Overview of Diaphragmatic Pacing
Diaphragm dysfunction is a condition that may not be diagnosed frequently but can cause unexplained difficulty in breathing. This disorder can be minor to severe, affecting either one side of the diaphragm (a muscle that assists in breathing) or both sides.
Spinal cord injuries (SCI) and a group of severe illness-related nerve damages are common causes of diaphragm dysfunction. As per the National Spinal Cord Injury Statistics Center, there were around 17,000 traumatic SCI cases reported in the United States in 2016.
Typically, severe spinal cord injuries can result in diaphragm paralysis, while damage to the mid-neck area can lead to partial weakness. SCI often causes permanent disability. About half of the affected patients develop a condition called tetraplegia, a form of paralysis that affects all four limbs, and 4% of these patients need long-term assistance with breathing through a device.
Critical illness polyneuropathy (CIP) is another common cause of diaphragm dysfunction. CIP occurs during severe illnesses affecting our motor and sensory nerves. The involvement of nerves and muscles in conditions like CIP can lead to muscle loss and weakness, and even complete paralysis of the diaphragm, leading to severe outcomes such as long hospital stays and dependency on a breathing machine.
The traditional treatment approach has been to wait for spontaneous recovery while supporting the patient with a breathing machine, but this comes with its own complications. Recently, diaphragmatic pacing (DP) has shown positive results in helping spinal cord injury patients get off breathing machines. It’s a process where a catheter-based device activates the diaphragm, assisting in the breathing process. A crucial study named RESCUE 2 is currently investigating temporary transvenous diaphragm pacing compared to the standard treatment for getting patients off breathing machines.
Anatomy and Physiology of Diaphragmatic Pacing
The diaphragm is a structure shaped like a dome that divides the belly area from the chest area. It is made up of two types of muscle fibers, known as slow-twitch and fast-twitch fibers. These muscle fibers begin from parts of your lower back, belly area, ribs, and the pointy bone at the bottom of your sternum, as well as some floating ribs. Signals from the brain to move the diaphragm are sent via the phrenic nerves, which begin from the nerve roots found at the third to fifth levels of your neck (C3 to C5). The phrenic nerve breaks into three parts just before it stimulates the diaphragm.
The diaphragm touches the lower part of your rib cage at the sides. This part is called a zone of apposition. When the diaphragm tightens or contracts, it pushes down into your belly, leading to a drop in pressure within your lungs. This causes air to be drawn into your lungs. When the diaphragm loosens or relaxes, the natural bounce-back effect of the lungs pushes air out.
In a situation where there’s damage to the spinal cord at the neck region or a cervical spinal cord injury (SCI), the pathways that carry signals from the brain to the breathing muscles are directly affected. For high-level SCIs, the pathways to the phrenic nerves are protected, but the pathways from the breath control center in the brain to a part of the brain called the medulla get disrupted.
Why do People Need Diaphragmatic Pacing
People with a spinal cord injury (SCI) above the third vertebra in the neck (C3) are often good candidates for a treatment known as phrenic nerve stimulation or diaphragmatic pacing stimulation. This treatment works by sending electrical signals to the phrenic nerve, which controls the diaphragm and plays a major role in breathing. In these patients, the phrenic nerve is still working and can be stimulated at various points along its path such as the neck, chest, or directly at the diaphragm.
On the other hand, patients with an SCI in the middle of their neck can’t have this type of stimulation at neck or chest levels because their phrenic nerve is not functional. However, a newer technique which stimulates the nerve endings directly at the diaphragm has been showing good results.
Besides spinal cord injuries, there are other conditions in which this treatment might be helpful. These conditions include a birth defect causing abnormal breathing (congenital central alveolar hypoventilation), a condition that causes parts of the brain to descend into the spinal cord (Arnold-Chiari malformations), an infection causing inflammation of the brain’s and spinal cord’s protective membranes (basilar meningitis), brainstem tumors, stroke (cerebrovascular accidents), a disease that compromises the body’s ability to process sugar into energy (Pompe disease), a condition that creates a fluid-filled cyst in the spinal cord (syringomyelia), and a birth defect affecting the spine and spinal cord (meningomyelocele).
Additionally, there have been instances where diaphragmatic pacing stimulation has been successful in treating patients with unintentional damage to one side of the phrenic nerve, as well as certain diseases that affect the nerves controlling muscle movement such as Charcot Marie Tooth disease, spinal muscular atrophy, polio, a rare condition that causes the diaphragm to flutter (diaphragmatic flutter), and a sudden onset of muscle weakness (acute flaccid myelitis).
When a Person Should Avoid Diaphragmatic Pacing
There’s some debate among doctors about the use of a treatment called DP for patients with a condition known as amyotrophic lateral sclerosis (ALS), which is a type of nerve disease that affects muscles. One study found that DP could help these patients live longer by delaying the need for a machine to help with breathing. The authors of this study checked on these patients after a while and their results supported their earlier findings.
However, two other studies have indicated that these patients may not live as long with DP treatment. Until we have more definite proof showing clear advantages, we suggest carefully considering the pros and cons of the procedure with a group of experts at a specialized center. Patients who have functioning phrenic nerves, which are nerves that help move the diaphragm for breathing as determined by nerve conduction studies should not undertake DP. Nerve conduction studies are tests that measure how well your nerves are working.
Equipment used for Diaphragmatic Pacing
There are two main types of equipment often used for a treatment known as diaphragmatic pacing:
1. Traditional Diaphragmatic Pacer – This device has an internal electrode (a conductor through which electricity enters or leaves) that is attached to the phrenic nerve (a nerve that originates in the neck and passes down between the lung and heart to reach the diaphragm) at the neck, chest, or diaphragm level. Thin wires, known as pacing wires, link the electrode to a receiver placed beneath the skin. There’s also an external box that sits on the surface of the skin right above the receiver, functioning as the main control unit. It releases signals in the form of radiofrequency waves.
2. Diaphragmatic Pacing System (DPS) – The DPS is composed of four electrodes implanted directly into the diaphragm for direct muscle stimulation, and a fifth electrode placed beneath the skin that works as a grounding wire. There’s an electrode connector that organizes these five electrodes and brings them out from the skin to an outlet named the external pulse generator (EPG). This EPG is connected to the electrode outlet by a removable cable.
Who is needed to perform Diaphragmatic Pacing?
The process of diaphragm pacing, a surgery that helps the diaphragm (the main muscle that helps us breathe) work better, requires the help and expertise of many healthcare professionals, both before and after the operation. This team includes a doctor called a surgeon who does the actual operation and a neurologist, a doctor who treats diseases of the nervous system. The neurologist is especially important in carefully checking and interpreting what’s called ‘phrenic nerve conduction velocities’. This is a test that checks how well the nerves in the diaphragm are working.
People who need this surgery have often become very weak due to their condition, so it’s important that a skilled team of rehab experts is ready to help after the operation. This team may include a physical medicine and rehabilitation clinician (a healthcare professional who oversees a patient’s physical rehabilitation), a physical therapist (who helps with movement and exercise), an occupational therapist (who helps people get back to their everyday activities), and a speech therapist (who aids with communication and swallowing problems).
Preparing for Diaphragmatic Pacing
Choosing the right patient is an essential part of preparing for a certain type of surgery. Part of this process includes performing tests to check how well the phrenic nerve (a nerve that controls the diaphragm – the muscle that helps us breathe) is working. All this should be done following the guidelines of the medical institution.
Before the surgery, these patients should have a procedure known as a tracheostomy, which is where a hole is made in the neck to help the patient breathe. This is necessary because diaphragm pacing (DP), a technique used during the surgery, can cause a sudden closure of the upper airway due to uncoordinated muscle contractions between the diaphragm and the upper airway. If this happens, the tracheostomy provides emergency access to the airway.
Doctors also need to think carefully about the anesthesia being used during the procedure. They should avoid using drugs that paralyze muscles since they need to stimulate the phrenic nerve to look for contractions in the diaphragm muscle during the procedure.
How is Diaphragmatic Pacing performed
When a doctor needs to place pacing electrodes, they can use one of three methods: the cervical approach, thoracic approach, and diaphragmatic approach.
With the cervical approach, the doctor finds the required nerve in the middle of your neck, beneath a layer of fat. To do this, they gently move a muscle in your neck called the sternocleidomastoid. Once they’ve located the nerve, they double-check it’s the right one using a device that stimulates the nerve and causes a muscle contraction. This activity is confirmed by using a tool called fluoroscopy that allows them to see inside the body. When they’re sure they have the right nerve, they carefully remove any surrounding tissue. Then, they attach two electrodes (small electrical devices) to the nerve and fix them in place. A wire is then placed beneath your skin, connecting the electrodes to a pulse generator (a device that sends electrical pulses), which is also placed under the skin on the same side of your chest.
For a thoracic approach, the doctor uses video-assisted thoracoscopic surgery, or VATS. This means they use a camera to help them see what they’re doing. For the right phrenic nerve, it can be found just behind the esophagus. The left phrenic nerve is situated slightly to the side of the pericardium, which is the outer lining of the heart. Once they find the nerve, they separate it from its protective sheath and attach electrodes to it, just like in the cervical approach. Usually, the pacemakers are placed one at a time, about two weeks apart.
Lastly, the diaphragmatic approach is done using a laparoscopic procedure, meaning they use a camera to see what they’re doing. Here, the electrodes are attached to points where the phrenic nerve inserts into the diaphragm, the main muscle for breathing. These points are figured out during the surgery by stimulating the phrenic nerve. When all electrodes are attached, a wire is brought out through a port in the upper abdomen (tummy), near the stomach. This wire is connected to the EPG (a device that measures electrical activity), which is placed underneath the skin in the chest.
Possible Complications of Diaphragmatic Pacing
When we talk about possible risks or complications with any medical operation, there are several problems that can happen but are not limited to during the operation. Here are some potential complications:
Damage to a nerve called the phrenic nerve, which is a crucial nerve serving your diaphragm, the muscle that plays a vital role in breathing. There could also be injuries to blood vessels; acute lung injury, which is a severe lung condition that causes low oxygen levels in the blood.
In addition, injuries could happen to the pericardium (the protective layer around your heart), and the esophagus (the tube that connects your mouth to your stomach). There could also be accidental perforations or holes in the diaphragm (your main muscle for breathing), and viscous (any hollow organ like stomach or intestines risk potential perforation).
Lastly, peritonitis is a possible complication. This is an inflammation of the inner lining of the abdomen caused often by an infection. Despite this long list of potential risks, medical professionals take all necessary precautions to prevent them.
What Else Should I Know About Diaphragmatic Pacing?
Diaphragmatic pacing is a treatment for people who have breathing problems due to weakened or paralyzed diaphragm muscles, which are crucial for breathing. The goal is to help these patients avoid or delay the need for a breathing machine, which can improve their quality of life. Since this specific treatment is not common, it is important for patients to be evaluated at specialized medical centers that have expertise in this area.
