HONOLULU — Kalma Wong has tried almost everything for her two autistic children: special diets, intense behavioral therapies, flying in experts from the U.S. mainland at exorbitant costs.

Some efforts have yielded modest success. Others have done next to nothing.

But like many other parents of the more than 500,000 children that the Centers for Disease Control estimates to be autistic in the U.S., Wong has vowed to keep trying until she pinpoints the treatment that most helps her kids.

Her latest attempt is one of the most long-shot therapies yet, a protocol some doctors praise but that others declare to be a waste of time that gives desperate parents false hope and exploits them financially.

It is called hyperbaric oxygen therapy, a treatment in which pure oxygen is delivered to patients confined to pressurized chambers for an hour a day for several weeks. The theory is that extreme doses of oxygen — essentially the same kind of treatment used for decades to cure divers with decompression illness — would spur dormant or damaged neurons in the brain to become reinvigorated or even transformed.

In the case of children with autism, considered the fastest-growing developmental disability in the U.S. today, the new treatment is claimed to have produced some stunning results: transforming nonverbal children into fluent speakers; helping children hypersensitive to outside stimuli become calm enough to attend public schools; changing kids once averse to any personal interaction or touching into affectionate toddlers.

"I don't know what to expect from this," Wong said, "but the minute I heard about the upcoming trial, I called and got my kids on the list. I feel like it's worth a shot."

Her reaction is just what some autism experts fear.

"I understand that what all parents want is to be able to look back and say they did everything they possibly could to help their child," said Dr. Tina Iyama, professor of pediatrics at the University of Wisconsin-Madison and an expert on autism. "That's why they are trying all these experimental new treatments. But ... there is absolutely no reason to think that improving oxygen levels in a child with autism will be helpful."

The debate over hyperbaric oxygen therapy, or HBOT, illustrates the fault lines over autism, a disorder that the Centers for Disease Control and Prevention estimates afflicts as many as 1 in every 150 children in America. Because there is no medical consensus on what causes autism, there also is little agreement on how best to treat it.

Some doctors who believe that the components of childhood vaccines, such as mercury, have been responsible for many cases of autism advocate detoxification programs in which children take chemicals that bind with metals in the body and force them out through urine. Others promote gluten-free diets under the theory that autistic children have high levels of a certain type of yeast in their digestive tracts. And then there are the proponents of HBOT, which has gained a following among parents who claim it has helped children with neurological problems, including cerebral palsy, traumatic brain injury, encephalitis and, most recently, autism.