Abstract: A breathing circuit for a tracheostomized patient provides respiratory care and pulmonary function testing. The breathing circuit includes a flow control adapter that directs an inspiratory flow of air and an expiratory flow of air. The flow control adapter includes a subject port for coupling to a tracheostomy tube, an inspiratory port for coupling to an incentive spirometer, and an expiratory port. The flow control adapter further includes an adapter body and a one-way valve. The adapter body is configured to define an inspiratory fluid flow path between the inspiratory port and the subject port and to define an expiratory fluid flow path between the subject port and the expiratory port. The one-way valve substantially prevents air that flows generally along the inspiratory fluid flow path from flowing through the expiratory port during inspiration and allows air flowing generally along the expiratory fluid flow path to flow through the expiratory port during expiration.