Unilateral Vocal Fold Paralysis: Does the Paralyzed Vocal Fold Oscillate Slower or Faster Than the Healthy One?

Objective/hypothesis: This study aims to analyze the oscillatory behavior of healthy and paralyzed vocal folds in patients with unilateral vocal fold paralysis (UVFP) using laryngeal high-speed videoendoscopy (HSV). We analyzed the left-right oscillatory differences to test the hypotheses that the effective tension of the paralyzed vocal fold is: (h₁) lower, (h₂) higher, or (h₀) similar, when compared with the healthy vocal fold.

Methods: Digital kymograms were obtained from sustained phonations of 20 patients (10 females, 10 males) with UVFP. Oscillatory parameters, including phase difference, axis shift, and amplitude difference index, were calculated for all cycles. Statistical tests, including the Shapiro-Wilk normality test, one-sample t test, and Pearson correlation, were performed with significance level α = 0.05, adjusted for multiple comparisons using the Holm method.

Results: The vocal folds were entrained to the same oscillatory frequency in 18 cases; in one case, the paralyzed fold oscillated at a lower frequency than the healthy one, and in one case, the healthy vocal fold did not oscillate. Significant phase differences between the entrained oscillations of the paralyzed and healthy fold were found in 16 patients, with the paralyzed fold being delayed in 12 and leading in four cases. The axis shift was toward the leading vocal fold and correlated positively with phase difference (r = 0.88, P < 0.001). Amplitude differences varied, with equal instances of significantly greater amplitudes on the healthy or paralyzed fold (nine cases each). In 11 out of 18 subjects, the left-right phase differences significantly changed with phonatory pitch.

Conclusion: The oscillatory behavior of UVFP patients' vocal folds does not follow a uniform pattern, indicating that the paralyzed fold tension can be lower, higher, as well as similar to that of the healthy fold. The effective tension tends to increase more steeply in the paralyzed than in the healthy vocal fold when increasing vocal pitch.