An independent, objective calibration check for the reduced oxygen breathing device

Normobaric hypoxia, which does not entail an altitude chamber, but reduces the fraction of inspired oxygen (02) by diluting air with nitrogen, is finding increased use. The reduced oxygen breathing device (ROBD-2) is one of several commercial devices for generating such normobaric hypoxia. Reported here are results of a procedure to check the calibration of the ROBD-2 using methods that may be readily available in physiology and psychophysiology facilities.

The %O2 output by the ROBD-2 was measured concurrently in two ways for altitudes from mean sea level (MSL) to 34,000 ft above MSL at 2000-ft intervals five times over 2 d. One measurement method used was the one built into the ROBD-2, which reports the %O2 the device is delivering at the selected target altitude. The other method diverted a sample of the ROBD-2's output gas to the paramagnetic O2, sensor of a metabolic measuring system via its sampling line. The %O2, measured with the two techniques was compared using Bland-Altman statistical procedures.

The two measurement methods produced %O2 readings differing by no more than 0.18% O2 from MSL to 34,000 ft (from 20.95 to about 4.40% oxygen, respectively), the full operating range of the device. Calculating altitude from the measured %O2 showed the ROBD-2 operated within its design error margins over its whole operational range.

The purpose for which the ROBD-2 is used should determine whether the reliability of its output in normobaric equivalent altitude is adequate. Differences between devices and device stability over time and with use have yet to be assessed. Our assessment does not address the accuracy of the algorithm the ROBD-2 uses to provide an equivalent target altitude under normobaric conditions.