In this study we suggest that the velocity of water entering the cervical esophagus can be used as an index of pharyngeal swallowing function. In this article, the basic in vitro principles of water and viscous water flow velocity evaluation using ultrasonic methods are introduced. Water flow involving small gas bubbles passing through a silicon tube could be monitored in the B-mode images and the flow velocity could be measured by Doppler shift spectra produced by a medical ultrasound imaging (GE YOKOGAWA LOGIQ500 and linear convex probe 739L). By an in vitro experiment, we confirmed that the maximum water flow velocity (Vmax) obtained from Doppler shift spectra and actually measured water flow velocity showed a high correlation. The maximum velocity of viscous water flow measured from Doppler shift spectra and actually measured viscous water flow velocity also showed a high correlation.
We measured Doppler spectra of water flow speed through the cervical esophagus of five subjects (two male, 41-50 y. o; three females, 28-42 y. o) without dysphasia 10 times and examined the coefficient of variation of Vmax. Values of the coefficient variation of Vmax were 3.4, 3.8, 8.8, 12.7, 15.5% (median 8.8%). It seemed that Vmax could be used as an index of the speed of water flow during swallowing. We suggest that the Doppler spectra of water flow speed through the cervical esophagus in swallowing analysis may be useful for assessing pharyngeal swallowing function, and that it may be useful in the diagnosis of pharyngeal swallowing disorders.
