Brainstem changes associated with increased muscle sympathetic drive in obstructive sleep apnoea

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Sleep Medicine

Background:

• Obstructive sleep apnoea (OSA) is linked to elevated muscle sympathetic nerve activity (MSNA), contributing to hypertension and cardiovascular risks.
• The specific brainstem mechanisms driving this sympathoexcitation in OSA remain unclear.

Purpose of the Study:

• To identify brainstem regions responsible for the increased muscle vasoconstrictor drive observed in obstructive sleep apnoea.
• To investigate potential functional and anatomical alterations in the brainstem associated with OSA-related sympathoexcitation.

Main Methods:

• Voxel-based morphometry (VBM) of T1-weighted MRI to assess regional grey matter volume in 20 OSA patients and 19 controls.
• Concurrent functional magnetic resonance imaging (fMRI) measuring BOLD signal and muscle sympathetic nerve activity (MSNA) in 15 OSA patients and 15 controls.

Main Results:

• OSA subjects exhibited significantly elevated MSNA, correlated with altered BOLD signals in the dorsolateral pons, rostral ventrolateral medulla, medullary raphe, and midbrain.
• Increased grey matter volumes were found in the medullary raphe, rostroventrolateral medulla, and dorsolateral pons of OSA subjects compared to controls.
• Obstructive sleep apnoea was also associated with increased grey matter volume near the hypoglossal nucleus.

Conclusions:

• Functional and anatomical changes in the dorsolateral pons, rostroventrolateral medulla, and medullary raphe likely contribute to elevated muscle vasoconstrictor drive in obstructive sleep apnoea.
• These brainstem regions directly or indirectly modulate sympathetic output.
• Increased grey matter volume in the hypoglossal nucleus region may relate to the heightened genioglossus muscle activity seen in OSA.