Performance of ventilators at simulated altitude: study of fraction of inspired oxygen

Introduction

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.

Methods

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.

Results

Figure 1 shows the data with FiO₂ set at 50%.

Figure 1

Conclusions

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.