Effect of acute intermittent hypoxia on cortico-diaphragmatic conduction in healthy humans

• Published in: Experimental neurology 2021-05, Vol.339, p.113651-113651, Article 113651
• Main Authors: Welch, Joseph F., Perim, Raphael R., Argento, Patrick J., Sutor, Tommy W., Vose, Alicia K., Nair, Jayakrishnan, Mitchell, Gordon S., Fox, Emily J.
• Format: Article
• Language: English
• Subjects: Acute Disease; Acute intermittent hypoxia; Adult; Cervical Cord - physiology; Cervical magnetic stimulation; Diaphragm; Diaphragm - innervation; Diaphragm - physiology; Electromyography; Electromyography - methods; Evoked Potentials, Motor - physiology; Female; Humans; Hypoxia - physiopathology; Long-Term Potentiation - physiology; Male; Neuroplasticity; Phrenic; Phrenic Nerve - physiology; Respiratory Mechanics - physiology; Transcranial magnetic stimulation; Transcranial Magnetic Stimulation - methods; Young Adult
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/j.expneurol.2021.113651

Acute intermittent hypoxia (AIH) is a strategy to improve motor output in humans with neuromotor impairment. A single AIH session increases the amplitude of motor evoked potentials (MEP) in a finger muscle (first dorsal interosseous), demonstrating enhanced corticospinal neurotransmission. Since AIH elicits phrenic/diaphragm long-term facilitation (LTF) in rodent models, we tested the hypothesis that AIH augments diaphragm MEPs in humans. Eleven healthy adults (7 males, age = 29 ± 6 years) were tested. Transcranial and cervical magnetic stimulation were used to induce diaphragm MEPs and compound muscle action potentials (CMAP) recorded by surface EMG, respectively. Stimulus-response curves were generated prior to and 30–60 min after AIH. Diaphragm LTF was assessed by measurement of integrated EMG burst amplitude and frequency during eupnoeic breathing before and after AIH. Following baseline measurements, AIH was delivered from an oxygen generator connected to a facemask under poikilocapnic conditions (15 one minute episodes of 9% inspired oxygen with one minute room air intervals). There were no detectable changes in MEP (−1.5 ± 12.1%, p = 0.96) or CMAP (+0.1 ± 7.8%, p = 0.97) amplitudes across the stimulus-response curve. At stimulation intensities approximating 50% of the difference between minimum and maximum baseline amplitudes, MEP and CMAP amplitudes were also unchanged (p > 0.05). Further, no AIH effect was observed on diaphragm EMG activity during eupnoea post-AIH (p > 0.05). We conclude that unlike hand muscles, poikilocapnic AIH does not enhance diaphragm MEPs or produce diaphragm LTF in healthy humans. •Acute intermittent hypoxia (AIH) increases motor evoked potential (MEP) amplitude in a finger muscle, demonstrating enhanced corticospinal neurotransmission.•We examined AIH effects on diaphragm MEPs induced by transcranial magnetic stimulation in healthy young adults.•After a single AIH session, no detectable changes in MEP amplitudes were observed.•Differences between AIH effects on respiratory and non-respiratory motor systems are discussed.