Respiratory function curves are a graphic representation of changes in volume, pressure or flow during the respiratory cycle. These changes can represent changes with respect to time (curves of volume-time, pressure-time and flow-time) or changes in one variable with respect to another (curves of flow-volume and of volume-pressure). Respiratory function curves enable analysis of the physiopathology in a patient, detection of changes in clinical status, optimization of ventilatory strategy, and evaluation of treatment response. They can also be used to facilitate patient comfort, prevent complications and iatrogeny, evaluate the course of weaning from mechanical ventilation, and help to establish a prognosis. In clinical practice these curves can show the presence of air leaks, indicate possible high resistance in the airway, suggest the possibility of trapped air, detect the presence of anomalous expiratory volume, identify the presence of secretions in the airway or water in the circuit, indicate the optimal PEEP, and reveal changes in pulmonary compliance.