The effect of nitrous oxide on hearing

Area of Science:

• Audiology
• Anesthesiology
• Neuroscience

Background:

• A common belief suggests nitrous oxide (N2O) enhances hearing acuity, potentially by increasing sensitivity to low-intensity sounds.
• This perception warrants scientific investigation to understand N2O's true effects on auditory function.

Purpose of the Study:

• To investigate the impact of inhaling 10% and 20% end-tidal nitrous oxide (N2O) on auditory threshold levels, acoustic impedance, and acoustic perception.
• To determine if N2O alters subjective interpretations of sound intensity and auditory discrimination.

Main Methods:

• A study involving 16 human subjects in a quiet room, comparing auditory measurements during room air inhalation (control) with stages of N2O and oxygen inhalation.
• Auditory threshold levels, middle ear pressure (acoustic impedance), acoustic perception, memory, and discrimination were assessed.
• Subjects also performed a subjective intensity test to qualitatively interpret sound levels.

Main Results:

• Breathing 10% and 20% N2O significantly increased middle ear pressure.
• A significant effect was observed on the subjective interpretation of sound intensity.
• No significant alteration in auditory threshold was found across a range of frequencies.

Conclusions:

• Inhalation of 10% or 20% N2O does not enhance hearing acuity as measured by auditory threshold.
• N2O at these concentrations appears to induce a state resembling pre-sleep, diminishing hearing sensitivity but preserving perception of loud sounds.
• The findings challenge the notion of improved hearing acuity under N2O, highlighting instead effects on middle ear pressure and sound perception.