Static versus Dynamic Compliance

Lung Compliance

Compliance answers the question “How easily will an elastic structure stretch?” or “What is the elastic resistance of a system?”

The following defines compliance in an equation form:

*** Pending moderator approval, image of compliance equation V/P ***

Where

ΔV = change in volume

ΔP = change in pleural pressure

*** Pending moderator approval, image of pressure volume loop ***

In a high compliance state, a minimal increase in pressure translates to a large increase in volume. In a low compliance state, a large increase in pressure translates to only a minimal increase in volume.

Static Compliance

Static compliance characterizes pulmonary compliance at the level of the alveoli when there is no active airflow, such as at the beginning or end of a breath.

The following defines static compliance in an equation form, where static compliance is the tidal volume divided by the plateau pressure minus the positive end expiratory pressure (PEEP).

*** Pending moderator approval, image of formula for static compliance formula. ***

Examples of medical conditions that primarily affect static compliance: pneumonia, pneumothorax, acute respiratory distress syndrome (ARDS), pulmonary fibrosis, pulmonary edema, pneumonectomy, and emphysema.

Dynamic Compliance

Dynamic compliance characterizes pulmonary compliance at the level of the alveoli during active airflow during the inspiratory and expiratory phases of a breath.

The following defines dynamic compliance in an equation form, where dynamic compliance is the tidal volume divided by the peak pressure minus the positive end expiratory pressure (PEEP).

*** Pending moderator approval, image of formula for dynamic compliance formula. ***

Examples of medical conditions that primarily affect dynamic compliance: asthma, tachypnea, mucus plug, foreign body, and bronchitis.

YouTube Video Reviewing Static vs Dynamic Compliance

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