Heart rate and autonomic balance during stand tests before and after fighter combat missions.

Background: High workload during combat missions is a critical factor in the use of modern aircraft. Our objective was to evaluate the impact of piloting in war zones on the kinetics of the sympathovagal balance during recovery. Methods: There were 40 military pilots who were monitored during operational flights in Afghanistan. Electrocardiographic activity was recorded during stand tests performed 1 h before takeoff (T-1), immediately after landing (L+0), 2 h after (L+2), and 4 h after (L+4) the flight. Missions were divided in two groups according to flight duration. Results: The mean length of long flights was 4:31 ± 0:53 h and of short flights 1:27 ± 0:09 h. For long flights, at L+0, all indices related to parasympathetic modulation rose significantly in comparison to T-1, L+2, and L+4 (total power L+0: 2083 ± 414 ms 2 · Hz -1 ,T-1: 1269 ± 158 ms 2 · Hz -1 , L+2:1095 ± 148 ms 2 · Hz -1 , and L+4: 1238 ± 124 ms 2 · Hz -1 ; high-frequency normalized units (HFnu) L+0: 16 ± 2%, T-1:11 ± 1 %, L+2: 10 ± 1 %, and L+4: 11 ± 1%). At the same time the sympathetic frequency components significantly decreased (low-frequency normalized units (LFnu) L+0: 83 ± 2%, T-1: 88 ± 1 %, L+2: 90 ± 1 %, and L+4: 89 ± 1 %; LF/HF L+0: 7 ± 1, T 1: 11 ± 1, L+2: 13 ± 2, and L+4: 16 ± 3). For short flights, the sympathetic components were higher at L+0 (LFnu: 77 ± 2%; LF/HF: 14 ± 3) than at T-1 (LFnu: 66 ± 5%; LF/HF: 6 ± 1). A concomitant reduction of vagal components was observed. Conclusions: Modulations of autonomic balance differed with the type of mission. A postflight sympathetic increase represents an autonomic adaptation due to stress and flight. A raise of parasympathetic modulation after flight may be related to the decrease of alertness.