The reduced oxygen breathing paradigm for hypoxia training: physiological, cognitive, and subjective effects.

UNLABELLED: The current training program for hypoxia familiarization requires a low-pressure chamber that places aviator trainees at risk for decompression sickness. A cost-effective reduced oxygen-breathing (ROB) paradigm that decreases oxygen (O2) concentration leading to normobaric hypoxia was assessed as an alternative to the hypobaric chamber. PURPOSE: To help establish the validity of the ROB paradigm, this report documents cognitive performance, cardiopulmonary and subjective changes during ROB exposure. METHODS: Performance on a two-dimensional tracking task, as well as BP, heart rate, end-tidal carbon dioxide (ETCO2), O2 saturation, and subjective reports of hypoxia symptoms were observed in 12 U.S. Navy divers during exposure to normoxic air followed by one of four experimental gas mixtures per session. All participants received all gas conditions that differed in their relative concentrations of O2 and nitrogen (6.20/93.80, 7.00/93.00, 7.85/92.15, and 20.85/79.15% O2/N2). RESULTS: ROB caused increases in tracking task error (p < 0.0001). ROB also increased heart rate (p < 0.001) and systolic BP (p = 0.004), and decreased ETCO2 and O2 saturation (p < 0.0001). Finally, subjects responded to ROB-induced hypoxia with higher subjective symptom ratings (p < 0.0001). CONCLUSIONS: These data are consistent with those expected from hypoxic states and support the validity of the ROB paradigm for hypoxia training. Future validation studies comparing a ROB device with hypobaric chambers are needed.

SPH-4 helmet damage and head injury correlation.

Human tolerance to head impact was assessed by correlating the force levels required to duplicate damage seen in 14 SPH-4 aviator helmets retrieved from U.S. Army helicopter crashes with resulting head injury. Head injury occurred at peak acceleration levels far below 400 G, which is the value currently used by the U.S. Army as the pass-fail criterion in evaluating the impact attenuation performance of prospective aircrew helmets. Concussive head injuries occurred below Severity Index values of 1500 and below Head Injury Criterion values of 1000. These are considered concussive threshold values by the National Operating Committee on Standards for Athletic Equipment and by the Department of Transportation, respectively. Because peak transmitted force was the best estimator of the Abbreviated Injury Scale values assigned to the 14 cases, it may be a more effective criterion to use in the evaluation of helmet impact attenuation performance than is peak G, Severity Index, or Head Injury Criterion.