Diaphragm

The diaphragm is a dome-shaped, unpaired musculotendinous structure that forms the floor of the thorax and the roof of the abdomen. As the body’s primary muscle of inspiration, it plays a decisive role in respiration, intra-abdominal pressure, and global core stability.

Origin and Insertion

The muscular fibres of the diaphragm arise from three distinct regions and converge into a central fibrous tendon, the centrum tendineum.

Sternal Part

The sternal part originates as two broad, flat muscular slips from the posterior surface of the xiphoid process and the adjacent portion of the sternal body. These fibres course superiorly and posteriorly and contribute to stabilisation of the anterior thoracic wall.

Costal Part

The costal part attaches to the internal surfaces of ribs 7–12 and their costal cartilages. The fibres arch upward toward the central tendon and constitute the largest portion of the diaphragmatic surface. This region is primarily responsible for elevation of the rib cage during inspiration.

Lumbar Part

The lumbar part consists of two strong muscular crura:

• Right crus: attaches to the vertebral bodies of L1–L3 and the intervening intervertebral discs.

• Left crus: attaches correspondingly to the vertebral bodies of L1–L2.

Between these fibres run the medial arcuate ligament and lateral arcuate ligament, tendinous arches anchoring the diaphragm to the psoas major and quadratus lumborum muscles. These arcuate ligaments function both as attachment points and as passageways for lumbar nerves and vessels.

All fibres converge into the centrum tendineum, a multilayered fibrous plate without bony attachment. This central tendon is essential for even transmission of muscular force across both diaphragmatic domes.

Anatomical Relations

The two diaphragmatic domes have distinct topographical relationships.

Thoracic Surface

The thoracic surface is covered by the visceral pleura on each side and by the pericardium centrally. The right dome typically lies at vertebral level T8–T9, whereas the left dome lies at T9–T10, reflecting the position of the liver on the right and cardiac compression on the left.

Beneath the pericardium lies a small pericardial fossa (fossa centralis), a relative weak point where pleural contact may produce a sensation of pressure.

Abdominal Surface

The abdominal surface is in contact with the liver on the right and with the stomach and spleen on the left. Peripherally, the diaphragm relates to the renal fossae, where it is anchored via the crura.

A subphrenic bursa provides a smooth gliding interface against the liver, which is important during abdominal pulsations.

Openings and Passages

• Caval opening (T8): Located within the central tendon; transmits the inferior vena cava and small branches of the phrenic nerve.

• Oesophageal hiatus (T10): Serves as the passage for the oesophagus and vagal trunks; surrounded by fibres of the right crus, forming a functional valve during swallowing.

• Aortic hiatus (T12): Situated posterior to the muscular diaphragm; allows passage of the descending aorta, thoracic duct, and azygos vein without muscular compression.

These openings balance the need for separation between the thoracic and abdominal cavities with the requirement for unobstructed transport of vital structures.

Histological and Biomechanical Structure

The central tendon consists of dense fibrous tissue lacking striations, whereas the peripheral musculature is striated and organised into radially oriented fibre bundles.

A mixed composition of type I (slow-twitch) and type II (fast-twitch) fibres enables both endurance for quiet respiration and rapid force generation during forced inspiration. The domed geometry allows uniform distribution of muscular force toward the centre, enabling efficient volume change without local fibre overload.

Clinical Anatomical Significance

Injury to the phrenic nerve (C3–C5) results in unilateral or bilateral diaphragmatic paralysis. In unilateral paralysis, the affected dome moves paradoxically upward during inspiration.

Eventration refers to congenital or acquired thinning of a diaphragmatic dome, leading to permanent elevation and reduced ventilatory efficiency without a true defect in the central tendon.

Hiatal hernias occur when abdominal contents herniate through the oesophageal hiatus, often causing reflux symptoms and requiring surgical repair in larger defects.

Primary Inspiration

During quiet tidal breathing, the vertical fibre components of the diaphragm are activated first. Contraction flattens the domes and lowers them by approximately 1–2 cm. Thoracic volume increases primarily in the vertical dimension, and intrathoracic pressure decreases by about 2–3 mmHg, sufficient to draw in approximately 0.5 L of air. This mechanism is highly energy-efficient and dominant at rest.

Forced Inspiration

During deep or forceful breathing, additional volume and rapid response are required. Costal fibres elevate the lower rib cage through pump-handle and bucket-handle mechanics, working in tandem with the diaphragmatic domes. Accessory muscles such as the sternocleidomastoid, scalenes, and pectoralis minor stabilise the upper thorax and assist rib elevation when diaphragmatic action alone is insufficient.

Eccentric Control During Expiration

Although expiration at rest is passive, the diaphragm contributes actively during controlled exhalation. Gradual relaxation allows smooth reduction of thoracic volume and prevents abrupt collapse driven by elastic recoil. During speech and singing, precise eccentric control is required to regulate airflow, with coordinated activity between the diaphragm and abdominal muscles to maintain stable expiratory pressure.

Interaction With the Abdominal Wall

The diaphragm, abdominal wall, and pelvic floor form a functional “respiratory cylinder.” Simultaneous diaphragmatic contraction and abdominal wall tightening markedly increase intra-abdominal pressure, which is essential during coughing, lifting, and heavy loading. This pressure stabilises the lumbar spine, improves lifting mechanics, and reduces the risk of spinal injury.

Respiratory Patterns and Adaptation

During hyperventilation, such as high-intensity interval exercise, the diaphragm may approach its maximal shortening velocity and require increased assistance from the scalenes and sternocleidomastoid. In hypoventilation due to diaphragmatic fatigue or neuromuscular disease, breathing is partially offloaded to intercostal and abdominal muscles, which is inefficient over time.

Diaphragm and Circulation

Diaphragmatic contraction acts as a muscular pump for the inferior vena cava, enhancing venous return to the heart and supporting orthostatic regulation. Pressure fluctuations across diaphragmatic surfaces also promote lymphatic drainage from the abdominal cavity toward the thorax.tudents, 3rd Edition, Churchil Livingston Elsevier (2015).

Clinical Findings and Typical Symptoms

Dyspnoea on Exertion

Patients experience shortness of breath particularly during physical activity or demanding inspiratory movements. Unilateral diaphragmatic paresis often causes mild symptoms at rest, but a clearly reduced exercise capacity during uphill walking or stair climbing.

Orthopnoea

In cases of bilateral diaphragmatic paresis or marked weakness, patients experience breathing difficulties when lying flat and must sit upright to breathe more comfortably. This occurs because the abdominal organs displace the diaphragm cranially in the supine position.

Paradoxical Breathing

During inspiration, the affected dome is drawn inward toward the thorax instead of descending, while the healthy dome bulges outward. This is associated with reduced tidal volume and an increased respiratory rate.

Reduced Cough Effectiveness

Impaired ability to generate a forceful expiration followed by an effective cough, increasing the risk of secretion retention and respiratory infections.

Assessment Methods

Diaphragm Ultrasound

Measurement of dome excursion during deep breathing. Normal excursion is approximately 1.5–2.5 cm during quiet deep inspiration; significantly reduced values indicate paresis.

Fluoroscopy (“Sniff Test”)

The patient performs a rapid nasal inspiration. In diaphragmatic paresis, paradoxical movement of the affected side is observed.

Measurement of Transdiaphragmatic Pressure (Pdi)

Catheters placed in the oesophagus and stomach measure differential pressure during inspiration. Reduced Pdi indicates diaphragmatic weakness.

Spirometry: Supine vs. Standing

A reduction in vital capacity (VC) of more than 20% when moving from standing to supine position is suggestive of diaphragmatic paresis.

Rehabilitation Strategies

Early Phase (0–2 weeks)

Goal: Activate and maintain muscle fibres without overload.

Interventions:

• Diaphragmatic “sniff” exercises: Short, rapid nasal inspirations, 10–15 repetitions × 3 sets.

• Respiratory biofeedback using ultrasound or guided instruction to enhance conscious control of diaphragmatic function.

Intermediate Phase (2–6 weeks)

Goal: Increase inspiratory strength and endurance.

Interventions:

• Inspiratory Muscle Training (IMT): Resistance set at 30–50% of maximal inspiratory pressure, 5 minutes × 2–3 times daily.

• Combined with abdominal breathing: Teaching the patient to allow the abdomen to expand during inspiration to maximise dome excursion.

Late Phase (>6 weeks)

Goal: Integrate diaphragmatic training into functional activity and increased load.

Interventions:

• Progressive increase of IMT resistance toward 60–80% of maximal inspiratory strength.

• Functional exercises: Breathing exercises during walking and stair climbing with controlled respiration.

• Core stability programme: Integration of diaphragmatic activation with pelvic floor and deep abdominal and spinal muscles to promote global stability.

Compensatory Patterns

Intercostal Muscles

In diaphragmatic dysfunction, intercostal muscles are overrecruited during inspiration. This produces less efficient volume expansion and leads to faster muscle fatigue.

Accessory Respiratory Muscles

The sternocleidomastoid and scalenes become dominant during deep inspiration, increasing workload on the neck and shoulders and often resulting in muscle pain and headaches.

Abdominal Bracing

In the absence of effective diaphragmatic action, patients may compensate by rigidly bracing the abdominal cavity using abdominal muscles. This leads to poorly controlled lung volumes and impaired gas exchange.

Long-Term Follow-Up

• Regular monitoring of transdiaphragmatic pressure and spirometry to document progress.

• Adjustment of training intensity based on clinical improvement and patient-reported functional capacity.

• In persistent paresis, surgical diaphragmatic plication may be considered to improve respiratory mechanics on the affected side.

Exercises for the Diaphragm

1. Supine Diaphragmatic Breathing

Target: Isolated activation of the costal and lumbar fibres of the diaphragm to maximise dome excursion.

Execution:

• Lie supine with knees bent and feet flat on the surface.

• Place one hand on the upper chest and one hand on the abdomen just below the rib cage.

• Inhale slowly through the nose, directing the breath toward the abdominal hand so that it rises more than the chest hand.

• Exhale through pursed lips (“as if blowing out a candle”), allowing the abdomen to fall slowly.

• Repeat for 5 minutes, 2–3 times daily.

Evidence: Studies show that supine diaphragmatic breathing increases diaphragmatic dome excursion by up to 30% compared with thoracic breathing and improves ventilatory efficiency¹.

2. Inspiratory Muscle Training (IMT) With Resistance Valve

Target: Increases strength and endurance of inspiratory muscles, including the diaphragm.

Equipment: Inspiratory muscle training device (e.g. POWERbreathe).

Execution:

• Set resistance to 30–50% of the patient’s measured maximal inspiratory pressure (MIP).

• Sit upright and seal the mouth firmly around the device.

• Perform 30 forceful, rapid inspirations over 5 minutes.

• Gradually increase resistance weekly toward 60–80% of MIP.

Frequency: 2 times daily, 5 days per week.

Evidence: Meta-analyses show that IMT reduces dyspnoea and increases MIP by an average of 25% after eight weeks of training².

3. Segmental Diaphragmatic Breathing

Target: Selective activation of the right or left hemidiaphragm in cases of asymmetrical or unilateral paresis.

Execution:

• Lie on the unaffected side in 90° side-lying with a pillow between the knees.

• Place one hand on the mid-thoracic region of the affected side.

• Inhale while focusing on expanding the hand upward toward the ceiling, increasing local dome excursion.

• Exhale slowly.

• Perform 10 repetitions, switching sides if needed.

Sets: 3, twice daily.

Evidence: Randomised controlled trials demonstrate that segmental breathing improves side-to-side differences in diaphragmatic motion and reduces paradoxical movement in patients with unilateral paresis³.

4. Abdominal Resistance Breathing (Book on Abdomen)

Target: Enhances proprioceptive input and eccentric control of the diaphragm during inspiration and expiration.

Equipment: A small book (500–1000 g) placed on the abdomen.

Execution:

• Lie supine with the book positioned on the abdomen just below the rib cage.

• Perform diaphragmatic breathing as in Exercise 1, lifting the book slightly during inspiration.

• Lower the book in a controlled manner during expiration.

• Repeat 10–15 times.

Sets: 3, once daily.

Evidence: Studies show that added abdominal resistance increases diaphragmatic force by approximately 20% and improves expiratory control in patients with respiratory insufficiency⁴.

5. Forced Inspiration With PEP Mask

Target: Enhances the diaphragm’s ability to work against positive expiratory pressure, improving lung volumes and secretion mobilisation.

Equipment: PEP device (5–10 cmH₂O resistance).

Execution:

• Sit upright with the PEP mask sealed firmly over the mouth.

• Inhale forcefully over 2–3 seconds.

• Exhale slowly against the resistance until the lungs are partially emptied.

• Perform 10 breathing cycles, rest for 1 minute, repeat 3 times.

Evidence: PEP training increases functional residual capacity and improves diaphragmatic control, with studies demonstrating a 15% increase in FRC after four weeks of daily use⁵.

References

• Netter, F. (2014). Atlas of Human Anatomy (6th ed.). Elsevier Saunders.

• Gosling, J. A., Harris, P. F., Humpherson, J. R., et al. (2008). Human Anatomy: Colour Atlas and Textbook (5th ed.). Mosby Elsevier.

• Drake, R., Vogl, A. W., & Mitchell, A. W. M. (2015). Gray’s Anatomy for Students (3rd ed.). Churchill Livingstone Elsevier.