A method of estimating a parameter indicative of respiratory flow of a patient being administered flow therapy, comprising: optionally administering a gas at a flow rate to the patient using a flow therapy apparatus with a patient interface, determining a terminal pressure in, at or proximate the outlet of the patient interface or in, at or proximate the nares of the patient, determining nasal RTF, determining a nasal flow parameter being or indicative of nasal flow based on the pressure and a nasal RTF, and optionally outputting the nasal flow parameter or parameter derived therefrom.
