HP2 Laboratory, Joseph Fourier University & CHU Grenoble, Grenoble, France.
J Neurophysiol. 2012 Sep;108(5):1270-7. doi: 10.1152/jn.01162.2011. Epub 2012 Jun 13.
Contradictory results regarding the effect of hypoxia on cortex excitability have been reported in healthy subjects, possibly depending on hypoxia exposure duration. We evaluated the effects of 1- and 3-h hypoxia on motor corticospinal excitability, intracortical inhibition, and cortical voluntary activation (VA) using transcranial magnetic stimulation (TMS). TMS to the quadriceps cortex area and femoral nerve electrical stimulations were performed in 14 healthy subjects. Motor-evoked potentials (MEPs at 50-100% maximal voluntary contraction; MVC), recruitment curves (MEPs at 30-100% maximal stimulator power output at 50% MVC), cortical silent periods (CSP), and VA were measured in normoxia and after 1 (n = 12) or 3 (n = 10) h of hypoxia (Fi(O(2)) = 0.12). One-hour hypoxia did not modify any parameters of corticospinal excitability but reduced slightly VA, probably due to the repetition of contractions 1 h apart (96 ± 4% vs. 94 ± 4%; P = 0.03). Conversely, 3-h hypoxia significantly increased 1) MEPs of the quadriceps muscles at all force levels (+26 ± 14%, +24 ± 12%, and +27 ± 17% at 50, 75, and 100% MVC, respectively; P = 0.01) and stimulator power outputs (e.g., +21 ± 14% at 70% maximal power), and 2) CSP at all force levels (+20 ± 18%, +18 ± 19%, and +14 ± 22% at 50, 75, and 100% MVC, respectively; P = 0.02) and stimulator power outputs (e.g., +9 ± 8% at 70% maximal power), but did not modify VA (98 ± 1% vs. 97 ± 3%; P = 0.42). These data demonstrate a time-dependent hypoxia-induced increase in motor corticospinal excitability and intracortical inhibition, without changes in VA. The impact of these cortical changes on physical or psychomotor performances needs to be elucidated to better understand the cerebral effects of hypoxemia.
关于健康受试者中缺氧对皮质兴奋性的影响，已有相互矛盾的结果报告，这可能取决于缺氧暴露时间。我们使用经颅磁刺激（TMS）评估了 1 小时和 3 小时缺氧对运动皮质脊髓兴奋性、皮质内抑制和皮质自愿激活（VA）的影响。在 14 名健康受试者中，对股四头肌皮质区域进行 TMS 和股神经电刺激。在常氧和 1 小时（n = 12）或 3 小时（n = 10）缺氧后（Fi(O(2)) = 0.12）测量运动诱发电位（50-100%最大随意收缩的 MEP；MVC）、募集曲线（50% MVC 时 30-100%最大刺激器功率输出的 MEP）、皮质静息期（CSP）和 VA。1 小时的缺氧并没有改变皮质脊髓兴奋性的任何参数，但略微降低了 VA，可能是由于 1 小时间隔的收缩重复（96 ± 4%比 94 ± 4%；P = 0.03）。相反，3 小时的缺氧显著增加了 1）股四头肌肌肉的 MEP 在所有力量水平（分别为 50、75 和 100% MVC 时为+26 ± 14%、+24 ± 12%和+27 ± 17%；P = 0.01）和刺激器功率输出（例如，70%最大功率时为+21 ± 14%），以及 2）所有力量水平的 CSP（分别为 50、75 和 100% MVC 时为+20 ± 18%、+18 ± 19%和+14 ± 22%；P = 0.02）和刺激器功率输出（例如，70%最大功率时为+9 ± 8%），但 VA 没有改变（98 ± 1%比 97 ± 3%；P = 0.42）。这些数据表明，缺氧诱导的运动皮质脊髓兴奋性和皮质内抑制呈时间依赖性增加，而 VA 没有改变。需要阐明这些皮质变化对身体或心理运动表现的影响，以更好地理解低氧血症对大脑的影响。
