A closed-loop reduced oxygen breathing device for inducing hypoxia in humans

Background: Hypoxia poses a documented threat to aerospace and diving operations in healthy people and is a component of many clinical conditions. Practical training for aircrew, and research on clinically relevant hypoxic conditions frequently rely exclusively on large, expensive hypobaric chambers. Purpose: Here we describe and report the efficacy of a compact, economical, closed-loop rebreather-type reduced-oxygen breathing device (ROBD) for hypoxia induction in humans. Methods: Subjects were four healthy student Naval flight surgeons. During baseline, subjects breathed normoxic air (21% O-2, equivalent to sea-level). Baseline was followed by an altitude period, during which participants were exposed to hypoxic air (about 10% O-2, approximating 5,486 m [18,000 ft mean sea-level]) for 30 min followed by a normoxic recovery period. Subjects' peripheral arterial oxygen saturation (SpO(2)), BP, impedance cardiography, cardiac output, and systemic vascular resistance served as dependent measures along with the fraction of inspired oxygen (FIO2). Results: Circuit FIO2 and subjects' SpO(2) were significantly lower during the altitude period than the baseline and recovery periods. HR and cardiac output were significantly higher, and systemic vascular resistance was significantly lower, during hypoxic air exposure than during baseline or recovery. Conclusions: These data support the closed-loop ROBD as a potentially useful device for training and research involving acute hypoxia in healthy and clinical populations.