Efficiency of constant-flow oxygen masks for general aviation: a new method of mask evaluation.

Three commercially popular oxygen masks for general aviation were tested by measuring arterial blood gases at altitude and alveolar gases at ground level with a respiratory mass spectrometer. At 4,575 m (15,000 ft) and 3.65 1/min oxygen flow, calculated fractional inspired oxygen (F102) averaged 38.1% for the Hudson-type mask; 49.6% for the Scott Sky Mask; and 52.4% for the Scott Duo Seal Mask. At ground level, 1280 m (4,200 ft) 2.6 1/min oxygen flow, F102 calculated from alveolar gases averaged 41.5% plus or minus S.D. 5.3 for the Hudson Mask; 48.0% plus or minus 5.2 for the Scott Sky Mask; and 54.9% plus or minus S.D. 6.2 for the Scott Duo Seal Mask. The asymptomatic hyperventilation observed in all subjects at altitude degraded the performance of all three masks to a sufficient degree to offset the benefits of increased oxygen flow achieved through the regulator at higher altitudes. The respiratory mass spectrometer provides a new technique for analyzing efficiency of oxygen masks and the effect of changes in mask design.