Diaphragmatic disorders

🫁 Physiology of Diaphragmatic Disorders

• The diaphragm is the major muscle of inspiration, responsible for approximately 70–80% of resting minute ventilation.
• During inspiration, diaphragmatic contraction flattens the dome, displacing abdominal contents downward and outward, while lowering intrathoracic pressure to draw air into the lungs.
• During expiration, it relaxes and ascends, allowing passive elastic recoil of the lungs and chest wall.
• Accessory muscles (scalene, sternocleidomastoid, external intercostals) assist during increased ventilatory demand or diaphragmatic dysfunction.
• Neural control: The diaphragm is innervated exclusively by the phrenic nerves (C3–C5) – remember “C3, 4, and 5 keep the diaphragm alive.”
• Each phrenic nerve descends over the pericardium to reach the respective hemidiaphragm; injury along this course can cause unilateral paralysis.
• Paradoxical movement — upward motion of the affected hemidiaphragm during inspiration — indicates paralysis or severe weakness and is detectable on fluoroscopy (‘sniff test’).
• Diaphragmatic fatigue occurs with sustained high inspiratory workloads as in COPD, leading to hypoventilation.

📚 Anatomy — Structures Passing Through the Diaphragm

• Inferior Vena Cava (IVC) — at T8; passes through the central tendon (caval opening) with the right phrenic nerve → “Ven₈ cava at T8”.
• Oesophagus — at T10; accompanied by the vagal trunks → “Oesoph₁₀agus at T10”.
• Aortic Hiatus — at T12; transmits the aorta, thoracic duct, and azygos vein → “Aor₁₂ta at T12.”
• Smaller openings allow passage of sympathetic chains, splanchnic nerves, and hemiazygos veins.

⚡ Causes of Diaphragmatic Weakness or Paralysis

• Neurological (Central or Peripheral):
  • Cervical spinal cord lesions (above C3–5), trauma, or infarction.
  • Phrenic nerve infiltration by lung or mediastinal tumors.
  • Syringomyelia, multiple sclerosis affecting cervico‑medullary area.
• Neuromuscular Disorders: Guillain–Barré Syndrome, Myasthenia Gravis, Amyotrophic Lateral Sclerosis (MND), Poliomyelitis, Critical illness neuropathy/myopathy.
• Myopathic / Metabolic:
  • Pompe (acid α‑glucosidase deficiency), muscular dystrophies, mitochondrial myopathies.
  • Electrolyte disturbances (severe hypophosphataemia, hypokalaemia) may transiently impair contractility.
• Mechanical / Traumatic: Post‑operative injury during cardiothoracic surgery, cervical spine surgery, or blunt neck trauma.
• Local Compression / Infiltration: Lung cancer (especially apical “Pancoast” tumors), mediastinitis, aneurysm causing phrenic compression.
• Idiopathic / Iatrogenic: Sometimes occurs after cardiac surgery, radiofrequency ablation, or cryotherapy near the phrenic nerve.

🩺 Clinical Manifestations

• Orthopnoea: Breathlessness when supine — due to loss of abdominal support and diminished diaphragmatic excursion; relieved when sitting upright.
• Paradoxical abdominal movement: Abdomen moves inward during inspiration instead of outward — diagnostic clue for diaphragmatic dysfunction.
• Dyspnoea on exertion or while talking, shallow rapid breathing pattern, accessory‑muscle use.
• Nocturnal hypoventilation: Due to reduced diaphragmatic tone during sleep → morning headaches, fatigue, hypercapnia.
• Unilateral paralysis: Often asymptomatic unless comorbid lung disease; may show elevation of one hemidiaphragm on CXR.
• Bilateral paralysis: Severe orthopnoea, sleep‑related hypoventilation, possible respiratory failure.

🔎 Investigations

• Chest X‑ray: Elevated hemidiaphragm, reduced lung volume on affected side.
• Fluoroscopic “Sniff Test”: Paradoxical upward movement of the affected hemidiaphragm during sharp inspiratory sniff = diagnostic of paralysis.
• Ultrasound: Non‑invasive tool to measure thickness, motion amplitude, and diaphragmatic thickening fraction — reduced in paralysis & fatigue.
• Spirometry: 
  • Restrictive pattern (↓ FVC, normal FEV₁/FVC).
  • ≥ 25% fall in vital capacity supine vs upright suggests bilateral weakness.
• Arterial Blood Gases (ABG): Mild hypoxaemia ± hypercapnia if ventilatory failure develops.
• Electromyography (EMG) and Phrenic Nerve Conduction Studies: Differentiate neuropathy from myopathy.
• Sniff Nasal Pressure (SnP) or Twitch Transdiaphragmatic Pressure (Pdi): Quantifies strength objectively in labs.
• MRI / CT Cervical Spine & Thorax: Identify lesions compressing phrenic nerve or root damage.
• FVC Threshold for Intubation: FVC ≈ 1 L or < 20 mL/kg → imminent respiratory failure → need for mechanical support.

💊 Management & Treatment Principles

• Address Underlying Cause:
  • Cervical cord decompression for trauma or disk lesion.
  • Treat neuromuscular conditions (IVIg for GBS, immunosuppressants for MG, enzyme therapy for Pompe).
  • Remove/irradiate compressive tumors or masses.
• Non‑Invasive Ventilatory Support:
  • Night‑time BiPAP or CPAP to offload respiratory muscles and prevent hypercapnia.
  • Portable ventilators (“sip and puff”) for neuromuscular patients with good bulbar function.
• Invasive Ventilation: Required for acute respiratory decompensation or bulbar failure.
• Diaphragmatic Pacing: Phrenic nerve stimulators may restore ventilation in select cases with intact nerve pathways (high cervical injury or central hypoventilation).
• Respiratory Muscle Training: Inspiratory muscle training (IMT) gradually improves strength in partial paresis or COPD patients.
• Positioning Strategies: Sleeping semi‑upright reduces orthopnoea and hypercapnia.
• Oxygen Therapy: For hypoxaemia but should be combined with ventilatory support if hypercapnia present.
• Physiotherapy & Cough Assistance: Assisted cough devices or mechanical insufflation‑exsufflation (MI‑E) help clear secretions when cough is weak.
• Follow‑Up: Monitor vital capacity and sleep CO₂ levels to prevent chronic hypercapnic failure.

🌟 Prognosis & Clinical Pearls

• Unilateral phrenic nerve paralysis is usually benign and may recover in months if traumatic; bilateral lesions carry high morbidity.
• Both acute and progressive cases require close monitoring of lung volumes and daytime hypercapnia.
• Diaphragm pacing success depends on preserved phrenic nerve integrity and no severe lung pathology.
• In ICU patients, ventilator‑induced diaphragm dysfunction (VIDD) can occur after prolonged mechanical ventilation → early spontaneous‑breathing trials help prevent it.
• Rehabilitation focuses on strength training and optimising nutrition and electrolytes to preserve muscle function.

📚 References

• StatPearls – Diaphragm Disorders
• ATS/ERS Statement: Respiratory Muscle Testing
• BMJ Thorax – Clinical Evaluation of Diaphragm Weakness
• NEJM Review – Respiratory Muscle Dysfunction