In this EPicks videos, The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits.
Find out more in Experimental Physiology:
The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits.
Daniel J. McKeown, Glenn M. Stewart, Justin J. Kavanagh
108(9) pp. 1203-1214
physoc.onlinel...
Transcript:
*Introduction:*
Hello, I'm Daniel McKeown, and I’m a Post-doctoral Researcher in the Department of Psychology at Bond University on the Gold Coast Australia.
*Outline of Research:*
In our study, we delved into the effects of continuous hypoxemia on motor circuit function. We exposed participants to two hypoxemia methods. In one protocol we ti trated the fraction of inspired oxygen to 0.13 (FiO2) and in the second protocol we titrated the peripheral capillary oxygen saturation to a target of 80% SpO2. We did this across a 15 min titration phase and participants remained at these exposures for 2 hrs. During this time, we assessed the excitability of motor pathways by measuring motor evoked potential responses (or MEPs) in the first dorsal interosseous muscle when applying transcranial magnetic stimulation to the motor cortex.
*Findings:*
What we discovered was intriguing. Blood oxygen levels were reduced immediately after the titration phase in both protocols. However, the blood oxygen level during the FIO2 clamped protocol was significantly greater than during the SpO2 clamped protocol. Furthermore, the blood oxygen level during the FIO2 clamped protocol progressively increased throughout the 2 hr duration whereas remained lower during the SpO2 clamped protocol. This resulted in a less severe and severe occurrence of hypoxemia. Interestingly, this variance in hypoxemia influenced the inhibition and facilitation of MEP responses. By 2 hr of exposure, the activity of circuits responsible for inhibiting the excitability of motor pathways was reduced in the more severe exposure of hypoxemia but not the less severe, while the activity of circuits responsible for facilitating the excitability of motor pathways was less during the severe hypoxemic stimulus, but not the less severe stimulus.
*Importance of the Study:*
One critical aspect our research highlighted is the significance of how hypoxemia is induced in laboratory settings. The traditional methods of inducing hypoxia based on clamping the oxygen content of the inspired air can lead to progressively different levels of hypoxemia at the tissue level. Whether we titrate the air stimulus input (FIO2 changes) or the system's response (SpO2 changes), the outcomes vary. This understanding is pivotal for future hypoxia research, urging a need to standardize and consider these methodological differences.
*Significance and Future Implications:*
Understanding how hypoxemia affects our motor circuits is vital. Our findings shed light on the nuanced impact of oxygen levels on motor responses, with potential implications for conditions related to oxygenation. This research opens doors for future studies exploring the link between oxygen saturation, neural circuits, and physiological responses, paving the way for translational applications into other extreme environments and beyond.
If you’d like to know more about this study, you can find it in the September issue of Experimental Physiology. Thanks for watching!
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