Ventilator

People who have severe breathing difficulties or neuromuscular diseases such as Amyotrophic Lateral Sclerosis (ALS), must rely on surgically placed breathing tubes for ventilation. Pipes can be bulky and affect their quality of life.

But the MIT engineers whose a study was recently published in Nature Biomedical Engineering, we hope to change that by creating a soft ventilator that experts can implant directly into someone’s chest. When tested on pigs, it tripled the amount of air inhaled.

“There are many muscle degenerative diseases where the diaphragm will fail,” leading to the need for long-term ventilation, says biomedical engineer Ellen Roche, who led the work. Roche had previously developed a device that helps weakened hearts pump bloodand so she thought, “perhaps we can help the diaphragm as we do the heart.”

The soft impact of the fan

Many people whose diaphragm has lost function now rely on a fan which pushes air in and out of the lungs through a tube permanently placed in the throat. This may extend their lives, but it means they are tied to a machine, likely to lose their ability to speak, and often need round-the-clock care.

In contrast, the new device works as an additional set of muscles that expand and contract on the diaphragm, which is a dome-shaped muscle. Instead of pushing air into the lungs, it creates a negative pressure that pulls it in.

“Overall, it’s a simple mechanical concept,” Roche says.

Most importantly, the new ventilator will eventually avoid the surgical tube down the throat. Neuroscientist Robert C. Bucelli of the University of Washington ALS Center, who was not involved in the work, thinks the approach could make a “marked difference” for people who have trouble breathing due to neuromuscular diseases like ALS.

“It’s absolutely exciting and a wonderful starting point,” Bucelli says.

Testing the fan

So far, Roche and her team have tested the device on pigs that have been anesthetized to slow their breathing. Using a sensor that measures changes in airflow in the pigs’ mouths as they try to inhale, they can time the contracting ventilator “muscles” to the natural rhythm of breathing. In the best-responding pig, the new ventilator nearly tripled the amount of air drawn into its lungs.

“I was so impressed with how well their device worked,” said Andrew Cohn, a soft robotics engineer at the University of Bristol who was not involved in the work. He emphasizes that supporting the diaphragm in its natural function, rather than completely bypassing it, will make the fan particularly useful for many different users.

This is because while some people will need ventilation for the rest of their lives, others can regain theirs natural function of the diaphragm through rehabilitation and treatment.

“[In such cases] these devices are really ideal,” Cohn says, because they can be set to provide only as much help as is needed.

I expect

However, the new fan is still a work in progress. For example, Roche and her team want to upgrade the sensing mechanism to one that uses implanted electrodes to pick up nerve signals in the diaphragm, rather than airflow from the mouth.

From a clinical perspective, Bucelli says the individual will need this tuned to their own diaphragm function, as this varies widely. Another concern is whether people can clear their throats. With a traditional ventilator, caregivers have direct access to the airway through the tube and can intervene to help.

This is a key point and Roche is working on how to deal with various respiratory actions such as coughing, sneezing and deep breathing.

“We’re not there yet, but we’re moving toward trying to synchronize so that the patient can easily say, ‘I’m going to cough’ or ‘I’m going to take a deep breath,’ and the system continues,” says Roche. For advanced ALS, however, Bucelli worries that weakness in other surrounding muscles can make coughing difficult or regardless of airway protection.

The machines that power and control the fan are the final hurdles. The artificial muscles require a certain amount of compressed air to contract, Cohn says, which means a pump must connect them. Currently, this happens through airlines that go through the skin.

Roche’s group wants to make both the pump and its controller fit into a small hip bag, giving users the freedom to move around independently. But Cohn says the long-term plan should be a fully implantable system, because anything that requires lines going through the skin permanently can pose a risk of infection.

That would require an implantable pump, and research groups around the world, including Kohn’s own, are busy trying to develop one. He is optimistic that it is achievable.

“We’re quite interested in trying to solve this problem,” Cohn says. “Pacemakers in the human body show that this is possible.”

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