Neuroscience Research Australia, Sydney, New South Wales, Australia.
University of New South Wales, Sydney, New South Wales, Australia.
J Appl Physiol (1985). 2024 Jul 1;137(1):51-62. doi: 10.1152/japplphysiol.00010.2024. Epub 2024 May 9.
Acute intermittent hypoxia (AIH) can induce sustained facilitation of motor output in people with spinal cord injury (SCI). Most studies of corticospinal tract excitability in humans have used 9% fraction inspired oxygen ([Formula: see text]) AIH (AIH-9%), with inconsistent outcomes. We investigated the effect of single sessions of 9% [Formula: see text] and 12% [Formula: see text] AIH (AIH-12%) on corticospinal excitability of a hand and leg muscle in able-bodied adults. Ten naïve participants completed three sessions on separate days comprising 15 epochs of 1 min of AIH-9%, AIH-12%, or sham (SHAM-21%) followed by 1 min of room air (21% [Formula: see text]) in a randomized crossover design. Motor-evoked potentials (MEPs; = 30, ∼1 mV) elicited at rest by transcranial magnetic stimulation and maximal M-waves (M) evoked by peripheral nerve stimulation were measured from the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles at baseline and at ∼0, 20, 40, and 60 min post intervention. AIH-9% induced the greatest reduction in peripheral oxygen saturation (to 85% vs. 93% and 100% in AIH-12% and SHAM-21%, respectively; < 0.001) and the greatest increase in ventilation [by 22% vs. 12% and -3% in AIH-9%, AIH-12%, and SHAM-21%, respectively ( < 0.001)]. There was no difference in MEP amplitudes (%M) after any of the three conditions (AIH-9%, AIH-12%, SHAM-21%) for both the FDI ( = 0.399) and TA ( = 0.582). Despite greater cardiorespiratory changes during AIH-9%, there was no evidence of corticospinal facilitation (tested with MEPs) in this study. Further studies could explore variability in response to AIH between individuals and other methods to measure motor facilitation in people with and without spinal cord injuries. This is the first study that tests whether acute intermittent hypoxia (AIH) induces motor output facilitation in humans after two different doses of AIH (9% and 12% [Formula: see text]) and the reproducibility of participant responses after a repeat AIH intervention at 9% AIH. There was no motor output facilitation in response to either dose of AIH. The results question the effectiveness of a single 30-min session of AIH in inducing motor output facilitation, tested in this way.
急性间歇性低氧（AIH）可诱导脊髓损伤（SCI）患者运动输出的持续易化。大多数关于人类皮质脊髓束兴奋性的研究都使用了 9%吸入氧分数（[Formula: see text]）的 AIH（AIH-9%），但结果不一致。我们研究了单次 9%[Formula: see text]和 12%[Formula: see text]AIH（AIH-12%）对健全成年人手部和腿部肌肉皮质脊髓兴奋性的影响。10 名未接受过训练的参与者在 3 天内完成了 3 次实验，每次实验包括 15 个 1 分钟的 AIH-9%、AIH-12%或假（SHAM-21%）期，随后是 1 分钟的室内空气（21%[Formula: see text]），采用随机交叉设计。通过经颅磁刺激诱发静息时的运动诱发电位（MEP；[Formula: see text] = 30，约 1 mV）和外周神经刺激诱发的最大 M 波（M），从第一背侧骨间肌（FDI）和胫骨前肌（TA）测量。在基线和干预后约 0、20、40 和 60 分钟测量。AIH-9% 诱导的外周血氧饱和度下降最大（降至 85%，而 AIH-12%和 SHAM-21%分别降至 93%和 100%；<0.001），通气增加最大[增加 22%，而 AIH-9%、AIH-12%和 SHAM-21%分别增加 12%和-3%（<0.001）]。在 FDI（[Formula: see text] = 0.399）和 TA（[Formula: see text] = 0.582）中，三种条件（AIH-9%、AIH-12%、SHAM-21%）后 MEP 幅度（%M）均无差异。尽管 AIH-9% 期间的心肺变化更大，但本研究并未发现皮质脊髓易化的证据（通过 MEP 测试）。进一步的研究可以探索个体对 AIH 的反应变异性，以及在脊髓损伤患者和非脊髓损伤患者中测量运动易化的其他方法。这是第一项测试两种不同剂量的急性间歇性低氧（AIH）（9%和 12%[Formula: see text]）后，人类运动输出是否易化的研究，以及在 9%AIH 下重复 AIH 干预后参与者反应的可重复性。两种剂量的 AIH 均未引起运动输出易化。结果质疑单次 30 分钟 AIH 诱导运动输出易化的有效性，以这种方式进行测试。
