Biomedical subjects

Christy L Ludlow

Publications and source records attributed to Christy L Ludlow.

At least 19 recordsLinked to original sources

PubMed2007

Effects of surface electrical stimulation both at rest and during swallowing in chronic pharyngeal Dysphagia.

We tested two hypotheses using surface electrical stimulation in chronic pharyngeal dysphagia: that stimulation (1) lowered the hyoid bone and/or larynx when applied at rest, and (2) increased aspiration, penetration, or pharyngeal pooling during swallowing. Bipolar surface electrodes were placed on the skin overlying the submandibular and laryngeal regions. Maximum tolerated levels of stimulation were applied while patients held their mouth closed at rest. Videofluoroscopic recordings were used to measure hyoid movements in the superior-inferior and anterior-posterior dimensions and the subglottic air column position while stimulation was on or off. Patients swallowed 5 ml liquid when stimulation was off, at low sensory stimulation levels, and at maximum tolerated levels (motor). Speech pathologists, blinded to condition, tallied the frequency of aspiration, penetration, pooling, and esophageal entry from videofluorographic recordings of swallows. Only significant (p = 0.0175) hyoid depression occurred during stimulation at rest. Aspiration and pooling were significantly reduced only with low sensory threshold levels of stimulation (p = 0.025) and not during maximum levels of surface electrical stimulation. Those patients who had reduced aspiration and penetration during swallowing with stimulation had greater hyoid depression during stimulation at rest (p = 0.006). Stimulation may have acted to resist patients' hyoid elevation during swallowing.

Adult↗

PubMed2006

The effect of surface electrical stimulation on hyolaryngeal movement in normal individuals at rest and during swallowing.

Surface electrical stimulation is currently used in therapy for swallowing problems, although little is known about its physiological effects on neck muscles or swallowing. Previously, when one surface electrode placement was used in dysphagic patients at rest, it lowered the hyolaryngeal complex. Here we examined the effects of nine other placements in normal volunteers to determine 1) whether movements induced by surface stimulation using other placements differ, and 2) whether lowering the hyolaryngeal complex by surface electrical stimulation interfered with swallowing in healthy adults. Ten bipolar surface electrode placements overlying the submental and laryngeal regions were tested. Maximum tolerated stimulation levels were applied at rest while participants held their mouths closed. Videofluoroscopic recordings were used to measure hyoid bone and subglottic air column (laryngeal) movements from resting position and while swallowing 5 ml of liquid barium, with and without stimulation. Videofluoroscopic recordings of swallows were rated blind to condition using the National Institutes of Health-Swallowing Safety Scale. Significant (P < 0.0001) laryngeal and hyoid descent occurred with stimulation at rest. During swallowing, significant (P <or= 0.01) reductions in both the larynx and hyoid bone peak elevation occurred during stimulated swallows. The stimulated swallows were also judged less safe than nonstimulated swallows using the National Institutes of Health-Swallowing Safety Scale (P = 0.0275). Because surface electrical stimulation reduced hyolaryngeal elevation during swallowing in normal volunteers, our findings suggest that surface electrical stimulation will reduce elevation during swallowing therapy for dysphagia.

Adult↗

PubMed2006

Speech perception and short-term memory deficits in persistent developmental speech disorder.

Children with developmental speech disorders may have additional deficits in speech perception and/or short-term memory. To determine whether these are only transient developmental delays that can accompany the disorder in childhood or persist as part of the speech disorder, adults with a persistent familial speech disorder were tested on speech perception and short-term memory. Nine adults with a persistent familial developmental speech disorder without language impairment were compared with 20 controls on tasks requiring the discrimination of fine acoustic cues for word identification and on measures of verbal and nonverbal short-term memory. Significant group differences were found in the slopes of the discrimination curves for first formant transitions for word identification with stop gaps of 40 and 20 ms with effect sizes of 1.60 and 1.56. Significant group differences also occurred on tests of nonverbal rhythm and tonal memory, and verbal short-term memory with effect sizes of 2.38, 1.56, and 1.73. No group differences occurred in the use of stop gap durations for word identification. Because frequency-based speech perception and short-term verbal and nonverbal memory deficits both persisted into adulthood in the speech-impaired adults, these deficits may be involved in the persistence of speech disorders without language impairment.

Adolescent↗

PubMed2006

Alterations in CNS activity induced by botulinum toxin treatment in spasmodic dysphonia: an H215O PET study.

Speech-related changes in regional cerebral blood flow (rCBF) were measured using H(2)(15)O positron-emission tomography in 9 adults with adductor spasmodic dysphonia (ADSD) before and after botulinum toxin (BTX) injection and 10 age- and gender-matched volunteers without neurological disorders. Scans were acquired at rest and during production of continuous narrative speech and whispered speech. Speech was recorded during scan acquisition for offline quantification of voice breaks, pitch breaks, and percentage aperiodicity to assess correlations between treatment-related changes in rCBF and clinical improvement. Results demonstrated that speech-related responses in heteromodal sensory areas were significantly reduced in persons with ADSD, compared with volunteers, before the administration of BTX. Three to 4 weeks after BTX injection, speech-related responses were significantly augmented in these regions and in left hemisphere motor areas commonly associated with oral-laryngeal motor control. This pattern of responses was most strongly correlated with the objective measures of clinical improvement (decreases in the frequency of voice breaks, pitch breaks, and percentage aperiodicity). These data suggest a pathophysiological model for ADSD in which BTX treatment results in more efficient cortical processing of sensory information, making this information available to motor areas that use it to more effectively regulate laryngeal movements.

Adult↗

PubMed2005

Self-triggered functional electrical stimulation during swallowing.

Hyolaryngeal elevation is essential for airway protection during swallowing and is mainly a reflexive response to oropharyngeal sensory stimulation. Targeted intramuscular electrical stimulation can elevate the resting larynx and, if applied during swallowing, may improve airway protection in dysphagic patients with inadequate hyolaryngeal motion. To be beneficial, patients must synchronize functional electrical stimulation (FES) with their reflexive swallowing and not adapt to FES by reducing the amplitude or duration of their own muscle activity. We evaluated the ability of nine healthy adults to manually synchronize FES with hyolaryngeal muscle activity during discrete swallows, and tested for motor adaptation. Hooked-wire electrodes were placed into the mylo- and thyrohyoid muscles to record electromyographic activity from one side of the neck and deliver monopolar FES for hyolaryngeal elevation to the other side. After performing baseline swallows, volunteers were instructed to trigger FES with a thumb switch in synchrony with their swallows for a series of trials. An experimenter surreptitiously disabled the thumb switch during the final attempt, creating a foil. From the outset, volunteers synchronized FES with the onset of swallow-related thyrohyoid activity (approximately 225 ms after mylohyoid activity onset), preserving the normal sequence of muscle activation. A comparison between average baseline and foil swallows failed to show significant adaptive changes in the amplitude, duration, or relative timing of activity for either muscle, indicating that the central pattern generator for hyolaryngeal elevation is immutable with short term stimulation that augments laryngeal elevation during the reflexive, pharyngeal phase of swallowing.

Adult↗

PubMed2005

Central nervous system control of the laryngeal muscles in humans.

Laryngeal muscle control may vary for different functions such as: voice for speech communication, emotional expression during laughter and cry, breathing, swallowing, and cough. This review discusses the control of the human laryngeal muscles for some of these different functions. Sensori-motor aspects of laryngeal control have been studied by eliciting various laryngeal reflexes. The role of audition in learning and monitoring ongoing voice production for speech is well known; while the role of somatosensory feedback is less well understood. Reflexive control systems involving central pattern generators may contribute to swallowing, breathing and cough with greater cortical control during volitional tasks such as voice production for speech. Volitional control is much less well understood for each of these functions and likely involves the integration of cortical and subcortical circuits. The new frontier is the study of the central control of the laryngeal musculature for voice, swallowing and breathing and how volitional and reflexive control systems may interact in humans.

Brain↗

PubMed2005

Laryngeal muscle responses to mechanical displacement of the thyroid cartilage in humans.

Speakers may use laryngeal sensory feedback to adjust vocal fold tension and length before initiating voice. The mechanism for accurately initiating voice at an intended pitch is unknown, given the absence of laryngeal muscle spindles in animals and conflicting findings regarding their existence in humans. Previous reports of rapid changes in voice fundamental frequency following thyroid cartilage displacement suggest that changes in vocal fold length modulate laryngeal muscle contraction in humans. We tested the hypothesis that voice changes resulting from mechanical perturbation are due to rapid responses in the intrinsic laryngeal muscles. Hooked wire electrodes were used to record from the thyroarytenoid, cricothyroid, and sternothyroid muscles along with surface electrodes on the skin overlying the thyroid cartilage in 10 normal adults. Servomotor displacements produced consistent changes in the subjects' vocal fundamental frequency at 70-80 ms, demonstrating changes in vocal fold length and tension. No simultaneous electromyographic responses occurred in the thyroarytenoid or cricothyroid muscles in any subjects. Instead, short-latency responses at 25-40 ms following stimulus onset occurred in the sternothyroid muscles, simultaneous with responses in the surface recordings. The sternothyroid responses may modulate long-latency changes in voice fundamental frequency (approximately 150 ms). The absence of intrinsic laryngeal muscle responses is consistent with a lack of spindles in these muscles. Our results suggest that other sensory receptors, such as mucosal mechanoreceptors, provide feedback for voice control.

Adult↗

PubMed2005

Distal spinal and bulbar muscular atrophy caused by dynactin mutation.

Impaired axonal transport has been postulated to play a role in the pathophysiology of multiple neurodegenerative disorders. In this report, we describe the results of clinical and neuropathological studies in a family with an inherited form of motor neuron disease caused by mutation in the p150Glued subunit of dynactin, a microtubule motor protein essential for retrograde axonal transport. Affected family members had a distinct clinical phenotype characterized by early bilateral vocal fold paralysis affecting the adductor and abductor laryngeal muscles. They later experienced weakness and atrophy in the face, hands, and distal legs. The extremity involvement was greater in the hands than in the legs, and it had a particular predilection for the thenar muscles. No clinical or electrophysiological sensory abnormality existed; however, skin biopsy results showed morphological abnormalities of epidermal nerve fibers. An autopsy study of one patient showed motor neuron degeneration and axonal loss in the ventral horn of the spinal cord and hypoglossal nucleus of the medulla. Immunohistochemistry showed abnormal inclusions of dynactin and dynein in motor neurons. This mutation of dynactin, a ubiquitously expressed protein, causes a unique pattern of motor neuron degeneration that is associated with the accumulation of dynein and dynactin in neuronal inclusions.

Action Potentials↗

PubMed2005

Suppression of thyroarytenoid muscle responses during repeated air pressure stimulation of the laryngeal mucosa in awake humans.

Repeated stimulation of the laryngeal mucosa occurs during speech. Single stimuli, however, can elicit the laryngeal adductor response (LAR). Our hypothesis was that the LAR to repeated rapid air pressure stimuli is centrally suppressed in humans. Hooked-wire electrodes were inserted into the thyroarytenoid and cricothyroid muscles on both sides and into the posterior cricoarytenoid muscle on one side. Pairs of air puff stimuli were presented to the mucosa over the arytenoids at pressure levels three times threshold with interstimulus intervals from 250 to 5,000 ms. Bilateral thyroarytenoid responses occurred at around 150 ms to more than 70% of the initial stimuli. With repeated presentation at intervals of 2 seconds or less, the percent occurrence decreased to less than 40% and response amplitudes were reduced by 50%. Central suppression of adductor responses to repeated air puff stimuli may allow speakers to produce voice without eliciting reflexive spasms that could disrupt speech.

Adult↗

PubMed2004

Neuronal activation in the medulla oblongata during selective elicitation of the laryngeal adductor response.

Swallow and cough are complex motor patterns elicited by rapid and intense electrical stimulation of the internal branch of the superior laryngeal nerve (ISLN). The laryngeal adductor response (LAR) includes only a laryngeal response, is elicited by single stimuli to the ISLN, and is thought to represent the brain stem pathway involved in laryngospasm. To identify which regions in the medulla are activated during elicitation of the LAR alone, single electrical stimuli were presented once every 2 s to the ISLN. Two groups of five cats each were studied; an experimental group with unilateral ISLN stimulation at 0.5 Hz and a surgical control group. Three additional cats were studied to evaluate whether other oral, pharyngeal, or respiratory muscles were activated during ISLN stimulation eliciting LAR. We quantified < or = 22 sections for each of 14 structures in the medulla to determine if regions had increased Fos-like immunoreactive neurons in the experimental group. Significant increases (P < 0.0033) occurred with unilateral ISLN stimulation in the interstitial subnucleus, the ventrolateral subnucleus, the commissural subnucleus of the nucleus tractus solitarius, the lateral tegmental field of the reticular formation, the area postrema, and the nucleus ambiguus. Neither the dorsal motor nucleus of the vagus, usually active for swallow, nor the nucleus retroambiguus, retrofacial nucleus, and the lateral reticular nucleus, usually active for cough, were active with elicitation of the laryngeal adductor response alone. The results demonstrate that the laryngeal adductor pathway is contained within the broader pathways for cough and swallow in the medulla.

Animals↗

PubMed2004

Correspondence between laryngeal vocal fold movement and muscle activity during speech and nonspeech gestures.

To better understand the role of each of the laryngeal muscles in producing vocal fold movement, activation of these muscles was correlated with laryngeal movement during different tasks such as sniff, cough or throat clear, and speech syllable production. Four muscles [the posterior cricoarytenoid, lateral cricoarytenoid, cricothyroid (CT), and thyroarytenoid (TA)] were recorded with bipolar hooked wire electrodes placed bilaterally in four normal subjects. A nasoendoscope was used to record vocal fold movement while simultaneously recording muscle activity. Muscle activation level was correlated with ipsilateral vocal fold angle for vocal fold opening and closing. Pearson correlation coefficients and their statistical significance were computed for each trial. Significant effects of muscle (P < or = 0.0005) and task (P = 0.034) were found on the r (transformed to Fisher's Z') values. All of the posterior cricoarytenoid recordings related significantly with vocal opening, whereas CT activity was significantly correlated with opening only during sniff. The TA and lateral cricoarytenoid activities were significantly correlated with vocal fold closing during cough. During speech, the CT and TA activity correlated with both opening and closing. Laryngeal muscle patterning to produce vocal fold movement differed across tasks; reciprocal muscle activity only occurred on cough, whereas speech and sniff often involved simultaneous contraction of muscle antagonists. In conclusion, different combinations of muscle activation are used for biomechanical control of vocal fold opening and closing movements during respiratory, airway protection, and speech tasks.

Adult↗

PubMed2004

Practice parameter: laryngeal electromyography (an evidence-based review).

This paper reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. The review yielded 584 articles of which 33 met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the 2 techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing other applications in the use of laryngeal EMG for other applications.

Electromyography↗

PubMed2004

Practice parameter: laryngeal electromyography (an evidence-based review).

This paper reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders, including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. Thirty-three of the 584 articles met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the two techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing other applications in the use of laryngeal EMG for other applications.

Electromyography↗

PubMed2004

Recent advances in laryngeal sensorimotor control for voice, speech and swallowing.

PURPOSE OF REVIEW: This article reviews advances in knowledge on laryngeal sensorimotor control affecting the assessment, understanding, and treatment of laryngeal motor control disorders in voice, speech, and swallowing. Three topics are covered: new knowledge on laryngeal innervation and central nervous system control from basic research studies, the role of laryngeal sensation in normal swallowing and dysphagia in patients, and new approaches to the restoration of laryngeal motor control after recurrent laryngeal nerve disorders. RECENT FINDINGS: A significant advance this year was tracing the efferent pathways from the cortex to the brainstem in monkeys. This provided new information on subcortical and brainstem connections in the laryngeal efferent pathways. Laryngeal sensory feedback continued to receive attention, and the role of sensory feedback in the control of the pharyngeal phase of swallowing is now well established. Further developments in neuromotor monitoring of the recurrent laryngeal nerve during thyroidectomy were seen, and a large case series recommended that these techniques become standard practice for surgery for thyroid benign recurrence or malignancy. Finally, the first tissue engineering papers in the field of vocal fold tissue and nerve restoration were published this year, beginning an exciting new approach to restoration of laryngeal motor control. SUMMARY: Considerable attention has been given to laryngeal muscle physiology, denervation, and sensation in neurolaryngology. Relatively limited understanding is available regarding the central nervous system integrative control of laryngeal function for speech, respiration, and swallowing.

Animals↗

PubMed2003

Mutant dynactin in motor neuron disease.

Impaired axonal transport in motor neurons has been proposed as a mechanism for neuronal degeneration in motor neuron disease. Here we show linkage of a lower motor neuron disease to a region of 4 Mb at chromosome 2p13. Mutation analysis of a gene in this interval that encodes the largest subunit of the axonal transport protein dynactin showed a single base-pair change resulting in an amino-acid substitution that is predicted to distort the folding of dynactin's microtubule-binding domain. Binding assays show decreased binding of the mutant protein to microtubules. Our results show that dysfunction of dynactin-mediated transport can lead to human motor neuron disease.

Amino Acid Motifs↗

PubMed2003

Laryngeal electromyography: an evidence-based review.

This article reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. Thirty-three of the 584 articles met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the two techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing the use of laryngeal EMG for other applications.

Electrodiagnosis↗

PubMed2003

Stuttering: a dynamic motor control disorder.

UNLABELLED: The purpose of this review is to determine what neural mechanisms may be dysfunctional in stuttering. Three sources of evidence are reviewed. First, studies of dynamic inter-relationships among brain regions during normal speech and in persons who stutter (PWS) suggest that the timing of neural activity in different regions may be abnormal in PWS. Second, the brain lesions associated with acquired stuttering are reviewed. These indicate that in a high percentage of cases, the primary speech and language regions are not affected but lesions involve other structures, such as the basal ganglia, which may modulate the primary speech and language regions. Third, to characterize the motor control disorder in stuttering, similarities and differences from focal dystonias such as spasmodic dysphonia (SD) and Tourette's syndrome (TS) are reviewed. This review indicates that the central control abnormalities in stuttering are not due to disturbance in one particular brain region but rather a system dysfunction that interferes with rapid and dynamic speech processing for production. EDUCATIONAL OBJECTIVES: The reader will be able to describe: (1) the similarities and differences between stuttering and other speech motor control disorders, (2) which brain lesions are most likely to produce acquired stuttering in adults, and (3) what type of brain abnormality most likely underlies stuttering.

Basal Ganglia↗

PubMed2003

Laryngeal elevation achieved by neuromuscular stimulation at rest.

During swallowing, airway protection is achieved in part by laryngeal elevation. Although multiple muscles are normally active during laryngeal elevation, neuromuscular stimulation of select muscles was evaluated to determine which single muscle or muscle pair best elevates the larynx and should be considered during future studies of neuromuscular stimulation in dysphagic patients. Hooked-wire monopolar electrodes were inserted into mylohyoid, thyrohyoid, and geniohyoid muscle regions in 15 healthy men selected for having a highly visible thyroid prominence for videotaping. During trials of single, bilateral, and combined muscle stimulations, thyroid prominence movements were video recorded, digitized, and normalized relative to elevation during a 2-ml water swallow. Individual muscle stimulation induced approximately 30% of the elevation observed during a swallow and approximately 50% of swallow velocity, whereas paired muscle stimulation resulted in approximately 50% of the elevation and approximately 80% of the velocity produced during a swallow. Paired muscle stimulation produced significantly greater elevation than single muscle stimulation and could assist with laryngeal elevation in dysphagic patients with reduced or delayed laryngeal elevation.

Adolescent↗