How Do Quadriplegics Breathe After a Spinal Cord Injury?

Quadriplegia, a condition involving paralysis of all four limbs, arises from an injury to the cervical region of the spinal cord. This type of injury can significantly affect breathing by interrupting the nerve signals from the brain to the respiratory muscles. When these signals are disrupted, the mechanics of breathing are altered, presenting a considerable challenge for affected individuals and their families.

Understanding Normal Respiration

Breathing is a complex process controlled by the autonomic nervous system. The primary muscle for this action is the diaphragm, a large, dome-shaped muscle at the base of the lungs. When you inhale, the diaphragm contracts and moves downward, creating space in the chest cavity for the lungs to expand. This process is powered by the phrenic nerve, which originates in the neck at the C3, C4, and C5 spinal levels.

Assisting the diaphragm are the intercostal muscles between the ribs. These muscles contract to lift the rib cage up and outward, further increasing the volume of the chest cavity. Exhalation is a passive process where the diaphragm and intercostal muscles relax, causing the chest cavity to shrink and push air out. Forceful expiration, such as coughing, requires the active contraction of abdominal muscles.

Spinal Cord Injury and Respiratory Impairment

A spinal cord injury in the cervical (neck) region can disrupt nerve signals to the respiratory muscles, with the level of injury determining the extent of impairment. Injuries at the C1 and C2 levels are the most severe, interrupting the nerve supply to both the diaphragm and intercostal muscles. This results in complete paralysis of the breathing muscles, requiring immediate and continuous mechanical ventilation.

Injuries at the C3 and C4 levels can also impact breathing, as an injury here can lead to partial or complete paralysis of the diaphragm. Individuals with C3 or C4 injuries often require a ventilator at first, although some may have the potential to be weaned off the device as their condition stabilizes. For injuries at C5 or below, the diaphragm is functional because the phrenic nerve remains intact, but paralysis of the intercostal and abdominal muscles still compromises breathing.

The loss of intercostal muscle function prevents the chest from expanding properly, leading to shallower breaths. Paralysis of the abdominal muscles weakens the ability to cough. An effective cough is needed to clear secretions from the airways, and its absence increases the risk of respiratory infections like pneumonia.

Altered Breathing Mechanics in Quadriplegia

Following a spinal cord injury, the body adapts its breathing method based on which muscles remain functional. If the phrenic nerve is intact but the intercostal muscles are paralyzed, an individual relies on diaphragmatic breathing. In this pattern, the abdomen rises during inhalation as the diaphragm pushes down, but the chest wall shows little outward movement. This method is less efficient and results in smaller lung volumes.

In some cases, individuals may recruit accessory muscles in the neck and shoulders to assist with inhalation. These muscles help lift the upper rib cage but are not designed for continuous respiration, and their use can lead to fatigue. A phenomenon known as paradoxical chest wall movement is also common. This occurs when the chest wall moves inward during inhalation instead of outward, a result of the flaccid intercostal muscles being pulled in by the negative pressure created by the diaphragm’s contraction.

These altered breathing mechanics lead to a reduction in lung capacity, including tidal volume (the amount of air moved during normal breathing) and vital capacity (the maximum amount of air that can be exhaled after a deep breath).

Ventilation and Respiratory Aids

When natural breathing is insufficient to maintain adequate oxygen levels, mechanical ventilation or other respiratory aids are used. For individuals with high cervical injuries (above C3), this support is often lifelong. Several aids and techniques are available to support breathing, maintain airway health, and prevent complications like pneumonia.

• Mechanical ventilation: Invasive ventilation involves a tracheostomy, where a tube is surgically inserted into the windpipe to connect to a ventilator. Non-invasive options, like BiPAP or CPAP machines, deliver pressurized air through a mask and may be used for less severe impairment or intermittent support.
• Phrenic nerve pacing: An implanted device electrically stimulates the phrenic nerve, causing the diaphragm to contract. This can enable a more natural breathing pattern and reduce or eliminate the need for a mechanical ventilator.
• Glossopharyngeal breathing: Also known as “frog breathing,” this is a learned technique where individuals use their tongue and throat muscles to gulp air and force it into the lungs, allowing for short periods of ventilator independence.
• Assisted cough techniques: To compensate for a weak cough, a caregiver can apply a firm, upward push on the abdomen (a manual “quad cough”) to help expel mucus from the airways.
• Suctioning: This technique involves using a device to physically remove secretions from the airway to prevent blockages and reduce the risk of infection.