MINNEAPOLIS, Minn. (The New York Times News Service) -- Catherine Dunaway's life returned in small, almost mundane ways. She walked the dog. She went to a movie. She helped with dinner. She shed her PJs and went back to work.

During her two-decade battle with severe depression, the 45-year-old Minneapolis social worker tried drugs, psychotherapy and 12 rounds of shock treatment, with little success. Then she heard about a University of Minnesota study using a "brain pacemaker." It proved to be her salvation.

The device, called VNS Therapy, is now available for people suffering from treatment-resistant depression, a condition afflicting 4.4 million Americans.

But the Food and Drug Administration's (FDA) approval of VNS Therapy has attracted the attention of Congress. The Senate Finance Committee issued a report in February questioning whether the $15,000 device had been studied sufficiently.

The Senate's second-guessing of VNS Therapy approval highlights the increasing regulatory scrutiny of the medical technology industry after the highly publicized recalls of heart devices last year.

And it's a debate that may have implications for Medtronic Inc. and St. Jude Medical Inc., Twin Cities-based companies that are testing deep brain stimulation to treat depression.

The report also could make it tougher for the device's maker to persuade Medicare and private insurance companies to pay for the new treatment.

VNS Therapy is the only FDA-approved device therapy available to patients suffering from depression -- competitors are years away from commercializing their therapies.

Made by Houston-based Cyberonics, Inc., the stopwatch-size device is surgically implanted in the chest and attached to a wire that snakes inside the neck to the vagus nerve. It delivers tiny electrical pulses to the nerve at 30-second intervals every five minutes -- 24 hours a day, seven days a week.

Settings vary depending on the patient, but when the device fires in Dunaway, her voice quavers a little. "I don't even notice it," she said. She's now a convert, and Cyberonics pays her travel expenses when she discusses the device with groups.

About 550 patients have been implanted with the device since it won FDA approval last July. But some doctors are unsure why VNS Therapy works in some patients and not in others.

REDIRECTING SIGNALS TO BRAIN

Cyberonics says the vagus nerve sends signals to the central nervous system that control mood and other symptoms related to depression.

"We used to think your brain told your internal organs what to do, but it turns out that the vast majority of the signals in the vagus nerve are your internal organs sending information to your brain," said Dr. Barry Rittberg, director of the University of Minnesota's Division of Adult Psychiatry, who headed the U's clinical trial. "How that translates to improve depression is not clear. I look at it kind of simplistically, it's sending some message that all is well in Organland."

Critics worry that the only randomized clinical trial conducted with the device, involving 235 patients at 21 centers nationwide, failed to demonstrate that it is effective. While all participants in the study received a device, only half were turned on. After a year, the company says, one in three patients experienced significant mood improvement, and one in six showed no symptoms of depression.

A May 2005 letter to the FDA from the consumer advocacy group Public Citizen expressed concern about reports of worsening depression, suicides and sudden deaths in the clinical trial's follow-up phase. "With so many uncertainties and red flags, it is a serious mistake for the FDA to be prepared to approve this device," Public Citizen said.

Cyberonics' CEO Robert (Skip) Cummins said, "the only controversy is in the minds of the inexperienced and overruled group at the FDA who were attempting to misapply drug regulations to a device."

FIRST USED TO TREAT EPILEPSY

VNS Therapy first was approved by the FDA in 1997 to treat epilepsy. In 2003, Cyberonics applied to the FDA to expand its use, triggering a review by agency scientists and medical officers.

An FDA advisory panel later recommended approval in a 5-to-2, nonbinding vote. But in August 2004, the FDA issued a letter indicating that approval was not forthcoming because the data did not prove the device was safe and effective.

Cyberonics submitted more data and, in a highly unusual move, the FDA reversed itself in February 2005. Formal approval came in July.

The Senate Finance Committee questioned why the director of the agency's device division overruled "the comprehensive scientific evaluation of more than 20 FDA scientists, medical officers and management staff who reviewed Cyberonics' application."

An FDA spokesman defended the reversal, saying the agency weighed scientific data, staff concerns, the panel's recommendation, the impact the therapy would have on people with no other options, and data tied to the device's use for epilepsy.

VNS Therapy can be used only as an add-on therapy for people suffering treatment-resistant depression -- patients who have unsuccessfully tried at least four treatments of antidepressants.

Cyberonics has launched a massive effort to market VNS Therapy, tripling the number of staff who sell the device and help with reimbursement issues.

Last month, Blue Cross and Blue Shield of Alabama said it would pay for the device. Other insurers have approved payment on a case-by-case basis, but Piper Jaffray & Co. analyst Thomas Gunderson said the congressional inquiry could slow reimbursement efforts.

Sen. Charles Grassley, the Iowa Republican who chairs the Senate Finance Committee, could not be reached for comment.

It would be unprecedented for the FDA to reverse its pre-market approval, and most observers doubt that will happen, anyway.

"People said, 'Well, you only had a third of patients showing any improvement,' " said Dr. Rittberg. "But these were people who were proven to not respond to medications and other therapies. So from that perspective, the results were pretty good."

Copyright 2006 The New York Times News Service. All rights reserved.