Findings and conclusions of a workshop on sudden loss of consciousness in divers, held in Madison, Wisconsin, are presented. In a study of 150 episodes of diver loss of consciousness, the divers in over half of the cases had no advance warning. In cases where some warning signs were noted, the major factor was a respiratory problem. Possible causes of diver unconsciousness are outlined. Predisposing factors include hypoglycemia, fatigue, cold, immersion and exit from the water, overheating dehydration, drug use, emotional state, and inexperience. Environmental factors include hypoxia, carbon-dioxide retention, oxygen toxicity, presence of toxic gases, drowning, strangulation, cold, thermal shock, overheating, electric shock, physical injury, and abrupt surfacing or rapid decompression. Physiological factors such as hyperventilation, improper control of breathing rate, fainting, and carbon-dioxide retention; preexisting medical problems such as epilepsy, stroke, heart failure, or adrenal cortical insufficiency may be important. Respiratory stimulation by carbon-dioxide is discussed. Under certain circumstances, an individual may respond insufficiently to carbon-dioxide with the result that breathing resistance restricts alveolar gas exchange, resulting in passing out under stress. Regulations that select out divers with abnormal carbon-dioxide responses are considered premature and inappropriate.
NIOSH, U.S. Department of Health and Human Services, Cincinnati, Ohio, Undersea Medical Society, Bethesda, Maryland, 15 pages