Physiological substrates of normal deglutition

Deglutition and the Regulation of the Swallow Motor Pattern

Despite centuries of investigation, questions and controversies remain regarding the fundamental genesis and motor pattern of swallow. Two significant topics include inspiratory muscle activity during swallow (Schluckatmung, i.e., "swallow-breath") and anatomical boundaries of the swallow pattern generator. We discuss the long history of reports regarding the presence or absence of Schluckatmung and the possible advantages of and neural basis for such activity, leading to current theories and novel experimental directions.

Alterations in oropharyngeal sensory evoked potentials (PSEP) with Parkinson's disease

Movement of a food bolus from the oral cavity into the oropharynx activates pharyngeal sensory mechanoreceptors. Using electroencephalography, somatosensory cortical-evoked potentials resulting from oropharyngeal mechanical stimulation (PSEP) have been studied in young healthy individuals. However, limited information is known about changes in processing of oropharyngeal afferent signals with Parkinson's disease (PD). To determine if sensory changes occurred with a mechanical stimulus (air-puff) to the oropharynx, two stimuli (S1-first; S2-s) were delivered 500ms apart. Seven healthy older adults (HOA; 3 male and 4 female; 72.2±6.9 years of age), and thirteen persons diagnosed with idiopathic Parkinson's disease (PD; 11 male and 2 female; 67.2±8.9 years of age) participated. Results demonstrated PSEP P1, N1, and P2 component peaks were identified in all participants, and the N2 peak was present in 17/20 participants. Additionally, the PD participants had a decreased N2 latency and gated the P1, P2, and N2 responses (S2/S1 under 0.6). Compared to the HOAs, the PD participants had greater evidence of gating the P1 and N2 component peaks. These results suggest that persons with PD experience changes in sensory processing of mechanical stimulation of the pharynx to a greater degree than age-matched controls. In conclusion, the altered processing of sensory feedback from the pharynx may contribute to disordered swallow in patients with PD.

Suppression of Abdominal Motor Activity during Swallowing in Cats and Humans

Diseases affecting pulmonary mechanics often result in changes to the coordination of swallow and breathing. We hypothesize that during times of increased intrathoracic pressure, swallow suppresses ongoing expiratory drive to ensure bolus transport through the esophagus. To this end, we sought to determine the effects of swallow on abdominal electromyographic (EMG) activity during expiratory threshold loading in anesthetized cats and in awake-healthy adult humans. Expiratory threshold loads were applied to recruit abdominal motor activity during breathing, and swallow was triggered by infusion of water into the mouth. In both anesthetized cats and humans, expiratory cycles which contained swallows had a significant reduction in abdominal EMG activity, and a greater percentage of swallows were produced during inspiration and/or respiratory phase transitions. These results suggest that: a) spinal expiratory motor pathways play an important role in the execution of swallow, and b) a more complex mechanical relationship exists between breathing and swallow than has previously been envisioned.

Tongue movements during water swallowing in healthy young and older adults

PURPOSE

The purpose of this study was to explore the nature and extent of variability in tongue movement during healthy swallowing as a function of aging and gender. In addition, changes were quantified in healthy tongue movements in response to specific differences in the nature of the swallowing task (discrete vs. sequential swallows).

METHOD

Electromagnetic midsagittal articulography (EMMA) was used to study the swallowing-related movements of markers located in midline on the anterior (blade), middle (body), and posterior (dorsum) tongue in a sample of 34 healthy adults in 2 age groups (under vs. over 50 years of age). Participants performed a series of reiterated water swallows, in either a discrete or a sequential manner.

RESULTS

This study shows that age-related changes in tongue movements during swallowing are restricted to the domain of movement duration. The authors confirm that different tongue regions can be selectively modulated during swallowing tasks and that both functional and anatomical constraints influence the manner in which tongue movement modulation occurs. Sequential swallowing, in comparison to discrete swallowing, elicits simplification or down-scaling of several kinematic parameters.

CONCLUSION

The data illustrate task-specific stereotyped patterns of tongue movement in swallowing, which are robust to the effects of healthy aging in all aspects other than movement duration.

The neurobiology of swallowing and dysphagia

The neurobiological study of swallowing and its dysfunction, defined as dysphagia, has evolved over two centuries beginning with electrical stimulation applied directly to the central nervous system, and then followed by systematic investigations that have used lesioning, transmagnetic stimulation, magnetoencephalography, and functional magnetic resonance imaging. The field has evolved from mapping the central neural pathway and peripheral nerves, to defining the importance of specific regions of the lower brain stem in terms of interneurons that provide sequential control for multiple muscles in the most complex reflex elicited by the nervous system, the pharyngeal phase of swallowing. The field is now emerging into defining how the higher cortical regions interact with this brain stem control and is providing a broader perspective of how the intact nervous system functions to control the three phases of swallowing (i.e., oral, pharyngeal, and esophageal). Much of the present interest focuses on how to retrain a damaged nervous system using a variety of stimulus techniques, which follow fundamentals in rehabilitation of the nervous system.

A comparison of the reliability and stability of oro-lingual swallowing pressures in patients with head and neck cancer and healthy adults

The ability to measure normality and abnormality and to accurately assess true changes in swallowing function over time, is important for the management of dysphagia. Despite this, there is a paucity of information regarding the stability and reliability of measurements tools used for dysphagia research. As both head and neck (H&N) cancer and its treatment(s) have been shown to significantly affect deglutitive tongue function, it is important that we have a reliable method to measure swallowing tongue function in this population. In this study we evaluate the reliability and stability of oro-lingual swallowing pressures captured from H&N cancer patients and from healthy, age- and gender-matched controls using the Kay Swallowing Workstation (KSW) fixed, three-transducer tongue pressure array. Significant differences between the two samples (H&N cancer and controls), with respect to mean peak oro-lingual pressures were recorded during swallowing. Furthermore, reliability of these measures was lower in H&N cancer patients. These differences highlight the importance of obtaining information about the reliability of dysphagia assessment tools with the specific population with whom they will be used.

Neurologisch bedingte und neuromuskuläre Funktionsstörungen des Pharynx und Ösophagus

Neurologic swallowing disorders are an increasing diagnostic problem in our overaged population. Undiagnosed chronic aspiration pneumonia is the cause of death in 20-40% of all inhabitants of nursing homes. In neurologic diseases of the pharynx, the physiologic interaction of pharyngeal contraction, closure of the pharynx, and esophageal motility are frequently disturbed. This may be due to cortical, bulbar, or cerebellar brain damage of ischemic or traumatic origin. Furthermore diseases or peripheral nerves, muscles, and synapses cause disturbances. The most life-threatening complication of these disturbances is tracheal aspiration, which requires an iso-osmolar contrast medium for imaging studies that cause no or minimal pulmonary problems. Utilizing fast dynamic documentation we can analyze the swallowing act in 35 images within the passage time of 0.7 s. This requires digital frame sequences from 15-50 images/s, which can be provided by DSI or videofluoroscopy. Neurologic and neuromuscular patterns are demonstrated with and without tracheal aspiration. The differentiation of aspiration in a so-called pre-, intra-, and postdeglutitive form is possible. We distinguish four grades of severity of aspiration, which is also of great clinical impact for the differential rehabilitation therapy. The efficiency of the rehabilitation protocol can be assessed by the dynamic swallowing studies.

Predictors of survival after severe dysphagic stroke

BACKGROUND AND PURPOSE

Dysphagia is estimated to occur in up to 50% of the stroke neurorehabilitation population. Those patients with severe neurogenic oropharyngeal dysphagia (NOD) may receive feeding gastrostomy tubes (FGT) if noninvasive therapies prove ineffective in eliminating aspiration or sustaining adequate nutritional intake. Our aim was to quantify the recovery of swallowing function, and to identify variables predictive of survival after dysphagic stroke requiring FGT placement.

METHODS

We identified consecutive stroke patients with severe dysphagic stroke requiring FGT placement admitted to a rehabilitation hospital between May 1998 and October 2001. The medical records were reviewed, and demographic, clinical, videofluoroscopic (VSS) and neuroimaging information were abstracted. A follow-up telephone interview was performed to determine whether the FGT was still in use, had been removed,or if the patient had died. State death certificate records were reviewed to ascertain date of death for subjects who had expired by the time of follow-up. Univariate and multivariate analyses were performed.

RESULTS

11.6 % (77/664) of stroke patients admitted during the study period had severe dysphagic stroke with FGT insertion. Follow-up was available for 66 (85.7 %) of these individuals at a mean of two years after acute stroke. On follow-up 64% (42/66) of the patients were alive and 45 % had had the FGT removed and resumed oral diets. On univariate analysis patients who were alive at the time of follow-up had received FGT feeding for a shorter period of time (p < 0.0003), showed no signs of aspiration on the Clinical Assessment of Feeding & Swallowing (CAFS,p < 0.020) and on the Videofluoroscopic Swallowing Study (VSS, 0.001), had a better discharge FIM-Score (Functional Independence Measure) for eating (p < 0.0002) and cognitive function (p < 0.002) as well as better discharge FCM-Score (Functional Communication Measure) for swallowing (p < 0.0001). On multivariate analysis we developed a model consisting of FGT removal at discharge from the rehabilitation hospital (p < 0.011) and non-aspiration during VSS (p < 0.040) that was significantly associated with longer survival time during follow-up.

CONCLUSIONS

Severe dysphagia requiring FGT is common in patients with stroke referred for neurorehabilitation. Patients who had a FGT in place at the time of discharge from the stroke rehabilitation unit or aspirated during VSS were substantially more likely to have died by the time of follow-up compared to those who had had the FGT removed and had no signs of aspiration on VSS. However functional outcome measurements (FIM, FCM) including the cognitive function (attention, concentration etc.) could play an important role for prediction of swallowing regeneration and survival in neurorehabilitation. These findings may have practical utility in guiding physicians and speech language pathologists when advising patients and families about prognosis in stroke survivors with severe dysphagia.

Quantitative lingual, pharyngeal and laryngeal ultrasonography in swallowing research: a technical review

Because of its distinct advantage in radiation-free soft tissue imaging, ultrasonography has been widely used to study lingual, pharyngeal, hyoid, laryngeal, and even esophageal action during swallowing in individuals of all ages. Qualitative ultrasonographic observations have made considerable contributions to our understanding of deglutition. Quantitative ultrasonographic swallowing research has also grown by leaps and bounds over the years with advances in imaging technologies and analytical methodologies. As a technical primer for new investigators, this paper reviews the modem methods for quantitative analysis in ultrasonographic swallowing research. The intended outcome is a basic understanding of the application of ultrasonography with various analysis options to the quantitative study of the deglutitive action of selected upper aerodigestive structures. Though proven useful for swallowing research, ultrasonography has inherent limitations and methodological issues. Future technological advancement and sophisticated image processing and analysis algorithms will resolve some of these issues.

Measuring tongue volumes and visualizing the chewing and swallowing process using real-time TrueFISP imaging--initial clinical experience in healthy volunteers and patients with acromegaly

This study assessed both two-dimensional (2D) TrueFISP imaging for quantifying tongue volume and real-time TrueFISP imaging for evaluating chewing and swallowing in healthy volunteers and patients with acromegaly. In 50 healthy volunteers, tongue volumes were measured using a 2D TrueFISP sequence. Chewing and swallowing were visualized using a real-time TrueFISP sequence. Ten patients with acromegaly were examined twice with the same magnetic resonance imaging protocol: once prior to therapy and a second time 6 months after therapy. Prior to therapy, healthy volunteers had an average tongue volume of 140 ml for men and 90 ml for women, and patients with acromegaly had an average tongue volume of 180 ml for men and 145 ml for women. However, 6 months after therapy the mean tongue volumes in patients with acromegaly had decreased to 154 ml in the men and to 125 ml in the women. The chewing and swallowing process was normal in all volunteers. Prior to therapy, just two patients showed a chewing and swallowing pathology, which disappeared after therapy. Patients with acromegaly had larger tongue volumes than healthy volunteers, and TrueFISP imaging proved feasible for visualizing chewing and swallowing in real time and is capable of detecting possible pathologies. Furthermore, TrueFISP imaging can be used to monitor therapeutic approaches in patients with acromegaly.

Dissociating the spatio-temporal characteristics of cortical neuronal activity associated with human volitional swallowing in the healthy adult brain

Human swallowing represents a complex highly coordinated sensorimotor function whose functional neuroanatomy remains incompletely understood. Specifically, previous studies have failed to delineate the temporo-spatial sequence of those cerebral loci active during the differing phases of swallowing. We therefore sought to define the temporal characteristics of cortical activity associated with human swallowing behaviour using a novel application of magnetoencephalography (MEG). In healthy volunteers (n = 8, aged 28-45), 151-channel whole cortex MEG was recorded during the conditions of oral water infusion, volitional wet swallowing (5 ml bolus), tongue thrust or rest. Each condition lasted for 5 s and was repeated 20 times. Synthetic aperture magnetometry (SAM) analysis was performed on each active epoch and compared to rest. Temporal sequencing of brain activations utilised time-frequency wavelet plots of regions selected using virtual electrodes. Following SAM analysis, water infusion preferentially activated the caudolateral sensorimotor cortex, whereas during volitional swallowing and tongue movement, the superior sensorimotor cortex was more strongly active. Time-frequency wavelet analysis indicated that sensory input from the tongue simultaneously activated caudolateral sensorimotor and primary gustatory cortex, which appeared to prime the superior sensory and motor cortical areas, involved in the volitional phase of swallowing. Our data support the existence of a temporal synchrony across the whole cortical swallowing network, with sensory input from the tongue being critical. Thus, the ability to non-invasively image this network, with intra-individual and high temporal resolution, provides new insights into the brain processing of human swallowing.

Changes in pharyngeal corticobulbar excitability and swallowing behavior after oral stimulation

Faucial pillar (FP) stimulation is commonly used in swallowing rehabilitation, yet its physiological basis remains uncertain. We investigated the effects of intraoral FP stimulation on human corticobulbar excitability and swallowing behavior, to explore the possibility of a central mechanism for functional change. In 10 healthy subjects, corticobulbar projections to pharynx were investigated with transcranial magnetic stimulation, via intraluminal electrodes, before and up to 1 h after 10 min of electrical FP stimulation with three frequencies (0.2, 1, and 5 Hz) or sham and peripheral (median nerve) stimulation. In a second study, swallowing behavior was assessed with videofluoroscopy before and after FP stimulation. FP stimulation at 5 Hz inhibited the corticobulbar projection (-14 +/- 6%, P < 0.02) and lengthened swallow response time (+114 +/- 24%, P = 0.02). By comparison, FP stimulation at 0.2 Hz facilitated this projection (+60 +/- 28%, P < 0.04), without enhancing swallowing behavior. Neither 1-Hz, sham, nor median nerve stimulation altered excitability. Thus changes in corticobulbar excitability to FP stimulation are frequency dependent with implications for the treatment for neurogenic swallowing dysfunction.

Sequence variability during hypopharyngeal bolus transit

The pharyngeal phase of deglutition is considered to occur in a reflexive, preprogrammed fashion. Previous studies have determined a general sequence of events based on the mean timing of bolus transit and swallowing gestures. Individual variability has not been studied, however. The purpose of this study was to determine the amount of sequence variability that normally occurs during the hypopharyngeal phase of deglutition. Dynamic swallow studies from 60 normal volunteers were evaluated and event sequence variability was determined for 12 two-event sequences during swallowing of three bolus sizes. There was found to be some variability in event sequences for almost all events evaluated except for the following: (1) arytenoid cartilage elevation always began prior to opening of the upper esophageal sphincter, (2) the sphincter always opened prior to the arrival of the bolus at the sphincter, (3) larynx-to-hyoid approximation always occurred after the onset of upper esophageal sphincter opening, and (4) maximum pharyngeal constriction always occurred after maximal distension of the upper esophageal sphincter. Variability was more common during swallowing of the smallest bolus size. This information may be helpful in evaluating event coordination in patients with dysphagia.

Predictors of feeding gastrostomy tube removal in stroke patients with dysphagia

Dysphagia is a common consequence of stroke, estimated to be present in 25% to 50% of the stroke rehabilitation population. Relatively few data exist concerning outcome following insertion of feeding gastrostomy/jejunostomy tubes (FGT) in stroke patients with dysphagia. Our aim was to identify variables predictive of FGT removal. We studied stroke patients admitted to a single rehabilitation hospital and identified consecutive stroke patients with FGT placement. Each patient's medical records were reviewed, and demographic, clinical, and neuroimaging information were abstracted. Follow-up status was obtained by telephone interviews and review of state death certificates. Univariate and multivariate analyses were performed. Seventy-seven of the 664 (11.1%) stroke patients admitted in the 42-month study period had FGT insertion for dysphagia. Multivariate regression analysis revealed that bilateral stroke (bilateral vs unilateral; P < .022), aspiration during videofluoroscopic swallowing study (VSS; P < .012), and age greater than 52 years (P < .001) were negative predictors of FGT removal prior to discharge from the rehabilitation hospital. We identified three independent variables (bilateral stroke, aspiration during VSS, and age > 52) in stroke patients with severe dysphagia requiring FGT placement that are negative predictors of FGT removal prior to discharge from rehabilitation. These findings may help physicians and speech language pathologists predict who is likely to have a FGT removed before rehabilitation hospital discharge.

Oropharyngeal swallowing variability

OBJECTIVES/HYPOTHESIS

The pharyngeal phase of deglutition is considered to occur in a reflexive, preprogrammed fashion. Previous studies have determined a general sequence of events based on the mean timing of bolus transit and swallowing gestures. However, individual variability has not been studied. The purpose of the present study was to evaluate the amount of sequence variability that normally occurs during the oropharyngeal phase of deglutition.

STUDY DESIGN

Prospective analysis of conservative subjects.

METHODS

Dynamic swallow studies from 60 normal volunteers were evaluated, and event sequence variability was determined around two event sequences during swallowing of three bolus sizes.

RESULTS

There was found to be substantial variability in event sequences for all events analyzed. Variability was greater during a smaller bolus swallow.

CONCLUSIONS

The evaluation of variability within the study group of individuals reveals the complexity of the swallowing mechanism and underscores the importance of not relying on general guidelines in evaluating the coordination of swallowing gestures in a given individual with dysphagia complaints.

Oropharyngeal swallowing and aging: a review

This article provides an overview of normal oropharyngeal swallowing in relation to advanced age, with specific attention to oropharyngeal movement patterns and temporospatial swallowing durations. Swallowing disorders associated with aging are addressed with specific attention to the need for application of normative data to the diagnostic process. Attention is drawn to the need for continued research on swallowing function in the normal adult if efforts to maximize functional independence in eating and swallowing in the institutionalized adult are to be realized.

Lesion localization in acute stroke patients with risk of aspiration

The objective of this prospective study was to determine whether specific neuroanatomical sites were associated with increased risk of aspiration in acute stroke patients. Videofluoroscopic swallow studies (VSS) and computed tomography or magnetic resonance imaging scans were completed on consecutive male stroke patients (n = 54). Videofluoroscopic swallow studies were scored on a scale from 0 (normal swallowing) to 4 (severe dysphagia). Patients with scores of 0-1 were grouped together as having no risk of aspiration, and patients with scores of 2-4 were grouped together as having a risk of aspiration. Lesion analyses revealed that location appeared to be more critical than hemisphere or lesion size in predicting patients at risk of aspiration. Anterior locations and subcortical periventricular white matter sites were commonly lesioned in patients with risk of aspiration, whereas patients without risk of aspiration were more likely to have posterior lesions and lesions to subcortical gray matter structures. These data demonstrate that swallowing appears to be mediated by a distributed neural network that involves both cerebral hemispheres with descending input to the medulla; however, specific lesion locations may put patients at a greater risk of aspiration.

Thermal application reduces the duration of stage transition in dysphagia after stroke

The present study had two purposes. The first was to provide variability data on objectively measured durational parameters of swallowing as accomplished by dysphagic patients secondary to stroke. The second was to examine the short-term effects of thermal application on these same durational measures. The study employed a cross-over design with each dysphagic stroke subject swallowing 10 times in both untreated and treated conditions. Two findings emerged: (1) swallowing durations in the 22 dysphagic stroke subjects were highly variable within and across subjects and have distributions that were nonnormal with nonhomogeneous variances; (2) thermal application reduced duration of stage transition (DST) and total swallow duration (TSD). Implications of these findings are discussed.

The influence of bolus volume and viscosity on anterior lingual force during the oral stage of swallowing

The influence of bolus volume and viscosity on the distribution of anterior lingual force during the oral stage of swallowing was investigated using a new force transducer technology. The maximum force amplitudes from 5 normal adults were measured simultaneously at the mid-anterior, right, and left lateral tongue margins during 10 volitional swallows of 5-, 10-, and 20-ml volumes of water, applesauce, and pudding. Results indicated significant increases in peak force amplitude as viscosity increased. Volume did not significantly influence maximum lingual force amplitudes. Individual subjects demonstrated consistent patterns of asymmetrical force distribution across the lingual margins tested. The results suggest that bolus-specific properties influence the mechanics of oral stage lingual swallowing. This finding has important clinical implications in the assessment and treatment of dysphagic individuals.

A direct intervention program for chronic neurogenic dysphagia secondary to brainstem stroke

Little objective documentation is available regarding the efficacy of therapies for oropharyngeal dysphagia. Information specifying efficacy of treatment for chronic dysphagic conditions is almost nonexistent. This report describes a direct therapy program for chronic neurogenic dysphagia resulting from brainstem stroke, and provides information on immediate and long-term clinical outcome. Changes in swallowing physiology reflect goals of therapy. Long-term follow-up shows that functional benefits are long lasting without related health complications.

Larynx motion associated with swallowing during radiation therapy

PURPOSE

A basis is presented for predicting the reduction in radiation dose to the larynx attributable to swallowing during radiation therapy treatment.

METHODS AND MATERIALS

Laryngeal movement associated with swallowing can occur during radiation therapy even when the patient's head is immobilized. Data on the extent and timing of laryngeal motions and the frequency of swallowing were used to predict the effect such motion would have on accuracy of radiation dose to the larynx.

RESULTS

In a nontracheostomized adult the larynx elevates approximately 2 cm during a swallow and moves anteriorly less than 1 cm. The normal frequency of swallowing in the supine position is once every 1-2 min. During therapy, the likelihood of a swallow occurring during an irradiation interval depended on the duration of the interval. For irradiation intervals less than 2 min long the ratio of number of swallows to number of intervals was 0.27. For irradiation intervals between 2-3 min long the ratio was 1.76. Based on conservative estimates of radiation field dimensions, larynx motion, and incidence of swallowing, the reduction in radiation dose attributable to swallowing during treatment would be approximately 0.5%.

CONCLUSION

With small fields the total dose is only decreased by 0.5% with swallowing, so the change in the total dose is insignificant.

Temperature acceleration in cold oral stimulation

This study measured the temperature acceleration of a cold probe as it contacts human tissue. Both the effects of touching a cold probe to the oral cavity were investigated. The results indicated a rapid warming pattern. This warming is effected first by temperature changes resulting from the probe being moved from ice into room temperature and second by the contact to oral mucosa. In fact, in some cases, the probe had reached minimal cold sensation levels by the time it reached the oral cavity. Results also indicated that 6 sec after the probe is lifted from the ice, the temperature closely approximates temperatures perceived as warm or at least neutral, but not cold.

Swallowing recovery following anterior tongue and floor of mouth surgery

Videofluoroscopic and clinical data are presented for postsurgical recovery of tongue and hyoid activity during swallowing. Comparison is made to normal controls. Postsurgery, but prior to radiotherapy, both the lingual propulsive gesture and hyoid velocity were slower than normal. These features of the swallow had returned to the normal range following radiotherapy. The general sequencing of swallowing events, and the relationship of the end of the tongue propulsion to anterior hyoid motion were normal in those patients able to swallow. In this patient group, postsurgical radiotherapy did not prevent continued recovery of swallowing function sufficient for oral nutrition.