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PubMed2002

Neuronal NO modulates spontaneous and ANG II-stimulated fetal swallowing behavior in the near-term ovine fetus.

Spontaneous fetal swallowing occurs at a markedly higher rate compared with spontaneous adult drinking activity. This high rate of fetal swallowing is critical for amniotic fluid volume regulation. Central NO is critical for maintaining the normal rate of fetal swallowing, as nonselective inhibition of NO (with central N(G)-nitro-L-arginine methyl ester) suppresses spontaneous and angiotensin II (ANG II)-stimulated swallowing. We sought to differentiate the contributions of central endothelial vs. neuronal NO in the regulation of spontaneous and stimulated fetal swallowing, using a selective neuronal NO synthase (nNOS) inhibitor. Six time-dated pregnant ewes and fetuses were chronically prepared with fetal vascular and intracerebroventricular (i.c.v.) catheters and electrocorticogram (ECoG) and esophageal electromyogram electrodes and studied at 130 +/- 1 days of gestation. After an initial 2-h baseline period (0-2 h), the selective nNOS inhibitor N-propyl-L-arginine (NPLA) was injected i.c.v. (2-4 h). At 4 h, the dose of NPLA was repeated, together with ANG II, and fetal swallowing was monitored for a final 2 h. Four fetuses also received an identical control study (on an alternate day) in which NPLA was replaced with artificial cerebrospinal fluid (aCSF). Suppression of nNOS by i.c.v. NPLA significantly reduced mean (+/- SE) spontaneous fetal swallowing (1.35 +/- 0.12 to 0.50 +/- 0.07 swallows/min; P < 0.001). Injection of ANG II in the presence of NPLA had no dipsogenic effect on fetal swallowing (0.68 +/- 0.09 swallows/min). In the aCSF study, i.c.v. aCSF did not change fetal swallowing (0.93 +/- 0.10 vs. 0.95 +/- 0.09 swallows/min), whereas i.c.v. ANG II resulted in a significant increase in the rate of fetal swallowing (2.0 +/- 0.04 swallows/min; P = 0.001). We speculate that the suppressive dipsogenic effects of central NPLA indicate that spontaneous and ANG II- stimulated fetal swallowing is dependent on central nNOS activity.

Angiotensin II↗
PubMed2004

Cerebral areas processing swallowing and tongue movement are overlapping but distinct: a functional magnetic resonance imaging study.

Although multiple regions of the cerebral cortex have been implicated in swallowing, the functional contributions of each brain area remain unclear. The present study sought to clarify the roles of these cortical foci in swallowing by comparing brain activation associated with voluntary saliva swallowing and voluntary tongue elevation. Fourteen healthy right-handed subjects were examined with single-event-related functional magnetic resonance imaging (fMRI) while laryngeal movements associated with swallowing and tongue movement were simultaneously recorded. Both swallowing and tongue elevation activated 1) the left lateral pericentral and anterior parietal cortex, and 2) the anterior cingulate cortex (ACC) and adjacent supplementary motor area (SMA), suggesting that these brain regions mediate processes shared by swallowing and tongue movement. Tongue elevation activated a larger total volume of cortex than swallowing, with significantly greater activation within the ACC, SMA, right precentral and postcentral gyri, premotor cortex, right putamen, and thalamus. Although a contrast analysis failed to identify activation foci specific to swallowing, superimposed activation maps suggested that the most lateral extent of the left pericentral and anterior parietal cortex, rostral ACC, precuneus, and right parietal operculum/insula were preferentially activated by swallowing. This finding suggests that these brain areas may mediate processes specific to swallowing. Approximately 60% of the subjects showed a strong functional lateralization of the postcentral gyrus toward the left hemisphere for swallowing, whereas 40% showed a similar activation bias for the tongue elevation task. This finding supports the view that the oral sensorimotor cortices within the left and right hemispheres are functionally nonequivalent.

Adult↗
PubMed2007

Swallowing difficulties reported by adults infected with HIV/AIDS attending a hospital outpatient clinic in Gauteng, South Africa.

OBJECTIVE: Swallowing difficulties can exert a profound effect on quality of life, may result in reduced nutritional intake and place individuals at risk of aspiration. However, there is little data available on the swallowing difficulties occurring within the HIV/AIDS population in South Africa. A descriptive study was therefore conducted to document the presence of reported swallowing difficulties in a sample of adults with HIV. PATIENTS AND METHODS: One-to-one semi-structured interview schedules were administered to 120 adults with HIV attending a clinic in Gauteng, and medical records were evaluated to document the presence of reported swallowing difficulties. RESULTS: Participants described a range of swallowing difficulties and the number of swallowing difficulties reported by participants was negatively correlated with CD4 count. Swallowing difficulties were significantly associated with various opportunistic diseases and related medical pathologies. Prescribed medications were associated with reported swallowing difficulties. Treatment of swallowing difficulties was mainly medical in nature. Swallowing difficulties had affected quality of life. CONCLUSIONS: From the results it was concluded that speech therapists have a role to play in the assessment and treatment of swallowing difficulties in individuals with HIV/AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1984

Frequency and significance of swallowing during prolonged apnea in infants.

To better document and describe the phenomenon of swallowing during apneic spells, we compared the frequency of swallowing during epidsodes of prolonged apnea with nonapnea control periods in 9 preterm and 1 term infant. Infants with a history of idiopathic prolonged apnea were studied for 2 to 3 h by monitoring, electrocardiogram, nasal air flow, oral CO2, abdominal respiratory movements, chin electromyogram, pharyngeal pressure, and pH. In 7 of the infants, additional observations were performed without the intrapharyngeal recording devices. One or more swallows occurred during 75% of the 100 spells observed. Swallows were far more common during apneic spells than during nonapnea control periods, and were more frequent during mixed and obstructive apnea than during central apnea (p less than .01). Asphyxia, regurgitation, and the intrapharyngeal recording devices did not appear to cause the increased frequency of swallows during apneic spells. Swallowing was temporally related to spontaneous recovery from apnea, with a swallow usually preceding recovery by 5 to 6 s. During apneic spells, we observed that swallows were often associated with a brief obstructed inspiratory effort ("swallow-breath"), a normal component of nonfeeding swallows in infants. These swallow-breaths were interspersed with higher amplitude "ordinary" obstructed breaths during apneic episodes. Thus, 2 distinctly different types of obstructed inspiratory efforts were identified during mixed and obstructive apnea episodes in infants. The sequence of events during apneic spells in the term and preterm infants was similar.

Apnea↗
PubMed2002

Acoustic signature of the normal swallow: characterization by age, gender, and bolus volume.

Despite growing clinical use, cervical auscultation suffers from a lack of research-based data. One of the strongest criticisms of cervical auscultation is that there has been little research to demonstrate how dysphagic swallowing sounds are different from normal swallowing sounds. In order to answer this question, however, one first needs to document the acoustic characteristics of "normal," nondysphagic swallowing sounds. This article provides the first normative database of normal swallowing sounds for the adult population. The current investigation documents the acoustic characteristics of normal swallowing sounds for individuals from 18 to more than 60 years of age over a range of thin liquid volumes. Previous research has shown the normal swallow to be a dynamic event. The normal swallow is sensitive to aging of the oropharyngeal system, and also to the volume of bolus swallowed. The current investigation found that the acoustic signals generated during swallowing were sensitive to an individual's age and to the volume of the bolus swallowed. There were also some gender-specific differences in the acoustic profile of the swallowing sound. It is anticipated that the results will provide a catalyst for further research into cervical auscultation.

Acoustics↗
PubMed1999

Impaired swallowing reflex in patients with obstructive sleep apnea syndrome.

BACKGROUND: The swallowing reflex is well coordinated with breathing patterns in normal humans. However, patients with obstructive sleep apnea syndrome (OSAS) may have a swallowing disorder that reflects the abnormal function of nerves and muscles in the suprapharynx. OBJECTIVE: To examine the relationship between the swallowing function and sleep-disordered breathing in patients with OSAS. PARTICIPANTS: Twenty patients with OSAS with a mean (+/-SD) age of 53.4+/-8.9 years old, and 20 age-matched control subjects with a mean age of 51.4+/-9.1 years old. METHODS: OSAS was diagnosed using the recordings of overnight polysomnography. The swallowing function in the subject was tested using a swallowing provocation test. The swallowing reflex was determined according to the following criteria: latent time (LT), the time following a bolus injection of distilled water at the suprapharynx to the onset of swallowing; inspiratory suppression time (IST), the time from the termination of swallowing to the next onset of inspiration; and threshold volume, the minimum volume of water (range, 0.4 to 2 mL) that could evoke the swallowing response. RESULTS: Whereas the LT values in patients with OSAS were larger than the LT values in the control subjects, the IST values (which may reflect the switching mechanism from deglutition apnea to breathing) were actually shorter. In addition, a greater bolus volume was necessary to elicit swallowing in patients with OSAS than was necessary in the control subjects. CONCLUSION: Patients with OSAS are likely to exhibit an impaired swallowing reflex, probably due to the perturbed neural and muscular function of the upper airways.

Case-Control Studies↗
PubMed2003

Videofluoroscopic studies of swallowing dysfunction and the relative risk of pneumonia.

OBJECTIVE: The purpose of our investigation was to determine the relationship between the degree of swallowing dysfunction observed on barium studies and the likelihood of developing pneumonia in a large series of patients. MATERIALS AND METHODS: The findings on videofluoroscopic swallowing studies in 381 patients were used to classify these patients into one of five groups: those with normal swallowing; those with abnormal swallowing but no laryngeal penetration or tracheobronchial aspiration; those with laryngeal penetration; those with tracheobronchial aspiration; and those with silent tracheobronchial aspiration. Clinical data were also reviewed to determine how many patients had developed pneumonia during the 6 months before or after the barium studies. The data were then analyzed to determine whether the risk of developing pneumonia increased significantly with each level of swallowing dysfunction seen on barium studies. RESULTS: No significant difference was found in the frequency of pneumonia in patients with abnormal swallowing but no laryngeal penetration or tracheobronchial aspiration compared with patients with normal swallowing on barium studies (p = 0.85). In contrast, patients with laryngeal penetration, tracheobronchial aspiration, or silent tracheobronchial aspiration were approximately four times (p = 0.008), 10 times (p < 0.0001), and 13 times (p < 0.0001), respectively, more likely to develop pneumonia than those with normal swallowing. CONCLUSION: Our findings indicate that the likelihood of developing pneumonia is directly related to the degree of swallowing dysfunction seen on videofluoroscopic studies. Patients with no laryngeal penetration-regardless of whether they had normal or abnormal swallowing-have the lowest risk of developing pneumonia. Patients with laryngeal penetration, tracheobronchial aspiration, or silent tracheobronchial aspiration are, in increasing order of magnitude, significantly more likely to develop pneumonia than patients with normal swallowing.

Adult↗
PubMed1990

[Interaction of swallowing and control of breathing].

Although it is well known that swallowing interacts with respiration, information about the relationship between respiration and swallowing is limited. In this paper we described the interaction between swallowing reflex and respiration. In experimental animals, reflex swallowing can be elicited readily by electrical stimulation of the superior laryngeal nerve, and the effects of depressants on this reflex can be assessed by changes in the latency of responses and the number of swallows elicited. The swallowing reflex is independent of the background respiratory activity and a decrease in PaO2 depresses the swallowing reflex, whereas changes in Paco2 have no effect. In human subjects, the swallowing reflex can be induced by injections of a small amount of water into the pharynx. Like the responses in animals, the responses in humans can be assessed by changes in the latency of responses and the number of swallows. Using this technique, we evaluated the effects of nasal CPAP on the swallowing reflex. Our results showed that nasal CPAP remarkably depresses the swallowing reflex.

Animals↗
PubMed2005

Pill swallowing by adults with dysphagia.

OBJECTIVE: To evaluate differences in swallowing physiology and safety in patients with dysphagia between conventional tablets and a new method of tablet transportation, orally disintegrating technology (ODT) (RapiTab; Schwarz Pharma Inc, Milwaukee, Wis). DESIGN: The study observed a single group, crossover design. SETTING: Outpatient clinic within an academic teaching hospital. PARTICIPANTS: A total of 36 adult dysphagic patients referred to the clinic. INTERVENTIONS: All subjects underwent simultaneous nasopharyngeal endoscopic evaluation, surface electromyographic (sEMG) measurement, and respiratory monitoring during swallowing. Subjects were evaluated swallowing the ODT and a conventional tablet formulation. Tablets were randomly and blindly presented to each subject. Subjects completed a preference survey subsequent to swallowing both tablets. RESULTS: Significant differences included greater sEMG amplitude and longer apneic duration when swallowing a conventional tablet compared with the ODT (P<.001). Patients with dysphagia demonstrated significantly longer total swallow durations (P<.001), a higher number of swallows per tablet (P<.002), and the need for fluid to assist in the clearance of the conventional tablet (P<.001). No significant difference was noted between the 2 tablet preparations in amount of residue or airway compromise during or following the swallow. On a postevaluation survey, patients reported that they preferred the ODT preparation for most of the parameters assessed. CONCLUSIONS: Patients with dysphagia frequently complain of trouble swallowing medication. In this study, an ODT formulation provided a method of delivery that required less effort to swallow, did not result in increased levels of airway compromise, and was preferred by dysphagic patients. The ODT medication delivery technology may provide benefit to adults with dysphagia in convenience, compliance, and accuracy of dosing.

Administration, Oral↗
PubMed2001

Routine fiberoptic endoscopic evaluation of swallowing following prolonged intubation: implications for management.

HYPOTHESIS: Fiberoptic endoscopic evaluation of swallowing (FEES) will identify patients who are at high risk for pulmonary aspiration due to swallowing dysfunction after prolonged intubation. Based on the results of FEES, dietary recommendations can be made to decrease the incidence of aspiration after prolonged intubation. DESIGN: Patients who were intubated for at least 48 hours were evaluated for swallowing dysfunction by bedside FEES within 48 hours of extubation. Differences in potential risk factors between aspirators and nonaspirators were analyzed. Dietary recommendations were made and patients were followed up for signs of clinically significant aspiration. SETTING: Community teaching hospital. PATIENTS: Fifty-one consecutive patients with no previously documented swallowing disorder who required a minimum of 48 hours of intubation for mechanical ventilation. INTERVENTIONS: Fiberoptic endoscopic evaluation of swallowing was performed by a speech pathologist. Initial diet orders were determined by results of the swallowing study. MAIN OUTCOME MEASURES: Incidence of swallowing dysfunction following prolonged intubation and incidence of clinically significant aspiration following initiation of oral feeding. RESULTS: Incidence of swallowing dysfunction was 56% (27/48); 12 (25%) of 48 patients were silent aspirators. In comparing aspirators with nonaspirators, no significant differences in potential risk factors or comorbidities were seen. Nineteen (70%) of the 27 patients aspirated with thin-consistency test liquids, and the other 8 (30%) with puree consistency. No patients in this study group developed a clinically significant aspiration following initiation of appropriately modified diets. CONCLUSIONS: Fiberoptic endoscopic evaluation of swallowing identified swallowing dysfunction in more than 50% of patients intubated for longer than 48 hours, many of whom are silent aspirators. Dietary recommendations based on FEES results prevented clinically significant aspiration.

Aged↗
PubMed2000

Pretreatment swallowing function in patients with head and neck cancer.

BACKGROUND: Few objective data characterizing the pretreatment swallow function of patients with head and neck cancer are available. METHODS: Pretreatment swallowing function in 352 patients with various lesions was evaluated with videofluoroscopy and compared with control subjects. RESULTS: Patients had significantly longer oral and pharyngeal transit times, greater amounts of oral and pharyngeal residue, shorter cricopharyngeal opening durations, and lower swallow efficiencies. Swallow function worsened significantly with increased tumor stage, and patients with oral or pharyngeal lesions had worse swallow function than patients with laryngeal lesions. Frequency of complaint of swallow difficulty before treatment was 59%. Patients with lower stage tumors had fewer complaints of swallowing, as did patients with oral cavity lesions. CONCLUSIONS: Despite demonstrating significant differences from control subjects, patients had highly functional swallows before treatment. The tendency for patients not to perceive a swallowing problem is consistent with the highly functional nature of their pretreatment swallow.

Adult↗
PubMed1996

Unexplained dysphagia: viscous swallow-induced esophageal dysmotility.

Dysphagia is a manifestation of several clinical conditions of diverse origin. In spite of the variation in these disease entities in terms of their etiology, clinical presentation, natural history, and treatment, the mechanism of this clinical complaint is not always clear. We studied a group of patients with dysphagia for solids in whom no anatomic or motor abnormalities were encountered on standard studies. The group consisted of 37 patients, 25 women and 12 men, who were complaining of dysphagia of 6 months or longer duration and they did not demonstrate structural or motor abnormalities on barium esophagogram, esophagoscopy, and standard esophageal manometry. A group of 24 age-matched patients, 14 women and 10 men, with noncardiac chest pain served as the patient control. Esophageal contractile activities were studied after 10 wet swallows (5 ml of water) and 10 viscous swallows (5 cubic cm of marshmallow). Resting lower esophageal sphincter pressure and its relaxation response to swallows, amplitude of peristaltic activities, rate of dysphagia provoked during the study, and the frequency of abnormal esophageal contractions were evaluated. Six abnormal esophageal contractile activities-failed peristalsis, dropout, repetitive, simultaneous, spontaneous contractions, and aperistalsis-were utilized to generate an esophageal peristaltic dysfunction index. The mean LESP was 8.1 +/- 4.7 in the dysphagia group and 16.1 +/- 4.3 in the chest pain group. The mean amplitude of peristaltic contractions was 47.1 +/- 16.1 and 89.0 +/- 27.0 mmHg after wet swallows for dysphagia and chest pain groups, respectively. These values were 58.2 +/- 12.4 and 92.4 +/- 22.1 for viscous swallows. Swallowing provoked dysphagia in 89% of the dysphagia group after viscous swallows and 9% after wet swallows. In contrast, only 11% and 3% of control group complained of dysphagia during the study. This group of patients probably represent a cohort of patients with a nonspecific esophageal motor disorder in whom both clinical symptom and their esophageal motor counterpart can only be elicited in response to viscous swallows. We strongly believe in addition of viscous swallows in evaluating dysphagic patients in whom symptoms remain unexplained in light of standard studies.

Adult↗
PubMed1992

Coordination of mastication and swallowing.

The coordination of mastication, oral transport, and swallowing was examined during intake of solids and liquids in four normal subjects. Videofluorography (VFG) and electromyography (EMG) were recorded simultaneously while subjects consumed barium-impregnated foods. Intramuscular electrodes were inserted in the masseter, suprahyoid, and infrahyoid muscles. Ninety-four swallows were analyzed frame-by-frame for timing of bolus transport, swallowing, and phases of the masticatory gape cycle. Barium entered the pharynx a mean of 1.1 s (range -0.3 to 6.4 s) before swallow onset. This interval varied significantly among foods and was shortest for liquids. A bolus of food reached the valleculae prior to swallow onset in 37% of sequences, but most of the food was in the oral cavity at the onset of swallowing. Nearly all swallows started during the intercuspal (minimum gape) phase of the masticatory cycle. Selected sequences were analyzed further by computer, using an analog-to-digital convertor (for EMG) and frame grabber (for VFG). When subjects chewed solid food, there were loosley linked cycles of jaw and hyoid motion. A preswallow bolus of chewed food was transported from the oral cavity to the oropharynx by protraction (movement forward and upward) of the tongue and hyoid bone. The tongue compressed the food against the palate and squeezed a portion into the pharynx one or more cycles prior to swallowing. This protraction was produced by contraction of the geniohyoid and anterior digastric muscles, and occurred during the intercuspal (minimum gape) and opening phases of the masticatory cycle. The mechanism of preswallow transport was highly similar to the oral phase of swallowing. Alternation of jaw adductor and abductor activity during mastication provided a framework for integration of chewing, transport, and swallowing.

Adult↗
PubMed2006

Cerebral cortical processing of swallowing in older adults.

While brain-imaging studies in young adults have implicated multiple cortical regions in swallowing, investigations in older subjects are lacking. This study examined the neural representations of voluntary saliva swallowing and water swallowing in older adults. Nine healthy females were examined with event-related functional magnetic resonance imaging (fMRI) while laryngeal swallow-related movements were recorded. Swallowing in the older adults, like young adults, activated multiple cortical regions, most prominently the lateral pericentral, perisylvian, and anterior cingulate cortex. Activation of the postcentral gyrus was lateralized to the left hemisphere for saliva and water swallowing, consistent with our findings in young female subjects. Comparison of saliva and water swallowing revealed a fourfold increase in the brain volume activated by the water swallow compared to the saliva swallow, particularly within the right premotor and prefrontal cortex. This task-specific activation pattern may represent a compensatory response to the demands of the water swallow in the face of age-related diminution of oral sensorimotor function.

Aged↗
PubMed2002

Swallow-induced alterations in breathing in normal older people.

Respiratory parameters in 29 normal older subjects (mean age-73 years, SD = 5.7) were studied at rest, during single water swallows, and in continuous drinking. Respiration was recorded by intranasal air pressure changes and the moment of swallowing by pharyngoesophageal manometry. Compared with respiration at rest, respiratory rate increased immediately after 5 mL swallows as duration of breath cycles decreased from a mean of 3.8 s at rest to 3.5 s after swallowing (p = 0.003), but regularity of respiration was maintained. Deglutition apnea showed a trend toward increasing duration from a median of 1.06 to 1.24 s (p = 0.096) as bolus volume increased from 5 to 20 mL. Oxygen saturation levels were also compared, with a median fall of 2% during swallowing, but with larger and unexplained falls in several subjects. Direction of airflow monitoring showed 91% of single 5 mL swallows were followed by expiration, with postswallow inspiratory breaths occurring in 41% of subjects. Continuous swallowing of 100 mL of water from a cup and straw was typically performed with a pattern of multiple swallows per breath, with expiration occurring after 78.5% (cup) and 63.5% (straw) of swallows. This definition of swallowing-induced respiratory changes in normal older people forms a valuable basis for future comparison with elderly dysphagic patients.

Aged↗
PubMed2002

Swallow respiration patterns in dysphagic patients following acute stroke.

The aim of this study was to examine swallow respiratory characteristics using a notebook computer system. A relatively simple system assessing easily identifiable features is more likely to be incorporated into everyday clinical practice. Eighteen patients (age range = 51-82 years) with dysphagia poststroke and 50 healthy volunteers (age range = 20-78 years) were recruited. The patient group was less likely to always breathe out postswallow on water (9/15 cf 46/49), and some did not breathe out immediately postswallow at all (3/15 cf 0/49, p < 0.01). The pattern was similar with yogurt. Multiple swallowing was identified in the patient group and surprisingly with a large number of the volunteers for all bolus types but was more common in the patient group (p < 0.01). This trait is usually attributed to impaired swallows; that it is prevalent in the normal population has implications for using it as a dysphagia marker in clinical assessments. Yogurt has intrinsic features that increase multiple swallowing and caution should be used when identifying an impairment based on multiple swallowing with such a test substance. In the control group there was a high correlation of swallow apnea on 5 mL of water compared with 20 mL of water (r = 0.759, p < 0.01) and 5 mL of yogurt (r = 0.871, p < 0.01), indicating a possible individual swallow respiration pattern. This was also evident in the patient group. No significant difference in length of swallow apnea was found between the two groups. No evidence was found to link swallow respiration characteristics with aspiration as identified on simultaneous videofluoroscopy. The patient group had a wide range of impairments which suggests that stroke severity is not the sole determinant of swallow respiratory changes.

Aged↗
PubMed2004

Effects of withdrawal of phasic lung inflation during normocapnia and hypercapnia on the swallowing reflex in humans.

PURPOSE: This study was done to test the hypothesis that hypercapnia has a direct, inhibitory effect on swallowing. METHODS: We investigated changes in the frequency and timing of repeated swallows induced by continuous infusion of water into the pharynx before, during, and after transient airway occlusion at normocapnia and hypercapnia in 12 healthy volunteers. Hypercapnia was induced by adding a dead space. Ventilation was monitored using a pneumotachograph, and swallowing was identified by submental electromyogram. RESULTS: We found that hypercapnia decreased the frequency of swallows (8.2 +/- 3.7 vs 11.4 +/- 5.3 swallows.min-1 [mean +/- SD]: hypercapnia vs normocapnia; P < 0.05), together with a loss of the preponderant coupling of swallows with expiratory phase observed at normocapnia. We also found that the withdrawal of phasic lung inflation produced by airway occlusion at end-expiration suddenly increased the swallowing frequency, both at normocapnia (from 11.4 +/- 5.3 to 16.7 +/- 3.7 swallows.min-1; P < 0.01) and at hypercapnia (from 8.2 +/- 3.7 to 22.0 +/- 6.7 swallows.min-1; P < 0.01). Although the degree of increased swallowing frequency during airway occlusion was more prominent at hypercapnia than at normocapnia ( P < 0.05), the distribution of the timing of swallows in relation to the phase of the respiratory cycle during airway occlusion at hypercapnia was similar to that during airway occlusion at normocapnia. CONCLUSION: The results of our study strongly suggest that the attenuation of the swallowing reflex during hypercapnia is not due to the direct, inhibitory effect of CO2 on the swallowing center, but, rather, is due to the increased inhibitory influence of a lung-volume-related reflex.

Adult↗
PubMed1989

Swallowing during ongoing fluid ingestion in the rat.

In order to identify fixed versus flexible aspects of swallowing and oromotor control, we developed a method for the concurrent analysis of swallow frequency, swallow volume, and the temporal correlation between swallowing and rhythmic orolingual movements during prolonged bouts of fluid ingestion in unanesthetized, unrestrained rats. Rats actively ingested 0.1 M sucrose solutions infused intraorally: (a) at a constant rate within sessions; and (b) during separate sessions across which the rate of intraoral infusion (= ingestion rate) was varied. Salient characteristics of 'intraoral intake' included: (1) covariation of swallow frequency and swallow volume to mediate adjustments in the rate of ingestion; (2) emission of rhythmic coupled movements (5-7 Hz) of the jaw and tongue that serve to transport fluid through the mouth; (3) a 20-40 ms increase in the duration of the rhythmic movement cycle associated with swallow onset; and (4) emergence of pauses between bursts of rhythmic oromotor behavior with increases in cumulative intake. That intraoral intake and fluid ingestion via spout-licking (Weijnen et al., Brain Behav. Evol., 25, 1985) share all of these features suggests strongly that common neural processes, relatively uninfluenced by sources of sensory feedback attending contact with an environmental fluid source, underlie these aspects of normal fluid ingestion. The dynamic adjustment of swallow frequency and swallow volume presents a challenge to traditional models of reflexive swallow initiation derived primarily from the neurophysiological study of acute, non-behaving preparations.

Animals↗