Animals were placed on an operating platform in the supine position. To prepare for surgery, the neck was shaved from the submentum to the chest. Local anesthesia (0.2% lidocaine) was administered at the surgical site and a midline incision was made from the hyoid bone to the sternal notch to expose the larynx and trachea. A tracheostomy was then created to provide a stable airway. The trachea was transected just proximal to the sternum and the lower portion of the trachea was suspended to the sternal fascia. A 3.5 cuffed endotracheal tube (Willy Rusch GmbH, Kernen, Germany) was inserted into the upper portion of the bisected trachea and positioned 2 cm below the glottal opening. The cuff of the endotracheal tube was inflated to seal off the trachea and deliver airflow. Continuous humidified airflow was delivered to the glottis heated at 37° C using a Gilmont Instruments flowmeter (GF-8522, Barrington, IL) and Conch Therm III humidifier (Hudson, RCI, Temecula, CA). A bilateral Isshiki type IV thyroplasty2 (link) was performed to simulate the action of the cricothyroid muscle. The thyroid cartilage and cricoid cartilage were sutured together using 3–0 Webcryl sutures (Patterson Veterinary, Saint Paul, MN) to approximate one another. Suture positioning provided increased lengthening and tension to the vocal folds, providing medial movement of the arytenoid cartilages and vocal fold approximation. Tenseness of the sutures was adjusted until there was audible phonation. Figure 1 is an image demonstrating the in vivo suture placement and approximation of the thyroid and cricoid cartilages.
The larynx was suspended using an 11-cm Hollinger-Tucker pediatric anterior commissure side-slotted laryngoscope (Karl Storz Endoscopy-America, Inc., El Segundo, CA). Three trials of vocal fold vibration were recorded using a 0-degree, 4.0-mm rigid endoscope coupled to a FASTCAM MC 2.1 high-speed camera (KayPENTAX, Montvale, NJ). The images were captured in black and white with 512 × 96 pixel resolution at a rate of 10,000 frames per second. To obtain acoustic measurements, three trials of phonation were recorded using a Perception 170 Condenser microphone (AKG, Vienna, Austria) positioned 10 cm from the opening of the laryngoscope. Uninterrupted, continuous phonation was recorded for approximately 10–20 seconds. Recordings were digitized using Computerized Speech Lab Model 4500 (KayPENTAX, Montvale, NJ). The most stable 1-second portion of the acoustic waveform was selected and analyzed to obtain mean vocal intensity sound pressure level (dB) and mean fundamental frequency (Hz) values. Following acoustic analyses, sound waveforms were edited using Cool Edit Pro v. 2.1 (Syntrillium Software, Phoenix, AZ, 2003). To improve visualization of the waveforms, signals were amplified and excessive noise was removed. Sound spectrograms were created for spectrographic feature analysis. In addition, three trials of airflow rate (ml/s) and subglottal pressure (cm H2O) were documented. At the end of the phonation procedure, humidified airflow was discontinued and the sutures between the thyroid and cricoid cartilages remained in place. The animals were sacrificed and larynges were harvested.
The larynx was suspended using an 11-cm Hollinger-Tucker pediatric anterior commissure side-slotted laryngoscope (Karl Storz Endoscopy-America, Inc., El Segundo, CA). Three trials of vocal fold vibration were recorded using a 0-degree, 4.0-mm rigid endoscope coupled to a FASTCAM MC 2.1 high-speed camera (KayPENTAX, Montvale, NJ). The images were captured in black and white with 512 × 96 pixel resolution at a rate of 10,000 frames per second. To obtain acoustic measurements, three trials of phonation were recorded using a Perception 170 Condenser microphone (AKG, Vienna, Austria) positioned 10 cm from the opening of the laryngoscope. Uninterrupted, continuous phonation was recorded for approximately 10–20 seconds. Recordings were digitized using Computerized Speech Lab Model 4500 (KayPENTAX, Montvale, NJ). The most stable 1-second portion of the acoustic waveform was selected and analyzed to obtain mean vocal intensity sound pressure level (dB) and mean fundamental frequency (Hz) values. Following acoustic analyses, sound waveforms were edited using Cool Edit Pro v. 2.1 (Syntrillium Software, Phoenix, AZ, 2003). To improve visualization of the waveforms, signals were amplified and excessive noise was removed. Sound spectrograms were created for spectrographic feature analysis. In addition, three trials of airflow rate (ml/s) and subglottal pressure (cm H2O) were documented. At the end of the phonation procedure, humidified airflow was discontinued and the sutures between the thyroid and cricoid cartilages remained in place. The animals were sacrificed and larynges were harvested.
