Yamazaki F, Shiraki K, Sagawa S, Endo Y, Torii R, Yamaguchi H, Mohri M, Lin Y C
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Aviat Space Environ Med. 1998 Jul;69(7):643-6.
This experiment was designed to examine the involvement of the autonomic nervous system in the production of hyperbaric bradycardia.
Four male divers were exposed to a He-O2 (heliox) environment at 24 atmosphere absolute (atm abs) for 7 d. The heart rate (HR) and respiratory rate were recorded at rest in the morning (0700 h) and at night (2230 h) on 1 d during a 5-d predive control, 2 d during a 7-d saturation dive at 24 atm abs, 2 d during decompression, and on 1 d during a 4-d postdive period. Cardiac sympathetic and parasympathetic activities were estimated by using a spectral analysis of the variability of R-R intervals.
The morning HR did not fluctuate throughout the experimental days. The night time HR decreased (p < 0.05) by 11.8% on the first day at 24 atm abs compared with that of the predive control. The bradycardia diminished gradually and returned to the predive level with continued exposure at 24 atm abs. The high-frequency power of the cardiac variability, an index of cardiac parasympathetic activity, increased (p < 0.05) only in the first night at 24 atm abs, whereas the low-frequency power and a ratio of low- to high-frequency power, an index of cardiac sympathetic activity, were unchanged.
The present results suggest that an increased parasympathetic activity rather than a decrease in the sympathetic activity is responsible for the bradycardia on exposure to heliox dry saturation dive at 24 atm abs. The mechanism of the gradual disappearance of the bradycardia is unknown, but perhaps it may be related to the development of cardiovascular deconditioning.
本实验旨在研究自主神经系统在高压性心动过缓产生过程中的作用。
4名男性潜水员在24绝对大气压（atm abs）的氦氧（氦氧混合气）环境中暴露7天。在5天潜水前对照期的1天、24 atm abs的7天饱和潜水期的2天、减压期的2天以及潜水后4天的1天，于上午（0700时）和晚上（2230时）静息状态下记录心率（HR）和呼吸频率。通过对R-R间期变异性进行频谱分析来评估心脏交感神经和副交感神经活动。
整个实验期间，上午心率无波动。与潜水前对照相比，在24 atm abs的第一天晚上心率降低（p < 0.05）了11.8%。随着在24 atm abs持续暴露，心动过缓逐渐减轻并恢复到潜水前水平。心脏变异性的高频功率（心脏副交感神经活动指标）仅在24 atm abs的第一个晚上增加（p < 0.05），而低频功率以及低频与高频功率之比（心脏交感神经活动指标）未改变。
目前的结果表明，在24 atm abs进行氦氧混合气干式饱和潜水时，导致心动过缓的原因是副交感神经活动增加而非交感神经活动减少。心动过缓逐渐消失的机制尚不清楚，但可能与心血管功能失调的发展有关。
