Aerodynamic measurements of patients with parkinson''s disease

Patients with Parkinson's disease commonly complain of voice dysfunction. Most of these complaints can be attributed to the known muscular control disorders that occur with Parkinson's disease. However, the manifestations of Parkinson's disease muscular dysfunction on parameters of phonation such as airflow, laryngeal resistance, and subglottal pressure necessary to sustain phonation have not been reported. The purpose of this study was to examine the aerodynamic characteristics of flow, laryngeal resistance, and phonation pressure threshold in a heterogeneous population of patients with Parkinson's disease who had varying voice complaints and to compare the data to similar studies for human subjects who have no voice complaints. The studies used a noninvasive method of detecting flow and acoustic signal from the lips, oral cavity and nose during phonation and used an external flow interruption technique to estimate subglottal pressure and phonation threshold pressure. About one third of the patients could not produce phonation at regular and loud intensities that were comfortable for normal subjects. The mean subglottal pressure (SGP) of patients with Parkinson disease who could produce 3 levels of intensity comparable to normal subjects was significantly higher than the mean SG-Ps for normal subjects for the same intensities of vocal production. The mean flow rates measured from patients with Parkinson's disease at the same 3 intensities of phonation was not significantly greater than in normal subjects. This indicated that the mean laryngeal resistance calculated for patients with Parkinson's disease was notably and significantly greater than mean laryngeal resistance calculated for normal subjects at the same intensity levels. The mean vocal efficiency (VE) for normal subjects was not significantly different than the mean VE for patients with Parkinson's disease, because greater pressure was used to generate similar flow and acoustic energy. These findings correlate with the perception of patients with Parkinson's disease that they are working harder to produce phonation. The observation of notably greater laryngeal resistance and phonation threshold pressure in patients with Parkinson's disease suggests that further studies of the glottic aperture in patients with Parkinson' disease may be useful for understanding how this common motor disorder disturbs phonation.     

Pressure-flow relationships during phonation in the canine larynx

Measurements of air pressure and flow were made using an in vivo canine model of the larynx. Subglottic pressures at varying flow rates were taken during phonation induced by laryngeal nerve stimulation. Results showed that during constant vocal fold stiffness, subglottic pressure rose slightly with increased air flow. The larynx in the in vivo canine model exhibited a flow-dependent decrease in laryngeal airway resistance. Increasing flow rate was associated with an increase in frequency of phonation and open quotient, as measured glottographically. Results from this experiment were compared with a theoretical two-mass model of the larynx and other theoretical models of phonation. The influence of aerodynamic forces on glottal vibration is explained by increased lateral excursion of the vocal folds during the open interval and shortening of the closed interval during the glottal cycle.     

A lumped mucosal wave model of the vocal folds revisited: recent extensions and oscillation hysteresis

This paper examines an updated version of a lumped mucosal wave model of the vocal fold oscillation during phonation. Threshold values of the subglottal pressure and the mean (DC) glottal airflow for the oscillation onset are determined. Depending on the nonlinear characteristics of the model, an oscillation hysteresis phenomenon may occur, with different values for the oscillation onset and offset threshold. The threshold values depend on the oscillation frequency, but the occurrence of the hysteresis is independent of it. The results are tested against pressure data collected from a mechanical replica of the vocal folds, and oral airflow data collected from speakers producing intervocalic /h/. In the human speech data, observed differences between voice onset and offset may be attributed to variations in voice pitch, with a very small or inexistent hysteresis phenomenon.     

Vocal intensity in speakers and singers.

Vocal intensity is studied as a function of fundamental frequency and lung pressure. A combination of analytical and empirical models is used to predict sound pressure levels from glottal waveforms of five professional tenors and twenty five normal control subjects. The glottal waveforms were obtained by inverse filtering the mouth flow. Empirical models describe features of the glottal flow waveform (peak flow, peak flow derivative, open quotient, and speed quotient) in terms of lung pressure and phonation threshold pressure, a key variable that incorporates the Fo dependence of many of the features of the glottal flow. The analytical model describes the contributions to sound pressure levels SPL by the vocal tract. Results show that SPL increases with Fo at a rate of 8-9 dB/octave provided that lung pressure is raised proportional to phonation threshold pressure. The SPL also increases at a rate of 8-9 dB per doubling of excess pressure over threshold, a new quantity that assumes considerable importance in vocal intensity calculations. For the same excess pressure over threshold, the professional tenors produced 10-12 dB greater intensity than the male nonsingers, primarily because their peak airflow was much higher for the same pressure. A simple set of rules is devised for predicting SPL from source waveforms.     

Effects of consonant manner and vowel height on intraoral pressure and articulatory contact at voicing offset and onset for voiceless obstruents

In obstruent consonants, a major constriction in the upper vocal tract yields an increase in intraoral pressure (P(io)). Phonation requires that subglottal pressure (P(sub)) exceed P(io) by a threshold value, so as the transglottal pressure reaches the threshold, phonation will cease. This work investigates how P(io) levels at phonation offset and onset vary before and after different German voiceless obstruents (stop, fricative, affricates, clusters), and with following high vs low vowels. Articulatory contacts, measured using electropalatography, were recorded simultaneously with P(io) to clarify how supraglottal constrictions affect P(io). Effects of consonant type on phonation thresholds could be explained mainly in terms of the magnitude and timing of vocal-fold abduction. Phonation offset occurred at lower values of P(io) before fricative-initial sequences than stop-initial sequences, and onset occurred at higher levels of P(io) following the unaspirated stops of clusters compared to fricatives, affricates, and aspirated stops. The vowel effects were somewhat surprising: High vowels had an inhibitory effect at voicing offset (phonation ceasing at lower values of P(io)) in short-duration consonant sequences, but a facilitating effect on phonation onset that was consistent across consonantal contexts. The vowel influences appear to reflect a combination of vocal-fold characteristics and vocal-tract impedance.     

Glottal flow through a two-mass model: comparison of Navier-Stokes solutions with simplified models

A new numerical model of the vocal folds is presented based on the well-known two-mass models of the vocal folds. The two-mass model is coupled to a model of glottal airflow based on the incompressible Navier-Stokes equations. Glottal waves are produced using different initial glottal gaps and different subglottal pressures. Fundamental frequency, glottal peak flow, and closed phase of the glottal waves have been compared with values known from the literature. The phonation threshold pressure was determined for different initial glottal gaps. The phonation threshold pressure obtained using the flow model with Navier-Stokes equations corresponds better to values determined in normal phonation than the phonation threshold pressure obtained using the flow model based on the Bernoulli equation. Using the Navier-Stokes equations, an increase of the subglottal pressure causes the fundamental frequency and the glottal peak flow to increase, whereas the fundamental frequency in the Bernoulli-based model does not change with increasing pressure.     

An evaluation of the effects of three laryngeal lubricants on phonation threshold pressure (PTP)

Clinicians frequently offer advice to performers and voice-disordered patients aimed ostensibly to manipulate the water content and/or viscosity of the mucus blanket covering the vocal folds. To evaluate the relative effects of three potential laryngeal lubricants on phonatory function (ie, water, Mannitol--an osmotic agent, and Entertainer's Secret Throat Relief (Kli Corp., Carmel, IN)--a glycerin-based product), phonation threshold pressure (PTP) was measured in 18 healthy, vocally normal female participants twice before (baseline) and then four times after 2 ml of each substance were nebulized. PTP is the minimum subglottal pressure required to initiate vocal fold oscillation, and the lowering of PTP is assumed to correspond to physiologically more efficient phonation and reduced phonatory effort. Over a 3-week period, participants were tested on three separate occasions (at 1-week intervals). On each occasion, a different nebulized treatment was administered. PTP for both comfortable and high fundamental frequency productions was measured using an oral pressure-flow system (Perci-Sars, MicroTronics Corp., Chapel Hill, NC). Analysis of the results revealed that Mannitol, an agent that encourages osmotic water flux to the luminal airway surface, lowered PTP immediately after its administration (ie, p = 0.071, for high-pitched productions only). However, the duration of its PTP lowering effect was less than 20 minutes. The other two substances did not demonstrate any significant postadministration effect on PTP.     

Direct measurement of subglottic pressure and laryngealresistance in normal subjects and in spasmodic dysphonia

This study tested the accuracy of indirect methods of measurementof laryngeal airway resistance in normal subjects and in spasmodic dysphonia (SD). The indirect method assumes that subglottic air pressure remains constant during the voiced segment of a syllable. In this study subglottic air pressure was directly measured via puncture of the cricothyroid membrane in seven normal subjects and seven subjects with SD. The true laryngeal airway resistance was calculated and compared with airway resistance measured using indirect techniques based on intraoral air pressure. In five of the seven normal subjects, subglottic air pressure did not remain constant during the voiced segment. As a result, the error produced using indirect method of calculating average laryngeal resistance for the normal subjects varied from −44% to +50%. For SD subjects the error ranged from −49% to +22%. In general, the indirect technique over-estimated laryngeal airway resistance in normal subjects and underestimated the resistance in subjects with SD.     

Fundamental Frequency Change During Offset and Onset of Voicing in Individuals with Parkinson Disease

SUMMARY: After years of treatment with the medication levodopa, most individuals with Parkinson disease (PD) experience fluctuations in response to their medications. Although relatively consistent perceptual voice improvements have been documented to correspond with these fluctuations, consistent quantitative data to support this finding are lacking. This mismatch may have occurred because most of this phonation research has centered on long-term phonatory measures (ie, across speaking samples and prolonged vowel tasks). The current study examined short-term phonatory behavior in individuals with PD, specifically examining fundamental frequency (F0) at the offset and onset of phonation, before and after a voiceless consonant. The F0 analysis at phonatory offset supported the conclusion that individuals with PD have difficulty with the rapid offset of voicing, and that they are stopping vocal fold vibration primarily through vocal fold abduction (without adding tension). The F0 analysis at phonatory onset revealed that all groups use some laryngeal tension at the initiation of voicing. The tension was lowest for the PD participants who were in their OFF medication state, and it was highest for the age-matched control participants and the PD participants in their ON medication states.     

Multidimensional analyses of voicing offsets and onsets in female speakers

This study investigates cross-speaker differences in the factors that predict voicing thresholds during abduction-adduction gestures in six normal women. Measures of baseline airflow, pulse amplitude, subglottal pressure, and fundamental frequency were made at voicing offset and onset during intervocalic /h/, produced in varying vowel environments and at different loudness levels, and subjected to relational analyses to determine which factors were most strongly related to the timing of voicing cessation or initiation. The data indicate that (a) all speakers showed differences between voicing offsets and onsets, but the degree of this effect varied across speakers; (b) loudness and vowel environment have speaker-specific effects on the likelihood of devoicing during /h/; and (c) baseline flow measures significantly predicted times of voicing offset and onset in all participants, but other variables contributing to voice timing differed across speakers. Overall, the results suggest that individual speakers have unique methods of achieving phonatory goals during running speech. These data contribute to the literature on individual differences in laryngeal function, and serve as a means of evaluating how well laryngeal models can reproduce the range of voicing behavior used by speakers during running speech tasks.     

Control of static pressure by expiratory muscles during expiratory effort and phonation

Surface electromyography (EMG) impulse frequency was measured in six subjects at eight recording sites on the chest and abdomen during the maintenance of positive mouth pressures and the phonation of a long vowel ([a:] in the Finnish word aamu) at three intensity levels. The pattern of muscle activation was similar in these two behavioral tasks. In upright posture, at lung volumes from 20% vital capacity (VC) below to 30% above functional residual capacity (FRC), EMG frequency increased rather linearly with increasing mouth pressure within 0 and 20 cm H₂O. A qualitatively similar relationship was observed between EMG frequency and phonation intensity. The results suggest that the expiratory effort task can be used as a model for the control of subglottal pressure during phonation at static subglottal pressures     

Data on subglottal pressure and SPL at varied vocalloudness and pitch in 8- to 11-year-old children

Phonation threshold pressure has been defined as the minimum subglottalpressure to generate phonation. Previous research has indicated that children may habitually employ higher subglottal pressures than adults. In the present investigation sound pressure level (SPL) and subglottal pressures at different pitch levels were measured at and above phonation threshold in nine children. Phonation threshold values were scattered in reasonable agreement with Titzes' prediction, although a discrepancy was noted regarding the frequency dependence in some voices. At normal conversational loudness and loudest level of phonation the children's PS values were between two to four and four to eight times the predicted threshold values, respectively. At normal conversational loudness and habitual pitch subglottal pressures were lower than those previously observed for children, but similar to those found for female adults. The SPL in softest and loudest phonation were somewhat lower as compared to previous phonetogram data for children and for female adults. At normal loudness and habitual pitch the SPL values were similar to those of female adults. For a doubling of P_s mean SPL increased by 10.5 dB on the average.     

Neuromuscular control of fundamental frequency and glottal posture at phonation onset

The laryngeal neuromuscular mechanisms for modulating glottal posture and fundamental frequency are of interest in understanding normal laryngeal physiology and treating vocal pathology. The intrinsic laryngeal muscles in an in vivo canine model were electrically activated in a graded fashion to investigate their effects on onset frequency, phonation onset pressure, vocal fold strain, and glottal distance at the vocal processes. Muscle activation plots for these laryngeal parameters were evaluated for the interaction of following pairs of muscle activation conditions: (1) cricothyroid (CT) versus all laryngeal adductors (TA/LCA/IA), (2) CT versus LCA/IA, (3) CT versus thyroarytenoid (TA) and, (4) TA versus LCA/IA (LCA: lateral cricoarytenoid muscle, IA: interarytenoid). Increases in onset frequency and strain were primarily affected by CT activation. Onset pressure correlated with activation of all adductors in activation condition 1, but primarily with CT activation in conditions 2 and 3. TA and CT were antagonistic for strain. LCA/IA activation primarily closed the cartilaginous glottis while TA activation closed the mid-membranous glottis.     

Vocal loudness and frequency capabilities of the voice

A phonetogram is a graph showing the sound pressure level (SPL) of softest and loudest phonation over the entire fundamental frequency range of a voice. A physiological interpretation of a phonetogram is facilitated if the SPL is measured with a flat frequency curve and if the vowel /a/ is used. It was found that in soft phonation, the SPL is mainly dependent on the amplitude of the fundamental, while in loud phonation, the SPL is mainly determined by overtones. The short-term SPL variation, i.e., the level variation within a tone, was about 5 dB in soft phonation and close to 2 dB in loud phonation. For two normal voices the long-term SPL variation, calculated as the mean standard deviation of SPL for day-to-day variation, was found to be between 2.4 and 3.4 dB in soft and loud phonation. Speakers who raise their loudness of phonation also tend to raise their mean voice fundamental frequency. Measures obtained from speaking at various voice levels were combined so that typical pathways could be introduced into the phonetogram. The average slope of these pathways was 0.3–0.5 st/dB for healthy subjects. Averaged phonetograms for male singers and male nonsingers did not differ significantly, but averaged phonetograms for female singers and female nonsingers did, in that the upper contour was higher for the female singers. Averaged phonetograms for female patients with non-organic dysphonia showed significantly lower SPL values in loudest phonation as compared to healthy female subjects, while no corresponding difference was seen for males in this regard. With respect to the SPL values for softest phonation, male dysphonic patients showed significantly higher SPL values than healthy male subjects, while no corresponding difference was seen in female subjects. The subglottal pressure mirrored these phonetogram differences between healthy and pathological voices. The averaged phonetograms of female patients after voice therapy showed an increased similarity with those of normal voices. For the male patients the averaged phonetogram did not change significantly after therapy.     

Reflex activation of laryngeal muscles by sudden induced subglottal pressure changes.

In measuring the effect of subglottal pressure changes on fundamental frequency (Fo) of phonation, the effects of changing laryngeal muscle activity must be eliminated. Several investigators have used a strategy in which pulsatile increases of subglottal pressure are induced by pushing on the chest or abdomen of a phonating subject. Fundamental frequency is then correlated with subglottal pressure changes during an interval before laryngeal response is assumed to occur. The present study was undertaken to repeat such an experiment while monitoring electromyographic (EMG) activity of some laryngeal muscles, to discover empirically the latency of the laryngeal response. The results showed a consistent response to each push, with a latency of about 30 ms. Despite this response, analyses of fundamental frequency versus subglottal pressure changes during the interval of constant EMG activity were in general agreement with previously published values. With respect to the nature of the electromyographic response itself, its timing was found to be within the range of latencies appropriate for peripheral feedback, and was also similar to that for an acoustically--or tactually--elicited startle reflex.     

Some effects of deafness on the generation of voice

Glottal volume-velocity waveform data were collected from twenty male and female hearing-impaired adolescents by means of a reflectionless tube. The subjects each provided samples of phonation in normal- and soft-voice modes and in a three-syllable word with primary stress on the medial syllable. Analysis of the data, in comparison with characteristics of phonation produced by normally hearing subjects, indicates that deafness affects primarily the time-varying characteristics of the glottal source. Among the hearing-impaired subjects, the following abnormalities were noted; diplophonia and creaky-voice episodes at the onset or middle of phonation, and irregular patterns of change in the frequency and intensity of the glottal waveform. For some subjects, the period-to-period changes of frequency and intensity may be greater than normal. For the hearing-impaired subjects, the shape of the isolated glottal pulse and its spectrum are similar or identical to normal, while striking abnormalities may be seen in the way the glottal pulse changes over time. The effect of deafness is thus that it may prevent a speaker from learning the phonatory consequences of the muscular gestures which maintain and alter vocal-fold tension and subglottal air pressure dynamically in the production of voice.     

Laryngeal closure pressure during phonation in humans.

We investigated the laryngeal closure pressure during sustained phonation in five healthy adult men with no pathological lesions in the glottis using a round pressure transducer with a diameter of 10 mm and a thickness of 1 mm. The transducer was placed between the vocal processes through the mouth. Subjects were asked to utter a sustained phonation of the vowel sound /eh/ at varying pitch and intensity in modal register. The laryngeal closure pressure ranged from 0 to 200 cmH2O. At a comfortable pitch and intensity, the pressure was below 50 cmH2O. The pressure was correlated with pitch, but not with intensity.     

Stroboscopic and acoustic measures of inspiratory phonation

Inspiratory phonation (IP) is the production of voice as air is taken into the lungs. Although IP is promoted as a laryngeal assessment and voice treatment technique, it has been described quantitatively in very few speakers. This study quantified changes in laryngeal adduction, fundamental frequency, and intensity during IP relative to expiratory phonation (EP). We hypothesized that IP would increase laryngeal abduction and fundamental frequency. The experiment was a within-subjects, repeated measures design with each subject serving as her own control. Participants were 10 females (ages 19-50 years) who underwent simultaneous transoral videostrobolaryngoscopy and acoustic voice recording. We found that membranous vocal fold contact decreased significantly during IP relative to EP, while the trends for change of ventricular fold squeeze during IP varied across individuals. Vocal fundamental frequency increased significantly during IP relative to EP, but intensity did not vary consistently across conditions. Without teaching or coaching, changes that occurred during IP did not carry over to EP produced immediately following IP within the same respiratory cycle.     

Significance of mechanoreceptors in the subglottal mucosa for subglottal pressure control in singers

According to Wyke and Kirchner (Wyke B, Kirchner J. Neurology of the larynx. In: Hinchcliffe R, Harrison D, eds. Scientific foundation of otolaryngology. London: William Heinemann Medical Books, 1976:546–66) mechanoreceptors in the subglottal mucosa play a significant role in the control of laryngeal muscle activity in response to changes of subglottal pressure during phonation. In singers this pressure is adapted not only to phonatory loudness but also to fundamental frequency. By spraying Xylocaine solution with a needle inserted into the trachea through the anterior gap between the cricoid and thyroid cartilages, the subglottal mucosa was anesthetized in three singers. The effects on subglottal pressure and fundamental frequency of this anesthesia were examined. The pressure effects varied between the subjects, whereas the fundamental frequency accuracy was adversely affected in all three subjects. The implications of these findings are discussed.