Estimation of pharyngeal residue after swallowing by retronasal aroma

Background Pharyngeal residue can trigger aspiration and choking after swallowing. Various studies to assess the amount of pharyngeal residue have been conducted; however, an easy and quantitative method is yet to be established. The aroma released from the pharyngeal residue is thought to be delivered from the pharynx to the nasal cavity via velopharynx by expiration, that is, retronasal pathway. Objective This study verified that the amount of pharyngeal residue could be estimated by aroma intensity. Methods Ten healthy adult subjects had tubes in from the oral cavity to the pharynx. Varying amounts of essence were dispensed into the pharynx through the tube either at rest or after swallowing the essence. Pharyngeal residue was simulated by retention essence in the pharynx without swallowing. An odour sensor was placed in the nostril, and the aroma intensity of the retained essence was measured over time. Results The aroma intensity level flattened after a certain period of time had elapsed, and a significant correlation was found between the amount of essence dispensed and the flattened aroma intensity, both at rest and after swallowing. Furthermore, to estimate in a short period of time, changes in aroma intensity over time were estimated by fitting to a decay curve. The estimated intensity at convergence, calculated from the fitted curve from 80 to 120 seconds after swallowing, was significantly correlated to the measured intensity. Conclusion The amount of pharyngeal residue can be estimated in a short period of time by measuring the aroma intensity.