What causes alternobaric vertigo during a dive?

Alternobaric vertigo occurs when there is a difference in pressure between the middle ear spaces, specifically between the two eustachian tubes. This discrepancy can happen if one ear is unable to equalize pressure effectively during a dive. When a diver descends, the external pressure increases, and if the pressure in one ear is allowed to remain lower than in the other, it can lead to conflicting sensory signals that disrupt the body's balance, resulting in vertigo.

Inadequate equalization is typically due to various factors, such as technique, congestion, or anatomical differences, which may prevent one eustachian tube from functioning properly compared to the other. This failure to equalize can lead to the sensation of dizziness or vertigo as the central nervous system interprets the conflicting information from the inner ears.

Each of the other choices relates to different physiological effects or issues but does not directly cause alternobaric vertigo in the same manner that unequal pressure between the ears does.