Voice Quality Changes Following Phonatory-Respiratory Effort Treatment (LSVT®) Versus Respiratory Effort Treatment for Individuals with Parkinson Disease

Abstract

Perceptual ratings of hoarseness and breathiness were used to assess the efficacy of two intensive methods for treating dysarthrophonia in individuals with idiopathic Parkinson disease. One method emphasized phonatory-respiratory effort (the Lee Silverman Voice Treatment, LSVT®) and the other emphasized respiratory effort alone (RET). Perceptual ratings were performed by two expert listeners based on random order presentation of the patients' pretreatment and posttreatment recordings of the “Rainbow Passage.” The listeners were blinded to the patients and their treatment group. Statistically significant pretreatment to posttreatment improvement in hoarseness and breathiness was observed in the LSVT® group but not in the RET group. The present findings are consistent with acoustic and physiologic findings reported previously, providing further evidence for the efficacy of the LSVT®.

Introduction

Parkinson disease (PD) is a progressive neurological disease caused by dopamine deficiency in the substantia nigra.¹ Approximately 1.5 million individuals in the United States suffer from PD, and at least 75% of them have voice and speech abnormalities related to their disease.2, 3, 4 Some of these abnormalities, for example, breathy phonation, hoarseness, reduced loudness, imprecise articulation, and reduced prosody are likely to affect speech intelligibility, which in turn may adversely affect the patient's communication and social, economic, and psychological well-being.5, 6, 7

Traditional speech therapy methods for dysarthric individuals with PD, typically administered once or twice a week and emphasizing articulation, rate, and prosody intervention, have been largely ineffective.8, 9 In contrast, intensive voice therapy methods, administered almost daily and emphasizing simple phonatory effort tasks, have been found to produce favorable, long-term results in dysarthric individuals with PD.10, 11, 12

In 1987 Ramig et al.¹³ developed an intensive treatment program to improve vocal fold adduction and overall voice and speech production in individuals with PD. The program, known as the Lee Silverman Voice Treatment, or LSVT®, is unique in that it focuses on a simple set of tasks designed to maximize phonatory and respiratory functions. This is done by instructing and constantly stimulating individuals to produce good quality loud voice with maximum effort during sustained phonation and in various speech tasks. These individuals are also constantly reminded to monitor the loudness of the voice and the effort it takes to produce it.14, 15

The loud and effortful phonatory tasks with the LSVT® are aimed at improving respiratory drive, vocal fold adduction, and more generally laryngeal muscle activity and synergy, laryngeal and supralaryngeal articulatory movements, and vocal tract configuration. These physiologic changes should improve voice quality and intensity, articulatory precision, prosodic inflection, resonance, and speech intelligibility. Such changes accompanying loud phonation are expected based on similar effects seen in nondisordered speakers.7, 16, 17

The implementation of high-effort, intensive phonatory-respiratory therapy is based on evidence from clinical practices in neurology and physical therapy18, 19, 20 suggesting that when individuals with PD are pushed to higher effort levels, they learn to compensate for, or overcome, some of the deficits that underlie their motor impairment. This increase in effort level, especially when practiced intensively and daily, appears to help individuals with PD rescale or upscale the magnitude of their motor output, as seen in improved letterstroke in writing and stride length in walking.21, 22, 23 In line with certain principles of motor learning,24, 25, 26, 27 Ramig and her colleagues²⁸ have argued that intensive high-effort treatment of vocal functions, especially when coupled with proprioceptive feedback and auditory-vocal self-monitoring, should help individuals with PD rescale the magnitude of their speech motor output and habituate this level in conversation. Emphasis on self-monitoring is an important part of the treatment since motor deficits in individuals with PD appear to be related to factors such as impaired sensorimotor processing, inability to appropriately scale and regulate movement parameters, reduced ability to automatically execute learned motor plans, impairment in effort-demanding processes, and other abnormalities involving high-level executive functions.23, 29, 30, 31, 32, 33, 34, 35

Several acoustic, aerodynamic, stroboscopic, and electroglottographic studies have demonstrated significant improvement in glottic closure, vocal fold vibratory movements, sound pressure level (SPL), and voice fundamental frequency (F₀) range and modulations following LSVT®.28, 36, 37 In a study where LSVT® was compared with an alternative treatment method that emphasizes high respiratory effort treatment (RET), the former method proved superior to the latter in improving SPL and phonatory function.³⁶ For example, whereas LSVT® significantly increased vocal fold adduction and SPL, RET produced inconsistent results, with some patients showing slight or moderate increases in SPL and vocal fold adduction, and others showing marked decreases in these variables posttreatment.

From a clinical standpoint, it is important to study perceptual changes that occur in voice and speech following treatment. Preliminary perceptual studies have already documented improvement in voice loudness, pitch inflection, speech intelligibility, and functional communication following LSVT®.14, 28, 36 To our knowledge, perceptual changes in voice quality following LSVT® have not been experimentally studied. Such information is important since abnormal voice quality can impact significantly on speech intelligibility and acceptability.⁷

The purpose of the present study was to assess the effects of LSVT® and RET on the perception of voice quality in individuals with idiopathic PD. Two percepts of voice quality were chosen for the study—hoarseness and breathiness. These percepts characterize the voices in many individuals with PD. They are likely to be related to incomplete vocal fold adduction; reduced laryngeal muscle activation or synergy; muscle atrophy or fatigue; asymmetrical vocal fold tension or movements; stiffness or rigidity, or a combination of these.37, 38, 39, 40, 41, 42

Acoustically, hoarseness and breathiness are characterized by excessive aperiodic energy superimposed on periodic (harmonic) energy.⁴³ In general, breathiness reflects transglottal air turbulence due to incomplete glottic closure, and hoarseness reflects irregular and asymmetrical vocal fold vibration.43, 44, 45 Although hoarseness and breathiness are, to some degree, perceptually distinct, there is a considerable overlap between them in terms of their acoustic and physiologic characteristics.46, 47, 48

Studies in normal adult speakers have shown that as one increases loudness from normal to high levels, there tend to be significant increases in SPL, subglottal air pressure, transglottal airflow, vibratory movement of the vocal folds, and glottal closure, and significant decreases in jitter and shimmer (acoustic indices of abnormal voice quality) as well as in breathiness or hoarseness.16, 45, 49, 50, 51, 52, 53, 54 There is also evidence that increasing voice intensity by vocal fold medial adduction and compression (through the contraction of the lateral cricoarytenoid, interarytenoid, and thyroarytenoid muscles) is more efficient than by increasing transglottal airflow or vocal fold tension.55, 56, 57, 58 Given these facts, and given the differential effects of LSVT® and RET treatments on acoustic and physiologic measures mentioned above, one would expect to observe significant improvement in voice quality following LSVT® and to a lesser degree following RET.

While anticipated that the LSVT® will produce a more favorable effect on voice quality, it is possible that as patients attempt to increase loudness, they may induce excessive medial compression or tension in the vocal folds, or excessive transglottal airflow. These physiologic changes may result in an increase in breathiness or hoarseness, and possibly phonotrauma.42, 59 Thus, one might argue that the RET may be a more reasonable approach to improve voice quality since it increases respiratory drive with less phonatory adjustments which might be conducive to phonatory trauma and dysphonia.

Another reason for comparing the two treatment methods was to assess the potential influences of extraneous variables such as the Hawthorne or placebo effects on treatment outcome. We reasoned that if the two treatment methods yielded different results, such differences are less likely to be related to extraneous effects and more likely to be attributed to treatment-specific mechanisms.