Lung Elastance, Compliance and Work of Breathing

DR NILESH KATE
MBBS,MD
PROFESSOR
DEPT. OF PHYSIOLOGY
LUNG ELASTANCE,
COMPLIANCE &
WORK OF
BREATHING.

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

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

ELASTANCE OF THORACIC CAGE
 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.

ELASTANCE OF LUNGS
 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.

ALVEOLAR SURFACE TENSION
 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.

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

PULMONARY SURFACTANT
 Source – type II alveolar epithelial
cells(granular pneumocytes).
 Composition – DPPC (Dipalmitoyl-
phosphatidylcholine)
 Mechanism of action
 Hydrophilic portion
 Hydrophobic portion

Mechanism of 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 oedema Pulls fluid from the
capillaries into the interstitial space surrounding the
alveoli and into the alveoli leading to pulmonary oedema.
 Alveolar stabilization.
 Pulling pressure 18 cm of H2O
4 cm of H2O

MECHANISM OF ALVEOLAR
STABILIZATION
 In the presence of
surfactant
 ST = 1/ Surfactant.
 Other factors
 Interdependence of
alveolar septa
 Fibrous tissue.

Factors affecting pulmonary
surfactant
.
• Long term inhalation
of 100% O2
.
• Occlusion
• Main bronchus
• Pulmonary artery.
.
• Cigarate smoking.
• Cutting vagi.
• Thyroid hormones
. • Glucocorticoids
.

APPLIED ASPECTS.
 Respiratory distress syndrome of
newborn.(Hyaline membrane disease)
 Adult respiratory distress syndrome
 Patchy atelectasis.

PULMONARY COMPLIANCE
 Definition & Normal value
 Measurement
 Procedure
 Factors affecting compliance

Definition & Normal value
 C= δV/ δ P
 Transpulmonary pressure = alveolar
pressure – pleural pressure.
 Normal value
 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.

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

Static vs Specific Lung
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.

LUNG COMPLIANCE CHANGES
• Emphysema
• Ageing process
• .
• Lung diseases (TB,
Silicosis)
• Destruction of
functional lung tissue.
• RLD

Work of breathing
Contraction of respiratory
muscles.
Expansion of thoracic cage
& Lungs
Decreases intra alveolar
pressure & push air inside

RESISTANCE TO BREATHING
 Tissue resistance
 Airway resistance

TISSUE RESISTANCE
 Elastic resistance
 Thoracic cage
 Lungs
 Elastic fibres
 Surface tension
 Viscous resistance.
 Non-elastic tissue.

AIRWAY RESISTANCE
 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

CONTROL OF AIRWAY DIAMETER
 Sympathetic adrenergic – Bronchodilataion
 Vagus – bronchoconstriction & Mucous
formation.

COMPONENTS OF WORK OF
BREATHING
 Work done to overcome
 Elastic resistance (65%)
 Viscous resistance (7%)
 Airway resistance (28%)

CALCULATION OF WORK OF
BREATHING
 Work done during inspiration
 Work done during Expiration

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

Non-elastic resistance 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%).

WORK DONE DURING
EXPIRATION
 Since in quiet breathing,
expiration is a passive
process so no work is done
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.

WORK OF BREATHING IN
RESTRICTIVE LUNG DISEASES

WORK OF BREATHING IN
OBSTRUCTIVE LUNG DISEASES

APPLIED
 Work of breathing in
 Restrictive lung diseases
 Obstructive lung diseases.

FACTORS AFFECTING TOTAL WORK
OF BREATHING.
 Total work of breathing in quiet respiration
 0.3-0.8 kg mt/min.
 Increases
 As resistance increases
 Muscular exercise.

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

Lung Elastance, Compliance and Work of Breathing

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