In an indication that the power of mind over body isn't limited to grownups, researchers report that advanced relaxation techniques help kids endure a grueling medical procedure.

Kids who learned to relax themselves through self-hypnosis were less likely to suffer from distress during painful urinary tract checkups, a new study has found. In addition, the children's greater sense of calm appeared to shorten the grueling procedures by nearly a third -- an average of 14 minutes each.

Previous research in adults has found that self-hypnosis helps many patients deal with the physical stress of surgeries, said study co-author Dr. David Spiegel, associate chairman of psychiatry and behavioral science at Stanford University. "Just getting people to focus their attention on something besides what they're afraid of can help reduce their pain and help the procedures go better," he said.

According to Spiegel, healers have used the powers of hypnosis for hundreds of years, but scientists have only recently begun to launch sophisticated studies into its effects. Meanwhile, the popular image of hypnosis is still largely based on stage performances featuring volunteers quacking like ducks or clucking like chickens.

"While there's been a lot of mysticism about it, [hypnotism] is just a kind of focused attention," Spiegel said. "You learn to enter a different frame of mind, focusing on breathing, and the inference is that other things like pain and anxiety will not bother you as much."

In the new study, Spiegel and his colleagues recruited 44 children, aged 4 to 15, who were about to undergo a procedure known as voiding cystourethrography. Children with malformed urinary tracts -- an estimated 1 percent to 2 percent of all kids -- need the procedure every year or so, explained study co-author Lisa Butler, a senior research scholar at Stanford.

To make sure urine isn't backing up into the kidneys, doctors insert a radioactive dye into a child's urethra and take X-rays, then watch as the child urinates. Children stay awake through the procedure, and it can be extremely distressing, Butler said.

In the study, 21 of the children underwent routine treatment, while 23 were trained in relaxation techniques through self-hypnosis. After training sessions with the children, therapists accompanied them to the procedures.

First, the therapists told the children to imagine they were floating in a hot tub, lake, or bathtub. Then the children imagined they were absorbed in another experience -- perhaps a jet-skiing trip or a visit to an amusement park. Ideally, the children would "disassociate" from the procedure, Butler said.

Adults who become absorbed in a book or movie experience a similar sensation, she said. Disassociation "allows you to put something out of your focal attention. You know what's going on, but it's not in the central part of your awareness."

The children in the second group weren't hypnotized, although they could optionally learn about the medical procedure and get training in simple relaxation techniques such as controlled breathing.

The findings appear in the January issue of Pediatrics.

According to parents and doctors, the self-hypnotized children experienced less trauma, and their average length of the procedure was 35 minutes compared to 49 minutes in the control group.

The children who were most resistant to hypnosis had the most difficulty during the procedures, Butler said.

Indeed, hypnosis doesn't work on everyone, although children are more easily hypnotized than adults, said Dr. Timothy Culbert, a hypnosis specialist and medical director of the integrative medicine program at Children's Hospitals and Clinics in Minneapolis.

According to Culbert, the findings suggest that self-hypnosis -- "they're doing it for themselves" -- can help children endure other difficult procedures that tap blood, bone marrow, or spinal fluid from the body. "There's no reason to think it wouldn't," he said.