disease," Brown said.

She has already tested, for the first time, in a rat model with a mild form of pulmonary hypertension, the use of high intensity interval training, which alternates short periods of intense exercise with less-intense recovery periods.

The results were startling, Brown said.

She found improvement in blood pressures in the lungs, not only during exercise but at rest as well. Further, the enlargement in the size of the right ventricle, caused by pulmonary hypertension, was reversed.

"We've never seen reversal of the right heart hypertrophy," she said. "My first thought was this can't be right, so the experiment was repeated, but we got the same results again."

With the NIH grant, Brown will now conduct similar high intensity interval training using a rat model with a more severe form of pulmonary hypertension to see if there is as much or more benefit as occurred with a mild form of the disease.

She will employ implantable telemetry to measure pulmonary pressures during exercise in her rat model, over course of disease development and treatment, which has never been done.

"That's important because patients don't always have problems when they are just resting. They have them when they are walking across the room or going up a flight of stairs," Brown said. "We need to understand the hemodynamics during physical exertion so we can better optimize exercise protocols."

With findings from an earlier study that showed a drop in pulmonary pressures to normal levels for a period of time in animals that performed a single exercise session, Brown's research will determine which exercise protocols give the best window of time of normalized pulmonary pressures, Brown said.

"That in itself could potentially produce a huge benefit," Brown said. "Patients who exercised daily would have more of these post-exercise windows of lower pressure, and less load on the heart."

Source: Indiana University