Mechanisms of airway protection and upper esophageal sphincter opening during belching REZA SHAKER, JUNLONG REN, MARK KERN, WYLIE J. DODDS, WALTER J. HOGAN, AND QUN LI Departments of Medicine and Radiology, The Medical College of Wisconsin, Milwaukee 53226; and Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295 Shaker, Reza, Junlong Ren, Mark Kern, Wylie J. Dodds, Walter J. Hogan, and Qun Li. Mechanisms of airway protection and upper esophageal sphincter opening during belching. Am. J. Physiol. 262 (Gastrointest. Liver Physiol. 25): G621-G628,1992.-The mechanisms of airway protection, upper esophageal sphincter (UES) opening, and their coordination during belching were studied with a concurrent videoendoscopic, videofluoroscopic, and manometric technique. Analysis of videoendoscopic recordings revealed that glottal function during gastric and esophageal belching was similar and consisted of vocal cord adduction resulting in closure of introitus to trachea, followed by anterior-caudad movement of the glottis, followed by slitlike or triangular UES opening. When a belch episode was associated with an intragastric pressure increase, in addition to the above features, there was approximation of arytenoids to the base of the epiglottis before the UES opened. Duration of vocal cord closure during belches induced by 40 ml intraesophageal air injection was significantly longer than belches induced by 20 ml (P < 0.01). Vocal cord closure preceded the UES opening invariably. Analysis of videofluorostopic recordings showed that hyoid bone movement during belching had a distinctive pattern different from its movement during swallowing. UES opening started generally when the hyoid bone was pulled anteriorly. Anterior hyoid excursion of 0.78 & 0.1 cm during belching was significantly shorter than its excursion of 1.8 t 0.09 cm during swallowing (P < 0.01). We conclude that glottal closure is an integral component of both esophageal and gastric belch reflexes that prevents aspiration of regurgitated material into the airway. Glottal closure mechanism during belching has two tiers of closure: 1) vocal cord closure and 2) aryepiglottic approximation. Glottal and UES functions are closely coordinated during belching, and finally, during belching, UES is pulled open after its relaxation. glottis and belching; bone and belching
airway protection
during
belching;
hyoid
IS DEFINED as audible voiding of gas from the stomach through the mouth. However, it is known that distension of the esophagus by air may initiate an esophageal belching that does not involve gas reflux from the stomach. Mechanics of gas ventilation during belching have been described previously (4,5); however, the mechanisms of airway protection as well as upper esophageal sphincter (UES) opening during belching have not been completely studied. Because ventilation of gastric or esophageal gas across UES into the pharynx may be accompanied by entry of food particles, acid mist, etc., into the hypopharynx and predispose the airway to aspiration, we hypothesized that a glottal closure mechanism is activated during belching. A preliminary study in our laboratory confirmed the presence of such a mechanism (8). This earlier study also showed that the glottis moves anterior-caudad during belching. This finding suggested that extraglottal muscles, as well as the hyoid bone, may be involved in belching. For this reason, the
BELCHING
0193-1857/92
$2.00 Copyright
present study was undertaken to characterize further the glottal function during both gastric and esophageal belching and to determine its temporal relationship with UES relaxation and opening, as well as to define the mechanisms of UES opening and the role of extraglottal structures such as hyoid bone during eructation. METHODS A concurrent videoendoscopic and manometric technique was used. We studied 16 healthy volunteers while they were sitting in an upright position. Subject ages ranged between 20 and 30 yr. The investigation was approved by the Human Research Review Committee of the Medical College of Wisconsin and the Human Studies Subcommittee of the Zablocki Veterans Affairs Medical Center. Each volunteer gave informed consent before the study. The subjects fasted overnight, and their nasal cavities were anesthetized with 2% topical XyloCaine (Astra Pharmaceutical, Westborough, MA) applied by cotton-tipped applicators just before bilateral nasal insertion of the endoscope and manometric probe, respectively. To record glottal function, an endoscope (BFlO; Olympus, Lake Success, NY) of 5.3 mm diameter and 100” angle of vision was passed transnasally and positioned at the level of the free margin of the epiglottis, as described previously (7, 8). With the scope’s optical head in this position, the vocal cords, arytenoids, epiglottis, laryngeal vestibule, and pharyngeal wall as well as the area of the UES opening were readily visualized (Fig. 1). Endoscopic images were recorded on O.&in videotape with a beta max video recorder (Sony SLHF 900, Tokyo, Japan) that recorded at 30 frames/s. For UES pressure monitoring, we used a manometric assembly that incorporated a sleeve device (6 cm long) 15 cm from the assembly tip. The assembly had recording side holes at the proximal and distal margins of the sleeve. In addition, it had two proximal pharyngeal side holes located 3 and 6 cm proximal to the sleeve and two esophageal side holes located 5 and 10 cm distal to the lower margin of the sleeve. The sleeve and manometric channels were infused with distilled water (0.5 ml/ min) with a minimally compliant pneumohydraulic system (Arndorfer Specialties, Greendale, WI), and pressure tracings were recorded on an eight-channel polygraph recorder (Grass Instrument, Quincy, MA). The manometric assembly was positioned so that the 6-cm sleeve device straddled the UES. The assembly was secured in place by taping it to the nose. To prevent pharyngeal and glottal stimulation the pharyngeal ports were not infused after placement of the manometric assembly. To induce esophageal belching, air volumes of 20,40, and 60 ml were injected abruptly into the midesophagus via a dedicated channel within the sleeve assembly that had its orifice located 7.5 cm distal to the lower margin of the sleeve. By use of an extracorporeal transducer, the onset and offset of air insufflation were recorded on the same polygraph tracing used for UES and esophageal manometry. A second catheter that had three side holes 3 cm apart at its distal end was passed transnasally alongside the sleeve assembly, and its recording sites were
0 1992 the American
Physiological
Society
G621
Downloaded from www.physiology.org/journal/ajpgi by ${individualUser.givenNames} ${individualUser.surname} (130.070.008.131) on January 12, 2019.
G622
AIRWAY
PROTECTION
DURING
BELCHING
Fig. 1. Endoscopic view of hypopharynx and glottis. Optical head of endoscope is positioned immediately below free margin of epiglottis. UES, upper esophageal sphincter.
positioned within the stomach. The middle side hole was used to inject 400 ml room air into the stomach to induce gastric belching, and the other two side holes were used to monitor the intragastric pressure during esophageal and gastric belching. To study the function of extraglottal structures during belching that were not seen by direct endoscopy, such as hyoid bone, the protocol was repeated with concurrent videofluoroscopy in nine subjects. Because of the unpredictability of onset of gastric belching, only esophageal belches were studied by concurrent videofluoroscopy. For videofluoroscopy, each subject sat in a chair positioned laterally to the face of an image intensifier. The subjects held their heads in a comfortable neutral position. Videofluoroscopic recordings were obtained at 90 keV with a 9in. image intensifier mode and appropriate collimation so that a lateral image was obtained of the entire mouth and pharynx (1). To compare the glottal and hyoid bone function during belching with swallowing, we recorded three dry swallows in each subject. Videofluoroscopic images were recorded on a second video recorder identical to the one used for videoendoscopy. Each fluoroscopic sequence was
airway protection
during
belching;
hyoid
IS DEFINED as audible voiding of gas from the stomach through the mouth. However, it is known that distension of the esophagus by air may initiate an esophageal belching that does not involve gas reflux from the stomach. Mechanics of gas ventilation during belching have been described previously (4,5); however, the mechanisms of airway protection as well as upper esophageal sphincter (UES) opening during belching have not been completely studied. Because ventilation of gastric or esophageal gas across UES into the pharynx may be accompanied by entry of food particles, acid mist, etc., into the hypopharynx and predispose the airway to aspiration, we hypothesized that a glottal closure mechanism is activated during belching. A preliminary study in our laboratory confirmed the presence of such a mechanism (8). This earlier study also showed that the glottis moves anterior-caudad during belching. This finding suggested that extraglottal muscles, as well as the hyoid bone, may be involved in belching. For this reason, the
BELCHING
0193-1857/92
$2.00 Copyright
present study was undertaken to characterize further the glottal function during both gastric and esophageal belching and to determine its temporal relationship with UES relaxation and opening, as well as to define the mechanisms of UES opening and the role of extraglottal structures such as hyoid bone during eructation. METHODS A concurrent videoendoscopic and manometric technique was used. We studied 16 healthy volunteers while they were sitting in an upright position. Subject ages ranged between 20 and 30 yr. The investigation was approved by the Human Research Review Committee of the Medical College of Wisconsin and the Human Studies Subcommittee of the Zablocki Veterans Affairs Medical Center. Each volunteer gave informed consent before the study. The subjects fasted overnight, and their nasal cavities were anesthetized with 2% topical XyloCaine (Astra Pharmaceutical, Westborough, MA) applied by cotton-tipped applicators just before bilateral nasal insertion of the endoscope and manometric probe, respectively. To record glottal function, an endoscope (BFlO; Olympus, Lake Success, NY) of 5.3 mm diameter and 100” angle of vision was passed transnasally and positioned at the level of the free margin of the epiglottis, as described previously (7, 8). With the scope’s optical head in this position, the vocal cords, arytenoids, epiglottis, laryngeal vestibule, and pharyngeal wall as well as the area of the UES opening were readily visualized (Fig. 1). Endoscopic images were recorded on O.&in videotape with a beta max video recorder (Sony SLHF 900, Tokyo, Japan) that recorded at 30 frames/s. For UES pressure monitoring, we used a manometric assembly that incorporated a sleeve device (6 cm long) 15 cm from the assembly tip. The assembly had recording side holes at the proximal and distal margins of the sleeve. In addition, it had two proximal pharyngeal side holes located 3 and 6 cm proximal to the sleeve and two esophageal side holes located 5 and 10 cm distal to the lower margin of the sleeve. The sleeve and manometric channels were infused with distilled water (0.5 ml/ min) with a minimally compliant pneumohydraulic system (Arndorfer Specialties, Greendale, WI), and pressure tracings were recorded on an eight-channel polygraph recorder (Grass Instrument, Quincy, MA). The manometric assembly was positioned so that the 6-cm sleeve device straddled the UES. The assembly was secured in place by taping it to the nose. To prevent pharyngeal and glottal stimulation the pharyngeal ports were not infused after placement of the manometric assembly. To induce esophageal belching, air volumes of 20,40, and 60 ml were injected abruptly into the midesophagus via a dedicated channel within the sleeve assembly that had its orifice located 7.5 cm distal to the lower margin of the sleeve. By use of an extracorporeal transducer, the onset and offset of air insufflation were recorded on the same polygraph tracing used for UES and esophageal manometry. A second catheter that had three side holes 3 cm apart at its distal end was passed transnasally alongside the sleeve assembly, and its recording sites were
0 1992 the American
Physiological
Society
G621
Downloaded from www.physiology.org/journal/ajpgi by ${individualUser.givenNames} ${individualUser.surname} (130.070.008.131) on January 12, 2019.
G622
AIRWAY
PROTECTION
DURING
BELCHING
Fig. 1. Endoscopic view of hypopharynx and glottis. Optical head of endoscope is positioned immediately below free margin of epiglottis. UES, upper esophageal sphincter.
positioned within the stomach. The middle side hole was used to inject 400 ml room air into the stomach to induce gastric belching, and the other two side holes were used to monitor the intragastric pressure during esophageal and gastric belching. To study the function of extraglottal structures during belching that were not seen by direct endoscopy, such as hyoid bone, the protocol was repeated with concurrent videofluoroscopy in nine subjects. Because of the unpredictability of onset of gastric belching, only esophageal belches were studied by concurrent videofluoroscopy. For videofluoroscopy, each subject sat in a chair positioned laterally to the face of an image intensifier. The subjects held their heads in a comfortable neutral position. Videofluoroscopic recordings were obtained at 90 keV with a 9in. image intensifier mode and appropriate collimation so that a lateral image was obtained of the entire mouth and pharynx (1). To compare the glottal and hyoid bone function during belching with swallowing, we recorded three dry swallows in each subject. Videofluoroscopic images were recorded on a second video recorder identical to the one used for videoendoscopy. Each fluoroscopic sequence was
