Figure 1 -.

Mechanical model. Components include: a large plastic box maintained at 37°C (1), preserved swine lungs (2, 3) and a cascade-type humidifier (7) inside the box. Three unidirectional valves (4, 5 and 6) were inserted within the tubing section external to the box (representing the airway) to direct flow through the humidifier prior so that it could ventilate the lungs. In this same simulated airway segment, a sensor (Vaisala, HMI 32, Woburn, MA, USA) (8) was positioned to detect AH and temperature. The HME (9) under test was individually installed using a random sequence for each testing period. A mechanical ventilator (10) was used to simulate different ventilatory conditions.