Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.
Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota.
J Neurophysiol. 2019 Oct 1;122(4):1386-1396. doi: 10.1152/jn.00319.2019. Epub 2019 Aug 7.
We sought to examine the effect of varying chemoreflex stress on sympathetic neural recruitment strategies during end-expiratory apnea. We hypothesized that increases in the firing frequency and probability of low-threshold axons at the asphyxic "break point" would be exaggerated during hypoxia and attenuated during hyperoxia. Multiunit muscle sympathetic nervous system activity (MSNA) (peroneal nerve microneurography) was measured in 10 healthy male subjects (31 ± 2 yr, 25 ± 1 kg/m). Individuals completed maximal voluntary end-expiratory apnea under normoxic, hypoxic (inspired O fraction: 0.17 ± 0.01), and hyperoxic (inspired O fraction: 0.92 ± 0.03) conditions. Action potential (AP) patterns were examined from the filtered raw signal with wavelet-based methodology. Multiunit MSNA was increased ( ≤ 0.05) during normoxic apnea, because of an increase in the frequency and incidence of AP spikes (243 ± 75 to 519 ± 134 APs/min, = 0.048; 412 ± 133 to 733 ± 185 APs/100 heartbeats, = 0.02). Multiunit MSNA increased from baseline ( < 0.01) during hypoxic apnea, which was due to an increase in the frequency and incidence of APs (192 ± 59 to 952 ± 266 APs/min, < 0.01; 326 ± 89 to 1,212 ± 327 APs/100 heartbeats, < 0.01). Hypoxic apnea also resulted in an increase in the probability of a particular AP cluster firing more than once per burst ( < 0.01). Hyperoxia attenuated any increase in MSNA with apnea, such that no changes in multiunit MSNA or frequency or incidence of AP spikes were observed ( > 0.05). We conclude that increases in frequency and incidence of APs during apnea are potentiated during hypoxia and suppressed when individuals are hyperoxic, highlighting the important impact of chemoreflex stress in AP discharge patterns. The results may have implications for neural control of the circulation in recreational activities and/or clinical conditions prone to apnea. Our results demonstrate that, compared with normoxic end-expiratory apnea, hypoxic apnea increases the frequency and incidence of action potential spikes as well as the probability of multiple firing. We further show that this response is suppressed when individuals are hyperoxic. These data highlight the potentially important role of chemoreflex stress in neural firing and recruitment and may have implications for neural control of the circulation in recreational and/or clinical conditions prone to apnea.
我们试图研究不同化学反射应激对呼气末暂停期间交感神经募集策略的影响。我们假设，在窒息的“突破点”，低频阈值轴突的放电频率和概率增加，在缺氧时会加剧，在高氧时会减弱。10 名健康男性受试者（31 ± 2 岁，25 ± 1 kg/m）进行了腓总神经微神经电图术测量的多单位肌肉交感神经活动（MSNA）。个体在正常氧合、缺氧（吸入 O 分数：0.17 ± 0.01）和高氧（吸入 O 分数：0.92 ± 0.03）条件下完成最大自主呼气末暂停。使用基于小波的方法从滤波原始信号检查动作电位（AP）模式。在正常氧合暂停期间，由于 AP 尖峰的频率和发生率增加（243 ± 75 至 519 ± 134 APs/min， = 0.048；412 ± 133 至 733 ± 185 APs/100 心跳， = 0.02），多单位 MSNA 增加（ ≤ 0.05）。缺氧暂停期间，多单位 MSNA 从基线增加（ < 0.01），这是由于 AP 的频率和发生率增加（192 ± 59 至 952 ± 266 APs/min， < 0.01；326 ± 89 至 1,212 ± 327 APs/100 心跳， < 0.01）。缺氧暂停还导致特定 AP 簇的发射概率增加，即每个爆发发射不止一次（ < 0.01）。高氧抑制了与暂停相关的 MSNA 的任何增加，因此没有观察到多单位 MSNA 或 AP 尖峰的频率或发生率发生变化（ > 0.05）。我们得出的结论是，在缺氧期间，AP 的频率和发生率增加，而在高氧时则受到抑制，这突出了化学反射应激对 AP 放电模式的重要影响。结果可能对娱乐活动和/或易发生呼吸暂停的临床情况下的循环神经控制有影响。我们的结果表明，与正常氧合呼气末暂停相比，缺氧呼气末暂停增加了动作电位尖峰的频率和发生率，以及多次发射的概率。我们进一步表明，当个体处于高氧状态时，这种反应会受到抑制。这些数据突出了化学反射应激在神经发射和募集中的潜在重要作用，可能对易发生呼吸暂停的娱乐和/或临床情况下的循环神经控制有影响。
