Alveolar pathways during 90-foot, breath-hold dives.

The gas tensions of mixed expired and alveolar air were measured at various depths during descent and ascent. A reversed carbon dioxide gradient from the lungs into the blood was demonstrated at the 50-foot depth. At 90 feet, 45 percent of the pre-dive carbon dioxide content of the lungs had disappeared. There was no indication of a reversed oxygen gradient during ascent.