Laryngeal function and vocal fatigue after prolonged reading in individuals with unilateral vocal fold paralysis

The purpose of the present study was to examine the effect of prolonged loud reading, intended to induce fatigue, on vocal function in adults with unilateral vocal fold paralysis (UVFP). Subjects were 20 adults, 37-60 years old, with UVFP secondary to recurrent laryngeal nerve paralysis. Subjective ratings and instrumental measures of vocal function were obtained before and after reading. Statistical analysis revealed subjects rated their vocal quality and physical effort for voicing more severely following prolonged loud reading, whereas expert raters did not detect a significant perceptual difference in vocal quality. Reading fundamental frequency (F0) was significantly increased following prolonged loud reading, as were mean airflow rates at all pitch conditions. Maximum phonation times for comfort and low pitches significantly decreased during posttests. Multiple regression analyses revealed significant associations between ratings of posttest physical effort and select posttest measures. Interpretation of results indicates the prolonged loud reading task was successful in vocally fatiguing most of the UVFP subjects. Key physiologic correlates of vocal fatigue, in individuals with UVFP, include further reduction of glottic efficiency, resulting in decreased regulation of glottic airflow and a temporary destabilization of speaking fundamental frequency.