To explain the very high frequency of cystic fibrosis (CF) mutations in most populations of European descent, it has been proposed that CF heterozygotes have a survival advantage when infected with Vibrio cholerae or Escherichia coli, the toxins of which induce diarrhea by stimulation of active intestinal chloride secretion. Two assumptions underlie this hypothesis: (1) chloride conductance by the CF transmembrane conductance regulator (CFTR) is the rate-limiting step for active intestinal chloride secretion at all levels of expression, from approximately zero in patients with CF to normal levels in people who are not carriers of a mutation; and (2) heterozygotes have smaller amounts of functional intestinal CFTR than do people who are not carriers, and heterozygotes therefore secrete less chloride when exposed to secretagogues. The authors used an intestinal perfusion technique to measure in vivo basal and prostaglandin-stimulated jejunal chloride secretion in normal subjects, CF heterozygotes, and patients with CF. Patients with CF had essentially no active chloride secretion in the basal state, and secretion was not stimulated by a prostaglandin analogue. However, CF heterozygotes secreted chloride at the same rate as did people without a CF mutation. If heterozygotes are assumed to have less-than-normal intestinal CFTR function, these results mean that CFTR expression is not rate limiting for active chloride secretion in heterozygotes. The results do not support the theory that the very high frequency of CF mutations is due to a survival advantage that is conferred on heterozygotes who contract diarrheal illnesses mediated by intestinal hypersecretion of chloride.

Background Premature birth affects millions of neonates each year, placing them at risk for respiratory disease due to prematurity. Bronchopulmonary dysplasia is the most common chronic lung disease of infancy, but recent data suggest that even premature infants who do not meet the strict definition of bronchopulmonary dysplasia can develop adverse pulmonary outcomes later in life. This post-prematurity respiratory disease (PPRD) manifests as chronic respiratory symptoms, including cough, recurrent wheezing, exercise limitation, and reduced pulmonary function. This document provides an evidence-based clinical practice guideline on the outpatient management of infants, children, and adolescents with PPRD. Methods A multidisciplinary panel of experts posed questions regarding the outpatient management of PPRD. We conducted a systematic review of the relevant literature. The Grading of Recommendations, Assessment, Development, and Evaluation approach was used to rate the quality of evidence and the strength of the clinical recommendations. Results The panel members considered the strength of each recommendation and evaluated the benefits and risks of applying the intervention. In formulating the recommendations, the panel considered patient and caregiver values, the cost of care, and feasibility. Recommendations were developed for or against three common medical therapies and four diagnostic evaluations in the context of the outpatient management of PPRD. Conclusions The panel developed recommendations for the outpatient management of patients with PPRD on the basis of limited evidence and expert opinion. Important areas for future research were identified.

A dysfunction of pathways that normally cause contraction or relaxation of airways has been proposed to explain heightened levels of responsiveness produced by various insults to the airway. For example, we previously reported (4) that infection of cotton rats with the human respiratory syncytial virus (HRSV) leads to a significant decrease in an airway's nonadrenergic noncholinergic inhibitory (NANCi) response shortly after the infection. In the present study we addressed the more chronic effects of HRSV infection on airway function in young ferrets during a period of rapid somatic growth. Animals 1 wk old received HRSV or uninfected cell culture medium intranasally. In vitro studies of airway function were performed on tracheal smooth muscle (TSM) segments at 4, 8, and 24 wk of age. To evaluate neurally mediated contractile responses, frequency-response curves to electrical field stimulation (EFS) were performed with results expressed in terms of the frequency causing 50% of the maximal contractile response (ES50). In addition, contractile responses of TSM to methacholine (MCh) were also assessed with results expressed as the concentration needed to produce 50% of the maximal contractile response (EC50). To gauge NANCi responses, TSM was contracted with neurokinin A in the presence of atropine, propranolol, and indomethacin. Relaxant responses to EFS were assessed at frequencies from 5 to 30 Hz, with results expressed as mean percent relaxation. We found increased contractile responses to EFS in infected animals compared with that in the control group in both 4- and 8-wk old animals (p = 0.001 and p = 0.008, respectively). This difference had resolved by 24 wk of age. There was no difference in TSM responses to MCh between the groups at any age. Although there were no NANCi responses in 4-wk-old ferrets from either group, NANCi responses were significantly decreased in 8-wk-old ferrets previously infected with HRSV in the first week of life (p = 0.0001). A significant difference persisted (p = 0.008), albeit to a lesser degree, at 24 wk of age. These findings demonstrate that HRSV produces prolonged alterations of TSM function in ferret airways in vitro.

IMPORTANCE The prevalence of asthma in US children with various developmental disabilities and delays is unclear, including how estimates vary by ethnic group. OBJECTIVE To report asthma prevalence estimates by various disability categories and developmental delays in a diverse sample of the US pediatric population. DESIGN, SETTING, AND PARTICIPANTS This population-based cross-sectional study encompassed a total of 71 811 families with children or adolescents aged 0 to 17 years (hereinafter referred to as children) who participated in the

We studied the effects of recurrent aspiration of milk on neural control of airways in young developing rabbits. Beginning at 1 week of age, rabbits received 0.5 ml/kg of whole milk or sterile physiologic saline intranasally while under light methoxyflourane anesthesia 5 days a week for a period of 3 weeks. At 4 and 8 weeks of age, in vitro studies of contractile and relaxant responses of tracheal smooth muscle (TSM) segments were evaluated. To assess the neurally mediated contractile responses, frequency response curves to electrical field stimulation (EFS) were performed with results expressed in terms of frequency of EFS causing 50% of the maximal contractile response (ES50) values. In addition, the contractile responsiveness of TSM to methacholine (MCh) as reflected by the concentration causing 50% of the maximal contractile response (EC50) values was also determined to evaluate the underlying cholinergic reactivity of this segment of airway. To assess nonadrenergic noncholinergic inhibitory (NANCi) responses, experiments were performed on TSM contracted with neurokinin A in the presence of atropine, propranolol, and indomethacin. EFS was delivered to the contracted tissue at stimulation frequencies ranging from 5 to 30 Hz with results expressed as mean percent relaxation. Recurrent aspiration of milk but not saline increased EFS‐induced contractile responses, as shown by significantly lower ES50 values compared with the control group: P = 0.02 and P = 0.001 at 4 and 8 weeks of age, respectively. TSM responsiveness to MCh was no different between the two groups, suggesting that alterations in prejunctional mechanisms of neural control were most likely responsible for the increased contractile response to EFS. The NANCi responses were significantly decreased by milk aspiration at both 4 and 8 weeks of age, with the abnormalities less pronounced at the later time point. These findings demonstrate that repeated aspiration of milk leads to abnormal mechanisms of neural control within airways of developing rabbits. While aspiration of milk altered both contractile and relaxant responses to EFS, the former abnormalities became more pronounced with time while the latter appeared to be resolving. These observations suggest that injury to an airway early in development does not necessarily resolve with time but may persist, with functional abnormalities becoming more pronounced even after the airway insult has ceased. Pediatr Pulmonol. 1997; 23:198–204 © 1997 Wiley‐Liss, Inc.

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Congenital central hypoventilation syndrome (CCHS) is a neurocristopathy caused by pathogenic heterozygous variants in the gene paired-like homeobox 2b (PHOX2B). It is characterized by severe infantile alveolar hypoventilation. Individuals may also have diffuse autonomic nervous system dysfunction, Hirschsprung disease and neural crest tumors. We report three individuals with CCHS due to an 8-base pair duplication in PHOX2B; c.691_698dupGGCCCGGG (p.Gly234Alafs*78) with a predominant enteral and neural crest phenotype and a relatively mild respiratory phenotype. The attenuated respiratory phenotype reported here and elsewhere suggests an emergent genotype:phenotype correlation which challenges the current paradigm of invoking mechanical ventilation for all infants diagnosed with CCHS. Best treatment requires careful clinical judgment and ideally the assistance of a care team with expertise in CCHS.

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