https://orcid.org/0000-0001-8516-9718
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Abstract
Purpose
An increase in resting motor threshold (RMT), prolonged cortical silent period duration (CSP), and reduced short-latency afferent inhibition (SAI), confirmed with previous transcranial magnetic stimulation (TMS), suggest decreased cortical excitability in obstructive sleep apnea syndrome (OSAS). The present study included MRI of OSAS patients for navigated TMS assessment of the RMT, as an index of the threshold for corticospinal activation at rest, and SAI as an index of cholinergic neurotransmission. We hypothesize to confirm findings on SAI and RMT with adding precision in the targeting of motor cortex in OSAS.
Subjects and Methods
After acquiring head MRIs for 17 severe right-handed OSAS and 12 healthy subjects, the motor cortex was mapped with nTMS to assess the RMT and SAI, with motor evoked potentials (MEPs) recorded from the abductor-pollicis brevis (APB) muscle. The 120%RMT intensity was used for the SAI by a paired-pulse paradigm in which the electrical stimulation to the median nerve is followed by magnetic stimulation of the motor cortex at inter-stimulus intervals (ISIs) of 18–28 ms (ISIs18-28). The SAI control condition included a recording of MEPs without peripheral stimulation. Latency and amplitude of MEP at RMT at 120%RMT for eleven different at ISIs18-28 were analyzed.
Results
The study showed a significantly lower percentage deviation of MEP amplitude at ISIs(18-28ms) from the control condition between OSAS and healthy subjects (U=44.0, p=0.01). The intensity of stimulation at RMT was significantly higher in OSAS subjects (U=55.0, p=0.04*). Correlation analysis showed that BMI significantly negatively correlated (ρ=−0.47) with MEP amplitude percentage deviation in OSAS patients.
Conclusion
The nTMS study results in increased RMT, and reduced cortical afferent inhibition in OSAS patients for SAI at ISIs18-28, confirming previous findings of impaired cortical afferent inhibition in OSAS. Future nTMS studies are desirable to elucidate the role of RMT and SAI in diagnostics and treatment of OSAS, and to elucidate the usefulness of nTMS in OSAS research.
Abbreviations
AASM, American Academy of Sleep Medicine; AHI, apnea-hypopnea index; APB, abductor pollicis-brevis; BMI, body mass index; CPAP, continuous positive airway pressure; EDS, excessive daytime sleepiness; ESS, Epworth sleepiness scale; MRI, magnetic resonance imaging; MEP, motor evoked potential; ODI, oxygen index desaturation; OSAS, obstructive sleep apnea syndrome; PSG, polysomnography; PG, polygraphy; RMT, resting motor threshold; SAI, short-latency afferent inhibition; SEP, somatosensory evoked potentials; SMC, Sleep Medicine Center; TMS, transcranial magnetic stimulation; nTMS, navigated transcranial magnetic stimulation.
Ethics Approval
Ethical standards of the institutional research committee and the 1964 Helsinki declaration with its last amendments were applied to the protocol of the study. Ethics approval was obtained from the Ethics Committee for Biomedical Research at the University of Split School of Medicine (Approval date: May 30, 2014; Code: 003-08/14-03/0001).
Informed Consent
Following the Ethics Committee for Biomedical research and institutional approvals at the University of Split School of Medicine, all participants were informed about the procedures and the aims of the study and signed the informed consent.
Acknowledgments
We would like to thank our colleagues Professor Krešimir Dolić, Professor Ante Buća, and technical and engineering personnel from the University Hospital Split, Department of Diagnostic and Interventional Radiology (Split, Croatia), who provided expertise that significantly assisted the research. We are especially thankful to all the patients and healthy subjects who participated in the study as well as medical personal from the Department of Neuroscience and Split Sleep Medicine Center, University of Split School of Medicine (Natalija Ivković, Ivana Pavlinac Dodig, Linda Lušić).
Author Contributions
All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; gave final approval of the version to be published; and agree to be accountable for all aspects of the work.
Disclosure
Part of the results of this paper was presented at the 7th Croatian Neuroscience Congress in Zadar, September 12th, 2019, to September 15th, 2019. The abstract is cited as: Maja Rogić Vidaković, Ana Jerković, Joško Šoda et al Short latency afferent cortical inhibition in obstructive sleep apnea syndrome: a TMS study (PP71 – Book of abstracts: http://www.hiim.unizg.hr/images/ostalo/VII_CNsC_Book_of_Abstracts.pdf).
The authors declare they have no conflict of interest. All authors have seen and approved the final version of the manuscript. No competing interests were reported by the authors for any financial interests or commercial associations held by the authors or their family members.