With flow-cycled ventilation, the ventilator cycles into the expiratory phase once the flow has decreased to a predetermined value during inspiration. Volume, pressure, and time vary according to changes in lung characteristics. Flow cycling is the most common cycling mechanism in the pressure-support mode. For example, the inspiratory flow on the Bear 1000 ends when the ventilator determines that flow has dropped to 25% of the peak flow that occurred during inspiration. This drop in flow indicates to the ventilator that the patient's inspiratory effort is slowing, and spontaneous exhalation is about to begin.