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Minerva Foundation Institute for Medical Research 00250 Helsinki, Finland
Recently, two interesting papers dealing with psychological stress produced by skydiving appeared in The Journal of Clinical Endocrinology and Metabolism (1, 2). Because in 1992 and 1993 we described the response of subjects about to make their first jump with a parachute (3, 4), we would like to offer some comments.
The plasma concentrations of a number of hormones were found not to increase significantly during the period preceding the jump (1, 2). However, in our hands, the skydiving test—before a novice enters the plane—induced a significant rise in plasma antidiuretic hormone and a similar tendency in serum cortisol (3, 4). Also, there was a significant and positive correlation between the changes in cortisol and C-reactive protein.
One explanation for the negative findings could be that the responses of some hormones were blunted, as each stressor might induce its specific hormone pattern (5). More likely, the discrepancy between our results is due to the different design of the experiments, the selection of controls, and the influence of preanalytical factors (factors acting before a specimen is collected and analyzed). Stress responses are known to exhibit considerable interindividual variation. To increase the detectability of the response, we used each individual as his or her own control (during a stress-free situation some days before or after the jump) instead of different control individuals. In the articles quoted there is no mention of the possibility of preanalytical influences (e.g. time of day, posture, food intake, exercise, experiencing cold, and changes in altitude and speed, etc. during the flight and the fall). Because we have previously demonstrated that physical activity and changes in posture have strong effects (e.g. refs. 6–10), the investigators (1, 2) may have been unable to keep the volunteers absolutely free of physical activity—parachutists need to change clothes, take on a harness, etc. Actually, we considered it important, as recommended (6), to collect the specimens after 15 min of sitting to achieve hemodynamic equilibrium and to eliminate the influence of many other preanalytical factors. Therefore, it would have been interesting to receive information on analytes that reflect physical activity (e.g. serum creatine kinase and lactate dehydrogenase) and hemoconcentration.
Because of ethical and legal considerations it is difficult to induce pure psychological stress experimentally. Therefore, imminent skydiving—before a novice enters the plane—seems to be an excellent model for such studies. However, later phases in the skydiving sport appear to involve so much somatic stress that one should be cautious in using them as models of pure psychological stress.
Footnotes
Address correspondence to: Dr. Benoit Dugué, Minerva Foundation Institute for Medical Research, Tukholmankatu 2, Helsinki 00250, Finland.
Received December 5, 1997.
References
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