A method of estimating respiratory demand of a patient being administered flow therapy can include: administering a gas flow rate to the patient through both nostrils using a flow therapy apparatus with a patient interface for each nostril, measuring a parameter associated with that nostril, the parameter being one or more of: respiratory demand of that nostril, indicative of respiratory demand of that nostril, or a parameter from which respiratory demand of that nostril can be derived, determining respiratory demand (or parameter indicative of respiratory demand) for the patient from the nostril parameter for each nostril.