The diaphragm is a dome-shaped muscle located beneath the lungs, separating the chest cavity from the abdomen. It plays a central role in breathing, with its rhythmic contraction and relaxation drawing air into and expelling it from the lungs.
How the Diaphragm Works and What Paresis Means
The diaphragm contracts to flatten and move downward, increasing chest cavity volume and pulling air into the lungs. During exhalation, it relaxes and moves upward, reducing chest cavity volume and pushing air out. The phrenic nerve, originating from the cervical spinal cord, controls this involuntary movement.
Diaphragmatic paresis is a condition where the diaphragm experiences weakness or partial loss of movement, meaning it is still somewhat active but not functioning at full capacity. This differs from diaphragmatic paralysis, which is a total loss of movement. In paresis, weak signals from the phrenic nerve can lead to reduced breathing efficiency.
Common Causes of Diaphragmatic Paresis
Diaphragmatic paresis often results from phrenic nerve damage or underlying medical conditions.
Nerve Damage
Surgical procedures, particularly those involving the chest or neck like cardiothoracic surgery, and blunt or penetrating trauma, are common causes of phrenic nerve injury. Tumors, such as lung cancer or mediastinal masses, can also compress the nerve, impairing its function.
Neurological Disorders
Conditions like Amyotrophic Lateral Sclerosis (ALS), Multiple Sclerosis, and muscular dystrophies directly impact the nervous system’s ability to control muscle movement, including that of the diaphragm. Guillain-Barré Syndrome, an autoimmune disorder, can cause acute respiratory muscle paralysis. Spinal cord disorders, especially injuries to the upper cervical spine, can disrupt the phrenic nerve’s pathway.
Systemic Diseases
Metabolic disorders like diabetic neuropathy can cause nerve damage affecting the phrenic nerve. Inflammatory conditions and certain viral infections, such as Lyme disease or Herpes Zoster virus, can lead to phrenic nerve inflammation and subsequent diaphragmatic weakness. Autoimmune diseases, including some thyroid disorders, have also been linked to impaired diaphragmatic function. In many cases, the cause of diaphragmatic paresis remains unknown, categorized as idiopathic.
Signs and Symptoms to Watch For
Individuals experiencing diaphragmatic paresis often present with symptoms related to impaired breathing.
Breathing Difficulties
Shortness of breath is a common complaint, particularly during physical exertion. This symptom can worsen when lying flat, a condition called orthopnea, as gravity further impedes diaphragmatic movement. Patients with bilateral diaphragmatic paresis may experience a 70% to 80% reduction in lung capacity, while those with unilateral paresis might see a 50% reduction.
Other Symptoms
Fatigue and general weakness are frequently reported, resulting from the increased effort required for breathing. Sleep disturbances, including sleep-disordered breathing and insomnia, can occur due to reduced oxygen levels overnight. Recurrent respiratory infections, such as pneumonia, may develop because of inefficient clearance of secretions from the lungs. A tell-tale sign is paradoxical abdominal movement, where the abdomen moves inward during inhalation instead of expanding outward, indicating the diaphragm is not contracting effectively. Morning headaches can also be a symptom, often a result of carbon dioxide retention during sleep.
Diagnosing and Managing Diaphragmatic Paresis
Diagnosing diaphragmatic paresis involves clinical assessment and specialized tests.
Diagnostic Tests
A physical examination may reveal paradoxical abdominal movement. Pulmonary function tests are often performed, with a significant drop in forced vital capacity (FVC) when moving from an upright to a supine position being highly suggestive of diaphragmatic weakness. Chest X-rays can show an elevated hemidiaphragm, indicating a potential issue.
Fluoroscopy, often referred to as a “sniff test,” provides real-time imaging of diaphragm movement, allowing visualization of paradoxical upward motion during inspiration on the affected side. Ultrasound of the diaphragm can assess its motion and thickness changes during breathing. Electromyography (EMG) of the diaphragm and nerve conduction studies of the phrenic nerve can evaluate the electrical activity of the muscle and the integrity of the nerve, helping to pinpoint the cause of the weakness.
Management Approaches
Management strategies for diaphragmatic paresis depend on the underlying cause and severity of symptoms. If an underlying cause, such as an infection or metabolic disorder, is identified, treating that condition can lead to improvement. Supportive care often includes breathing exercises and respiratory muscle training to enhance the strength of accessory breathing muscles. Non-invasive ventilation, such as CPAP or BiPAP, particularly at night, can provide ventilatory support and prevent paradoxical movements.
Surgical Interventions
In some cases, surgical interventions may be considered. Diaphragm plication involves tightening the diaphragm to prevent its paradoxical movement and improve lung expansion. For phrenic nerve injuries, nerve repair or reconstruction, including neurolysis or nerve grafting, may be performed to restore function. Phrenic nerve pacing, which involves implanting electrodes to stimulate the phrenic nerve and cause diaphragmatic contraction, is an option for patients with intact phrenic nerves but impaired brain signals, such as those with high spinal cord injuries.