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O2 pressures between 0.12 and 2.5 atm abs, circulatory function, and N2 elimination
D Anderson1, G Nagasawa, W Norfleet
1Hermann Rahn Laboratory of Environmental Physiology, State University of New York, Department of Physiology, School of Medicine, Buffalo 14214.
Undersea Biomedical Research
|July 1, 1991
Summary
Increasing inhaled oxygen pressure reduces nitrogen elimination by causing vasoconstriction. This impacts decompression schedules, suggesting oxygen breathing during decompression should occur at the lowest safe pressure.
Area of Science:
- Physiology
- Diving Medicine
- Aerospace Medicine
Background:
- Nitrogen (N2) elimination is crucial for safe decompression in diving and aerospace.
- Understanding how varying oxygen pressures affect N2 washout is essential for optimizing decompression protocols.
Purpose of the Study:
- To investigate the impact of different inhaled oxygen pressures on nitrogen elimination rates.
- To determine the physiological mechanisms underlying observed changes in N2 washout.
- To assess the implications for decompression strategy during exposure to altered oxygen environments.
Main Methods:
- Conducted 72 two-hour nitrogen washouts in 6 subjects.
- Utilized a closed-circuit system with an O2-argon mixture.
- Tested oxygen pressures ranging from 0.12 to 2.5 atmospheres absolute (atm abs).
- Monitored physiological parameters including heart rate, cardiac output, and blood flow.
Main Results:
- Hypoxia (low oxygen) significantly increased N2 elimination by 9.4% (P < 0.05).
- Increasing oxygen pressure led to significant decreases in N2 elimination (-8.9% at 2.0 atm abs, -16.9% at 2.5 atm abs).
- Physiological responses included decreased heart rate, cardiac output, skin perfusion, and leg blood flow, with increased mean arterial pressure.
Conclusions:
- Perfusion-dependent N2 elimination decreases with rising oxygen pressure due to vasoconstriction.
- Altered inhaled oxygen pressures during compression-decompression can affect inert gas exchange.
- Current decompression models may have added uncertainties; oxygen breathing during decompression should use the lowest safe ambient pressure.