Diaphragm Pacing System May Ease Breathing in ALS Patients

Yael Waknine

April 19, 2005

April 19, 2005 — Implantation of a minimally invasive diaphragm pacing system (DPS) with therapeutic electrostimulation may help maintain diaphragm function and slow or arrest the rate of respiratory decline in patients with amyotrophic lateral sclerosis (ALS), according to the initial results of a phase 1 trial presented at the 2005 annual meeting of the Society of American Gastrointestinal and Endoscopic Surgeons in Fort Lauderdale, Florida. DPS has previously been used to improve respiratory capacity in patients with spinal cord injuries, such as Christopher Reeve.

"Lou Gehrig's disease, or ALS, is a fatal neuromuscular disease where patients eventually have to choose to go on a ventilator or die of respiratory failure," Raymond P. Onders, MD, told Medscape, noting that less than 5% of ALS patients in the U.S. choose ventilators. "We're using [DPS] technology to try to waive the need to put these patients on a ventilator, thereby increasing their quality of life and allowing them to live longer."

Dr. Onders is an associate professor of surgery at Case Western Reserve University and director of minimally invasive surgery at the University Hospitals of Cleveland in Ohio.

DPS is designed to apply therapeutic electrostimulation to the diaphragm and phrenic nerves. Therapeutic electrostimulation has been shown to maintain the strength of peripheral muscles in ALS by maintaining physiologic activity, contractile properties, and calcium levels. Stimulation of phrenic nerves has also been shown to induce collateral axon sprouting that may compensate for degenerating motor neurons.

"If there are intact motor neurons that aren't functioning well due to loss of central control, use of the system may help overcome that and maintain muscle mass to increase the period of time before patients have to make a choice about tracheostomy," said Dr. Onders, noting that axonal sprouting will likely afford patients the longest survival time.

In the phase 1 study, a DPS has been laparoscopically implanted in three of 10 selected patients with ALS and a functional expiratory volume of greater than 50%. Each patient was followed for three months preoperatively with a battery of pulmonary function tests, ultrasound analysis of diaphragm thickness, and phrenic nerve conduction tests.

Laparoscopic mapping of the diaphragm was then performed to locate the phrenic nerve motor points; two electrodes were implanted in each hemidiaphragm and connected to an external battery pack via subcutaneous return electrode.

Two weeks later, each electrode was individually evaluated to determine the degree of diaphragm contraction and resulting inspired volume of air. The pacing parameters were then set and patients began diaphragm conditioning with three to five 30-minute sessions of therapeutic electrostimulation per day.

The first patient to undergo the procedure was a 49-year-old woman diagnosed with ALS in May 2002. She is wheelchair-dependent, nonvocal, and had been demonstrating respiratory decline at a rate of 1.6% per month since diagnosis. The implantation was performed on March 14, 2005, in less than two hours.

Preliminary results have confirmed the theory that diaphragm motor units radiate from the central tendon; electrode placement across the tendon therefore allows maximal recruitment of diaphragm muscle and offers the greatest potential for collateral sprouting.

Use of a DPS has, even at this early date, achieved greater motion of the diaphragm than the patient was previously capable of. "We saw that we could actually stimulate her diaphragm with the device to achieve a tidal volume of 700 cc — which is more than adequate for her," Dr. Onders said. "This showed that there were intact and functioning motor units that she no longer had control of."

Unfused contractions (quivers) observed in diaphragm muscle fibers under low-frequency 100-ms stimulation indicated the potential for increased contractility with training.

"What we may find is that as she continues to lose some of those motor neurons, she may realize that she can breathe better with our device," Dr. Onders said, adding that the patient's functional breathing time may be extended by about 10 months.

"We now have a new electrostimulation option that may significantly help patients with ALS," concluded Dr. Onders, suggesting that knowledge of the disease may be beneficial to surgeons laparoscopically implanting a DPS in the future.

The study was funded by the Winters Healthcare Foundation in California.

SAGES 2005 Annual Meeting: Abstract ET001. Presented April 16, 2005.

Reviewed by Gary D. Vogin, MD


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