Respiratory suppression and swallowing from introduction of fluids into the laryngeal region of the lamb

Transferring an extremely premature infant to an extra-uterine life support system: a prospective view on the obstetric procedure

To improve care for extremely premature infants, the development of an extrauterine environment for newborn development is being researched, known as Artificial Placenta and Artificial Womb (APAW) technology. APAW facilitates extended development in a liquid-filled incubator with oxygen and nutrient supply through an oxygenator connected to the umbilical vessels. This setup is intended to provide the optimal environment for further development, allowing further lung maturation by delaying gas exposure to oxygen. This innovative treatment necessitates interventions in obstetric procedures to transfer an infant from the native to an artificial womb, while preventing fetal-to-neonatal transition. In this narrative review we analyze relevant fetal physiology literature, provide an overview of insights from APAW studies, and identify considerations for the obstetric procedure from the native uterus to an APAW system. Lastly, this review provides suggestions to improve sterility, fetal and maternal well-being, and the prevention of neonatal transition.

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

BackgroundIt has been hypothesized that life-threatening events are caused by supraesophageal reflux (SER) of gastric contents that activates laryngeal chemoreflex-stimulated apnea. Placing infants supine decreases the risk of sudden infant death syndrome (SIDS). The aim of this study was to determine whether body position affects esophageal reflexes that control SER.MethodsWe instrumented the pharyngeal and esophageal muscles of decerebrate cats (N=14) to record EMG or manometry, and investigated the effects of body position on the esophago-upper esophageal sphincter (UES) contractile reflex (EUCR), esophago-UES relaxation reflex (EURR), esophagus-stimulated pharyngeal swallow response (EPSR), secondary peristalsis (SP), and pharyngeal swallow (PS). EPSR, EUCR, and SP were activated by balloon distension, EURR by air pulse, and PS by nasopharyngeal water injection. The esophagus was stimulated in the cervical, proximal thoracic, and distal thoracic regions. The threshold stimulus for activation of EUCR, EURR, and PS, and the chance of activation of EPSR and SP were quantified.ResultsWe found that only EPSR was significantly more sensitive in the supine vs. prone position regardless of the stimulus or the position of the stimulus in the esophagus.ConclusionWe hypothesize that the EPSR may contribute to the protection of infants from SIDS by placement in the supine position.

Determinants of Fatal Apnea Responses to Acid Stimulation of the Larynx in Piglets

Objectives:

This study explores the physiological determinants of laryngeal chemoreflex (LCR) response severity under hypoxic conditions.

Methods:

Thirty-four piglets underwent hypoxic laryngeal stimulation. Physiologic data were collected, and responses were graded as mild, moderate, or profound.

Results:

Prestimulation hypoxia caused respiratory depression and carbon dioxide retention in profound responders and respiratory stimulation in mild and moderate responders (p < .05). Resumption of respiration occurred in all animals when the Paco2 rose by a mean ± SD of 15.1 ± 6.5 mm Hg (p > .05). There was a significant difference between mild, moderate, and severe responders in change in arterial Pao2 and hydrogenated hemoglobin saturation during the LCR-induced response (p < .001 for both).

Conclusions:

Resumption of respiration is associated with accumulation of arterial Paco2. The respiratory response to hypoxia predicts the severity of the LCR response. The severity of the LCR-induced response is associated with changes in arterial Pao2 and hydrogenated hemoglobin saturation during the LCR-inducedapnea.

Food for Thought on Pediatric Feeding and Swallowing

“Food for Thought” provides an opportunity for review of pertinent topics to add to updates in areas of concern for professionals involved with feeding and swallowing issues in infants and children. Given the frequency with which speech-language pathologists (SLPs) make decisions to alter feedings when young infants demonstrate silent aspiration on videofluoroscopic swallow studies (VFSS), the need for increased understanding about cough and its development/maturation is a high priority. In addition, understanding of the role(s) of laryngeal chemoreflexes (LCRs), relationships (or lack of relationships) between cough and esophagitis, gastroesophageal reflux (GER), and chronic salivary aspiration is critical. Decision making regarding management must take into account multiple systems and their interactions in order to provide safe feeding for all children to meet nutrition and hydration needs without being at risk for pulmonary problems. The responsibility is huge and should encourage all to search the literature so that clinical practice is as evidence-based as possible; this often requires adequate understanding of developmentally appropriate neurophysiology and function.

Arousal has no effect on non-nutritive breathing-swallowing coordination during the first year of human life

Although the brainstem plays an important role in breathing-swallowing coordination (BSC), the role of suprabulbar structures is ill defined. Given the known decrease in global cerebral activity during sleep, the sleep-wake paradigm was used to elucidate suprabulbar influences. Non-nutritive BSC of 10 healthy human infants was monitored longitudinally during wakefulness and sleep from birth to 1 year of age. Time-locked recordings of submental muscle activity, nasal airflow, and thyroid acoustics enabled the categorization of swallows depending on the preceding and following respiratory phase. In contrast to the change in the overall pattern of BSC with age, and despite well-known marked postnatal cortical development over this time, no arousal-related differences were seen during the first year of life. This most likely reflects complete brainstem control of non-nutritive BSC in infants.

Laryngeal sensitivity in the neonatal period: from bench to bedside

Laryngeal sensitivity in the newborn has been a subject of great interest for both researchers and clinicians for a number of years. From a clinical standpoint, laryngeal sensitivity is essential for both preventing foreign substances from entering into the lower airway and for finely tuning upper airway resistance. However, heightened reflexes originating from the laryngeal receptors in newborns and infants, due to neural immaturity, can lead to potentially dangerous cardiorespiratory events. The latter have been linked to apneas of prematurity, apparent life-threatening events, and sudden infant death syndrome (SIDS). From a physiological standpoint, many mechanisms pertaining to reflexes originating from laryngeal receptors are yet to be fully understood. This short review is an attempt to summarize current knowledge on laryngeal sensitivity and its potential consequences upon control of breathing abnormalities encountered within the first weeks of life.

Maturation of cough and other reflexes that protect the fetal and neonatal airway

Although aspiration of contaminated amniotic fluid and gastric contents is common at birth, anecdotal evidence indicates that coughing occurs rarely if at all. Studies in which cough and other airway protective responses have been stimulated by introducing a small bolus of water or saline into the pharynx of sleeping infants have found that the predominant responses are swallowing, apnea and laryngeal closure. Coughing is rare. Collectively, these responses are known as the laryngeal chemoreflexes (LCR). These are mediated by receptors in the inter-arytenoid space. The LCR has been studied extensively in animal models. Upper airway infection increases the responses and in this case coughing becomes a common component. Studies in animal models indicate that with maturation, apnea and swallowing components of the LCR decrease while cough becomes increasingly prominent.

The early impact of feeding on infant breathing-swallowing coordination

This longitudinal study assessed the coordination of nutritive and non-nutritive swallowing with breathing in 10 healthy term infants from birth to 1 year of age. Swallows were classified into five respiratory-phase categories: mid-inspiration (II), mid-expiration (EE), inspiratory-expiratory cusp (IE), expiratory-inspiratory cusp (EI), and mid-pause (P). Breathing-swallowing coordination differed markedly between the two swallowing conditions, especially between 2 weeks and 2 months. Significant condition effects were found in up to four respiratory-phase categories (II, IE, EI, and P). The condition effect was minimal from 9 months with only IE swallow proportions differing between conditions. These data suggest a 'critical period' in infantile neural response to oropharyngeal stimulation during feeding and that the impact of this on infants with neurological and/or respiratory disorders should be further investigated.

Laryngeal chemoreflexes induced by acid, water, and saline in nonsedated newborn lambs during quiet sleep

Laryngeal chemoreflexes (LCR) are triggered by the contact of assorted liquids with the laryngeal mucosa. In the neonatal period, the immature LCR consist primarily of apnea and bradycardia, which at times can be life threatening. The aim of this study was to assess LCR induction in nonsedated, newborn full-term lambs by several acid solutions, compared with distilled water and saline. Twelve lambs were instrumented for recording of glottal adductor and diaphragm EMG, EEG, eye movements, heart rate, systemic arterial pressure, and respiratory movements. LCR were induced during quiet sleep by the injection (0.5 ml) of saline, distilled water or two acid solutions (HCl and citric acid, pH 2, diluted in either water or saline). A chronic supraglottal catheter was used to inject the solutions in a random order. Distilled water and acid solutions did not induce any significant decrease in heart rate or respiratory rate. However, significant lower airway protective responses (swallowing, cough, and arousal) were observed after distilled water and especially acid solution administration. In conclusion, LCR in full-term lambs, particularly with acid solutions, are merely characterized by lower airway protective responses resembling mature LCR reported in adult mammals.

Relationship between respiratory control and feeding in the developing infant

Simultaneous breathing and nursing from a bottle or breast requires intricate coordination of the muscles that serve both respiration and feeding. During the buccopharyngeal phase of feeding reflex input to the brainstem from the oropharynx and larynx, as well as suprabulbar and chemoreceptor areas controls the sequential activity of the muscles of deglutition. Coordinated development of buccopharyngeal functions generally occurs by 35 weeks post-conceptional age in infants, but can be disrupted by respiratory disease or neuropathology. During the oesophageal phase of feeding, the bolus of food traverses the oesophagus and lower oesophageal sphincter, whose tone is also regulated by nuclei in the brainstem and modulated by respiratory drive. Control of the lower oesophageal sphincter gradually develops postnatally in premature infants. Although symptomatic gastro-oesophageal reflux can be problematic for the term or preterm infant, it does not appear that reflux is a common stimulus for apnoea of prematurity.

Maturation and transformation of reflexes that protect the laryngeal airway from liquid aspiration from fetal to adult life

Several reflexes are initiated in the fetus and newborn when hypochloremic or strongly acidic solutions contact the epithelium that surrounds the entrance to the laryngeal airway. These reflexes, known collectively as the laryngeal chemoreflex (LCR), include startle, rapid swallowing, apnea, laryngeal constriction, hypertension, and bradycardia. Many studies have shown that prolonged apnea associated with the LCR may be life threatening and might conceivably be a cause of sudden infant death syndrome. This certainly may be true, but the concept of a lethal LCR paradoxically contrasts with the view that these several reflexes have an important airway-protective role. As the infant matures, rapid swallowing and apnea become much less pronounced, whereas cough and possibly laryngeal constriction become more prominent. This transformation is primarily related to central neural processing rather than to changes in the airway mucosal "water receptors" that initiate the reflex. The LCR develops in the fetus, in an all-aqueous environment, during a period in which aspiration of amniotic fluid poses a serious threat to life. This and other considerations suggest that the transformation in LCR responses from fetal to adult life can be viewed as functionally appropriate to their primary role in defending the airway from aspiration. The laryngeal "water receptors" that initiate the LCR in infants and adults alike appear to be the primary sensory mechanism for defending the airway from aspiration of liquids.

Age dependence of laryngeal chemoreflex in puppies

Previously collected data have indicated that the laryngeal chemoreflex (LCR) response is exaggerated during a critical period of postnatal development in several experimental animals. These animals had fewer anatomic and physiological similarities to humans than do puppies. This investigation of the LCR in 14 anesthetized puppies was undertaken to determine age-related differences in the response to stimulation of the supraglottic laryngeal mucosa by saline solution, distilled water, cow's milk, and acid at pH 1.0. The dogs were divided into 3 age groups: group 1 consisted of 4 dogs that were 2 weeks old, and in groups 2 and 3 there were 5 puppies each, of 4 and 6 weeks of age, respectively. The LCR response (laryngospasm, apnea, respiratory depression, and bradycardia) was found in the puppies only after stimulation of the laryngeal mucosa with acid at pH 1.0, and it was more easily achieved in the 4- and 6-week age groups than in the 2-week group. These findings suggest that the LCR is an age-dependent response that appears in dogs only after 2 weeks of age. The important implication of this finding is that postnatal neural maturation may influence the laryngeal reflex in humans to some extent.

Effects of intralaryngeal carbon dioxide and acetazolamide on the laryngeal chemoreflex

Sudden infant death syndrome is the leading cause of death in infants in the United States. The laryngeal chemoreflex (LCR) is thought to contribute to its pathogenesis. In adult animals, increasing levels of intralaryngeal CO2 result in a decrease in ventilatory activity. Intravenous acetazolamide (AZ) abolishes this response. The purpose of this study was to determine the effects of intralaryngeal CO2 and AZ on the LCR and respiratory physiology of piglets under normoxic and hypoxic conditions. We applied 0% or 10% CO2 in a randomized order to the larynx of 26 piglets. Intubation via tracheotomy prevented inhalation of the gas mixtures. Laryngeal stimulation was performed under normoxic conditions (PaO2 of >70 mm Hg) in 15 animals and under hypoxic conditions (PaO2 of 50 to 65 mm Hg) in 11 animals both with and without intravenous AZ (5 mg/kg). Respiratory and cardiovascular response data were recorded. Ten percent intralaryngeal CO2 has no significant effect on mean baseline respiratory rate, systemic PaCO2 or PaO2 levels, or apnea duration (p > .05). The use of AZ (versus no AZ) resulted in significantly higher baseline respiratory rates (64 versus 51 breaths per minute; p = .016), a decreased baseline systemic PaCO2 level (38.8 versus 45.9 mm Hg; p < .001), a higher baseline PaO2 level (97.9 versus 82.8 mm Hg; p < .001), shorter mean apnea durations (15.5 versus 24.8 seconds; p = .001), a higher lowest O2 saturation level after the stimulus (78.0% versus 68.4%; p = .003), and fewer profound apneas (10 of 90 versus 41 of 90 trials; p < .001). We conclude that 10% intralaryngeal CO2 does not decrease ventilatory activity in piglets and has no significant effect on the LCR. Acetazolamide, however, appears to have a protective effect against the LCR, resulting in shorter and less severe apneas. The protective effect of AZ against the LCR appears to be related to its ability to stimulate the respiratory drive and increase oxygenation at baseline.

Second place-resident clinical science award 1999: laryngeal chemoreflex severity and end-apnea PaO(2) and PaCO(2)

OBJECTIVE

The laryngeal chemoreflex (LCR) is a model for investigating the sudden infant death syndrome. The severity of the LCR-induced response may vary. This study examines the conditions under which recovery from the LCR-induced apnea occurs.

METHODS

Twenty-five piglets underwent normoxic laryngeal stimulation (Pao(2) > 70 mm Hg); 11 then underwent hypoxic stimulation (Pao(2) 50-65 mm Hg). Cardiovascular and respiratory responses were recorded.

RESULTS

Recovery Pao(2) was lower during profound responses (Pao(2) = 45.9 +/- 12.8 mm Hg) than during moderate (Pao(2) = 54.9 +/- 7.5 mm Hg) and mild (Pao(2) = 60.6 +/- 10.3 mm Hg) responses (analysis of variance [ANOVA], P = 0.05). Recovery PaCO(2) did not vary (ANOVA, P > 0.05). Blood pressure and O(2) saturation declined at faster rates with increasing severity of response (ANOVA, P < 0.05 for both).

CONCLUSIONS

Resumption of respiration after LCR-induced apnea is associated with a consistent level of PaCO(2). The severity of the response is associated with recovery PaO(2) levels.

The role of gastro-oesophageal reflux in the aetiology of SIDS

Gastro-oesophageal reflux (GOR) has been identified as a possible cause of SIDS. Several features of GOR unique to infants presenting with apparent life-threatening events (ALTEs) have led to its 'pathogenic' definition. One is that the life-threatening apnoea itself is initiated by GOR, another is that the ALTE relates to prolonged reflux during sleep, in a vulnerable sleep-state, and finally that the ALTE relates to excessive quantities of GOR. The presumption of GOR 'pathology' as a cause of SIDS however, is questionable in these susceptible infants for three reasons: firstly, GOR is physiological and occurs in most infants; secondly, there is no general consensus on what constitutes normal physiological reflux, and thirdly, variation in the recording technique and methods of data analysis and interpretation may account for the differences between study groups. It seems likely therefore if GOR is implicated in SIDS, additional factors are involved. Under certain circumstances, physiological GOR may trigger life-threatening apnoea in apparently healthy infants, that leads to SIDS. One mechanism that could explain such a death is reflex apnoea by stimulation of laryngeal chemoreceptors (LCR) during sleep. The conditions under which this could be fatal are the occurrence of gastric contents refluxed to the level of the pharynx during sleep, in the young infant who has depressed swallowing and arousal. That is, the occurrence of GOR to the level of the pharynx during sleep, an infrequent event that is usually innocuous, could be converted to a fatal event if swallowing is impaired and arousal depressed, by a variety of mediating factors such as prone sleeping, prematurity, sedatives, seizures or upper respiratory tract infections. The identification of LCR responses, particularly in prone sleeping and premature infants provide further evidence that this mechanism may be implicated in the aetiology of SIDS in apparently healthy infants.

Why the prone position is a risk factor for sudden infant death syndrome

INTRODUCTION

The laryngeal chemoreflex may explain why prone sleeping increases the risk of sudden infant death syndrome (SIDS). Swallowing and arousal are crucial to prevent laryngeal chemoreflex stimulation. Our aim was to examine these reflexes and breathing responses in healthy neonates after pharyngeal infusion of water in the supine versus the prone position, controlling for sleep state.

METHODS

A total of 10 term infants were recruited after parental consent and ethics approval. Polygraphic recordings included sleep state (active and quiet sleep by electroencephalogram, eye movements, breathing, and behavior), cardiorespiratory measurements (nasal airflow, chest wall movements, heart rate, and oxygen saturation), swallowing, and esophageal activity (solid state pressure catheter). Initial sleeping position was assigned randomly. Measurements were made for 1 minute before and after 0.4 mL of water was instilled into the oropharynx. To detect a 30% decrease in swallowing, power analysis indicated that >/=10 babies were required. Analysis, blinded to position, was made using nonparametric statistics.

RESULTS

Of the 164 infusions, the most commonly evoked airway protective responses to pharyngeal infusion were swallowing (95%) and arousal (54%). After infusion in active sleep, there was a significant reduction in swallowing and breathing when the prone position was compared with the supine position (prone: 21.3 [1.0] swallows/min and -9.6 [2.1] breaths/min; and supine: 32 (2.2) and -2. 9 (1.5), respectively). However, there was no difference in the occurrence of arousal after water infusion.

CONCLUSION

These data suggest that airway protection is compromised in the prone sleeping position during active sleep, even in healthy infants exposed to minute pharyngeal fluid volumes of 0.4 mL. This is because swallowing rate is reduced significantly, and there is no compensatory increase in arousal. The reduction in airway protective reflexes when in the prone position and in active sleep may be the mechanism for the increased risk of SIDS in the prone position.

Coordination between glottic adductor muscle and diaphragm EMG activity in fetal lambs in utero

It has previously been reported that active glottic adduction is present during prolonged apneas but absent during periods of breathing movements in fetal lambs in utero. The present study was aimed at examining the precise coordination between fetal breathing movements [diaphragm electromyographic (EMG) activity (Di EMG)] and glottic adduction [thyroarytenoid muscle EMG activity (TA EMG)]. Electrodes for electroencephalogram, eye movements, TA EMG, and Di EMG and an arterial catheter were surgically implanted in fetal lambs 123-142 days postconception. Polygraphic recordings were performed without sedation while the ewe breathed room air (n = 11) or various gas mixtures (hypoxia, n = 5; hyperoxia, n = 4; hypercapnia, n = 5; hypercapnia+hyperoxia, n = 5). Tonic TA EMG was observed throughout >90% of apneas (>6 s) in both non-rapid-eye-movement and rapid-eye-movement sleep, and when Di EMG frequency decreased in rapid-eye-movement sleep. In all but two fetuses, TA EMG was immediately inhibited when Di EMG appeared. Altering blood gases did not modify these results. In conclusion, Di EMG and TA EMG are well coordinated in late gestation in fetal lambs, except in a few cases. These findings may have consequences for understanding the pathogenesis of mixed/obstructive apneas of prematurity.

Ovine Fetal Laryngeal Chemoreflex Thresholds and Respiratory Effects

In newborn infants, laryngeal contact with solutions of low chloride concentration or pH evokes swallowing, laryngeal adduction, and respiratory inhibition (laryngeal chemoreflex). To determine whether the laryngeal chemoreflex is present during fetal life and its effect on fetal respiratory activity, eight time-bred ewes (128 ± 2 days) were prepared with fetal electrocortical diaphragm and esophageal electrodes and a nasopharyngeal catheter. After a 60-minute control period, increasing volumes (0.1 to 1.0 ml/kg) of 0.15 mol/L NaCl or distilled water (0.05 to 1.0 ml/kg) and decreasing concentrations of NaCl (0.15 to 0.02 mol/L) at a fixed volume (0.3 ml/kg) were sequentially administered through the nasopharyngeal catheter (38° C). The minimum water volume that stimulated swallowing was significantly less than the minimum 0.15 mol/L NaCl volume (0.10 ± 0.02 vs. 0.70 ± 0.05 ml/kg). The maximum NaCl concentration that stimulated swallowing was 0.04 ± 0.01 mol/L. During the control period, respiratory activity averaged 14.6 ± 0.7 breaths/minute and did not change during absent swallow responses or isotonic saline-induced swallows. However, respiratory activity significantly decreased during water (4.7 ± 0.6 breaths/minute) and hypotonic saline-induced swallow responses (3.7 ± 0.7 breaths/minute). Fetal electrocortical activity did not change during absent or stimulated swallows. We conclude that laryngeal water or hypotonic saline solution may stimulate fetal swallowing and suppress fetal respiratory activity, similar to the newborn laryngeal chemoreflex. We speculate that an exaggeration of the laryngeal chemoreflex apnea response in the newborn may predispose to sudden infant death syndrome.

Effect of continuous swallowing on respiration

We examined the effect of continuous swallowing on breathing pattern and ventilation in 7 adult subjects. Repetitive swallowing was induced by oral infusion of water at a variable rate of 40, 60, 80 or 100 ml/min, while the subject breathed through the nose. The number of swallows increased from a mean of 5.2 (+/- 2.7 SD) swallows/min during the control period to 9.2 +/- 2.0 to 13.7 +/- 2.9 swallows/min during infusion of 40 and 100 ml/min, respectively. The duration of interruption of breathing was bolus volume-dependent, increasing from 0.55 +/- 0.09 sec with a mean bolus volume of 4.6 +/- 1.4 ml to 0.87 +/- 0.23 sec with a bolus volume of 8.1 +/- 1.9 ml. The majority of swallows (73 +/- 12%) interrupted breathing during inspiration. The mean tidal volume, inspiratory and expiratory times during swallowing periods were higher than those recorded during the control period, but the mean level of ventilation was not different from control, at all swallowing frequencies. Repetitive swallowing did not result in a single incidence of aspiration or coughing. We conclude that mechanisms integrating breathing and swallowing allow repetitive swallowing to occur without compromising ventilation, and that these mechanisms perfectly orchestrate between breathing and deglutition to prevent aspiration.

Correlation between the laryngeal brain stem evoked response and the laryngeal chemoreflex in the porcine model

The laryngeal brain stem evoked response (LBR) represents the neural activity involved in laryngeal reflex pathways. The laryngeal chemoreflex (LCR) is a centrally mediated response consisting of apnea and hemodynamic changes that result from laryngeal stimulation. The purpose of this study is to determine the characteristics of the LBR that are predictive of LCR severity in the porcine model. The duration of apnea resulting from stimulation of the supraglottic larynx defined LCR severity. The LBR tracings were recorded from electrodes flanking the brain stem following direct electrical stimulation of the superior laryngeal nerve. The LBR peak latencies from piglets demonstrating prolonged LCR apnea were compared to those without an exaggerated LCR response. Two LBR peak latencies demonstrated a statistically significant difference between the two piglet groups. These peak latencies appear to be indicators of susceptibility to exaggerated laryngeal reflex sensitivity. Thus, the LBR may prove useful in identifying and evaluating subjects predisposed to conditions associated with dysfunctional laryngeal reflex activity.

Laryngeal brain stem evoked response in the porcine model

Exaggeration of normally protective laryngeal reflexes is thought to play a role in several disorders, including the sudden infant death syndrome. An analysis of brain stem neural activity following laryngeal stimulation may provide insight into the pathophysiology of pathologic laryngeal reflexes and help to identify individuals at risk for these disorders. The purpose of this study was to define the far-field brain stem activity following laryngeal stimulation in the porcine model. This activity has been termed the laryngeal brain stem evoked response and may represent a potentially useful and objective measure of the neuronal activity in the laryngeal reflex pathway. Electrical stimulation of the superior laryngeal nerve was performed in 14 mixed-breed piglets under a variety of physiologic conditions. A total of six positive and six negative discrete waves were detected, with mean latencies ranging from 1.24 to 7.16 milliseconds. Stimulations performed during hypoxic, hypercapneic, or hypocapneic conditions resulted in no significant differences in waveform latencies. There appears to be a reproducible, but somewhat variable, brain stem response elicited by superior laryngeal nerve stimulation that can be recorded via a far-field technique in the porcine model.

Lack of temporal relation between acid reflux in the proximal oesophagus and cardiorespiratory events in sleeping infants

We studied sleeping infants in order to investigate whether a temporal relation exists between acid reflux extending to the proximal portion of the oesophagus and cardiorespiratory events. One hundred infants with occasional regurgitations were studied: 50 infants admitted after an apparently life-threatening event (ALTE) that occurred during sleep and that remained unexplained despite medical investigation, and 50 asymptomatic infants (non-ALTE). The infants had a median age of 8 weeks (range 4-26 weeks); 54 were boys. In each child a pH probe was placed in the proximal portion of the thoracic oesophagus, under radiological control. Polygraphic monitoring of state of alertness, cardiorespiratory activity, and proximal oesophageal pH changes was conducted continuously during 1 night. The data were analysed blind. In 80 infants a total of 186 decreases in oesophageal pH below 4 units were seen; 37% occurred during wakefulness, and 40% during rapid eye movement (REM) sleep. A total of 7029 central and 61 obstructive apnoeas were monitored, mainly during REM sleep. Within 5 min before, and 5 min after the drops in pH, there was no difference in the number, or the duration of bradycardia, central, mixed, or obstructive apnoea. The infants with an ALTE could not be differentiated from the non-ALTE infants for any of the variables studied. It is concluded that spontaneous acid refluxes extending to the proximal portion of the oesophagus during sleep are usually not temporally related with the development of apnoeas or bradycardias.

Infant apnea and gastroesophageal reflux

The value of a combination of ultrasound studies and barium swallow examination in the analysis of temporal relationships between apnea and reflux is demonstrated. The two techniques allow acute apneic spells induced by gastroesophageal reflux to be documented and underlying specific digestive tract disorders demonstrated. The high incidence of digestive tract disorders in this area has been identified.

Site of upper airway obstruction in preterm infants with problematical apnoea

Airway obstruction is an important factor predisposing to the development of apnoea in preterm infants. An ultrafine fibreoptic scope was used to examine the upper airway of 12 preterm infants with recurrent problematical apnoea. Continuous visualisation of the airway was possible and recorded on to videotape together with simultaneous cardiorespiratory monitoring to detect apnoeic episodes in 12 infants studied. In seven infants obstruction was observed at laryngeal level with the arytenoid masses and aryepiglottic folds closing across the vocal cords. This was not only observed in obstructive apnoea but also during mixed apnoea in periods where no respiratory effort was detectable and again in apparently pure central apnoea. The findings confirm the larynx as an anatomical site of upper airway obstruction. They agree with other indirect methods of assessing airway patency that obstruction has an important role in the pathophysiology of apnoea of prematurity.

Upper GI examinations in older premature infants with persistent apnea: correlation with simultaneous cardiorespiratory monitoring

Upper gastrointestinal examinations with simultaneous cardiorespiratory monitoring were performed in 39 older premature infants with persistent apnea. Swallowing incoordination was documented to be causatively related to persistent apnea in such infants, especially with feeding. Direct relationship between apnea and gastroesophageal reflux was not documented in this study.

Combined disturbance of respiratory regulation and esophageal function in early infancy

An evident coincidence exists between increased and extended apneas during sleep and frequent gastroesophageal reflux as well as disturbances of propulsive esophageal peristalsis. The tendency to develop apnea and disturbed esophageal function are related to the degree of the maturity of the patient. This indicates that in some infants, a combined regulatory immaturity of the autonomic centers persists. Moreover, the gastroesophageal reflux fosters the clinical manifestation of sleep apneas. The risk of a reflex apnea accompanied by gastroesophageal reflux increases in proportion to the disturbance in the central respiratory regulation present at the same time. This pathomechanism can be considered one of the causes of the sudden infant death syndrome. The possibility of effective prophylaxis consists in treating the apneic tendency with aminophylline and the treatment of reflux by elevating the upper body and thickening the nourishment given.

Postnatal synaptic development of the rat

Presynaptic boutons of the dorsomedial region of the nucleus tractus solitarius (NTS) were studied during the first 30 days of postnatal development of the rat. Electron micrographs were analyzed by conventional and stereological techniques to determine the area and volumetric density and fraction, and the number per linear length on both the dendrites and cell bodies. The numerical density and volumetric fraction of boutons in the NTS increased rapidly within the first 10 postnatal days. The number of boutons per area and volume remained stable between 10 and 30 days. Twice as many boutons synapsed on the larger dendrites than the cell bodies during the first 10 days, and then increased to 4 times the number of synapses per linear length on the cell body after the tenth postnatal day. The rapid synaptic development and shift in shift in sites of synaptic contact on neurons of the NTS suggest synaptic contacts rapidly change during early postnatal development.

Gastroesophageal reflux causing respiratory distress and apnea in newborn infants

Respiratory distress, apnea, and chronic pulmonary disease since birth were identified in 14 infants who also had symptomatic gastroesophageal reflux. Birth weights varied from 760 to 4,540 gm. All infants had radiographic changes similar to those in bronchopulmonary dysplasia. Cessation of apnea and improvement of pulmonary disease occurred only after medical (8) or surgical (6) control of gastroesophageal reflux. Simultaneous tracings of esophageal pH, heart rate, impedance pneumography, and nasal air flow in five infants demonstrated that reflux preceded apnea. Apnea could be induced by instillation of dilute acid, but not water or formula, into the esophagus. Prolonged monitoring of esophageal pH more than two hours after feeding in 14 other infants less than 6 weeks of age (birth weight 780 to 3,350 gm) without a history of recent vomiting indicated that reflux was not greater than in normal older children.