Breathing comes naturally to many of us. Behind the scenes, our diaphragm — the dome-shaped muscle just below the rib cage — acts like a slow and steady trampoline, pushing down to create a vacuum for the lungs to expand and draw air in. Then it rests on pushing the air out. In this way, the diaphragm automatically controls the capacity of our lungs, and is the major muscle responsible for our ability to breathe.
But when the function of the diaphragm is compromised, the instinct of breathing becomes a laborious task. Chronic diaphragm dysfunction can occur in patients with ALS, muscular dystrophy, and other neuromuscular diseases, as well as in patients with paralysis and damage to the phrenic nerve, which stimulates the diaphragm to contract.
A new proof-of-concept design by MIT engineers aims to one day boost the life-sustaining function of the diaphragm and improve lung capacity for people with diaphragm dysfunction.
The MIT team has developed a soft, robotic and implantable ventilator designed to augment the natural contractions of the diaphragm. At the heart of the system are two soft, balloon-like tubes that can be implanted to lie over the diaphragm. When inflated with an external pump, the tubes act as artificial muscles to push down on the diaphragm and help the lungs expand. The tubes can be inflated at a frequency to match the natural rhythm of the diaphragm.
The researchers demonstrated the implantable ventilator in animal models, and showed that in cases of compromised diaphragm function, the system was able to significantly improve the amount of air the lungs could draw in.
There is still much work to be done before such an implantable system can be used to treat humans with chronic diaphragm dysfunction. But the preliminary results open a new avenue in assisted breathing technology that researchers are eager to optimize.
“It’s a proof of concept for a new way to ventilate,” says Alain Roche, associate professor of mechanical engineering and a member of the Institute for Medical Engineering and Science at MIT. “The biomechanics of this design are closer to normal breathing, versus ventilators that push air into the lungs, where you have a mask or a tracheostomy. There’s a long road before this can be implanted in a human. But it’s exciting that we show May be we can increase ventilation with something implantable.
Roche and his colleagues have published their results today in Nature Biomedical Engineering, His co-authors at MIT include first author and former graduate student Lucy Hu, as well as Manisha Singh and Diego Quevedo Moreno; With Jean Bonnemann of Lausanne University Hospital in Switzerland, and Mosab Saeed and Nikolay Vasiliev of Boston Children’s Hospital.
a gentle pressure
The team’s implantable ventilator design evolved from Roche’s previous work on an assistive device for the heart. While a graduate student at Harvard University, Roche developed a cardiac sleeve designed to wrap around the heart to relieve pressure and provide assistance as the organ pumps.
Now at MIT, she and her research group found that a similar soft, robotic aid could be applied to other tissues and muscles.
“We thought, what’s the big muscle that cyclically pumps and sustains life? The diaphragm,” Roche says.
The team began researching designs for the implantable ventilator long before the start of the COVID-19 pandemic, when the use of conventional ventilators increased along with cases. Those ventilators create positive pressure, in which air is forced down through the patient’s central airway and pushed into the lungs.
The diaphragm, in contrast, creates negative pressure. When the muscle contracts and pushes down, it creates a negative pressure that draws air into the lungs, similar to how the handle of a bike pump is pulled to draw in air.
Roche’s team wanted to design a negative pressure ventilator—a system that could help augment the natural function of the diaphragm, especially for people with long-term breathing dysfunction.
“We were thinking about really chronically ill people who have these degenerative diseases that are getting progressively worse,” she says.
The new system reported in the paper consists of two long, soft and inflatable tubes that adhere to a type of pneumatic device known as McKibben actuators. The team adapted the tubes to lie across the diaphragm (front to back) and attached to the ribcage on either side of the dome-shaped muscle. One end of each tube connects to a thin external airline, which is run by a small pump and control system.
By analyzing the contractions of the diaphragm, the team could program the pump to inflate the tubes at the same frequency.
“We realized that we didn’t need to completely mimic how the diaphragm moves—we just had to give it an extra push when it contracts naturally.”
The researchers tested the system on anesthetized pigs, implanting tubes on the animals’ diaphragms, and surgically attaching the ends of the tubes to muscles on either side. They monitored the animals’ oxygen levels and the function of their diaphragms using ultrasound imaging.
The team found that, in general, the implantable ventilator increased the pigs’ tidal volume, or the amount of air that the lungs can draw in with each breath. The most significant improvements were seen in cases where the contractions of the diaphragm and the prosthetic muscles were in sync. In these cases, the ventilator helped the diaphragm to draw in three times the amount of air it could without assistance.
“We were excited to see that we could get such changes in tidal volume, and we were able to preserve ventilation,” says Roche.
The team is working to optimize various aspects of the system, with the goal of someday implementing it in patients with chronic diaphragm dysfunction.
“In hindsight, we know that parts of this system can be miniaturized,” Roche says. “The pump and control system could be worn on a belt or backpack, or even potentially be fully implantable. There are implantable heart pumps, so we know it’s possible. For now, we are learning a lot about the biomechanics and how breathing works, and how we can enhance it with this new approach.
This research was supported by the CIHR, the Muscular Dystrophy Association, the National Institutes of Health, the SICPA Foundation and the Lausanne University Hospital Improvement Fund, the SMA2 Brown Fellowship, and the National Science Foundation.