Gaithersburg, Md. ? Stairs soon may no longer be insurmountable obstacles for some of the nation’s 2 million wheelchair users.

The first wheelchair that can climb stairs ” plus shift into four-wheel drive to scoot up a grassy hill and even elevate its occupant for eye-level conversation ” took a major step toward the market Wednesday, as advisers to the Food and Drug Administration unanimously recommended it be allowed to sell.

But the panel backed a few limitations on the Independence iBOT 3000 Mobility System ” which uses sensors and gyroscopes to balance on two wheels and navigate stairs ” including that it sell only with a doctor’s prescription and strict training to ensure users can drive it safely.

The FDA isn’t bound by its advisers’ recommendations, but it usually follows them ” and it granted the iBOT a special fast-track review reserved for important new medical technology, meaning a decision could come in a few months.

How does it climb? Most wheelchairs have two big back wheels and two smaller front wheels. The iBOT has four wheels the same size that rotate up and over one another to go up and down steps.

Well-known inventor Dean Kamen created the iBOT, and says wheelchair users tell him another feature is as appealing: The chair lifts onto two wheels so that its occupant, although still sitting, is elevated enough to reach high bookshelves and carry on eye-level conversations.

“One reason I built it was to let people stand up,” said Kamen, who licensed the iBOT to Johnson & Johnson. “We treat a lot of adults like children because they can’t stand up.”

“I wanted to take it home and keep it,” said Karl Barnard of Tilton, N.H., who tested the iBOT in a study required by the FDA, which regulates wheelchair safety.

In the iBOT, he rose to the height of a 6-feet-tall person to do his grocery shopping without help. Barnard, who lost use of his legs 25 years ago, has no stairs in his home, but he was impressed with the four-wheel drive that let him roll up hills and through gravel on his farm, places his manual wheelchair can’t go.

But with a predicted $29,000 price tag, Barnard, 46, calls it “more a luxury item” that he probably wouldn’t spring for until he’s too old to push his manual wheelchair easily.

Not for everyone

While several FDA advisers called the chair potentially revolutionary, they also cautioned that it’s not for everyone.

Patients must have the use of at least one arm to operate the chair, moving it with a joystick and other controls, and so far it’s built only for adults.

Also, it requires some exertion: Users lean forward or backward, directing the chair to climb up or down as it senses and adjusts to the person’s center of gravity. They must hold onto a stair rail to help guide it, although there is a feature that allows someone else to hold onto the chair back and assist.

Picking the right patient is crucial for safe use ” someone who not only is physically capable of handling the iBOT but has the right judgment skills to discern obstacles, such as which hills are too steep to try climbing, without risking serious falls, said Dr. Steve Stiens, a University of Washington rehabilitation specialist who uses a wheelchair himself.

Sales will be strictly controlled, responded manufacturer Independence Technology, a Johnson & Johnson subsidiary. Doctors and rehabilitation therapists must undergo special training to prescribe the iBOT, and potential users would have to pass a test proving they can drive it safely.

Taken for test drives

To prove iBOT works, 20 wheelchair users test-drove it for two weeks, allowing scientists to compare maneuverability, falls or other problems with their regular wheelchairs. They also took a road test, scooting up hills and over bumpy sidewalks, crossing curbs, reaching shelves and climbing stairs.

The patients performed most of the challenges more easily with the iBOT, said study leader Dr. Heikki Uustal of New Jersey’s Johnson Rehabilitation Institute. For example, everyone had to ask for help to reach a book atop a bookcase while in their own chairs, but merely pushed a button on the iBOT to slowly rise and reach it themselves.

Twelve patients could navigate stairs alone with the iBOT, while the rest used an assistant. In regular wheelchairs, two patients could literally bump their way down stairs, but no one could go up a single step.

Three people fell out of the iBOT and two fell out of their own wheelchairs during the study, suggesting the iBOT was as safe as today’s technology.