Our circuit is a flexible, single-patient-use, one-way valving system designed for pulmonary function measurements, such as tidal or minute volume, vital capacity and negative inspiratory force. Circuit comes with a U/Adapt-It™ adapter with 15 mm ID base, 6" flextube, two one-way valves, an oxygen tube connector, a 22 mm OD tube adapter and a 22 mm ID/15 mm ID adapter.