Thorax and its biomechanics during respiration.

1. BIOMECHANICS OF THORAX
Meenu Verma
Assistant Professor
MMIPR

2.  Thorax forms the upper part of the trunk of the
body.
 The trunk of the body is divided by the
diaphragm into an upper part, called the Thorax.
 The thorax is supported by a skeletal framework,
thoracic cage.
 The thorax contains the heart, lungs, and other
important structures within a skeletal framework

3. Thoracic cage is an osseocartiaginous, elastic
cage which is primarily designed for increasing
and decreasing the intrathoracic pressure, so
that air is sucked into the lungs during inspiration
and expelled during expiration.

4. Respiration
 It is a process of exchange of oxygen and
carbon dioxide between the alveoli of the lungs
and the blood and the tissues.
 Ventilation or breathing has 2 phases
 Inspiration
 Expiration

5.  According to Boyles’s Law volume and pressure are
inversely proportional.
 Mechanics of breathing happens on the basis of this law.

6. Formation
Thoracic cage is formed by
 Anteriorly by sternum
 Posteriorly by the 12 thoracic vertebrae and
intervertebral disc
 On each side by 12 ribs with their cartilage.
 Floor by the diaphragm

7. Shape
 It is a conical shape which is narrow above
and broad below.
 In a transverse section, the thorax is reniform
i.e., bean-shaped or kidney-shaped.
 The anteroposterior diameter is smaller than
the transverse diameter (1:2 or 5:7).
 Ribs are oblique in adult and articulates at an
angle of 45 degree with thoracic vertebras.

9. Thoracic cavity
 The thoracic cavity communicates with the
front of the neck by the superior thoracic
aperture, or thoracic inlet.
 It communicates with the abdomen by the
inferior thoracic aperture which is closed by
the diaphragm.

10. Thoracic Inlet
Boundaries
 Anteriorly – Upper border of the manubrium
sterni.
 Posteriorly – Superior surface of the body of
the T1
 Laterally – First rib with its cartilage.

11. Thoracic Outlet
Boundaries
 Anteriorly – Infrasternal angle between the two
costal margins.
 Posteriorly – inferior surface of the body of the
T12.
 Laterally – Costal margin formed by the
cartilages of 7th to 12th ribs.

12. Surface landmarks

13. Anteriorly

14. Posteriorly

15. Sternum
 Sternum is an osseous protective plate for the
heart.
 It is a spear-shaped flat bone.
Sternum consist of
 Manubrium
 Body
 Xiphoid process

16. Manubrium
Body
Xiphoid

17. Manubrium
 Quadrilateral in shape and the thickest and
strongest part of sternum.
 Has 2 surfaces – Anterior and Posterior
 4 borders – Superior
inferior
2 lateral

18.  Superior border is round and concave.
 Marked by suprasternal notch in the median
part and by the clavicular notch on each side.
 Inferior border forms a secondary
cartilagenous joint with the body of the
sternum.
 Lateral border forms a primary cartilagenous
joint with the first costal cartilage.
 Manubrium makes an angle with body called
the sternal angle of Louis.

19. Body
 It is stronger, narrower and thinner.
 It is marked by three ill-defined transverse
ridges indicating the fusion of four small
segments called Sternebrae.
 Lateral borders form synovial joints with
 The lower part of 2nd costal cartilage,
 The 3rd – 6th and
 Upper half of the 7th costal cartilage.

20. Xiphoid process
 It is the smallest part of the sternum.
 Generally cartilagenous but become ossified in
adulthood.
 It varies in shape and may be bifid or
perforated.
 Lies in the floor of epigastric fossa.

21. Ribs
 12 ribs on each side.
 They are elongated yet flattened bones that
curve inferior and anterior from the thoracic
vertebrae.
 Costa is used to represent rib and chondral for
cartilage.
 Space between the ribs are called as
Intercostal space.
 Ribs are placed obliquely.

22. Classification
Attachment
Structure

23. Structural Classification
Ribs can be classified as
 Typical ribs- 3rd to 9th rib
 Atypical ribs- first two and last third i.e., 1st,
2nd, 10th,11th and12th rib.

24. Attachments
True ribs
 1st -7th ribs are known as true ribs or
vertebrosternal ribs due to their connection
with sternum via costal cartilage
False ribs
 8th-12th ribs are known as false ribs.
 8th to 10th ribs are attaches indirectly to
sternum by attaching to cartilage of 7th rib and
called as vertebrochondral ribs.

25.  11th and 12th ribs are not attached to sternum
in any ways so they are known as floating ribs
or vertebral ribs.

26. Rib has 2 extremities
 Posterior or vertebral
 Anterior or sternal
 An intervening portion- body or shaft

28. Head, contains:
 Small upper demifacet for articulation with the
small lower demifacet on the side of the
vertebra above it.
 Large lower demifacet for articulation with the
large upper demifacet on the side of the
vertebra of the same number.
 Between both demifacets there is the crest of
the head.

29. Neck
 It is the flattened constriction next to the head.
Tubercle, formed by:
 Articular part (medial part), which articulates
with the circular facet on the tip of the
transverse process of the vertebra of the same
number.
 Non articular part (lateral part), which is
attached to the lateral costo-transverse ligament
.

30. T
h
o
r
a
c
i
c
v
e
r
t
e
b
r
a
e

31. Thoracic spine can be classified as
 Typical – 2nd to 8th vertebrae
 Atypical – 1st, 9th, 10th, 11th and 12th vertebrae

32.  Intermediate in size between those of the
cervical and lumbar regions.
 They increase in size from above downward.
 The bodies in the middle of the thoracic
region are heart-shaped, and as broad in the
antero-posterior as in the transverse direction.
 The tip of the transverse process contains
circular facet for articulation with the tubercle
of the rib of the corresponding number

33. Atypical thoracic vertebrae
 1st, 9th, 10th, 11th and 12th vertebra are known
as atypical vertebrae.

35. First thoracic vertebra
 Body is like cervical vertebra with concave
surface and broad transversely.
 It has a complete circular facet for head of the
first rib.
 Spinous process is thick, long and almost
horizontal.

37. Articulation
 Manubriosternal and Xiphisternal joint
 Costovertebral joint
 Costotransverse joint
 Costochondral and Chondrosternal joint
 Interchondral joint

38. Manubriosternal
 Joint between manubrium and sternum.
 It is also known as the sternal angle or angle
of Louise.
 It is a synchondrosis and has a
fibrocartilagenous disc between the hyaline
cartilage.
Xiphisternal joint
 Between the sternal end and xiphoid process.
 It is also a synchondrosis that tends to ossify
by 40 to 50 years of age.

39. Costovertebral joint

40.  It is a synovial joint formed by the 2 costal
facets on vertebral body and head of the ribs.
 The joint is divided by the an interosseous
ligament attached to the crest of the head of
the ribs and the intervertebral disc.
 The joint is surrounded by a single capsule,
into two distinct cavities, superior and inferior.
 The atypical CV joints of ribs 1 and 10 to 12
are more mobile than typical because their
head articulates with only one vertebra.

41. Costotransverse joint
 Joint formed by the two oval articular facets,
one on the tip of the transverse process and
other on the costal tubercle.
 It is a synovial joint.
 There are 10 pairs of CT joints (T1 through
T10)

42. Costochodral joint
 Thy are formed by the articulation of the 1st
through 10th ribs with the costal cartilages.
 They are synchondrosis.
 Theses joints have no ligamentous support.

43. Chondrosternal Joint
 Formed by costal cartilages of ribs 1 to 7
anteriorly with the sternum.
 Rib 1 attaches to the lateral facet of the
manubrium which is a synchondroses.
 Rib 2 is attached to manubriosternal junction
via demifacets
 Rib 3-7 articulate with the lateral facets of the
sternal body.
 2-5 are synovial joints
 1,6,7 are synchondrosis

44. Interchondral Joints
 7th through 10 costal cartilages each articulate
with the cartilage immediately above them.
 The interchondral joints are synovial joints and
are supported by a capsule and interchondral
ligaments

45. KINEMATICS

46.  The movement of the rib cage is an amazing
combination of complex geometrics.

47. At first rib
 The articulation of 1st rib anteriorly is thicker
and larger than others.
 1st costal cartilage is stiffer.
 1st chondrosternal joint is synchondrosis not
synovial, so it is attached more firmly to
manubrium.
 1st CS joint is just inferior and posterior to
sternoclavicular joint.
Due to all these reasons there is very little
st

48.  Posteriorly CV joint formed by the 1st rib has
single articulation which makes it more mobile.
 During inspiration CV joint moves superiorly
and posteriorly elevating the 1st rib anteriorly
 As the 1st rib is elevated so is the sternum

49.  Changes of thorax
during inspiration in
sagittal plane

50.  Most commonly accepted theory is that, there
is a single axis of motion for the 1st to 10th ribs
through the centre of the CV and CT joints.
 CV and CT forms a joint couple mechanically
linked with a common movement i.e., rotation
about an axis passing through the centre of
each joint.
 The direction of movement of the rib is
determined direction of the axis with respect to
the sagittal plane.

51. In lower ribs axis lies parallel to sagittal plane allowing the
motion in frontal plane.
Now, the elevation of ribs in frontal plane will increase the
transverse diameter.
Rotation of ribs around its axis makes them less oblique
and more transverse.
Most lateral border moves more laterally
Increase in transverse diameter.

52. Therefore both the diameters are increased.
In midzone CV joints have an axis which lies obliquely to
sagittal plane(45 degree).
Therefore elevation of the rib increases the anteroposterior
diameter.
In upper ribs axis lies closer to the frontal plane.

54. At Costal Cartilage and Sternum
 As the most lateral part of the rib is raised and
pushed more laterally, the anterior end of the
rib is also raised and pushed anteriorly.
 At the same time the sternum is raised and the
costal cartilage becomes more horizontal and
forms an angle with its initial position.
 This movements occurs at sternocostal joint.

55.  The excursion of the manubrium is less than
that of the body.
 It is due to shortness of 1st rib with the caudal
ribs increasing in length until rib 7.
 This discrepancy in length causes movement
at the MS joint.

56. Pump Handle Movement
 Basically an upward and outward movement of
ribcage anteriorly.

57.  Movements of upper rib in sagittal plane.
 Increase in A-P diameter.
 Elevation of sternum.
All these movements collectively causes PUMP
HANDLE MOVEMENT

58. Bucket Handle
Movement
 An upward and
outward
movement of
ribcage
laterally.

59.  Movement or lower rib in frontal plane.
 Increase in transverse diameter.
These movements collectively results in
BUCKET HANDLE MOVEMENT.

61. External intercostal
 Origin – Lower border of upper rib.
 Insertion – Upper border of lower rib
 Their course is obliquely, superiorly and
medially.
 External intercostals elevate the ribs and is a
muscle of inspiration.

62. Internal intercostal
 Origin – Upper border of lower rib.
 Insertion – Lower border of upper rib.
 They run superiorly and lateraly.
 They depresses the rib, therefore they help in
expiration.

64.  The diaphragm is a musculo-tendinous dome
forming the floor of the thorax and separating
the thorax and abdomen
 The diaphragm is a primary muscle of
ventilation.
 It accounts for approx. 70% to 80% of
inspiration force during quiet breathing.
 Structurally, the diaphragm consists of two
parts: the peripheral muscle and central
tendon.

66.  During tidal breathing diaphragm shortens,
increasing the thoracic size and decreasing
the pleural pressure.
 It will cause decrease in intrapulmonary
pressure responsible for inspiration.
 Theses pressures are so strong that if not
opposed by the scalene and parasternals,
there will be an inward collapse of the upper
chest.

67.  In adults, the diaphragm can generate airway
pressures of up to 150 to 200 cm H2O during
maximal inspiratory effort.
 During quiet breathing (tidal breathing), the
diaphragm moves approximately 1 cm;
however, during deep-breathing maneuvers
(vital capacity), the diaphragm can move as
much as 10 cm.
 The diaphragm is innervated by the right and
left phrenic nerves,

68.  The peripheral muscle is made up of many
radial muscle fibers – originating on the ribs,
sternum, and spine – that converge on the
central tendon.
 The central tendon – a flat aponeurosis made
of dense collagen fibers – acts as the tough
insertion point of the muscles.
 The sternal region is made up of two small
muscular segments that attach to the posterior
aspect of the xiphoid process.

69.  The costal region is made up of several wide
muscle segments whose origins are found on
the internal surface of the inferior six ribs and
costal cartilages.
 Costal fibers run vertically from their origin in
close apposition to rib cage called as zone of
apposition and curve to become more
horizontal before inserting into the central
tendon.

70.  During inspiration, the muscles in the
diaphragm contract, and pull the central
tendon inferiorly into the abdominal cavity. This
enlarges the thorax and allows air to inflate the
lungs.
 As the dome descends, central tendon is
pulled down thus increasing the vertical
diameter of the thorax.
 The abdominal content compress, increasing
the intra-abdominal pressure.

71.  This depression of the central tendon is rapidly
checked by the mediastinal contents as they
are stretched, and by the resistance offered by
the abdominal organs.
 The central tendon becomes fixed point and
the muscle fibers, now acting from the
periphery of this central tendon, elevate and
rotate the lower ribs in bucket handle motion.
 At the end of contraction, the fiber become
more horizontally aligned, and further
contraction no longer lifts the rib.

72.  With the help of sternum it also elevates the
upper ribs thus, increasing the antero-posterior
diameter.

73. Therefore the diaphragm can be considered as
the basic muscle of respiration as it increases
by itself all three diameters of the thoracic
cavity:
 It increases the vertical diameter by pulling
down the central tendon;
 It increases the transverse diameter by
elevating the lower ribs;
 It increases the anteroposterior diameter by
elevating the upper ribs with the help of the
sternum;

74.  One of the primary muscle of quite ventilation.
 Attaches on the transverse processes of C3 to
C7 and descend to the upper borders of the 1st
(anterior and medius) and 2nd rib(posterior).
 Action – Lifts the sternum and the first two ribs
in the pump-handle motion of the upper
ribcage.
 The scalene muscles also function as
stabilizers of the ribcage.

75.  They counteract the downward pull of the
parasternals on the sternum and the
paradoxical movement of the upper chest by
the negative pleural pressure of the
diaphragm’s contraction

76. Accessory Muscles of
Ventilation
 The muscles that attach the ribcage to the
shoulder girdle, head, vertebral column, or
pelvis may be classified as accessory
muscles.

77. Muscle Origin Insertion Action Innervation
SCM Manubrium
sterni and medi
al portion of
the clavicle
Mastoid
process of the
temporal
bone, superior
nuchal line
Bilaterally;
cervical
flexion, raises
the sternum and
assists in forced
inspiration.
Accessory
Trapezius Ligamentum
nuchae, C7-
T12
Clavicle, Spine
& acromion of
scapula
Stabilize the
scapulae, which
enables the
serratus ant.
And p.minor to
elevate the ribs
Accessory
Serratus
anterior
(ventralis)
Ribs 1-9 Scapula Elevate the rib
when scapula is
fixed.
Long Thoracic

78. Muscle Origin Insertion Action Innervation
Pectoralis
major
Sternum, Ribs
2-6
Inter-tubercular
groove of
humerus
In forced Insp,
it draws, the
ribs towards the
arm,increasing
ap diameter.
M & L
pectorals
Pectoralis
minor
Ribs 3-5 Coracoid
process of
scapula
During deep
inspiration,
elevate the ribs.
M & L
pectorals

79. Synergism and antagonism of
diaphragm and abdominal muscles
 The diaphragm is the main inspiratory muscle
and the abdominal muscles are accessory
expiratory muscles of great strength, which
can produce forced expiration.
 Though apparently antagonistic these muscles
are also synergistic. In fact the diaphragm
would be less effective in the absence of the
abdominal muscles.

80. During inspiration
 In inspiration the abdominal muscle act as a
girdle.
 The contraction of the diaphragm brings down
the central tendon increasing the vertical
diameter of the thorax; but this is soon
opposed by the elongation of the vertical
mediastinal elements (M) and especially the
resistance of the abdominal viscera.

81.  The abdominal contents are contained within
the 'abdominal girdle' formed by the powerful
abdominal muscles:
 the rectus muscles (R),
 The transversus muscles (T),
 the internal (IO) and external obliquus (EO).
 Without these muscles, the abdominal
contents would be displaced inferiorly and
anteriorly and the central tendon would not be
stabilized to allow the diaphragm to elevate
the lower ribs.

83. During expiration
 The diaphragm relaxes and contraction of the
abdominal muscles lowers the thoracic floor
thereby decreasing simultaneously the transverse
and antero-posterior diameters of the thorax.
 Also by increasing the intra-abdominal pressure
they push the viscera upwards and raise the
central tendon.
 This decreases the vertical diameter of the thorax
and 'closes' the costodiaphragmatic recesses.
Therefore the abdominal muscles are the perfect
antagonists of the diaphragm

85.  The respective roles of diaphragm and
abdominal muscles are therefore in a floating
equilibrium.
 These roles are constantly moving in both
directions.
 During inspiration, the tonus of the diaphragm
increases while that of the abdominal muscles
decreases.
 The reverse process occurs during expiration.

86.  Expiration in erect position
 There is contraction of the abdominal muscles
increasing the intra-abdominal pressure
pushing the viscera upwards and raising the
central tendon.
 In supine position
 Elevation of the diaphragm is entirely passive
as the weight of the abdominal viscera pushes
the relaxed muscle into the thorax.

88. Differences Associated with the
Neonates
 The compliance, configuration, and muscle
action of the chest wall changes significantly
from the infant to the elder.
 In new born the chest wall is primarily
cartilagenous, therefore it is highly compliant.
 In infants the chest wall muscles are the
primary stabilizers of thorax to counteract the
negative pleural pressure of the diaphragm
during inspiration.

89.  The ribs are more horizontally placed in
infants.
 This alters the angle of insertion of the costal
fibers of the diaphragm, which makes the
orientation more horizontal than vertical.
 Due to this orientation, there is an increased
tendency of these fibers to pull the ribs
inwardly, therefore decreasing the ventilation.
 In adults 50%of the diaphragm fibers are
fatigue-resistent, which is only 20% in healthy
new born leading to early diaphragmatic

90. Differences Associated with the
Elderly
 Changes that occur in elderly with aging are
skeletal changes which may affect the
pulmonary function.
 Costal cartilages ossify interfering with axial
rotation.
 The interchondral and costochonral joints –
fibrose
 Chondrosternal joint – obliterated with age.
 Xiphosternal joint – ossifies after approx. 40
yrs of age.

91.  True synovial joints can undergoes
morphological changes, reducing the mobility.
 Diaphragm-abdominal compliance also
reduces due to its relation with rib cage.
 Resting position of the thorax depends on the
balance between
 The elastic recoil properties of lungs pulling
inwards &
 The outward pull of the rib cage.

92. With increases age
Elasticity of lung tissue decreases( in recoil
property)
Thorax rest in more inspiratory position.
Increased AP diameter.

93.  These skeletal and tissue changes results in
increased FRC and decreased IC.
 There is reduction in strength of ventilatory
muscles with age.
 Due to decrease in abdominal tone, the resting
position of diaphragm becomes less domed.
 In conclusion, there is decreased compliance
of ribcage and lung tissue, and over-all
decreases compliance of respiratory system.

94. Scoliosis
 Scoliosis is a lateral curvature of the spine.
 It is caused by the lateral displacement and
rotation of the vertebral bodies.
 It is most common during periods of rapid
somatic growth.
 Scoliosis impedes on the movement of the
ribs, places the respiratory muscles at a
mechanical disadvantage and displaces the
various organs of the thoracic cavity.

95.  On the side of convexity, the transverse
processes of the vertebrae move posteriorly
carrying the ribs with them.
 This causes the classic posterior rib hump.
 Intercostal space is widened.
 On the concave side, effect are just opposite.
 The transverse processes move anteriorly,
bringing the articulated rib forward.
 Ribs are now approximated with each other
narrowing the intercostal space.

96.  If these changes are severe, the axis of
rotation of the ribs will move, affecting the
effecting the efficiency of the intercostal
muscles and other ventilatory muscles, and
will reduce the ribcage compliance.

98. Pectus excavatum
 Pectus excavatum is a depression of the
anterior chest wall of variable severity that may
be mild, moderate, or severe.
 It is also known as funnel chest.
 There is over growth of lower costal cartilages
and ribs, which is compensated for by
depression of the lower end of the sternum.

99. The asymmetry of the chest wall affects:
 - The paraspinal muscles
 - The vertebral bodies
 - The motion of the ribs

101.  Pulmonary effects also fall into three
categories: restrictive lung disease caused by
decreased intrathoracic capacity, atelectasis
caused by cardiac displacement causing left
lung compression, and paradoxical respiration
in severe cases caused by disturbed
mechanical forces

102. Barrel chest

103.  Barrel chest describes a rounded, bulging,
almost barrel-like appearance of the chest that
occurs as a result of long-term hyperinflation of
the lungs due to destruction of the alveolar
walls.
 There is increase in AP diameter.
 The barrel elevated thorax puts the SCM in
shortened position, making them less efficient.
 In hyperinflated chest, the diaphragmhas very
little available range of motion.

104.  The majority of inspiration is now performed by
accessory muscles, particularly parasternal
and scalenes.
 The upper rib cage is pulled upward and
outward.
 As diaphragm is not working efficiently,
abdominal contents are not pushed
downwards.
 The accessory muscles pulls the diaphragm
and abdominal contents upwards.
 Paradoxical thoracoabdominal breathing
pattern is seen.