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We studied the performance of two respirators employing an advanced turbine delivery system: LTV 1000, Tbird VSO2. We assessed the ability of the ventilators to deliver to a normal lung model a set fraction of inspired oxygen (FiO2) at different simulated cabin altitudes.
We used a decompression chamber to mimic the hypobaric environment at a range of simulated cabin altitudes of 1,500, 2,000 and 3,000 meters (4,000, 5,333, 8,000 feet). A model of normal lung was used. Concerning the Tbird VSO2, cabin altitude was input. Ventilators were tested with FiO2 set at 50% and Vt set at 700 ml. We noted the effective FiO2 assessed by the ventilators (paramagnetic analysis). We measured the FiO2 really delivered with a dedicated instrument of the French physiological laboratory of aviation and space medicine of the Air Force. Comparisons of preset and assessed FiO2 to actual measured FiO2 were accomplished using a t test for each altitude.
On one hand, both ventilators showed a moderate variation between FiO2 set and delivered. On the other hand, variations between FiO2 delivered and assessed are high, suggesting inefficacity of ventilators' paramagnetic analysis in hypobaric conditions.