Diaphragmatic paralysis is the loss of motor function in the primary muscle of breathing, occurring when the nerve signal to the diaphragm is interrupted. This dome-shaped muscle beneath the lungs is responsible for the majority of air intake, expanding the chest cavity when it contracts. When paralyzed, the diaphragm fails to move downward on inhalation, severely compromising lung capacity and breathing efficiency. Functional reversal is often possible, depending on the underlying cause and the nature of the nerve damage. Modern interventions offer options to restore movement or compensate for function loss, providing functional repair beyond simple supportive care.
Causes of Diaphragmatic Paralysis
Diaphragmatic paralysis nearly always traces back to impairment of the phrenic nerve, which originates in the neck and controls the diaphragm’s movement. Damage can result from direct physical trauma or, more commonly, iatrogenic injury during surgical procedures. Cardiac and thoracic surgeries, such as coronary artery bypass grafting, carry a known risk of phrenic nerve injury from cooling or mechanical manipulation. The nerve may also be compromised by compression from tumors, particularly lung cancer or growths in the mediastinum, which block signal transmission. Neurological diseases, including Guillain-Barré Syndrome or Amyotrophic Lateral Sclerosis (ALS), can cause progressive damage to the phrenic nerve or spinal cord motor neurons. Paralysis can be unilateral (minimally symptomatic) or bilateral, a severe condition often requiring mechanical ventilation.
Diagnosis and Initial Stabilization
Confirming diaphragmatic paralysis requires imaging and physiological tests to assess muscle movement and respiratory function. Diagnosis often begins with a chest X-ray, which may show an elevated diaphragm on the affected side. Pulmonary function tests compare results when the patient is sitting upright versus lying down; a significant drop in lung capacity in the supine position suggests diaphragm involvement.
The most specific test is fluoroscopy, or the “sniff test,” where the patient sniffs forcefully while the physician watches the diaphragm’s movement. A paralyzed diaphragm moves paradoxically upward instead of downward during inhalation. Electrodiagnostic studies evaluate the nerve signal’s integrity and the muscle’s electrical activity, using methods like phrenic nerve conduction velocity and diaphragm electromyography. Following diagnosis, immediate stabilization for patients with severe symptoms, particularly bilateral paralysis, involves supportive care, including non-invasive ventilation or a ventilator.
Surgical and Non-Surgical Restoration Techniques
Restoring function to a paralyzed diaphragm involves strategies ranging from structural repair to nerve regeneration and electrical stimulation.
Diaphragmatic Plication
Diaphragmatic plication does not restore nerve function but physically tightens the flaccid, dome-shaped muscle. Plication effectively lowers and stabilizes the diaphragm, preventing its paradoxical upward movement into the chest cavity during inhalation. This structural correction allows the lung to expand more fully, significantly improving breathing mechanics, especially in chronic unilateral paralysis.
Nerve Repair and Regeneration
For paralysis caused by phrenic nerve injury, the primary goal is nerve-based repair to reestablish the electrical pathway. If the nerve damage involves a clean cut or a short gap, direct end-to-end anastomosis (suturing the nerve ends together) is the preferred method. When a segment of the nerve is missing, such as after tumor removal, surgeons perform nerve grafting. This involves harvesting a segment of a less-essential nerve, like the sural nerve from the leg, to bridge the gap. A nerve transfer reroutes a functioning, redundant nerve to the non-functioning phrenic nerve, often allowing for functional recovery sooner due to the shorter distance for nerve fiber regeneration.
Diaphragm Pacing
In cases where the phrenic nerve is permanently damaged or paralysis is due to a neurological condition affecting the brainstem, phrenic nerve stimulation (diaphragm pacing) offers a bypass solution. This technique involves surgically implanting electrodes around the phrenic nerve or directly into the diaphragm muscle. An external transmitter sends electrical impulses to the electrodes, causing the diaphragm to contract rhythmically and mimic natural breathing. Diaphragm pacing is effective for patients with high spinal cord injury or central hypoventilation syndrome, where the nerve is intact but lacks central control.
Expected Functional Recovery
Functional recovery depends heavily on the chosen technique, with outcomes ranging from improved breathing mechanics to motor restoration. Following phrenic nerve reconstruction, reinnervation and muscle contraction are slow, often taking 18 to 24 months due to the slow rate of nerve fiber regeneration. Patients typically report overall improvement in breathing function, with studies showing symptomatic relief and increased physical functioning scores.
Objective measures of successful repair include increased diaphragm motor amplitude and improved nerve conduction latency, indicating successful signal transmission. Respiratory physical therapy is a necessary component of rehabilitation, beginning soon after surgery to maximize recovery. Therapists use specialized techniques, including diaphragmatic breathing exercises and postural correction, to retrain the muscle and address secondary musculoskeletal issues. A successful outcome is defined as weaning off ventilatory support, improving exercise tolerance, and experiencing better sleep quality, though complete restoration is not always achieved.