How Strong is Strong Enough to Clear Aspiration?

Introduction: Reflexive coughing (RC) is the process by which foreign material is expelled when airway invasion occurs. The strength of RC required for this process is unknown. This study objectively measures RC in response to airway invasion and determines RC strength required to expel aspirate from the airway. Materials & Methods: Data were collected on RC and prompted voluntary coughing (VC) in response to aspiration and penetration, during clinical video-fluoroscopic swallowing studies (VFSS). Cough strength was recorded in decibels with a lapel microphone placed anterior to the tragus of the ear. Cough effectiveness, defined as ejection of material from the laryngeal vestibule, was determined from VFSS. Results: Of 25 coughs in response to aspiration, 15 RC and 10 VC were analysed. Of 19 coughs in response to penetration, 11 RC and 8 VC were analysed. No coughs (100%) were effective in clearing aspiration. There was no significant difference in the decibel level of RC and VC to aspiration (p = 0.10). 74% of coughs were effective in clearing penetration and 26% were ineffective. There was no significant difference in the decibel level of RC and VC to penetration (p = 0.41), or between effective and ineffective coughing to penetration (p = 0.37). Conclusions: RC and VC were ineffective at expelling aspirate below the level of the vocal folds. RC and VC may eject penetration, but decibel levels were not sensitive for discriminating between effective or ineffective coughing. These findings question our current assumptions of the role of RC in expelling subglottic aspirate. Acoustic intensity of coughing was not a sensitive screening tool for identifying effective or ineffective clearance of aspirate.