Observations after loss of consciousness under water

Two diving incidents were investigated in which 1) an experienced professional diver (A) lost consciousness during an air dive to 69 meters, and 2) an amateur sports diver (D) lost consciousness during a 40-meter air dive. In subsequent tests both divers' ventilatory responses to inspired carbon dioxide were found to be extremely low. Under simulated diving conditions, Divers A and D exhibited marked carbon dioxide retention during exercise at 30 meters (end-tidal PCO2 = 65 and 57 mmHg, respectively) and at 70 meters, Diver A stopped work in less than 3 min because of severe dizziness. Reduced sensitivity to carbon dioxide, perhaps caused by the interaction of hypercapnia and nitrogen narcosis, is thought to have been partly responsible for these incidents.