Links Between Swallowing and Consciousness: A Narrative Review

Area of Science:

• Neuroscience
• Clinical Medicine
• Speech and Hearing Science

Background:

• Consciousness assessment historically relies on distinguishing reflexive from volitional behaviors.
• Swallowing encompasses a spectrum of volitional and reflexive actions.
• Altered consciousness states, like sleep and anesthesia, impact swallowing dynamics.

Purpose of the Study:

• To review the relationship between swallowing function and consciousness levels.
• To identify reliable indicators of consciousness within swallowing in patients with disorders of consciousness (DoC).
• To highlight gaps in assessment and treatment tools for dysphagia in DoC.

Main Methods:

• Literature review synthesizing theoretical and empirical data.
• Analysis of swallowing components across a volitional-reflexive continuum.
• Examination of swallowing alterations in non-pathological consciousness changes and severe brain injury.

Main Results:

• Consciousness level influences swallowing frequency, reflex initiation, pharyngeal phase efficacy, and respiratory coordination.
• In severe brain injury, consciousness correlates with extubation potential, pneumonia risk, feeding type, and oral/pharyngeal abnormalities.
• Oral phase efficacy and exclusive oral feeding ability are the strongest swallowing-related consciousness signs in DoC.

Conclusions:

• Efficacy of the oral phase and ability for exclusive oral feeding are robust indicators of consciousness in DoC.
• The role of pharyngeal phase components (saliva management) and evoked cough as consciousness signs requires further investigation.
• There is a critical need for improved tools and techniques for assessing and treating dysphagia in patients with DoC.