What is the emerging research on processes to help with breathing?

Author: Sharon Jang | Reviewer: Tova Plashkes | Published: 24 September 2020 | Updated: 7 December 2021

For people who are ventilator dependent, various electrical stimulation techniques are available to assist with breathing. This includes phrenic nerve stimulation/diaphragm pacing, abdominal electrical stimulation, and epidural stimulation.

The

diaphragm

is the main muscle responsible for breathing and is activated by the

phrenic nerve

to contract. After SCI, the connection between the brain and the phrenic nerve is disrupted, which contributes to impaired breathing. Researchers have been looking at ways we can stimulate this nerve to reactivate the diaphragm through a process called

phrenic nerve stimulation

. This process involves surgically implanting

electrodes

and a receiver close to the phrenic nerve, either in the chest or the neck, and a receiver in the chest wall. This device is controlled with an external remote and antenna (which is used to connect to the electrode receiver).

For phrenic nerve stimulation to work, the diaphragm must have normal function, and the phrenic nerve needs to be intact (i.e., sends a signal when stimulated). As a result, individuals who have a C3, C4, or C5 level injury may not be eligible as they often have impaired phrenic nerve function. It is important to note that this procedure can only facilitate inspiratory functions, but not expiratory. As a result, an individual who receives phrenic nerve stimulation may not require mechanical ventilation, but will still require assistance with coughing and clearing secretions. Tracheostomies and mechanical ventilation are often still used in combination with phrenic nerve stimulation as a back-up.

Some weak evidence supports the use of phrenic nerve stimulation. One study found that diaphragm pacemakers have better results with long term implantation (i.e., 6.3 years in the study). Another study showed that diaphragmatic paces can improve survival rates, decrease the cost of care, improve the quality of speech, increase rates of social participation, and improve management of using a powered wheelchair. Many complications have been reported in the research in regards to using a phrenic nerve stimulator. These complications include wires breaking or getting displaced, device failure, inhaling food when eating, shoulder or abdominal pain, and infections.

As diaphragm pacing only helps with inhalation, limited research suggests that electrically stimulating the abdominal muscles helps with expiration and coughing. Ideally, the abdominal muscles would be used to support voluntary efforts to cough. There have been mixed findings on the effectiveness of stimulating the abdominal muscles to enhance cough. While some weak studies have found abdominal stimulation to improve cough, other weak evidence studies have found no noticeable changes. More research is required to determine the efficacy of stimulating the abdominal muscles to enhance cough in SCI.

Epidural stimulation is conducted through surgically implanting an electrode over the spinal cord. Once done, the electrode, which is controlled with a remote outside of the body, stimulates various parts of the spinal cord. Emerging research on epidural stimulation suggests that it may benefit respiratory function after SCI. By directly stimulating nerve cells in the spinal cord, weak evidence suggests that breathing muscles can be activated. The muscles are activated in a pattern that resembles normal breathing, while reducing fatigue. Additionally, weak evidence suggests that epidural stimulation can improve other respiratory functions including coughing and speaking.