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Objective: To investigate associations between early low neutrophil count from routine blood samples, white blood count (WBC), pregnancy complications and neonatal outcomes for very low birth weight infants (VLBW

Rationale: Neonatal chronic lung disease (CLD), caused by prolonged mechanical ventilation (MV) with O(2)-rich gas, is the most common cause of long-term hospitalization and recurrent respiratory illness in extremely premature infants. Recurrent episodes of hypoxemia and associated ventilator adjustments often lead to worsening CLD. The mechanism that causes these hypoxemic episodes is unknown. Hypoxic pulmonary vasoconstriction (HPV), which is partially controlled by O(2)-sensitive voltage-gated potassium (K(v)) channels, is an important adaptive response to local hypoxia that helps to match perfusion and ventilation in the lung.Objectives: To test the hypothesis that chronic lung injury (CLI) impairs HPV.Methods: We studied preterm lambs that had MV with O(2)-rich gas for 3 weeks and newborn rats that breathed 95%-O(2) for 2 weeks, both of which resulted in airspace enlargement and pulmonary vascular changes consistent with CLD.Measurements and Main Results: HPV was attenuated in preterm lambs with CLI after 2 weeks of MV and in newborn rats with CLI after 2 weeks of hyperoxia. HPV and constriction to the K(v)1.x-specific inhibitor, correolide, were preferentially blunted in excised distal pulmonary arteries (dPAs) from hyperoxic rats, whose dPAs exhibited decreased K(v)1.5 and K(v)2.1 mRNA and K(+) current. Intrapulmonary gene transfer of K(v)1.5, encoding the ion channel that is thought to trigger HPV, increased O(2)-sensitive K(+) current in cultured smooth muscle cells from rat dPAs, and restored HPV in hyperoxic rats.Conclusions: Reduced expression/activity of O(2)-sensitive K(v) channels in dPAs contributes to blunted HPV observed in neonatal CLD. [ABSTRACT FROM AUTHOR]

Objectives: To compare serum ferritin and RET-He values among extremely low gestational age neonates ELGANs with other markers of iron-deficient erythropoiesis., Study Design: This is a secondary analysis of the NICHD Darbepoetin Trial. Study data from placebo recipients who had a serum ferritin, a RET-He, and a mean corpuscular volume (MCV) measurement within a 24-hour period were analyzed for correlation., Results: Mixed linear regression models showed no association between ferritin and RET-He at both early (β = 0.0016, p = 0.40) and late (β = -0.0001, p = 0.96) time points. Positive associations were observed between RET-He and MCV at baseline, early, and late time points (p < 0.01, =0.01, <0.001, respectively), while ferritin was not associated with MCV at any time point., Conclusions: Our study shows that RET-He is better correlated with MCV as a marker of iron-limited erythropoiesis than ferritin. The results suggest that ferritin is limited as a marker of iron sufficiency in premature infants., Study Identification: FDA IND Number 100138; ClinicalTrials.gov number NCT03169881; NRN ID number NICHD-NRN-0058 (Darbe)., (© 2023. The Author(s), under exclusive licence to Springer Nature America, Inc.)

Objective: To assess whether length of hospital stay is decreased among moderately preterm infants weaned from incubator to crib at a lower vs higher weight., Study Design: This trial was conducted in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network. Infants with gestational ages 29-33 weeks, birthweight <1600 g, and in an incubator were randomly assigned to a weaning weight of 1600 or 1800 g. Within 60 to 100 g of weaning weight, the incubator temperature was decreased by 1.0°C to 1.5°C every 24 hours until 28.0°C. The infants were weaned to the crib following stable temperature at 36.5°C to 37.4°C for 8 to 12 hours. Clothing and bedcoverings were standardized. The primary outcome was length of hospital stay from birth to discharge; secondary outcomes included length of stay and growth velocity from weaning to discharge. Adverse events were monitored., Results: Of 1565 infants screened, 885 were eligible, and 366 enrolled-187 to the 1600-g and 179 to the 1800-g group. Maternal and neonatal characteristics did not differ among weight groups. Length of hospital stay was a median of 43 days in the lower and 41 days in the higher weight group (P = .12). Growth velocity from completion of weaning to discharge was higher in the lower weight group, 13.7 g/kg/day vs 12.8 g/kg/day (P = .005). Groups did not differ in adverse events., Conclusions: Among moderately preterm neonates, weaning from incubator to crib at a lower weight did not decrease length of stay, but was safe and was accompanied by higher weight gain after weaning., Trial Registration: ClinicalTrials.gov: NCT02160002., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Importance: Previous studies of myo-inositol in preterm infants with respiratory distress found reduced severity of retinopathy of prematurity (ROP) and less frequent ROP, death, and intraventricular hemorrhage. However, no large trials have tested its efficacy or safety., Objective: To test the adverse events and efficacy of myo-inositol to reduce type 1 ROP among infants younger than 28 weeks' gestational age., Design, Setting, and Participants: Randomized clinical trial included 638 infants younger than 28 weeks' gestational age enrolled from 18 neonatal intensive care centers throughout the United States from April 17, 2014, to September 4, 2015; final date of follow-up was February 12, 2016. The planned enrollment of 1760 participants would permit detection of an absolute reduction in death or type 1 ROP of 7% with 90% power. The trial was terminated early due to a statistically significantly higher mortality rate in the myo-inositol group., Interventions: A 40-mg/kg dose of myo-inositol was given every 12 hours (initially intravenously, then enterally when feeding; n = 317) or placebo (n = 321) for up to 10 weeks., Main Outcomes and Measures: Type 1 ROP or death before determination of ROP outcome was designated as unfavorable. The designated favorable outcome was survival without type 1 ROP., Results: Among 638 infants (mean, 26 weeks' gestational age; 50% male), 632 (99%) received the trial drug or placebo and 589 (92%) had a study outcome. Death or type 1 ROP occurred more often in the myo-inositol group vs the placebo group (29% vs 21%, respectively; adjusted risk difference, 7% [95% CI, 0%-13%]; adjusted relative risk, 1.41 [95% CI, 1.08-1.83], P = .01). All-cause death before 55 weeks' postmenstrual age occurred in 18% of the myo-inositol group and in 11% of the placebo group (adjusted risk difference, 6% [95% CI, 0%-11%]; adjusted relative risk, 1.66 [95% CI, 1.14-2.43], P = .007). The most common serious adverse events up to 7 days of receiving the ending dose were necrotizing enterocolitis (6% for myo-inositol vs 4% for placebo), poor perfusion or hypotension (7% vs 4%, respectively), intraventricular hemorrhage (10% vs 9%), systemic infection (16% vs 11%), and respiratory distress (15% vs 13%)., Conclusions and Relevance: Among premature infants younger than 28 weeks' gestational age, treatment with myo-inositol for up to 10 weeks did not reduce the risk of type 1 ROP or death vs placebo. These findings do not support the use of myo-inositol among premature infants; however, the early termination of the trial limits definitive conclusions.

Objectives: This study tested the hypothesis that longer duration of any type of respiratory support is associated with an increased rate of death or neurodevelopmental impairment (NDI) at 18-22 months., Methods: Retrospective cohort study using the Generic Database of NICHD Neonatal Research Network from 2006 to 2010. Infants were born at <27 weeks gestational age with birth weights of 401-1000 g. Respiratory support received during initial hospitalization from birth was characterized as follows: no support, only invasive support, only non-invasive support or mixed invasive, and non-invasive support. The primary outcome was death after 24 h of life or NDI at 18-22 months corrected age., Results: In a cohort of 3651 infants, 1494 (40.9%) died or had NDI. Cumulative respiratory support of any type beyond 60 days was associated with the likelihood of death or NDI. Infants who only received invasive support had the highest rate (89.1%), followed by those received mixed support (26.1%). Infants who received only non-invasive support had the lowest rate (7.7%). When compared to the only non-invasive support group, both invasive [OR 62.7 (95%CI 25.7, 152.6)] and mixed [OR 6.1 (95%CI 2.6, 14.4)] support groups were significantly more likely to die or have NDI., Conclusion: Prolonged respiratory support, whether invasive or non-invasive, is associated with increased odds of a poor outcome. The proportion of infants with a poor outcome increased in a dose dependent manner by two factors: the cumulative duration of respiratory support beyond 60 days, and the extent to which invasive support is provided., (© 2018 Wiley Periodicals, Inc.)

Objective: To test the hypothesis that early caffeine treatment on the day of birth, compared with later treatment in very low birth weight (VLBW, <1500 g) infants receiving continuous positive airway pressure (CPAP) therapy, is associated with a decreased risk of CPAP failure in the first week of life., Study Design: Multicenter, observational cohort study in 366 US neonatal intensive care units. We evaluated inborn, VLBW infants discharged from 2000 to 2014, who received only CPAP therapy without surfactant treatment on day of life (DOL) 0, had a 5-minute Apgar ≥3, and received caffeine in the first week of life. We used multivariable conditional logistic regression to compare the risk of CPAP failure, defined as invasive mechanical ventilation or surfactant therapy on DOL 1-6, by timing of caffeine treatment as either early (initiation on DOL 0) or routine (initiation on DOL 1-6)., Results: We identified 11 133 infants; 4528 (41%) received early caffeine and 6605 (59%) received routine caffeine. Median gestational age was lower in the early caffeine group, 29 weeks (25th, 75th percentiles; 28, 30) vs the routine caffeine group, 30 weeks (29, 31); P < 0.001. The incidence of CPAP failure on DOL 1-6 was similar between the early and routine caffeine groups: 22% vs 21%; adjusted OR = 1.05 (95% CI: 0.93, 1.18)., Conclusions: Early caffeine treatment on the day of birth was not associated with a decreased risk of CPAP failure in the first week of life for VLBW infants initially treated with CPAP., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Importance: Hypothermia initiated at less than 6 hours after birth reduces death or disability for infants with hypoxic-ischemic encephalopathy at 36 weeks' or later gestation. To our knowledge, hypothermia trials have not been performed in infants presenting after 6 hours., Objective: To estimate the probability that hypothermia initiated at 6 to 24 hours after birth reduces the risk of death or disability at 18 months among infants with hypoxic-ischemic encephalopathy., Design, Setting, and Participants: A randomized clinical trial was conducted between April 2008 and June 2016 among infants at 36 weeks' or later gestation with moderate or severe hypoxic-ischemic encephalopathy enrolled at 6 to 24 hours after birth. Twenty-one US Neonatal Research Network centers participated. Bayesian analyses were prespecified given the anticipated limited sample size., Interventions: Targeted esophageal temperature was used in 168 infants. Eighty-three hypothermic infants were maintained at 33.5°C (acceptable range, 33°C-34°C) for 96 hours and then rewarmed. Eighty-five noncooled infants were maintained at 37.0°C (acceptable range, 36.5°C-37.3°C)., Main Outcomes and Measures: The composite of death or disability (moderate or severe) at 18 to 22 months adjusted for level of encephalopathy and age at randomization., Results: Hypothermic and noncooled infants were term (mean [SD], 39 [2] and 39 [1] weeks' gestation, respectively), and 47 of 83 (57%) and 55 of 85 (65%) were male, respectively. Both groups were acidemic at birth, predominantly transferred to the treating center with moderate encephalopathy, and were randomized at a mean (SD) of 16 (5) and 15 (5) hours for hypothermic and noncooled groups, respectively. The primary outcome occurred in 19 of 78 hypothermic infants (24.4%) and 22 of 79 noncooled infants (27.9%) (absolute difference, 3.5%; 95% CI, -1% to 17%). Bayesian analysis using a neutral prior indicated a 76% posterior probability of reduced death or disability with hypothermia relative to the noncooled group (adjusted posterior risk ratio, 0.86; 95% credible interval, 0.58-1.29). The probability that death or disability in cooled infants was at least 1%, 2%, or 3% less than noncooled infants was 71%, 64%, and 56%, respectively., Conclusions and Relevance: Among term infants with hypoxic-ischemic encephalopathy, hypothermia initiated at 6 to 24 hours after birth compared with noncooling resulted in a 76% probability of any reduction in death or disability, and a 64% probability of at least 2% less death or disability at 18 to 22 months. Hypothermia initiated at 6 to 24 hours after birth may have benefit but there is uncertainty in its effectiveness., Trial Registration: clinicaltrials.gov Identifier: NCT00614744.

Background: Approximately 8-23% of premature infants develop pulmonary hypertension (PH), and this diagnosis confers a higher possibility of mortality. As a result, professional societies recommend PH screening in premature infants. However, the risk factors for and the outcomes of PH may differ depending on the timing of its diagnosis, and little evidence is available to determine at-risk infants in the referral neonatal population. The objective of this study was to define clinical and echocardiographic characteristics of infants with pulmonary hypertension during the neonatal hospital course and at or near-term., Methods: Infants who had the following billing codes: < 32 weeks, birth weight < 1500 g, neonatal unit, and echocardiograph had records abstracted from a data warehouse at Children's Healthcare of Atlanta. The outcome was defined as late PH on the final echocardiogram for all patients, and, separately, for patients with multiple studies. Descriptive statistics, univariable, and multivariable models were evaluated, and odds ratios and 95% confidence intervals are expressed below as (OR, CI)., Results: 556 infants were included in the overall study, 59 had PH on their final echocardiogram (11%). In multivariable analyses, atrial septal defect (2.9, 1.4-6.1), and intrauterine growth restriction (2.7, 1.2-6.3) increased the odds of late PH, whereas caffeine therapy decreased PH (0.4, 0.2-0.8). When the analyses were restricted to 32 infants who had multiple echocardiograms during their hospitalization, the association between atrial septal defect (5.9, 2.0-16.5) and growth restriction (3.7, 1.3-10.7) and late PH was strengthened, but the effect of caffeine therapy was no longer significant. In this smaller subgroup, infants with late PH had their final echocardiogram at a median of 116 days of life, and 42-74% of them had right ventricular pathology., Conclusions: Early clinical variables are associated with PH persistence in a referral neonatal population. Identification of early clinical factors may help guide the ascertainment of infant risk for late PH, and may aid in targeting sub-groups that are most likely to benefit from PH screening.

Background: Preterm infants with respiratory distress syndrome (RDS) given inositol had reduced bronchopulmonary dysplasia (BPD), death and severe retinopathy of prematurity (ROP). We assessed the safety and pharmacokinetics of daily inositol to select a dose providing serum levels previously associated with benefit, and to learn if accumulation occurred when administered throughout the normal period of retinal vascularization., Methods: Infants ≤ 29 wk GA (n = 122, 14 centers) were randomized and treated with placebo or inositol at 10, 40, or 80 mg/kg/d. Intravenous administration converted to enteral when feedings were established, and continued to the first of 10 wk, 34 wk postmenstrual age (PMA) or discharge. Serum collection employed a sparse sampling population pharmacokinetics design. Inositol urine losses and feeding intakes were measured. Safety was prospectively monitored., Results: At 80 mg/kg/d mean serum levels reached 140 mg/l, similar to Hallman's findings. Levels declined after 2 wk, converging in all groups by 6 wk. Analyses showed a mean volume of distribution 0.657 l/kg, clearance 0.058 l/kg/h, and half-life 7.90 h. Adverse events and comorbidities were fewer in the inositol groups, but not significantly so., Conclusion: Multiple dose inositol at 80 mg/kg/d was not associated with increased adverse events, achieves previously effective serum levels, and is appropriate for investigation in a phase III trial.

Myofibroblast accumulation is a pathological feature of lung diseases requiring oxygen therapy. One possible source for myofibroblasts is through the epithelial-to-mesenchymal transition (EMT) of alveolar epithelial cells (AEC). To study the effects of oxygen on alveolar EMT, we used RLE-6TN and ex vivo lung slices and found that hyperoxia (85% O2, H85) decreased epithelial proteins, presurfactant protein B (pre-SpB), pro-SpC, and lamellar protein by 50% and increased myofibroblast proteins, α-smooth muscle actin (α-SMA), and vimentin by over 200% (P < 0.05). In AEC freshly isolated from H85-treated rats, mRNA for pre-SpB and pro-SpC was diminished by ∼50% and α-SMA was increased by 100% (P < 0.05). Additionally, H85 increased H2O2 content, and H2O2 (25-50 μM) activated endogenous transforming growth factor-β1 (TGF-β1), as evident by H2DCFDA immunofluorescence and ELISA (P < 0.05). Both hyperoxia and H2O2 increased SMAD3 phosphorylation (260% of control, P < 0.05). Treating cultured cells with TGF-β1 inhibitors did not prevent H85-induced H2O2 production but did prevent H85-mediated α-SMA increases and E-cadherin downregulation. Finally, to determine the role of TGF-β1 in hyperoxia-induced EMT in vivo, we evaluated AEC from H85-treated rats and found that vimentin increased ∼10-fold (P < 0.05) and that this effect was prevented by intraperitoneal TGF-β1 inhibitor SB-431542. Additionally, SB-431542 treatment attenuated changes in alveolar histology caused by hyperoxia. Our studies indicate that hyperoxia promotes alveolar EMT through a mechanism that is dependent on activation of TGF-β1 signaling.

Objective: Our aim was to examine the impact of a single enteral dose of vitamin E on serum tocopherol levels. The study was undertaken to see whether a single dose of vitamin E soon after birth can rapidly increase the low α-tocopherol levels seen in very preterm infants. If so, this intervention could be tested as a means of reducing the risk of intracranial hemorrhage., Methods: Ninety-three infants <27 weeks' gestation and <1000 g were randomly assigned to receive a single dose of vitamin E or placebo by gastric tube within 4 hours of birth. The vitamin E group received 50 IU/kg of vitamin E as dl-α-tocopheryl acetate (Aquasol E). The placebo group received sterile water. Blood samples were taken for measurement of serum tocopherol levels by high-performance liquid chromatography before dosing and 24 hours and 7 days after dosing., Results: Eighty-eight infants received the study drug and were included in the analyses. The α-tocopherol levels were similar between the groups at baseline but higher in the vitamin E group at 24 hours (median 0.63 mg/dL vs. 0.42 mg/dL, P = .003) and 7 days (2.21 mg/dL vs 1.86 mg/dL, P = .04). There were no differences between groups in γ-tocopherol levels. At 24 hours, 30% of vitamin E infants and 62% of placebo infants had α-tocopherol levels <0.5 mg/dL., Conclusions: A 50-IU/kg dose of vitamin E raised serum α-tocopherol levels, but to consistently achieve α-tocopherol levels >0.5 mg/dL, a higher dose or several doses of vitamin E may be needed.

Objective: To determine if early caffeine (EC) therapy is associated with decreased bronchopulmonary dysplasia (BPD) or death, decreased treatment of patent ductus arteriosus (PDA), or shortened duration of ventilation., Study Design: In a retrospective cohort of 140 neonates ≤1250 g at birth, infants receiving EC (initiation <3 days of life) were compared with those receiving late caffeine (LC, initiation ≥3 days of life) using logistic regression., Result: Of infants receiving EC, 25% (21/83) died or developed BPD compared with 53% (30/57) of infants receiving LC (adjusted odds ratio (aOR) 0.26, 95% confidence interval (CI) 0.09 to 0.70; P<0.01). PDA required treatment in 10% of EC infants versus 36% of LC infants (aOR 0.28, 95%CI 0.10 to 0.73; P=0.01). Duration of mechanical ventilation was shorter in infants receiving EC (EC, 6 days; LC, 22 days; P<0.01)., Conclusion: Infants receiving EC therapy had improved neonatal outcomes. Further studies are needed to determine if caffeine prophylaxis should be recommended for preterm infants.

Neonatal chronic lung disease is characterized by failed formation of alveoli and capillaries, and excessive deposition of matrix elastin, which are linked to lengthy mechanical ventilation (MV) with O(2)-rich gas. Vitamin A supplementation has improved respiratory outcome of premature infants, but there is little information about the structural and molecular manifestations in the lung that occur with vitamin A treatment. We hypothesized that vitamin A supplementation during prolonged MV, without confounding by antenatal steroid treatment, would improve alveolar secondary septation, decrease thickness of the mesenchymal tissue cores between distal air space walls, and increase alveolar capillary growth. We further hypothesized that these structural advancements would be associated with modulated expression of tropoelastin and deposition of matrix elastin, phosphorylated Smad2 (pSmad2), cleaved caspase 3, proliferating cell nuclear antigen (PCNA), VEGF, VEGF-R2, and midkine in the parenchyma of the immature lung. Eight preterm lambs (125 days' gestation, term approximately 150 days) were managed by MV for 3 wk: four were treated with daily intramuscular Aquasol A (vitamin A), 5,000 IU/kg, starting at birth; four received vehicle alone. Postmortem lung assays included quantitative RT-PCR and in situ hybridization, immunoblot and immunohistochemistry, and morphometry and stereology. Daily vitamin A supplementation increased alveolar secondary septation, decreased thickness of the mesenchymal tissue cores between the distal air space walls, and increased alveolar capillary growth. Associated molecular changes were less tropoelastin mRNA expression, matrix elastin deposition, pSmad2, and PCNA protein localization in the mesenchymal tissue core of the distal air space walls. On the other hand, mRNA expression and protein abundance of VEGF, VEGF-R2, midkine, and cleaved caspase 3 were increased. We conclude that vitamin A treatment partially improves lung development in chronically ventilated preterm neonates by modulating expression of tropoelastin, deposition of elastin, and expression of vascular growth factors.

Antenatal glucocorticoids are used to mature lung function in fetuses at risk for preterm delivery, but they also suppress cortisol synthesis in both pregnant women and their fetuses. We recently discovered in pregnant rabbits that even though exogenous betamethasone is not a mineralocorticoid, it also suppresses production of aldosterone. Lower aldosterone levels were linked to reduced P450 side chain cleavage(P450scc) messenger RNA levels in the rabbit maternal and fetal adrenal cortex. To establish whether this occurs in humans, we assayed aldosterone levels in women and newborns treated with antenatal betamethasone for preterm labor. In mothers treated with betamethasone, maternal cortisol depression after 48 hours was accompanied by aldosterone depression. Both pregnant women and their newborns treated with betamethasone showed depressed aldosterone levels in a 1- to 3-day period after the first betamethasone dose. We conclude that suppression of aldosterone biosynthesis is a side effect of antenatal steroids that has been largely overlooked, but may be clinically relevant at a time when the newborn is learning to control plasma electrolytes and blood volume.

Objective: Permissive hypercapnia is a respiratory-care strategy that is used to reduce the risk for lung injury. The goal of this study was to evaluate whether permissive hypercapnia is associated with higher risk for intraventricular hemorrhage and early childhood behavioral and functional problems than normocapnia among very low birth weight infants., Methods: Very low birth weight infants from a statewide cohort were eligible for this study when they were born at <32 weeks' gestational age and survived at least 24 hours. Infants were classified as receiving a permissive hypercapnia, normocapnia, or unclassifiable respiratory strategy during the first 24 hours after birth according to an algorithm based on Pco(2) values and respiratory-treatment decisions that were abstracted from medical charts. Intraventricular hemorrhage diagnosis was also abstracted from the medical chart. Behavioral and functional outcomes were assessed by parent interview at 2 to 3 years. Logistic regression was used to evaluate the relationship between intraventricular hemorrhage and respiratory strategy; ordinary linear regression was used to evaluate differences in behavior and function scores between children by respiratory strategy., Results: Infants who received a permissive hypercapnia strategy were not more likely to have intraventricular hemorrhage than those with normocapnia. There were no differences in any of the behavioral or functional scores among children according to respiratory strategy. There was a significant interaction between care strategy and 1-minute Apgar score, indicating that infants with lower Apgar scores may be at higher risk for intraventricular hemorrhage with permissive hypercapnia., Conclusions: This study suggests that permissive hypercapnia does not increase risk for brain injury and impairment among very low birth weight children. The interaction between respiratory strategy and Apgar score is a potential worrisome exception to this conclusion. Future research should further evaluate the effect of elevated Pco(2) levels among those who are sickest at birth.

In infants and children, elevated whole blood zinc protoporphyrin/heme (ZnPP/H) measures iron-deficient (ID) erythropoiesis. Because immature erythrocytes are less dense than mature erythrocytes, we hypothesized that the sensitivity of ZnPP/H is improved if measured in the least dense cells. Blood was collected from control suckling, mildly and severely ID suckling rats. Cord blood was collected after uncomplicated pregnancies (control), diabetic pregnancies (severe ID) and after pregnancies at-risk for iron deficiency (mild ID). ZnPP/H was measured before and after a two-step density centrifugation to obtain the lightest 6.25% of erythrocyte (top fraction). The difference between whole blood and top fraction was defined as DeltaZnPP/H. In rats, although the whole or top ZnPP/H differed by postnatal age, DeltaZnPP/H was greatest after the interval with least body iron accrual. In either rats or humans with mild ID, whole blood ZnPP/H was similar to, but DeltaZnPP/H was greater than controls. In rats and newborn humans, DeltaZnPP/H is more sensitive than whole blood ZnPP/H in identifying conditions associated with impaired erythrocyte iron delivery and may become a useful tool in measuring erythrocyte iron incorporation in early development.

Rationale: Inhaled nitric oxide (iNO) can reverse neonatal pulmonary hypertension and bronchoconstriction and reduce proliferation of cultured arterial and airway smooth muscle cells., Objectives: To see if continuous iNO from birth might reduce pulmonary vascular and respiratory tract resistance (PVR, RE) and attenuate growth of arterial and airway smooth muscle in preterm lambs with chronic lung disease., Methods: Eight premature lambs received mechanical ventilation for 3 weeks, four with and four without iNO (5-15 ppm). Four term lambs, mechanically ventilated without iNO for 3 weeks, served as additional control animals., Measurements: PVR and RE were measured weekly. After 3 weeks, lung tissue was processed for quantitative image analysis of smooth muscle abundance around small arteries (SMart) and terminal bronchioles (SMtb). Radial alveolar counts were done to assess alveolar number. Endothelial NO synthase (eNOS) protein in arteries and airways was measured by immunoblot analysis., Main Results: At study's end, PVR was similar in iNO-treated and untreated preterm lambs; PVR was less in iNO-treated preterm lambs compared with term control animals. RE in iNO-treated lambs was less than 40% of RE measured in preterm control animals. SMart was similar in iNO-treated and both groups of control lambs; SMtb in lambs given iNO was significantly less (approximately 50%) than in preterm control animals. Radial alveolar counts of iNO-treated lambs were more than twice that of preterm control animals. eNOS was similar in arteries and airways of iNO-treated preterm lambs compared with control term lambs., Conclusions: iNO preserves structure and function of airway smooth muscle and enhances alveolar development in preterm lambs with chronic lung disease.

Chronic lung injury from prolonged mechanical ventilation after premature birth inhibits the normal postnatal decrease in pulmonary vascular resistance (PVR) and leads to structural abnormalities of the lung circulation in newborn sheep. Compared with normal lambs born at term, chronically ventilated preterm lambs have increased pulmonary arterial smooth muscle and elastin, fewer lung microvessels, and reduced abundance of endothelial nitric oxide synthase. These abnormalities may contribute to impaired respiratory gas exchange that often exists in infants with chronic lung disease (CLD). Nitric oxide inhalation (iNO) reduces PVR in human infants and lambs with persistent pulmonary hypertension. We wondered whether iNO might have a similar effect in lambs with CLD. We therefore studied the effect of iNO on PVR in lambs that were delivered prematurely at approximately 125 days of gestation (term = 147 days) and mechanically ventilated for 3 wk. All of the lambs had chronically implanted catheters for measurement of pulmonary vascular pressures and blood flow. During week 2 of mechanical ventilation, iNO at 15 parts/million for 1 h decreased PVR by approximately 20% in 12 lambs with evolving CLD. When the same study was repeated in eight lambs at the end of week 3, iNO had no significant effect on PVR. To see whether this loss of iNO effect on PVR might reflect dysfunction of lung vascular smooth muscle, we infused 8-bromo-guanosine 3',5'-cyclic monophosphate (cGMP; 150 microg. kg(-1). min(-1) iv) for 15-30 min in four of these lambs at the end of week 3. PVR consistently decreased by 30-35%. Lung immunohistochemistry and immunoblot analysis of excised pulmonary arteries from lambs with CLD, compared with control term lambs, showed decreased soluble guanylate cyclase (sGC). These results suggest that loss of pulmonary vascular responsiveness to iNO in preterm lambs with CLD results from impaired signaling, possibly related to deficient or defective activation of sGC, the intermediary enzyme through which iNO induces increased vascular smooth muscle cell cGMP and resultant vasodilation.

Nitric oxide (NO), produced in lung vascular endothelium and airway epithelium, has an important role in regulating smooth muscle cell growth and tone. Chronic lung disease, a frequent complication of premature birth, is characterized by excess abundance, tone, and reactivity of smooth muscle in the pulmonary circulation and conducting airways, leading to increased lung vascular and airway resistance. Whether these structural and functional changes are associated with diminished pulmonary expression of endothelial nitric oxide synthase (eNOS) protein is unknown. Both quantitative immunoblot analysis and semiquantitative immunohistochemistry showed that there was less eNOS protein in the endothelium of small intrapulmonary arteries and epithelium of small airways of preterm lambs that were mechanically ventilated for 3 wk compared with control lambs born at term. No significant differences were detected for other proteins (inducible NOS, alpha-smooth muscle actin, and pancytokeratin). Lung vascular and respiratory tract resistances were greater in the chronically ventilated preterm lambs compared with control term lambs. These results support the notion that decreased eNOS in the pulmonary circulation and respiratory tract of preterm lambs may contribute to the pathophysiology of chronic lung disease.

Objective: To determine whether medications commonly used in the management of gastroesophageal reflux reduce the frequency of apnea in premature infants., Study Design: We reviewed the medical records of all infants

Chronic lung disease of early infancy, or bronchopulmonary dysplasia, is a frequent complication of prolonged mechanical ventilation after premature birth. Pulmonary hypertension and edema are common features of this condition, which is often attributed to long-term, repetitive overinflation of incompletely developed lungs. The overall objective of this work was to examine the effects on the pulmonary circulation and lung fluid balance of different ventilation strategies using large versus small inflation volumes in an animal model of bronchopulmonary dysplasia. We studied 16 newborn lambs that were delivered prematurely (124+/-3 d gestation, term = 147 d) by cesarean section and mechanically ventilated for 3 to 4 wk. Ten lambs were ventilated at 20 breaths/min, yielding a tidal volume of 15+/-5 mL/kg, and six lambs were ventilated at 60 breaths/min, yielding a tidal volume of 6+/-2 mL/kg. All lambs received surfactant at birth and had subsequent surgery for closure of the ductus arteriosus and catheter placement to allow serial measurements of pulmonary vascular resistance and lung lymph flow. Chronic lung injury, documented by serial chest radiographs and postmortem pathologic examination, developed in all lambs irrespective of the pattern of assisted ventilation. Pulmonary vascular resistance, which normally decreases during the month after birth at term, did not change significantly from the first to the last week of study. Lung lymph flow, an index of net transvascular fluid filtration, increased with time in lambs that were ventilated at 20 breaths/min, but not in lambs ventilated at 60 breaths/min. Lymph protein concentration decreased with time, indicative of increased fluid filtration pressure, without evidence of a change in lung vascular protein permeability. Postmortem studies showed interstitial lung edema, increased pulmonary arteriolar smooth muscle and elastin, decreased numbers of small pulmonary arteries and veins, and decreased capillary surface density in distal lung of chronically ventilated lambs compared with control lambs that were killed either 1 d (same postconceptional age) or 3 wk (same postnatal age) after birth at term. Thus, chronic lung injury from prolonged mechanical ventilation after premature birth inhibits the normal postnatal decrease in pulmonary vascular resistance and leads to lung edema from increased fluid filtration pressure. These abnormalities of the pulmonary circulation may contribute to the abnormal respiratory gas exchange that often exists in infants with bronchopulmonary dysplasia.

Background: The acute disappearance of neutrophils from the circulation can be associated with pulmonary leukostasis, lung injury, and respiratory distress., Objective: To determine whether a low concentration of mature neutrophils in the peripheral blood soon after birth is associated with an increase in subsequent respiratory distress in premature infants., Design: A cohort study performed by chart review at a tertiary medical center., Subjects: Premature infants (birth weight 500 to 1250 g) who had a complete blood count obtained within 2 hours of delivery (n = 237). Patients in the lowest quartile of mature neutrophil concentrations (early neutropenia, < or =0.90 x 10(9) neutrophils/L blood) were compared with patients in the remaining 3 quartiles (control group)., Results: Low neutrophil concentrations were transient in the early neutropenia group. The concentration of mature circulating neutrophils rose from 0.49 +/- 0.25 x 10(9) cells/L at an average of 1 hour after delivery to 2.8 +/- 2.2 x 10(9) cells/L within 6 to 8 hours in the early neutropenia group and from 4.6 +/- 4.8 x 10(9) cells/L to 8.2 +/- 8. 0 x 10(9) cells/L in the control group during the same time period. Respiratory support immediately after birth was similar in both groups of infants, but by 12 hours patients who had early neutropenia required significantly greater inflation pressures and concentrations of inspired oxygen. By 1 week after birth patients who had early neutropenia were more likely to require mechanical ventilation and supplemental oxygen. Pulmonary interstitial emphysema, serious intraventricular hemorrhage, and chronic lung disease occurred more frequently in patients with early neutropenia., Conclusion: A low concentration of mature neutrophils in the systemic circulation of premature infants within 2 hours of birth is associated with more severe respiratory distress during the first postnatal week and with an increased risk of serious complications of prematurity.

The cause of chronic lung disease of early infancy, often called bronchopulmonary dysplasia (BPD), remains unclear, partly because large-animal models that reliably reproduce BPD have not been available. We developed a model of BPD in lambs that are delivered prematurely and ventilated for 3 to 4 wk after birth to determine whether the histopathology of chronic lung injury in premature lambs mimics that which occurs in preterm infants who die with BPD, and to compare two ventilation strategies to test the hypothesis that differences in tidal volume (VT) influence histopathologic outcome. The two ventilation strategies were slow, deep ventilation (20 breaths/min, 15 +/- 2 ml/kg body weight VT; n = 5) or rapid, shallow ventilation (60 breaths/min, 6 +/- 1 ml/kg body weight VT; n = 5). Lambs were delivered at 125 +/- 4 d gestation (term = 147 d), treated with surfactant, and mechanically ventilated with sufficient supplemental oxygen to maintain normal arterial oxygenation (60 to 90 mm Hg). Quantitative histologic analysis revealed lung structural abnormalities for both groups of experimental lambs compared with lungs of control term lambs that were < 1 d old (matched for developmental age; n = 5) or 3 to 4 wk old (matched for postnatal age; n = 5). Compared with control lambs, chronically ventilated preterm lambs had pulmonary histopathology characterized by nonuniform inflation patterns, impaired alveolar formation, abnormal abundance of elastin, increased muscularization of terminal bronchioles, and inflammation and edema. Slow, deep ventilation was associated with less atelectasis, less alveolar formation, and more elastin when compared with rapid, shallow ventilation. We conclude that prolonged mechanical ventilation of preterm lambs disrupts lung development and produces pulmonary histopathologic changes that are very similar to those that are seen in the lungs of preterm infants who die with BPD. This chronic lung disease is not prevented by surfactant replacement at birth, does not appear to require arterial hyperoxia, and is influenced by VT.

To investigate the role of neutrophils in the pathogenesis of respiratory distress after premature birth, we assessed the relationship between circulating neutrophil concentration and neutrophil accumulation in the lung, lung lymph and pleural liquid flow, and extravascular lung water in 10 chronically catheterized preterm lambs (127 +/- 1 days gestation) that were mechanically ventilated for 8 h after birth. Circulating neutrophil concentration transiently decreased within 2 h after birth and then returned to prenatal values by 6-8 h. The decrease in circulating neutrophil concentration was related directly to the accumulation of neutrophils in the air spaces, drainage of liquid and protein from the lung 6-8 h after delivery, and postmortem extravascular lung water. In additional studies, we intravenously administered mechlorethamine to 5 fetal lambs to reduce circulating neutrophils before delivery (neutrophil concentration before birth: 9 +/- 11 cells/microl). Compared with control lambs, neutrophil-depleted lambs had significantly less drainage of liquid (7.8 +/- 5.9 vs. 2.6 +/- 1.9 ml/h, respectively) and protein (116 +/- 74 vs. 42 +/- 27 mg/h, respectively) from the lung 6-8 h after birth and significantly less extravascular lung water at postmortem (6.5 +/- 0. 8 vs. 4.8 0.6 g/g dry lung, respectively). Thus neutrophils contribute to the pathogenesis of respiratory distress after premature birth by increasing lung vascular protein permeability and promoting lung edema.

Prolonged mechanical ventilation of premature neonates is often associated with abnormal morphological development of the lung and chronic lung disease, sometimes called bronchopulmonary dysplasia (BPD). Impaired alveolar development is a hallmark of this disease. To better understand the effects of mechanical ventilation on lung elastin expression, we studied lung tissue from 10 preterm lambs (gestation = 125 days; term = 148 days) mechanically ventilated for 3-4 wk at a respirator rate of 20 breaths/min and tidal volume of 15 +/- 5 ml/kg (n = 5) or 60 breaths/min and tidal volume of 5 +/- 2 ml/kg (n = 5). Histopathology showed increased elastin accumulation and abnormal morphological development in the ventilated groups. Postmortem lung desmosine content was increased significantly in the 20 breaths/min group. Tropoelastin mRNA expression was increased in both ventilated groups. In situ hybridization localized increased tropoelastin mRNA expression to sites of accumulated elastin in extended alveolar walls with scant, attenuated secondary crests. Lung collagen content, as assessed by the amount of hydroxyproline in lung tissue, was similar to controls. These data suggest that excessive production and accumulation of elastin is associated with chronic lung injury from prolonged mechanical ventilation after premature birth.

The normal switch from placental to pulmonary gas exchange at birth requires rapid removal of liquid from the lungs. Previous reports contend that vasopressin may be important in regulating this process, but this notion derives from studies in which fetal sheep received very large doses of vasopressin that yielded plasma concentrations at least 10 times greater than those that have been measured during normal labor. To study the physiologic effects of vasopressin on lung liquid volume in fetal sheep, we made three sets of experiments. First, we measured plasma vasopressin concentrations [VP] in 15 late-gestation fetal sheep, five of which were at various stages of spontaneous labor. [VP] in these fetuses ranged from < 1 (prelabor) to 31 (during labor) microU/mL; postmortem extravascular lung water (EVLW) ranged from 4.5 to 14.5 g/g dry lung tissue. In a second series of studies, we measured EVLW in five sets of near-term (138 +/- 1 d, term = 147 d) twin fetal sheep that received an 8-h i.v. infusion of either isotonic saline (control twin) or AVP (AVP-treated twin) at a rate of approximately 1 (mU/kg)/min. This dose was chosen to mimic [VP] measured in fetuses that had been studied during labor. [VP] did not change in the control twins, whereas [VP] increased from 1.8 +/- 1.0 to 27.7 +/- 3.5 microU/mL in treated twins. There was a small, statistically significant difference in EVLW between twins that received AVP and untreated twins (11.9 +/- 1.8 versus 14.6 +/- 2.8 g/g dry lung).(ABSTRACT TRUNCATED AT 250 WORDS)

To study the effect of surfactant administration on fluid balance in the premature lung, we measured pulmonary vascular pressures, lung lymph and pleural liquid flow, and concentrations of protein in lymph, pleural liquid, and plasma before and after birth in 12 chronically catheterized preterm lambs (127-128 d gestation) treated with either placebo or surfactant just before surgical delivery. Eight lambs received intrapulmonary saline (placebo), and four lambs received surfactant; all lambs were mechanically ventilated with O2 for 8 h after birth. In control lambs, lung lymph and pleural liquid flow increased from 2.7 +/- 0.4 mL/h during the 2-4 h before birth to 9.2 +/- 2.1 mL/h by 6-8 h after birth; lymph and pleural space protein drainage increased from 58 +/- 7 mg/h during the 2-4 h before birth to 134 +/- 25 mg/h by 6-8 h after birth. In lambs treated with surfactant, there was no significant increase in lymph and pleural liquid flow after birth (before birth, 2.3 +/- 0.3 mL/h; 6-8 h after birth, 3.4 +/- 0.9 mL/h); likewise, lymph and pleural space protein drainage did not change after birth (before birth, 54 +/- 6 mg/h; 6-8 h after birth, 50 +/- 8 mg/h). Postmortem extravascular lung water was significantly less in lambs treated with surfactant compared with control lambs (control, 6.5 +/- 0.3 g/g dry lung; surfactant-treated, 5.0 +/- 0.2 g/g dry lung).(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to see whether there are developmental differences in the protein permeability of the pulmonary circulation that might contribute to the abnormal lung fluid balance seen in premature lambs with respiratory failure. In one series of experiments, we measured albumin turnover time, which reflects the escape rate of radiolabeled albumin from the pulmonary circulation, of five preterm fetal lambs (125 +/- 1 days gestation) and five newborn lambs (19 +/- 9 days old). Turnover time was not significantly different in fetuses (160 +/- 38 min) and newborns (141 +/- 54 min), implying a similar protein permeability of the pulmonary circulation. In additional experiments, we measured pulmonary hemodynamic and lung lymph flow responses to intravenous saline infusion in seven preterm fetal lambs (130 +/- 3 days gestation) and seven newborn lambs (14 +/- 3 days old). During saline infusion, calculated fluid filtration pressure increased by a similar amount in fetuses and newborns (3.4 +/- 0.8 and 2.8 +/- 0.9 Torr, respectively), resulting in a similar change in lung lymph flow in fetuses and newborns (0.59 +/- 0.27 and 0.55 +/- 0.25 ml.h-1.kg body wt-1, respectively). The results of these studies indicate that protein permeability of the pulmonary circulation does not change significantly during late fetal and early postnatal development.

The goals of this study were 1) to examine changes in lung liquid formation and composition during spontaneous labor in fetal lambs and 2) to determine the importance of beta-adrenergic stimulation and transepithelial Na+ flux in removing liquid from the lung lumen near birth. We measured net production of lung liquid (Jv), lung liquid composition, and transpulmonary electrical potential difference (PD) before and during labor in fetal sheep with chronically implanted tracheal and vascular catheters. We determined Jv by measuring rate of change in lung liquid concentration of 125I-albumin, an impermeant tracer that was mixed in lung liquid at the start of each study. In 17 paired experiments, Jv decreased from 11 +/- 2 ml/h (Jv > 0 = secretion) before labor to -1 +/- 2 ml/h (Jv < 0 = absorption) during labor; in 5 paired experiments, PD changed from -7 +/- 1 mV (lumen negative) before labor to -12 +/- 1 mV during labor. To determine whether absorption of lung liquid during labor is the result of beta-adrenergic stimulation, we studied the effect of propranolol on Jv during labor. When propranolol (40 microM) was added to lung liquid during active labor, Jv decreased from -2 +/- 2 to -8 +/- 3 ml/h (n = 9). Thus, propranolol did not inhibit lung liquid absorption during labor. To determine whether transepithelial Na+ movement provides the driving force for lung liquid clearance during labor, we tested the effects of amiloride, an Na+ transport inhibitor, on Jv and PD.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin endoperoxide synthase (PHS) catalyzes the committed step in the biosynthesis of prostaglandins and thromboxane. We recently observed dissociation of PHS activity and enzyme mass measured in an immunoassay of endothelial cells exposed to tumor necrosis factor. These data and observations by others suggested that endothelial cells express an alternate PHS. We now report the molecular cloning of human PHS type II from an endothelial cell cDNA library. The protein encoded by this cDNA shares 61% identity with the human PHS I. Southern analysis demonstrated a single copy of PHS II and we found a polymorphism in approximately 5% of the population. PHS II mapped to chromosome 1, in contrast to PHS I, which is on chromosome 9. The PHS II cDNA hybridized strongly to a 4.3-kilobase (kb) message from endothelial cells. Stimulation of the cells with tumor necrosis factor, phorbol 12-myristate 13-acetate, lipopolysaccharide, or interleukin-1 increased mRNA levels for PHS II, and this change correlated well with increased prostacyclin biosynthesis. Cycloheximide induced PHS II mRNA without a corresponding activity increase demonstrating that translation of the 4.3-kb message is required for increased prostacyclin biosynthesis. We conclude that expression of PHS II may have important pathophysiological effects in the vasculature.

To determine whether hypoproteinemia slows the rate at which liquid is cleared from the lung lumen, we studied 36 lambs, 18 of which underwent repeated plasmapheresis, reducing plasma protein concentration by 37% and plasma protein osmotic pressure by 39%. We killed 29 lambs (14 hypoproteinemic and 15 normoproteinemic) and removed their lungs 1, 2, or 6 h after intratracheal instillation of isotonic saline (6 ml/kg body wt). We measured extravascular lung water and determined the percentage of tracheally instilled liquid that was cleared from the lungs by comparison with control lambs that did not receive saline into their airways. The percent liquid cleared from the lungs after 1 and 2 h was significantly less in hypoproteinemic than in normoproteinemic lambs (37 vs. 65% at 1 h, 58 vs. 75% at 2 h, respectively). By 6 h nearly all the liquid (> 92%) was cleared from the lungs of all lambs. Thus hypoproteinemia slows the initial rate of clearance of liquid from the lungs of lambs. To determine whether reduced plasma protein osmotic pressure might redirect this liquid into lung lymphatics, we measured lung lymph flow (Q1) in five lambs (7.7 +/- 1.4 kg, 19 +/- 4 days old) for > or = 2 h before and 6 h after tracheal instillation of saline. In each lamb, paired studies were done 3-6 days apart; between studies the lambs underwent plasmapheresis.(ABSTRACT TRUNCATED AT 250 WORDS)

To test the hypothesis that liquid formation in the foetal lung reflects the balance between Cl- secretion and Na+ absorption by the respiratory tract epithelium, we studied the independent and combined effects of selective ion transport inhibitors on basal production of lung liquid in foetal lambs. We prepared 19 foetal lambs (gestation 125 +/- 4, term = 147 days) with chronic indwelling catheters for subsequent measurement of luminal liquid production over time (JV). Using an impermeant tracer technique, we measured JV before and after tracheal instillation of 2 different inhibitors of ion transport: bumetanide, a Na(+)-K(+)-2Cl- co-transport inhibitor, and amiloride, a Na+ transport inhibitor. In 7 foetuses we sequentially added bumetanide (10(-4) M) and 2 different concentrations of amiloride (10(-6) M, 10(-4) M) to the liquid within the lung lumen. After we gave bumetanide, JV decreased from 12 +/- 4 ml/h to 0 +/- 5 ml/h and subsequently increased during the 2 periods of amiloride exposure (10(-6) M: 6 +/- 5 ml/h; 10(-4) M: 7 +/- 7 ml/h). In 5 control studies we gave bumetanide, followed by only amiloride vehicle. JV for all time periods in the control studies was similar to the experimental group, demonstrating no effect of amiloride. In 5 foetuses we administered the 2 concentrations of amiloride before bumetanide. There was no change in JV with either concentration of amiloride (baseline: 13 +/- 2 ml/h; 10(-6) M amiloride: 15 +/- 5 ml/h; 10(-4) M amiloride: 13 +/- 6 ml/h).(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to determine whether an increase in pulmonary vascular filtration pressure affects net production of liquid within the lumen of the fetal lung. We studied 14 chronically catheterized fetal lambs [130 +/- 3 (SD) days gestation] before, during, and after a 4-h rapid (500 ml/h) intravenous infusion of isotonic saline. In seven fetuses we measured pulmonary arterial and left atrial pressures, lung lymph flow, and protein osmotic pressures in plasma and lymph. In eight lambs with a chronically implanted tracheal loop cannula, we measured the change in luminal lung liquid volume over time by progressive dilution of tracheally instilled 125I-albumin, which stays within the lung lumen. Saline infusion increased pulmonary vascular pressures by 2-3 mmHg and decreased the plasma-lymph difference in protein osmotic pressure by 1 mmHg. Lung lymph flow increased from 1.9 +/- 0.6 to 3.9 +/- 1.2 (SD) ml/h; net production of luminal lung liquid did not change (12 +/- 5 to 12 +/- 6 ml/h). Thus an increase in net fluid filtration pressure in the pulmonary circulation, which was sufficient to double lung lymph flow, had no significant effect on luminal lung liquid secretion in fetal sheep.

To see if phosphodiesterase inhibition might enhance the effect of beta-adrenergic stimulation on fetal lung liquid secretion, we studied the independent and combined effects of intrapulmonary terbutaline and aminophylline on net production of lung luminal liquid over time (Jv) in fetal lambs with chronically placed tracheal loop catheters. We calculated Jv during baseline and experimental periods (90-120 min each) by measuring serial concentrations of 125I-albumin, an impermeant tracer that was well mixed in the luminal liquid. In 21 experiments, tracheal instillation of terbutaline (10(-5) M) decreased Jv from 11 +/- 1 (mean +/- SEM) to -3 +/- 2 mL/h. In six other studies, aminophylline (10(-3) M) alone had no significant effect on Jv. In 12 experiments, we gave the two drugs sequentially: terbutaline decreased Jv from 11 +/- 2 to -3 +/- 2 mL/h and aminophylline further decreased Jv to -8 +/- 2 mL/h. Amiloride (10(-4) M), an inhibitor of epithelial Na+ transport, reversed the combined effect of terbutaline and aminophylline, increasing Jv to 8 +/- 1 mL/h. Thus, phosphodiesterase inhibition enhances the beta-adrenergic effect of terbutaline on Na(+)-dependent absorption of liquid from the lung lumen of fetal lambs.

The source of normal pleural liquid is thought to be the systemic circulation of the pleural membranes rather than the pulmonary circulation of the nearby lung. Evidence for a systemic origin comes from the low protein concentration of pleural liquid in adult sheep, which is consistent with protein sieving from a high-pressure circulation. During normal development from fetal to adult life, systemic vascular pressure increases. We therefore reasoned that if pleural liquid comes from the systemic circulation, pleural liquid protein concentration relative to plasma protein concentration should decrease during normal development. To test this hypothesis we did thoracotomies on 14 fetal, 9 newborn, and 15 adult sheep and collected pleural liquid and plasma for measurement of total protein and albumin concentrations. In separate experiments we measured steady-state systemic and pulmonary vascular pressures in age-matched chronically instrumented fetal, newborn, and adult sheep. The protein concentration in pleural liquid relative to that in plasma (pleural liquid/plasma) decreased progressively with age (fetuses, 0.50 +/- 0.15 [SD]; newborns, 0.27 +/- 0.08; adult, 0.15 +/- 0.05); the trend was similar for pleural liquid/plasma albumin ratios as a function of age. Systemic arterial pressure increased progressively during development, whereas pulmonary arterial pressure decreased from the fetus to the adult sheep. These observations support the hypothesis that normal pleural liquid originates from a systemic circulation.

To study the effects of inflation pressure and tidal volume (VT) on protein permeability in the neonatal pulmonary microcirculation, we measured lung vascular pressures, blood flow, lymph flow (QL), and concentrations of protein in lymph (L) and plasma (P) of 22 chronically catheterized lambs that received mechanical ventilation at various peak inflation pressures (PIP) and VT. Nine lambs were ventilated initially with a PIP of 19 +/- 1 cmH2O and a VT of 10 +/- 1 ml/kg for 2-4 h (base line), after which we overexpanded their lungs with a PIP of 58 +/- 3 cmH2O and a VT of 48 +/- 4 ml/kg for 4-8 h. QL increased from 2.1 +/- 0.4 to 13.9 +/- 5.0 ml/h. L/P did not change, but the ratio of albumin to globulin in lymph relative to the same ratio in plasma decreased, indicating altered protein sieving in the pulmonary microcirculation. Seven other lambs were mechanically ventilated for 2-4 h at a PIP of 34 +/- 1 cmH2O and a VT of 23 +/- 2 ml/kg (base line), after which their chest and abdomen were bound so that PIP increased to 54 +/- 1 cmH2O for 4-6 h without a change in VT. QL decreased on average from 2.8 +/- 0.6 to 1.9 +/- 0.3 ml/h (P = 0.08), and L/P was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to see if lung vascular protein permeability is greater in preterm lambs with respiratory distress than it is in lambs without lung disease. We measured pulmonary vascular pressures, lung lymph flow, and concentrations of protein in lymph and plasma of 10 chronically catheterized preterm lambs (gestation 133 +/- 1 d) for 2-4 h before and for 4-8 h after delivery by cesarean section. All lambs were treated with mechanical ventilation after birth and received a constant intravenous infusion of glucose-saline solution at an hourly rate of 10 ml/kg. Respiratory failure developed in six lambs, in which there was a sustained threefold postnatal increase in lung lymph flow and lymph protein flow, with an even greater increase in pleural liquid drainage. Concentrations of protein in lymph and pleural liquid were almost identical, averaging approximately 75% of the plasma protein concentration. In the four preterm lambs without lung disease, lymph flow and lymph protein flow were either near or below fetal values by 6-8 h after birth, and there was little or no pleural liquid drainage. Extravascular lung water averaged 7.3 +/- .8 g/g dry lung in lambs with respiratory failure compared to 4.8 +/- .5 g/g dry lung in lambs without lung disease. Thus, pulmonary edema with abnormal leakage of protein-rich liquid from the lung microcirculation into the interstitium is an important pathological feature of the respiratory disease that often occurs after premature birth.

In summary, the in utero diagnosis of nonimmune hydrops is associated with a grave prognosis. Antenatal evaluation will determine the cause in many cases, allowing appropriate decisions to be made regarding the management of the pregnancy. To date, no specific in utero therapy exists for most causes of nonimmune hydrops fetalis. At the time of delivery, a resuscitation team will be needed for the infant because extensive resuscitation is likely to be necessary. Many infants will die in the first day of life but some will survive; the survivors will probably require intensive newborn care, including mechanical ventilation. A major cause of mortality in babies with nonimmune hydrops is respiratory insufficiency. If pulmonary hypoplasia is present and severe, survival may not be possible despite intensive care. Review of our data suggests that the diagnosis of idiopathic nonimmune hydrops carries the same grave prognosis as other forms. Currently, only babies with nonimmune hydrops secondary to supraventricular tachycardia have a high probability of survival. Parents of hydropic infants should be counseled concerning the probable outcome and the risk of recurrence. A genetic consultant can help in this regard. Infants who die should have a complete postmortem examination, and placental pathology should be performed in all cases.