Investigation of the impact of thyroid surgery on vocal tract steadiness.

INTRODUCTION

Subjective nonspecific upper aerodigestive symptoms are not uncommon after thyroid surgery. These are postulated to be related to injury of an extrinsic perithyroid nerve plexus that innervates the muscles of the supraglottic and glottic larynx. This plexus is thought to receive contributing branches from both the recurrent and superior laryngeal nerves.

PATIENTS AND

METHODS

The technique of linear predictive coding was used to estimate the F(2) values from a sustained vowel /a/ in patients before and 48 hours after thyroid or parathyroid surgery. These patients were controlled against a matched pair undergoing surgery without any theoretical effect on the supraglottic musculature. In total, 12 patients were recruited into each group. Each patient had the formant frequency fluctuation (FFF) and the formant frequency fluctuation ratio (FFFR) calculated for F(1) and F(2).

RESULTS

Mixed analysis of variance (ANOVA) for all acoustic parameters revealed that the chiF(2)FF showed a significant "time" main effect (F(1,22)=7.196, P=0.014, partial eta(2)=0.246) and a significant "time by group interaction" effect (F(1,22)=8.036, P=0.010, eta(p)(2)=0.268), with changes over time for the thyroid group but not for the controls. Similarly, mean chiF(2)FFR showed a similar significant "time" main effect (F(1,22)=6.488, P=0.018, eta(p)(2)=0.228) and a "time by group interaction" effect (F(1,22)=7.134, P=0.014, eta(p)(2)=0.245).

CONCLUSIONS

This work suggests that thyroid surgery produces a significant reduction in vocal tract stability in contrast to the controls. This noninvasive measurement offers a potential instrument to investigate the functional implications of any disturbance that thyroid surgery may have on pharyngeal innervations.