Hope for an artificial lung

Patient's 107-day survival on old design shows promise for a new machine

October 24, 2007|By Dennis O'Brien | Dennis O'Brien,Sun reporter

With two transplanted lungs and a record-setting medical history, Tim McClellan inspires both his family and the doctors who treat him.

The 24-year-old waiter, recovering in an intensive-care wing at the University of Maryland Medical Center, can barely talk, mouthing words that require lip reading to understand him. But he can hear, nod slightly, sit up in a chair - and he knows the machinery attached to him is monitoring his vital signs.

Before his transplant, McClellan lasted 107 days - almost twice as long as anyone else - on an artificial lung designed 30 years ago. For Maryland researchers who have spent years trying to improve that design, he is an inspiration.

Researchers hope to develop artificial lungs that are mobile enough for patients with failing organs to use them at home - and effective enough to keep transplant candidates alive longer while they await new lungs.

Some 1,405 American patients received new lungs last year, but 254 died awaiting them. Another 342,000 patients with conditions too severe for transplants died of lung disease.

If McClellan can survive as long as he did on existing technology, researchers say, their new devices should increase survival rates for many of those patients.

"It's an affirmation that the concept of living with an artificial lung is sound. It basically says, `We can do this,'" said Dr. Bartley P. Griffith, chief of cardiac surgery and director of heart and lung transplantation at the University of Maryland Medical Center.

"It's a spectacular case," added Dr. Robert H. Bartlett, a lung expert at the University of Michigan Medical Center. Bartlett heads another of the four research teams around the country working on a new artificial lung.

At Maryland, Griffith secured a five-year, $3.7 million National Institutes of Health grant last spring to design portable devices to serve lung patients the way portable heart pumps now serve many cardiac patients.

The gadget will be about the size of a compact disc player, with a rolling, luggage-style case on wheels that includes a battery pack for power. A larger device, for hospital use, will pump blood into a cylinder about the size of a beer mug with power from a wall outlet.

In addition to doctors at Maryland and Michigan, researchers at the University of Pittsburgh and the University of Kentucky medical schools are at work on new artificial lungs. The groups meet periodically to discuss their progress.

All are focused on improving a technology known as Extracorporeal Membrane Oxygenation, or ECMO. The basic device, which today is about the size of a dishwasher, mimics the lung's functions by taking a patient's blood, enriching it with oxygen and filtering out carbon dioxide. It's a simplified version of the heart-lung machines used during bypass surgery.

Doctors generally prefer to use ventilators that pump air into the lungs of patients who are struggling for breath. But when the blood doesn't carry carry enough oxygen to a patient's vital organs, doctors try ECMO.

Unfortunately, ECMO is so cumbersome that patients are bed-bound, 24 hours a day. They also require a bedside team that includes a specially trained technician, respiratory therapist and critical-care nurse, Griffith said.

A portable system would improve the quality of life for people desperately in need of lung assistance, researchers say, and allow quicker recoveries as patients avoid the infections and sores that strike the bedridden.

But inventors working on a portable lung have struggled with a persistent problem: Blood tends to clot and blood cells are easily damaged when they leave the human body.

Griffith is counting on specially designed fibers in his device to minimize damage to the blood as oxygen is filtered into it. His group has partnered with a Massachusetts technology firm, and he's optimistic that devices will be available in two to four years.

"We'll have patients walking around with much more compact systems than what we have now," he said.

Recently, some hospitals have used ECMO as a "bridge" for patients awaiting lung transplants, but more often, it's a life-support tool for infants and young children with severe health problems whose lungs need time to heal, according to Griffith and other experts.

"In most cases, a patient is on ECMO for a day or a week while his lungs repair, but that's usually it," Griffith said.

Doctors usually put adults on ECMO when their lungs are so weak that the patients can't survive on a ventilator.

Once he's on ECMO, one of two things will happen: The lungs will improve on their own, or the patient will die, said Dr. Aldo T. Iacono, medical director of University of Maryland's lung transplant program.

That's where McClellan stumped the experts. He not only survived on ECMO longer than any other patient, but improved to being stable enough to manage the stress of a double lung transplant. At 24, McClellan had youth on his side - but he also had the right attitude, his doctor said.

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