Breathing and swallowing in normal man--effects of changes in body position, bolus types, and respiratory drive.

BACKGROUND: Coordination of breathing and swallowing is essential for airway protection and dyscoordination may cause morbidity and mortality. METHODS: Using a recently developed technique for high accuracy respiratory measurements of airflow during swallowing, we investigated the effects of body position (upright vs left lateral), bolus type (spontaneously swallowed saliva vs water), and respiratory drive (normo- vs hypercapnia) on coordination of breathing and swallowing in 32 healthy volunteers. KEY RESULTS: Swallows were in all cases (100%) proceded by expiration and 98% were also followed by expiration, regardless of body position, bolus type, or respiratory drive. While the endpoint of postswallow apnea correlated well to the endpoint of pharyngeal swallowing, duration of preswallow apnea was highly variable. In a small fraction of swallows followed by inspiration (3%), the expiratory phase before swallowing and duration of postswallow apnea was significantly longer. Body position and respiratory drive affected the increase in upper esophageal sphincter tone during inspiration. Increased respiratory drive also reduced swallowing frequency and shortened duration of preswallow apnea. Water swallows had longer duration of preswallow apnea. CONCLUSIONS & INFERENCES: Swallowing occurs during the expiratory phase of respiration, and the fraction of swallows preceded and followed by expiration approach 100% in healthy humans. This integration between breathing and swallowing remains unchanged regardless of body position, bolus characteristics, or respiratory drive. Our results provide a platform for future studies aiming at understanding how this integration is changed by aging, diseases, and drugs.

Swallowing and respiratory pattern in young healthy individuals recorded with high temporal resolution.

The coordination of swallowing and respiration is essential for a safe swallow. Swallowing consists of several subsecond events. To study this, it is important to use modalities with high temporal resolution. In this study, we have examined young healthy individuals with simultaneous videofluoroscopy, videomanometry and respiratory recording, all with high temporal resolution. The onset of 13 predetermined swallowing and respiratory events and the surrounding respiratory phase pattern were studied in different body positions and during different respiratory drives. An increased respiratory drive was induced by breathing 5% CO(2). The results demonstrated a highly repeatable and fixed temporal coordination of the swallowing pattern despite body position and respiratory drive. Previous studies have demonstrated a period of centrally controlled apnoea during swallowing. This apnoea period has a variable length, varying from 1 to 5 s. During increased respiratory drive, we could demonstrate a significantly shorter period of apnoea during swallowing, mainly due to an earlier resumption of respiration. The high temporal recordings in this study have revealed that swallowing during expiration is present basically in all healthy individuals. This swallowing respiratory pattern seems to be appropriate for a safe swallow. This knowledge will be used as a reference for future studies on how swallowing and respiratory coordination might be altered due to ageing and diseases.

Neuronal survival and glial reactions after recurrent laryngeal nerve resection in the rat.

OBJECTIVES/HYPOTHESIS: Complete axonal injury to the recurrent laryngeal nerve (RLN) leads to permanent loss of coordinated function of the intrinsic muscles of the larynx. The aim of the present study was to investigate retrograde reactions, neuronal survival, and glial reactions in the nucleus ambiguus after a distal resection of the RLN to evaluate the potential need for neuroprotective substances. STUDY DESIGN AND METHODS: A segment of the left RLN was resected in 31 adult rats. Before sacrifice of the animals at 2 to 28 days postlesion, the motor neurons in the nucleus ambiguus were retrogradely traced by the use of Fluorogold. Brainstems were isolated and processed for neuron quantification and immunohistochemical analysis. Neuron counts were performed in the nucleus ambiguus on serial sections. Glial reactions were investigated in the nucleus ambiguus using immunohistochemistry. RESULTS: No decrease in the number of motor neurons in the nucleus ambiguus could be demonstrated up to 1 month postlesion. Astroglia and microglia showed increased immunoreactivity at 7 to 14 days postinjury, followed by a slight decline in glial reaction. Microglia revealed no signs of transformation into macrophages during the study period, further indicating the absence of neuronal loss. CONCLUSIONS: Neuronal death does not occur within 1 month postlesion as a result of resection of the RLN in the adult rat, and neuroprotective substances should therefore be of minor value after RLN injury. Glial reactions appear in a similar fashion as after other peripheral nerve lesions not causing neuronal loss.

Fiber-type composition and fiber size of the human cricopharyngeal muscle and the pharyngeal constrictor muscle.

BACKGROUND: Despite a similar density of nicotinic acetylcholine receptors, the upper esophageal sphincter is sensitive to partial neuromuscular block, whereas the pharyngeal constrictor muscle is more resistant. In order to postulate possible mechanisms behind this difference in pharmacological response, basic knowledge of morphological and physiological features of these muscles is needed. The aim of this study was to compare the muscle fiber-type composition, the size and the morphology of the muscle fibers of the cricopharyngeal muscle, the main component of the upper esophageal sphincter, with that of the pharyngeal constrictor muscle. METHODS: Muscle specimens were obtained from five patients undergoing surgery with laryngectomy. Muscle fiber type was determined by myosin heavy chain immunohistochemistry and the muscle fiber cross-sectional area was measured for each fiber type by planimetry. Morphology of muscle fibers was evaluated by histochemistry. RESULTS: The muscle fiber cross-sectional area was generally smaller in the cricopharyngeal muscle compared with the pharyngeal constrictor muscle (P < 0.001). The composition of fiber types showed a large interindividual variability with no distinct difference between the studied muscles. Aberrant histological features were common in both the cricopharyngeal muscle and the pharyngeal constrictor muscle. CONCLUSION: The main morphological difference between the neuromuscular blocking agents sensitive cricopharyngeal muscle and the more resistant pharyngeal constrictor muscle is a uniformly smaller size of contributing fiber types in the cricopharyngeal muscle than in the pharyngeal constrictor muscle. The muscle fiber-type composition does not differ between the two studied muscles.

Acetylcholine receptor density in human cricopharyngeal muscle and pharyngeal constrictor muscle.

BACKGROUND: Upper esophageal sphincter resting tone is reduced during partial neuromuscular block, whereas contraction of the pharyngeal constrictor muscle is only slightly affected. We hypothesized that this difference may arise from differential nicotinic acetylcholine receptor (nAChR) density, the density supposedly being lower in the more sensitive cricopharyngeal muscle than in the resistant pharyngeal constrictor muscle. The aim of this study was to determine the density of nAChR in the main component of the upper esophageal sphincter, the cricopharyngeal muscle, and in the pharyngeal constrictor muscle. METHOD: After approval by the institutional ethics committee and informed consent, muscle specimens were obtained from five patients undergoing surgery with laryngectomy for malignancies of the larynx or thyroid gland. None had received radiation therapy to the affected area. The nAChR from these tissue specimens were solubilized and incubated with 125I-alpha-bungarotoxin. The quantity of radioligand-receptor complex was measured by radioactive decay in a liquid scintillation counter. The receptor density was expressed as femtomoles per milligram of protein (fmol/mg protein). RESULTS: The nAChR density was determined to 6.8 (3.5) fmol/mg protein (mean (SD)) in the cricopharyngeal muscle and 5.6 (2.1) fmol/mg protein in the pharyngeal constrictor muscle (P = 0.22). Although we could not find any difference in mean nAChR density, contrary to our hypothesis, the density in four of the five patients was higher in the cricopharyngeal muscle than in the pharyngeal constrictor muscle. CONCLUSION: Our results indicate that the density of nicotinic acetylcholine receptors is similar in the cricopharyngeal muscle and in the pharyngeal constrictor muscle. Nicotinic acetylcholine receptor density, as determined by 125I-alpha-bungarotoxin assay, cannot explain the difference in response to neuromuscular blocking drugs between the investigated muscles.

Pharyngeal function and airway protection during subhypnotic concentrations of propofol, isoflurane, and sevoflurane: volunteers examined by pharyngeal videoradiography and simultaneous manometry.

BACKGROUND: Anesthetic agents alter pharyngeal function with risk of impaired airway protection and aspiration. This study was performed to evaluate pharyngeal function during subhypnotic concentrations of propofol, isoflurane, and sevoflurane and to compare the drugs for possible differences in this respect. METHODS: Forty-five healthy volunteers were randomized to receive propofol, isoflurane, or sevoflurane. During series of liquid contrast bolus swallowing, fluoroscopy and simultaneous solid state videomanometry was used to study the incidence of pharyngeal dysfunction, the initiation of swallowing, and the bolus transit time. Pressure changes were recorded at the back of the tongue, the pharyngeal constrictor muscles, and the upper esophageal sphincter. After control recordings, the anesthetic was delivered, and measurements were made at 0.50 and 0.25 predicted blood propotol concentration (Cp50(asleep)) for propofol and 0.50 and 0.25 minimum alveolar concentration (MAC)(awake) for the inhalational agents. Final recordings were made 20 min after the end of anesthetic delivery. RESULTS: All anesthetics caused an increased incidence of pharyngeal dysfunction with laryngeal bolus penetration. Propofol increased the incidence from 8 to 58%, isoflurane from 4 to 36%, and sevoflurane from 6 to 35%. Propofol in 0.50 and 0.25 Cp50(asleep) had the most extensive effect on the pharyngeal contraction patterns (P < 0.05). The upper esophageal sphincter resting tone was markedly reduced from 83 +/- 36 to 39 +/- 19 mmHg by propofol (P < 0.001), which differed from isoflurane (P = 0.03). Sevoflurane also reduced the upper esophageal sphincter resting tone from 65 +/- 16 to 45 +/- 18 mmHg at 0.50 MAC(awake)(P = 0.008). All agents caused a reduced upper esophageal sphincter peak contraction amplitude (P < 0.05), and the reduction was greatest in the propofol group (P = 0.002). CONCLUSION: Subhypnotic concentrations of propofol, isoflurane, and sevoflurane cause an increased incidence of pharyngeal dysfunction with penetration of bolus to the larynx. The effect on the pharyngeal contraction pattern was most pronounced in the propofol group, with markedly reduced contraction forces.

Leakage around voice prosthesis in laryngectomees: treatment with local GM-CSF.

OBJECTIVES: The aim of this study was to investigate the possibility of treating leakage around voice prosthesis by local injection of granulocyte-macrophage colony-stimulating factor (GM-CSF). STUDY DESIGN: Three patients with nonhealing leaking tracheoesophageal (TE) fistula, resistant to common treatment, were treated with local GM-CSF. MATERIAL AND METHODS: Fistula size was measured and photo documented before and after treatment. RESULT: In all three patients, the fistula shrank, and the leakage ceased. No side effects were observed. CONCLUSION: Local injection with GM-CSF seems to be a simple and effective way of decreasing a leaking TE-fistula in laryngectomized patients. A great advantage was that the procedure could be done with the voice prosthesis in place.

[Fiberoptic endoscopy confirms the cause of upper respiratory obstruction in small children. The most common causes to referrals are sleep apnea syndrome and inspiratory stridor]. / Fiberskopi fastställer orsak till höga andningshinder hos små barn. Vanligaste remissorsakerna sömnapnésyndrom och inspiratorisk stridor.

Guidelines for the clinical investigation of young children with stridor and sleep apnea are presented. Clinical examination and flexible videolaryngoscopy performed in local anaesthesia are the most important diagnostic tools for this group of children. If the impairment is severe or an objective evaluation is needed the child should also undergo nocturnal polygraphic recording and lung function tests. Out of 43 children examined with flexible videolaryngoscopy 21 had positive findings, laryngomalacia being the most common diagnosis. Flexible videolaryngoscopy is a good complement to laryngoscopy under general anaesthesia. It can be performed as early as in the neonatal period.

Successful EXIT (ex utero intrapartum treatment) procedure in a fetus diagnosed prenatally with congenital high-airway obstruction syndrome due to laryngeal atresia.

Congenital high-airway obstruction syndrome (CHAOS) is due to rare malformations and has been reported previously in only few cases. If the diagnosis can be made prenatally, the ex utero intrapartum treatment (EXIT) procedure may be life-saving. A healthy 28-year old nulli-para was referred because of isolated ascites found at gestational week 16 during routine ultrasound scan. Repeated scans showed overdistended hyperechogenic lungs with inverted diaphragm and a dilated trachea, which was interpreted as a CHAOS resulting from laryngeal atresia. The ascites eventually disappeared. An EXIT procedure was performed at 35 weeks of gestation. Anesthesia of the mother was induced with thiopental, succinylcholine and fentanyl followed by intubation, and maintained with isoflurane and nitrous oxide. A low abdominal midline incision was performed followed by a low transverse incision of the uterus. The fetal head, right arm and shoulder were delivered and intramuscular anesthesia was administered to the fetus. Immediate laryngoscopy confirmed the diagnosis and a tracheostomy was therefore performed. Surfactant was given after a few minutes of ventilation. Compliance improved and when the fetus was easy to ventilate, it was delivered. The baby is developing normally at 18 months of age. Surgical correction of the malformation will be performed after two years of age. It is concluded that some fetuses with a prenatal diagnosis of CHAOS can benefit from the EXIT procedure at delivery. This necessitates a multidisciplinary management team.

The incidence and mechanisms of pharyngeal and upper esophageal dysfunction in partially paralyzed humans: pharyngeal videoradiography and simultaneous manometry after atracurium.

BACKGROUND: Residual neuromuscular block caused by vecuronium alters pharyngeal function and impairs airway protection. The primary objectives of this investigation were to radiographically evaluate the swallowing act and to record the incidence of and the mechanism behind pharyngeal dysfunction during partial neuromuscular block. The secondary objective was to evaluate the effect of atracurium on pharyngeal function. METHODS: Twenty healthy volunteers were studied while awake during liquid-contrast bolus swallowing. The incidence of pharyngeal dysfunction was studied by fluoroscopy. The initiation of the swallowing process, the pharyngeal coordination, and the bolus transit time were evaluated. Simultaneous manometry was used to document pressure changes at the tongue base, the pharyngeal constrictor muscles, and the upper esophageal sphincter. After control recordings, an intravenous infusion of atracurium was administered to obtain train-of-four ratios (T4/T1) of 0.60, 0.70, and 0.80, followed by recovery to a train-of-four ratio of more than 0.90. RESULTS: The incidence of pharyngeal dysfunction was 6% during the control recordings and increased (P < 0.05) to 28%, 17%, and 20% at train-of-four ratios 0.60, 0.70, and 0.80, respectively. After recovery to a train-of-four ratio of more than 0.90, the incidence was 13%. Pharyngeal dysfunction occurred in 74 of 444 swallows, the majority (80%) resulting in laryngeal penetration. The initiation of the swallowing reflex was impaired during partial paralysis (P = 0.0081). The pharyngeal coordination was impaired at train-of-four ratios of 0.60 and 0.70 (P < 0.01). A marked reduction in the upper esophageal sphincter resting tone was found, as well as a reduced contraction force in the pharyngeal constrictor muscles. The bolus transit time did not change significantly. CONCLUSION: Partial neuromuscular paralysis caused by atracurium is associated with a four- to fivefold increase in the incidence of misdirected swallowing. The mechanism behind the pharyngeal dysfunction is a delayed initiation of the swallowing reflex, impaired pharyngeal muscle function, and impaired coordination. The majority of misdirected swallows resulted in penetration of bolus to the larynx.

Predictive value of malignancy grading systems, DNA content, p53, and angiogenesis for stage I tongue carcinomas.

AIM: To assess the clinical value of malignancy grading systems compared with nuclear DNA content, protein p53, and angiogenesis for predicting recurrence of stage I (UICC, 1987) tongue carcinomas. METHODS: Histopathological malignancy grading according to Jakobsson and tumour front grading according to Bryne et al were performed on haematoxylin and eosin slides. DNA analysis was performed by image cytometry. Protein p53 and angiogenesis were evaluated by immunohistochemical analysis using antibody CM1 and antibody against factor VIII related antigen, respectively. RESULTS: 49 patients with stage I carcinomas of the mobile tongue were included, all treated by local surgical excision alone. Eight patients (16%) suffered from local recurrence during follow up, and 13 (27%) had regional recurrence. Both Jakobsson's malignancy grading system and p53 immunoreactivity proved to be useful predictors of regional recurrence in a Cox multivariate regression analysis. CONCLUSIONS: Histopathological malignancy grading systems provide valuable prognostic information and can still compete with current biological markers in this respect.

TP53 mutations do not correlate with locoregional recurrence in stage I tongue carcinomas.

BACKGROUND: The abrogation of the TP53 gene is considered to play a central role in the development of human cancers. Exons 5-8 harbor mutations most frequently, mainly of the missense type, resulting in accumulation of the p53 protein. The importance of these alterations as prognostic factors, are issues of controversy. MATERIAL AND METHODS: Thirty-four patients suffering from stage I tongue carcinoma had been treated with a local surgical excision of the tumor. Seventeen patients had developed a local recurrence in the tongue or cervical (regional) metastases while 17 patients, matched for age and gender to the former group, had no recurring disease within follow-up. Protein p53 was detected through immunohistochemical (IHC) analysis using antibody CM1. Exons 5-8 of the TP53 gene were amplified through the Polymerase Chain Reaction (PCR). The presence of mutations analyzed by CDGE (Constant Denaturant Gel Electrophoresis) and detected mutations were subjected to sequencing. RESULTS: 20 out of 34 tumors (59%) showed mutated TP53, 18 tumors were IHC p53 positive, but the correlation between CDGE and IHC was only 56%. Sequencing of the gene was possible in 8 cases. CONCLUSIONS: Neither the presence of mutations nor immunostaining had any impact on the risk of recurrence expressed as life-table analysis of time to recurrence.

Preneoplastic oral lesions: the clinical value of image cytometry DNA analysis, p53 and p21/WAF1 expression.

BACKGROUND: Various mucosal lesions are frequently encountered in the oral cavity. Neither macroscopic nor microscopic evaluation of these lesions gives any reliable information concerning the risk of cancer development. MATERIAL AND METHODS: From 21 patients, 29 mucosal lesions were found to precede development of invasive squamous cell carcinoma or carcinoma in situ at the same location. The lesions were matched to 29 control lesions, with the same grade of dysplasia and from exactly the same locations but without subsequent cancer during a mean follow up of 112 months (46-194). The specimens were evaluated using Image Cytometry DNA analysis and immunohistochemical analysis of p53 and p21/WAF1 expression. RESULTS: Lesions prior to carcinomatous development displayed a higher degree of DNA aberration as compared with the control lesions. p53 and p21/WAF1 evaluation did not reveal any differences between cases and controls. CONCLUSION: Image Cytometry DNA analysis is an useful adjunct to histopathological evaluation of oral mucosal lesions for prediction of risk of malignant transformation.

Swallowing disorders after esophageal atresia evaluated with videomanometry.

BACKGROUND: Patients with repaired esophageal atresia often show persistent motility disorders of the esophagus. METHODS: In this study, the authors used a newly developed method, videomanometry, to study intraluminal pressures and function of the pharynx and upper esophagus in such a group of patients and compared the results with those in healthy age-matched controls. RESULTS: A significant difference was found between timing of the pharynx contraction and upper esophageal sphincter (UES) relaxation, indicating a dyscoordination of swallowing in the patient group. Transit time of bolus from the pharynx to the esophagus was also shorter for the patient group. Such dyscoordination may be a risk factor that can cause aspiration and respiratory symptoms. CONCLUSION: UES resting pressure and residual pressure on swallowing, did not differ between the two groups.

[A revolutionary Japanese method for treatment of lymphangioma]. / Japansk metod revolutionerar behandlingen av lymfangiom.

Large cystic lymphangiomas of the neck (hygroma colli) have traditionally been treated surgically or by local injection of various sclerosing agents. Owing to the infiltrative growth of these cysts, radical surgery has often been difficult due to the risk of damage to nerves and adjacent organs; and the use of available sclerosing agents has often resulted in disfigurement due to extensive scarring, thus rendering secondary surgery even more difficult. However, OK-432, a new agent for local injection, has been tested with good results, especially in Japan. In five consecutive paediatric cases of lymphangioma, we found ultrasound-guided injection of the cysts with OK-432 to yield good response without complications. In three cases, the lymphangioma disappeared leaving the child's appearance quite normal, and there has been no recurrence. In one case, the lymphangioma disappeared but apparently recurred within half a year (during which time we had lost contact with the family). This was the only case of small cysts (cavernous lymphangioma), which are putatively more resistant to OK-432. The only child to be operated also had thoracic lymphangioma which was not injected, though the cervical part which was injected was reduced by 50 per cent pre-operatively, the final outcome being excellent with no visible cysts in any region. Thus, hitherto our results suggest the therapeutic effect of OK-432 to be good, and further clinical investigation is planned.

Stromelysin-3 mRNA expression in dysplasias and invasive epithelial cancer of the larynx.

Matrix metalloproteinases are believed to play an important role in tumor progression, invasion and metastasis. In order to investigate if the expression of stromelysin-3 (ST3) mRNA could add prognostic information concerning invasive laryngeal cancer and/or be indicative of a high risk for tumor progression in laryngeal dysplasias ST3 expression was analyzed by in situ hybridisation of formalin fixed paraffin embedded laryngeal specimens. Furthermore, all specimens underwent image cytometry (ICM) DNA analysis, and, p53 immunostaining. Invasive epithelial cancer, both localized (T1, T2) cancers, cured, as well as not cured, by radiotherapy, and cases with regional lymph node metastases were studied. Furthermore, high grade and low grade dysplasias, selected for rapid, slow and non-progression, as well as non-neoplastic inflammatory lesions were investigated. Expression of the ST3 gene was found in 9 out of 14 (64%) invasive cancer lesions, and in 3 out of 10 (30%) dysplasias, thus indicating that ST3 expression correlates to tumor progression. The ST3 positive laryngeal cancer lesions displayed a higher degree of DNA aberration than the ST3 negative lesions thus suggesting that ST3 positivity could indicate highly malignant tumors. Of the three ST3 positive dysplasias, the first progressed rapidly to cancer in situ with suspected microinvasion. The second ST3 positive dysplasia progressed to invasive cancer within five months. The third ST3 positive dysplasia had been radically excised and hereby cured. All but one of the dysplastic lesions showed p53 immunoreactivity, and all dysplasias exhibited aneuploid cells. ST3 expression appears to be a late event in the multistage process of carcinogenesis and could prove useful as an indicator of dysplasias with imminent risk for progression to invasive cancer.

Nuclear DNA content and p53 overexpression in stage I squamous cell carcinoma of the tongue compared with advanced tongue carcinomas.

AIMS: To evaluate the predictive value of the nuclear DNA content (image cytometry) and p53 overexpression (immuno-histochemistry using antibody CM-1) in uniformly treated stage I carcinomas of the mobile tongue. Also, to compare stage I carcinomas with advanced tongue carcinomas (stages II-IV). METHODS: Archival formalin fixed, paraffin wax embedded tumour specimens from 54 patients with stage I squamous cell carcinoma and 37 patients with advanced squamous cell carcinoma were analysed. Mean follow up time of the stage I carcinomas was 71 months (median, 62.5; range, 6-175). RESULTS: Twenty three patients (stage I) had recurring disease: 10 had local recurrence (in the tongue) and 13 had regional recurrence (cervical metastases). Locally recurring stage I carcinomas had a more pronounced DNA deviation than the other stage I carcinomas and this degree of deviation was comparable with the DNA content of advanced carcinomas. Stage I carcinomas that developed regional recurrences overexpressed p53 more frequently. In Cox multivariate regression analysis of time to recurrence, DNA deviation was a significant parameter in tumours that recurred locally (p = 0.032). p53 overexpression was the only parameter close to significance for regional recurrence (p = 0.065). CONCLUSIONS: Nuclear DNA content and p53 immunostaining are of value for the prediction of recurrence of stage I squamous cell carcinomas of the mobile tongue. Stage I tongue carcinomas that are prone to local recurrence show the same DNA content as do advanced tongue carcinomas.

Functional assessment of the pharynx at rest and during swallowing in partially paralyzed humans: simultaneous videomanometry and mechanomyography of awake human volunteers.

BACKGROUND: Functional characteristics of the pharynx and upper esophagus, including aspiration episodes, were investigated in 14 awake volunteers during various levels of partial neuromuscular block. Pharyngeal function was evaluated using videoradiography and computerized pharyngeal manometry during contrast bolus swallowing. METHODS: Measurements of pharyngeal constrictor muscle function (contraction amplitude, duration, and slope), upper esophageal sphincter muscle resting tone, muscle coordination, bolus transit time, and aspiration under fluoroscopic control (laryngeal or tracheal penetration) were made before (control measurements) and during a vecuronium-induced partial neuromuscular paralysis, at fixed intervals of mechanical adductor pollicis muscle train-of-four (TOF) fade; that is, at TOF ratios of 0.60, 0.70, 0.80, and after recovery to a TOF ratio > 0.90. RESULTS: Six volunteers aspirated (laryngeal penetration) at a TOF ratio < 0.90. None of them aspirated at a TOF ratio > 0.90 or during control recording. Pharyngeal constrictor muscle function was not affected at any level of paralysis. The upper esophageal sphincter resting tone was significantly reduced at TOF ratios of 0.60, 0.70, and 0.80 (P < 0.05). This was associated with reduced muscle coordination and shortened bolus transit time at a TOF ratio of 0.60. CONCLUSIONS: Vecuronium-induced partial paralysis cause pharyngeal dysfunction and increased risk for aspiration at mechanical adductor pollicis TOF ratios < 0.90. Pharyngeal function is not normalized until an adductor pollicis TOF ratio of > 0.90 is reached. The upper esophageal sphincter muscle is more sensitive to vecuronium than is the pharyngeal constrictor muscle.