A paralyzed diaphragm is a condition where one or both sides of the diaphragm, the dome-shaped muscle that separates your chest from your abdomen, can no longer contract on its own. Since the diaphragm is responsible for roughly 80% of the work of breathing, losing function in this muscle forces your body to rely on smaller, less efficient muscles in your chest and neck to pull air into your lungs. The result ranges from mild breathlessness during exertion to serious breathing difficulty that requires mechanical support, depending on whether one side or both sides are affected.
How the Diaphragm Normally Works
When you breathe in, your brain sends a signal down the phrenic nerve, which runs from the upper spinal cord (around the third through fifth vertebrae in your neck) to the diaphragm. The diaphragm contracts and moves downward, creating negative pressure in the chest cavity that draws air into the lungs. When you breathe out, the diaphragm relaxes and rises back up, pushing air out.
When the phrenic nerve is damaged or the muscle itself can’t respond, the paralyzed side doesn’t descend during a breath in. Instead, it moves paradoxically: it gets sucked upward while the healthy side pulls down. A doctor examining you might notice inward movement of the upper abdomen during inspiration, which is the opposite of what should happen. This paradoxical motion is the hallmark of diaphragm paralysis and the key feature doctors look for during diagnosis.
One Side vs. Both Sides
Unilateral diaphragm paralysis, where only one side is affected, has traditionally been considered a relatively mild condition. Many people with one-sided paralysis can go about daily life without major limitations, though exercise tolerance drops noticeably. In one study comparing patients with healthy controls, exercise time fell from an average of about 11 minutes in healthy subjects to roughly 8.5 minutes in those with one-sided paralysis, and peak breathing capacity dropped from 114 liters per minute to 84.
Bilateral paralysis, where both sides are affected, is more serious. Exercise time dropped further to about 7.5 minutes, and peak breathing capacity fell to 69 liters per minute. Bilateral paralysis often requires nighttime ventilatory support to prevent dangerous drops in oxygen levels during sleep. That said, patients who develop compensatory strategies over time can still sustain a reasonable level of physical activity, particularly if the muscles between the ribs remain strong.
Why Symptoms Get Worse Lying Down
One of the most distinctive features of diaphragm paralysis is that breathing becomes significantly harder when you lie flat. When you’re upright, gravity pulls your abdominal organs downward and away from the lungs, giving your chest more room to expand. When you lie down, those organs press upward against the paralyzed diaphragm, which can no longer resist the pressure. The lungs get compressed, and each breath becomes shallower.
This positional worsening is especially pronounced during sleep. During REM sleep, your body naturally suppresses most voluntary muscle activity, leaving the diaphragm as the primary breathing muscle. If the diaphragm can’t do its job, oxygen levels can drop significantly overnight. Sleep studies in patients with even one-sided paralysis show an average maximum oxygen drop of about 15%, with low-oxygen episodes lasting an average of 25 minutes per night. This can fragment sleep, reduce time spent in deep and REM stages, and leave you feeling unrested.
Common Causes
Diaphragm paralysis happens when the phrenic nerve is damaged or when the nerve signal is blocked by a neurological disease. The most common causes include:
- Surgical injury: Unintentional damage to the phrenic nerve during heart, lung, or neck surgery is one of the leading causes.
- Cancer: Tumors in the lung or lymph nodes can grow into or compress the phrenic nerve.
- Spinal cord injury: Damage above the mid-neck level can sever the nerve pathways that control the diaphragm. Quadriplegia is a common associated condition.
- Neurological diseases: ALS, multiple sclerosis, muscular dystrophy, and Guillain-Barré syndrome can all impair diaphragm function.
- Birth trauma: Phrenic nerve injury can occur in newborns during difficult deliveries.
- Idiopathic causes: In some cases, no clear cause is found. The paralysis may follow a viral illness or appear without explanation.
How It’s Diagnosed
The imaging gold standard is the fluoroscopic sniff test. You stand in front of a real-time X-ray machine and take quick, sharp sniffs through your nose. During a normal sniff, both sides of the diaphragm should move downward together. If one side moves upward while the other moves down, that 180-degree difference confirms paradoxical motion and is highly suggestive of paralysis. The sniffing motion tends to exaggerate the abnormal movement, making it easier to spot.
Pulmonary function testing is also standard. Patients with diaphragm paralysis typically show a restrictive pattern, meaning the total amount of air they can forcefully exhale and the speed of that exhalation are both reduced. A telling clue is when lung function drops significantly between sitting and lying-down measurements. If that ratio falls below 0.8, it strongly suggests diaphragm weakness.
For bilateral paralysis, diagnosis can be trickier because both sides move poorly rather than showing obvious one-sided paradoxical motion. More invasive testing with pressure sensors placed in the esophagus and stomach may be needed to confirm the diagnosis. If phrenic nerve damage is suspected, electrical nerve conduction studies can assess whether the nerve is still transmitting signals.
Recovery Without Surgery
A substantial number of people with diaphragm paralysis recover function on their own, particularly when the cause is idiopathic or related to a temporary nerve injury. In one study tracking 16 patients, 11 (about 69%) functionally recovered. The catch is that recovery takes time: the average was roughly 15 months, and some patients took well over a year and a half. Doctors typically recommend a waiting period of at least three months before considering surgery, to give the nerve a chance to heal.
Surgical Options
Diaphragm Plication
For patients with persistent one-sided paralysis and lifestyle-limiting breathlessness, diaphragm plication is the most common surgical treatment. The surgeon essentially folds and tightens the paralyzed diaphragm so it sits lower in the chest and can no longer balloon upward paradoxically. This gives the lung on the affected side more room to expand.
The procedure works well in the short to medium term. Patients typically see their lung function improve by 17 to 30% within the first six months, with the peak benefit averaging around a 27% increase in the amount of air they can forcefully exhale. However, this improvement tends to gradually decline, with lung function returning toward preoperative levels by the fourth year after surgery. Plication is generally reserved for patients with acquired, one-sided paralysis who remain symptomatic despite waiting for spontaneous recovery. People with bilateral paralysis, active cancer, or severe underlying lung or heart disease are usually not candidates.
Diaphragm Pacing
For patients whose phrenic nerve is still intact but isn’t receiving signals from the brain, most commonly people with high spinal cord injuries above the C3 level, an implanted pacing device can electrically stimulate the nerve to make the diaphragm contract rhythmically. This works similarly to a cardiac pacemaker but for breathing. Electrodes are placed either directly on the phrenic nerve in the neck or chest, or on the underside of the diaphragm muscle itself, and connected to a pulse generator under the skin.
Diaphragm pacing can reduce or eliminate dependence on a mechanical ventilator, which dramatically improves quality of life and mobility. It’s also used in certain congenital conditions where the brain’s automatic breathing drive is impaired. For patients with mid-cervical spinal cord injuries where the phrenic nerve itself is damaged, a newer approach stimulates the nerve endings directly at the diaphragm muscle, bypassing the injured section of nerve.