A respiratory assistance system can provide high flow therapy to patients. The respiratory assistance system can include a patient interface that can deliver a gas flow to a patient and a gas source that can drive the gas flow towards the patient interface at an operating flow rate. The system can include a controller for controlling the operating flow rate of the gas. The controller can apply multiple test flow rate values in a range as the operating flow rate. For each of the test flow rate values, the controller can measure a patient parameter. The controller can determine a new flow rate value based on the measured patient parameters. Patient parameters can include respiration rate, work of breathing, or any other parameters related to the respiratory circuit.
