The effect of body position on esophageal reflexes in cats: a possible mechanism of SIDS?

Rapid activation of esophageal mechanoreceptors alters the pharyngeal phase of swallow: Evidence for inspiratory activity during swallow

Swallow is a complex behavior that consists of three coordinated phases: oral, pharyngeal, and esophageal. Esophageal distension (EDist) has been shown to elicit pharyngeal swallow, but the physiologic characteristics of EDist-induced pharyngeal swallow have not been specifically described. We examined the effect of rapid EDist on oropharyngeal swallow, with and without an oral water stimulus, in spontaneously breathing, sodium pentobarbital anesthetized cats (n = 5). Electromyograms (EMGs) of activity of 8 muscles were used to evaluate swallow: mylohyoid (MyHy), geniohyoid (GeHy), thyrohyoid (ThHy), thyropharyngeus (ThPh), thyroarytenoid (ThAr), cricopharyngeus (upper esophageal sphincter: UES), parasternal (PS), and costal diaphragm (Dia). Swallow was defined as quiescence of the UES with overlapping upper airway activity, and it was analyzed across three stimulus conditions: 1) oropharyngeal water infusion only, 2) rapid esophageal distension (EDist) only, and 3) combined stimuli. Results show a significant effect of stimulus condition on swallow EMG amplitude of the mylohyoid, geniohyoid, thyroarytenoid, diaphragm, and UES muscles. Collectively, we found that, compared to rapid cervical esophageal distension alone, the stimulus condition of rapid distension combined with water infusion is correlated with increased laryngeal adductor and diaphragm swallow-related EMG activity (schluckatmung), and post-swallow UES recruitment. We hypothesize that these effects of upper esophageal distension activate the brainstem swallow network, and function to protect the airway through initiation and/or modulation of a pharyngeal swallow response.

The enigma of gastroesophageal reflux disease among convalescing infants in the NICU: It is time to rethink

Gastroesophageal reflux (GER) can be a normal physiological process, or can be bothersome, when aerodigestive consequences are associated; the latter is often interpreted as GER disease (GERD). However, the distinction between these two entities remains an enigma among infants surviving after neonatal intensive care (NICU) care. Symptoms related to GERD are heterogeneous, and are often managed with changes in diet, feeding methods, and acid suppressive therapy. However, none of these approaches have been well-tested in neonates; hence practice variation is very high world-wide. In this paper, we explain the variation in diagnosis, pathophysiology of the clinical presentation, and highlight approaches to diagnosis and management.

Mechanisms of Aerodigestive Symptoms in Infants with Varying Acid Reflux Index Determined by Esophageal Manometry

OBJECTIVE

To test whether symptom generation in infants is related to the severity of gastroesophageal reflux disease (GERD) symptoms as determined by the Acid Reflux Index (ARI), stimulus media, and stimulus volume during provocative esophageal manometry.

STUDY DESIGN

Symptomatic neonates (n = 74) born at a median of 28.9 weeks gestation (range, 23.4-39.4 weeks) were studied at a median of 41.0 weeks (range, 34.6-48.0 weeks) postmenstrual age using 24-hour pH-impedance methods to determine ARI severity, followed by provocative esophageal manometry with graded mid-esophageal infusions (0.1-5.0 mL) of air, water, and apple juice. Peristaltic reflexes and symptom characteristics were compared among ARI severity categories using linear mixed models and generalized estimating equations.

RESULTS

The effects of 2635 separate esophageal stimuli on reflexes and symptoms were analyzed. Peristaltic reflexes occurred in 1880 infusions (71%), and physical, cardiorespiratory, sensory symptoms were seen in 439 infusions (17%). Symptom prevalence did not differ across the ARI severity categories (ARI <3, 18%; ARI 3-7, 17%; ARI >7, 16%; P = 1.0). Symptom and peristaltic responses increased with incremental stimulus volumes (all media, P < .001).

CONCLUSIONS

Symptoms and peristaltic reflexes are manifestations of the recruitment of several neurosensory and neuromotor pathways evoked by mid-esophageal infusions. ARI severity grade plays no role in symptom generation, indicating that GERD should not be diagnosed and severity should not be assigned based on symptoms alone. An increase in symptom occurrence was noted with increasing stimulus volumes, which provided increased activation of receptors, afferents, and efferents in evoking peristaltic clearance reflexes.

Pharyngoesophageal and cardiorespiratory interactions: potential implications for premature infants at risk of clinically significant cardiorespiratory events

The aims of this study were to 1) examine pharyngoesophageal and cardiorespiratory responses to provoking pharyngeal stimuli, and 2) to determine potential contributory factors impacting heart rate (HR) changes to provide insight into cardiorespiratory events occurring in preterm infants. Forty-eight neonates (19 females and 29 males, born at 27.7 ± 0.5 wk; mean ± SE) pending discharge on full oral feeds were studied at 38.7 ± 0.2 wk postmenstrual age using concurrent pharyngoesophageal manometry, electrocardiography, respiratory inductance plethysmography, and nasal airflow thermistor. Pharyngoesophageal and cardiorespiratory responses (prevalence, latency, and duration) were quantified upon abrupt pharyngeal water stimuli (0.1, 0.3, and 0.5 ml in triplicate). Mixed linear models and generalized estimating equations were used for comparisons between HR changes. Contributory factors included stimulus characteristics and subject characteristics. Of 338 pharyngeal stimuli administered, HR increased in 23 (7%), decreased in 108 (32%), and remained stable in 207 (61%) neonates. HR decrease resulted in repetitive swallowing, increased respiratory-rhythm disturbance, and decreased esophageal propagation rates (all, P < 0.05). HR responses were related to stimulus volume, stimulus flow rate, and extreme prematurity (all, P < 0.05). In preterm infants, HR remains stable in a majority of pharyngeal provocations. HR decrease, due to pharyngeal stimulation, is related to aberrant pharyngoesophageal motility and respiratory dysregulation and is magnified by prematurity. We infer that the observed aberrant responses across digestive, respiratory, and cardiovascular systems are related to maladaptive maturation of the parasympathetic nervous system. These aberrant responses may provide diagnostic clues for risk stratification of infants with troublesome cardiorespiratory events and swallowing difficulty. NEW & NOTEWORTHY Cardiorespiratory rhythms concurrent with pharyngeal, upper esophageal sphincter, and esophageal body responses were examined upon pharyngeal provocation in preterm-born infants who were studied at full-term maturation. Decreased heart rate (HR) was associated with extreme preterm birth and stimulus flow/volume. With HR decrease responses, aerodigestive reflex abnormalities were present, characterized by prolonged respiratory rhythm disturbance, repetitive multiple swallowing, and poor esophageal propagation. Promoting esophageal peristalsis may be a potential therapeutic target.

Effects of esophageal acidification on esophageal reflexes controlling the upper esophageal sphincter

Esophageal acid exposure can alter upper esophageal sphincter (UES) function, but the mechanism is unknown. The aim of this study was to determine the effects of esophageal acid exposure on esophago-UES relaxation (EURR) and contractile (EUCR) reflexes. Cats, decrebrate ( n = 27) or chronic ( n = 4), were implanted with electromyographic electrodes on pharynx, larynx, and esophagus. The esophagus was infused with either NaCl (0.9%) or HCl (0.1 N). The EUCR was activated by balloon distension in acute cats and slow air injection in chronic cats, and the EURR was activated by rapid air injection in both sets of cats. We found that NaCl infused for 15 or 30 min had no effect on EUCR or EURR in acute cats. HCl infused for 15, 30, or 45 min significantly ( P < 0.05) decreased the sensitivity to activate EUCR. HCl infused for 15 min significantly ( P < 0.05) increased and for 45 min significantly ( P < 0.05) decreased sensitivity to activate EURR. In chronic cats, HCl infused for 15 min/day increased sensitivity to activate EURR and decreased ( P < 0.05) sensitivity to activate EUCR after 4 days of infusion. EURR occurred spontaneously during HCl infusions on the 3rd and 4th ( P < 0.05) days of HCl infusion. We conclude that esophageal acid exposure initially sensitizes the esophagus to activation of EURR and desensitizes to activation of EUCR, but with longer exposure desensitizes to both. The alteration in sensitivity to activate EURR and EUCR caused by gastroesophageal reflux may play a role in the generation of supraesophageal reflux. NEW & NOTEWORTHY In acute studies, short-term esophageal acid exposure sensitizes esophagus to activation of esophago-upper esophageal sphincter relaxation response (EURR), whereas longer-term exposure inhibits EURR. Short- or long-term esophageal acid exposure decreases sensitivity to activation of esophago-upper esophageal sphincter contractile response (EUCR). In chronic studies, short-term esophageal acid exposure has the same effects on EURR and EUCR as occur acutely, but these effects take days to develop. Alteration in EURR and EUCR caused by gastroesophageal reflux may play a role in reflux disease.