Response of cricopharyngeus muscle to esophageal stimulation by mechanical distension and acid and bile perfusion.

OBJECTIVES: The aim of this study was to identify the response of the cricopharyngeus muscle (CPM) to esophageal stimulation by intraluminal mechanical distension and intraluminal acid and bile perfusion. METHODS: In 3 adult pigs, electromyographic (EMG) activity of the CPM was recorded at baseline and after esophageal stimulation at 3 levels: proximal, middle, and distal. The esophagus was stimulated with 20-mL balloon distension and intraluminal perfusion of 40 mL 0.1N hydrochloric acid, taurocholic acid (pH 1.5), and chenodeoxycholic acid (pH 7.4) at the rate of 40 mL/min. The EMG spike density was defined as peak-to-peak spikes greater than 10 microV averaged over 10-ms intervals. RESULTS: In all 3 animals, the spike density at baseline was 0. The spike densities increased after proximal and middle distensions to 15.2 +/- 1.5 and 5.1 +/- 1.2 spikes per 10 ms, respectively. No change in CPM EMG activity occurred after distal distension. The spike density following intraluminal perfusion with hydrochloric acid at the distal level was 10.1 +/- 1.1 spikes per 10 ms. No significant change in CPM EMG activity occurred after acid perfusion at the middle and proximal levels. No change in CPM EMG activity occurred after intraluminal esophageal perfusion with either taurocholic acid or chenodeoxycholic acid. CONCLUSIONS: Proximal esophageal distension, as well as distal intraluminal acid perfusion, appeared to be important mechanisms in generation of CPM activity. Bile acids, on the other hand, failed to evoke such CPM activity. The data suggest that transpyloric refluxate may not be significant enough to evoke the CPM protective sphincteric function, thereby placing supraesophageal structures at risk of bile injury.

Modulating effects of hypoxia and hypercarbia on glottic closing force.

OBJECTIVES: Aspiration has been identified as one of the independent risk factors for development of respiratory tract infections, the incidence of which varies from 10% to 65% in patients in intensive care units. The primary defense mechanism for protection of the lower airway is the glottic closure reflex (GCR), elicited by stimulation of the internal branch of the superior laryngeal nerve. This reflex, once considered highly stable, is now considered vulnerable to a growing number of clinical factors. This study was designed to explore the biomechanical effects of hypoxia and hypercarbia, common occurrences among critically ill patients, on the GCR. METHODS: Five adult male Yorkshire pigs were used in the study. Both internal superior laryngeal nerves were simultaneously stimulated with bipolar platinum-iridium electrodes. The glottic closing force (GCF) was then measured by placing a pressure transducer between the adducting vocal folds under 3 different protocols: protocol 1 (control), protocol 2 (hypoxia: partial pressure of arterial oxygen [PaO2] levels of 90, 70, and 50 mm Hg), and protocol 3 (hypercarbia: partial pressure of arterial carbon dioxide [PaCO2] levels of 60 and 70 mm Hg). Six readings were recorded under each experimental paradigm, and Student's t-test was applied to calculate the statistical significance against the control. RESULTS: Hypoxia reduced the GCF to 75%, 40%, and 29% of control for PaO2 levels of 90, 70, and 50 mm Hg, respectively, and hypercarbia reduced the GCF to 40% and 27% of control for PaCO2 levels of 60 and 70 mm Hg, respectively. CONCLUSIONS: This is the first study that highlights the biomechanical impact of hypoxia and hypercarbia on the GCR, providing a unified explanation for the increased incidence of life-threatening aspiration in critically ill patients with such alterations.

Reflex vocal fold adduction in the porcine model: the effects of stimuli delivered to various sensory nerves.

OBJECTIVES: The aim of this study was to identify a panel of sensory nerves capable of eliciting an evoked glottic closure reflex (GCR) and to quantify the glottic closing force (GCF) of these responses in a porcine model. METHODS: In 5 pigs, the internal branch of the superior laryngeal nerve (iSLN) and the trigeminal, pharyngeal plexus, glossopharyngeal, radial, and intercostal nerves were surgically isolated and electrically stimulated. During stimulation of each nerve, the GCR was detected by laryngeal electromyography and the GCF was measured with a pressure transducer. RESULTS: The only nerve that elicited the GCR in the 5 pigs was the iSLN. The average GCF was 288.9 mm Hg. CONCLUSIONS: This study demonstrates that the only afferent nerve that elicits the GCR in pigs is the iSLN, and that it should remain the focus of research for the rehabilitation of patients with absent or defective reflex vocal fold adduction.

Effects of altered consciousness on the protective glottic closure reflex.

OBJECTIVES: The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal folds. We hypothesize that central facilitation is an essential component of a bilateral brain stem-mediated adductor reflex and that its disturbance by altered consciousness or physiologic sleep could result in weakened sphincteric closure. METHODS: In 10 adult pigs the glottic closure response was evaluated under light and deep isoflurane anesthesia. The internal branch of the left superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. The force of evoked glottic closure was measured with a pressure transducer positioned between the vocal folds. RESULTS: Consistent threshold responses (>90%) were obtained ipsilaterally from 0.5 to 2.0 minimal alveolar concentration (MAC) anesthesia. However, the contralateral reflex responses declined to 6.4% in successive trials as anesthetic levels approached 1.5 to 2.0 MAC. Furthermore, glottic closing force closely reflected these electromyographic changes, declining from 383 mm Hg at 0.5 to 1.0 MAC to 114 mm Hg at 1.5 to 2.0 MAC. CONCLUSIONS: Alteration of central facilitation by progressively deeper loss of consciousness abolishes a lower brain stem-mediated crossed adductor reflex, predisposing the subject to a weakened glottic closure response.

Protective glottic closure: biomechanical effects of selective laryngeal denervation.

Glottic closure constitutes the primary mechanism for prevention of intradeglutitive and postdeglutitive aspiration. Laryngeal paralysis therefore exerts a considerable impact on deglutition, yet little is understood regarding the biomechanical effects of selective denervation on the laryngeal protective function. We measured the glottic closing force (GCF) in each of 6 male, 40-kg Yorkshire pigs 1) after selective unilateral superior laryngeal nerve (SLN) section; 2) after selective unilateral recurrent laryngeal nerve (RLN) section; and/or 3) after combined SLN-RLN section as both right and left SLNs were simultaneously stimulated to evoke the glottic closure response. Stimulation was provided through an oscilloscope with bipolar platinum-iridium electrodes, and the GCF was measured with a pressure transducer positioned between the vocal cords. Six repetitive measures of GCF were obtained before nerve section, and 6 after nerve section, in each subject. Unilateral SLN section reduced the GCF to 54.14% of control, RLN section reduced the GCF to 23.39% of control, and combined SLN-RLN section reduced the GCF to 22.67% of control. These findings underscore the profound differential effects exerted by isolated lesions on the glottic closure function.

Bile-induced laryngitis: is there a basis in evidence?

Most agree that bile reflux occurs with regularity in an otherwise healthy population and that biliary and acid reflux may play a synergistic role in damaging esophageal mucosa. But to what extent is laryngeal mucosa at risk? We constructed a saline-controlled rat model (n = 40) in which active component solutions of bile--taurocholic acid and chenodeoxycholic acid--were applied to intact laryngeal mucosa at various pH levels. Histologic sampling of the laryngeal mucosa allowed inflammation scores to be generated by a pathologist blinded to the solutions used. Both taurocholic acid at acid pH and chenodeoxycholic acid at basic pH preferentially induced statistically greater inflammation scores than did the saline control, approaching or exceeding inflammation scores attributed to hydrochloric acid at pH 1.2. These observations may clarify reasons for failure to uniformly control laryngeal injury by adequate suppression of gastric acid alone and may further justify alternative methods of laryngeal protection in patients refractory to adequate acid control.

Microsurgical free flap reconstruction outcomes in head and neck cancer patients after surgical extirpation and intraoperative brachytherapy.

OBJECTIVES: The management of recurrent or persistent head and neck cancer poses a challenging problem. Salvage surgery for these individuals consists of ablative surgery, interstitial brachytherapy, and microsurgical free flap reconstruction. This study reviews complications after such reconstruction. METHODS: We reviewed 139 consecutive head and neck cancer patients undergoing free flap reconstruction from January 1994 to May 2002. These included 66 patients with recurrent head and neck cancer undergoing intraoperative brachytherapy (IOBT) and free flap reconstruction and 73 undergoing free flap reconstructions only. A total of 142 reconstructions were performed, with three patients in IOBT group receiving two free flap reconstructions per patient, giving us a total of 69 reconstructions in the IOBT group versus 73 in the non-IOBT group. Nine patients were excluded from the IOBT group because of nonsynchronous use of brachytherapy and reconstruction, and 10 patients were excluded from the other group because they had prior radiotherapy or surgical treatment, leaving us with a total of 123 reconstructions, 60 in the IOBT group and 63 in the non-IOBT group. The IOBT group patients received iodine Vicryl seed implants, palladium seed implants, or both, to deliver an average dose of 79.3 +/- 31.8 Gy (mean +/- 1SD) to the surgical bed. RESULTS: All patients were followed for evidence of local wound complications. The IOBT group showed multiple complications in 23 (38.33%) of 60 reconstructions, the most common being wound dehiscence in 11. This, when compared with the non-IOBT group complications (15.87%), was found to be statistically significant (chi test, P <.01). CONCLUSION: IOBT increases the rate of complications in patients undergoing microvascular free tissue transfer. This, however, should not deter or alter the aggressiveness of cancer therapy used for managing recurrent head and neck cancer.

Glottic closing force: impact of thyroplasty on vocal cord paralysis in a pig model.

Reflex glottic closure is an essential component of a normal swallow. A lesion of the unilateral recurrent laryngeal nerve weakens this reflex response, affecting the essential protective functions of the larynx and potentially resulting in aspiration pneumonia, sepsis, or death. Thyroplasty has been advocated to reduce glottic incompetence due to unilateral vocal cord paralysis (UVCP). Although medialization thyroplasty has traditionally been evaluated in terms of its phonatory effect, its role in improving protective glottic closure has never been studied. The present study was designed to evaluate the effect of UVCP and thyroplasty type I on the glottic closing force (GCF). Five male Yorkshire pigs weighing approximately 40 kg were used in this study. Both internal superior laryngeal nerves were simultaneously stimulated with bipolar platinum-iridium electrodes, and the force of evoked glottic closure was measured with a pressure transducer positioned between the vocal cords. Initial pressure readings (GCF) obtained with bilaterally intact recurrent laryngeal nerves served as a control. The GCF was then measured after the right recurrent laryngeal nerve was sectioned to simulate the conditions of UVCP. Finally, thyroplasty type I was performed on the affected side, and the GCF was measured again to evaluate its quantitative effect on reflex glottic closure. The mean GCF was reduced by UVCP to approximately 22.5% (49.71 mm Hg) of the control GCF (220.25 mm Hg). Thyroplasty enhanced the GCF to 57.7% (127.08 mm Hg) of the control GCF. These measures underscore the profound effect that UVCP exerts on the GCF and the limitations of vocal cord medialization in fully restoring it.

Association between Zenker diverticulum and gastroesophageal reflux disease: development of a working hypothesis.

A cause-and-effect relation between gastroesophageal reflux disease and Zenker diverticulum remains unclear. Convincing evidence exists demonstrating that patients with Zenker diverticula have increased resting tone of the cricopharyngeus muscle, and that this may be an important initiating factor for the development of Zenker diverticula. Yet some patients with cricopharyngeus hypertonicity never develop Zenker diverticulum. In this context, we hypothesize that acid-induced esophageal shortening may be an important cofactor. We suggest that acid reflux induces longitudinal esophageal shortening, which in turn increases the risk for the development of herniation between 2 spatially related structures, the pharyngeal constrictors and cricopharyngeus muscles, leading to the development of Zenker diverticulum. This hypothesis awaits clinical verification.

Central facilitation of the glottic closure reflex in humans.

The sphincteric function of the larynx, essential to lower airway protection, is most efficiently achieved through strong reflex adduction by both vocal cords. We hypothesize that central facilitation is an essential component of a bilateral adductor reflex and that its disturbance could result in weakened sphincteric closure. Five patients during supraglottic laryngectomy underwent evoked response laryngeal electromyography under 0.5 and 1.0 minimal alveolar concentration (MAC) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. Consistent threshold responses were obtained ipsilaterally from 0.5 to 1.0 MAC anesthesia. However, the contralateral reflex responses approached 0% in successive trials as anesthetic levels approached 1.0 MAC. In human subjects, alteration of central facilitation by deepening anesthesia abolishes the crossed adductor reflex, predisposing to a weakened glottic closure response. A precise understanding of this effect may improve the prevention of aspiration in patients emerging from prolonged sedation or under heavy psychotropic control.