For all its mystical powers, the heart is a pretty simple thing. It’s a pump—blood in, blood out. And that has made it not all that difficult to copy.
But the lungs are another matter. No one will ever advise you to “Follow your lungs” or bemoan a “broken lung,” which is a shame. Because it is one complicated organ.
Few people understand this as well as William Federspiel, a bioengineering researcher and professor at the University of Pittsburgh. For the past 20 years or so, he has been working on designing an artificial lung. It’s been a challenge, he concedes.
“The technology for patients who have lung failure is way behind the technology for people with heart failure,” he says. “It comes down to a pretty simple fact: It’s pretty easy to design a small pump that can pump blood at the flow rate the heart does.
“But the lung is just an incredible organ for exchanging gas between the atmosphere and the blood that’s flowing through your lungs. There’s no technology that’s ever been able to come close to what the human lung can do.”
Lung in a backpack
That said, Federspiel and his research team are getting closer. They’ve already invented a device called the Hemolung Respiratory Assist System (RAS) that performs what’s described as “respiratory dialysis,” removing carbon dioxide from a patient’s blood. It’s being produced by a Pittsburgh startup Federspiel founded called ALung Technologies, and could undergo testing in U.S. clinical trials late this year or early 2018. It’s already been approved for use in Europe, Canada and Australia.
Now they’re moving forward on a much smaller device, for which they've applied for a patent, only this one is designed to raise the oxygen levels in a person’s blood. Also, earlier this year, the researchers received a $2.35 million grant from the National Institutes of Health (NIH) to develop a version of their artificial lung for children.
Put simply, Federspiel’s latest research is focused on refining a mechanical lung that functions outside the body, but that is small enough to be carried inside a backpack or holster. It would be connected to the patient’s vena cava—a large vein carrying blood into the heart—through a cannula, or tube, inserted in the jugular vein in the throat. He or she would still need to breathe oxygen from a portable tank.
This, Federspiel notes, would allow the person to be more mobile in the hospital instead of being confined to a bed. That’s critical, because if patients can’t move around, their muscles become weaker, and their chances of recovering from a serious lung infection diminish. The device is seen as being particularly beneficial for patients waiting for a lung transplant, such as people with cystic fibrosis.
“We’re not intending right now that they would be able to leave the hospital with one of these systems,” he says, “but at least within the hospital, they’d be able to get up and walk around.”
The curse of clots
There have been other recent breakthroughs in recreating human lungs. Last year, scientists at Los Alamos National Laboratory in New Mexico announced that they’ve created a miniature device made of polymers that functions like a lung, and is designed to mimic the organ’s response to drugs, toxins and other environmental elements for test purposes.
In the Czech Republic, scientists at the Brno University of Technology said they’ve developed a 3D-printed version of a lung that can simulate conditions such as asthma and other chronic pulmonary problems, and that will enable doctors to bring more precision to how they treat lung conditions.
Both of those projects, however, are meant to help researchers learn more about conditions and treatments, whereas Federspiel’s research—as well as similar work being done nearby in Pittsburgh at Carnegie Mellon University—is geared more toward helping patients improve their long-term prognosis.
The new device—the one designed to raise blood oxygen levels—has to support a heavier blood flow than the machine that lowers carbon dioxide. So, as Federspiel points out, it faces the challenge of dealing with what often happens to blood when it flows over a manmade surface—it clots.
It all has to do with the sophisticated gas exchange that’s key to lung function, and how it’s mimicked in the device. “The gas exchange unit [in the device] is composed of a large number of polymer tubes that are about twice the thickness of a human hair,” he explains. “They’re permeable to gas, so when blood is flowing on the outside of these tubes, we run 100 percent oxygen through the inside of the tubes. The oxygen moves into the blood by diffusion and carbon dioxide moves out of the blood into the gas stream flowing through the device.”
The problem is that the blood passing through comes in contact with a relatively large artificial surface, increasing the chance that clots will form. It is a big reason why it’s not realistic at this point to consider implanting lung devices like this inside a patient’s body. They would likely need to be replaced every few months.
Federspiel says that recently his team was able to test the new device on sheep for five days without any problems. Sheep are used because their cardiovascular systems are similar to humans’. But he and his team are also working with a company to develop special coatings that they hope will greatly reduce clotting. That would also allow doctors to significantly lower the level of anti-coagulation drugs patients would need to take.
The next step, he says, is a 30-day animal trial that would compare the results of devices both with the coating and without it. He estimates that human clinical trials could still be four to five years away.
But Federspiel’s not deterred by the deliberate pace of creating a device that works as well as the human lung. He’s well aware of how demanding that can be.
“An artificial lung still has to function like the human lung,” he says. “When I give talks on this, the first thing I say is the lung is an incredible organ.”