Temperature distribution in expiratory speaking flow, and early detection of vocal fold pathology

This paper describes an application of heat transfer fundamentals to the development and testing of an instrument with potential use for speech production analysis. The method exploits an assumed difference between the air flow patterns of individuals with healthy and breathy voices: during breathy speech production, the glottis does not close completely, and the leakage of warm air through the glottis increases the extent of the temperature field outside the oral cavity. The proposed instrument is a pipe through which the tested individual breathes out while producing a sustained vowel. The pipe wall temperature is maintained uniform at a level considerably lower than the body temperature. The temperature gradient along the pipe centreline is measured and related to the average air velocity through the glottis. The measurements compare favourably with numerical results for the temperature field inside the instrument. These findings therefore suggest that the temperature distribution outside the oral cavity could be useful in understanding changes in air flow patterns through the vocal folds. The centreline temperature chart to be used in conjunction with the instrument is reported in dimensionless terms.