Nitrogen partial pressures in man after decompression from simulated scuba dives at rest and during exercise

Area of Science:

• Physiology
• Diving Medicine
• Biophysics

Background:

• Scuba diving involves exposure to increased ambient pressure, leading to nitrogen absorption.
• Decompression procedures aim to safely off-gas absorbed nitrogen to prevent decompression sickness.
• Understanding nitrogen elimination kinetics is crucial for optimizing diving safety.

Purpose of the Study:

• To measure arterial and central venous nitrogen partial pressures (PN2) after simulated scuba dives.
• To investigate the effect of exercise during the dive on nitrogen elimination.
• To assess the adequacy of standard decompression schedules for nitrogen washout.

Main Methods:

• Five subjects underwent simulated air dives to 50m for 30 minutes in a hyperbaric chamber.
• Decompression followed a standard schedule with multiple stops over 67 minutes.
• Arterial and venous blood samples were analyzed for PN2 using a manometric Van Slyke apparatus up to 240 minutes post-decompression.
• Three subjects repeated measurements after exercising at 75W during the bottom phase.

Main Results:

• Venous PN2 remained elevated for up to 160 minutes post-decompression, indicating incomplete nitrogen washout.
• No significant difference in PN2 was observed between dives with rest and dives with exercise.
• Computer modeling confirmed that nitrogen elimination was consistent with Haldanian theories for the applied decompression profile.

Conclusions:

• Nitrogen elimination is prolonged after simulated dives, extending beyond the typical decompression time.
• Exercise during the bottom phase of a dive does not appear to accelerate nitrogen washout.
• Current decompression schedules may require adjustments to ensure complete nitrogen elimination.