The diaphragm is the primary muscle responsible for human respiration, acting as a dome-shaped partition that separates the chest cavity from the abdomen. When a person inhales, this muscle contracts and flattens, moving downward to increase the volume of the chest cavity, which draws air into the lungs. Diaphragmatic paralysis occurs when this muscle loses its ability to function, either partially or completely. This impairment is typically due to a problem with the phrenic nerve, which carries signals from the brain, or less commonly, a disease affecting the muscle tissue itself. The resulting impairment significantly reduces the amount of air a person can inhale, impacting overall breathing capacity.
Causes of Diaphragmatic Paralysis
The most frequent cause of diaphragmatic paralysis is damage to the phrenic nerve, which originates in the neck and travels down to the diaphragm. The nerve can be injured during surgical procedures, particularly cardiothoracic or cardiac bypass surgery. Trauma to the chest or neck, or conditions like cervical spine arthritis, can also lead to nerve compression, interrupting the signals required for muscle contraction.
Tumors or masses growing within the chest cavity can press directly on the phrenic nerve pathway, causing compression and subsequent paralysis. Certain neurological diseases also directly affect the motor neurons or the nerve itself, leading to diaphragmatic failure. These examples include amyotrophic lateral sclerosis (ALS), multiple sclerosis, Guillain-Barré syndrome, and diabetic neuropathy.
Disorders that directly affect the muscle fibers, such as muscular dystrophies, are rare causes of paralysis. In cases of bilateral paralysis, the underlying cause may be an inflammatory or infectious process affecting the nerve, such as herpes zoster (shingles) or post-polio syndrome. Up to 20% of cases are classified as idiopathic, meaning a specific cause cannot be identified despite comprehensive testing.
Recognizing the Symptoms
The symptoms depend heavily on whether one side (unilateral) or both sides (bilateral) of the muscle are affected. The most common complaint is dyspnea, or shortness of breath, which is often more noticeable during physical exertion. Difficulty breathing worsens significantly when lying flat, a condition known as orthopnea. This occurs because gravity no longer assists the functioning lung and the abdominal contents push up against the chest.
A telltale sign is the paradoxical movement of the abdomen during inspiration. Instead of the abdomen moving outward as the diaphragm contracts, the paralyzed side moves inward. This happens because the negative pressure created by the working lung pulls the flaccid diaphragm upward, further compressing the lung on the affected side.
The reduced breathing capacity, particularly when lying down, often leads to disturbed sleep patterns and sleep-disordered breathing. Patients may wake up feeling unrested or experience morning headaches due to poor ventilation overnight. The effort required to breathe with a weakened diaphragm results in persistent fatigue and limited tolerance for physical activities.
Methods for Diagnosis
Diagnosis typically begins with a standard chest X-ray, which may reveal an elevated position of the diaphragm on the affected side. This elevation occurs because the paralyzed muscle lacks the tone to maintain its normal position. The most definitive test for assessing diaphragmatic movement is fluoroscopy, often referred to as the “sniff test.”
During this dynamic imaging procedure, the patient is asked to sniff sharply. A healthy diaphragm moves downward, while a paralyzed one will move paradoxically upward, confirming the diagnosis. Pulmonary Function Tests (PFTs) are also used to measure lung capacity, often revealing a significant reduction in forced vital capacity (FVC) when comparing sitting versus lying down measurements. To assess the health of the nerve itself, doctors may perform phrenic nerve conduction studies, which measure how effectively electrical signals travel along the nerve.
Treatment and Management Options
Treatment is customized based on symptom severity, whether the paralysis is unilateral or bilateral, and the likelihood of phrenic nerve recovery. For mild or temporary unilateral cases, observation and conservative management may be recommended, as some nerve injuries can spontaneously heal. If the paralysis is permanent and causes significant breathing difficulty, a surgical procedure called diaphragmatic plication may be performed.
Diaphragmatic plication involves surgically flattening and stiffening the paralyzed, elevated diaphragm. This allows the healthy lung to expand more effectively, reduces the paradoxical movement, and increases lung volume, offering symptomatic relief. For patients with severe bilateral paralysis, mechanical assistance is often necessary. This assistance ranges from non-invasive ventilation (NIV), such as a BiPAP machine used at night, to more intensive support.
In specific cases where the phrenic nerve is intact but non-functional, a diaphragm pacing system may be implanted. This device uses electrical impulses to stimulate the phrenic nerve, causing the diaphragm to contract rhythmically.