Airway resistance is calculated as (PIP - Pplat) divided by which quantity?

Airway resistance is calculated as (PIP - Pplat) divided by which quantity?

• A. Flowrate
• B. PEEP
• C. Paw
• D. Pes

Answer: (A)

Airway resistance reflects how much pressure is needed to push the delivered air through the conducting airways at a given flow. The pressure difference that represents resistance is the drop from peak inspiratory pressure to plateau pressure (PIP minus Pplat). Plateau pressure is measured when there is no flow, so it mainly reflects elastic recoil of the lungs and chest wall. The portion of pressure that accounts for moving air through the airways is the difference between PIP and Pplat, and to turn that pressure drop into a resistance value you divide by how fast the air is moving—the inspiratory flow rate. Therefore, airway resistance equals (PIP − Pplat) divided by the inspiratory flow rate. PEEP is a baseline end-expiratory pressure and does not determine the current resistive pressure drop. Paw and Pes are other pressures that do not itself define the resistive relationship in this simple formula.

Airway resistance reflects how much pressure is needed to push the delivered air through the conducting airways at a given flow. The pressure difference that represents resistance is the drop from peak inspiratory pressure to plateau pressure (PIP minus Pplat). Plateau pressure is measured when there is no flow, so it mainly reflects elastic recoil of the lungs and chest wall. The portion of pressure that accounts for moving air through the airways is the difference between PIP and Pplat, and to turn that pressure drop into a resistance value you divide by how fast the air is moving—the inspiratory flow rate. Therefore, airway resistance equals (PIP − Pplat) divided by the inspiratory flow rate.

PEEP is a baseline end-expiratory pressure and does not determine the current resistive pressure drop. Paw and Pes are other pressures that do not itself define the resistive relationship in this simple formula.