Static Compliance in Respiratory Care

Definition and Measurement

Static compliance is typically expressed as volume change per unit of pressure change (ml/cmH₂O) and measures the elastic recoil properties of the respiratory system 1, 2
It is measured during conditions of no airflow, such as during an inspiratory hold maneuver on mechanical ventilation, to eliminate the resistance component of the respiratory system 1
Normal lung compliance in adults ranges from 1.2 to 2.0 ml/cmH₂O per kilogram body weight 2, 3

Decreased static compliance indicates stiffened lungs that require more pressure for a given volume change 1, 2
In acute respiratory distress syndrome (ARDS), static compliance may be reduced to less than one-fourth of normal values (approximately 20 ml/cmH₂O) 1
Static compliance can help differentiate between different types of respiratory pathology and guide ventilator management strategies 1

Alveolar edema and surfactant dysfunction reduce the volume of aeratable lung, decreasing compliance 1
Pulmonary fibrosis decreases compliance by stiffening lung tissue 2, 3
Left ventricular dysfunction increases lung water content, leading to decreased compliance 3, 4
In chronic lung disease of infancy, specific compliance (corrected for body weight or lung volume) is typically 30-50% of control values in early infancy but improves to 80-90% of normal by ages 2-3 years 2, 3

Serial measurements of static compliance can track disease progression and response to treatment 1, 2

Measurements should be made during zero-flow conditions to eliminate the resistance component 1
In spontaneously breathing patients, esophageal pressure measurements may be needed to accurately determine transpulmonary pressure 5
Despite its clinical value, static compliance measurement is not routinely performed outside research settings due to technical challenges 6, 7

The American Thoracic Society recommends that static lung compliance in healthy adults is normally in the range of 1.2-2.0 ml/cmH₂O/kg of body weight 8

In young adults (20-29 years), the compliance of the thoracic wall is approximately 350 ml/cmH₂O, with a Ccw/CL ratio of around 5 9, 10
The compliance of the thoracic wall decreases with age, with values of 250 ml/cmH₂O (Ccw/CL ratio = 3.5) for 30-59 years, 136 ml/cmH₂O (Ccw/CL ratio = 2) for 60-69 years, and 210 ml/cmH₂O (Ccw/CL ratio = 3) for 70-79 years 9, 10