There is provided a method of monitoring the lung function of a patient, the method comprising determining one or both of an inhalation time and a rest time for a patient that is using a respiratory apparatus, the one or both of an inhalation time and a rest time for the patient being determined from measurements obtained from the respiratory apparatus, wherein the inhalation time is the amount of time for which the patient inhales through the respiratory apparatus, and the rest time is the amount of time between the end of an exhalation and the start of the next inhalation; and analyzing the determined one or both of the inhalation time and rest time to determine an indication of the lung function of the patient.