Alveolar gas exchange during breath-hold diving

¹ Department of Physiology, State University of New York at Buffalo, Buffalo, New York

Use of a recompression chamber permitted simulation of breath-hold dives to 33 ft of sea water (2 atm abs). Four normal subjects made such dives during rest and mild exertion while delivering alveolar gas samples at frequent intervals by a partial-rebreathing procedure. The course of alveolar gas exchange differed greatly from that in ordinary breath holding. Oxygen uptake remained at near normal levels until ascent owing to the maintenance of alveolar Po₂ by increased ambient pressure. Reversal of CO₂ transfer occurred during descent, and little CO₂ moved in the normal direction until ascent. Greater uptake of oxygen and retention of CO₂ in the body led to lower final values of both alveolar Po₂ and Pco₂ than in comparable breath holding at the surface. Hyperventilation made possible longer dives with harder work, and in these the Po₂ reached very low values on ascent. One subject showed a final Po₂ of 24 mm Hg with evidence of reversed O₂ transfer. Acute hypoxia on ascent is a likely cause of drowning in breath-hold diving.

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