Determinants

of upper esophageal sphincter pressure in dogs

P. JACOB, P. J. KAHRILAS, G. HERZON, AND B. MCLAUGHLIN Departments of Medicine and Otolaryngology, Northwestern University Medical School and the Veterans Administration Lakeside Medical Center, Chicago, Illinois 60611

JACOB, LAUGHLIN.

P., P. J.

KAHRILAS, of upper

Determinants

G.

HERZON,

esophageal

AND

sphincter

B. Mcpres-

sure in dogs. Am. J. Physiol. 259 (Gastrointest. Liver Physiol.

22): G245-G251,1990.-Chronic experiments were done on six dogs fitted with EMG electrodes on pharyngeal and esophageal musculature. Electromyographic activity of the cricopharyngeus was recorded in awake and sedated animals with and without manometric recordings as well as during esophageal distension. Intraluminal upper esophageal sphincter (UES) pressure had two distinct components; active contraction accompanied by cricopharyngeal EMG activity and passive elasticity that persisted in the absence of EMG activity. Between swallows, the cricopharyngeal EMG activity patterns observed were of either tonic activity, no activity, or phasic activity with inspiratory bursts. The activity level was markedly affected by anesthesia, phonating, whining, panting, level of alertness, or changes in head posture. A brisk UES contraction was elicited in response to passage of the manometric assembly and to intraesophageal balloon distension. Persistent EMG augmentation after stationing of the manometric sensor suggested that intraluminal manometry tends to exaggerate resting sphincter pressure. We conclude that electrical activity of the cricopharyngeus, and by inference UES pressure, is markedly affected by many variables that are difficult to control during clinical or experimental determinations of UES pressure. cricopharyngeus; manometry; electromyography

THE UPPER ESOPHAGEAL SPHINCTER (UES) is a complex musculoskeletal valve comprised of the lamina of the cricoid cartilage anteriorly and striated muscle posteriorly. The major component of the striated muscle is the cricopharyngeus muscle, which is attached like a sling to the lateral aspects of the cricoid lamina. Studies in opossums suggest that the myogenic component of UES pressure is generated by the tonic contraction of the cricopharyngeus muscle, as evidenced by the marked reduction in the pressure following either sectioning of the motor nerve supply to the cricopharyngeus or dtubocurarine administration (1). The intraluminal UES pressure that persists after abolition of the myogenic component is attributed to the passive elasticity of surrounding structures and this is eliminated during swallowing in conjunction with contraction of the geniohyoid muscle (1). The distinction between sphincter relaxation and sphincter opening has been further detailed by combined manometric and fluoroscopic studies showing that swallow-related sphincter relaxation precedes sphincter opening and that opening coincides with anterior traction on the cricoid cartilage mediated by the infrahyoid muscles (8, 11).

Experimental studies of the UES using a variety of manometric techniques have reported a wide range of intraluminal pressure values (1,5-7,9,16,17). Asoh and Goyal (1) observed that the passage of an intraluminal manometric catheter increased cricopharyngeal electromyographic (EMG) activity in opossums, supporting the observations made during surgery or endoscopy in humans that the insertion of an object into the sphincter prompted contraction. Studies (9) on human volunteers have shown that the UES pressure of a given subject varies widely with the manometric technique employed, leading to the speculation that the intraluminal stimulation caused by a manometric sensor prompted sphincter contraction. UES pressures determined using a stationary sleeve sensor were significantly lower than those recorded by pull-through methods, and the UES pressure values of a given subject were found to diminish over time as the subjects adapted to the presence of the recording assembly (9). Furthermore, during long interval recordings of intraluminal UES pressure, periods of sleep were characterized by UES pressures of Cl0 mmHg compared with resting pressures of -40 mmHg during awake periods (10). Intraluminal manometric sensors are routinely used for clinical and experimental studies of the UES. However, UES resting pressure determined with intraluminal recording devices may not be representative of sphincter activity in the absence of an intraluminal measuring device. The aims of the present study were to define the electrical activity of the cricopharyngeus in unsedated awake dogs, to examine the relationship between intraluminal UES pressure and cricopharyngeal EMG activity, and to test the effects of sedation, esophageal distension, and the insertion of a manometric catheter on cricopharyngeal EMG activity. MATERIALS

AND

METHODS

Six adult male mongrel dogs weighing 11-14 kg were used. The study protocol was approved by the Northwestern University Animal Welfare Committee. Electrode implantations were done through a midline neck incision by an experienced otolaryngologist (G. Herzon) while the animals were under intravenous pentobarbital anesthesia. The horizontal fibers of the cricopharyngeus muscle were identified by blunt dissection. Bipolar patch electrodes with recording wires 5 mm apart were sutured to each side of the cricopharyngeus muscle as far posteriorly as possible as well as to the inferior aspect of the pharyngeal constrictor muscle and to the proximal G245

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esophagus. Electrode wires were tunneled subcutaneously to a metal 20-pin connector mounted to the exposed vertex of the skull with stainless steel screws and dental acrylic. Recording sessions were started no less than 3 days after surgery. Autopsies were done on all animals after completing the protocol to confirm electrode positions. Manometric recordings were obtained using a miniature sleeve assembly. The manometric assembly was flattened in cross section (3 x 4 mm) and incorporated both a 6-cm sleeve sensor and side hole recording sites axially located at each end and at the center of the sleeve sensor. The manometric assembly was passed through a bite block held between the dogs’ incisors by tape around the muzzle. The axial position of the UES was determined during the initial recording session in each dog by observing the pressure recordings while slowly withdrawing the side hole sensors across the UES high-pressure zone. After this, the catheter was repositioned with the sleeve element facing posteriorly and the UES highpressure zone axially centered on the sleeve. With the assembly so positioned, the proximal side hole recorded pharyngeal contractions, the sleeve and the middle side hole recorded UES pressure, and the distal side hole recorded proximal esophageal contractions. The manometric catheter was secured in place by taping it to the bite block. Each lumen of the recording assembly was connected to a pressure transducer and perfused with sterile water at 0.6 ml/min by a low-compliance pneumohydraulic infusion pump (Arndorfer Medical Specialties, Greendale, WI). The pressure transducers were connected to preamplifiers (model 7PlG, Grass Instruments, Quincy, MA), th e output of which were both displayed on a polygraph (model 7D, Grass Instruments) and recorded on magnetic tape (model 3968A, Hewlett-Packard, San Diego, CA). EMG recordings were obtained by plugging the male component of the 20-pin connector to the receptacle on the animal’s skull. Each EMG channel was connected to an alternating-current amplifier (model 7P3C, Grass Instruments), the output of which was both displayed on the polygraph and recorded on magnetic tape simultaneously with the manometric signals. Recording sessions on conscious dogs were conducted with the animals passively restrained in a Pavlov sling. Resting EMG recordings (without the manometric assembly in place) were obtained for 30-45 min. After this, the manometric assembly was positioned, and concurrent UES pressure and EMG recordings were obtained for an additional 30-45 min. Both resting EMG and simultaneous EMG and UES pressure recordings were also obtained for 30-45 min after the dogs were given an intravenous bolus dose of pentobarbital (22 mg/kg). Additional smaller doses of pentobarbital were administered as necessary to maintain a level of anesthesia so that the dogs lay quietly on their sides, breathing spontaneously, during recording sessions. Balloon distension of the esophagus was also accomplished with the animals sedated. The balloon (OB W/40/8/2/65, Medi-Tech, Watertown, MD) was passed orally along with the sleeve device and positioned so that the proximal end of the inflated balloon was 5 cm distal to the UES high-pressure

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zone. EMG activity and the UES pressure recordings were obtained while the balloon was inflated with 25 ml of air (O.D. 3 cm) for at least three 30- to 60-s periods. Completion of all experiments on each dog required two or three recording sessions done on successive days. Each recording session included a recording of resting EMG activity without a manometric catheter in place for comparative purposes. The cricopharyngeal EMG signal was quantitatively analyzed by replaying the tape through a band-pass filter (model 3550, Kron Hite, Avon, MA) into a Grass integrator (model 7P3C, Grass Instruments) with the time constant set at 0.2 s and the threshold set at 0. For each dog, the better of the two cricopharyngeal EMG recordings was analyzed. Both the integrated cricopharyngeal EMG recording and sleeve recording of the UES pressure were analyzed during resting periods, periods with the manometric catheter in place, and periods of intraesophageal balloon distension. In each experimental condition, mean integrated EMG activity and UES pressure were determined during interswallow periods of stable recording using a digital planimeter. The esophageal EMG signal was a reliable swallow marker. Twenty to sixty minutes of EMG and pressure recordings were analyzed in each dog in each condition. Average integrated EMG values were normalized for each dog by setting the values obtained during the period with the manometric sensor in place at 100% and expressing activity during other experimental conditions as a ratio of this. Data are expressed as means t SE unless otherwise specified. Statistical comparisons among conditions were made before normalizing the values using Student’s paired t test. RESULTS

EMG recordings. Reliable EMG recordings of the pharyngeal constrictor, cricopharyngeus, and proximal esophagus were obtained in all dogs, and postmortem examination revealed consistent electrode placement. The predominant activity pattern of the pharyngeal constrictor and of the proximal esophagus was of negligible basal activity with a burst of activity after each swallow coinciding with the manometric recording of a pharyngeal or esophageal contraction. A highly variable pattern observed in the pharyngeal constrictor was of inspiratory bursts similar to those observed in the cricopharyngeus (see below). The EMG response of the cricopharyngeus during swallowing was constant, always showing inhibition followed by a discrete burst during the passage of the pharyngeal contraction through the UES. On the other hand, the basal EMG activity of the cricopharyngeus was variable, showing two distinct patterns among animals. Figure 1 is a continuous recording that illustrates the transition from the more common EMG pattern (tonic activity) to the less common pattern (inspiratory bursts followed by nearly complete cessation of activity during expiration). The initiation of whining or panting always changed the pattern from tonic to phasic. In other instances, the transition from the tonic to the phasic pattern was associated with a shift in head posture. However, in 23% of instances there was no noted

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DETERMINANTS

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OF UES PRESSURE

mm Hg 80 UES Sleeve 40 Recording 0

--------------------------

FIG. 1. Continuous EMG recording illustrating the abrupt transition from a tonic to a phasic activity pattern. Top tracing is of the intraluminal upper esophageal sphincter (UES) pressure recorded by the sleeve sensor, the middle tracing is the electromyography (EMG) signal from the right side of the cricopharyngeus (CP), and the bottom tracing is the integration of the cricopharyngeal EMG. In this instance, the transition from tonic to phasic pattern was not associated with an observed change in posture or respiration.

AJ Volts +lOO

CP EMG



4

t

5 seconds

cause of the shift in pattern. Of the six dogs, one exhibited exclusive phasic EMG activity of the cricopharyngeus, two exhibited exclusively tonic activity, and three exhibited both patterns in roughly equal proportion. The two dogs most tolerant of the experiment exhibited exclusively tonic activity. Of the three dogs that exhibited both patterns, the tonic pattern was observed while the dogs were relaxed, and the phasic pattern was commonly associated with panting or obvious restlessness. Aside from there being two distinct patterns of activity, the magnitude of activity encountered in each pattern also varied widely. However, the most vigorous EMG activity was always of the phasic pattern, being as much as six times greater than that during periods without respiratory variation. Effect of anesthesia on UES tone. The administration of anesthetic had the abrupt and consistent effect of reducing both the intraluminal UES pressure and the average integrated EMG activity of the cricopharyngeus. Figure 2 shows the data for all animals. The cricopharyngeal EMG activity decreased from 100% while the animals were awake to 41 t 19% after the administration of pentobarbital (P < 0.05). Similarly, the UES pressure decreased from 42 t 5 mmHg before to 17 t 2 mmHg after pentobarbital anesthesia (P < 0.05). Anesthesia also affected the pattern of UES activity observed during swallowing. Figure 3 illustrates a sample data record of a swallow recorded in the awake state and during anesthesia. In this instance, the pattern of EMG activity was of the tonic type both while the animal was awake and while it was sedated (although activity was

mmHg

%

INTEGRATED CP EMG

UES PRESSURE

FIG. 2. Effect of pentobarbital anesthesia (lightly shaded bars) on cricopharyngeal EMG activity (left) and intraluminal UES pressure measured with a sleeve sensor (right). Results shown are for all 6 dogs. Average integrated EMG activity for each dog was normalized so that 100% activity was that recorded while the animals were awake with the manometric assembly in place (heavily shaded bars); this corresponded to a mean UES pressure of 42 mmHg. Both the average integrated EMG activity and the UES pressure showed a 60% reduction relative to the unanesthetized condition.

zero during sedation). Note that in the awake state, the swallow was associated with inhibition of the cricopharyngeal EMG followed by a burst of activity corresponding to the passage of the pharyngeal contraction. The corresponding manometric record shows complete relaxation during the period of EMG inhibition. The record obtained during anesthesia was, however, quite different. The basal EMG activity was nearly zero so that inhibition was not evident at the time of swallow-associated manometric relaxation. On the other hand, the postswal-

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AWAKE

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I I

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SEDATED

120 UES Sleeve Recording

FIG. 3. Sample data tracings from dog 3 showing the UES pressure tracing (top), the raw cricopharyngeal EMG recording (middle), and the integrated cricopharyngeal EMG activity (bottom) while the animal was awake (left) and anesthetized with pentobarbital ( right). In the awake recording, the swallow (SW) is associated with inhibition followed by a burst of activity in the cricopharyngeal EMG record temporally related to the complete relaxation seen in the manometric recording. In the record obtained from the anesthetized animal, there was no detectable resting cricopharyngeal EMG activity and hence no detectable cricopharyngeal inhibition at the time of UES relaxation. On the other hand, the postrelaxation EMG burst that corresponds to the pharyngeal contraction was of similar magnitude in both the awake and anesthetized conditions. These findings suggest that the residual UES pressure of 15 mmHg observed in the anesthetized animal was the result of passive elastic forces in the neck rather than active contraction of the cricopharyngeus.

80 40

CP EMG



150 Integrated CP EMG

100 50

5 seconds

low EMG burst was of nearly identical magnitude to that recorded in the awake state. The contrast between these two tracings also illustrates the two components of resting UES pressure. In the awake recording, the resting UES pressure was between 60 and 80 mmHg and this was associated with tonic cricopharyngeal EMG activity. On the other hand, while the animal was anesthetized, there was a resting UES pressure of 15 mmHg and this was not associated with tonic cricopharyngeal EMG activity, suggesting that this residual UES pressure was attributable to passive elastic forces rather than active muscular contraction. Effect of a manometric assembly on cricopharyngeal EM% activity. Passage of the manometric assembly in-

stantaneously augmented the cricopharyngeal EMG activity. Figure 4 illustrates a continuous recording made as the manometric assembly was being inserted. Note that the positioning of the assembly prompted considerable cricopharyngeal EMG activity and that once the catheter was stationed in place the EMG activity lessened but continued at a rate greater than that before intubation. The contrast between the before and after conditions is most evident in the tracing of the integrated cricopharyngeal EMG record. Augmentation of cricopharyngeal EMG activity associated with passage of the manometric assembly was evident in EMG tracings of both the tonic and phasic activity patterns. Although some evidence of adaptation was evident immediately after positioning of the manometric catheter, the EMG

activity usually did not return to its base-line level. In fact, there was no statistical difference between the mean EMG activity or the UES pressure obtained during the initial 2 min of recordings (after a stable recording was achieved) compared with the final 2 min of the recording sessions. However, it is important to note that in all animals, intermittent recordings were obtained in both the awake and anesthetized conditions during which the EMG activity was zero despite the presence of the manometric assembly. The excitatory effect of passage and presence of the manometric assembly was evident in both the awake and in the anesthetized conditions. Figure 5 summarizes the quantitative analysis of EMG activity among the different recording conditions for all six animals. As in Fig. 2, data among animals were normalized by establishing the EMG activity in the awake condition with the manometric assembly in place as the 100% value. Note that in the awake condition, the manometric assembly more than doubled the EMG activity level (48 t 8% without vs. 100% with the manometric catheter in place; P < 0.05), and in the anesthetized condition, the increase was greater than fivefold (8 t 5% without vs. 44 t 7% with the catheter in place; P c 0.05). Unlike the basal cricopharyngeal EMG activity during the interswallow period, the magnitude of the EMG burst associated with passage of the pharyngeal contraction was not affected by the presence of the manometric assembly (610 t 162%with vs. 569 t 157% without the manometric assembly in place).

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DETERMINANTS

G249

OF UES PRESSURE

mm Hg 120 UES

80 1

1

1

A

A

FIG. 4. Sample data tracing from dog 5 obtained during passage of the manometric assembly. Top tracing is from the UES sleeve sensor, middle tracing is from the right-sided cricopharyngeal EMG electrodes, and bottom tracing is integrated EMG activity. Introduction of the manometric assembly was associated with a brisk EMG response from the cricopharyngeus. Although this activity decreased somewhat after the sleeve assembly was fixed in place, activity continued at an increased level. The contrast between the period before and after passage of the manometric assembly is best compared in the bottom tracing showing the integrated EMG activity.

Sleeve Jl Volts

+100 CP EMG

’ -100

3

P’

AI Volts

Integrated

lJo E;g

100 50

4

I 5 seconds

Effect of esophageal balloon distension. Esophageal balloon distension was consistently accomplished only with sedated animals. There was an instantaneous increase in both cricopharyngeal EMG activity and UES pressure during balloon inflation, and this was maintained until %

WHILE AWAKE

the balloon was deflated. Balloon distension also tended to increase the swallowing rate but did not alter the complete inhibition of cricopharyngeal EMG activity associated with swallowing. Figure 6 shows the significant increase in the cricopharyngeal EMG activity and on UES pressure resulting from esophageal balloon distension (P < 0.01). Relationship between integrated cricopharyngeal EMG activity and UES pressure. Several problems were encountered in attempting to correlate the values of the integrated cricopharyngeal EMG activity with the si-

UNDER ANESTHESIA

FIG. 5. Effect of a manometric device on the mean integrated cricopharyngeal EMG activity. Results shown are for all 6 dogs with the heavily shaded bars depicting periods with the manometric catheter in place and the lightly shaded bars depicting periods without the manometric catheter. Average integrated EMG activity for each dog was normalized so that 100% activity was that recorded while the animals were awake with the manometric assembly in place; this corresponded to a mean UES pressure of 42 mmHg. In the awake condition, the manometric device more than doubled the cricopharyngeal EMG activity, while in the anesthetized condition the increase was more than fivefold (P < 0.05). The condition with minimal cricopharyngeal EMG activity (animal anesthetized without a manometric assembly in place) was characterized by mean integrated EMG activity 8 + 5% that was recorded in the awake condition with the manometric assembly in place.

INTEGRAlED CP EMG

UES PRESSURE

FIG. 6. Effect of proximal esophageal balloon distension on the mean integrated cricopharyngeal EMG activity (left) and UES pressure (right). Relative to the period with the balloon deflated (heavily shaded bars), the average integrated EMG activity during the period of balloon inflation (lightly shaded bars) increased from 41 -C 19 to 408 f 186% and UES pressure increased from 17 f 2 to 100 f 15 mmHg (P C 0.01).

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multaneous UES pressure. One observation made was that the pressure recording lacked the brisk transient response characteristic of the EMG recording. This limitation is evident in Fig. 1 as the EMG pattern shifts from the tonic pattern to the phasic pattern. The manometric sensor achieves a stable recording during the tonic activity but, because of its slow rise rate, is always relatively under-recording during the phasic activity. Thus transients (inspiratory bursts, postswallow potentials) were well recorded by the EMG but imperfectly recorded by the manometric sensor. On the other hand, a limitation of the EMG was the lack of calibration among animals; whereas a pressure value of 30 mmHg had a consistent meaning among animals, the integrated cricopharyngeal EMG value of 100 PV had no such interchangeable meaning. Although the general recording level among animals was similar, comparisons among animals could only be made by normalizing the EMG values to a given experimental condition. Despite the limitations mentioned above, some observations could be made regarding the correlation between the EMG and the pressure recordings. The two tended to covary; increases in EMG activity were associated with increased UES pressure, as illustrated in Figs. 2 and 6. Second, absent EMG activity was associated with a persistent UES pressure, averaging 13 mmHg among animals. Third, the most brisk EMG response and the highest UES pressure values were recorded during swallow-related pharyngeal contractions. Fourth, respiratory oscillations in the cricopharyngeal EMG activity were associated with inspiratory augmentation of UES pressure, although the converse of this was not always true (as illustrated in Fig. 3). Finally, the cricopharyngeal EMG activity during awake periods without a manometer in place had a magnitude intermediate between values obtained during sedation and those obtained with a manometer, allowing us to estimate resting UES pressure without a manometer in place to be 31 t 8 mmHg by extrapolation. DISCUSSION

Current techniques of UES pressure determination use small-diameter intraluminal manometric devices passed orally or nasally. A recent investigation (9) concluded that the manometric method itself may augment UES pressure after determining that pressures measured by a slow pull-through or by a stationary sleeve sensor were less than those recorded by a rapid pull-through. Realizing that the impact of manometric measurement cannot be determined by using the method in question, we elected to examine the electrical activity of the cricopharyngeus as a reflection of UES contractile activity. Our data suggest that, with limitations, a reasonable correlation existed between intraluminal UES pressure and integrated cricopharyngeal EMG activity, thereby allowing us to indirectly examine determinants of UES pressure. Applying this methodology, passage of a manometric sensor was always associated with augmentation of the cricopharyngeal EMG activity. Furthermore, the continued presence of the catheter within the sphincter, causing pharyngeal stimulation and slight sphincter dis-

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tension, was associated with increased average cricopharyngeal EMG activity, suggesting that even under optimal conditions of a small, stationary manometric device, measurements of resting UES pressure are probably exaggerated. By extrapolating between the observed UES pressures and corresponding cricopharyngeal EMG activity values we obtained in awake and sedated animals, average resting UES pressure of dogs without a manometric catheter in place was estimated at 31 t 8 mmHg, a value significantly less than that recorded in awake animals with the manometer in place. Controversy continues regarding whether the cricopharyngeus muscle is tonically active. In experiments on anesthetized animals, neither Lund (14), Levitt et al. (l3), nor Doty and Bosma (4) detected tonic activity. Asoh and Goyal (1) reported tonic activity with or without phasic variation of the cricopharyngeus in unanesthetized opossums, but notably these animals were forcibly restrained during recordings by bars mounted to the skull. The discrepancy among these studies may be explained by the effect of anesthesia and stress (in the restrained animals) on cricopharyngeal EMG activity. The most careful study of anesthesia was by Levitt et al. (13), who found that during stages I, II, and III anesthesia, the cricopharyngeus contracted only with inspiration in synchrony with the ala nasi muscle. During light anesthesia (stages I and II) tonic contraction could be elicited by breath holding, straining, painful stimulation, or stimulation of the hypopharynx. The muscle was completely flaccid during stage III, plane 4 anesthesia (13). Findings from the present study additionally demonstrated marked reduction in both UES pressure and cricopharyngeal EMG activity during the transition from the unsedated condition to light sedation. Furthermore, it should also be noted that every dog we studied exhibited intermittent periods both while awake and while sedated, characterized by negligible EMG activity of the cricopharyngeus. Similar quiescent periods were also recently reported by Lang et al. (12). During such periods of absent cricopharyngeal EMG activity we found the mean intraluminal UES pressure to be 13 mmHg. Thus, we conclude, as have previous investigators (1, 3), that this persistent intraluminal pressure is attributable to elastic forces within the neck rather than to persistent tone in the cricopharyngeal muscle. A similar pattern of activity was observed during long-interval manometric recordings of the UES in humans (10). Periods of sleep and deep relaxation were characterized by a UES pressure of -10 mmHg. The opposite experimental condition of sleep or restfulness, stress, has also been implicated as a determinant of UES pressure. Cook et al. (2) showed that the stress of a dichotic listening task augmented UES pressure in humans. Our observations suggest that periods of obvious restlessness in awake dogs were associated with increased UES pressure. An advantage of the present study, done on unanesthetized dogs, was that it allowed us to observe the impact of many proposed influences on cricopharyngeal EMG activity and UES pressure. Our findings suggest that this sphincter is best described as the servant of many masters. The most stereotyped activity pattern was during

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DETERMINANTS

swallowing, which resulted in a brief interval of inhibition followed by a pulse of maximal excitation regardless of the preexisting tone or activity pattern of the UES, supporting the conclusion of Doty (3) that the medullary swallow center has preeminent control over the swallow musculature, including the cricopharyngeus. The cricopharyngeus also functions as a respiratory muscle, particularly during vigorous breathing, supporting the contention of Negus (15) that a function of the cricopharyngeus is to exclude air from the esophagus during respiration. Levitt et al. (13) had concluded from acute dog experiments that the cricopharyngeus contracted only with inspiration, in synchrony with the ala nasi muscle. Although we did observe the activity pattern described by Levitt et al. (Fig. l), this was not the exclusive pattern encountered. Tonic cricopharyngeal EMG activity was more common in our experiments unless the dog was vigorously panting, which was invariably associated with phasic activity. We also observed as had Lund (14) that phonation greatly increased cricopharyngeal EMG activity. Changes in head posture also frequently changed the pattern or level of cricopharyngeal EMG activity. Thus, taken together, these findings suggest that, rather than being driven at a constant rate by a designated medullary center, the cricopharyngeus is a participant in many complex responses, such as posturing, breathing, intraluminal distension, phonating, and stress. Thus the activity that the sphincter exhibits at any point in time depends on the net activation of all of these more global activities. At a particular instant the predominant influence may be swallowing, posturing, panting, phonating, or nothing at all (at which time minimal EMG activity is seen); in short, this is a very economical sphincter. Furthermore, many of the experimental conditions imposed in studying the UES or cricopharyngeus (pharyngeal stimulation, intraluminal distension by a catheter, anesthesia, or fixed head posture) influence the activity level and pattern observed. The authors thank Dr. John Dent for providing a suitable manometric catheter for these studies and both Drs. John Dent and Ivan Lang for scholarly advice regarding the experimental design and data interpretation. We also thank Dr. Tony Ha for technical assistance in conducting the experiments. This project was supported by National Institutes of Health National Research Service Award Fellowship 0821201 (P. Jacob), NIH Grant DK-00669 (P. J. Kahrilas), a fellowship from the Schweppe Foundation (P. J. Kahrilas), and a grant from the Veterans Admin-

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stration Medical Research Service (P. J. Kahrilas). Address for reprint requests: P. J. Kahrilas, Northwestern Univ. Medical School, GI Section, Dept. of Medicine, 1526 Wesley Towers, 250 E. Superior St., Chicago, IL 60611. Received 2 October 1989; accepted in final form 2 April 1990. REFERENCES R., AND R. K. GOYAL. Manometry and electromyography the upper esophageal sphincter in the opossum. Gustroenterology

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S. SHANNON, AND S. M. COLLINS. Measurement of upper esophageal sphincter pressure: effect of acute emotional stress. Gastroenterology 93: 526-532, 1987. 3. DOTY, R. W. Neural organization of deglutition. In: Handbook of Physiology. Alimentary Canal. Washington, DC: Am. Physiol. Sot., 1968, sect. 6, vol. 4, chapt. 12, p. 1861-1902. 4. DOTY, R. W., AND J. F. BOSMA. An electromyographic analysis of reflex deglutition. J. Neurophysiol. 19: 44-60, 1956. 5. ENZMANN, D. R., G. S. HARRELL, AND F. F. ZBORALSKE. Upper esophageal responses to intraluminal distension in man. Gustroenterology 6. FREIMAN,

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J. M., T. Y. EL-SHARKAWY, AND N. E. DIAMANT. Effect of bilateral vagosympathetic nerve blockade on response of the dog upper esophageal sphincter (UES) to intraesophageal distension and acid. Gastroenterology 81: 78-84, 1981. 7. GERHARDT, D., J. HEWETT, M. MOESCHBERGER, T. SHUCK, AND D. WINSHIP. Human upper esophageal sphincter pressure profile. Am. J. Physiol. 239 (Gastrointest. Liver Physiol. 2): G49-G52,1980. J. A. LOGEMANN, V. SHAH, AND T. 8. JACOB, P., P. J. KAHRILAS, HA. Upper esophageal sphincter opening and modulation during swallowing. Gastroenterology 97: 1469-1478, 1989. P. J., J. DENT, W. J. DODDS, W. J. HOGAN, AND R. C. 9. KAHRILAS, ARNDORFER. A method for continuous monitoring of upper esophageal sphincter pressure. Dig. Dis. Sci. 32: 121-128, 1987. P. J., W. J. DODDS, J. DENT, B. HAEBERLE, W. J. 10. KAHRILAS, HOGAN, AND R. C. ARNDORFER. The effect of sleep, spontaneous

gastroesophageal

reflux and a meal on UES pressure in humans.

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Manometric videoradiographic and electromyographic evaluation of upper esophageal sphincter function in the dog (Abstract). Gastroenterology M. 13. LEVITT,

96: A286,

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N., H. H. DEDO, AND J. H. OGURA. The cricopharyngeus muscle, an electromyographic study in the dog. Laryngoscope

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Determinants of upper esophageal sphincter pressure in dogs.

Chronic experiments were done on six dogs fitted with EMG electrodes on pharyngeal and esophageal musculature. Electromyographic activity of the crico...
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