Droplet applicator module for reproducible and controlled endoscopic laryngeal adductor reflex stimulation

Computational Analysis of the Droplet-Stimulated Laryngeal Adductor Reflex in High-Speed Sequences

OBJECTIVES/HYPOTHESIS

The laryngeal adductor reflex (LAR) is an important protective mechanism of the airways. Its physiology is still not completely understood. The available methods for LAR evaluation offer limited reproducibility and/or rely on subjective interpretation. A new approach, termed Microdroplet Impulse Testing of the LAR (MIT-LAR), was recently introduced. Here, the LAR is elicited by a droplet and a laryngoscopic high-speed recording is acquired simultaneously. In the present work, image-processing algorithms for autonomous MIT-LAR sequence analysis were developed. This allowed the automated approximation of kinematic LAR parameters in humans.

STUDY DESIGN

Development and testing of computational methods.

METHODS

Computational image processing enabled the autonomous estimation of the glottal area, the glottal angle, and the vocal fold edge distance in MIT-LAR sequences. A suitable analytical representation of these glottal parameters allowed the extraction of seven relevant LAR parameters. The obtained values were compared to the literature.

RESULTS

A generalized logistic function showed the highest average goodness of fit among four different analytical approaches for each of the glottal parameters. Autonomous sequence analysis yielded bilateral LAR response latencies of (229 ± 116) ms and (182 ± 60) ms for cases of complete and incomplete glottal closure, respectively. The initial/average/maximum angular vocal fold adduction velocity was estimated at (157 ± 115) °s^-1 /(891 ± 516) °s^-1 /(929 ±  583) °s^-1 and (88 ± 53) °s^-1 /(421 ± 221) °s^-1 /(520 ± 238) °s^-1 for complete and incomplete glottal closure, respectively.

CONCLUSION

The automated extraction of LAR parameters from laryngoscopic high-speed sequences can potentially increase the objectiveness of optical LAR characterization and reduce the associated workload. The proposed methods may thus be helpful for future research on this vital reflex.

LEVEL OF EVIDENCE

NA Laryngoscope, 132:2412-2419, 2022.

Upper Esophageal Sphincter Response to Laryngeal Adductor Reflex Elicitation in Humans

OBJECTIVE

The laryngeal adductor reflex (LAR) is an important mechanism to secure the airways from potential foreign body aspiration. An involvement of the upper esophageal sphincter (UES) in terms of a laryngo-UES contractile reflex has been identified after laryngeal mucosa stimulation. However, the LAR-UES relationship has not yet been fully explained. This study aimed to determine the magnitude, latency, and occurrence rate of the UES pressure response when the LAR is triggered in order to elucidate the functional relationship between the larynx and the UES.

METHODS

This prospective study included seven healthy volunteers (5 female, 2 male, age 22-34 years). Laryngeal penetration was simulated by eliciting the LAR 20 times in each individual by applying water-based microdroplets onto the laryngeal mucosa. UES pressures were measured simultaneously using high-resolution manometry.

RESULTS

Two distinct pressure phases (P1, P2) associated with the LAR were identified. P1 corresponded with a short-term UES pressure decrease in two subjects and a pressure increase in five subjects occurring 200 to 500 ms after the stimulus. In P2, all subjects experienced an increase in UES pressure with a latency time of approximately 800 to 1700 ms and an average of 40 to 90 mmHg above the UES resting tone.

CONCLUSION

Foreign bodies penetrating the laryngeal inlet lead to a reflex contraction of the UES. Phase P1 could be a result of vocal fold activity caused by the LAR, leading to pressure changes in the UES. The constriction during P2 could strengthen the barrier function of the UES in preparation to a subsequent cough that may be triggered to clear the airways.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E1778-E1784, 2021.