Modulations in respiratory and laryngeal activity associated with changes in vocal intensity during speech.

We tested the hypothesis that different strategies are used to alter tracheal pressure (Pt) during sustained and transient increases in intensity. It has been suggested that the respiratory system plays the primary role in Pt changes associated with alteration in overall intensity, whereas laryngeal adjustment is primary for transient change in Pt related to emphasis. Tracheal pressure, obtained via tracheal puncture, airflow (U), and laryngeal electromyography from the thyroarytenoid muscle (TA EMG) were collected from 6 subjects during sentence production at different intensity levels and with various stress patterns. Using a technique described in a previous study, we computed lower airway resistance (Rlaw) from measures of Pt and U obtained during a sudden change in upper airway resistance. We used this resistance value, together with direct measures of Pt and U during speech, to derive a time-varying measure of alveolar pressure (Pa), the pressure created by respiratory muscle activity and elastic recoil of the lungs. Pa provided a measure of respiratory drive that was unaffected by laryngeal activity. Laryngeal airway resistance (Rlx) and TA EMG provided measures of laryngeal activity. The results of this study indicated that, contrary to the outcome predicted by the hypothesis, there was no difference in the strategies used to alter Pt during sustained and transient increases in intensity. Although changes in both Pa and Rlx contributed to increase in Pt, the contribution of Pa was substantially greater. On average, Pa contributed to 94% and Rlx to 6% of the increase in Pt associated with vocal intensity. A secondary purpose of the study was to determine the extent to which laryngeal muscle activity was related to Rlx during speech. We found TA EMG activity increased with intensity but was not well correlated with Rlx, suggesting that when it contracts, the TA muscle may affect intensity by loosening the cover, which allows for greater amplitude of vocal fold vibration, without necessarily increasing laryngeal airway resistance.

Estimation of alveolar pressure during speech using direct measures of tracheal pressure.

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 (Pa). The extent to which tracheal pressure (Pt) approximates Pa 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 Pa, Pt, 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 (Rlow), (b) use these Rlow values to estimate Pa during speech, and (c) quantify the degree to which Pt approximates Pa 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, Rlow 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 Rlow values ranged from 0.14 to 0.32 kPa/(l/s). Each subject's mean Rlow was used to derive a time-varying measure of Pa during speech from continuous measures of tracheal pressure and airflow. Pt was approximately 95% of Pa during phonation (i.e., when the vocal folds were adducted), 75% of Pa during release of the voiceless stop consonant /p/, and 55% of Pa 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 Pa provides a measure of the pressure produced by the respiratory system that is not influenced by laryngeal activity.

Increased stability of airflow following botulinum toxin injection.

OBJECTIVES: The purpose of this study was to determine whether stability of airflow, as well as mean airflow, increased following botulinum toxin injection to laryngeal and extralaryngeal muscles in persons with spasmodic dysphonia (SD), some with associated vocal tremor (VT). STUDY DESIGN: Aerodynamic data were collected from five subjects before and at 2, 4, and 8 weeks after they received treatment by each of two different arms in an injection protocol in a crossover study. One arm of the protocol involved treatment of the thyroarytenoid muscles only. The other arm involved treatment of both the thyroarytenoid muscles and the strap muscles. METHODS: Measures of mean airflow and coefficient of variation (COV) of airflow during phonation were obtained. A decrease in the COV of airflow would indicate increased stability of phonatory airflow. RESULTS: Before treatment, all subjects with SD/VT exhibited mean airflows that were similar to controls. The COV of airflow ranged from normal to substantially elevated. Following botulinum injection, mean airflow characteristically increased and COV of airflow decreased. CONCLUSIONS: This finding suggests there is a change in the type, as well as the level, of activity in the muscles of speech production following botulinum toxin injection. The increase in airflow stability identified could be due to increased stability of the laryngeal system and possibly of the respiratory system as well.

Sources of error in estimation of laryngeal airway resistance in persons with spasmodic dysphonia.

Estimation of laryngeal airway resistance is a noninvasive method that has proven useful in the study of people with normal and some types of disordered voices. We were interested in examining more closely the application of this method to persons with spasmodic dysphonia (SD), a voice disorder sometimes associated with fluctuating airflow. We speculated unstable airflow could affect the estimation of subglottal pressure and laryngeal airway resistance. Oral pressure and airflow were collected from 10 subjects with SD and 10 control subjects during repetition of /pi/. The coefficient of variation (COV) of airflow during vowel production was calculated to quantify stability of airflow. The results indicated that although some SD subjects produced steady flows during the syllable repetition task, others exhibited substantially varying flows. Inability on the part of the subject to attain steady flows could compromise the usefulness of a midpoint measure of airflow and/or estimation of subglottal pressure, resulting in sources of error in estimation of laryngeal airway resistance. As a result, of the 10 subjects with SD in this study, laryngeal airway resistance could not be estimated in 6 subjects with unsteady flows. Laryngeal airway resistance was estimated in 4 SD subjects who produced steady airflow. Two of these subjects exhibited high laryngeal airway resistance; the others exhibited normal laryngeal airway resistance.

A preliminary study of the prognostic role of electromyography in laryngeal paralysis.

Confidence in the reliability of laryngeal electromyography to predict recovery is critical if this tool is to be used to select the type and timing of surgical intervention. The characteristics of electromyography of 14 patients with unilateral vocal fold paralysis were assessed to determine which factor or combination of factors would be most useful in determining prognosis. We examined the duration, amplitude, waveform morphology, root-mean-square, and time interval from onset to electromyography recording. The results supported the concept that electromyography recordings are valuable in determining prognosis if performed before 6 months and preferably within 6 weeks of onset of laryngeal paralysis. A positive prognosis for laryngeal recovery was indicated when the following electromyography features were present in the immobile vocal fold: (1) normal motor unit waveform morphology, (2) overall electromyography activity characterized by a root-mean-square value greater than 40 microV in any one task, and (3) no electrical silence during voluntary tasks. On the basis of this criteria our overall correct prognostic rate was 89%.

Secondary tracheoesophageal puncture for voice rehabilitation after laryngectomy.

Since the introduction of the tracheoesophageal puncture technique for restoration of voice in 1980, 125 secondary punctures have been performed in 117 patients at the Cleveland Clinic Foundation. Preoperative evaluation, pharyngeal preparation, and their relation to final speech results were reviewed retrospectively. Critical factors in the rehabilitation of these patients are discussed based on our experience and a review of the literature.