Lung Elastance, Compliance and Work of Breathing

DRNILESHKATE
MBBS,MD
PROFESSOR
DEPT.OFPHYSIOLOGY
LUNGELASTANCE,
COMPLIANCE&
WORKOF
BREATHING.

OBJECTIVES.
 Pulmonary Elastance
 Elastance of thoracic cage
 Elastance of Lungs
 Alveolar surface tension
 Pulmonary surfactant
 Pulmonary Compliance
 Def, NR
 Measurement
 Static Vs Specific
 Workof breathing

PULMONARYELASTANCE
Friday, May 14, 2021
 Elastance –
 Def – recoil of Retractive tendency of any structure.
 Elastance of Thoracic cage
 Elastance of lungs

ELASTANCEOFTHORACICCAGE
 Constant tendency of thoracic cage to expand
which is normally kept partially pulled inward.
 It is because of the elastic nature of ribs, muscles
and tendons.

ELASTANCEOFLUNGS
 Constant tendency of lungs to collapse
 Tissue forces
 Presence of many elastic tissues such as smooth
muscle, elastic and collagen in the lung parenchyma
 Surface forces – alveolar surface tension.

ALVEOLARSURFACETENSION
 Surface of alveolar
membrane lined by liquid
 Unbalance attraction of
liquid molecules at surface
creates surface tension --
Vander wall forces.
 Surface tension increases
the tendency of the lungs
to deflate/collapse.

Lawof laplace
 P=2T/r
 Therefore, small alveoli
tend to become still smaller
whereas large alveoli tend
to become still larger

PULMONARYSURFACTANT
 Source– type IIalveolarepithelial
cells(granular pneumocytes).
 Composition– DPPC(Dipalmitoyl-
phosphatidylcholine)
 Mechanismofaction
 Hydrophilic portion
 Hydrophobic portion

Mechanismof action.
 Hydrophilic portion
 Hydrophobic portion
 This causes spreading of surfactant molecules
over the surface of fluid lining the alveoli.
 Apoproteins and calcium ions are responsible
for uniform and quick spreading of surfactant
molecules over the surface.

Functions


The tendency of alveoli to collapse
Work of breathing
 Prevents pulmonary oedemaPulls fluid from the
capillaries into the interstitial space surrounding the
alveoli and into the alveoli leading to pulmonaryoedema.
 Alveolar stabilization.
 Pulling pressure 18 cm ofH2O
4 cm of H2O

MECHANISMOFALVEOLAR
STABILIZATION
 Inthe presence of
surfactant
 ST=1/ Surfactant.
 Other factors
 Interdependence of
alveolar septa
 Fibrous tissue.

Factorsaffectingpulmonary
surfactant
.
• Longterminhalation
of100% O2
.
• Occlusion
• Mainbronchus
• Pulmonaryartery.
.
• Cigaratesmoking.
• Cuttingvagi.
• Thyroidhormones
• Glucocorticoids

APPLIEDASPECTS.
 Respiratorydistress syndrome of
newborn.(Hyalinemembrane disease)
 Adultrespiratory distress syndrome
 Patchy atelectasis.

PULMONARYCOMPLIANCE
 Definition & Normal value
 Measurement
 Procedure
 Factors affecting compliance

Definition&Normal value
 C=δV/ δP
 Transpulmonary pressure =alveolar
pressure – pleural pressure.
 Normalvalue
 Both 0.13L/cm of H2O
 Lung alone 0.22 L/cm of H2O

Measurement

PROCEDURE
 Intra-oesophageal
balloon measures
intra-pleural pressure.
 Pt made to inspire 100
ml of air &
intrapleural pressure
measured.
 Curved lines due to 2
resistance
 Viscous resistance
 Airway resistance.

FACTORSAFFECTINGCOMPLIANCE
 Elastic forces of the
lung tissue – mainly
due to elastic &
collagen fibres (1/3rd)
 Elastic forces caused
by surface tension
(2/3rd)

Staticvs SpecificLung
Compliance
 Static compliance
 Depend upon size
 Amount of functional
lung tissue.
 Specific lung
compliance
 Compliance of the lung
at relaxation volume
i.e. at the end of tidal
expiration
 FRC.

LUNGCOMPLIANCECHANGES
• Emphysema
• Ageingprocess
• .
• Lungdiseases (TB,
Silicosis)
• Destructionof
functionallung tissue.
• RLD

Workof breathing
Contractionofrespiratory
muscles.
Expansionofthoraciccage
& Lungs
Decreasesintraalveolar
pressure&pushair inside

RESISTANCETOBREATHING
 Tissue resistance
 Airway resistance

TISSUERESISTANCE
 Elastic resistance
 Thoracic cage
 Lungs
 Elastic fibres
 Surface tension
 Viscousresistance.
 Non-elastic tissue.

AIRWAYRESISTANCE
 Friction of gas molecules and wall of airways.
 Factors affecting
 Rate of gas flow
 Airway radius. Poiseuille-Hagen formula
Resistance α 1/r4
 Length of airway
 Type of airflow

CONTROLOFAIRWAYDIAMETER
 Sympathetic adrenergic – Bronchodilataion
 Vagus – bronchoconstriction&Mucous
formation.

COMPONENTSOFWORKOF
BREATHING
 Workdoneto overcome
 Elastic resistance (65%)
 Viscous resistance (7%)
 Airway resistance (28%)

CALCULATIONOFWORKOF
BREATHING
 Work done during inspiration
 Work done during Expiration

WORKDONEDURING
INSPIRATION
 Compliance work refers to
the work done by respiratory
muscles to inflate the lungs
against the elastic resistance
of chest wall andlungs.
 It is represented by the
triangular area Thus most of
the work done (65%) isused
to overcome elastic
resistance.

Non-elasticresistance work
 Work is done to overcome the nonelastic
resistance.
 It includes the work done to overcome:
 Viscous resistance of lungs (7%) and
 Airway resistance (28%).

WORKDONEDURING
EXPIRATION
 Since in quiet breathing,
expiration is a passive
process so no work isdone
during expiration.
 When the lungs are recoiling
back some energy is required
to overcome non-elastic
resistance, i.e. the airway
resistance plus viscous tissue
resistance.

WORKOFBREATHINGIN
RESTRICTIVELUNGDISEASES

WORKOFBREATHINGIN
OBSTRUCTIVELUNGDISEASES

APPLIED
 Workofbreathing in
 Restrictive lung diseases
 Obstructivelung diseases.

FACTORSAFFECTINGTOTALWORK
OFBREATHING.
 Total work of breathing in quiet respiration
 0.3-0.8kg mt/min.
 Increases
 As resistance increases
 Muscular exercise.

Objectivesseen……
 Pulmonary Elastance
 Elastance of thoracic cage
 Elastance of Lungs
 Alveolar surface tension
 Pulmonary surfactant
 Pulmonary Compliance
 Def, NR
 Measurement
 Static Vs Specific
 Workof breathing

Lung Elastance, Compliance and Work of Breathing

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