Vol. 275, Issue 3, G521-G525, September 1998
Pharyngoglottal closure reflex: identification and
characterization in a feline model
Reza
Shaker,
Bidyut K.
Medda,
Junlong
Ren,
Safwan
Jaradeh,
Pengyan
Xie, and
Ivan M.
Lang
Medical College of Wisconsin Dysphagia Institute, and Division of
Gastroenterology and Hepatology, Departments of Medicine,
Neurology, and Otolaryngology, Medical College of Wisconsin and
Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin
53226
 |
ABSTRACT |
Earlier studies in humans have shown that
pharyngeal stimulation by water at a threshold volume induces a brief
vocal cord adduction, i.e., pharyngoglottal closure reflex. The present
study was undertaken to 1) develop a
suitable animal model for physiological studies of this reflex and
2) delineate its neural pathway and effector organs. Studies were done in cats by concurrent videoendoscopy and manometry followed by electromyographic studies. At a threshold volume (0.3 ± 0.06 ml), injection of water into the pharynx
resulted in a brief closure of the vocal folds, closing the introitus
to the trachea. Duration of this closure averaged 1.1 ± 0.1 s.
Bilateral transection of the glossopharyngeal nerve completely
abolished this reflex but not swallows induced by pharyngeal water
stimulation. The pharyngoglottal closure reflex is present in the cats.
The glossopharyngeal nerve is the afferent pathway of this reflex, and
the interarytenoid and lateral cricoarytenoid muscles are among its
target organs.
airway protection; gastroesophageal reflux
| |
INTRODUCTION |
PREVIOUS STUDIES IN HUMANS (3) have shown that
stimulation of pharyngeal mucosa by injection of minute amounts of
water at a threshold volume induces a brief vocal cord adduction,
indicating the existence of a pharyngoglottal closure reflex. Sudden
entry of liquid stimulates complete vocal cord closure, whereas gradual entry induces partial vocal cord closure. It is possible that this
reflex may play a contributory role in airway protection against
aspiration during premature spill of swallowed material, as well as
retrograde entry of gastric refluxate into the pharynx. The neural
pathway that mediates this reflex, however, has not been determined. In
addition, an animal model is needed for future studies investigating
the role of this reflex in airway protection. For this reason, the
present study was undertaken to 1)
develop a suitable animal model for physiological studies of the
pharyngoglottal closure reflex and
2) identify the neural pathway and
effector organs of this reflex.
| |
METHODS |
Studies were approved by the Animal Care Committee of the Medical
College of Wisconsin and were done in two stages.
Stage 1: Concurrent videoendoscopic and manometric studies.
During this stage, we studied 10 cats of either sex, weighing 2-4
kg, by concurrent videoendoscopic and manometric technique. The animals
were anesthetized using intramuscular injection of 4 mg/kg Telazol
(tiletamine HCl and zolazepam HCl; Avelco, Fort Dodge,
IA). To record the glottal function an endoscope (GIF-XV10 Olympus, Lake Success, NY) of 11-mm diameter and 100° angle of vision was passed transorally through a bite block and positioned at
the level of the free margin of the epiglottis. With the optical head
of the scope in this position, the vocal folds, arytenoids, posterior
surface of the epiglottis, laryngeal vestibule, pharyngeal wall, and
the area of the upper esophageal sphincter (UES) opening were
visualized. Endoscopic images were recorded on 0.5-in. videotape using
a super VHS video recorder (AG1960; Panasonic, Secaucus, NJ) that
recorded at 30 frames/s.
To monitor the UES pressure, we used a manometric assembly that
incorporated a sleeve device (60 × 6 × 4 mm). The assembly had recording side holes at the proximal and distal margins of the
sleeve for manometric positioning. The sleeve and manometric channels
were infused with distilled water (0.3 ml/min) using a minimally
compliant pneumohydraulic system (Arndorfer Specialties, Greendale,
WI), and pressure tracings were recorded on an eight-channel polygraph
recorder (Grass Instruments, Quincy, MA). To prevent pharyngeal and
glottal stimulation, the pharyngeal port was not infused after the
sleeve device was positioned within the UES.
To stimulate the pharyngeal receptors, we injected incrementally (0.1 ml) increasing volumes of water colored with food dye, directed
posteriorly into the pharynx. Injections were done via a designated
port on the manometric assembly 1.5 cm above the sleeve. The interval
between injections ranged between 4 and 8 min. We started with
injections of 0.1 ml of water and increased the injection volume until
a swallow occurred. The injection port was connected to the chart
recorder via an extracorporeal transducer, thus each injection induced
a pen deflection that was used to correlate the glottal response
recorded on videotape with pharyngeal water injection. Manometric and
video endoscopic recordings were synchronized using a specially
designed timer (Thalner Electronics, Ann Arbor, MI), and each volume
was tested three times.
Stage 2: EMG studies.
Experiments in this stage were carried out on seven cats of either sex
weighing 2.0-4.0 kg. Under ketamine anesthesia (20 mg/kg; ketamine
HCl, Aveco), animals were prepared with venous and arterial lines, and
carotid arteries were ligated bilaterally. The trachea was severed ~2
cm below the cricoid cartilage, and animals were intubated and given
0.6-1.0% halothane anesthesia for midcollicular decerebration.
After decerebration, halothane was discontinued and the animals
breathed room air spontaneously and did not receive any anesthetics.
Temperature was maintained at 37-38°C by an external heating
pad. Mean arterial blood pressure was kept >80 mmHg by intravenous
infusion of 5% dextrose in 0.9% NaCl solution, as required. Laryngeal
adductor and cricopharyngeus (CP) muscles were exposed through midline
incision. The electromyographic (EMG) activity of the right lateral
cricoarytenoid and the muscle equivalent to human interarytenoid
muscles were monitored using stainless steel wires (Grass E-2 or
Medwire AS632) embedded in the muscles. We recorded bipolar
(interelectrode distance of 3-5 mm) EMG activity from the
interarytenoid (human equivalent) muscle, but because of the small size
of the lateral cricoarytenoid muscles we recorded EMG activity from a
single electrode in the muscle and an indifferent electrode on the
skin. The CP EMG activities were recorded using bipolar electrodes
(AS632). The EMG signals were high-pass filtered at 100 Hz and
amplified 10 times using an AC preamplifier. The EMG signal was fed
into a Grass model 7P3 preamplifier and integrator, where the signal
was further amplified, full-wave rectified, and electronically
integrated at a time constant of 0.25. The output was calibrated using
the internal 500-Hz test signal, and the threshold level was set just below the spontaneous EMG level at the end of expiration. The 0.5-A
high filter frequency was set at 0.5 kHz and 3 Hz for the raw EMG
signal and the integrated EMG signal, respectively. Integrated and raw
EMG signals were recorded simultaneously on a Grass multichannel polygraph machine. The raw and integrated EMG responses were also digitized and stored on the hard drive of a computer (IBM clone, 120 MHz Pentium processor) using a computerscope (RC Electronics, Goleta,
CA), hardware, and software. Experimentation was started at least 2 h
after the cats were decerebrated and pharyngeal water stimulation
(described above) was repeated, and EMG activities of the glottal
adductor muscles were recorded.
The occurrence of swallow was determined by a signal recorded through
the nonperfused pharyngeal port, as well as the characteristic loss of
CP tone seen on CP-EMG recordings.
After obtaining control responses to pharyngeal water stimulation, the
glossopharyngeal nerves were transected bilaterally. Ten minutes after
nerve transection the reflex responses were tested again, and changes
in responses were recorded.
| |
RESULTS |
Videoendoscopic studies.
Real-time and frame-by-frame analysis of the videoendoscopic recordings
showed that at a threshold volume (0.3 ± 0.1 ml) injection of water
into the pharynx directed posteriorly resulted in a brief closure of
the vocal folds, completely closing the introitus to the trachea (Fig.
1). The vocal fold closure was not accompanied by
movement of the closed glottis toward the epiglottis. Analysis of
videoendoscopic recordings also demonstrated the exit of colored water
from the injection port staining the posterior pharyngeal wall without
contacting the
glottis.
View larger version (79K):
[in this window]
[in a new window]
|
Fig. 1.
Still frame from videoendoscopic recording of vocal fold closure
response to pharyngeal water stimulation.
A: cat glottis immediately
before the injection of 0.3 ml of colored water into the pharynx
directed posteriorly. Vocal folds are fully open and free of color
staining. B: vocal folds are
completely adducted 0.1 s after the injection of 0.3 ml of colored
water into the pharynx. The glottis remains free of blue staining,
indicating that the injected water has not come in contact with the
glottis. VF, vocal folds; T, introitus to trachea; P, pyriform sinus;
PH, posterior pharyngeal wall; M, manometric catheter.
|
|
Further increase in the volume of injected water resulted in
swallowing. The average volume of water that induced swallowing (1.0 ± 0.3 ml) was significantly larger than that of the threshold for
stimulation of the pharyngoglottal closure reflex. In each animal,
injection of volumes larger than the threshold volume for activation of
the reflex, but smaller than that of swallowing, consistently activated
the pharyngoglottal closure reflex.
Duration of glottal closure from the onset of closure to its return to
resting position, induced by injection of the threshold volume,
averaged 1.1 ± 0.1 s. This duration did not increase with injection
of volumes larger than the threshold volume. Duration of glottal
closure induced by swallowing (1.8 ± 0.3 s) was significantly longer than that of the pharyngoglottal closure reflex
(P < 0.05). This difference was due
to a longer duration of the complete adduction period for pharyngeal
swallow compared with the pharyngoglottal closure reflex (Fig.
2). The time interval between the onset of closure to
maximum closure and onset of opening to full opening of the vocal folds
for both functions was similar.
View larger version (16K):
[in this window]
[in a new window]
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 2.
Vocal fold kinetics during pharyngoglottal closure reflex (PGCR;
A) and pharyngeal swallow (PSW;
B). VC-Ad-O, onset of closure of
vocal folds; VC-Ad-Max, maximum closure of vocal folds; VC-Ab-O, onset
of opening of vocal folds; VC-Ab-Max, return of vocal folds to resting
open position. During swallowing, due to vestibular closure and
pharyngeal contraction, laryngeal vestibule was closed and vocal folds
were obscured; they remained visible during initial and final stages of
swallow-induced vocal fold kinetics. During the pharyngoglottal closure
reflex, the laryngeal vestibule remained open, thus vocal fold kinetics
were visible during the entire event. Both total duration (1.1 ± 0.1 s) and duration of complete closure (0.87 ± 0.12 s) for
pharyngoglottal closure reflex were significantly shorter than those
for pharyngeal swallows (1.8 ± 0.3 s and 1.47 ± 0.24 s,
respectively) (P < 0.05).
|
|
EMG studies.
Pharyngeal water injected at the threshold volume, determined in
endoscopic studies, induced myoelectrial activities in both studied
glottal adductor muscles (Fig. 3,
A and
B). In addition, it frequently
stimulated the CP muscle. On the other hand, whereas pharyngeal swallow
resulted in contraction of glottal adductor muscles, it induced a brief
relaxation of the CP, followed by its contraction (Fig. 3,
C and
D).
View larger version (41K):
[in this window]
[in a new window]
|
Fig. 3.
Example of the effect of pharyngeal water stimulation on myoelectrical
activity of the interarytenoid (human equivalent), lateral
cricoarytenoid, and cricopharyngeus muscles (CP). Whereas pharyngeal
water injection resulted in contraction of the glottal adductor as well
as CP muscles (A and
B), swallows triggered by pharyngeal
water injection resulted in contraction of glottal adductors and
relaxation of the CP muscles (C and
D). This relaxation, however, was
followed by a postdeglutitive contraction. IA, interarytenoid muscle;
LCA, lateral cricoarytenoid muscle; EMG, raw electromyographic
activity;  , integrated EMG activity.
|
|
For both glottal adductor muscles studied, EMG activities induced by
the pharyngoglottal closure reflex were significantly less compared
with that of swallowing (P < 0.05;
see Table 1). Bilateral transection of the
glossopharyngeal nerves completely abolished the pharyngoglottal
closure reflex but not swallows induced by pharyngeal water stimulation
(Fig. 4).
View larger version (35K):
[in this window]
[in a new window]
|
Fig. 4.
Example of effect of bilateral transection of the glossopharyngeal
nerves on pharyngoglottal closure reflex and pharyngeal swallow.
Intrapharyngeal injection of any volume of water did not elicit any
myoelectrical activity in the interarytenoid or lateral cricoarytenoid
muscles following bilateral transection of the glossopharyngeal nerves.
On the contrary, stimulation of pharyngeal swallow remained intact
after glossopharyngeal transection and resulted in contraction of the
above-mentioned glottal adductor muscles and relaxation followed by
contraction of the CP muscle. Abbreviations defined in legend for Fig.
3.
|
|
| |
DISCUSSION |
In this study we identified and characterized the existence of a
pharyngoglottal closure reflex in cats. A similar reflex has been
previously identified in humans (3). Previous investigation of another
airway closure reflex, esophagoglottal closure reflex (5), has shown
interspecies variability in regard to its existence. These studies
documented this reflex in humans, cats, and monkeys but not in opossum
(6). In the current study other species were not investigated and the
interspecies variation of the pharyngoglottal closure reflex remains to
be investigated.
The afferent arm of this reflex seems to include the glossopharyngeal
nerve, because bilateral transection of this nerve abolishes the
reflex. The central control mechanism, although undoubtedly located in
the brain stem, has not been completely studied. Because glottal
closure is known to be mediated through the recurrent laryngeal nerve,
the efferent limb of the pharyngoglottal closure reflex undoubtedly
includes this nerve. The effector organs include the glottal adductor
muscles such as interarytenoid (human equivalent) and lateral
cricoarytenoid muscles. The possible participation of other
adductor/tensor muscles of the larynx, such as the vocalis, thyroarytenoid, and cricothyroid muscles awaits investigation.
It is known that tactile stimulation of the glottis induces its closure
(9). In this study, using colored water, it was ascertained that the
injected water did not come in contact with the glottis, thus assuring
that the posterior pharyngeal wall was stimulated and not the glottis.
Previous studies have documented various pharyngeal receptive fields
capable of stimulating pharyngeal reflexive swallow. These fields
include posterior tonsillar pillars, epiglottis, larynx, and posterior
pharyngeal wall (2, 7, 8). In the present study contact of larger
volumes of colored water than threshold volume for the pharyngoglottal
reflex also initiated swallowing, indicating that various reflexes may
be evoked from similar receptive fields in the pharynx. Whether similar or different groups of receptors mediate the various reflexes arising
from a single receptive field is not currently known.
It is known that glottal closure is mediated through recurrent
laryngeal nerves (4). The findings of this study indicate that the
pharyngoglottal closure reflex and the glottal closure during
pharyngeal (reflexive) swallow share similar efferent nerves (recurrent
laryngeal nerve) as well as target organs. Our finding that bilateral
transection of the glossopharyngeal nerve abolished this reflex, but
reflexive swallowing and its associated glottal closure still remained
intact suggests that 1) contrary to
swallowing that may be initiated via multiple and complex afferent
pathways including the glossopharyngeus and superior laryngeal nerves, the pharyngoglottal reflex seems to be initiated through a single afferent pathway via the glossopharyngeus nerve and
2) although the pharyngoglottal
closure reflex shares its afferent and efferent pathways with the
swallowing reflex, it probably has its reflex circuitry functionally
distinct from that of swallowing.
Our finding that a larger volume of injected water was required to
trigger a reflexive swallow compared with that of the pharyngoglottal closure reflex suggests either the involvement of different types of
receptors for mediating these two reflexes or activation of a larger
number of the same receptor types for triggering swallowing than for
triggering the pharyngoglottal closure reflex.
Previous studies in humans (3) have documented a smaller threshold
volume for triggering the pharyngoglottal closure reflex compared with
the threshold volume determined in this study in cats. This difference,
in addition to interspecies variation, could potentially be due to the
effect of anesthetics used in our current animal studies. However, in
both species the duration of closure does not increase by increasing
the volume of injected water, indicating a stereotypical "all or
none" response.
The physiological role of the pharyngoglottal closure reflex in cats
has not been studied completely; however, previous reports in humans
indicate that it is triggered when a portion of the oral bolus is
spilled into the pharynx and contacts the pharyngeal wall during the
preparatory phase of swallowing (1). In addition, it is postulated that
in humans this reflex may be triggered during reflux of gastric content
into the pharynx, thereby preventing aspiration by closing the
introitus to the trachea.
In summary, the pharyngoglottal closure reflex is present in the feline
species. The threshold volume for triggering this reflex and the EMG
activities of its target organs are significantly lower than that of a
reflexive (pharyngeal) swallow. The glossopharyngeal nerve is the
afferent pathway of this reflex and the interarytenoid (human
equivalent) and lateral cricoarytenoid muscles are among its target
organs.
| |
ACKNOWLEDGEMENTS |
This work was supported in part by National Institutes of Health
Grants R01-DC-00669 and R01-DK-25731.
| |
FOOTNOTES |
Address for reprint requests: R. Shaker, Div. of Gastroenterology and
Hepatology, Froedtert Memorial Lutheran Hospital, 9200 W. Wisconsin
Ave., Milwaukee, WI 53226.
Received 6 October 1997; accepted in final form 15 May 1998.
| |
REFERENCES |
1.
Dua, K. S.,
J. Ren,
E. Bardan,
P. Xie,
and
R. Shaker.
Coordination of deglutitive glottal function and pharyngeal bolus transit during normal eating.
Gastroenterology
112:
73-83,
1997[Medline].
2.
Pommerenke, W.
A study of the sensory areas eliciting the swallowing reflex.
Am. J. Physiol.
84:
36-41,
1928.
3.
Ren, J.,
R. Shaker,
K. Dua,
A. Trifan,
B. Podvrsan,
and
Z. Sui.
Glottal adduction response to pharyngeal water stimulation: evidence for a pharyngoglottal closure reflex (Abstract).
Gastroenterology
106:
A631,
1994.
4.
Sasaki, C. T.,
and
G. Isaacson.
Functional anatomy of the larynx.
Otolaryngol. Clin. North Am.
21:
595-612,
1988[Medline].
5.
Shaker, R.,
W. J. Dodds,
J. Ren,
W. J. Hogan,
and
R. C. Arndorfer.
Esophagoglottal closure reflex: a mechanism of airway protection.
Gastroenterology
102:
857-861,
1992[Medline].
6.
Shaker, R.,
J. Ren,
B. Medda,
I. Lang,
V. Cowles,
and
S. Jaradeh.
Identification and characterization of the esophagoglottal closure reflex in a feline model.
Am. J. Physiol.
266 (Gastrointest. Liver Physiol. 29):
G147-G153,
1994[Abstract/Free Full Text].
7.
Shaker, R.,
J. Ren,
Z. Zamir,
A. Sarna,
J. Liu,
and
Z. Sui.
Effect of aging, position, and temperature on the threshold volume triggering pharyngeal swallows.
Gastroenterology
107:
396-402,
1994[Medline].
8.
Storey, A.
Interactions of alimentary and upper respiratory tract reflexes.
In: Mastication and Swallowing, edited by B. J. Sessle,
and A. G. Hannon. Toronto, Canada: Univ. of Toronto Press, 1976, p. 22-36.
9.
Woodson, G. E.
Upper airway anatomy and function.
In: Head and Neck Surgery
Otolaryngology, edited by J. Byron,
and J. B. Baily. Philadelphia, PA: Lippincott, 1993, vol. 1, chapt. 39, p. 492-500.
Am J Physiol Gastroint Liver Physiol 275(3):G521-G525
0002-9513/98 $5.00
Copyright © 1998 the American Physiological Society
Top
Abstract
Introduction
