Compliance refers to the change in lung volume for a given change in pressure. It is the reciprocal of elastance. Compliance of the respiratory system (CRS) depends on the interaction of lung compliance (CL) and chest wall compliance (CW). CL is affected by lung volume, surface tension, blood volume, and edema, while CW is affected by posture, obesity, costal cartilage ossification, and scarring. Dynamic compliance includes the effects of resistance and hysteresis during breathing, while static compliance is measured without gas flow at equilibrium. The difference between static and dynamic compliance reflects airway resistance.

1. COMPLIANCE & WORK
OF BREATHING
Presentor: Arthi . P.R

2. COMPLIANCE
Compliance - Change in Lung volume for the
given change in atmospheric pressure
It is the reciprocal of Elastance
Compliance of the respiratory system = CRS
Change in Lung Volume
Change in Airway Pressure
V
P
=

3. Compliance RS - Interaction of the compliance of lungs and
compliance of chest wall
Reciprocal of Compliance is the sum of reciprocal of Lung
and Chest wall
CL = Alveolar Presssure - Intrapleural Pressure
CW= Intrapleural Pressure - Ambient Pressure
Intrapleural Pressure is difficult to measure - Esophageal Pressure from Ballon
Manometry is commonly used as an approximation of intrapleural pressure
1
CRS
1
CL
1
CW
+=

4. Factors Affecting Compliance (CL)
1. Lung Volume - Compliance is related to Normal FRC
2. Surface Tension of Alveoli - Surfactant the major factor determining the Lung
Recoil
Without Surfactant Lung will normally behave like an air bubble following Laplace
Equation
P = 2T/R
Normally- when radius of bubble decreases without change is surface tension the
pressure increases
But in Lung - When the radius decreases the surface tension also decreases and
this opposes the collapse of smaller lung unit.
P- Gas Pressure
T- Surface Tension
R- Radius

5. Other Factors Affecting Compliance (CL)
3. Pulmonary Blood Volume
4. Interstitial Edema
Factors Affecting Chest Wall Compliance (CCW)
1. Posture
2. Obesity
3. Ossification of Costal Cartilages
4. Scaring of Skin

6. DYNAMIC COMPLIANCE
Normal Healthy person- As the respiratory system inflates to 60% of
the TLC - the chest wall is aiding the Muscle of respiration to inflate.
Above this level the muscles of Inspiration should work to distend
both the Lungs and the Chest wall - Dynamic Compliance
P = Peak Airway Pressure - PEEP
DC - Also include Effect of Airway resistance & Normal Hysteresis of
Lung Parenchyma(Resistance to Change of Shape both during
Stretch & Contraction)
DC- Affected by frequency of Respiration & Velocity of Gas Flow

7. STATIC COMPLIANCE
It is measured at a point of No gas flow and when the pressure
gradient is allowed to Equilibrate to the entire airway.
(Eg)In Anesthetised & Paralysed Patient during ventilation in VCV
mode with a fixed inspiratory flow and using an end expiratory
pause
P = Plateau Airway Pressure - PEEP
SC - refers to Actual Distending pressure in the patients alveoli
Difference between Static & Dynamic Compliance reflects Airway
resistance