Quadriplegia, also known as tetraplegia, involves the dysfunction or loss of motor and sensory function that affects all four limbs, the trunk, and the pelvis. This condition most often results from a spinal cord injury (SCI) in the neck region, which contains the seven cervical vertebrae. The extent of the resulting paralysis and functional loss depends entirely on the specific location and severity of the damage to the spinal cord. For individuals with a cervical SCI, the ability to breathe without assistance is not guaranteed, as the nerves controlling respiration can be interrupted, and independence correlates directly with the specific segment of the spinal cord that was injured.
The Essential Role of the Diaphragm and Intercostals
Breathing is a muscular process that relies on a coordinated effort. The primary muscle responsible for inhalation is the diaphragm, a large, dome-shaped sheet of muscle situated beneath the lungs. When the diaphragm contracts, it moves downward, increasing the volume of the chest cavity and drawing air into the lungs.
This movement is regulated by the phrenic nerves, which originate high in the spinal cord from the C3, C4, and C5 cervical segments. Damage to these segments can directly impair the diaphragm’s function. Other muscles, known as the intercostals, are located between the ribs and assist in expanding the chest wall during normal breathing.
These muscles are important for forceful actions like deep breaths and generating a strong cough. The abdominal muscles also contribute significantly to respiration, especially during exhalation, as they help push air out of the lungs. The nerve supply for the intercostal and abdominal muscles originates lower down in the thoracic spinal cord, making them vulnerable in high cervical injuries.
Injury Level and Respiratory Independence
The degree of breathing impairment is directly tied to the level of the spinal cord injury in the neck. Injuries occurring at the C1 or C2 level are the most severe, as they cause complete paralysis of the muscles that control breathing. Individuals with C1-C3 injuries are typically fully dependent on mechanical ventilation for survival.
An injury at the C3 level carries a slightly better, though still precarious, prognosis for independent breathing. Damage at this level often causes a complete interruption of the nerve pathways to the diaphragm, but some patients may be able to be weaned from full ventilator assistance. The C4 spinal segment contributes significantly to the phrenic nerve. A C4 injury may allow for partial function of the diaphragm, often resulting in shallow, weak breathing.
Patients with C4 injuries may sometimes be weaned off a mechanical ventilator, but they frequently require assistance with respiratory maintenance. Moving lower down the spine, injuries at the C5 level and below rarely result in the need for permanent ventilatory assistance, as the phrenic nerve function is preserved. These individuals have sufficient diaphragmatic function for basic breathing, but their respiratory stamina may be low, causing them to tire easily.
Even with a fully functional diaphragm, lower cervical injuries (C6-C8) still severely affect respiratory health. Because the nerves controlling the intercostal and abdominal muscles originate in the thoracic spine, they are often paralyzed in quadriplegia. The inability to contract these muscles means the person cannot generate a strong, forceful cough. This loss of cough strength is a major concern, as it greatly increases the risk of lung complications like pneumonia due to retained secretions.
Assisted Breathing and Long-Term Respiratory Health
For those who cannot breathe independently, mechanical ventilation via a tracheostomy remains a standard therapy for long-term respiratory support. This method forces air into the lungs, which is a positive pressure system that increases the likelihood of upper airway infections and ventilator-associated pneumonia. An alternative for specific patients is the use of a diaphragm pacing system.
This device involves surgically implanting electrodes near the phrenic nerve or directly into the diaphragm muscle. The diaphragm pacing system delivers electrical impulses to stimulate the diaphragm to contract, thereby mimicking the natural process of breathing. Pacing is preferred over mechanical ventilation because it uses negative pressure, which allows for better speech and reduced secretion issues.
Regardless of the diaphragm’s strength, managing pulmonary secretions is a major challenge for nearly all quadriplegics due to the weak cough reflex. A manually assisted cough (MAC) technique is often employed, where a caregiver applies a quick, firm push inward and upward on the abdomen just below the rib cage, coordinating with the person’s attempt to cough. This external pressure helps generate the force that the paralyzed abdominal muscles cannot provide.
Another option for improving cough effectiveness is a mechanical insufflation-exsufflation device, which delivers a deep breath, then rapidly reverses pressure to simulate a cough. Regular use of these assisted coughing techniques is important for clearing mucus from the lungs, which helps prevent the development of respiratory illnesses. Breathing complications remain a leading cause of death for people with spinal cord injuries, emphasizing the importance of these management strategies.