Background   Previous evidences indicate that electromagnetic radiation may damage the cardiovascular system. However, there are few studies on the effects of long-term exposure to electronic countermeasures (ECM) electromagnetic environment on cardiac autonomic nerve system (CANS).

  Objective   To investigate the effects of long-term exposure to high frequency electromagnetic environment on indicators of CANS of electronic countermeasure operators.

  Methods  From April to October in 2019, officers and soldiers of an electronic countermeasures force were recruited, and 456 cases were assessed with propensity score matching method to balance confounding factors. The subjects were divided into the exposed group (age: 32.08±9.44 years) and the non-exposed group (age: 31.59±9.45 years) according to the operating environment, with 228 cases in each group, including 214 males and 14 females. The 24 h ambulatory electrocardiogram and 24 h ambulatory blood pressure were monitored in all subjects to compare the differences in heart rate, heart rate variability (HRV), and circadian blood pressure between the two groups.

  Results  The electromagnetic environment frequency band was 5.5MHz to 1.84GHz, ranging from high frequency to ultra-high frequency. No significant difference was found in age, gender, body mass index (BMI), smoking history and drinking history between the exposed group and the non-exposed group. The 24 h dynamic electrocardiogram showed that the number of disturbed heart beats (MdIQR: 18 643.00 8 006.00, 53 010.75 vs 8 006.00 8 006.00, 21 826.75) and sinus bradycardia (MdIQR: 12.5 0.00, 209.25 vs 0.00 0.00, 9.00) in the exposed group were higher than those in the non-exposed group (P < 0.001, respectively). However, the minimum heart rate was significantly lower than that of the non-exposed group (43.39±5.15/min vs 44.68±4.44/min, P=0.004). HRV indexes indicated that the square root of the mean squared difference of successive normal RR intervals (RMSSD) (52.64±23.95 vs 48.28±18.58) reflecting vagal nerve activity and VLF (4 650.923 094.00, 5 519.50 ms² vs 4 650.923 235.50, 4 650.92 ms²) reflecting sympathetic nerve activity improved obviously in comparison to those in the non-exposed group (P < 0.05, respectively). In addition, 24 h mean systolic blood pressure (BP) (117.46±6.70 mmHg vs 118.73±6.61 mmHg), 24 h mean diastolic BP (69.25±5.62 mmHg vs 70.76±5.68 mmHg), daytime mean diastolic BP (71.22±5.72 mmHg vs 72.70±5.69 mmHg) and night mean diastolic BP (62.22±6.98 mmHg vs 63.54±6.06 mmHg) in the exposed group were lower than those in the non-exposed group (all P < 0.05). The proportion of reverse-dippers diastolic BP at night in the exposed group (114.82% vs 20.88%) showed an increasing trend in comparison to the non-exposed group (P < 0.05).

  Conclusion   The sympathetic and vagal nerve tone increase simultaneously in the electronic countermeasure operators exposed to high frequency electromagnetic radiation for a long time. Both 24 h heart rate and blood pressure decrease significantly accompanied by sinus bradycardia increasing in the exposed group, suggesting a preponderance of the vagus nerve and an increasing risk of arrhythmia.