Estimation of Alveolar Pressure During Speech Using Direct Measures of Tracheal Pressure

eileenfinnegan{at}uiowa.edu

The pressure in the alveoli of the lungs, created by the elastic recoil of the lungs and respiratory muscle activity, is referred to as alveolar pressure (P_a). The extent to which tracheal pressure (P_t) approximates P_a depends on the resistance to airflow offered by structures above and below the point at which tracheal pressure is measured. An understanding of the relationship among P_a, P_t, and upper and lower airway resistance, and how these values fluctuate during speech, could aid in interpretation and modeling of speech aerodynamics. The purpose of this study was to (a) obtain values for lower airway resistance (R_law), (b) use these R_law values to estimate P_a during speech, and (c) quantify the degree to which P_t approximates P_a during production of voiced and voiceless sounds, in comparison to inhalation. In addition, the results were discussed in terms of the degree to which the respiratory system functions as a pressure source. Tracheal pressure (obtained with tracheal puncture) and airflow were measured during sentence production in 6 subjects. Using a technique introduced in this paper, R_law was determined from measures of tracheal pressure and flow obtained during a sudden change in upper airway resistance because of release of a voiceless plosive. Mean R_law values ranged from 0.14 to 0.32 kPa/(l/s). Each subject's mean R_law was used to derive a time-varying measure of P_a during speech from continuous measures of tracheal pressure and airflow. P_t was approximately 95% of P_a during phonation (i.e., when the vocal folds were adducted), 75% of P_a during release of the voiceless stop consonant /p/, and 55% of P_a during inhalation (i.e., when the vocal folds were abducted). Therefore, the degree to which the respiratory system functioned as an ideal pressure source varied during speech. The ability to estimate P_a provides a measure of the pressure produced by the respiratory system that is not influenced by laryngeal activity.

KEY WORDS: alveolar pressure, tracheal puncture, lower airway resistance, tracheal pressure, aerodynamics

Submitted on May 11, 1998
Accepted on April 5, 1999

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