CGRP-immunoreactive endocrine cell proliferation in normal and hypoxic rat lung studied by immunocytochemical detection of incorporation of 5'-bromodeoxyuridine

We have tested the suggestion that the reported increase, in hypoxic rats, in the number of lung endocrine cells immunoreactive for the regulatory peptide CGRP is caused by an accumulation of peptide within the cells which renders them more detectable, rather than by a real increase in proliferation. The incorporation of continuously infused 5'-bromodeoxyuridine (BrdU) into nuclei of CGRP-containing cells was studied by immunohistochemistry in the airway and respiratory epithelium of rats kept in a hypoxic (10% O2), normobaric conditions for 7 days and in normoxic, normobaric controls. Some CGRP-immunoreactive cells could also be labelled for BrdU. However, the ratio of the number of cells labelled with both CGRP and BrdU to the number of cells labelled with CGRP alone did not differ significantly between hypoxic and normoxic rats (7.1 +/- 0.7 and 6.1 +/- 1.2, respectively; mean +/- SEM; P = 0.49). These data strongly suggest that CGRP-containing endocrine cells or their precursors do proliferate in adult rat lung, but that the proliferation is not increased significantly in hypoxia.

Quantitative immunocytochemistry shows calcitonin gene-related peptide-like immunoreactivity in lung neuroendocrine cells is increased by chronic hypoxia in the rat

We have previously shown that the vasodilator calcitonin gene-related peptide (CGRP) is increased in pulmonary neuroendocrine cells in response to hypoxia. To quantify the change, we have now examined lung of adult male Wistar rats exposed to hypoxia (FIO2 = 0.1) for 1 wk and littermate controls. Sections of lung were immunostained simultaneously using rabbit antiserum to rat alpha-CGRP with the peroxidase antiperoxidase technique. The area and integrated optical density of each group of endocrine cells were measured using an image analyzer. For each animal, the summed integrated optical density of endocrine cells divided by the sum of their areas was used as a measure of CGRP-like immunoreactivity. The intensity of immunostaining of endocrine cells in the respiratory portion of the lung was 43% greater than that of endocrine cells along the conducting airways (P less than 0.001). The intensity of staining was increased by approximately 12% (P less than 0.04) after 7 d of hypoxia with no apparent difference in the response of central and peripheral endocrine cells. Measurements of staining intensity of CGRP-coupled agarose beads indicated that a 12% change in staining intensity corresponded to a 15 to 20% change in the concentration of CGRP or CGRP-like immunoreactive material. The supra-optimal dilution technique (measurement of the increase in the number of immunoreactive cells upon sequential immunostaining with a supra-optimal and then an optimal dilution of primary antiserum) detected the increase in CGRP-like immunoreactivity after 7 d of hypoxia with a high degree of statistical significance (P less than 0.005) using the same number of sections.

Early ribavirin treatment of respiratory syncytial viral infection in high-risk children

A 3-year prospective, blinded, multicenter study was done to assess the efficacy of early ribavirin intervention in mild respiratory syncytial virus illness in children with bronchopulmonary dysplasia or with congenital heart disease. A cohort of 178 children younger than 36 months of age with bronchopulmonary dysplasia or congenital heart disease were followed. Forty-seven infants whose respiratory syncytial virus infection resulted in mild symptoms of less than or equal to 72 hours' duration received ribavirin (n = 20) or water placebo aerosol (n = 27) either in a hospital or at home. Outcome measures included respiratory and analog score, room air oxygen, saturation, and oxygen flow needed to maintain saturation at greater than or equal to 91%. No difference in age, gender, family size, passive smoking, baseline oxygen saturations in room air, or duration of symptoms before treatment was found between groups. After 3 days of therapy, ribavirin produced a greater rate of improvement of analog scores (p = less than or equal to 0.001), lower oxygen requirements (p = 0.01), and higher oxygen saturation (p = 0.01). Respiratory scores and total hospital days did not differ significantly between the groups. Treatment failure occurred in 2 of 20 children (10%) in the ribavirin group versus 5 of 27 children (18%) in the placebo group, a nonsignificant difference. No child required assisted ventilation or had an adverse reaction. We conclude that early ribavirin therapy may help to reduce morbidity from respiratory syncytial virus infection in high-risk young children.

Study design considerations for ribavirin: efficacy studies

Five placebo-controlled double-blind studies, each including approximately 30 subjects, have addressed the question of the effect of aerosolized ribavirin on the course of RSV lower respiratory infection in infancy. The fact that each was able to establish a beneficial effect despite the small number of subjects studied is convincing evidence that such an effect exists. The studies from Rochester using oximetry and an analog illness severity scale indicate that this effect is both statistically significant and clinically relevant. These tools are reliable and easily applicable measures for multicenter studies when illness severity is selected as an outcome measure. Characteristics that should be taken into consideration when assigning experimental groups include age, sex, a history of prematurity or underlying conditions and arterial oxygen saturation. Future studies will address additional questions about the efficacy of ribavirin, such as its role in critically ill children, the economic benefits of its use in terms of duration of hospitalization, the usefulness of early treatment of RSV disease in high risk infants, and the impact of treatment on long-term consequences of RSV infection. These studies may require outcome variables and subject selection strategies different from those used in earlier studies.

Effects of corticosteroids on postnatal lung and airway growth in the ferret

To investigate the influence of corticosteroids on postnatal lung and airway growth, young male ferrets were given cortisone acetate (20 mg/kg im daily) beginning at 8 wk of age. At 19 wk of age pulmonary function was measured. The lungs were excised for measurements of recoil pressures and wet and dry weights. The dimensions of central and peripheral airways were estimated from analysis of bronchial casts. Corticosteroid-treated animals were shorter and tended to be lighter than control animals but were heavier in relation to length. Total lung capacity was reduced in proportion to the reduction in body size. Lung recoil and wet-to-dry weight ratios were nearly identical. Maximal expiratory flows were reduced in proportion to the reduction in body size. Size-corrected airway conductance was reduced, suggesting a sensitivity of central airways to growth suppression by corticosteroids. Peripheral airways, on the other hand, were not smaller in treated animals and were larger in proportion to body size. In the ferret corticosteroid administration is associated with a suppression of lung parenchymal growth similar to that of overall body growth. The peripheral airways may be less sensitive and the central airways more sensitive to the effect of corticosteroids on growth.

Changes in airway length after unilateral pneumonectomy in weanling ferrets

We have previously shown that airway cross-sectional area increases 15-20% after pneumonectomy in weanling ferrets by measuring bronchial casts. We have now reanalyzed these same casts to quantitate changes in airway length after pneumonectomy. In each cast the distance from each of 120 airways to the terminal bronchiole along its axial pathway was measured. The relationship between the logarithm of this distance and that of the fraction of the lobe subtended by an airway could be described by a quadratic equation with a correlation coefficient greater than 0.85. Subsegmental and more distal airways of postpneumonectomy animals were 33-47% longer than those of controls. Overall the main axial pathway of airways in the left lower lobes was 12% longer in operated animals, but this increase was primarily accounted for by an increase in the length of the more peripheral airways. Central airways were little if any longer in operated animals. After pneumonectomy in weanling ferrets, subsegmental and peripheral airway lengths increase to a greater degree than lung volume and airway cross-sectional area, whereas central airway lengths increase to a lesser extent if at all. The mechanisms responsible for this difference between central and intralobar compensatory airway growth are unknown.

Lung volumes after an increase in lung distension in pneumonectomized ferrets

To investigate the role of lung distension in compensatory lung growth, the right lung of each of 21 adult male ferrets was replaced with a silicone rubber balloon filled with mineral oil. Three to thirteen weeks after surgery, the oil was removed through a subcutaneous port. Lung volumes were measured serially until 3-6 wk after balloon deflation. With pneumonectomy the total lung capacity (TLC) decreased to less than 50% of the preoperative value and remained essentially unchanged while the balloon was inflated. At balloon deflation, TLC and vital capacity did not change immediately, whereas functional residual capacity increased by 44%, indicating a change of 2-3 cmH2O in end-expiratory transpulmonary pressure. TLC increased by 10% within 3 days and continued to increase over the subsequent 3-5 wk by a total of 25% over TLC at balloon deflation. There was little difference in this response between animals whose balloons were deflated 3 wk after surgery and those in which deflation was delayed up to 13 wk. After pneumonectomy in the adult ferret, the remaining lung increases in volume in response to an increase in lung distension even weeks or months after surgery. The extent to which this volume increase involves lung tissue growth or depends on previous lung resection is at present unknown. This model may be useful for studies of the mechanisms by which lung distension influences lung volume and compensatory lung growth.

Ventilatory chemosensitivity in parents of infants with sudden infant death syndrome

We measured ventilatory responses to progressive isocapnic hypoxia and to hyperoxic hypercapnia (CO2) using rebreathing techniques in 16 parents of infants with autopsy-confirmed sudden infant death syndrome (SIDS) and 18 control parents matched for age, sex, and body size. Response to ventilatory loading was assessed by repeating the CO2 test with an inspiratory flow-resistive load (16 cm H2O/L/sec). During loaded and unloaded CO2 tests, respiratory effort was also assessed by measuring the pressure generated in the first 0.1 second (P0.1) of the subsequent inspiratory effort after brief manual occlusion of the inspiratory line. Ventilatory responses of the parents of victims of SIDS to chemical and mechanical stimulation were not significantly different from those of control parents. Responses in both groups were similar to previously reported normal values. There was a linear increase in ventilation (VE) in response to hypercapnia and hypoxia and in P0.1 in response to hypercapnia. We found expected increases in P0.1/PCO2 and decreases in VE/PCO2 slopes during loaded breathing in all subjects, but no difference between groups. We conclude that parents of SIDS victims have normal ventilatory chemosensitivity and respiratory drive.

Airway hyperreactivity and a history of clinical manifestations of asthma in childhood

The relationship between airway hyperreactivity and a history of the clinical manifestations of asthma was investigated in 54 children between the ages of 8 and 12. Airway reactivity was assessed by measuring the change in pulmonary function following the hyperventilation of subfreezing air. Clinical manifestations of asthma were assessed by a standardized questionnaire regarding lower respiratory symptoms and by medical records review. The subjects were participating in a study of the sequelae of bronchiolitis; 25 had seen a physician for mild bronchiolitis during the first 2 years of life, and the remainder had not. Airway hyperreactivity was demonstrated in 8 of the 54 children and correlated with use of medication for asthma in the 2 years before pulmonary testing and positive parental response to the question, "Does your child wheeze apart from colds?" Airway hyperreactivity did not correlate with a history of other respiratory symptoms or with a history of physician-diagnosed wheezing or asthma. No questionnaire or chart review item identified over 50% of the children with reactive airways, and most subjects identified by each of the items did not demonstrate hyperreactive airways. These data suggest that airway reactivity is only weakly associated with a history of the clinical manifestations of asthma in childhood, in part because children with clinically inactive asthma do not consistently demonstrate airway hyperreactivity and in part because many children with hyperreactive airways have never had respiratory symptoms.

Ribavirin treatment of respiratory syncytial viral infection in infants with underlying cardiopulmonary disease

Aerosolized ribavirin was evaluated in the treatment of respiratory syncytial virus lower respiratory tract disease in 53 infants, 36 of whom had underlying diseases. Of the total infants, 26 were studied in a double-blind, placebo-controlled manner; 14 received ribavirin and 12 received placebo, a water aerosol, for an average of five days. When the infants with bronchopulmonary dysplasia and congenital heart disease treated with ribavirin were compared with those receiving placebo, the treated infants showed a significantly faster rate of improvement in their illness severity score. The degree of improvement in the total group of infants receiving ribavirin compared with those receiving placebo was similarly greater, and at the end of therapy significantly greater improvement was also demonstrated in their arterial blood gas values and in the amount of virus shed from their nasal washes. No toxic or adverse effects of the aerosol therapy were observed in any of the 53 infants studied, and resistance to ribavirin did not develop in any of the respiratory syncytial virus strains isolated, despite prolonged treatment in some of the more ill infants.

Normal pulmonary function measurements and airway reactivity in childhood after mild bronchiolitis

Concern about the long-term sequelae of bronchiolitis has been raised through studies of children hospitalized for bronchiolitis, but the long-term sequelae of mild bronchiolitis have not been studied. We assessed the hypothesis that 25 children with mild bronchiolitis (index subjects) were at greater risk for abnormalities of pulmonary function or airway reactivity to cold air between the ages of 8 and 12 years than were randomly selected, matched controls. There were no consistent differences in pulmonary function or airway reactivity between index and control groups. Airway hyperreactivity was found in five control subjects and three index subjects, and all children with symptomatic asthma were identified by cold air challenge. Our data suggest that children with a history of mild bronchiolitis are not at increased risk between ages 8 and 12 years for airway hyperreactivity or for abnormalities in pulmonary function.

Postpneumonectomy airway growth in the ferret

To investigate the participation of the conducting airways in compensatory growth following partial lung resection, bronchial casts of six ferrets having undergone right-sided pneumonectomy at 8 wk of age were compared with those of five sham-operated control animals. At maturity, the left lungs of the postpneumonectomy animals were 65% larger than those of the controls. Central airway cross-sectional areas at 10 specific locations in each cast were 12% larger in the postpneumonectomy animals compared with controls. To characterize the size of more peripheral airways, the size and number of the terminal bronchioles subtended by each airway in each left lower lobe cast were identified so that the fraction of the lobe served by that airway could be estimated. The characteristic cross-sectional areas of airway serving 0.7, 2.2, and 9.5% of the left lower lobe in postpneumonectomy animals were 18, 13, and 13% larger than those of controls, but this difference was statistically significant only at the two more peripheral levels. Although airway areas were larger in postpneumonectomy animals, the ratio of airway cross-sectional area to the 0.67 power of lung volume was 20-26% smaller in operated than in control animals at each of the four levels. Following pneumonectomy in the weanling ferret, central and peripheral conducting airways increase in cross-sectional area to similar degrees, but this airway growth is less than the compensatory increase in lung volume.

A technique for quantitating airway size from bronchial casts

To develop a technique for quantitating the size of airways at various positions in the bronchial tree, we analyzed casts of formalin-fixed excised lungs of five mature male ferrets. The left lower lobe of each cast was dissected, the diameter and position of each terminal bronchiole were entered into a computer programmed to reconstruct the airway system, and the cross-sectional areas of 120 conducting airways were measured. The fraction of the lobe served by each measured airway was estimated by dividing the sum of the squared diameters of the terminal bronchioles subtended by that airway by the summed squared diameters of all terminal bronchioles in the lobe. In each cast the relationship between an airway's cross-sectional area (Y) and the fraction of the lobe it was estimated to subtend (X) was described (0.91 less than R2 less than 0.95) by the expression ln(Y) = A + B ln(X) + C [ln(X)]2. Linear regression of ln(Y) on ln(X) for 30-50 airways estimated to serve fractions of the lobe around each of three arbitrarily selected levels (airways serving 0.7, 2.2, and 9.5% of the lobe) was adequate to characterize the area of airways at each level in each of the five animals with 95% confidence intervals narrower than 8% of the estimated area. Variability of airway size at each level among the five casts was modest, suggesting that this technique identified analagous airways in the various animals. Interindividual variability did not increase when the data were reanalyzed with terminal units defined on the basis of airway diameters rather than on the morphological identification of terminal bronchioles.

Ventilatory chemosensitivity in subjects with a history of childhood cyanotic breath-holding spells

The ability of children with cyanotic breath-holding spells to respond to anger or frustration by voluntary breath-holding for prolonged periods (often to the point of precipitating hypoxic seizure activity) suggested the hypothesis that such children may have a less powerful urge to breathe in the presence of hypoxia and/or hypercapnia than children who do not have breath-holding spells. Because ventilatory chemosensitivity is difficult to measure in infants and young children, this hypothesis was tested indirectly by measuring the ventilatory responses to hyperoxic progressive hypercapnia and to isocapnic progressive hypoxia of seven individuals who had a history of cyanotic breath-holding spells in infancy and 17 control subjects. The mean values for sensitivity to hypoxia and to hypercapnia were not significantly different between the two groups, and the responses of the majority of the subjects with cyanotic breath-holding spells were clearly within the normal range. There were fewer individuals with high-normal ventilatory responses among the subjects with cyanotic breath-holding spells. Although children with cyanotic breath-holding spells may have decreased ventilatory chemosensitivity transiently during infancy or may differ from other children in some other aspect of the control of breathing, the pathogenesis of infantile cyanotic breath-holding spells does not involve a permanently blunted sensitivity to hypercapnia or hypoxia.

Stridor in childhood

The acute onset of stridor in a young child usually represents viral croup, particularly during the fall and early winter. If the clinical picture is entirely consistent with this diagnosis and gas exchange is maintained, management with cool mist at home is appropriate. Rapid deterioration is unusual in viral croup; however, if obstruction is prolonged or becomes unusually severe, racemic epinephrine aerosols, hospitalization for careful observation, a brief course of corticosteroid therapy, and, rarely, endotracheal intubation may be required. Many of the other causes of acute stridor in childhood represent true pediatric emergencies: epiglottitis, foreign body aspiration, bacterial tracheitis, allergic airway edema, and retropharyngeal abscess, all requiring management with a consultant. Chronic stridor in infancy most often represents laryngomalacia, a developmental abnormality of the laryngeal cartilage which usually resolves by the second year of life and rarely requires specific treatment. Other causes of chronic stridor in childhood include subglottic hemangioma, vocal cord paralysis, and a long list of abnormalities. In the older child with chronic stridor or in the infant whose clinical picture is unusual for laryngomalacia, airway roentgenograms, barium studies, or laryngoscopy/bronchoscopy should be obtained to establish the definitive diagnosis.

Ultrasonic and jet aerosolization of phospholipids and the effects on surface activity

Surface active aerosols were produced from aqueous dispersions of mixed lipids (CLL), extracted from bovine lung lavage. Particle size distributions were measured as a function of humidity for two types of aerosol generators: ultrasonic and jet. Lipid dispersions before aerosolization were prepared by sonication in an ice bath and by mechanical vortexing. Over a range of high humidity greater than 60-70%, ultrasonic nebulization gave CLL aerosols with mass median aerodynamic diameters (MMAD) of 1.4 +/- 0.1 micron, compatible with predicted alveolar deposition fractions of 0.2-0.3 according to current deposition models. For humidities of 30-95%, jet nebulization gave MMAD values of 0.4-0.5 micron, which have lower predicted alveolar deposition. The surface pressure-time (pi - t) adsorption characteristics at 35 +/- 2 degrees C of CLL dispersions prepared initially by vortexing or sonication were not significantly affected by ultrasonic nebulization over a 1-2 h time period. In addition, the dynamic surface tension lowering of both kinds of CLL dispersion was not affected by ultrasonic nebulization (minimum surface tension less than 1 dyne/cm at 37 degrees C and 100% humidity). Current interest in the treatment of the respiratory distress syndrome (RDS) with exogenous surfactant replacement has focused largely on the delivery of surfactant replacement has focused largely on h delivery of surfactants to infants by tracheal instillation at birth. However, the ability to form multi-component surfactant aerosols with appreciable alveolar deposition fractions and high surface activity may help to expand the utility of replacement therapy to patients with aerated lungs.

Aerosolized ribavirin treatment of infants with respiratory syncytial viral infection. A randomized double-blind study

We evaluated a new antiviral agent, ribavirin, in the treatment of infants hospitalized with lower-respiratory-tract disease from respiratory syncytial virus. Ribavirin or placebo was administered to 33 infants in a double-blind manner by continuous aerosol for three to six days. Seventeen infants were treated with placebo, and 16 with ribavirin. By the end of treatment, infants receiving ribavirin had significantly greater improvement in their overall score for severity of illness, in lower-respiratory-tract signs, and in arterial oxygen saturation. Viral shedding was also diminished in the treated groups as compared with the placebo group. No side effects or toxicity were associated with the aerosol therapy. Isolates of respiratory syncytial virus obtained from the infants over the course of therapy showed no change in sensitivity to ribavirin.

Lung growth and airway function after lobectomy in infancy for congenital lobar emphysema

To characterize the outcome of lobectomy in infancy and the low expiratory flows which persist after lobectomy for congenital lobar emphysema, 15 subjects with this history were studied at age 8-30 yr. Total lung capacity was normal in all, but higher values (P < 0.05) were observed in nine subjects with upper lobectomy than in five subjects with right middle lobectomy. Ratio of residual volume to total lung capacity was correlated (P < 0.05) with the amount of lung missing as estimated from normal relative weights of the respective lobes. Xe(133) radiospirometry in eight subjects showed that the operated and unoperated sides had nearly equal volumes at total lung capacity, but that the operated side was larger than the unoperated side at residual volume. Perfusion was equally distributed between the two sides. Similar findings were detected radiographically in four other subjects. Forced expiratory volume in 1 s and maximal midexpiratory flow rate averaged 72 and 45% of predicted, respectively. Low values of specific airway conductance and normal density dependence of maximal flows in 12 subjects suggested that obstruction was not limited to peripheral airways. Pathologic observations at the time of surgery and morphometry of the resected lobes were not correlated with any test of pulmonary function. These data show that lung volume can be completely recovered after lobectomy for congenital lobar emphysema in infancy. The volume increase occurs on the operated side, and probably represents tissue growth rather than simple distension. The response to resection is influenced by the particular lobe resected and may be associated with decreased lung recoil near residual volume. Low expiratory flows in these subjects could be explained by several mechanisms, among which a disproportion between airway and parenchymal growth in infancy (dysanaptic growth) is most compatible with our data.