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Aviation History
1976
1976 - 0458.PDF
688 AIR TRANSPORT FLIGHT International, 20 March 1976 Do we really need stress heart tests? By Dr P.J.C. CHAPMAN T HE OBJECT of medical standards for flying personnel is the maintenance of crew health and, consequently, the safety ot passengers. Whatever some may say, such standards are vitally necessary. While the possibility of ill health must concern any sensible pilot, it is the spectre of sudden and potentially catastrophic incapacita tion that chiefly haunts licensing authorities, and it is reasonable to view their actions in this light. To do this the problem has to be quantified. What is the extent of the pilot-incapacitation problem? Is it real or apparent? Is the incapacitation rate acceptable as it is? Does it require and, indeed, is it even capable of improve ment? Have present suggestions, especially those concern ing further medical testing, any relevance? The facts appear to reveal two things: first, the problem is not as great as commonly supposed; second, the solution is a great deal more simple than is generally made out. During a recent nine-year period (1961-69) lata member airlines reported 17 "on duty" pilot deaths from medical causes. In an almost similar period (1960-68) 66 non-fatal medical incapacitations were recorded and in the subse quent five years (1969-73) a further 80 non-fatal incidents occurred. All 17 of the deaths were due to coronary heart disease of one form or another, whereas of the non-fatal incapacitations only four of the 66 and nine of the sub sequent 80 (that is 13 out of 146, or about nine per cent) were so caused. Epilepsy, food poisoning and kidney stone each exceeded heart disease as a cause of non-fatal seizure. Because not all carriers provide full statistics, it is not possible to show the incident rate over the pilot population and, as it affects the travelling public, over hours and distance flown. But of the 17 in-flight deaths, five probably caused accidents and 12 did not. None of the 146 non-fatal incidents was reported as causing an aircraft accident. In a 24-year period (up to 1973) the French carriers separately reported 17 cases of incapacitation, of which ten were due to coronary disease. They also recorded three interesting facts: no in-flight death occurred, in only two cases was incapacitation complete and no acci dent resulted from any of these incidents. 12-year Alpa study A study has been made by the US Air Line Pilots' Association covering the period 1955-66. Although the response to their questionnaire was poor and the definition of incapacitation somewhat broad, by far the most frequent reported cause of incapacitation was gut trouble (three out of four cases). The statistics allowed the con struction of some very interesting age-specific estimates of complete in-flight pilot incapacitation from various causes. The predicted number of such cases was computed for the pilot population at risk for the period of the study (nine cases), and corresponded very closely to the actually reported number of occurrences (ten cases). This method appears therefore to be of considerable predictive value and by using it one can reasonably forecast future incident rates when pilot numbers and age group ing are known. Applied to the total of UK professional licence-holders (about 10,000 in all), it produces a pre diction of between four and five complete in-flight incapaci tations from coronary heart disease during the next ten years. The lata figures recorded 30 such occurrences (17 fatal and 13 non-fatal) with five ensuing accidents, a rate of just over 15 per cent, and one might expect one fatal accident to a UK-registered public-transport aircraft operated by a two-man crew every 13a4 years. As the medical problem is mainly that of coronary- artery disease the measures now being considered con cern themselves mainly with this type of illness. All pilots are familiar with the present procedures and, especially, with the frequency of electrocardiograms (ECGs). Real or suspected heart disease now forces the retirement of some 40 UK aircrew each year. Unfortunately, there is no * way of knowing just how necessary this attrition may be. * Because of the supposed threat of in-flight incapacita tion it seems certain that we will see a further tightening ' of medical requirements, probably through adoption of the | stress EGC. Whatever else this will achieve, it will certainly produce a greater "yield" in terms of licence •* loss, and this means the loss of a man's livelihood. _ The stress EGG is a simple device, and its logic is compelling. A marginal heart blood supply, which may be # adequate at rest and which reveals no cardiography abnormality, is insufficient when demand is raised by exer- • cise. It then reveals certain abnormalities, exposing hidden^-^ resting deficiencies. Like many other good and logical theories, this needs to be tested by experiment and experi- * ence before firm decisions are made. Much evidence is , available, perhaps too much in view of its sometimes contradictory nature. For example, in one large-scale study A of nearly 13,000 men between 40 and 59 years old, those giving positive results to stress tests were found to have * three times the incidence of overt coronary disease in the ^ next five years than the normals. In a UK study of over 600 men (of whom no fewer than 22 per cent showed > some abnormality) the follow-up showed an incidence of heart disease eight times greater in the "abnormals" than in the normal group. But it was also found that of the 20 men with the grossest abnormalities, not only did 13 re- i main fit and well but four actually reverted to a normal result in subsequent re-testing. This lack of specificity was once more borne out when, of 33 men tested annually over three years who showed positive results, almost half reverted to "normalcy" within the test period. Stress ECG lacks sensitivity Not only is the stress ECG lacking specificity, it can be shown to lack sensitivity also. For example, of 2,000 men under careful stress-testing study, 189 developed 1 heart disease while never giving anything other than a normal response to the test. In fact, of all those who subsequently developed signs of the disease, only 18 per cent were "picked up" by the stress test. Seventy-five symptom-free pilots showed "positive" on the stress ECG, and 47 per cent of them were later proved to have normal coronary arteries. Even in the US, where enthusiasm for such procedures is often greater than our own, a recent editorial survey of this subject in the American Heart Association Journal could do no better than record the facts and feelings both for and against the procedure. Whatever else stress EGG may provide, it is bound to produce a significant number of false results, probably more than 15 per cent. Whether we consider this an accep table price to pay must depend on the weight we attach to the problem it is supposed to rectify. The status of the stress test is at present very simple; it shows promise, but is neither sensitive or specific enough to play an import ant role in aircrew licensing. Perhaps it never will be. It is of interest and use as one of a number of comple mentary tests which together give an overall guide, but to j promote the stress ECG beyond this status is to stretch an otherwise adequate test beyond its capabilities. The answer to cockpit incapacitation lies where it occurs, within the cockpit, and its solution is within the competence of operational rather than medical men. The j action taken by United Airlines, for example, clearly j points the way. The risk is an operational matter, demand- ' ing an operational answer. Whether incapacitation is complete or incomplete, I obvious or subtle, the crew task is basically simple—to
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