ST. LOUIS (Reuters) - A machine that 'reconditions' a donor's lungs outside the body before being transplanted into a recipient is undergoing tests in the United States in the hope that it can radically improve survival rates for people with chronic respiratory diseases.

The XPS, manufactured by Swedish company XVIVO Perfusion, is in clinical trials at 16 U.S. medical centers. Known as "the box," it ventilates the lungs after removal from the donor and infuses them with a fluid mix of drugs and steroids, effectively drying them out and getting them in better shape for use in a transplant operation.

The technology, which has not been used widely before, aims to increase the donor pool by reconditioning marginal lungs not suitable for transplant.

"It allows the lungs to stay alive ... and allows us as providers to assess the function of the organ in a unique, well-controlled environment," said Dr. Varun Puri, an associate professor of cardiothoracic surgery at Washington University in St. Louis.

The XPS, which is under test at Washington University, Duke University Medical Center, New York-Presbyterian Hospital and more than a dozen other U.S. sites, has been cleared for use in Europe and Canada and was approved for clinical trials by the U.S. Food and Drug Administration as a Humanitarian Use Device.

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Michele Coleman, 63, credits 'the box' with saving her life. A former smoker, she was diagnosed with chronic obstructive pulmonary disease, a lung ailment with no cure.

"You don't want to, but you kind of lose hope because when you are sick like that you know how fast you are going downhill," Coleman said.

Last year, Coleman's doctors asked if she wanted to participate in a clinical trial, explaining that she would receive donor lungs that needed to take an out-of-body detour for reconditioning before her transplant.

"It's scary, but anything that they could give me was going to be better than I had, and actually I figured I wouldn't make it to the end of the year," she said.

The machine is made up of a ventilator to simulate breathing and a bypass machine to perfuse the organs with a drug-laden solution aimed at improving their function. It mimics the human body, but with one major difference.

"The lungs in the body are performing a function, they are providing oxygen to the body and they are removing carbon dioxide, they are performing gas exchange, thus there is some degree of stress on the lungs," said Puri. "When they are in the box or on the circuit, there is really no function they are expected to perform." That gives them time to heal, he said.

The statistics for lung transplants make grim reading. Fewer than 20 percent of donor lungs are considered suitable for transplant and up to 25 percent of candidates die waiting for a transplant. Even after receiving donor lungs, just over half survive five years.

The device addresses the first two statistics by potentially increasing the donor pool. Doctors say that with further research it could help increase survival rates as well.