What is it about?
This study examines how the paralyzed vocal fold vibrates compared with the healthy fold in 20 patients (10 female and 10 male) with unilateral vocal fold paralysis (UVFP). Using high-speed videoendoscopy, the authors analyzed cycle-by-cycle vibration patterns and found that, although the two folds usually oscillate at the same frequency, the paralyzed fold may lead or lag in phase and may show either greater or smaller amplitude depending on the patient and the pitch produced. These variations indicate that the effective tension of the paralyzed fold is not consistently lower than that of the healthy fold—it can be lower, higher, or similar. Because the behavior differs across individuals and changes with pitch, the authors conclude that patients require individualized strategies to balance vocal fold tension for optimal voice production.
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Why is it important?
The study provides quantitative, cycle-by-cycle evidence (thanks to HSV) of how paralyzed and healthy folds interact dynamically in UVFP. It offers novel quantitative parameters designed for providing insights into the VF kinematics in UVFP. It challenges simplistic assumptions (e.g., “paralyzed fold is always looser / lower tension”) by showing the behavior is complex and patient-specific. It supports a personalized medicine approach in voice therapy: practitioners should not assume the same biomechanical state for all paralyzed folds. It could also inform biomechanical models of vocal fold vibration in pathology: data on phase, axis shift, amplitude asymmetries, and pitch dependence are invaluable for computational models.
Perspectives
As a physicist working with laryngologists treating voice disorders, I have long wondered whether, in patients with unilateral vocal fold paralysis, the paralyzed fold vibrates more slowly or more quickly than the healthy fold. This paper allowed us to answer the question. The vocal fold oscillations were usually entrained to the same frequency; however, significant phase differences were observed, with the paralyzed fold delayed in 12 cases and leading in four. These phase differences suggest that the paralyzed fold generally oscillates more slowly and operates under lower tension, although it may occasionally be more tense than the healthy fold. The data also indicate that the effective tension in the paralyzed vocal fold increases more steeply with pitch than in the healthy fold. Patients may potentially use this phenomenon to find their optimal pitch, where the phase delay is minimized and the vocal folds oscillate symmetrically. Note for physics-oriented voice scientists: For simplicity, in this paper we use the rather general term "tension" instead of the more accurate technical term "tensile stress". This is defined as the tensile force divided by the cross-sectional area of vocal fold vibration, and that area is related to the vibrating mass. In principle, a lower tensile stress could result from a lower tensile force or from a higher vibrating mass, and vice versa.
Dr. Jan G. Svec
Univerzita Palackeho v Olomouci
Read the Original
This page is a summary of: Unilateral Vocal Fold Paralysis: Does the Paralyzed Vocal Fold Oscillate Slower or Faster Than the Healthy One?, Journal of Voice, May 2025, Elsevier,
DOI: 10.1016/j.jvoice.2025.03.045.
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