The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits
Abstract The purpose of this study was to examine how two common methods of continuous hypoxaemia impact the activity of intracortical circuits responsible for inhibition and facilitation of motor output, and spinal excitability. Ten participants were exposed to 2 h of hypoxaemia at 0.13 fraction of...
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Wiley
2023-09-01
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| Series: | Experimental Physiology |
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| Online Access: | https://doi.org/10.1113/EP091224 |
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| author | Daniel J. McKeown Glenn M. Stewart Justin J. Kavanagh |
| author_facet | Daniel J. McKeown Glenn M. Stewart Justin J. Kavanagh |
| author_sort | Daniel J. McKeown |
| collection | DOAJ |
| description | Abstract The purpose of this study was to examine how two common methods of continuous hypoxaemia impact the activity of intracortical circuits responsible for inhibition and facilitation of motor output, and spinal excitability. Ten participants were exposed to 2 h of hypoxaemia at 0.13 fraction of inspired oxygen (FIO2 clamping protocol) and 80% of peripheral capillary oxygen saturation (SpO2 clamping protocol) using a simulating altitude device on two visits separated by a week. Using transcranial magnetic and peripheral nerve stimulation, unconditioned motor evoked potential (MEP) area, short‐interval intracortical inhibition (SICI) and intracortical facilitation (ICF), and F‐wave persistence and area were assessed in the first dorsal interosseous (FDI) muscle before titration, after 1 and 2 h of hypoxic exposure, and at reoxygenation. The clamping protocols resulted in differing reductions in SpO2 by 2 h (SpO2 clamping protocol: 81.9 ± 1.3%, FIO2 clamping protocol: 90.6 ± 2.5%). Although unconditioned MEP peak to peak amplitude and area did not differ between the protocols, SICI during FIO2 clamping was significantly lower at 2 h compared to SpO2 clamping (P = 0.011) and baseline (P < 0.001), whereas ICF was higher throughout the FIO2 clamping compared to SpO2 clamping (P = 0.005). Furthermore, a negative correlation between SICI and SpO2 (rrm = −0.56, P = 0.002) and a positive correlation between ICF and SpO2 (rrm = 0.69, P = 0.001) were determined, where greater reductions in SpO2 correlated with less inhibition and less facilitation of MEP responses. Although F‐wave area progressively increased similarly throughout the protocols (P = 0.037), persistence of responses was reduced at 2 h and reoxygenation (P < 0.01) during the SpO2 clamping protocol compared to the FIO2 clamping protocol. After 2 h of hypoxic exposure, there is a reduction in the activity of intracortical circuits responsible for inhibiting motor output, as well as excitability of spinal motoneurones. However, these effects can be influenced by other physiological responses to hypoxia (i.e., hyperventilation and hypocapnia). |
| format | Article |
| id | doaj-art-ada8bd6d35e9421dbaef692e1e064520 |
| institution | Kabale University |
| issn | 0958-0670 1469-445X |
| language | English |
| publishDate | 2023-09-01 |
| publisher | Wiley |
| record_format | Article |
| series | Experimental Physiology |
| spelling | doaj-art-ada8bd6d35e9421dbaef692e1e0645202025-08-20T03:39:45ZengWileyExperimental Physiology0958-06701469-445X2023-09-0110891203121410.1113/EP091224The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuitsDaniel J. McKeown0Glenn M. Stewart1Justin J. Kavanagh2Neural Control of Movement LaboratoryMenzies Health Institute QueenslandGriffith UniversityGold CoastQueenslandAustraliaMenzies Health Institute QueenslandGriffith UniversityGold CoastQueenslandAustraliaNeural Control of Movement LaboratoryMenzies Health Institute QueenslandGriffith UniversityGold CoastQueenslandAustraliaAbstract The purpose of this study was to examine how two common methods of continuous hypoxaemia impact the activity of intracortical circuits responsible for inhibition and facilitation of motor output, and spinal excitability. Ten participants were exposed to 2 h of hypoxaemia at 0.13 fraction of inspired oxygen (FIO2 clamping protocol) and 80% of peripheral capillary oxygen saturation (SpO2 clamping protocol) using a simulating altitude device on two visits separated by a week. Using transcranial magnetic and peripheral nerve stimulation, unconditioned motor evoked potential (MEP) area, short‐interval intracortical inhibition (SICI) and intracortical facilitation (ICF), and F‐wave persistence and area were assessed in the first dorsal interosseous (FDI) muscle before titration, after 1 and 2 h of hypoxic exposure, and at reoxygenation. The clamping protocols resulted in differing reductions in SpO2 by 2 h (SpO2 clamping protocol: 81.9 ± 1.3%, FIO2 clamping protocol: 90.6 ± 2.5%). Although unconditioned MEP peak to peak amplitude and area did not differ between the protocols, SICI during FIO2 clamping was significantly lower at 2 h compared to SpO2 clamping (P = 0.011) and baseline (P < 0.001), whereas ICF was higher throughout the FIO2 clamping compared to SpO2 clamping (P = 0.005). Furthermore, a negative correlation between SICI and SpO2 (rrm = −0.56, P = 0.002) and a positive correlation between ICF and SpO2 (rrm = 0.69, P = 0.001) were determined, where greater reductions in SpO2 correlated with less inhibition and less facilitation of MEP responses. Although F‐wave area progressively increased similarly throughout the protocols (P = 0.037), persistence of responses was reduced at 2 h and reoxygenation (P < 0.01) during the SpO2 clamping protocol compared to the FIO2 clamping protocol. After 2 h of hypoxic exposure, there is a reduction in the activity of intracortical circuits responsible for inhibiting motor output, as well as excitability of spinal motoneurones. However, these effects can be influenced by other physiological responses to hypoxia (i.e., hyperventilation and hypocapnia).https://doi.org/10.1113/EP091224high altitudeneuromodulationtranscranial magnetic stimulation |
| spellingShingle | Daniel J. McKeown Glenn M. Stewart Justin J. Kavanagh The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits Experimental Physiology high altitude neuromodulation transcranial magnetic stimulation |
| title | The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits |
| title_full | The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits |
| title_fullStr | The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits |
| title_full_unstemmed | The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits |
| title_short | The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits |
| title_sort | severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits |
| topic | high altitude neuromodulation transcranial magnetic stimulation |
| url | https://doi.org/10.1113/EP091224 |
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