Voluntary breathholding; pulmonary gas exchange during breathholding.

When a subject is totally immersed in water while holding his breath, a loss of buoyancy occurs.This phenomenon can be demonstrated by resting the subject on 1 pan of a balance, the loss of buoyancy being reflected as a gain in weight on the balance. This gain in weight (or loss of buoyancy) was first observed by us while determining body density by an underwater weighing method (1). This gain in weight amounts to 200 to 500 grams per minute, depending on the size of the subject, and is due to a decrease in the volume of gas in the lungs during breathholding. This report presents data describing this phenomenon and indicating its significance with respect to pulmonary gas exchange during breathholding.