Arterial blood gas tensions during breath-hold diving in the Korean ama

Korean female unassisted divers (cachido ama) breath-hold dive > 100 times to depths of 3-7 m during a work day. We sought to determine the extent of arterial hypoxemia during normal working dives and reasonable time limits for breath-hold diving by measuring radial artery blood gas tensions and pH in five cachido ama who dove to a fixed depth of 4-5 m and then continued to breath hold for various times after their return to the surface. Eighty-two blood samples were withdrawn from indwelling radial artery catheters during 37 ocean dives. We measured compression hyperoxia [arterial PO2 = 141 +/- 24 (SD) Torr] and hypercapnia (arterial PCO2 = 46.6 +/- 2.4 Torr) at depth. Mean arterial PO2 near the end of breath-hold dives lasting 32-95 s (62 +/- 14 s) was decreased (62.6 +/- 13.5 Torr). Mean arterial PCO2 reached 49.9 +/- 5.4 Torr. Complete return of these values to their baseline did not occur until 15-20 s after breathing was resumed. In dives of usual working duration (< 30 s), blood gas tensions remained within normal ranges. Detailed analysis of hemoglobin components and intrinsic oxygenation properties revealed no evidence for adaptive changes that could increase the tolerance of the ama to hypoxic or hypothermic conditions associated with repetitive diving.