[Characterization of the Laryngeal Adductor Reflex by Stimulation with Microdroplets Impulses (Microdroplet Impulse...

The larynx is considered a crossing point between breathing and swallowing pathways. During swallowing, the airway below the glottis must be protected against food components by an appropriate laryngeal closure mechanism. The laryngeal adductor reflex (LAR) with an early, probably di- or oligosynaptic interconnected ipsilateral LAR1- and a late ipsilateral and contralateral LAR2 polysynaptic component is believed to serve as such a mechanism. Here we aimed to measure and characterize the LAR in healthy volunteers and to compare the data obtained with previously published data.

We designed a prospective pilot study. 10 healthy volunteers (22-57 years) participated. To elicit the LAR we used a newly designed microdroplet impulse testing (MIT) device: very small waterdroplets were shot onto the endolaryngeal mucosa. By simultaneously observing the anatomical structures with a high speed glottography system, the time between impact of the microdroplet on the mucosa and the beginning of the adduction movement and thus an approximate value for the reflex latency could be determined.

An early adduction movement corresponding to LAR1 could not be detected. The measured LAR2 latency time was higher than the EMG LAR2 data. No significant latency difference between right and left stimulation was found.

Since we were unable to demonstrate any LAR1 component it may be that muscle activity observable by EMG may not be sufficient to lead to a visible medial vocal cord movement. The longer LAR2 latency compared to EMG data may be explained by the fact that the visually vocal cord movement occurs after a delay although muscle activity already started as evidenced by EMG.Further studies on LAR are warranted, especially since our results also raise questions about the clinical significance of the LAR.