Effect of vocal fold injury location on vibratory parameters in excised canine larynges

Development of Excised Larynx

The larynx is a complex organ which has a role in a variety of functions such as phonation, breathing, and swallowing. To research these functions, it is widely accepted that in vivo studies provide more anatomically and physiologically relevant findings. However, invasive procedures are generally needed to measure variables such a subglottal pressure, vocal fold tension and stiffness, and cricothyroid muscle stretch. Performing studies using excised larynges is a useful technique which makes it possible to not only measure phonation parameters but control them as well. Early studies using excised larynges mainly focused on controlling specific parameters and mathematical modeling simulations. The use of these studies has helped further research in laryngeal anatomy, imaging techniques, as well as aerodynamic, acoustic, and biomechanical properties. Here, we describe the progress of this research over the past 5 years. The number of accepted animal models has increased and ideas from excised larynx studies are starting to be applied to treatment methods for laryngeal disorders. These experiments are only valid for an excised situation and must continue to be combined with animal experimentation and clinical observations.

Excised larynx evaluation of subthyroid cartilage approach to medialization thyroplasty

OBJECTIVES/HYPOTHESIS

To describe an alternative approach to medialization thyroplasty involving dissection underneath the thyroid cartilage with placement of a Gore-Tex implant, and to evaluate its effect on a range of phonatory measures using an excised canine larynx model.

STUDY DESIGN

Animal model.

METHODS

On each of eight excised canine larynges, the conditions of normal, paralysis, medialization thyroplasty by standard transthyroid cartilage approach, and medialization thyroplasty by experimental subthyroid cartilage approach were performed. Aerodynamic, acoustic, and mucosal wave parameters were measured for each condition.

RESULTS

Compared to the vocal fold paralysis state, both the transthyroid and subthyroid approaches for Gore-Tex insertion resulted in significant decreases in phonation threshold pressure and phonation threshold flow. Both approaches also significantly decreased percent jitter, decreased percent shimmer, and improved signal-to-noise ratio. The mucosal wave was preserved after insertion of the Gore-Tex implant for both approaches. For all the phonatory measures except phonation threshold flow, there were no significant differences between the transthyroid and subthyroid approaches.

CONCLUSIONS

Gore-Tex implantation via a subthyroid approach in an excised canine larynx model can produce effective medialization, preserve the mucosal wave, and significantly improve aerodynamic and acoustic parameters without meaningful difference compared to a traditional transthyroid approach. The subthyroid approach does not require creation of a thyroid cartilage window and could be a potentially valuable alternative method of performing medialization thyroplasty.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:675-681, 2018.

Classification for animal vocal fold surgery: resection margins impact histological outcomes of vocal fold injury

OBJECTIVES/HYPOTHESIS

Extent of vocal fold injury impacts the nature and timing of wound healing and voice outcomes. However, depth and extent of the lesion created to study wound healing in animal models vary across studies, likely contributing to different outcomes. Our goal was to create a surgery classification system to enable comparison of postoperative outcomes across animal vocal fold wound-healing studies.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Rats underwent one of three types of unilateral vocal fold surgeries classified by depth and length of resection. The surgeries were: for subepithelial injury, resection of epithelium and superficial layer of the lamina propria at the midmembranous portion of the vocal fold; for transmucosal injury, resection of epithelium and lamina propria; and for transmuscular injury, resection of epithelium, lamina propria, and superficial portion of the vocalis muscle. Wound healing was evaluated histologically at various time points up to 35 days postinjury.

RESULTS

Complete healing occurred by 14 days postsurgery for subepithelial injury, and by day 35 for transmucosal injury. Injury remained present at day 35 for transmuscular injury.

CONCLUSIONS

Timing and completeness of healing varied by extent and depth of resection. Scarless healing occurred rapidly following subepithelial injury, whereas scarring was observed at 5 weeks after transmuscular injury. The proposed classification system may facilitate comparison of surgical outcomes across vocal fold wound-healing studies.

LEVELS OF EVIDENCE

N/A.

Characterization of extracellular matrix proteins during wound healing in the lamina propria of vocal fold in a canine model: a long-term and consecutive study

The characterization of vocal fold wound healing can be reflected by the changes of extracellular matrix (ECM) proteins in the lamina propria. Although the expression of ECM proteins after vocal fold injury has been widely studied, such observations have lacked time continuity and integrity of marker proteins. In this study, we observed the morphology of injured vocal folds in a canine model. We used immunofluorescence staining to evaluate the expression and distribution of ECM proteins, such as collagen, elastin, hyaluronic acid, decorin and fibronectin, from 15 days to 6 months after injury. The results showed that large amounts of ECM proteins were secreted 15-40 days after injury. Collagen and fibronectin secretion increased significantly, and were disorderly deposited. The secretion of decorin and elastin increased slightly, while hyaluronic acid decreased. The 15-40 day post-injury period may be the critical intervention stage in wound healing of vocal folds. From 3 to 6 months after injury, the secretion of ECM proteins declined. However, collagen and fibronectin secretion were still significantly higher than normal with irregular arrangement, while the secretion of elastin, hyaluronic acid and decorin decreased significantly at 6 months. This led to vocal fold inelasticity and stiffness, which required effective long-term interventions to treat scar formation.

Voice Outcome of Modified Frontolateral Partial Laryngectomy in Excised Canine Larynges and Finite Element Model

OBJECTIVE

To evaluate vocal parameters after modified frontolateral partial laryngectomy (MFLPL) and frontolateral partial laryngectomy (FLPL) in both excised canine and finite element models.

STUDY DESIGN

FLPL and MFLPL were compared, using a prospective paired case control laboratory study with excised canine larynx and computational modeling.

SETTING

Basic science study conducted in university laboratory.

METHODS

FLPL and MFLPL were performed serially on 9 excised canine larynges. The excised larynx bench apparatus was used to collect phonation threshold pressure (PTP) and high-speed video data. A finite element model was built to compare a normal vocal fold with applied tension, a cut fold with no applied tension (simulating FLPL), and a cut fold with applied tension (simulating MFLPL). Stress values and distributions across the 3 conditions were computed.

RESULTS

The mean PTP increase after MFLPL (15.45-17.46 cmH2O) was not statistically significant. In the excised canine model, fundamental frequency (F0) showed a significant increase for the MFLPL (P = .039). Differences in vibration amplitudes were not statistically significant. Von Mises stress distribution was most similar between the MFLPL model and the normal fold. Maximum von Mises stresses at the midline were 17.56, 21.63, and 5.10 kPa for the normal, MFLPL, and FLPL, respectively, and 47.57, 63.98, and 101.97 kPa at the peripheries.

CONCLUSIONS

From these results, we conclude that MFLPL has the potential to give a better voice outcome while avoiding tracheotomy in partial laryngectomy patients. In vivo study in canines to examine the healing process would lend further evidence-based support for this surgical method.