The problem of loss of consciousness in flying personnel ∗

Abstract

L oss OF consciousness is one of the more serious problems currently facing aviation and space medicine. Split-second human failure in the modern supersonic aircraft of today and the rocket-propelled space craft of tomorrow can have disastrous consequences. At ground level syncope is regarded quite casually by the lay public and the medical profession alike because of the usual lack of complications and sequelae. But in the environments of the atmosphere and space, transitory loss of conciousness is more likely to result in serious accidents with loss of life and property. Therefore, it becomes obvious that persons in primary control of aircraft must not be prone to syncope. Although syncope is a common occurrence, little information is available concerning its incidence in the general population, in an apparently healthy adult male population and in flying personnel. More important, little is known concerning the likelihood of recurrence in any given subject, or the relationship of clinical syncope to experimental syncope. Criteria for selection of U. S. Air Force flying personnel are based upon an absence of syncopal episodes in the past and a rigorous physical examination. It is difficult to judge the adequacy of these technics for selection. However, they seem inadequate when an attempt is being made to determine whether or not a subject who has fainted at ground level is apt to have a similar episode during flight. The School of Aviation Medicine studied 132 apparentlyhealthy persons, ninety-seven with a history of clinical syncope and thirty-live without such a history. This survey provided an opportunity for reviewing the mechanisms resulting in syncope in apparently healthy people. It was believed that the incidence of such mechanisms would differ from that of the general population because of the initial selection criteria, and that such classic mechanisms as aortic stenosis,1-3 anemia and central nervous system disorders4 would account for little, if any, of the syncopal episodes in flying personnel. MATERIAL AND METHODS In an attempt to determine the true incidence of syncope in an apparently healthy population of young adult men, 5,000 questionnaires were sent to Air Force personnel on a single base. It was requested that the questionnaires be returned unsigned to avoid any motivation to withhold information. No attempts were made regarding further selection within this population. Fifty aviation cadets in preflight training volunteered as subjects for a special medical study. As an incentive, each was given additional time off from duty. None knew that the study was related to loss of consciousness. All cadets had previously denied syncopal episodes in order to gain admittance to the flight training program. Each cadet was assigned a number which he selected from a hat. He was never identified by name and thus was guaranteed anonymity. The cadets were then asked to report in writing any past history of syncope and the circumstances surrounding any episode. The purpose was to obtain some idea as to the percentage of people entering the flying training program who had experienced syncopal episodes. It was also hoped that, with a battery of special tests designed to tesi. the cardiovascular system. those cadets with a me-existing history of syncope could be selected. The examiners did not know the cadet’s history until the special tests had been completed. An additional eighty-two apparently healthy, flying personnel who had experienced 113 syncopal episodes were also studied. All 132 subjects were studied with a detailed history, complete physical examination, complete blood counts, erythrocyte sedimentation rate, fasting blood sugar, urinalysis, roentgenogram of the chest and electrocardiogram. Roentgenograms of the skull and additional studies were obtained as indicated when a history of syncope was noted.