Resistance to Breathing in Normal Subjects During Simulated Dives

Maximal inspiratory and expiratory flow rates and resistance to air flow, using an esophageal balloon technique, were measured in three normal subjects at atmospheric pressure and during dives to various simulated depths in a compression chamber. Increased ambient pressure caused a decrease in maximal flow rates so that at a depth of 99 feet the maximal flow rates were approximately halved. At rates of flow up to 2 liters per second, the resistance at 99 feet was approximately double that at the surface.