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A hospital gown hung limply on Shelley Sable’s small frame as she waited in a cubicle at Abbott Northwestern Hospital just over a year ago. The waiting was tedious. Nurses checked, rechecked and then triple-checked her vital information before she was finally wheeled into an operating room for a heart procedure.

Or no procedure at all. Sable, now 44, had eagerly enrolled in a clinical trial that is probing a possible link between the small hole in her heart and the crippling migraine headaches she’s suffered for the past 16 years.

The 400-patient study is sponsored by Plymouth-based AGA Medical Corp., which makes a device that plugs the hole, called a patent foramen ovale, or PFO.

Because the study is double-blinded, Sable and her physician did not know for the past year whether she was treated with the device, although she certainly had her suspicions. And even if she was treated with the device, there was no guarantee that it would work.

The Rosemount resident is among the hundreds — perhaps thousands — of patients each year who agree to enroll in studies testing experimental medical devices and drugs. Their participation is crucial for companies hoping to prove their device is safe and effective, and an essential step before gaining regulatory approval to sell the product.

“If we didn’t have people like Shelley willing to enroll in clinical trials, the medical field would not be where it is today,’’ said Dr. Anil Poulose, a cardiologist with the Minneapolis Heart Institute, who is involved in the AGA study.

Sable, a nurse, thinks the possible link between her heart and brain makes sense. After suffering, on average, one to three migraines a week for most of her adult life, Sable was willing to consider unusual alternatives.

The experimental part of the bargain didn’t bother her one bit.

A swinging door

The path to that chilly hospital cubicle has been a fortuitous one not only for Sable, but for companies making devices intended to plug the hole in the heart.

As Poulose explained, a PFO is more like a door without a latch that swings open and shut between the upper chambers of the heart. The opening is normal in fetuses, and usually closes shortly after birth.

But in about 20 percent of adults, the hole never closes, allowing blood to bypass the normal filtering systems of the lungs. Most people never know if they have the defect. Some doctors — though not all — believe that substances such as small blood clots or chemicals in the unfiltered blood that travel directly to the brain may trigger severe migraines.

More than 30 million Americans suffer from migraine, roughly 10 percent of the U.S. population, according to the Migraine Research Foundation. About 15 to 20 percent of sufferers have migraine with “aura” — symptoms such as flashes of light, blind spots or tingling in the arms or legs.

There is no cure for the debilitating condition, which is usually treated with drugs. And the cause of migraines has confounded doctors.

“We know what happens with migraine, but no one has ever been able to explain why it happens,’’ said Dr. Ronald Tarrel, a neurologist with the Noran Neurological Clinic in Minneapolis, who is an investigator in the AGA Medical clinical trial and Sable’s doctor.

In the 1990s, an association between PFO and migraines was noticed by doctors who treated PFOs in young stroke patients and scuba divers suffering from decompression illness. But that was purely anecdotal.

“Enough of these people came in with PFOs who said they had migraines,’’ said Tarrel. “And then, anecdotally, they’d come in after having their PFO closed and say, 'Hey, I haven’t had a migraine since.’”

The first serious study probing the connection was conducted between 2005 and 2006 in the United Kingdom by Massachusetts-based NMT Medical Inc. It enrolled 147 patients with PFO who were suffering from migraines with aura.