Safety Pressure Effects in a Mechanical Demand Regulator.

Introduction: Most U.S. Navy, but few U.S. Air Force, tactical jets use safety pressure (SP) regulators. SP effects have been studied only with confounding differences in regulator design. We compared a CRU-103 SP regulator to a CRU-103 with SP removed. The hypothesis was that SP does not alter breathing, only shifts pressure more positive.

Methods: Inspiratory flows and mask and hose pressures were measured in 24 subjects (29 for speech at rest, 31 for lung volumes) who breathed in counterbalanced order from both regulators while blind to SP condition.

Results: Both were easy to breathe. Neither was preferred overall. Between regulators, end-expiratory lung volume did not differ. SP stabilized hose pressure and favored inspiration: without speech, hose pressure swings were significantly lower (rest: 25%, exercise: 33%), as were inspiratory work of breathing at rest (33%) and peak inspiratory flow magnitude (rest: 14%; exercise: 11%). Waveforms showed interactions of mask valves and SP at the start and end of expiration. Mask leaks with SP activated the regulator during speech.

Discussion: SP as implemented in the CRU-103 causes mostly subtle differences in pressures and flows. The sensed difference during expiration may result from the initial large pressure gradient for expiratory flow. Shykoff BE, French DC, Warkander DE, Robinson FE. Safety pressure effects in a mechanical demand regulator. Aerosp Med Hum Perform. 2025; 96(7):547-555.