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