Here Dr Hudson explore the relationship between pressure and volume, expressed as compliance.

The equation of motion

Here Dr Hudson explores the a critical equation in the physiology of mechanical ventilation–the equation of motion. This equation helps describe how the ventilator pressure and/or pressure generated by the respiratory muscles must overcome the elastic load and resistive load to achieve movement of air.

The equation of motion

Pmus + Pvent= (E x V) + (R x *V)

Pvent= pressure generated by ventilator                                             Pmus= pressure generated by respiratory muscles                                    E= elastance (inverse of compliance)                                                         V= volume (mL)                                                                                                 R= resistance( cm/H20/L/s)                                                                              *V= flow (L/min)

Elastic load

(E x V) =elastic load                                                                           Depends on volume

Resistive load

(R x *V)= resistive load                                                                              Depends on flow


WHen patient is passive on the vent, Pmus= 0

Pvent= (E x V) + (R x *V)

Plateau pressure

Here Dr Hudson explores the theory and calculation behind the plateau pressure. Keep in mind the equation of motion–as here we are eliminating the resistive flow element.