1. A system for detecting an ineffective effort of a patient being mechanically ventilated by a ventilator, the system comprising: a flow sensor that is configured to: monitor a respiratory flow of air of the patient during expiration that is after cycling of the ventilator and before triggering of the ventilator; and generate a signal indicative of the respiratory flow of the patient during expiration; a processing system that includes at least one processor, the processing system configured to: determine a peak expiratory flow (PEF) of the patient based on the generated signal; calculate a second derivative of the signal that is indicative of the respiratory flow of the patient during expiration; determine an occurrence of a significant declivity within the signal when the second derivative of the signal is greater than a negative, non-zero threshold; and detect perturbations within the generated signal by classifying the perturbations between at least ineffective efforts and non-ineffective efforts based on determination of the occurrence of the significant declivity within the signal.