Aerodynamic and sound intensity measurements in tracheoesophageal voice

In laryngectomized patients, tracheoesophageal voice generally provides a better voice quality than esophageal voice. Understanding the aerodynamics of voice production in patients with a voice prosthesis is important for optimizing prosthetic designs and successful voice rehabilitation.

To measure the aerodynamics and sound intensity in tracheoesophageal voice production.

We built a special setup, which consisted of a Pentium 200 MHz computer with an AD-DA interface card and Labview 4.01 software. In an oral/nasal mask we constructed several mass flow sensors and a microphone. This measured both the oral airflow and the level of sound. For the measurement of endotracheal pressure, which is the driving force behind the airflow, we used a transducer which was connected to the tracheostoma. The endoesophageal pressure was measured at the level of the prosthesis in the esophagus by a Mikrotip transducer. Using this we could determine how much the voice prosthesis contributes to the overall pressure drop of the phonatory tract. Furthermore, the average airflow rate as a function of the sound pressure levels could be determined.

In our population, 6 out of 7 patients showed a positive relationship between trans-source airflow and generated sound intensity. We compared our prosthesis pressure drop values with in vitro data and found that there are some differences, possibly due to difference in age of the prosthesis and physiological circumstances in vivo. The overall contribution of the voice prosthesis to the airway resistance depends on the level of phonation and the type of device. In our patient group it is apparent that the pharyngoesophageal (PE) segment has the greatest share of the total pressure drop, especially at higher airflow rates. We measured a 27% pressure drop in airflow over the voice prosthesis. Different tracheostoma occlusion methods did not have any effect on the aerodynamics and sound intensity. One patient that had had a jejunal graft for reconstruction showed, not unexpectedly, extremely different aerodynamic values. We were unable to define optimal airflow rates or optimal resistance values for sound production in the PE segment.

The aerodynamic characteristics of voice production in laryngectomized patients with voice prostheses are determined by both prosthetic factors and PE segment tissue factors. In our patient group the PE segment is responsible for the greatest pressure drop. We found no significant difference in pressure drop and sound intensity for different tracheostoma occlusion methods.