This disclosure describes systems and methods for compensating for leakage when during delivery of gas from a medical ventilator (20) in a proportional assist mode to a patient. The technology described herein includes systems and methods to compensate the delivery of PA ventilation for leakage in the patient circuit (30) by using leak-compensated lung flows as well as leak-compensated respiratory mechanics parameters (lung compliance and lung resistance) estimated in a manner that compensates for elastic and inelastic leaks from the ventilation system.
