Temme Leonard A, Wittels Harrison L, Wishon Michael J, St Onge Paul, McDonald Samantha M, Hecocks Dustin, Wittels S Howard
Army Aeromedical Research Laboratory, Fort Novosel, AL 36362, USA.
Tiger Tech Solutions, Inc., Miami, FL 33140, USA.
Biology (Basel). 2023 Nov 3;12(11):1398. doi: 10.3390/biology12111398.
Military aviators endure high cognitive loads and hypoxic environments during flight operations, impacting the autonomic nervous system (ANS). The synergistic effects of these exposures on the ANS, however, are less clear. This study investigated the simultaneous effects of mild hypoxia and high cognitive load on the ANS in military personnel. This study employed a two-factor experimental design. Twenty-four healthy participants aged between 19 and 45 years were exposed to mild hypoxia (14.0% O), normoxia (21.0% O), and hyperoxia (33.0% O). During each epoch ( = 5), participants continuously performed one 15 min and one 10 min series of simulated, in-flight tasks separated by 1 min of rest. Exposure sequences (hypoxia-normoxia and normoxia-hyperoxia) were separated by a 60 min break. Heart rate (HR), heart rate variability (HRV), and O saturation (SpO) were continuously measured via an armband monitor (Warfighter Monitor, Tiger Tech Solutions, Inc., Miami, FL, USA). Paired and independent -tests were used to evaluate differences in HR, HRV, and SpO within and between exposure sequences. Survival analyses were performed to assess the timing and magnitude of the ANS responses. Sympathetic nervous system (SNS) activity during hypoxia was highest in epoch 1 (HR: +6.9 bpm, = 0.002; rMSSD: -9.7 ms, = 0.003; SDNN: -11.3 ms, = 0.003; SpO: -8.4%, < 0.0000) and appeared to slightly decline with non-significant increases in HRV. During normoxia, SNS activity was heightened, albeit non-significantly, in epoch 1, with higher HR (68.5 bpm vs. 73.0 bpm, = 0.06), lower HRV (rMSSD: 45.1 ms vs. 38.7 ms, = 0.09 and SDNN: 52.5 ms vs. 45.1 ms, = 0.08), and lower SpO (-0.7% = 0.05). In epochs 2-4, HR, HRV, and SpO trended towards baseline values. Significant between-group differences in HR, HRV, and O saturation were observed. Hypoxia elicited significantly greater HRs (+5.0, = 0.03), lower rMSSD (-7.1, = 0.03), lower SDNN (-8.2, = 0.03), and lower SpO (-1.4%, = 0.002) compared to normoxia. Hyperoxia appeared to augment the parasympathetic reactivation reflected by significantly lower HR, in addition to higher HRV and O relative to normoxia. Hypoxia induced a greater ANS response in military personnel during the simultaneous exposure to high cognitive load. The significant and differential ANS responses to varying O levels and high cognitive load observed highlight the importance of continuously monitoring multiple physiological parameters during flight operations.
军事飞行员在飞行任务期间承受着高认知负荷和低氧环境，这会影响自主神经系统（ANS）。然而，这些暴露因素对自主神经系统的协同作用尚不清楚。本研究调查了轻度低氧和高认知负荷对军事人员自主神经系统的同时影响。本研究采用双因素实验设计。24名年龄在19至45岁之间的健康参与者分别暴露于轻度低氧（14.0%氧气）、常氧（21.0%氧气）和高氧（33.0%氧气）环境中。在每个时段（n = 5），参与者连续进行一组15分钟和一组10分钟的模拟飞行任务，中间休息1分钟。暴露顺序（低氧 - 常氧和常氧 - 高氧）之间间隔60分钟的休息时间。通过臂带监测仪（Warfighter Monitor，Tiger Tech Solutions公司，美国佛罗里达州迈阿密）连续测量心率（HR）、心率变异性（HRV）和血氧饱和度（SpO₂）。使用配对t检验和独立t检验来评估暴露顺序内和暴露顺序之间HR、HRV和SpO₂的差异。进行生存分析以评估自主神经系统反应的时间和幅度。低氧期间交感神经系统（SNS）活动在第1时段最高（HR：+6.9次/分钟，p = 0.002；rMSSD：-9.7毫秒，p = 0.003；SDNN：-11.3毫秒，p = 0.003；SpO₂：-8.4%，p < 0.0000），并且随着HRV的非显著增加似乎略有下降。在常氧期间，第1时段交感神经系统活动有所增强，尽管不显著，HR较高（68.5次/分钟对73.0次/分钟，p = 0.06），HRV较低（rMSSD：45.1毫秒对38.7毫秒，p = 0.09；SDNN：52.5毫秒对45.1毫秒，p = 0.08），SpO₂较低（-0.7%，p = 0.05）。在第2至4时段，HR、HRV和SpO₂趋向于基线值。观察到HR、HRV和血氧饱和度在组间存在显著差异。与常氧相比，低氧引起的HR显著更高（+5.0，p = 0.03），rMSSD更低（-7.1，p = 0.03），SDNN更低（-8.2，p = 0.03），SpO₂更低（-1.4%，p = 0.002）。与常氧相比，高氧除了使HRV和SpO₂相对更高外，似乎增强了由显著更低的HR所反映的副交感神经再激活。在同时暴露于高认知负荷期间，低氧在军事人员中诱导了更大的自主神经系统反应。观察到对不同氧气水平和高认知负荷的显著且有差异的自主神经系统反应，这突出了在飞行任务期间持续监测多个生理参数的重要性。
