Respiratory Movement: Clinical Anatomy

Overview

1. Thoracic Dimensions That Change During Breathing

2. Movements of the Thoracic Wall

Pump Handle Movement (Anteroposterior)

Bucket Handle Movement (Lateral)

"Any muscles attaching to the ribs can potentially move one rib relative to another and therefore act as accessory respiratory muscles. Muscles in the neck and the abdomen can fix or alter the positions of upper and lower ribs." - Gray's Anatomy for Students

3. The Diaphragm (Vertical Dimension)

Inspiratory Action

• Muscular fibers of the diaphragm contract, pulling the central tendon inferiorly
• The domes flatten - this expands the thoracic cavity caudally
• The abdominal contents are pushed downward
• The deeper the inspiration, the flatter the costodiaphragmatic recess becomes, allowing the inferior border of the lung to expand into this supplementary space

Expiratory Action

• The diaphragm relaxes, and elastic recoil returns it upward
• The domes ascend

Position of the Domes at Quiet Expiration (Clinically Important)

• Right dome: at the level of rib V (pushed higher by the liver)
• Left dome: at the fifth intercostal space (slightly lower due to the stomach and spleen)

Diaphragm Openings (Clinically Relevant Structures Passing Through)

Innervation

4. Respiratory Muscles

Muscles of Inspiration

• Diaphragm - most important; contraction pushes abdominal contents down and lifts ribs upward and outward
• External intercostal muscles - elevate the ribs, aid in inspiration

• Sternocleidomastoid
• Scalene muscles (anterior, middle, posterior)
• Pectoralis major/minor

Muscles of Expiration

• Internal intercostal muscles - depress ribs downward and inward
• Abdominal muscles (especially transversus abdominis) - compress the abdominal cavity, push the diaphragm upward, and increase intra-abdominal pressure

5. Pressure Changes During Breathing

6. Clinical Correlations

Diaphragmatic Paralysis (Phrenic Nerve Palsy)

• Unilateral paralysis: often asymptomatic, or mild exertional dyspnea
• Bilateral paralysis: rare but causes significant respiratory compromise

Diaphragmatic Hernia

Paradoxical Breathing

Referred Pain from the Diaphragm

• Subphrenic abscess (right shoulder tip pain)
• Hemoperitoneum (e.g., ruptured ectopic pregnancy, splenic rupture)
• Ruptured spleen (left shoulder tip - Kehr's sign)

Intercostal Nerve Block

Clinical Assessment of Breathing Pattern

• Abdominal breathing (normal in males and children): diaphragm dominates
• Thoracic breathing (normal in females): intercostal muscles more prominent
• Paradoxical breathing: sign of respiratory failure or phrenic nerve palsy
• Accessory muscle use: sign of increased work of breathing (COPD, asthma, upper airway obstruction)

Summary Table: Muscles, Movements, and Dimensions

• Gray's Anatomy for Students (9780323934237) - Movements of the thoracic wall and diaphragm during breathing, Diaphragm innervation and openings
• Color Atlas of Human Anatomy Vol. 2 (9783132424487) - Mechanics of Breathing
• Costanzo Physiology 7th Ed. (9780323793339) - Muscles of Inspiration and Expiration
• Medical Physiology (Boron & Boulpaep) (9780323319737) - Opposing elastic recoils, intrapleural pressure

Muscles & Mechanism - Quick Brief

INSPIRATION (Active)

EXPIRATION (Passive at rest)

Rib Movement Types

• Pump handle → ribs elevate → sternum moves up & forward → ↑ anteroposterior diameter
• Bucket handle → lateral rib shafts swing outward → ↑ transverse diameter

Muscles of Inspiration vs Expiration

INSPIRATION - Active Process

EXPIRATION - Passive at Rest / Active When Forced

Memory Summary

INSPIRATION = ACTIVE
  Diaphragm (main) + External intercostals
  + Accessory: Scalenes, SCM, Pec minor

EXPIRATION = PASSIVE (quiet) / ACTIVE (forced)
  Forced: Internal intercostals + 4 abdominal muscles

Key rule: Diaphragm accounts for 60-70% of all lung volume change during quiet breathing.

Muscles of Inspiration - Detailed Breakdown

PRIMARY Muscle (always active in quiet breathing)

SECONDARY / ACCESSORY Muscles (recruited during deep/forced inspiration, exercise, respiratory distress)

1. External Intercostal Muscles

• Origin: Lower border of rib above
• Insertion: Upper border of rib below
• Nerve: Intercostal nerves (T1-T11)
• Action in inspiration: Elevate the ribs upward and outward → increases anteroposterior and lateral diameters (pump handle + bucket handle)
• Note: Fibers run downward and forward (like hands in pockets)

2. Scaleni Group (Anterior, Middle, Posterior)

• Origin: Transverse processes of cervical vertebrae (C2-C7)
• Insertion: Ant/Mid → 1st rib; Post → 2nd rib
• Nerve: Cervical nerves (C4-C8)
• Action in inspiration:
  • Elevate ribs 1 and 2 to expand the upper thorax
  • Prevent inward collapse of the upper ribs during diaphragm contraction
  • Active even in quiet breathing - they stabilize the upper chest wall
• Clinical note: Hypertrophy visible in COPD patients ("barrel chest")

3. Sternocleidomastoid (SCM)

• Origin: Manubrium sterni + medial clavicle
• Insertion: Mastoid process + superior nuchal line
• Nerve: Accessory nerve (CN XI) + C2, C3
• Action in inspiration: Elevates the sternum and clavicle → lifts the entire anterior chest wall → ↑ AP diameter
• Clinical note: Visible SCM contraction at rest = sign of severe respiratory distress (e.g., acute asthma, COPD exacerbation, upper airway obstruction)

4. Pectoral Muscles (Pectoralis Major + Minor)

• Pectoralis Major
  • Origin: Clavicle, sternum, costal cartilages 1-6
  • Nerve: Medial + lateral pectoral nerves (C5-T1)
  • Action: When arm is fixed (hands on knees / gripping a surface), reverses its action → elevates ribs and sternum → ↑ AP diameter
• Pectoralis Minor
  • Origin: Ribs 3, 4, 5
  • Insertion: Coracoid process
  • Nerve: Medial pectoral nerve (C8, T1)
  • Action: When shoulder is fixed, elevates ribs 3-5 upward
• Clinical note: Patients in respiratory distress instinctively lean forward on their arms ("tripod position") to fix the shoulder girdle and activate pectorals as inspiratory muscles

5. Serratus Anterior

• Origin: Outer surfaces of ribs 1-8 (digitations)
• Insertion: Costal surface of medial border of scapula
• Nerve: Long thoracic nerve (C5, C6, C7)
• Action in inspiration: When scapula is fixed, pulls ribs upward and outward → elevates and expands the lateral thorax
• Also: Rotates scapula upward - if scapula is held fixed by other muscles, the ribs are raised instead
• Clinical note: Long thoracic nerve palsy → winged scapula → impaired accessory inspiration

6. Erector Spinae (Sacrospinalis Group)

• Includes: Iliocostalis, Longissimus, Spinalis
• Origin: Sacrum, iliac crest, lumbar vertebrae
• Insertion: Ribs, transverse processes, spinous processes
• Nerve: Posterior rami of spinal nerves
• Action in inspiration:
  • Extends the thoracic spine → opens up the thoracic cage anteriorly
  • Elevates ribs by straightening the thoracic kyphosis → ↑ AP diameter
  • Counteracts the tendency of the spine to flex during deep inspiration
• Note: Particularly important during deep breath in - allows the chest to "open up" fully

7. Quadratus Lumborum

• Origin: Iliac crest + iliolumbar ligament
• Insertion: 12th rib + transverse processes of L1-L4
• Nerve: Subcostal nerve (T12) + lumbar plexus (L1-L3)
• Action in inspiration:
  • Fixes and stabilizes the 12th rib from below
  • This gives the diaphragm a firm lower attachment point to pull against
  • Without QL fixation, the 12th rib would be pulled upward by the diaphragm, reducing its mechanical efficiency
• Analogy: Acts as an anchor for the diaphragm - like staking down a tent
• Clinical note: Paralysis of QL (L1-L2 lesion) → paradoxical elevation of 12th rib during inspiration → reduced diaphragmatic efficiency

Summary Table

Key clinical point: Visible use of SCM and scalenes at rest = accessory muscle recruitment - a sign the patient is working hard to breathe. The tripod position (leaning forward on hands) maximizes pectoral and serratus contribution.

Mechanism of Respiration - Full Description

The Three Diameters of the Thorax

The Joints (Centers / Axes of Rotation)

Joints Involved

The axis of rotation passes through the costovertebral joint posteriorly and the sternocostal joint anteriorly - a line connecting these two points is the hinge on which the rib rotates.

Pump Handle Movement

Anatomy

• Applies mainly to upper ribs (1-6)
• The anterior end of the rib lies lower than the posterior end
• The axis of rotation runs roughly transversely (side to side) through the costovertebral and sternocostal joints

Movement

• When the rib rotates around this transverse axis:
  • The anterior end (sternum) moves upward and forward
  • The sternum swings like the handle of an old water pump
• Result: Increases the anteroposterior (AP) diameter of the thorax

Analogy

Like the handle of a water pump - it hinges at the back (costovertebral joint) and the front swings upward.

Muscles Responsible

• External intercostals (upper fibers)
• Scaleni (fix ribs 1 and 2 as the upper pivot)
• SCM (lifts the sternum directly)

Bucket Handle Movement

Anatomy

• Applies mainly to lower ribs (7-10)
• The middle of the rib shaft lies lower than both ends
• The axis of rotation runs in an anteroposterior direction (front to back) through the neck of the rib

Movement

• When the rib rotates around this AP axis:
  • The lateral part of the shaft swings outward and upward
  • Like the handle of a bucket being lifted sideways
• Result: Increases the transverse (lateral) diameter of the thorax

Analogy

Like lifting the handle of a bucket - the midpoint of the handle rises outward to the side.

Muscles Responsible

• External intercostals (lower fibers)
• Diaphragm (pulls the lower ribs outward - zone of apposition effect)

Vertical Diameter - Diaphragm

• The diaphragm is the sole driver of vertical diameter change
• At rest (quiet expiration): Right dome at rib V, Left dome at 5th intercostal space
• During inspiration: Central tendon descends 1.5 to 7 cm depending on depth
• The costodiaphragmatic recess fills as the lungs expand downward into it

Complete Summary - The Mechanism Step by Step

INSPIRATION:

1. Diaphragm contracts
   → descends 1.5-7 cm
   → VERTICAL diameter ↑

2. Upper ribs rotate on TRANSVERSE axis (costovertebral + sternocostal joints)
   → sternum moves UP and FORWARD (pump handle)
   → ANTEROPOSTERIOR diameter ↑

3. Lower ribs rotate on ANTEROPOSTERIOR axis (neck of rib)
   → lateral rib shafts swing OUTWARD (bucket handle)
   → TRANSVERSE (LATERAL) diameter ↑

4. All three together → thoracic VOLUME ↑
   → Intrapleural pressure ↓ (becomes more negative)
   → Alveolar pressure < Atmospheric pressure
   → Air flows INTO the lungs

EXPIRATION (quiet):
   → Elastic recoil of lungs + chest wall
   → All movements reverse passively
   → Volume ↓ → air flows OUT

Quick Reference: Which Ribs, Which Movement