Alveolar formation is dysregulated by restricted nutrition but not excess sedation in preterm lambs managed by noninvasive support

Postnatal growth restriction impairs rat lung structure and function

The negative impact of nutritional deficits in the development of bronchopulmonary dysplasia is well recognized, yet mechanisms by which nutrition alters lung outcomes and nutritional strategies that optimize development and protect the lung remain elusive. Here, we use a rat model to assess the isolated effects of postnatal nutrition on lung structural development without concomitant lung injury. We hypothesize that postnatal growth restriction (PGR) impairs lung structure and function, critical mediators of lung development, and fatty acid profiles at postnatal day 21 in the rat. Rat pups were cross-fostered at birth to rat dams with litter sizes of 8 (control) or 16 (PGR). Lung structure and function, as well as serum and lung tissue fatty acids, and lung molecular mediators of development, were measured. Male and female PGR rat pups had thicker airspace walls, decreased lung compliance, and increased tissue damping. Male rats also had increased lung elastance, increased lung elastin protein abundance, and lysol oxidase expression, and increased elastic fiber deposition. Female rat lungs had increased conducting airway resistance and reduced levels of docosahexaenoic acid in lung tissue. We conclude that PGR impairs lung structure and function in both male and female rats, with sex-divergent changes in lung molecular mediators of development.

Baby breaths: Honoring Kurt Albertine and his contributions to respiratory research in young mammals and to The Anatomical Record

In January 2021, Kurt Albertine, PhD, stepped down as the Editor of The Anatomical Record after 15 years of dedicated service. As Editor-In-Chief, he oversaw incredible growth, expanded scope, and increased impact of the journal. At the same time, he directed an active research lab in neonatal pulmonary biology at the University of Utah, with an exceptional track record of mentoring students, fellows, clinicians, and junior faculty. This special issue of The Anatomical Record honors Kurt's contributions to the journal, as well as to the fields of respiratory anatomy, physiology, and neonatology. Several of the invited papers were contributed by Kurt's collaborators and former trainees who cover topics related to neonatal lamb development, bronchopulmonary dysplasia, postnatal lung pathology, respiratory physiology, and the relationship of anatomy to function. Additional papers relating to Kurt's passion for dinosaur anatomy and human embryonic anatomy based on the Kyoto Collection of Human Embryos and Fetuses. Kurt's tireless enthusiasm for the journal and devotion to the field are reflected in the papers in this special issue in his honor. His tenure at the journal was transformative and provided a foundation for continued growth and impact in anatomical sciences research from dinosaurs to clinical applications in humans. We celebrate Kurt's accomplishments and broader impact on anatomical sciences in this Special Issue of The Anatomical Record.

Early nutritional management and risk of neonatal bronchopulmonary dysplasia: a systematic review and mata analysis

This study examines the relationship between early postnatal nutrition, fluid management in preterm infants, and the risk of bronchopulmonary dysplasia (BPD). A comprehensive review was conducted across multiple databases, including PubMed, Embase, Cochrane Library, Web of Science, and major Chinese databases, covering studies up to 31 August 2024. Case-control and cohort studies on nutritional management and BPD were analyzed using meta-analysis in Stata 15.0. The study is registered on Prospero (CRD42023484951). A total of 11 studies involving 1,826 infants (894 with BPD, 931 controls) were included. Findings showed significantly lower calorie intake in the BPD group during the first postnatal week (Mean Difference = -6.20, 95% CI: -8.91 to -3.48, P < 0.05). While fluid intake differences were not statistically significant (Mean Difference = 5.31, 95% CI: -0.57 to 11.19, P = 0.077), the BPD group had lower protein (Mean Difference = -0.13, 95% CI: -0.22 to -0.04, P < 0.05), lipid (Mean Difference = -0.39, 95% CI: -0.49 to -0.299, P < 0.05), and carbohydrate intake (Mean Difference = -0.74, 95% CI: -0.95 to -0.54, P < 0.05). Time to full enteral nutrition was also prolonged in the BPD group (Mean Difference = 11.23, 95% CI: 9.68-12.78, P < 0.05). These results suggest that inadequate early nutrition may increase BPD risk. Optimizing nutritional and fluid management, alongside respiratory support, is essential for prevention.

Predictive value of serum MED1 and PGC-1α for bronchopulmonary dysplasia in preterm infants

OBJECTIVE

This study aimed to predict the bronchopulmonary dysplasia (BPD) in preterm infants with a gestational age(GA) < 32 weeks utilizing clinical data, serum mediator complex subunit 1 (MED1), and serum peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α).

METHODS

This prospective observational study enrolled 70 preterm infants with GA < 32 weeks. The infants were categorized into two groups: non-BPD group(N = 35) and BPD group(N = 35), including 25 cases with mild BPD and 10 patients with moderate/severe subgroups. We performed multifactorial regression analysis to investigate the postnatal risk factors for BPD. Furthermore, we compared serum levels of biomarkers, including MED1 and PGC-1α, among infants with and without BPD at postnatal days 1, 7, 14, 28, and PMA 36 weeks. A logistic regression model was constructed to predict BPD's likelihood using clinical risk factors and serum biomarkers.

RESULTS

Serum levels of MED1 on the first postnatal day, PGC-1α on the 1st, 7th, and 28th days, and PMA at 36 weeks were significantly lower in the BPD group than in the non-BPD group (P < 0.05). Furthermore, the predictive model for BPD was created by combing serum levels of MED1 and PGC-1α on postnatal day 1 along with clinical risk factors such as frequent apnea, mechanical ventilation time > 7 d, and time to reach total enteral nutrition. Our predictive model had a high predictive accuracy(C statistics of 0.989) .

CONCLUSION

MED1and PGC-1α could potentially serve as valuable biomarkers, combined with clinical factors, to aid clinicians in the early diagnosis of BPD.

Mesenchymal stromal cell extracellular vesicles improve lung development in mechanically ventilated preterm lambs

Novel therapies are needed for bronchopulmonary dysplasia (BPD) because no effective treatment exists. Mesenchymal stromal cell extracellular vesicles (MSC-sEVs) have therapeutic efficacy in a mouse pup neonatal hyperoxia BPD model. We tested the hypothesis that MSC-sEVs will improve lung functional and structural development in mechanically ventilated preterm lambs. Preterm lambs (∼129 days; equivalent to human lung development at ∼28 wk gestation) were exposed to antenatal steroids, surfactant, caffeine, and supported by mechanical ventilation for 6-7 days. Lambs were randomized to blinded treatment with either MSC-sEVs (human bone marrow MSC-derived; 2 × 1011 particles iv; n = 8; 4 F/4 M) or vehicle control (saline iv; 4 F/4 M) at 6 and 78 h post delivery. Physiological targets were pulse oximetry O2 saturation 90-94% ([Formula: see text] 60-90 mmHg), [Formula: see text] 45-60 mmHg (pH 7.25-7.35), and tidal volume 5-7 mL/kg. MSC-sEVs-treated preterm lambs tolerated enteral feedings compared with vehicle control preterm lambs. Differences in weight patterns were statistically significant. Respiratory severity score, oxygenation index, A-a gradient, distal airspace wall thickness, and smooth muscle thickness around terminal bronchioles and pulmonary arterioles were significantly lower for the MSC-sEVs group. S/F ratio, radial alveolar count, secondary septal volume density, alveolar capillary surface density, and protein abundance of VEGF-R2 were significantly higher for the MSC-sEVs group. MSC-sEVs improved respiratory system physiology and alveolar formation in mechanically ventilated preterm lambs. MSC-sEVs may be an effective and safe therapy for appropriate functional and structural development of the lung in preterm infants who require mechanical ventilation and are at risk of developing BPD.NEW & NOTEWORTHY This study focused on potential treatment of preterm infants at risk of developing bronchopulmonary dysplasia (BPD), for which no effective treatment exists. We tested treatment of mechanically ventilated preterm lambs with human mesenchymal stromal cell extracellular vesicles (MSC-sEVs). The results show improved respiratory gas exchange and parenchymal growth of capillaries and epithelium that are necessary for alveolar formation. Our study provides new mechanistic insight into potential efficacy of MSC-sEVs for preterm infants at risk of developing BPD.

Dose-dependent impact of human milk feeding on tidal breathing flow-volume loop parameters across the first 2 years of life in extremely low-birth-weight infants: a cohort study

The purpose of this study is to test the hypothesis that higher consumption of human milk (HM) in preterm infants with birth weight (BW) <1000 g is associated with improved lung function in a dose-dependent manner over the first 2 years of corrected age (CA). This retrospective study at an academic medical center included infants with BW <1000g. They had lung function assessment by the tidal breathing flow-volume loop (TBFVL) follow-up visits at 0-3-, 3-6-, 6-12-, 12-18-, and 18-24-month CA. One hundred eighty infants were included in the study with a mean (SD) gestational age 26.5 (1.90) weeks and BW 772.4 (147.0) g, 50% were female, and 60% developed BPD. 62.8% of infants received HM during the NICU stay. According to a general linear model (including GA, being small for GA (SGA), sex, human milk percentage, sepsis, and BPD), on average, each week of GA resulted in a higher tPTEF/tE of 1.24 (p = 0.039) and being SGA in a lower tPTEF/tE of 5.75 (p = 0.013) at 0-3-month CA. A higher percentage of human milk out of the total enteral intake was associated with better tPTEF/tE z-scores at 0-3 months (p = 0.004) and 18-24 months of CA (p = 0.041). BPD diagnosis was associated with a relevantly worse tPTEF/tE z-score at 6-12 months of CA (p = 0.003).

CONCLUSION

Preterm infants with higher consumption of HM had significantly less airway obstruction across the first 2 years, suggesting that human milk may contribute in a dose-dependent manner to improve lung function in early childhood in former preterm infants born ELBW.

WHAT IS KNOWN

• Human milk feeding reduces the risk of prematurity-related morbidities, including necrotizing enterocolitis, sepsis, lower respiratory tract infections, and BPD. Both exclusive and partial human milk feeding appear to be associated with a lower risk of BPD in preterm infants.

WHAT IS NEW

• This cohort study of 180 preterm infants with birth weight < 1000 g found that exposure to human milk during hospitalization improves airway obstruction markers tPTEF/tE z-score over the first 2 years of corrected age in a dose-dependent manner.

Pilot dose-ranging of rhIGF-1/rhIGFBP-3 in a preterm lamb model of evolving bronchopulmonary dysplasia

BACKGROUND

Low levels of insulin-like growth factor-1 (IGF-1) protein in preterm human infants are associated with bronchopulmonary dysplasia (BPD). We used our preterm lamb model of BPD to determine (1) dosage of recombinant human (rh) IGF-1 bound to binding protein-3 (IGFBP-3) to reach infant physiologic plasma levels; and (2) whether repletion of plasma IGF-1 improves pulmonary and cardiovascular outcomes.

METHODS

Group 1: normal, unventilated lambs from 128 days gestation through postnatal age 5 months defined normal plasma levels of IGF-1. Group 2: continuous infusion of rhIGF-1/rhIGFBP-3 (0.5, 1.5, or 4.5 mg/kg/day; n = 2) for 3 days in mechanically ventilated (MV) preterm lambs determined that 1.5 mg/kg/day dosage attained physiologic plasma IGF-1 concentration of ~125 ng/mL, which was infused in four more MV preterm lambs.

RESULTS

Group 1: plasma IGF-1 protein increased from ~75 ng/mL at 128 days gestation to ~220 ng/L at 5 months. Group 2: pilot study of the optimal dosage (1.5 mg/kg/day rhIGF-1/rhIGFBP-3) in six MV preterm lambs significantly improved some pulmonary and cardiovascular outcomes (p < 0.1) compared to six MV preterm controls. RhIGF-1/rhIGFBP-3 was not toxic to the liver, kidneys, or lungs.

CONCLUSIONS

Three days of continuous iv infusion of rhIGF-1/rhIGFBP-3 at 1.5 mg/kg/day improved some pulmonary and cardiovascular outcomes without toxicity.

IMPACT

Preterm birth is associated with rapid decreases in serum or plasma IGF-1 protein level. This decline adversely impacts the growth and development of the lung and cardiovascular system. For this pilot study, continuous infusion of optimal dosage of rhIGF-1/rhIGFBP-3 (1.5 mg/kg/day) to maintain physiologic plasma IGF-1 level of ~125 ng/mL during mechanical ventilation for 3 days statistically improved some structural and biochemical outcomes related to the alveolar formation that would favor improved gas exchange compared to vehicle-control. We conclude that 3 days of continuous iv infusion of rhIGF-1/rhIGFBP-3 improved some physiological, morphological, and biochemical outcomes, without toxicity, in mechanically ventilated preterm lambs.

Effect of human milk and other neonatal variables on lung function at three months corrected age

OBJECTIVE

To evaluate the impact of human milk and different neonatal variables on tidal breathing flow-volume loop (TBFVL) parameters within three months' corrected age (CA) in infants born ≤32 wks or weighing <1500 g.

METHODS

We retrospectively studied 121 infants with gestational age (GA) ≤ 32 weeks or birth weight (BW) <1500 gr who had lung function assessment within three months' CA by TBFVL analysis between June 2009 and April 2018. We investigated the impact of GA, gender, being Small for GA (SGA), sepsis, days of mechanical ventilation (MV) and human milk feeding (HMF) on later respiratory function, both in the entire group and according to BW ( ≤1000 g and >1000 g).

RESULTS

The mean(SD) z-score for tidal volume (Vt) and time to peak expiratory flow to expiratory time (tPTEF/tE) were respectively -4.3 (2.5) and -0.8 (2.0) for the overall population with no significant differences between infants <1000 g or ≥1000 g. The mean(SD) Vt standardized for body weight was 6.2(2.0) ml/kg. Being female was associated with better Vt/Kg, whereas longer MV or being born SGA were associated with worst tPTEF/tE. For infants with BW < 1000 gr, tPTEF/tE was positively associated with HMF.

CONCLUSION

An early TBFVL assessment within three months' CA already reveals lung function alteration in preterm infants. Being female is associated with better Vt/Kg, while longer duration of MV or being born SGA negatively affect tPTEF/tE. The positive association between HMF and better tPTEF/tE in infants with BW <1000 g has emerged, which deserves further investigation.

Nutrition and growth in infants with established bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) remains the most common late morbidity of preterm birth. Ongoing clinical care and research have largely focused on the pathogenesis and prevention of BPD in preterm infants. However, preterm infants who develop BPD have significant medical needs that persist throughout their neonatal intensive care unit course and continue post-discharge, including those associated with growth and nutrition. The objective of this manuscript was to provide a review on nutrition and growth in infants with established BPD after discharge from the hospital and to identify the knowledge and research gaps to provide direction for future studies.

Hippocampal epigenetic and insulin-like growth factor alterations in noninvasive versus invasive mechanical ventilation in preterm lambs

BACKGROUND

The brain of chronically ventilated preterm human infants is vulnerable to collateral damage during invasive mechanical ventilation (IMV). Damage is manifest, in part, by learning and memory impairments, which are hippocampal functions. A molecular regulator of hippocampal development is insulin-like growth factor 1 (IGF1). A gentler ventilation strategy is noninvasive respiratory support (NRS). We tested the hypotheses that NRS leads to greater levels of IGF1 messenger RNA (mRNA) variants and distinct epigenetic profile along the IGF1 gene locus in the hippocampus compared to IMV.

METHODS

Preterm lambs were managed by NRS or IMV for 3 or 21 days. Isolated hippocampi were analyzed for IGF1 mRNA levels and splice variants for promoter 1 (P1), P2, and IGF1A and 1B, DNA methylation in P1 region, and histone covalent modifications along the gene locus.

RESULTS

NRS had significantly greater levels of IGF1 P1 (predominant transcript), and 1A and 1B mRNA variants compared to IMV at 3 or 21 days. NRS also led to more DNA methylation and greater occupancy of activating mark H3K4 trimethylation (H3K4me3), repressive mark H3K27me3, and elongation mark H3K36me3 compared to IMV.

CONCLUSIONS

NRS leads to distinct IGF1 mRNA variant levels and epigenetic profile in the hippocampus compared to IMV.

IMPACT

Our study shows that 3 or 21 days of NRS of preterm lambs leads to distinct IGF1 mRNA variant levels and epigenetic profile in the hippocampus compared to IMV. Preterm infant studies suggest that NRS leads to better neurodevelopmental outcomes later in life versus IMV. Also, duration of IMV is directly related to hippocampal damage; however, molecular players remain unknown. NRS, as a gentler mode of respiratory management of preterm neonates, may reduce damage to the immature hippocampus through an epigenetic mechanism.

Bronchopulmonary dysplasia and postnatal growth following extremely preterm birth

OBJECTIVES

To report the current incidence of bronchopulmonary dysplasia (BPD) and to compare changes in weight and head circumference between infants who developed BPD and infants who did not.

DESIGN

Retrospective, whole-population study.

SETTING

All neonatal units in England between 2014 and 2018.

PATIENTS

All liveborn infants born <28 completed weeks of gestation.

INTERVENTIONS

The change in weight z-score (ΔWz) was calculated by subtracting the birthweight z-score from the weight z-score at 36 weeks postmenstrual age (PMA) and at discharge. The change in head circumference z-score (ΔHz) was calculated by subtracting the birth head circumference z-score from the head circumference z-score at discharge.

MAIN OUTCOME MEASURE

BPD was defined as the need for any respiratory support at 36 weeks PMA.

RESULTS

11 806 infants were included in the analysis. The incidence of BPD was 57.5%, and 18.9% of the infants died before 36 weeks PMA. The median (IQR) ΔWz from birth to 36 weeks PMA was significantly smaller in infants who developed BPD (-0.69 (-1.28 to -0.14), n=6105) than in those who did not develop BPD (-0.89 (-1.40 to -0.33), n=2390; adjusted p<0.001). The median (IQR) ΔHz from birth to discharge was significantly smaller in infants who developed BPD (-0.33 (-1.69 to 0.71)) than in those who did not develop BPD (-0.61 (-1.85 to 0.35); adjusted p<0.001).

CONCLUSIONS

Postnatal growth was better in infants diagnosed with BPD compared with infants without BPD possibly due to more aggressive nutrition strategies.

Early extubation to noninvasive respiratory support of former preterm lambs improves long-term respiratory outcomes

Invasive mechanical ventilation (IMV) and exposure to oxygen-rich gas during early postnatal life are contributing factors for long-term pulmonary morbidities faced by survivors of preterm birth and bronchopulmonary dysplasia. The duration of IMV that leads to long-term pulmonary morbidities is unknown. We compared two durations of IMV (3 h vs. 6 days) during the first 6-7 days of postnatal life in preterm lambs to test the hypothesis that minimizing the duration of IMV will improve long-term respiratory system mechanics and structural outcomes later in life. Moderately preterm (∼85% gestation) lambs were supported by IMV for either 3 h or 6 days before weaning from all respiratory support to become former preterm lambs. Respiratory system mechanics and airway reactivity were assessed monthly from 1 to 6 mo of chronological postnatal age by the forced oscillation technique. Quantitative morphological measurements were made for smooth muscle accumulation around terminal bronchioles and indices of alveolar formation. Minimizing IMV to 3 h led to significantly better (P < 0.05) baseline respiratory system mechanics and less reactivity to methacholine in the first 3 mo of chronological age (2 mo corrected age), significantly less (P < 0.05) accumulation of smooth muscle around peripheral resistance airways (terminal bronchioles), and significantly better (P < 0.05) alveolarization at the end of 5 mo corrected age compared with continuous IMV for 6 days. We conclude that limiting the duration of IMV following preterm birth of fetal lambs leads to better respiratory system mechanics and structural outcomes later in life.

Uteroplacental Insufficiency with Hypoxia Upregulates Placental PPARγ-KMT5A Axis in the Rat

The placenta represents a critical node in fetal lipid acquisition, yet the mechanisms by which the placenta handles lipids under normal and pathologic conditions are incompletely understood. A key player in placental lipid handling is peroxisome proliferator-activated receptor gamma (PPARγ). PPARγ influences global gene expression via its regulation of the epigenetic modifier lysine methyltransferase 5A (KMT5A), which places a methyl group on histone 4 lysine 20 (H4K20me) of target genes. Here we test the hypothesis that KMT5A is present in both the human and rat placentas and is affected by uteroplacental insufficiency (UPI) in the rat in association with increased placental lipid accumulation. We assessed levels and localization of KMT5A, as well as lipid droplet accumulation, in human placental tissue collected from maternal donors after delivery by planned cesarean section. Using a rat model of UPI, we also evaluated the effects of UPI on lipid accumulation, PPARγ, KMT5A, and H4K20me in the rat placenta. In this study, we show for the first time the presence and activity of KMT5A, in human and in rat placentas. We also demonstrate that in the rat placenta, UPI increases hypoxia, KMT5a expression, and activity in association with increased lipid accumulation in placenta supporting male fetuses. Placental PPARγ-KMT5A axis may be an important mediator of placental lipid handling.

[Association of early nutrition deficiency with the risk of bronchopulmonary dysplasia: a Meta analysis]

OBJECTIVE

To systematically evaluate the association of early nutrition intake with the risk of bronchopulmonary dysplasia (BPD).

METHODS

PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, Wanfang Data, and Weipu Periodical Database were searched for the observational studies on the association between early nutrition intake and BPD. RevMan 5.3 software was used to perform a Meta analysis of eligible studies.

RESULTS

Eight observational studies were included, with 548 infants with BPD and 522 infants without BPD. The Meta analysis showed that the BPD group had a significantly lower caloric intake than the non-BPD group within the first week after birth and in the first 2 weeks after birth (P < 0.05). The BPD group had a significantly lower enteral nutrition intake than the non-BPD group (WMD=-18.27, 95%CI:-29.70 to -6.84, P < 0.05), as well as a significantly lower intake of carbohydrate, fat, and protein (P < 0.05). The BPD group had a significantly longer duration of parenteral nutrition than the non-BPD group (WMD=14.26, 95%CI:13.26-15.25, P < 0.05).

CONCLUSIONS

Early nutrition deficiency may be associated with the development of BPD, and more attention should be paid to enteral feeding of infants at a high risk of BPD to achieve total enteral feeding as soon as possible.

Transforming Growth Factor-induced Protein Promotes NF-κB-mediated Angiogenesis during Postnatal Lung Development

Pulmonary angiogenesis is a key driver of alveolarization. Our prior studies showed that NF-κB promotes pulmonary angiogenesis during early alveolarization. However, the mechanisms regulating temporal-specific NF-κB activation in the pulmonary vasculature are unknown. To identify mechanisms that activate proangiogenic NF-κB signaling in the developing pulmonary vasculature, proteomic analysis of the lung secretome was performed using two-dimensional difference gel electrophoresis. NF-κB activation and angiogenic function was assessed in primary pulmonary endothelial cells (PECs) and TGFBI (transforming growth factor-β-induced protein)-regulated genes identified using RNA sequencing. Alveolarization and pulmonary angiogenesis was assessed in wild-type and Tgfbi null mice exposed to normoxia or hyperoxia. Lung TGFBI expression was determined in premature lambs supported by invasive and noninvasive respiratory support. Secreted factors from the early alveolar, but not the late alveolar or adult lung, promoted proliferation and migration in quiescent, adult PECs. Proteomic analysis identified TGFBI as one protein highly expressed by the early alveolar lung that promoted PEC migration by activating NF-κB via αvβ3 integrins. RNA sequencing identified Csf3 as a TGFBI-regulated gene that enhances nitric oxide production in PECs. Loss of TGFBI in mice exaggerated the impaired pulmonary angiogenesis induced by chronic hyperoxia, and TGFBI expression was disrupted in premature lambs with impaired alveolarization. Our studies identify TGFBI as a developmentally regulated protein that promotes NF-κB-mediated angiogenesis during early alveolarization by enhancing nitric oxide production. We speculate that dysregulation of TGFBI expression may contribute to diseases marked by impaired alveolar and vascular growth.

Non-invasive Respiratory Support of the Premature Neonate: From Physics to Bench to Practice

Premature births continue to rise globally with a corresponding increase in various morbidities among this population. Rates of respiratory distress syndrome and the consequent development of Bronchopulmonary Dysplasia (BPD) are highest among the extremely preterm infants. The majority of extremely low birth weight premature neonates need some form of respiratory support during their early days of life. Invasive modes of respiratory assistance have been popular amongst care providers for many years. However, the practice of prolonged invasive mechanical ventilation is associated with an increased likelihood of developing BPD along with other comorbidities. Due to the improved understanding of the pathophysiology of BPD, and technological advances, non-invasive respiratory support is gaining popularity; whether as an initial mode of support, or for post-extubation of extremely preterm infants with respiratory insufficiency. Due to availability of a wide range of modalities, wide variations in practice exist among care providers. This review article aims to address the physical and biological basis for providing non-invasive respiratory support, the current clinical evidence, and the most recent developments in this field of Neonatology.

Non-invasive measurements of respiratory system mechanical properties by the forced oscillation technique in spontaneously breathing, mixed-breed, normal term lambs from birth to five months of age

OBJECTIVE

To provide a non-invasive approach to monitoring lung function in spontaneously breathing lambs, from birth to five months of life, by the forced oscillation technique (FOT). This report describes the experimental set-up, data processing, and identification of normal predicted values of resistance (Rrs) and reactance (Xrs) of the respiratory system, along with normal bronchodilator response for bronchial reversibility testing.

APPROACH

Rrs and Xrs at 5, 11, and 19 Hz were measured monthly for five months in 20 normal term lambs that breathed spontaneously. In seven lambs, repeated measurements also were made within the first month of life (at 3, 7, 14, and 21 d of life). We determined the repeatability and reproducibility of the measurements and characterized the relationship between lung mechanics and age, sex, and body dimensions, using regression analysis, and measured changes in lung mechanics in response to inhaled bronchodilator.

MAIN RESULTS

The measurements provided repeatable and reproducible data. Rrs decreased, whereas Xrs increased, with growth from birth through the first two months of life, after which no statistically significant differences were detected. We identified normal value equations for Rrs and Xrs and for each of the measured anthropometric variables. Respiratory system mechanics were not affected by the bronchodilator.

SIGNIFICANCE

The FOT provides reliable non-invasive measurement of respiratory system mechanics in spontaneously breathing term lambs from birth to five months of age. The methods and normal reference values defined in this study will facilitate testing of the pathophysiological consequences of preterm birth and prolonged respiratory support on respiratory system mechanics.

Gestational Age Influences the Early Microarchitectural Changes in Response to Mechanical Ventilation in the Preterm Lamb Lung

Background: Preterm birth is associated with abnormal lung architecture, and a reduction in pulmonary function related to the degree of prematurity. A thorough understanding of the impact of gestational age on lung microarchitecture requires reproducible quantitative analysis of lung structure abnormalities. The objectives of this study were (1) to use quantitative histological software (ImageJ) to map morphological patterns of injury resulting from delivery of an identical ventilation strategy to the lung at varying gestational ages and (2) to identify associations between gestational age-specific morphological alterations and key functional outcomes. Method: Lung morphology was compared after 60 min of a standardized ventilation protocol (40 cm H₂O sustained inflation and then volume-targeted positive pressure ventilation with positive end-expiratory pressure 8 cm H₂O) in lambs at different gestations (119, 124, 128, 133, 140d) representing the spectrum of premature developmental lung states and the term lung. Age-matched controls were compared at 124 and 128d gestation. Automated and manual functions of Image J were used to measure key histological features. Correlation analysis compared morphological and functional outcomes in lambs aged ≤128 and >128d. Results: In initial studies, unventilated lung was indistinguishable at 124 and 128d. Ventilated lung from lambs aged 124d gestation exhibited increased numbers of detached epithelial cells and lung tissue compared with 128d lambs. Comparing results from saccular to alveolar development (120-140d), lambs aged ≤124d exhibited increased lung tissue, average alveolar area, and increased numbers of detached epithelial cells. Alveolar septal width was increased in lambs aged ≤128d. These findings were mirrored in the measures of gas exchange, lung mechanics, and molecular markers of lung injury. Correlation analysis confirmed the gestation-specific relationships between the histological assessments and functional measures in ventilated lambs at gestation ≤128 vs. >128d. Conclusion: Image J allowed rapid, quantitative assessment of alveolar morphology, and lung injury in the preterm lamb model. Gestational age-specific patterns of injury in response to delivery of an identical ventilation strategy were identified, with 128d being a transition point for associations between morphological alterations and functional outcomes. These results further support the need to develop individualized respiratory support approaches tailored to both the gestational age of the infant and their underlying injury response.

Former-preterm lambs have persistent alveolar simplification at 2 and 5 months corrected postnatal age

Preterm birth and mechanical ventilation (MV) frequently lead to bronchopulmonary dysplasia, the histopathological hallmark of which is alveolar simplification. How developmental immaturity and ongoing injury, repair, and remodeling impact completion of alveolar formation later in life is not known, in part because of lack of suitable animal models. We report a new model, using former-preterm lambs, to test the hypothesis that they will have persistent alveolar simplification later in life. Moderately preterm lambs (~85% gestation) were supported by MV for ~6 days before being transitioned from all respiratory support to become former-preterm lambs. Results are compared with term control lambs that were not ventilated, and between males (M) and females (F). Alveolar simplification was quantified morphometrically and stereologically at 2 mo (4 M, 4 F) or 5 mo (4 M, 6 F) corrected postnatal age (cPNA) compared with unventilated, age-matched term control lambs (4 M, 4 F per control group). These postnatal ages in sheep are equivalent to human postnatal ages of 1-2 yr and ~6 yr, respectively. Multivariable linear regression results showed that former-preterm lambs at 2 or 5 mo cPNA had significantly thicker distal airspace walls ( P < 0.001 and P < 0.009, respectively), lower volume density of secondary septa ( P < 0.007 and P < 0.001, respectively), and lower radial alveolar count ( P < 0.003 and P < 0.020, respectively) compared with term control lambs. Sex-specific differences were not detected. We conclude that moderate preterm birth and MV for ~6 days impedes completion of alveolarization in former-preterm lambs. This new model provides the opportunity to identify underlying pathogenic mechanisms that may reveal treatment approaches.

Vitamin A Protects the Preterm Lamb Diaphragm Against Adverse Effects of Mechanical Ventilation

Background: Preterm infants are deficient in vitamin A, which is essential for growth and development of the diaphragm. Preterm infants often require mechanical ventilation (MV) for respiratory distress. In adults, MV is associated with the development of ventilation-induced diaphragm dysfunction and difficulty weaning from the ventilator. We assessed the impact of MV on the preterm diaphragm and the protective effect of vitamin A during MV.

Methods: Preterm lambs delivered operatively at ∼131 days gestation (full gestation: 150 days) received respiratory support by synchronized intermittent mandatory ventilation for 3 days. Lambs in the treated group received daily (24 h) enteral doses of 2500 IU/kg/day vitamin A combined with 250 IU/kg/day retinoic acid (VARA) during MV, while MV control lambs received saline. Unventilated fetal reference lambs were euthanized at birth, without being allowed to breathe. The fetal diaphragm was collected to quantify mRNA levels of myosin heavy chain (MHC) isoforms, atrophy genes, antioxidant genes, and pro-inflammatory genes; to determine ubiquitin proteasome pathway activity; to measure the abundance of protein carbonyl, and to investigate metabolic signaling.

Results: Postnatal MV significantly decreased expression level of the neonatal MHC gene but increased expression level of MHC IIx mRNA level (p < 0.05). Proteasome activity increased after 3 days MV, accompanied by increased MuRF1 mRNA level and accumulated protein carbonyl abundance. VARA supplementation decreased proteasome activity and FOXO1 signaling, down-regulated MuRF1 expression, and reduced reactive oxidant production.

Conclusion: These findings suggest that 3 days of MV results in abnormal myofibrillar composition, activation of the proteolytic pathway, and oxidative injury of diaphragms in mechanically ventilated preterm lambs. Daily enteral VARA protects the preterm diaphragm from these adverse effects.

Prevention of bronchopulmonary dysplasia: current strategies

Bronchopulmonary dysplasia (BPD) is one of the few diseases affecting premature infants that have continued to evolve since its first description about half a century ago. The current form of BPD, a more benign and protracted respiratory failure in extremely preterm infants, is in contrast to the original presentation of severe respiratory failure with high mortality in larger premature infants. This new BPD is end result of complex interplay of various antenatal and postnatal factors causing lung injury and subsequent abnormal repair leading to altered alveolar and vascular development. The change in clinical and pathologic picture of BPD over time has resulted in new challenges in developing strategies for its prevention and management. While some of these strategies like Vitamin A supplementation, caffeine and volume targeted ventilation have stood the test of time, others like postnatal steroids are being reexamined with great interest in last few years. It is quite clear that BPD is unlikely to be eliminated unless some miraculous strategy cures prematurity. The future of BPD prevention will probably be a combination of antenatal and postnatal strategies acting on multiple pathways to minimize lung injury and abnormal repair as well as promote normal alveolar and vascular development.

Preterm birth and ventilation decrease surface density of glomerular capillaries in lambs, regardless of postnatal respiratory support mode

BACKGROUND

Prematurity is often complicated by respiratory support, including invasive mechanical ventilation (IMV) and noninvasive support (NIS). Compared with IMV, NIS reduces injury to the lung and brain. Prematurity may also disrupt glomerular architecture. Whether NIS differentially affects glomerular architecture is incompletely understood. We hypothesized that IMV would lead to greater disruption of glomerular architecture than NIS.

METHODS

This is a secondary analysis of kidneys from moderately preterm lambs delivered at ~131 d gestation (term ~150 d) that had antenatal steroid exposure and surfactant treatment before resuscitation by IMV. At ~3 h of age, half of the lambs were switched to NIS. Support was for 3 d or 21 d. Structural indices of glomerular architecture were quantified.

RESULTS

The number of glomerular generations was unaffected by moderate preterm birth and respiratory support, either IMV or NIS. At 3 d and 21 d of IMV or NIS, glomerular capillary surface density was not different. Glomerular capillary surface density was significantly lower in the inner and outer cortex compared with unventilated gestation age-matched or postnatal age-matched reference lambs.

CONCLUSION

Moderate preterm birth and invasive or noninvasive respiratory support decreases glomerular capillarization in the lamb kidney. This adverse effect on glomerular development may contribute to increased risk for adult-onset hypertension and renal dysfunction.