Not all spinal cord injuries affect breathing. The location of the injury on the spinal cord and the nature of the injury determine whether breathing is affected. In general, an injury at a higher section of the spinal cord may affect functioning in the upper body, including functioning of the lungs and the muscles surrounding them. An injury to the lower part of the spinal cord may affect functioning in the lower body.
Typically, breathing is most affected if the injury occurs above the C5 level. (See illustration with levels of the spine and spinal cord.) The three segments of the spinal cord that most significantly control breathing are at the C3, C4 and C5 levels. The C stands for “cervical,” which refers to the neck area. If an injury occurs in this range, it will likely affect the ability to breathe naturally.
If the injury occurs in the C3 to C5 levels, there is improved likelihood that some type of natural breathing can be recovered with physical, speech and respiratory therapy. If a complete injury occurs at the C2 level and above, breathing will likely require use of an external machine called a ventilator (a “vent”).
Why does a spinal cord injury (SCI) interfere with breathing?
The spinal cord is a thick bundle of nerves that runs from the brain through the protective bone “tunnel” of the spine. The cord acts like a highway that connects the brain to the nerves — from the brain stem to the tail bone. The nerves then spread out through the body to activate muscles.
Any injury to the spinal cord becomes a “roadblock” for these messages. If messages are weakened or blocked completely, nerve and muscle function will be impaired or lost — including functions required for breathing.
What muscles do the work of breathing?
The muscles used in breathing are located in the torso from below the ribs up through the neck. The major muscle we use to breathe is called the diaphragm, which is a large dome-shaped muscle located under the lungs, beneath the rib cage.
The intercostal muscles are located between the ribs, and the accessory muscles are located in the upper chest and neck. Examples of accessory muscles include the trapezius, scalene and sternocleidomastoids, among others.
How do these breathing muscles work together to inhale and exhale?
When the body inhales, the lungs draw in air. To initiate inhalation, the diaphragm contracts and flattens, allowing the chest cavity to expand as the lungs fill with more air. At the same time, the intercostal muscles spread the sides of the rib cage open, like wings, also making room for the expanding lungs.
When the body exhales, these muscles release, pushing air out of the lungs. That is, as the diaphragm returns to its dome shape, it pushes up on the lungs to expel the air, the intercostal muscles return the rib cage to their original shapes and the accessory muscles aid throughout the in-out cycle.
If breathing is affected by the SCI, will you still be able to breathe on your own?
At the time of the injury, the area of the spinal cord around the injury is always swollen, regardless of the type or location of the injury. Because of the swelling, initially it’s difficult to assess the extent of injury. So, in the very early stages of recovery from an injury to the upper cervical spine, breathing will often require use of a ventilator. The ventilator takes over breathing for the body. See "What is a ventilator, and how does it work?".
As swelling decreases — and therapy strengthens the still functioning breathing muscles — the chances increase that natural breathing may return to varying degrees.
It is important to remember that each spinal cord injury and each body is different, so the degree to which natural breathing can return is equally variable.