* This study was supported in part by the Catholic University of Daegu and Research Institute of Biomimetic Sersory Cortrol.

Transcription

1 Effects of Deep Brain Stimulation (DBS) on Speech and Voice in Parkinson s Disease: Acoustic Measures of Vowels from Sustained Phonation and Running Speech Using Perturbation and Nonlinear Dynamic Analysis Seong Hee Choi Department of Audiology and Speech-Language Pathology and Research Institute of Biomimetic Sensory Control, College of Medical Sciences, Catholic University of Daegu, Kyungsan, Korea Correspondence to Prof. Seong Hee Choi, PhD, Department of Audiology and Speech-Language Pathology and Research Institute of Biomimetic Sensory ControlCollege of Medical Sciences, Catholic University of Daegu, 5 Gumgokri, Hayangup, Kyungsansi, Kyungsanbookdo, Korea shgrace@cu.ac.kr tel.: Background & Objectives: Deep brain stimulation (DBS) of the thalamus or basal ganglia has been considered one of the most stable and long-term effective neurosurgical therapeutic interventions for Parkinson s Disease (PD). Evidence of a surgical approach with DBS in PD with regard to voice and speech is still lacking. The present study aims to investigate if nonlinear dynamic analysis with vowels from sustained phonation and running speech can be used to investigate the effects of electrode implantation and stimulation of the thalamic nucleus (STN) on patients voice and speech in advanced stages of PD. Methods: Nineteen idiopathic PD patients that received DBS-STN surgery and ten idiopathic PD patients that did not receive DBS-STN surgery participated in the present study. Participants did not receive medication for 12 hours overnight prior to the recording session. For surgical patients, recordings were taken with the stimulator on (for at least 12 hours) and off (for 30 minutes). The sustained and running vowel segments were used to analyze the perturbation including percent jitter, shimmer, signal-to-noise ratio (SNR) values, and nonlinear dynamic method of correlation dimension (D2). Results: Results showed that the mean D2 value of the surgical group was significantly lower than the mean D2 value of the non-surgical group for sustained and running vowels. The perturbation results failed to achieve significance with DBS, contradicting the results of nonlinear dynamic analysis. Discussion & Conclusion: Nonlinear dynamic analysis showed effects of DBS on PD patients voice and speech and may be a useful substitute for perturbation analysis in the evaluation of running speech because of the short signal length and high noise level. The results indicate that nonlinear dynamic analysis may be useful to evaluate the treatment effect in PD patients with severe voice and speech disorders. (Korean Journal of Communication Disorders 2012;17: ) Key words: Deep Brain Stimulation (DBS), Parkinson s speech and voice, nonlinear dynamic analysis, perturbation analysis, sustained phonation, running speech Ⅰ. Introduction Parkinson s disease (PD) is progressive neuromuscular disorder (Kim, Kearney & Atkins, 2002). The Characteristic movements of abnormalities such as resting tremor, rigidity, bradykinesia, and postural abnormalities observed in PD are caused by dopamine deficiency associated with degeneration of the substantia nigra (Marsden, 1994). Laryngeal dysfunction or experience voice difficulties were reported 89% of PD patients as the disease progresses as well as speech abnormalities (Hanson, Gerratt & Ward, 1984). It is of significant clinical interest to reduce voice and speech symptoms and explore the suitable treatment option for PD patients. The common deficit in speech and voice is hypokinetic * This study was supported in part by the Catholic University of Daegu and Research Institute of Biomimetic Sersory Cortrol. Received January 19, 2012 Final revision received February 29, 2012 Accepted March 7, c 2012 The Korean Academy of Speech-Language Pathology and Audiology 143

2 Korean Journal of Communication Disorders 2012;17: dysarthria and its typical characteristics include abnormal prosody, variability in speech rate, imprecise movements of the articulators, reduced loudness, monotone, breathiness and harsh voice (Hanson, Gerratt & Ward, 1984; Gentil & Pollak, 1995; Ramig et al., 1995; Sewall, Jiang & Ford, 2006). Laryngeal tremor was observed early in the Parkinson s disease patients (Perez et al., 1996) and the major laryngeal abnormalities in advanced PD patients are prominent vocal fold bowing with glottal incompetence (Blumin, Pcolinsky & Atkins; 2004), hypophonia (Hartelius & Svensson, 1994; Liotti et al., 2003) and abnormal phase closure and phase asymmetry (Perez et al., 1996). Several studies on PD speech and voice treatment including pharmacological treatment such as levodopa (Rascol et al., 1994; Sanabria et al., 2001; Pahwa, 2006), neurosurgery such as stereotactic pallidotomy (Schulz et al.,1999; Schulz & Grant, 2000), laryngoplasty for vocal folds medialization (Sewall, Jiang & Ford, 2006) have been attempted to investigate treatment efficacy of parkinson s related dysphoinia and dysarthria. Although some results demonstrated clinically significant efficacy, treatment outcomes were limited to small samples of PD, short-term effect or different depended on different level of dysarthria severity. Additionally, levodopa has been used widely to treat symptoms of PD, but the drug side effects including dystonia and dyskinesia were reported (Parkin et al., 2002). Recently deep brain stimulation (DBS) of the thalamus or basal ganglia has been considered one of the most stable and long-term effective neurosurgical therapeutic intervention which significantly improves all areas of limb motor performance such as rigidity, tremor, and akinesia (Benabid, 2003; Burchiel et al., 1999; Iansek, Rosenfeld & Huxham, 2002, Krack et al., 2003; Kumar & Mullick, 1996; Limousin et al., 1998; Xie et al., 2001) and preferred treatment method for patients with advanced PD due to improvement of the major symptoms of the disease more effectively than globus pallidus stimulation (Wang et al., 2003). The effect of DBS on speech and voice, however, has yielded inconsistent outcomes. Multiple preliminary studies have shown that DBS of the subthalamic nucleus (STN) improved maximal phonation time, vocal intensity level, and fundamental frequency variability (Gentil et al., 2001; Gentil et al., 2003; Hoffman-Ruddy et al., 2001). In contrast, Farrell et al. (2005) found that individuals with PD who had surgery including thalamotomy, pallidotomy, or DBS exhibited an improved Hoehn & Yahr stage of PD score compared to a non-surgery PD group whereas there were no significant changes in speech for surgical PD group. Likewise, Wang et al. (2003) reported subthalamic nucleus had some positive effects or no changes in speech and the recent study by Dromey & Bjarnason (2011) displayed that articulation (corner vowel formants, diphthong slopes) and phonation (perturbation, long-term average spectrum) outcomes showed some speakers improved while others became worse, but only 6 PD with DBS were participated in this study. Additionally, some studies revealed the DBS effects on speech deteriorated (Gentil et al., 2003; Törnqvist, Schalén & Rehncrona, 2005). Sung et al. (2004) evaluated maximum phonation time (MPT), jitter (pitch perturbation), shimmer (intensity perturbation),tremor indices, and diadochokinetic rate (DDK) to investigate the effects of DBS with bilateral STN on the phonation and articulation of 7 PD with levodopa on and off treatments. They found no significant changes in the DDK rate under any condition at the articulatory level and only percent shimmer values decreased when the patients were levodopa off while both the DBS and levodopa treatment caused significant prolongation of the MPT suggesting STN DBS improved phonation, but had limited effects on articulation in individuals with PD in advanced stage. Acoustic perturbation measures have been commonly used as an objective method for evaluation and diagnose of pathologic voice quality. Percent jitter, and shimmer as well as harmonic to noise ratio (HNR) have traditionally been used to describe voice quality. On the other hand, some studies have cautioned against applying of perturbation acoustic analysis to severely impared pathologic voice which 144

3 Choi / Effects of Deep Brain Stimulation (DBS) on Speech and Voice in Parkinson s Disease are presented in voice of some PD patients (Titze, 1995; Karnell et al., 1997; Yiu, 1999). In addition, some hypophonic PD voices cannot be analyzed by using some commercialized voice analysis system. Non-linear dynamic analysis methods (e.g., Phase space reconstruction and correlation dimension (D 2 ) as complement of perturbation analysis have been employed broadly to quantify highly aperiodic and chaotic pathologic voice signals including speakers with vocal polyps, parkinson s voice, unilateral vocal fold paralysis, muscle tension dysphonia, esophageal voice as well as pediatric dysphonia (Awan, Roy & Jiang, 2010; MacCallum et al., 2009; Meredith et al., 2008; Rahn et al., 2007; Zhang et al., 2004; 2005a; Zhang, Jiang & Rahn, 2005). Thus, nonlinear dynamic approach can be applied to quantify aperiodic and chaotic laryngeal activity and give reliable outcomes to clinician to assess treatment effects of laryngeal pathologies. Zhang, Jiang & Rahn (2005) studied to theoretical nonlinear model for identifying vocal fold vibrations in Parkinson s disease, and pathologic vocal characteristics including reduced vibratory intensity, incomplete vocal closure, increased phonation threshold pressure, glottal tremor, subharmonics, and chaotic vocal fold vibration are suitable to apply to the nonlinear analysis model. Similarly, Rahn et al. (2007) used non-linear analysis with voices of PD patients and normal with sustained phonation. The results showed PD subjects have significantly higher D 2 values than control subjects (p = 0.016), which indicates increased signal complexity in PD vocal pathology. Differences in the comparison of two groups were significant in jitter (p = 0.014) but no significant in shimmer (p = 0.695). In addition, Choi (2011) used nonlinear analysis of PD voices with sustained vowel to test the effect of LSVT (Lee Silverman Voice Treatment) and found significantly lower percent jitter and D 2 values in LSVT group compared to non- LSVT group. Sustained vowels only could be used in most commercialized voice analysis systems and simple methods to evaluate in the clinical setting because sustained vowels are obtained in more clearly controlled environment related to aspects of voice source, vocal tract and relatively devoid of individual speech characteristics such as speaking rate, speaker s dialect, intonation, and articulatory behavior (Parsa & Zamieson, 2001). In contrast, running speech involves dynamic and rapid adjustment of vocal mechanisms, which is important indicator of vocal quality. Even though running speech is natural and reflect day-to-day speech, Parsa & Zamieson (2001) noted that careful selection of the region of fo contour for valid of perturbation was needed when extracting perturbation analysis from running speech. According to Zhang & Jiang (2008), nonlinear dynamic analysis, such as correlation dimension (D 2 ), allows a more stable analysis with shorter signal lengths such as extracting vowels from running speech and lower sampling rates and high noise level. It is hypothesized that some prior studies might represent weak or no significant DBS effect on PD voice and speech since the utility of some commercialized voice analysis system may not be suitable or reliable to analyze severe PD voice in advanced stages and analysis of running speech might also give better understanding of the DBS effects than that of sustained vowels. The objective of this study, therefore, is to investigate the effects of implantation of electrode and stimulation of the thalamic nucleus (STN) on parkinson s voice and speech with both perturbation and non-linear analysis using both sustained phonation and running speech. 1. Participants Ⅱ. Method The protocol and consent procedure was approved by the University of Wisconsin Institutional Review Board and the Committee of Ethics at Shanghai Second Military Medical University Hospital. All participants were Chinese. An attending neurologist recruited 19 idiopathic PD patients, 11 males and 8 females with an average age of 63.8 years, that received DBS-STN surgery <Table- 1>, and 10 idiopathic PD patients, 6 females and 4 males with a mean age of 66.8 years, that did not receive DBS- 145

4 Korean Journal of Communication Disorders 2012;17: <Table-1> Demographics and clinical characteristics in DBS surgical PD group Patient # Gender Age Hoehn-Yahr Side of STN UPDRS a) -Ⅲ UPDRS-Ⅲ Item 18 (Speech) Perceptual Rating b) (General Vocal Impairment) PD Duration 1 Female 68 Ⅲ Bilateral Female 62 Ⅲ Bilateral Male 67 Ⅳ Bilateral Male 61 Ⅲ Left Male 50 Ⅲ Bilateral Male 56 Ⅲ Bilateral Male 65 Ⅳ Bilateral Female 65 Ⅲ Bilateral Female 57 Ⅴ Left Male 72 Ⅲ Left Male 76 Ⅲ Left Male 63 Ⅲ Left Male 58 Ⅳ Left Male 77 Ⅲ Bilateral Female 48 Ⅲ Left Female 66 Ⅲ Right Female 65 Ⅲ Right Female 68 Ⅳ Bilateral Male 69 Ⅲ Right Mean SD N/A (Ⅲ=3, Ⅳ=4, Ⅴ=5) a) UPDRS: Unified Parkinson s Disease Rating Scale b) Perceptual ratings (5-point equal appearing interval (EAI) rating scale, 1: normal; 5: largest deviation from normal) STN surgery <Table-2>. The surgical and nonsurgical patients were selected for consistency in the criteria shown in Tables 1 and 2. Three speechlanguage pathologists with clinical specialization in PD voice disorders (3-5 years) rated overall voice quality for all vowel samples using a five-point equalappearing-interval (EAI) rating scale (1: normal; 5: largest deviation from normal). The surgical procedure was identical to that discussed in Benabid (2003), and the decision to undergo DBS-STN surgery was made independent from the interests of this study. Participants did not have vocal deficits caused by diseases other than PD, symptoms outside of those common to PD as detected by laryngeal endoscopy, cognitive hearing impairment, or depression. T-test was used to compare the differences regarding age, Unified Parkinson s Disease Rating Scale (UPDRS) for speech, stage of disease (Hoehn & Yahr, 1967) between surgical and non-surgical groups <Table -3> and no significant differences were found for any of the variables between groups in the baseline of this study (p >.05). 146

5 Choi / Effects of Deep Brain Stimulation (DBS) on Speech and Voice in Parkinson s Disease <Table-2> Demographics and clinical characteristics in non-surgical PD group Patient # Gender Age Hoehn-Yahr UPDRS a) -Ⅲ UPDRS-Ⅲ Item 18 (Speech) Perceptual Rating (General Vocal Impairment) PD Duration Since Diagnosis (years) 1 Female 74 Ⅲ Female 74 Ⅳ Female 73 Ⅲ Female 59 Ⅳ Female 57 Ⅲ Female 77 Ⅲ <1 7 Male 61 Ⅳ Male 68 Ⅲ Male 49 Ⅲ Male 76 Ⅳ Mean SD N/A a) UPDRS: Unified Parkinson s Disease Rating Scale 3.4 (Ⅲ=3, Ⅳ=4, Ⅴ=5) <Table-3> Mean (SD) values of demographics and clinical characteristics for surgical and non-surgical PD group Surgical PD (N=19) Non-surgical PD (N=10) p-value Age(yr) 63.8(7.7) 66.8(9.7) p > 0.05 UPDRS a) (speech) 0.74(0.6) 0.9(0.7) p > 0.05 H & Y b) 3.32(0.6) 3.4(0.7) p > 0.05 Perceptual rating 3.6(1.0) 3.4(1.1) p > 0.05 a) UPDRS = Unified Parkinson s Disease Rating Scale, b) H & Y = Hoehn & Yahr stage 2. Recording Procedure Participants did not receive medication for 12 hours overnight prior to the recording session (medication-off condition). For surgical patients, recordings were taken with the stimulator-on (for at least 12 hours). The stimulator-off recordings, however, were not reported because of the short duration of the stimulator-off period, which was the longest the patients were able to tolerate. For nonsurgical patients, recordings were taken once. In each session, sustained /a/ vowel phonations of no less than 5 seconds and /a/ vowel from running speech by reading a sentence in Mandarin Chinese were recorded in a sound-attenuated room using a head-mounted microphone (AKG Acoustics, Vienna, Austria) positioned at 15 cm from the mouth at a 45 degree angle. Audio files were recorded at a sampling rate of 25 khz using Multispeech software (Kay Elemetrics Corporation, Lincoln Park, NJ). Patients were directed to perform sustained phonation and running speech within their normal vocal range. For the sustained phonations, relatively more stable 3 replicate recordings were selected for analysis from 5 replicates, and 1-second segments were cut to eliminate the offset and onset of phonation. For running speech, 2 replicate recordings from 3 replicates were taken for analysis, and the running vowel /a/ was selected to eliminate the effects of fricative and silence segments. Each running vowel segment, with a minimum length of 100 ms, was cut to eliminate the offset and onset of voice. Both sustained and running vowel segments were processed using perturbation and nonlinear dynamic analysis. The research assistant that directed the patient 147

6 Korean Journal of Communication Disorders 2012;17: was blind to the patient group for the first set of recordings and the stimulator condition. The patient was blind to the stimulator condition. Therefore, data collection satisfied double blindness. Another research assistant, blind to the patient group and stimulator condition, analyzed the data, achieving blindness at this stage of data processing. 3. Data Analysis CSpeech 4.0 software (Paul Milenkovic, Madison, Wisconsin) was used to obtain percent jitter, percent shimmer, and signal-to-noise ratio (SNR) values for both sustained and running vowel segments. CSpeech was also used to calculate err, the number of counts the algorithm failed to extract a pitch period, for all patients (Milenkovic & Read, 1992). An error greater than 10 indicated an unreliable pitch period. The waveforms of the segments with err values greater than 10 had type 2 (bifurcations and modulations evident) or type 3 (aperiodic and chaotic) signals. Previous studies have shown that perturbation analysis is only reliable for nearly periodic voice samples and therefore, perturbation results for these segments were eliminated (Titze, 1995). The nonlinear dynamic method of correlation dimension (D 2 ), which studies have shown does not have the periodicity requirement that limits perturbation methods, was also used to analyze sustained and running vowel segments. The theory, usage, and determination of correlation dimension calculations have been described extensively in previous studies (Herzel et al., 1994; Jiang, Zhang & Ford, 2003; Jiang, Zhang & McGilligan, 2006; Kumar & Mullick, 1996; Narayanan & Alwan, 1995; Titze, Baken & Herzel 1993; Zhang et al., 2004, Zhang et al. 2005a; 2005b ; Zhang, Jiang & Rahn, 2005). Compared to perturbation methods, nonlinear dynamic analysis such as correlation dimension (D 2 ) do not require determination of a pitch period, which is a component of the algorithms used in perturbation analysis. Briefly, <Figure-1> shows a phonatory time series χ(t i ), t i = t 0 +iδt, (i =1,2,,N) from a surgical patient sampled at Δt = 1/ƒ s. The time length analyzed is 1 s (figures were magnified) (N=25000). The reconstructed phase space, shown in <Figure-2>, plots the voice signal against itself at a time delay τ calculated by Fraser and Swinney s mutual information method (1986). Correlation dimension (D 2 ) measures the correlation of any two points in this phase space, or the complexity and irregularity of this phase space. Higher correlation dimension indicates higher aperiodic vocal pathology and a more severely impaired Parkinsonian voice; a zero-dimensional fixed point(static states), a one-dimensional limit cycle(periodic oscillations), a two-dimensional quasiperiodic torus(superposition of two or more oscillations), or a fractal dimensional chaotic trajectory (apeirodic oscillations (Herzel et al., 1994; Jiang, Zhang & McGilligan, 2006). Grassberger and Procaccia s correlation dimension (1983) was calculated based on the definition, logc( r) D2 = lim r 0 log r, where r is the radius around Ⅹ i and 2 C( W, N, r) = ( N + 1 W )( N W ) N 1N 1 n n= W i= 0 θ ( r X i X i+ n was calculated using Theiler s formula (1986). W was set as the time delay τ and θ (χ) satisfies 1 θ ( x) = 0 x > 0 x 0. The correlation dimension is obtained with a linear curve fit to D 2 vs. r in the scaling region where the slopes of these two curves increase transiently and then converge as embedding dimension m is increased. <Figure-3> shows the curves D 2 vs. r from the same surgical patient as shown in <Figure-1>. The slopes of the D 2 vs. r curves approach ± in the indicated scaling region, which is the estimated D 2 of this voice. Using the steps outlined above, correlation dimension values were obtained for all vowel segments. ) 148

7 Choi / Effects of Deep Brain Stimulation (DBS) on Speech and Voice in Parkinson s Disease 4. Statistical Analysis <Figure - 1> A waveform in DBS-STN surgical PD group Means were calculated for each of 4 measures (percent jitter, percent shimmer, SNR, D 2 ) for sustained and running vowel segments of non-surgical patients and surgical patients. A Mann-Whitney rank sum test was used to test for differences between the non-surgical and surgical patients. Statistical p-values less than 0.05 were considered significant. Statistical computations were run on SigmaStat 2.0 (Jandel Scientific, San Rafael, CA) software, and graphs generated using SigmaPlot 4.0 (Jandel Scientific) software. Ⅲ. Results <Figure - 2> A reconstructed phase space in non-surgical PD group It represents the dynamic behavior of one PD voice signal with no surgery showing aperiodic voice signal which looks irregular and chaotic not closed trajectory in phase space <Table-4> shows mean percent jitter, shimmer, SNR, and D 2 values of sustained and running vowel segments for the non-surgical and surgical groups. <Figure-4 > through <Figure-7> displays boxplots of percent jitter, shimmer, SNR and D 2 values from sustained and running vowel segments for each group. <Table-4> Mean (SD) values of percent jitter, percent shimmer, SNR, and D2 for vowels from sustained phonation and running speech between the non-surgical and surgical PD groups <Figure - 3> The curves D2 vs. r from the same surgical patient as shown in <Figure - 1> The slopes of the D2 vs. r curves approach ± in the indicated scaling region, which is the estimated D2 of the voice signal Sustained vowel Running vowel Percent jitter Percent shimmer SNR Non -surgical group (±0.318) (±3.169) (±5.165) D 2 (±0.772) Percent jitter (±0.509) Percent shimmer (±4.197) SNR (±3.758) D 2 (±0.990) Surgical group (±0.433) (±3.550) (±4.875) (±0.828) (±0.743) (±4.274) (±3.385) (±1.340) p-value <

8 Korean Journal of Communication Disorders 2012;17: <Figure - 4> Percent Jitter for the non-surgical and surgical group with sustained and running vowels <Figure - 5> Percent Shimmer for the non-surgical and surgical group with sustained and running vowels <Figure - 6> SNR for the non-surgical and surgical group with sustained and running vowels <Figure - 7> D2 for the non-surgical and surgical group with sustained and running vowels For sustained vowels, the mean percent jitter and shimmer values were and respectively for the non-surgical and surgical group and and respectively for the surgical group. As shown in <Table-4>, mean percent jitter and shimmer were higher in the surgical group than non-surgical group, but this difference was not significant (p =.1741, p =.7393). For running vowels, the mean percent jitter and shimmer values were and respectively for the non-surgical group and and respectively for the surgical group. As with sustained vowels, percent jitter and shimmer were higher in the surgical group than nonsurgical group, but this difference was not significant (p =.2688, p =.3741). For sustained vowels, mean SNR values were for the non-surgical and surgical groups were and respectively. For running vowels, the mean of SNR values for the non-surgical and surgical group were and respectively. Mean SNR values were neither significantly lower for sustained vowels (p =.4253) nor significantly higher for running vowels in the surgical group (p =.1291). For sustained vowels, mean D 2 values for the nonsurgical and surgical groups were and respectively. The mean D 2 value of the surgical group was significantly lower than the mean D 2 value of the non-surgical group (p <.0001). For running vowels, mean D 2 values for the non-surgical and surgical groups were and respectively. As with sustained vowels, the mean D 2 value of the surgical group was significantly lower than the mean D 2 value of the non-surgical group (p <.0002). IV. Discussion and Conclusion The current study attempted to extend the measures vowels from sustained phonation to running speech 150

9 Choi / Effects of Deep Brain Stimulation (DBS) on Speech and Voice in Parkinson s Disease to explore the effect of DBS on treatment of PD speech and voice with acoustic measures under levodopa off condition with advanced PD patients who exhibited more than Hoehn & Yahr stage Ⅲ. The symptoms of speech and voice dysfunction in PD (hypokinetic dysarthria) are weak voice, variable speech rate, short rushes of speech, imprecise consonants, breathy and harsh voice, and monotonous pitch. Effects of STN-DBS on speech and voice motor function are less well defined and have been reported either as variable (Dromey et al., 2000; Hoffman et al., 2001; Gentil et al., 2003; Murdoch, 2010) or as an adverse side effect of the stimulation (Deuschl et al., 2006). Farrell et al. (2005) found that neurosurgical intervention including the procedures of pallidotomy, thalamotomy, and deep-brain stimulation (DBS) did not significantly change the 22 surgical participants perceptual voice and speech dimensions including reduced vocal intensity, reduced vocal pitch, monopitch, monoloudness, imprecise articulation, and oromotor function despite significant postoperative improvements in ratings of general motor function and disease severity. In addition, Dromey et al. (2000) measured the acoustic recordings and neurologic assessments with 7 PD patients who were implanted with deep brain stimulators and found significant improvements in limb motor performance when the subthalamic nucleus was stimulated following surgery. Although there was small, significant increases in sound pressure level and fundamental frequency variability in response to stimulation in the medication-on condition while no significant speech changes were found. Another study revealed that reaction and movement time of the articulatory organs decreased and their maximal strength and articulatory precision as well as voice function significantly improved (Gentil et al., 2003). Most recently, a preliminary study for measuring DBS effect on voice and speech with 6PD demonstrated only 2PD with DBS improved percent jitter, shimmer following stimulation on while most PD with DBS (4PD) became worse by increasing percent jitter and shimmer values and represented variable outcomes in speech intelligibility with vowel space area and smaller formant transitions, reflecting poorer perceived speech (Dromey & Bjarnason, 2011). Recently, most of the aperiodic voice signals and severe dysphonia as well as periodic voice signals so far have been successfully quantified with nonlinear dynamic approach. Nonlinear dynamic methods, including reconstructed phase space and correlation dimension (D 2 ), have been considered as new acoustic methods to describe aperiodic and chaotic activities and can predict period-doublings, bifurcations, deterministic chaotic or nonlinear dynamic system rather than stochastic chaos (Titze et al., 1993; Zhang et al., 2005a; 2005b ; Zhang, Jiang & Rahn, 2005). Typically, sustained vowels are much more commonly used in acoustic measures because they can be obtained in a more easily controlled environment, reducing variances in acoustic parameters. Furthermore, sustained vowels do not vary with dialect, intonation, and articulation of the speaker, which may affect the acoustic results (Zhang & Jiang, 2008). Running speech, however, exhibits the dynamic, natural phonation characteristics of everyday speech whereas sustained vowels are more characteristic of singing (Klingholtz, 1990; Parsa & Jamieson, 2001). In addition, running speech has variations in pitch and loudness, which are important properties when assessing the effectiveness of treatments on PD voice and speech (Askenfelt & Hammarberg, 1986). The present study showed mean D 2 value of the surgical group was significantly lower than the mean D 2 value of the non-surgical group for both sustained and running vowels, indicating an improvement in sustained phonation and running speech with DBS. Our initial study has reported aperiodicity improvement in sustained vowel phonation in PD patients with DBS (Lee et al., 2008). Many PD vocal samples in this study have type 2 signals containing subharmonics or even type 3 signals, making the D 2 results more reliable and nonlinear dynamic method may provide measurable improvement in patients with severe vocal impairment. For sustained phonations, the improvement in D 2 may be associated with a decrease in vocal fold rigidity and stiffness, a common vocal symptom of 151

10 Korean Journal of Communication Disorders 2012;17: PD. The contribution of current study is an analogous finding for running speech. As a result, the improvement in running speech in PD patients with DBS found in this study may serve as a useful starting point for further studies on the investigation of the effects of DBS on PD speech. In the present study, perturbation results fail to achieve significance with DBS, contradicting the results of nonlinear dynamic analysis. Previous studies have shown that nonlinear dynamic analysis may be more reliable because of the aperiodicity associated with PD voice and speech (Choi, 2011; Rahn et al., 2007). In addition, analysis of running speech is more challenging for acoustic analysis in general but poses additional difficulties for acoustic perturbation analysis. Perturbation measures may not be able to discriminate between variations inherent in running speech and variations associated with PD. Furthermore, running vowels have very short signal lengths. As a result, running vowel segments may not contain the requisite number of cycles for stable and convergent perturbation measures. Correlation dimension (D 2 ), however, is reliable for the shorter signal length and higher noise levels characteristic of running speech and severe dysphonic voice (Zhang & Jiang, 2008). Although a few studies have applied nonlinear dynamic analysis to running speech, this study goes one step further by using nonlinear dynamic analysis to evaluate treatment effects on running speech. The current study may not address the specific speech characteristics of common hypokinetic PD speech dimensions. However, the perturbation and nonlinear dynamic analysis using vowels from the running speech in addition to sustained phonation might be a new attempt to reflect the various speech characteristics including intonation and articulation of PD speaker rather than PD speech itself. There were some limitations in this study. First, although carefully selected to be as consistent as possible, the non-surgical group was composed of different individuals (in terms of years since onset). However, there were no differences between two groups in other parameters including age, H & Y stage, and UPDRS. Second, the small sample size might be also limited the conclusions of this study. Third, the sides of STN in surgical group were heterogeneous (e.g., left, right, bilateral). Future study could investigate the effects of DBS treatment regarding this factor. In addition, the evaluation of running speech should be viewed as a complement to rather than substitute for the evaluation of sustained phonation. Nevertheless, the findings of this study show nonlinear dynamic analysis may be useful substitute for perturbation analysis in the evaluation of running speech because of the short signal length and high noise level. The current study extends the use of nonlinear dynamic analysis of running speech to the effects of DBS on PD voice and speech. Therefore, this indicates the possibility of clinical application of running speech as well as sustained vowels based on nonlinear dynamic methods in investigating treatment effects. This study was supported in part by the Catholic University of Daegu and Research Institute of Biomimetic Sensory Control and the author would like to thank Jack J. Jiang MD. PhD to support this research in laryngeal physiology lab, Department of Surgery, Division of Otolaryngology, University of Wisconsin-Madison. REFERENCES Askenfelt A. G., & Hammarberg, B. (1986). Speech waveform perturbation analysis: A perceptual-acoustical comparison of seven measures. Journal of Speech and Hearing Research, 29(1), Awan, S. N., Roy, N., & Jiang, J. J. (2010). Nonlinear dynamic analysis of disordered voice: The relationship between the correlation dimension (D 2) and pre-/post-treatment change in perceived dysphonia severity. Journal of Voice, 24(3), Benabid, A. L. (2003). Deep brain stimulation for Parkinson s disease. Current Opinion in Neurobiology, 13(6), Blumin, J. H., Pcolinsky, D. E., & Atkins, J. P. (2004). Laryngeal findings in advanced Parkinson s disease. Annal Otolaryngology Rhinology Laryngology, 113(4), Burchiel, K. J., Anderson, V. C. Favre, J., & Hammerstad, J. P. (1999). Comparison of pallidal and subthalamic nucleus deep brain stimulation for advanced Parkinson s disease: Results of a randomized, blinded pilot study. Neurosurgery, 45(6),

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13 최성희 / 파킨슨씨병환자의뇌심부자극술에대한말음성효과 파킨슨씨병환자의뇌심부자극술에대한말음성효과 : 섭동적분석과비선형역동적분석을이용한연장발성과연속발화모음의음향학적분석 최성희 대구가톨릭대학교의료과학대학언어청각치료학과, 생체모방감각제어연구소 교신저자 최성희대구가톨릭대학교의료과학대학언어청각치료학과교수경산북도경산시하양읍금곡리 5 번지 shgrace@cu.ac.kr tel.: 배경및목적 : 시상이나기저핵의뇌심부자극술은증상이중심도로진행된파킨슨씨병환자의가장안정되고장기간효과를가지는신경외과치료방법중하나로간주되고있다. 하지만, 말과음성개선에대한뇌심부자극술의효과는연구마다일치하지않거나역효과가보고되기도하였다. 본연구는연장발성과연속발화의모음을이용하여전통적인섭동적분석과비선형역동적분석을통해뇌심부자극술에대한말음성의개선효과를조사하는데목적을두고있다. 방법 : 3~5 H & Y 단계에있는뇌심부자극술 - 시상핵자극을받은 19 명의파킨슨씨병환자와뇌심부자극술 - 시상핵자극을받지않은 10 명의파킨슨씨병환자를각각치료군과통제군으로할당하였다. 파킨슨씨병환자들은모두음성과발화를녹음하기전밤사이 12 시간동안약을복용하지않았고, 시상핵에뇌심부자극술을받은환자군은최소한 12 시간동안자극을받았고, 30 분동안휴지기를가졌다. 뇌심부자극술을받지않은통제군과뇌심부자극술을받은환자군으로연장발성과연속발화에서모음을채취하여 percent jitter, shimmer, SNR 과비선형역동적분석인 D 2 값을얻었고통계학적으로분석되었다. 결과 : 뇌심부자극술을받은파킨슨씨병환자군은통제군에비해모음연장발성과연속발화에서모두유의미하게낮은 D 2 값을보였으나 (p < 0.001). 섭동적분석에서는모음연장발성과연속발화의모음에서 percent jitter, shimmer, SNR 가모두뇌심부자극술후개선을보이지않았다. 논의및결론 : 비선형역동적분석은뇌심부자극술의말음성개선치료효과를보여주었다. 게다가, 연속발화는짧은음성신호길이와높은소음치를가지기때문에연속발화를평가할때, 비선형역동적분석은섭동적분석방법을대치할수있는음향학적측정방법임을제시하였다. 이러한결과들은비선형역동적분석이중심도로질병이진행된파킨슨씨병환자의말음성에대한치료효과를평가하는데유용하게사용될수있음을보여주었다. 언어청각장애연구, 2012;17: 핵심어 : 뇌심부자극술, 파킨슨씨병, 모음연장발성, 연속발화, 섭동적분석, 비선형역동적분석 * 본연구는부분적으로대구가톨릭대학교와생체모방감각제어연구소의연구지원으로수행되었음. 게재신청일 : 2012 년 1 월 19 일 최종수정일 : 2012 년 2 월 29 일 게재확정일 : 2012 년 3 월 7 일 c 2012 한국언어청각임상학회 155