Evaluation of the effect of flights in supersonic fighters on sinus rhythm variability parameters

Heart rate variability is a widely used method to evaluate vagal and sympathetic influences on the heart. The purpose of this study was to assess the relationship of autonomic nervous system components' interaction in supersonic fighter pilots by means of a sinus rhythm variability analysis. The following frequency domain parameters were analyzed: low-frequency (LF) power spectral of 0.05 to 0.15 Hz (ms2); high-frequency (HF) power spectral of 0.15 to 0.45 Hz (ms2); LF and HF power spectral index; total spectral power (HF + LF); percent, LF distribution in total spectral power; percent HF, HF distribution in total spectral power; and an average heart rate per minute. The study comprised 30 healthy military pilots (age, 24-48 years) in whom heart rate variability parameters were determined 10 to 12 minutes before take off, 10 to 12 minutes after four successive flights, and 1, 2, and 12 to 16 hours after completing the flights. The control group was comprised of 20 healthy nonpilots (age, 24-49 years). The statistical significance was estimated by means of the following methods: Student's t test for normal distribution and a rank test for the non-normal one (between the groups of the same subjects); and the Cochran-Cox test for normal distribution and the Wilcoxon test for the non-normal one (between the groups of different subjects). Higher activity of sympathetic components of the autonomic nervous system was shown in pilots in the course of the first examination before flights as compared with the controls (higher LF, LF/HF, percent LF). Predominance of the sympathetic nervous system in pilots might reflect adaptation to repeated short-term exposures to high values of accelerations acting in head-leg axis.