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

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.

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.

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 ms2 x Hz(-1),T-1: 1269 +/- 158 ms2 x Hz(-1), L+2: 1095 +/- 148 ms2 x Hz(-1), and L+4: 1238 +/- 124 ms2 x 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.

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.