The ability to breathe after paralysis from the neck down depends entirely on the location and completeness of the high cervical spinal cord injury (SCI). This type of paralysis interrupts the communication pathways between the brain and the body below the neck. The physiological challenge arises because the nerves controlling the muscles necessary for lung function originate high in the neck. The specific location of the damage dictates how much respiratory muscle control is lost or retained.
The Mechanics of Unimpaired Breathing
Breathing is an automatic process that relies on a coordinated system of muscles to move air in and out of the lungs. The primary muscle of inspiration is the diaphragm, a large, dome-shaped sheet of muscle located beneath the lungs. When the diaphragm contracts, it flattens and moves downward, which increases the volume of the chest cavity and draws air into the lungs. This process occurs without conscious thought, governed by the respiratory center in the brainstem.
The intercostal muscles, situated between the ribs, also play an important part in expanding the rib cage during inhalation. These muscles work to lift the chest wall up and out, further increasing lung capacity. Exhalation is typically a passive process at rest, as the diaphragm and intercostal muscles simply relax, allowing the natural elastic recoil of the lungs to push air out.
For more forceful breathing, accessory muscles in the neck and shoulders are recruited to assist with inhalation. Active exhalation requires the contraction of the abdominal muscles, which push the diaphragm upward to expel air more rapidly. The nervous system controls both the involuntary, rhythmic breathing and the voluntary actions.
Respiratory Function Based on Injury Level
The degree of breathing impairment following a spinal cord injury is directly proportional to the height of the damage within the cervical spine. This is because the phrenic nerve, which solely controls the diaphragm, originates from the C3, C4, and C5 segments of the spinal cord. Damage at or above the origin of this nerve can compromise the signals that drive the primary muscle of breathing.
At the C1 or C2 level, the descending nerve signals to the diaphragm are completely severed. Individuals with this level of damage experience total paralysis of the diaphragm and cannot initiate a breath on their own. This outcome necessitates immediate and permanent reliance on mechanical ventilation to sustain life.
Injuries around the C3 or C4 levels result in a partial or compromised function of the diaphragm. Some weakened spontaneous breathing may be possible. However, the respiratory muscles tire quickly, often requiring support, particularly during sleep when the body’s automatic breathing drive is reduced.
When the spinal cord is injured at C5 or below, the diaphragm’s function is generally preserved because the phrenic nerve’s roots are intact. While the ability to breathe in is maintained, the person loses control of the intercostal and abdominal muscles below the injury. This loss significantly reduces the strength of the cough reflex, making it difficult to clear secretions from the lungs and increasing the risk of respiratory infections.
Medical Intervention and Long-Term Support
For individuals with high cervical spinal cord injury, immediate medical intervention involves the use of mechanical ventilation. This machine moves air into and out of the lungs to maintain oxygen and carbon dioxide levels in the blood. This support is often required in the acute phase of injury, especially when swelling around the spinal cord temporarily worsens function.
Some patients with injuries at the C3 or C4 level may be able to undergo a process called ‘weaning’ to gradually reduce their dependence on the ventilator. This is possible if their diaphragm function improves sufficiently over time. However, many individuals benefit from alternative technologies, such as a phrenic nerve pacing system, which is a surgically implanted device.
This pacing system works by sending electrical impulses directly to the phrenic nerve or the diaphragm muscle itself, causing it to contract rhythmically. Diaphragm pacing can allow some patients to breathe without a ventilator for part or all of the day, offering greater mobility and quality of life. Managing respiratory secretions is a continuous need, which is addressed through respiratory therapy.
Techniques like manually assisted coughing or mechanical insufflation-exsufflation devices are used to help clear the airway by simulating a strong cough. These methods are important for preventing secondary complications like pneumonia, which is a leading cause of illness after cervical SCI. Specialized breathing exercises and positioning are also used to maximize the remaining lung capacity and muscle function over the long term.