Acute Intermittent Hypoxia Boosts Spinal Plasticity in Humans with Tetraplegia

Exp Neurol, 2021 · DOI: 10.1016/j.expneurol.2020.113483 · Published: January 1, 2021

Spinal Cord Injury Neuroplasticity Rehabilitation

Simple Explanation

The study investigates whether combining paired corticospinal-motoneuronal stimulation (PCMS) with acute intermittent hypoxia (AIH) can enhance spinal plasticity in humans with spinal cord injury (SCI). PCMS involves stimulating the motor cortex and a peripheral nerve, while AIH involves alternating periods of low and normal oxygen levels. The researchers found that PCMS combined with AIH led to greater increases in motor evoked potentials (MEPs) compared to PCMS with sham AIH, suggesting that AIH can potentiate the effects of PCMS on spinal synapses. MEPs are a measure of how easily the motor cortex can activate muscles. However, the combined treatment did not result in significant changes in voluntary motor output, indicating that the physiological changes may not always translate directly into improved motor function. This suggests that different thresholds may exist for physiological versus behavioral gains.

Study Duration

Not specified

Participants

16 spinal cord injured participants (mean age 50.2±12.8 years; 4 females)

Evidence Level

Level 2: Randomized controlled trial

Key Findings

1
PCMS combined with AIH resulted in a significantly greater increase in MEP amplitude compared to PCMS with sham AIH, suggesting enhanced corticospinal excitability.
2
The potentiation of MEPs was observed with both magnetic and electrical stimulation, indicating a spinal origin for the observed plasticity.
3
While both PCMS+AIH and PCMS+sham-AIH increased EMG activity during small voluntary contractions, there was no significant difference between the two protocols, and no changes were observed in maximal voluntary contraction (MVC).

Research Summary

This study investigated the effects of combining PCMS with AIH on spinal plasticity in humans with chronic incomplete SCI. The hypothesis was that PCMS combined with AIH would boost spinal plasticity more than PCMS combined with sham AIH. The results showed that PCMS combined with AIH significantly increased MEP amplitudes elicited by both magnetic and electrical stimulation compared to PCMS combined with sham AIH, suggesting a synergistic effect on corticospinal excitability at the spinal level. Despite the enhanced physiological outcomes, the combined intervention did not significantly improve voluntary motor output (small voluntary contractions or MVC), suggesting that the threshold for physiological changes may be lower than that for behavioral changes in this population.

Practical Implications

Combinatorial Therapy Potential

AIH can be used as an effective strategy to enhance PCMS-induced spinal synaptic plasticity.

Targeted Plasticity

PCMS and AIH may target different motoneuron pools, with PCMS favoring low-threshold and AIH potentially influencing high-threshold motoneurons.

Threshold Considerations

The study highlights the need to consider different thresholds for physiological and behavioral gains when using combinatorial treatment approaches for SCI.

Study Limitations

1
The study used a fixed FiO2 of 9% for all participants, regardless of individual responsiveness to hypoxia.
2
Only EMG activity was measured during maximal voluntary contraction; future studies should include torque measurements.
3
The study only assessed the immediate effects of a single session of PCMS and AIH; longer-term effects need investigation.

Your Feedback

Was this summary helpful?

Back to Spinal Cord Injury