Nitrogen narcosis attenuates shivering thermogenesis

Area of Science:

• Environmental Physiology
• Hyperbaric Medicine
• Human Thermoregulation

Background:

• Divers face risks of hypothermia due to prolonged exposure to cold, high-pressure environments.
• Understanding thermoregulatory responses under hyperbaric conditions is crucial for diver safety.
• Previous research indicates potential alterations in physiological responses at increased ambient pressures.

Purpose of the Study:

• To compare thermoregulatory responses in healthy subjects during cold water immersion at 1 ATA and 6 ATA.
• To investigate the effects of hyperbaric nitrogen on heat production and cold perception.
• To elucidate the mechanisms contributing to hypothermia development in compressed-air divers.

Main Methods:

• Eight healthy subjects underwent head-out immersion in 15°C water within a hyperbaric chamber.
• Esophageal and skin temperatures, along with oxygen uptake, were monitored at 1 and 6 ATA.
• The order of trials was alternated, and measurements were taken at regular intervals.

Main Results:

• The rate of esophageal temperature (T(es)) cooling was significantly greater at 6 ATA (2.1°C/h) compared to 1 ATA (1.3°C/h).
• Oxygen uptake, indicative of heat production, was lower at 6 ATA for similar T(es) decrements.
• Subjects perceived the 6 ATA immersion as less cold than the 1 ATA immersion for comparable T(es) changes.

Conclusions:

• Hyperbaric exposure attenuates both heat production and cold perception, contributing to hypothermia in divers.
• Nitrogen narcosis under hyperbaric conditions likely inhibits central neural pathways regulating temperature.
• These findings highlight the importance of addressing altered autonomic and sensory responses in hyperbaric environments.