Approximate entropy in the analysis and monitoring of voice quality changes in larynx cancer patients following radiotherapy
Kathiresan Manickam · 2002
Trans-larynx impedance waveforms or electroglottograms (EGG) are used by speech and language therapists (SALT) in the management of larynx cancer patients, a population dominated by males. EGG is known to be perturbed by the presence of malignant disease in and around the vocal folds and its treatment by radiotherapy. These perturbations have defied concise interpretation in terms of 'normality'. Hence, this study reports the use of approximate entropy (ApEn) complexity analysis in a fundamental-harmonic normalised (FHN) EGG spectral domain that is free from the effects of pitch variability, to characterise phonation in a single parameter. The approach was first used on waveforms from 89 healthy male volunteers in order to quantify 'normality' of phonation, and then on 48 larynx cancer patients, presenting with varying degrees of voice impairment, before and 12 months after treatment. Results are compared to subjective ranking by a senior SALT. FHN-spectral features divided the healthy volunteers into two statistically distinct groups, one with high, the other with moderate, but both with consistent complexity values. Two thirds of larynx cancer patients presenting with at least some residual vocal fold functionality showed an improvement in their complexity values from pretreatment lows to post treatment highs that were clearly normal. A comparison of complexity changes with expert SALT categorisation demonstrated 70 % agreement, with exceptions concentrated in the most severely affected pre-treatment individuals. (5 pages)