Respiratory Equation of Motion

Ptotal = 0cmH₂OTotal Pressure above PEEP (Pvent+Pmus) Sum of ventilator and patient effort

=

Resistive P = 0cmH₂OResistive Pressure = Flow × Resistance overcomes airway resistance

+

Elastic P = 0cmH₂OElastic Pressure = Volume ÷ Compliance Expands the lungs and chest wall

VCVVolume Control PCVPressure Control

Total efforts

Pvent 15cmH₂O

Pmus 0cmH₂O

In passive patients, airway pressure comes entirely from the ventilator because Pmus is zero. In active patients, the patient’s muscle effort affects pressures and can change how compliance and resistance appear

PEEP 5cmH₂O

PEEP represents the baseline pressure and is not included in the calculation of the dynamic total airway pressure

=

Resistive Force

Resistance 10cmH₂O/L/s

Peak Flow 1.0L/s

Resistive P = 10cmH₂O

+

Elastic Force

Compliance 50mL/cmH₂O

Volume 500mL

Elastic P = 10.0cmH₂O