Negative pressure oxygen breathing and head-down tilt increase nitrogen elimination

Area of Science:

• Physiology
• Respiratory Medicine
• Aerospace Medicine

Background:

• Negative pressure breathing (NPB) enhances nitrogen elimination, potentially via increased cardiac output.
• Hyperoxia (100% oxygen breathing) reduces nitrogen elimination rates.
• The combined effects of NPB and hyperoxia on nitrogen elimination are not well understood.

Purpose of the Study:

• To investigate if NPB and head down tilt (HDT) can counteract the reduced nitrogen elimination caused by hyperoxia.
• To determine the efficacy of NPB and HDT in enhancing nitrogen elimination during 100% oxygen breathing.

Main Methods:

• Nitrogen elimination was measured in 12 subjects breathing 100% oxygen under various conditions: supine (control), NPB at -10 cm H2O, NPB at -15 cm H2O, and 6-degree HDT.
• Measurements were taken over a two-hour washout period.
• Cardiac output and calf blood flow were monitored.

Main Results:

• NPB significantly increased nitrogen elimination by over 14% compared to control.
• HDT significantly increased nitrogen elimination by almost 8%.
• Neither NPB nor HDT significantly altered cardiac output, but NPB at -15 cm H2O reduced calf blood flow.

Conclusions:

• Both NPB and HDT effectively increase nitrogen elimination during 100% oxygen breathing.
• These techniques may be valuable for improving preoxygenation before decompression procedures.
• Further consideration of NPB and HDT is warranted in clinical and operational settings requiring enhanced nitrogen washout.