Postural respiratory-related cortical activation and rostral fluid shift in awake healthy humans.

NEW FINDINGS: What is the central question of this study? Moving to supine induces upper airway modifications and fluid shift to the neck, which represent inspiratory load that predisposes to upper airway collapse. Is there cortical participation in the response to the load induced by moving to supine in awake healthy subjects? What is the main finding and its importance? Moving to supine induces transient cortical activation in awake healthy subjects with greater fluid shift, supporting possible cortical participation in the response to upper airway load induced by moving to supine. Our findings open new perspectives in the understanding of the pathogenesis of obstructive sleep apnoea.

ABSTRACT: Moving from sitting upright to lying supine causes anatomical modifications and fluid shift to the neck, which represent inspiratory loads that predispose to upper airway collapse. Preinspiratory potential (PIP) corresponds to the cortical activity observed during inspiratory loads. In the sitting position during wakefulness, some obstructive sleep apnoea (OSA) patients exhibit PIP probably in relation with upper airway abnormalities. The aim of this study was to investigate if moving to the supine position induces respiratory-related cortical activation (PIP) in awake healthy subjects. Electroencephalogram was analyzed to detect PIP, and electromyographic activity of the genioglossus muscle and ventilation were measured in the sitting position, immediately after moving to the supine position, and during application of leg-positive-pressure in the supine position to promote fluid shift, which was measured by bioelectrical impedance. Twenty-four subjects were included. From sitting to lying, PIP prevalence increased from 1/24 to 11/24 (p = 0.002), and ventilation decreased with no change in genioglossus activity. The fluid shift from sitting to supine was higher in the subjects exhibiting PIP while supine compared with the subjects without PIP (median [25th;75th centiles] 440[430;520] vs 320[275;385] ml, p = 0.018), without any other differences. From before to during leg-positive-pressure, PIP disappeared (p = 0.006). These results indicate that moving from sitting to lying induces transient respiratory-related cortical activity in awake healthy subjects with greater fluid shift, supporting possible cortical participation in the response to upper airway loading induced by moving from sitting upright to lying supine. This study offers new perspectives in the understanding OSA pathogenesis. This article is protected by copyright. All rights reserved.