Glottic Closing Force Versus Laryngeal Adductory Pressure in the Canine Larynx

Introduction: The strength of glottic closure with recurrent laryngeal nerve (RLN) stimulation has been indirectly measured experimentally by determining the squeezing pressure on a balloon inserted between the vocal folds, termed laryngeal adductory pressure (LAP). In this study, we sought to measure glottic closing force (GCF) directly and compare these results to LAP measures obtained with identical stimulation parameters. Methods: In canines, a method for measuring GCF was developed in which a suture was looped through a lateral thyrotomy hole, around the vocal process and back, then attached to a force gauge. The RLN was maximally stimulated and GCF recorded. The LAP was then measured as previously described, using the same stimuli. This process was repeated at 9 stimulation frequencies in 10-Hz intervals from 20 to 100 Hz. The GCF and LAP were compared using Pearson's correlation coefficient (PCC). Results: Both sides were measured in 16 dogs, resulting in 32 data sets. The LAP measures were obtained at all frequencies, while GCF was obtained in 246 of 288 (85.4%) attempts. The maximum GCF for each dog typically occurred at 80 to 100 Hz and averaged 0.287 ± 0.106 newtons. Plotting GCF versus LAP for each hemilaryngeal preparation, the mean PCC was 0.932 ±.042 (range, 0.802-0.987). The mean PCC did not differ between control (n = 26) and postoperative (n = 6) hemilarynges. Conclusion: This method for measuring GCF appears valid. The high Pearson's correlation coefficient indicates strong covariance between GCF and LAP, demonstrating that they are both measures of the same physical property. The LAP is easier to perform and more consistently obtained.