The aging voice: a review, treatment data and familial and genetic perspectives.

This paper will provide a review of aspects of vocal aging within the context of general body aging and describe two data sets related to the aging voice. Data will be presented which document pre- to posttreatment improvement in select voice characteristics (sound pressure level, subglottal air pressure, thyroarytenoid laryngeal muscle activity and voice quality) following application of an intensive voice treatment program (the LSVT) to 3 individuals with aged voice. Additionally, physiological data (forced expiratory volume, visual accommodation, bone density, taste discrimination, white blood count and resting heart rate) and select perceptual (perceived age) and acoustic measures (reflecting both cycle-to-cycle and longer-term intensity and frequency stability) from 67 subjects will be reviewed from the work of Gray and colleagues to document the differential impact of the global aging process across organ systems including the aging voice.

The effect of cricothyroid muscle action on the relation between subglottal pressure and fundamental frequency in an in vivo canine model.

The relation between subglottal pressure (Ps) and fundamental frequency (F0) in phonation was investigated with an in vivo canine model. Direct muscle stimulation was used in addition to brain stimulation. This allowed the Ps-F0 slope to be quantified in terms of cricothyroid muscle activity. Results showed that, for ranges of 0-2 mA constant current stimulation of the cricothyroid muscle, the Ps-F0 slope ranged from 10 Hz/kPa to 60 Hz/kPa. These results were compared to similar slopes obtained in a previous study on excised larynges in which the vocal fold length was varied instead of cricothyroid activation. A physical interpretation of the Ps-F0 slope is that the amplitude-to-length ratio of the vocal folds decreases with CT activity, resulting in a smaller time-varying stiffness. In other words, there is less dependence of F0 on amplitude of vibration when the vocal folds are long instead of short.

Control of vocal loudness in young and old adults.

This study examined the effect of aging on respiratory and laryngeal mechanisms involved in vocal loudness control. Simultaneous measures of subglottal pressure and electromyographic (EMG) activity from the thyroarytenoid (TA), lateral cricoarytenoid (LCA), and cricothyroid (CT) muscles were investigated in young and old individuals while they attempted to phonate at three loudness levels, "soft," "comfortable," and "loud." Voice sound pressure level (SPL) and fundamental frequency (F ) measures were also obtained. Across loudness conditions, subglottal pressure levels were similar for both age groups. Laryngeal EMG measures tended to be lower and more variable for old compared with young individuals. These differences were most apparent for the TA muscle. Finally, across the three loudness conditions, the old individuals generated SPLs that were lower overall than those produced by the young individuals but modulated loudness levels in a manner similar to that of the young subjects. These findings suggest that the laryngeal mechanism may be more affected than the respiratory system in these old individuals and that these changes may affect vocal loudness levels.

Response of the cricothyroid and thyroarytenoid muscles to stereotactic injection of substance P into the region of the nucleus tractus solitarius in developing dogs.

Substance P (SP), a putative sensory neurotransmitter, mediates reflex laryngeal adductor activity in developing dogs. Such reflex activity includes life-threatening laryngospasm induced by stimulation of distal esophageal afferent nerves. The site of SP's activity is unknown. This research was undertaken to determine whether injection of SP into the nucleus tractus solitarius (NTS) of developing beagles alters laryngeal adductor motor activity. Six animals, 57 to 78 days of age, underwent stereotactic injection of 5 to 10 microL of SP into the region of the NTS, identified by electrical stimulation of the ipsilateral superior laryngeal nerve. In 8 additional studies, SP was injected into the cerebellum (2) or brain stem (6) distant from the NTS. Cardiovascular and electromyographic (EMG) responses of the diaphragm and the cricothyroid (CT) and/or thyroarytenoid (TA) muscles were recorded in all 6 animals. Injection of SP into the region of the NTS induced a decrease in blood pressure in all animals and an increase in either ipsilateral CT or TA activity. Three of these animals experienced mixed apnea characterized by sustained EMG activity (spasm) of the ipsilateral CT or TA muscles and an absence of diaphragm EMG activity. The apnea event was fatal in 1 of these animals. In the 6 animals who underwent injections in the brain stem but outside the region of the NTS, diaphragm and laryngeal EMG activity generally did not change after injection of SP, with the exception of 1 animal who experienced a mild, short-lived increase in ipsilateral CT activity. A brief phasic increase in ipsilateral CT activity was seen in both animals who underwent injection of SP into the cerebellum. A putative sensory neurotransmitter, SP evokes ipsilateral CT and/or TA EMG activity when injected into the region of the NTS in developing beagle dogs. This research suggests that SP in the NTS may play a role in mediating life-threatening laryngeal adductor reflexes in developing mammals and may provide important information regarding therapeutic intervention.

Quantitative analysis of the anatomy of the epineurium of the canine recurrent laryngeal nerve.

The purpose of this investigation was to determine the amount of epineurium surrounding the recurrent laryngeal nerve (RLN) compared with a limb nerve, that to flexor hallicus longus (NFHL). Nerve samples were obtained from 10 adult dogs and studied using scanning electron microscopy and light microscopy to measure the relative proportion of epineurium and the relative proportions of adipose and collagenous tissue comprising the epineurium in both nerves. Significantly greater relative epineurial cross-sectional areas and adipose content were found in the RLN than in the NFHL. Based on observations on noncranial peripheral nerves, the findings indicate that the RLN is better protected against deformational forces associated with compression than stretching forces. The RLN may not be structured well for successful reinnervation after injury. The patterns observed for adipose tissue in RLN epineurial tissue appeared unique compared with those previously reported in peripheral nerves. The primary role associated with adipose tissue is to 'package' the nerve for protection. The RLN is considered to be a vital nerve in the body, as are other cranial nerves. The large proportions of adipose tissue in the epineurium may relate to the importance of protecting this nerve from injury.

Strength, endurance, and stability of the tongue and hand in Parkinson disease.

Weakness and fatigue in the orofacial system often are presumed to contribute to the dysarthria associated with neuromotor disorders, although previous research findings are equivocal. In this study, tongue strength, endurance, and stability during a sustained submaximal effort were assessed in 16 persons with mild to severe Parkinson disease (PD) and a perceptible speech disorder. The same measures were taken from one hand for comparison. Only tongue endurance was found to be significantly lower in these participants than in neurologically normal control participants matched for sex, age, weight, and height. Analyses of data from a larger sample comprising the present and retrospective data revealed lower-than-normal tongue strength and endurance in participants with PD. No significant correlations were found between tongue strength and endurance, interpause speech rate, articulatory precision, and overall speech defectiveness for the present and previously studied participants with PD, bringing into question the influence of modest degrees of tongue weakness and fatigue on perceptible speech deficits.

Modulations in respiratory and laryngeal activity associated with changes in vocal intensity during speech.

We tested the hypothesis that different strategies are used to alter tracheal pressure (Pt) during sustained and transient increases in intensity. It has been suggested that the respiratory system plays the primary role in Pt changes associated with alteration in overall intensity, whereas laryngeal adjustment is primary for transient change in Pt related to emphasis. Tracheal pressure, obtained via tracheal puncture, airflow (U), and laryngeal electromyography from the thyroarytenoid muscle (TA EMG) were collected from 6 subjects during sentence production at different intensity levels and with various stress patterns. Using a technique described in a previous study, we computed lower airway resistance (Rlaw) from measures of Pt and U obtained during a sudden change in upper airway resistance. We used this resistance value, together with direct measures of Pt and U during speech, to derive a time-varying measure of alveolar pressure (Pa), the pressure created by respiratory muscle activity and elastic recoil of the lungs. Pa provided a measure of respiratory drive that was unaffected by laryngeal activity. Laryngeal airway resistance (Rlx) and TA EMG provided measures of laryngeal activity. The results of this study indicated that, contrary to the outcome predicted by the hypothesis, there was no difference in the strategies used to alter Pt during sustained and transient increases in intensity. Although changes in both Pa and Rlx contributed to increase in Pt, the contribution of Pa was substantially greater. On average, Pa contributed to 94% and Rlx to 6% of the increase in Pt associated with vocal intensity. A secondary purpose of the study was to determine the extent to which laryngeal muscle activity was related to Rlx during speech. We found TA EMG activity increased with intensity but was not well correlated with Rlx, suggesting that when it contracts, the TA muscle may affect intensity by loosening the cover, which allows for greater amplitude of vocal fold vibration, without necessarily increasing laryngeal airway resistance.

Contributions of individual muscles to the submental surface electromyogram during swallowing.

Submental surface electromyographic recordings are commonly used in the investigation of swallowing disorders. The measured electromyography is thought to reflect the actions of floor-of-mouth muscles. Although this is a reasonable assumption, to date there have been no investigations to delineate which muscles contribute to this surface recording. The primary goal of this experiment was to determine which muscles contribute most to the submental surface. Electromyography was recorded simultaneously from the submental surface as well as from five individual muscles: mylohyoid, anterior belly of the digastric, geniohyoid, genioglossus and platysma. Three analysis methods were performed to estimate individual muscle contributions: correlation, numeric, and analytic. For the numeric and analytic analyses, a linear model was defined and used to represent the relationship between the surface and intramuscular recordings. Muscles that received a high correlation, numeric and/or analytic value were considered to be primary contributors to the submental recording. Regardless of analysis approach, the primary contributions to the submental surface recording were the mylohyoid, anterior belly of the digastric, and the geniohyoid muscles. Contributions from the genioglossus and the platysma muscles were minimal. Contributions as a function of bolus volume and viscosity are also discussed.

Estimation of alveolar pressure during speech using direct measures of tracheal pressure.

The pressure in the alveoli of the lungs, created by the elastic recoil of the lungs and respiratory muscle activity, is referred to as alveolar pressure (Pa). The extent to which tracheal pressure (Pt) approximates Pa depends on the resistance to airflow offered by structures above and below the point at which tracheal pressure is measured. An understanding of the relationship among Pa, Pt, and upper and lower airway resistance, and how these values fluctuate during speech, could aid in interpretation and modeling of speech aerodynamics. The purpose of this study was to (a) obtain values for lower airway resistance (Rlow), (b) use these Rlow values to estimate Pa during speech, and (c) quantify the degree to which Pt approximates Pa during production of voiced and voiceless sounds, in comparison to inhalation. In addition, the results were discussed in terms of the degree to which the respiratory system functions as a pressure source. Tracheal pressure (obtained with tracheal puncture) and airflow were measured during sentence production in 6 subjects. Using a technique introduced in this paper, Rlow was determined from measures of tracheal pressure and flow obtained during a sudden change in upper airway resistance because of release of a voiceless plosive. Mean Rlow values ranged from 0.14 to 0.32 kPa/(l/s). Each subject's mean Rlow was used to derive a time-varying measure of Pa during speech from continuous measures of tracheal pressure and airflow. Pt was approximately 95% of Pa during phonation (i.e., when the vocal folds were adducted), 75% of Pa during release of the voiceless stop consonant /p/, and 55% of Pa during inhalation (i.e., when the vocal folds were abducted). Therefore, the degree to which the respiratory system functioned as an ideal pressure source varied during speech. The ability to estimate Pa provides a measure of the pressure produced by the respiratory system that is not influenced by laryngeal activity.

Increased stability of airflow following botulinum toxin injection.

OBJECTIVES: The purpose of this study was to determine whether stability of airflow, as well as mean airflow, increased following botulinum toxin injection to laryngeal and extralaryngeal muscles in persons with spasmodic dysphonia (SD), some with associated vocal tremor (VT). STUDY DESIGN: Aerodynamic data were collected from five subjects before and at 2, 4, and 8 weeks after they received treatment by each of two different arms in an injection protocol in a crossover study. One arm of the protocol involved treatment of the thyroarytenoid muscles only. The other arm involved treatment of both the thyroarytenoid muscles and the strap muscles. METHODS: Measures of mean airflow and coefficient of variation (COV) of airflow during phonation were obtained. A decrease in the COV of airflow would indicate increased stability of phonatory airflow. RESULTS: Before treatment, all subjects with SD/VT exhibited mean airflows that were similar to controls. The COV of airflow ranged from normal to substantially elevated. Following botulinum injection, mean airflow characteristically increased and COV of airflow decreased. CONCLUSIONS: This finding suggests there is a change in the type, as well as the level, of activity in the muscles of speech production following botulinum toxin injection. The increase in airflow stability identified could be due to increased stability of the laryngeal system and possibly of the respiratory system as well.

Effect of intravenous calcitonin gene-related peptide antagonist on the laryngeal chemoreflex in piglets.

The laryngeal chemoreflex (LCR) is characterized by mixed apnea and cardiovascular instability and is elicited by applying water to the laryngeal mucosa of developing animals. The LCR may be fatal in very young animals, and the reflex has been postulated as a possible mechanism of sudden infant death syndrome. Several antagonists have been found to alter the severity of the LCR, but the primary neurotransmitters involved in mediating the reflex response are not yet well understood. This study investigates the effect, on the LCR, of the pharmacologic antagonism of calcitonin gene-related peptide (alphaCGRP), a neurochemical found in abundance in the mammalian laryngeal mucosa and its innervating system. The LCR was elicited in 10 mixed breed piglets, 17.7 days of age (12 to 22 days), before and during infusion of alphaCGRP 8-37, a pharmacologic inhibitor of alphaCGRP, and cardiorespiratory and laryngeal responses were compared. The duration of obstructive apnea decreased from 17.9 to 9. 8 seconds (P < 0.03) in the presence of alphaCGRP 8-37. Mean central apnea did not change for the group (P > 0.05), although it was completely inhibited in 2 animals. Cardiovascular changes were not significantly altered by the alphaCGRP inhibitor. alphaCGRP appears to play a regulatory role in the apneic response of the LCR, particularly its obstructive component, but not the cardiovascular response.

Discharge characteristics of laryngeal single motor units during phonation in young and older adults and in persons with parkinson disease.

Discharge characteristics of laryngeal single motor units during phonation in young and older adults, and in persons with Parkinson disease. The rate and variability of the firing of single motor units in the laryngeal muscles of young and older nondisordered humans and people with idiopathic Parkinson disease (IPD) were determined during steady phonation and other laryngeal behaviors. Typical firing rates during phonation were approximately 24 s/s. The highest rate observed, during a cough, was 50 s/s. Decreases in the rate and increases in the variability of motor unit firing were observed in the thyroarytenoid muscle of older and IPD male subjects but not female subjects. These gender-specific age-related changes may relate to differential effects of aging on the male and female voice characteristics. The range and typical firing rates of laryngeal motor units were similar to those reported for other human skeletal muscles, so we conclude that human laryngeal muscles are probably no faster, in terms of their contraction speed, than other human skeletal muscles. Interspike interval (ISI) variability during steady phonation was quite low, however, with average CV of approximately 10%, with a range of 5 to 30%. These values appear to be lower than typical values of the CV of firing reported in three studies of limb muscles of humans. We suggest therefore that low ISI variability is a special although not unique property of laryngeal muscles compared with other muscles of the body. This conceivably could be the result of less synaptic "noise" in the laryngeal motoneurons, perhaps as a result of suppression of local reflex inputs to these motoneurons during phonation.

Effect of intravenous substance P on laryngeal adductor activity in young dogs.

Reflex laryngeal adduction is a component of both the laryngeal chemoreflex and the esophagolaryngeal adductor reflex, two life-threatening reflexes that occur in immature animals. These two reflex responses are also thought to exist in infants and may play a role in causing life-threatening laryngospastic events and perhaps sudden infant death syndrome. Identifying neurotransmitters that mediate laryngeal adduction is important to understanding the mechanism of reflex laryngeal responses and to identifying potential means of pharmacologic prevention. Substance P (SP), a tachykinin, putatively functions as a sensory neurotransmitter and may play a role in mediating laryngeal reflexes. Substance P-immunoreactive-like fibers and receptors are present in the subepithelial tissues of the larynx, the vagus nerves, the nodose and jugular ganglia, and the vagal brain stem nuclei. In this investigation, the effect of SP infusion on laryngeal motor activity in an in vivo model is reported. Substance P was infused intravenously into 8 puppies (20 to 133 days of age, mean 81.2), on a mean of 3.0 occasions (range 1 to 6). Cardiovascular, respiratory, arterial blood gas, and cricothyroid (CT), thyroarytenoid (TA), and genioglossus electromyographic (EMG) responses to infusion of the tachykinin were recorded and subsequently analyzed. The SP infusion induced a marked increase in CT or TA EMG activity in 23 of 24 studies, and the increase was typically apparent within 60 seconds of the infusion. An increase in genioglossus EMG activity did not occur. An immediate, profound decrease in mean arterial pressure and an increase in respiratory rate and depth of chest wall excursion accompanied the laryngeal response. Arterial blood gas values remained unchanged (p > .05). The laryngeal adductor response to SP infusion was blocked when animals were pretreated with a systemic SP antagonist (Pfizer CP-96,345). This study demonstrates that peripheral infusion of the tachykinin SP induces a marked increase in laryngeal adductor activity. The response may be blocked by pretreatment of animals with a systemic SP antagonist. Because SP is thought to act primarily as a sensory neurotransmitter, these findings may be important in understanding the mechanism of reflex laryngeal adductor responses.

Thyroarytenoid muscle activity associated with hypophonia in Parkinson disease and aging.

OBJECTIVE: To compare electromyographic (EMG) amplitudes of the thyroarytenoid (TA) muscle in young and older individuals and individuals with idiopathic PD (IPD) under conditions of known vocal loudness (sound pressure level). BACKGROUND: Voice disorders frequently accompany aging and IPD, but it is unclear how laryngeal muscle physiology is affected by these processes and how changes in laryngeal muscle activity result in characteristic changes of the voice. METHODS: Absolute and relative (to maximum) EMG amplitudes of the TA muscle were compared during speech and nonspeech tasks. Corresponding sound pressure level (SPL) measures were obtained for the speech tasks. RESULTS: Absolute TA amplitudes were consistently the highest in the young individuals, lowest in the individuals with IPD, and intermediate in the older individuals. Relative TA amplitudes were generally the highest for the young individuals, lowest for the older individuals, and intermediate for the individuals with IPD. SPL findings showed the older individuals and individuals with IPD produced most of the speech tasks with comparable SPLs, and these levels were consistently lower than those of the young individuals. CONCLUSIONS: Reduced levels of TA muscle activity may contribute to the characteristic hypophonic voice disorders that frequently accompany IPD and aging.

Midbrain regions for eliciting vocalization by electrical stimulation in anesthetized dogs.

Eliciting vocalization in anesthetized dogs by midbrain stimulation is a useful procedure for studies of laryngeal and respiratory physiology. The goal of this report has been to construct a canine stereotaxic "map" that would allow investigators to locate midbrain stimulus sites producing vocalization. Motor responses to electrical stimulation at currents of 1.5 mA or less were observed at 1,158 stimulus sites throughout the midbrains of 8 dogs. Vocalization was observed at 213 stimulus sites. The highest probability of observing vocalization was for sites located 6 to 10 mm anterior, 6 to 7 mm lateral, and 5 to 8 mm dorsal to earbar zero. The vocalization region most likely consists of axons arising in the midbrain periaqueductal gray and coursing through the adjacent tegmentum; low-threshold sites are close to the medial lemniscus. The relationship between stimulus sites at which vocalization was elicited and sites producing other motor responses is described.

Comparison of concentric needle versus hooked-wire electrodes in the canine larynx.

BACKGROUND: The use of a specific electrode type in laryngeal electromyography has not been standardized. Laryngeal electromyography is usually performed with hooked-wire electrodes or concentric needle electrodes. Hooked-wire electrodes have the advantage of allowing laryngeal movement with ease and comfort, whereas the concentric needle electrodes have benefits from a technical aspect and may be advanced, withdrawn, or redirected during attempts to appropriately place the electrode. OBJECTIVES: This study examines whether hooked-wire electrodes permit more stable recordings than standard concentric needle electrodes at rest and after large-scale movements of the larynx and surrounding structures. A histologic comparison of tissue injury resulting from placement and removal of the two electrode types is also made by evaluation of the vocal folds. METHODS: Electrodes were percutaneously placed into the thyroarytenoid muscles of 10 adult canines. Amplitude of electromyographic activity was measured and compared during vagal stimulation before and after large-scale laryngeal movements. Signal consistency over time was examined. Animals were killed and vocal fold injury was graded and compared histologically. RESULTS: Waveform morphology did not consistently differ between electrode types. The variability of electromyographic amplitude was greater for the hooked-wire electrode (p < 0.05), whereas the mean amplitude measures before and after large-scale laryngeal movements did not differ (p > 0.05). Inflammatory responses and hematoma formation were also similar. CONCLUSIONS: Waveform morphology of electromyographic signals registered from both electrode types show similar complex action potentials. There is no difference between the hooked-wire electrode and the concentric needle electrode in terms of electrode stability or vocal fold injury in the thyroarytenoid muscle after large-scale laryngeal movements.

Sources of error in estimation of laryngeal airway resistance in persons with spasmodic dysphonia.

Estimation of laryngeal airway resistance is a noninvasive method that has proven useful in the study of people with normal and some types of disordered voices. We were interested in examining more closely the application of this method to persons with spasmodic dysphonia (SD), a voice disorder sometimes associated with fluctuating airflow. We speculated unstable airflow could affect the estimation of subglottal pressure and laryngeal airway resistance. Oral pressure and airflow were collected from 10 subjects with SD and 10 control subjects during repetition of /pi/. The coefficient of variation (COV) of airflow during vowel production was calculated to quantify stability of airflow. The results indicated that although some SD subjects produced steady flows during the syllable repetition task, others exhibited substantially varying flows. Inability on the part of the subject to attain steady flows could compromise the usefulness of a midpoint measure of airflow and/or estimation of subglottal pressure, resulting in sources of error in estimation of laryngeal airway resistance. As a result, of the 10 subjects with SD in this study, laryngeal airway resistance could not be estimated in 6 subjects with unsteady flows. Laryngeal airway resistance was estimated in 4 SD subjects who produced steady airflow. Two of these subjects exhibited high laryngeal airway resistance; the others exhibited normal laryngeal airway resistance.

Sense of effort and the effects of fatigue in the tongue and hand.

Fatigue and increased effort are common symptoms for people with movement disorders and dysarthria, but they are rarely quantified. In an attempt to develop a clinically useful and physiologically meaningful measure of fatigue, we used a task that involves sustaining a target effort level without visual feedback while squeezing a bulb connected to a pressure transducer. In the first experiment, 12 healthy young adults performed the constant-effort task with the tongue and the preferred hand at 3 submaximal levels of effort. The resulting pressure declined over time as a negative exponential function with a nonzero asymptote. In the second experiment, 6 subjects performed the constant-effort task before and after acutely fatiguing the tongue and hand. The rate of pressure decline was significantly greater after fatigue. One possible mechanism for the characteristic negative exponential function is that it reflects a constant descending drive from higher centers in the CNS to the appropriate motoneuron pools. Thus, this technique may elucidate the contribution of central fatigue to normal and disordered speech.

Fundamental frequency and tracheal pressure during three types of vocalizations elicited from anesthetized dogs.

Electrical stimulation of the midbrain was used to elicit a variety of vocalizations from six anesthetized dogs. This study was conducted to investigate the ranges of and relationships between fundamental frequency of the vocalizations (F0) and tracheal pressure (Pt) produced during the vocalizations. The vocalizations were described according to type (growl, howl, and whine); F0 and Pt, as well as patterns of laryngeal muscle activity, were examined for each vocalization type. Natural-sounding growl and howl vocalizations were elicited from five dogs; three dogs also produced whines. With few exceptions, F0 was categorically different for the three vocalization types (low for growls, average for howls, very high for whines). Pt values overlapped for the three vocalization types, although, on average, howls were produced with greater Pt than growls. Patterns and degrees of laryngeal muscle activity varied across and within vocalization types, but general findings were consistent with the presumed function of most of the muscles. Laryngeal muscle activity may help explain some of the variability in the acoustic and aerodynamic data.

A model of "sense of effort" during maximal and submaximal contractions of the tongue.

Fatigue in the oral motor system may be accompanied by the perception of an increased "sense of effort." Awareness of centrally generated motor commands that result in synaptic inputs to motoneuron pools are thought to be responsible for these perceptions of effort (e.g., Muller, 1840; McCloskey, 1981). Few studies of the perceptual phenomenon of sense of effort exist, particularly of the oral motor system. The present study required 20 normal adults to push on a fluid-filled bulb using their tongue and hand. Subjects repeatedly exerted from 10 to 100% of the maximal effort, in random order, in 10% increments. The pressure produced by pushing on fluid-filled bulbs was compared to the effort level attempted. Subjects produced consistent, reliable pressures related to effort level. The best mathematical model for both the tongue and hand data was third-order polynomial. It is hypothesized that the perception of effort derives from a central source that operates across various motor systems.