Estimating of alveolar pressure during speech using direct measures of tracheal pressure

The pressure in the alveoli of the lungs, created by the 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-l) 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 valves 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 Row 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/(1/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,;he 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.