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Published on: May 4, 2021
Lower exhaled nitric oxide in hypobaric than in normobaric acute hypoxia
Tryggve Hemmingsson1, Dag Linnarsson
1Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden. tryggve.hemmingsson@ki.se
Respiratory Physiology & Neurobiology
|August 19, 2009
Summary
Exhaled nitric oxide (NO) levels decrease at high altitudes due to reduced gas density, not just hypoxia. This study found hypobaric conditions significantly lower NO partial pressures compared to normobaric hypoxia.
Area of Science:
- Respiratory Physiology
- Environmental Medicine
Background:
- Exhaled nitric oxide (NO) is a marker for airway inflammation.
- Previous studies linked reduced exhaled NO at altitude to hypoxia.
Purpose of the Study:
- To investigate the effect of reduced ambient pressure (hypobaria) versus normobaric hypoxia on exhaled NO partial pressures (Pe(NO)).
- To determine the cause of decreased exhaled NO at altitude.
Main Methods:
- Measured Pe(NO) in eight healthy subjects at sea level and reduced pressure (540 hPa, ~5000 m).
- Used equivalent hypoxic breathing gases (11.3% O2) under both normobaric and hypobaric conditions.
- Corrected Pe(NO) readings for gas density effects.
Main Results:
- Sea level Pe(NO) averaged 2.4 mPa and remained stable with normobaric hypoxia.
- Hypobaric Pe(NO) decreased to 1.4 mPa under equivalent hypoxia.
- A reduction of up to 33% in hypobaric Pe(NO) was observed compared to normobaric conditions.
Conclusions:
- Reduced gas density at altitude, not just hypoxia, causes lower exhaled NO.
- Enhanced axial back diffusion of NO and increased alveolar NO uptake in hypobaria likely explain the findings.
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