The diaphragm is a large, dome-shaped sheet of skeletal muscle separating the chest cavity from the abdomen. It serves as the primary engine for normal, quiet breathing, accounting for up to 80% of the muscular effort required for inhalation. When the diaphragm contracts, it flattens and moves downward, increasing the volume inside the chest cavity and creating a negative pressure. This pressure differential forces the lungs to expand, drawing air inward.
Immediate Symptoms and Physiological Consequences
When the diaphragm stops working, the immediate mechanical effect is a profound disruption of breathing. The most distinct manifestation is paradoxical breathing, where the abdomen sucks inward during inhalation instead of expanding outward. This occurs because accessory muscles create a negative pressure inside the chest, passively pulling the paralyzed diaphragm upward into the thoracic cavity.
The severity of symptoms depends on whether the paralysis is unilateral (affecting one side) or bilateral (involving both sides). Unilateral paralysis may be asymptomatic at rest, as the remaining lung and accessory muscles can compensate. However, patients often experience exertional dyspnea (shortness of breath during physical activity) and sleep-disordered breathing.
Bilateral diaphragm paralysis is far more serious, leading to severe respiratory compromise and often requiring immediate medical intervention. With both sides inactive, overall lung capacity can be reduced by 70% to 80%, compared to a roughly 50% reduction in unilateral cases. This loss of ventilatory power results in rapid, shallow breathing patterns and excessive use of neck and shoulder muscles to move air.
A specific symptom of diaphragm failure is orthopnea, which is severe shortness of breath occurring when lying flat. When a person with a paralyzed diaphragm lies down, the weight of the abdominal contents pushes the flaccid diaphragm further up into the chest. This drastically reduces lung volume, explaining why patients often sleep propped up in a chair or with multiple pillows. The failure to generate sufficient negative pressure results in the inability to move an adequate volume of air, leading to fatigue and eventually insufficient oxygen and excessive carbon dioxide in the blood.
Common Causes of Diaphragm Dysfunction
The most frequent reason the diaphragm stops working is damage to the phrenic nerves, which originate in the neck from the C3, C4, and C5 spinal nerves and provide the sole motor supply. A common source of injury is iatrogenic, meaning it is an unintended consequence of medical treatment, such as surgical trauma during cardiothoracic or neck procedures. The phrenic nerve can be inadvertently stretched, compressed, or severed, particularly during complex heart surgeries.
Neurological diseases are a significant category of causes, as they directly attack the nerves or the motor neurons that control them. Conditions like Amyotrophic Lateral Sclerosis (ALS) are motor neuron diseases causing progressive weakness. Guillain-Barré Syndrome is an immune-mediated disorder that can cause acute phrenic nerve damage and rapid respiratory failure. Spinal cord injuries, especially those affecting the cervical spine at the C3 to C5 level, can immediately disconnect the brain’s breathing signal from the diaphragm.
In some instances, the diaphragm itself is the target of disease, rather than its nerve supply. Myopathies, which are diseases of the muscle tissue like muscular dystrophy, can lead to diaphragm weakness over time. Masses like lung cancer or mediastinal tumors can also cause dysfunction by compressing the phrenic nerve. Although the cause remains unknown in many cases, the underlying problem is nearly always a failure of the electrical signal to reach the muscle or the muscle’s inability to respond.
Medical Diagnosis and Management
Diagnosing diaphragm dysfunction begins with clinical suspicion based on specific symptoms, especially orthopnea or unexplained shortness of breath. Initial imaging often includes a chest X-ray, which may reveal an elevated hemidiaphragm on the affected side, suggesting volume loss in the corresponding lung.
The definitive diagnostic tool is often a fluoroscopic sniff test, which provides a dynamic, real-time view of the diaphragm’s movement. During this test, the patient sniffs sharply, and a paralyzed diaphragm moves paradoxically upward instead of contracting downward. Ultrasound is also increasingly used as a non-invasive tool to measure the diaphragm’s excursion distance and its thickening fraction during inspiration.
Management of a failed diaphragm depends on the cause and severity of respiratory distress. For patients with mild, unilateral paralysis, simple observation may be appropriate, as some phrenic nerve injuries can recover spontaneously over months. Those with severe symptoms, particularly bilateral paralysis, often require ventilatory support, ranging from non-invasive positive pressure ventilation (NIV) used primarily at night to full mechanical ventilation.
Surgical options are considered for select patients to improve breathing mechanics. Diaphragmatic plication involves surgically tightening and flattening the elevated, paralyzed side of the diaphragm, allowing the lung to expand more fully. For patients with a functioning phrenic nerve but a central nervous system injury, such as high spinal cord trauma, a diaphragmatic pacing system can be implanted to electrically stimulate the nerve and restore rhythmic contraction.