The diaphragm is the primary muscle responsible for breathing, a dome-shaped structure situated at the base of the chest that separates the thoracic cavity from the abdomen. Its contraction causes it to flatten and move downward, creating a vacuum that draws air into the lungs. Diagnosing problems with this muscle can be difficult because symptoms, such as shortness of breath, often overlap with those of common heart or lung conditions. The diagnostic process must be systematic, moving from initial suspicion to precise identification of whether the problem is structural, functional, or related to the nerves.
The Initial Clinical Assessment
The diagnostic process begins with a detailed review of the patient’s medical history and a physical examination. Unexplained shortness of breath, especially when lying flat (orthopnea), is a significant indicator of potential diaphragmatic dysfunction. Patients may also report difficulty sleeping, recurrent respiratory infections, or a history of recent surgery or trauma near the chest or neck, which could have damaged the phrenic nerve.
The physical examination focuses on observing the patient’s breathing pattern. A specific finding is paradoxical breathing, where the abdomen moves inward instead of outward during inspiration. This occurs because a weakened or paralyzed diaphragm is pulled upward by the negative pressure generated by accessory breathing muscles. A doctor will also listen for reduced breath sounds and observe asymmetric chest wall movement, suggesting unilateral dysfunction. This initial assessment guides subsequent functional and imaging tests.
Structural Diagnosis Through Imaging
If the initial assessment suggests a diaphragm problem, imaging is used to evaluate the muscle’s structure and position. A standard Chest X-ray is often the first test, revealing an abnormally elevated hemidiaphragm, a common sign of paralysis or eventration. Elevation is defined if the right hemidiaphragm sits more than two centimeters higher than the left, or if the left is at the same level or higher than the right.
While the X-ray is excellent for initial screening, it cannot confirm the cause of the elevation. Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) provides detailed cross-sectional views. These advanced scans identify structural defects, such as a diaphragmatic rupture or hernia, where abdominal organs protrude into the chest cavity. They also help rule out masses, like tumors or cysts, that might be pushing the diaphragm upward and mimicking dysfunction.
Evaluating Diaphragmatic Function
To determine if the diaphragm is moving correctly, dynamic function tests are required, especially for diagnosing paralysis or weakness. Diaphragmatic Fluoroscopy, known as the “Sniff Test,” is a primary evaluation tool. This procedure uses a continuous X-ray beam to create a real-time video of the diaphragm’s movement as the patient inhales deeply and sniffs rapidly.
In a healthy person, the diaphragm moves downward with inhalation; with paralysis, the affected side moves paradoxically upward. This reverse motion confirms functional impairment and is highly specific for detecting unilateral paralysis. Pulmonary Function Tests (PFTs) offer an indirect measure of diaphragm strength. The Maximum Inspiratory Pressure (MIP) test measures the greatest pressure a person can generate when inhaling against a blocked mouthpiece, reflecting overall inspiratory muscle strength.
Another key PFT measures the change in Vital Capacity (VC) between standing and lying down. When a patient with weakness lies flat, the weight of the abdominal contents pushes the diaphragm further into the chest, significantly reducing lung capacity. A drop in VC greater than 20% when moving from standing to supine position strongly suggests diaphragmatic weakness. These functional tests classify the severity and nature of the dysfunction.
Advanced Diagnostic Procedures
When the cause of dysfunction remains unclear or a neurological origin is suspected, specialized procedures are employed. Diaphragmatic Electromyography (EMG) and Nerve Conduction Studies (NCS) assess the health of the phrenic nerve and the muscle’s electrical activity. NCS involves stimulating the phrenic nerve in the neck to measure how quickly the signal reaches the diaphragm, pinpointing nerve damage or blockages.
Diaphragmatic EMG involves inserting a thin needle electrode to record electrical signals, differentiating between nerve problems (neuropathy) and muscle tissue problems (myopathy). EMG can detect denervation and is sometimes enhanced by ultrasound guidance for improved accuracy. Ultrasound-guided measurements of diaphragm thickness are a non-invasive method for assessing muscle health. A healthy diaphragm thickens significantly during inspiration, while a paralyzed or atrophied diaphragm shows reduced or no thickening. A thickening fraction of less than 20% is indicative of dysfunction, and in rare instances, direct visualization or biopsy may be necessary to confirm pathology.