Effects of submerged operation on the heart rate variability of oceanauts in"Jiaolong"submersibles

Objective To observe the effects of submerged operation on the sympathetic nerve and vagus nerve of the autonomic nervous system(ANS)in"Jiaolong"oceanauts and also to explore the regulation of human cardiovascular function during submerged operation. Methods Six oceanauts underwent simulated submerged operation in"Jiaolong". Electrocardiogram(ECG)was detected before submerged operation, at hour 1.5 and 2.5 respectively. Quantitative analyses were made on various indicators of heart rate variability(HRV), including low-frequency(LF), high-frequency(HF), total power(TP), LF/HF ratio and HF/TP ratio by using frequency spectral method. Results LF control value before submerged operation was(2 950±248)ms2. The LF value at hour 1.5 during submerged operation increased to(3 633±232)ms2, and statistical significance could be noted when comparisons were made between them(P<0.05). The LF value at hour 2.5 during submerged operation decreased to(2 800±184)ms2. Statistical significance could be noticed when it was compared with that at hour 1.5(P<0.05), however, no statistical significance could be found when it was compared with the control value before submerged operation(P<0.05). The control value of HF before submerged operation was(1 700±107)ms2, the HF-value decreased to(1 200±156)ms2 at hour 1.5 after submerged operation, and statistical significance could be noted when comparisons were made between them(P<0.05). The HF value increased to(1 917±15)ms2 at hour 2.5 after submerged operation, and statistical significance could be seen when it was compared with that at hour 1.5(P<0.05). However, no statistical significance could be found when it was compared with the value before submerged operation(P<0.05). And no statistical significance could be seen when it was compared with the control value(P<0.05). The LF/HF ratio detected before submerged operation was 1.73±0.81, but its value at hour 1.5 after submerged operation increased to a significant value of 3.02±1.11, with statistical significance(P<0.05). However, its value at hour 2.5 after submerged operation decreased to 1.46±0.82, and statistical significance could be noted, when it was compared with that at hour 1.5(P<0.05). The HF/TP ratio detected before submersion was 0.36±0.22, but it decreased to a value of 0.25±0.23 at hour 1.5 after submerged operation, with statistical significance(P<0.05). However, at hour 2.5 after submerged operation, its value increased to 0.76±0.11, which was significantly higher than that detected at hour 1.5, also with statistical significance(P<0.05). The TP value detected before submerged operation was(4 650±280)ms2, no changes could be detected at hour 1.5 after submersion. As could be seen, the TP value detected at hour 2.5 after submersion was significantly lower than the control value and that detected at hour 1.5 after submersion(P<0.05). Conclusions The sympathetic nerve activity increased, while the parasympathetic activity decreased at hour 1.5 after submersion, which might be associated with the difficult and complicated manipulation of the submersible, intensive work load, mental strain and stress reactions of the oceanauts. The reversal changes displayed at hour 2.5 after submersion might be correlated with the following factors, gradual adaption to the cabin and subsea environment, alleviation of stress reactions and decreased work load. Key words: Oceanauts; Underwater operation; Heart rate variability; Sympathetic nerve; Vagus nerve