Prolonged expiratory apnoea and implications for control of breathing

Pathogenesis of apparent life-threatening events in infants with esophageal atresia

Many infants with a repaired esophageal atresia (EA) undergo fundoplication, aortopexy, or glossopexy because the mechanisms most responsible for airway obstruction and/or apparent life-threatening event (AO/ALTE) syndrome are considered to be gastroesophageal reflux (GER), tracheal compression (TC), or obstructive apnea, respectively. In the present study, we investigated whether these mechanisms are independent or interrelated. We developed a database of 120 consecutive patients with EA treated by the senior author between 1967-2002. We studied the clinical manifestations of patients with a cervical esophagostomy and/or blind lower esophageal stump, which ruled out TC and/or proximal esophageal GER as a mechanism for AO/ALTE. Of 25 neonates who underwent section/ligation of lower tracheo-esophageal fistula and/or feeding gastrostomy, 10 critically ill neonates died. Of 15 survivors, 9 infants had a feeding gastrostomy without an esophagostomy. Of these, 6 infants presented one or more episodes of AO, and 8 presented ALTE with or without AO. Subsequently, 5 of the 9 infants underwent an esophagostomy. Eventually, 11 infants had a feeding gastrostomy with an esophagostomy. Of the latter, 5 infants presented one or more episodes of AO, and 6 presented ALTE without AO. In conclusion, oral feeding, proximal esophageal GER, and TC are not essential for AO/ALTE syndrome to occur. They are probably factors which offer evidence of an underlying problem with control of upper airway patency.

Abnormalities in surfactant in sudden infant death syndrome as a postmortem marker and possible test of risk

OBJECTIVE

To determine whether physical abnormalities in lung surfactant, particularly inversion of the hysteresis between surface tension and surface area, are an effective postmortem marker for sudden infant death syndrome (SIDS).

METHODOLOGY

Bronchoalveolar lavage (BAL) was employed to obtain lung rinsings from 55 infants under 24 months of age at autopsy, comprising 34 index cases and 21 controls. Folch reagent was used to extract the lipoid content which was then applied at two surface concentrations, fixed and BAL-determined (BALD), to the pool of a Langmuir trough in which surface tension (gamma) was measured continuously by the Wilhelmy method as surface area (A) was cycled.

RESULTS

The gamma:A loops from SIDS samples were inverted relative to controls (i.e. they were hysteresis reversed, this inversion being quantified by an empirical surface tension: area reversal (STAR) score). There was a wide scatter of STAR scores, but a critical value was found which offered a significant (P = 0.017) separation of SIDS cases from controls for a fixed surface concentration and a highly significant separation (P = 1.0 x 10(-4)) for BALD surface concentrations. Differences in the yields of phospholipid and proteolipid, or their correlation to STAR scores, did not reach statistical significance.

CONCLUSIONS

Inversion of the gamma :A loops (i.e. hysteresis inversion) would appear to offer a better postmortem marker of SIDS than any reported previously, the procedure having potential for development as a prospective test indicating the risk of this disease.

Assessment of pulmonary mechanics and breathing patterns during posturally induced glossoptosis in infants

Respiratory mechanics were studied in nine infants with glossoptosis-apnoea syndrome to determine whether glossoptosis may account for signs of both inspiratory and expiratory airway obstruction. Airflow, oesophageal pressure, inspiratory and expiratory time (Ti and Te), and inspiratory and expiratory resistance (Ri and Re) were measured before and during ventilatory phases characterised by glossoptotic pharyngeal obstruction, induced by turning the infants onto their backs. In addition, an attempt was made to correlate the abnormalities in pulmonary mechanics with the clinical features. During partial glossoptotic pharyngeal obstruction, a significant increase was observed in Te and Re and variable changes in Ti and Ri. During severe obstruction, the infants displayed obstructed inspiratory efforts often associated with stridor, as well as obstructed expiratory efforts often associated with audible grunting and retarded expiratory flow pattern. The expiratory grunt was loudest over the neck and mimicked bronchospasm over the chest. These findings indicate that glossoptotic pharyngeal obstruction induces functional airway obstruction which may affect both inspiration and expiration. Expiratory airway obstruction seems, at least in part, to be due to active braking of expiratory flow.

A novel role for surfactant in the lung with implications for the sudden infant death syndrome

Feedback from mechanoreceptors in the lungs to the brainstem has long been known to be vital for control of rhythmogenesis during normal breathing. Action potentials transmitted via the vagi are shown to display an irreversible relationship with respect to lung area (A), i.e. hysteresis, which closely resembles the hysteresis in surface tension (gamma) versus A for normal surfactant which coats that surface. Since lung recoil is largely determined by surface tension for resting tidal volumes, this will dominate the stretch of mechanoreceptors. Hence, it is postulated that, through the Hering-Breuer reflex, surfactant largely determines afferent neural feedback, explaining the above similarity in clockwise hysteresis loops. Thus the ability of normal surfactant to impart normal clockwise gamma: A hysteresis is seen as a desirable property enabling the brainstem to differentiate between the inspiratory and expiratory phases of the breathing cycle at the same lung volume. It is further hypothesized that the very abnormal surfactant found recently in some infants with prolonged expiratory apnoea by displaying anti-clockwise gamma: A loops would render afferent neural feedback to the brainstem highly confusing and could cause prolonged expiratory apnoea. This concept is discussed as a possible cause of sleep apnoea, recurrent cyanotic episodes and the Sudden Infant Death Syndrome (SIDS).

Laryngeal morphology in sudden unexpected death in infants

One hundred and four larynges removed from infants registered as dying from Sudden Infant Death Syndrome (SIDS) and 20 control larynges from infants of matching ages, were examined histologically. Excessive amounts of subglottic submucosal glandular tissue had reduced the available airway by more than half in 35 per cent of the SIDS larynges within the age group two of four months. In 30 per cent of this group the airway reduction was more than 60 percent. It is suggested that hyperplasia of subglottic mucous glands is one cause of fatal hypoxia in sudden unexpected infant death.

Esophageal atresia, choanal atresia, and dysautonomia

Patients with esophageal atresia (EA) or choanal atresia (CA) manifest similar clinical and pathophysiological features. To determine the significance of this observation, the clinical records of 80 patients with EA and 57 with CA were reviewed. This survey showed that similarities between the two conditions included inspiratory and expiratory dyspnea, episodes of reflex apnea and/or bradycardia, oropharyngeal dysphagia, vomiting, convulsions, hyperhydrosis, hyperthermia, sialorrhea, and sudden death. After the second year of life most symptoms disappeared spontaneously. In both conditions, respiratory effort resulted in partial or complete obstruction affecting both the inspiratory and expiratory phases of the respiratory cycle. Support for this finding was obtained by studying the breathing pattern of 3 patients with EA and 3 with CA, before and during postural respiratory loading. The data suggest that patients with EA are similar to those with CA, having upper airway instability that may result in obstructive hypopnea or apnea associated with expiratory grunting. It is possible that this upper airway instability is a manifestation of more general maturational dysautonomia previously not recognised in patients with EA.