Pulmonary hypertension in the premature infant: a challenging comorbidity in a vulnerable population

Seeing pulmonary hypertension through a paediatric lens: a viewpoint

Pulmonary hypertension (PH) is a life-threating condition associated with abnormally elevated pulmonary pressures and right heart failure. Current epidemiological data indicate that PH aetiologies are different between the adult and paediatric population. The most common forms of PH in adults are PH from left heart disease or chronic lung disease, followed by pulmonary arterial hypertension (PAH) [1]; in paediatric patients, PH is most often associated with developmental lung disorders and congenital heart disease (CHD) [2, 3]. In contrast to adults with PH, wherein patients worsen over time despite therapy, PH in children can improve with growth. For example, in infants with bronchopulmonary dysplasia (BPD) and PH morbidity and mortality are high, but with lung growth and ensuring no ongoing lung injury pulmonary vascular disease can improve as evidenced by discontinuation of vasodilator therapy in almost two-thirds of BPD-PH survivors by age 5 years [3, 4].

Paediatric pulmonary hypertension (PH) offers unique genetic and developmental insights that can help in the discovery of novel mechanisms and targets to treat adult PH https://bit.ly/3TMm6bi

Taking Care of Preterm Infants: Outpatient Considerations

In recent decades, the number of pre-term infants born each year has been on the rise as mortality rates decline with improvements in technology and medical care. As a result, many preterm infants are successfully discharged from the neonatal intensive care unit (NICU). However, with prematurity comes the increased risk of ongoing health and development needs. Special attention must be given to certain chronic conditions by the outpatient provider, including growth and nutrition; gastroesophageal reflux; immunizations; vision and hearing impairments; chronic lung diseases, including bronchopulmonary dysplasia and pulmonary hypertension; and neurodevelopmental outcomes. This article will detail some of these topics to better inform the primary care provider of appropriate strategies to manage these chronic conditions and sequalae on NICU discharge. [Pediatr Ann. 2023;52(6):e200-e205.].

The Effect of Preterm Birth on Maximal Aerobic Exercise Capacity and Lung Function in Healthy Adults: A Systematic Review and Meta-analysis

BACKGROUND

A negative impact of premature birth on health in adulthood is well established. However, it is not clear whether healthy adults who were born prematurely but have similar physical activity levels compared to adults born at term have a reduced maximal aerobic exercise capacity (maximum oxygen consumption [VO2max]).

OBJECTIVE

We aimed to determine the effect of premature birth on aerobic exercise capacity and lung function in otherwise healthy, physically active individuals.

METHODS

A broad literature search was conducted in the PubMed database. Search terms included 'preterm/premature birth' and 'aerobic exercise capacity'. Maximal oxygen consumption (mL/kg/min) was the main variable required for inclusion, and amongst those investigations forced expiratory volume in 1 s (FEV1, % predicted) was evaluated as a secondary parameter. For the systematic review, 29 eligible articles were identified. Importantly, for the meta-analysis, only studies which reported similar activity levels between healthy controls and the preterm group/s were included, resulting in 11 articles for the VO2max analysis (total n = 688, n = 333 preterm and n = 355 controls) and six articles for the FEV1 analysis (total n = 296, n = 147 preterm and n = 149 controls). Data were analysed using Review Manager ( Review Manager. RevMan version 5.4 software. The Cochrane Collaboration; 2020.).

RESULTS

The systematic review highlighted the broad biological impact of premature birth. While the current literature tends to suggest that there may be a negative impact of premature birth on both VO2max and FEV1, several studies did not control for the potential influence of differing physical activity levels between study groups, thus justifying a focused meta-analysis of selected studies. Our meta-analysis strongly suggests that prematurely born humans who are otherwise healthy do have a reduced VO2max (mean difference: - 4.40 [95% confidence interval - 6.02, - 2.78] mL/kg/min, p < 0.00001, test for overall effect: Z = 5.32) and FEV1 (mean difference - 9.22 [95% confidence interval - 13.54, - 4.89] % predicted, p < 0.0001, test for overall effect: Z = 4.18) independent of physical activity levels.

CONCLUSIONS

Whilst the current literature contains mixed findings on the effects of premature birth on VO2max and FEV1, our focused meta-analysis suggests that even when physical activity levels are similar, there is a clear reduction in VO2max and FEV1 in adults born prematurely. Therefore, future studies should carefully investigate the underlying determinants of the reduced VO2max and FEV1 in humans born preterm, and develop strategies to improve their maximal aerobic capacity and lung function beyond physical activity interventions.

Extremely premature infants born at 23-25 weeks gestation are at substantial risk for pulmonary hypertension

OBJECTIVE

Extremely low gestational age newborns (ELGANs) represent an especially vulnerable population. Herein, we aimed to determine incidence and severity of pulmonary hypertension associated with bronchopulmonary dysplasia (BPD-PH) in extremely immature ELGANs (gestational age: 23^0/6-25^6/7 weeks).

METHODS

In this prospective observational cohort study, we assessed BPD-PH by means of several echocardiography markers and serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels at 3 and 12 months of chronological age. In addition, we analyzed incidence and efficacy of pharmacologic treatment for BPD-PH.

RESULTS

At 3 months 15/34 ELGANs had echocardiographic evidence of BPD-PH, while at 12 months of age 6/34 still had PH. PH-targeted therapy consisted of sildenafil monotherapy in 11 and dual oral combination therapy (sildenafil and macitentan) in four ELGANs at 3 and 12 months.

CONCLUSION

44% (15/34) of ELGANs developed BPD-PH. All received PH-targeted pharmacotherapy at 3 months, leading to hemodynamic improvements at 12 months in most infants.

Pulmonary Function Tests in Very Low Birth Weight Infants Screened for Pulmonary Hypertension: A Pilot Study

OBJECTIVE

To compare pulmonary function tests (PFTs), specifically respiratory system resistance (Rrs) and compliance (Crs), in very low birth weight (VLBW) infants with and without pulmonary hypertension.

STUDY DESIGN

Infants were included who underwent PFTs at 34-38 weeks postmenstrual age (PMA) as part of our pulmonary hypertension screening guidelines for infants born at ≤1500 g requiring respiratory support at ≥34 weeks PMA. One pediatric cardiologist reviewed and estimated right ventricular or pulmonary arterial pressure and defined pulmonary hypertension as an estimated pulmonary arterial pressure or right ventricular pressure greater than one-half the systemic pressure. Rrs and Crs were measured with the single breath occlusion technique and functional residual capacity with the nitrogen washout method according to standardized criteria.

RESULTS

Twelve VLBW infants with pulmonary hypertension and 39 without pulmonary hypertension were studied. Those with pulmonary hypertension had significantly lower birth weight and a trend toward a lower gestational age. There were no other demographic differences between the groups. The infants with pulmonary hypertension had significantly higher Rrs (119 vs 78 cmH₂O/L/s; adjusted P = .012) and significantly lower Crs/kg (0.71 vs 0.92 mL/cmH₂O/kg; P = .04).

CONCLUSIONS

In this pilot study of VLBW infants screened for pulmonary hypertension at 34-38 weeks PMA, those with pulmonary hypertension had significantly increased Rrs and decreased Crs compared with those without pulmonary hypertension. Additional studies are needed to further phenotype infants with evolving BPD and pulmonary hypertension.

Lower oxygen saturation targets in preterm infants are not associated with increased rates of pulmonary hypertension

BACKGROUND

The optimal oxygen saturation target in preterm infants is not known. In this study, we aimed to assess the effect of lower oxygen saturation targets on the rate of bronchopulmonary dysplasia (BPD), retinopathy of prematurity (ROP), and pulmonary hypertension (PH) in preterm infants.

METHODS

Retrospective cohort study comparing BPD, ROP, and PH incidence among two cohorts of infants born at≤32 weeks gestation with different oxygen saturation targets at≥34 weeks post-menstrual age (PMA): cohort 1, 94-98% (n = 126); cohort 2, 92-97% (n = 121). Groups compared by Chi-square test, t-test, and multivariable logistic regression.

RESULTS

When comparing cohort 1 (average gestational age 29.8 weeks, average birth weight 1271g) with cohort 2 (average gestational age 29.6 weeks, average birth weight 1299g), there was no difference in rate of BPD (24% vs. 19%, p = 0.38), ROP (4% vs. 3%, p = 0.49), or PH (2% vs. 4%, p = 0.44).

CONCLUSION

An oxygen saturation target of 92-97% at≥34 weeks PMA was not associated with a higher rate of PH or lower rate of BPD or ROP when compared with a higher target of 94-98%.

DDAH1 regulates apoptosis and angiogenesis in human fetal pulmonary microvascular endothelial cells

Nitric Oxide (NO) is an endogenous pulmonary vasodilator produced by endothelial NO synthase (eNOS). Asymmetric dimethyl L‐arginine (ADMA) is an endogenous inhibitor of eNOS activity. In endothelial cells, ADMA is hydrolyzed to L‐citrulline primarily by dimethylarginine dimethyl‐aminohydrolase‐1 (DDAH1). We tested the hypothesis that DDAH1 expression is essential for maintaining NO production in human fetal pulmonary microvascular endothelial cells (hfPMVEC), such that knockdown of DDAH1 expression will lead to decreased NO production resulting in less caspase‐3 activation and less tube formation. We found that hfPMVEC transfected with DDAH1 siRNA had lower NO production than control, with no difference in eNOS protein levels between groups. hfPMVEC transfected with DDAH1 siRNA had lower protein levels of cleaved caspase‐3 and ‐8 than control. Both DDAH1 siRNA‐ and ADMA‐treated hfPMVEC had greater numbers of viable cells than controls. Angiogenesis was assessed using tube formation assays in matrigel, and tube formation was lower after either DDAH1 siRNA transfection or ADMA treatment than controls. Addition of an NO donor restored cleaved caspase‐3 and ‐8 protein levels after DDAH1 siRNA transfection in hfPMVEC to essentially the levels seen in scramble control. Addition of a putative caspase‐3 inhibitor to DDAH1 siRNA transfected and NO‐donor treated cells led to greater numbers of viable cells and far less angiogenesis than in any other group studied. We conclude that in hfPMVEC, DDAH1 is central to the regulation of NO‐mediated caspase‐3 activation and the resultant apoptosis and angiogenesis. Our findings suggest that DDAH1 may be a potential therapeutic target in pulmonary hypertensive disorders.

Initial Experience With Patent Ductus Arteriosus Ligation in Pre-term Infants With Bidirectional Shunt Pattern

Background: Patent ductus arteriosus (PDA) with a bidirectional shunt reflects critical clinical conditions. The operability of PDA with a bidirectional shunt in pre-term infants is still not clearly clarified. This study aimed to investigate the feasibility and the outcomes of PDA ligation in pre-term infants with a bidirectional shunt PDA. Methods: All pre-term infants receiving PDA ligation between 2013 and 2019 were enrolled in this prospective study. Patients were allocated into two groups based on the shunting direction of PDA, which were the left-to-right group (group A) and the bidirectional group (group B). Clinical characteristics and pre-op comorbidities were analyzed. Intraoperative complications, post-op neurological sequelae, necrotizing enterocolitis, survival, and mortality were compared between these two groups. Results: Thirty-seven pre-term infants were enrolled (18 in group A, 19 in group B). The mean post-menstrual age at PDA surgery was 32.0 ± 1.3 and 32.8 ± 1.5 weeks, respectively. Before surgery, 44.4 and 89.5% (group A vs. B) of the patients were using invasive mechanical ventilator (p < 0.01). The requirement of high-frequency oscillatory ventilatory support was significantly higher in group B. PDA rupture-related bleeding during exposing PDA or ligating PDA occurred in four infants, and all were all in group B, including one with delayed hemothorax. Early surgical mortality within 30 days of surgery was higher in group B (0 vs. 21.1%, p < 0.05), but only one death could be attributed to the surgery, which was caused by a pain-induced pulmonary hypertension crisis. The 5-year survival was 100% in group A, and 73.7% in group B (p < 0.05). Conclusion: We did not recommend routine PDA ligation in pre-term infants with a bidirectional shunt. However, a bidirectional shunt should not be an absolute contraindication if they fulfill indications of PDA closure. Unexpected intraoperative PDA rupture and delayed hemothorax in a bidirectional shunt PDA should be carefully monitored. Aggressive post-op pain control is also warranted to avoid pulmonary hypertension crisis. The post-op early mortality rate was higher in the bidirectional group, which could be inherent to their poor pre-operative lung condition. Only one death was directly related to the surgery.

Bronchopulmonary Dysplasia: An Update on Experimental Therapeutics

Bronchopulmonary dysplasia (BPD) is a chronic inflammatory lung disease that affects thousands of newborns and infants every year. Although it is accepted that BPD results from lung damage and inflammation triggered by mechanical ventilation and hyperoxia, the causes and molecular events leading to lung damage and arrested development remain unknown. While recent advances in neonatal care have improved the survival of very low-weight infants, the rates of BPD have not improved accordingly. This is mainly due to our limited understanding of the disease’s pathogenesis and the effective therapeutic options available. Current therapeutics for BPD involve ventilation management, steroid treatment, and administration of various agents, such as pulmonary surfactant, caffeine, vitamin A, nitric oxide, and stem cells. However, the efficacy of these agents in preventing and ameliorating BPD symptoms varies depending on the populations studied and the disease stage. As the field moves towards personalised therapeutic approaches, this review summarises clinical and experimental studies conducted in various models, aiming to increase understanding of the cellular and molecular mechanisms by which these agents can prevent or treat BPD. Due to the increasing number of extremely premature infants, it is imperative that we continue to work towards understanding the mechanisms of BPD pathogenesis and generating more effective therapeutic options.

Bronchopulmonary Dysplasia: An Update on Experimental Therapeutics

Bronchopulmonary dysplasia (BPD) is a chronic inflammatory lung disease that affects thousands of newborns and infants every year. Although it is accepted that BPD results from lung damage and inflammation triggered by mechanical ventilation and hyperoxia, the causes and molecular events leading to lung damage and arrested development remain unknown. While recent advances in neonatal care have improved the survival of very low-weight infants, the rates of BPD have not improved accordingly. This is mainly due to our limited understanding of the disease's pathogenesis and the effective therapeutic options available. Current therapeutics for BPD involve ventilation management, steroid treatment, and administration of various agents, such as pulmonary surfactant, caffeine, vitamin A, nitric oxide, and stem cells. However, the efficacy of these agents in preventing and ameliorating BPD symptoms varies depending on the populations studied and the disease stage. As the field moves towards personalised therapeutic approaches, this review summarises clinical and experimental studies conducted in various models, aiming to increase understanding of the cellular and molecular mechanisms by which these agents can prevent or treat BPD. Due to the increasing number of extremely premature infants, it is imperative that we continue to work towards understanding the mechanisms of BPD pathogenesis and generating more effective therapeutic options.

Evidence of Echocardiographic Markers of Pulmonary Vascular Disease in Asymptomatic Infants Born Preterm at One Year of Age

OBJECTIVE

To test the hypothesis that echocardiographic markers of pulmonary vascular disease (PVD) exist in asymptomatic infants born preterm at 1-year corrected age.

STUDY DESIGN

We conducted a prospective cohort study of 80 infants born preterm (<29 weeks of gestation) and 100 age- and weight-matched infants born at term and compared broad-based conventional and quantitative echocardiographic measures of pulmonary hemodynamics at 1-year corrected age. Pulmonary artery acceleration time (PAAT), a validated index of pulmonary vascular resistance, arterial pressure, and compliance, was used to assess pulmonary hemodynamics. Lower PAAT is indicative of PVD. Subanalyses were performed in infants with bronchopulmonary dysplasia (BPD, n = 48, 59%) and/or late-onset pulmonary hypertension (n = 12, 15%).

RESULTS

At 1 year, there were no differences between conventional measures of pulmonary hypertension in the infants born at term and preterm. All infants born preterm had significantly lower values of PAAT than infants born at term (73 ± 8 milliseconds vs 98 ± 5 milliseconds, P < .001). Infants born preterm with BPD had even lower PAAT than those without BPD (69 ± 5 milliseconds vs 79 ± 4 milliseconds, P < .01). The degree of PVD at 1-year corrected age was inversely related to gestation in all infants born preterm. Data analysis included adjustment for ventricular function and other confounding factors.

CONCLUSIONS

In comparison with infants born at term, infants born preterm exhibit abnormal PAAT at 1-year corrected age irrespective of neonatal lung disease status, suggesting the existence of PVD beyond infancy. PAAT measurements offer a reliable, noninvasive tool for screening and longitudinal monitoring of pulmonary hemodynamics in infants.

Pulmonary hypertension in the premature infant population: Analysis of echocardiographic findings and biomarkers

OBJECTIVE

Extremely low gestational age neonates (ELGANs) are at risk for pulmonary hypertension (PH). We hypothesized that PH, defined by echocardiogram at 36 weeks gestational age (GA), would associate with respiratory morbidity, increased oxidant stress, and reduced nitric oxide production.

STUDY DESIGN

ELGANs in the Vanderbilt fraction of the Prematurity and Respiratory Outcomes Program (PROP) who had echocardiograms at 36 ± 1 weeks GA were studied. Echocardiogram features of PH were compared with clinical characteristics as well as markers of oxidant stress and components of the nitric oxide pathway. Biomarkers were obtained at enrollment (median day 3), 7, 14, and 28 days of life.

RESULTS

Sixty of 172 infants had an echocardiogram at 36 weeks; 11 had evidence of PH. Infants did not differ by PH status in regards to demographics, respiratory morbidity, or oxidant stress. However, odds of more severe PH were significantly higher in infants with higher nitric oxide metabolites (NOx) at enrollment and with a lower citrulline level at day 7.

CONCLUSIONS

Respiratory morbidity may not always associate with PH at 36 weeks among ELGANs. However, components of nitric oxide metabolism are potential biologic markers of PH in need of further study.

Pediatric pulmonary arterial hypertension: on the eve of growing up

PURPOSE OF REVIEW

Current recommendations for diagnosis and treatment of pulmonary arterial hypertension (PAH) during childhood are expert opinion based, because of lacking pediatric data. In recent years, however, important pediatric data have emerged on PAH.

RECENT FINDINGS

PAH in children shows similarities as well as differences compared to adults. Neonates and children know specific clinical presentations and a hemodynamic profile that differs from adults with PAH. Children identified as acute vasodilator responders according to the criteria proposed for adults rather than the pediatric criteria have better outcome when treated with calcium channel blockers. For nonresponders, combination PAH-targeted therapy leads to improved outcome compared to monotherapy. In pediatric PAH, WHO functional class, N-terminal pro-brain natriuretic peptide and tricuspid annular plane systolic excursion were identified as surrogates for survival and therefore qualify to be treatment goals in a goal-oriented treatment strategy.

SUMMARY

In order to refine current pediatric treatment guidelines, data on efficacy of specific treatment regiments and strategies are needed. The recently validated composite endpoint of clinical worsening allows for trials that will provide these data. For the first time, evidence-based treatment goals have been identified that will allow for a goal-oriented treatment strategy. Furthermore, various prognostic predictors have been identified that may prove treatment goals in future.

The evolution of disease: chronic lung disease of infancy and pulmonary hypertension

PURPOSE OF REVIEW

Bronchopulmonary dysplasia (BPD) or chronic lung disease of infancy BPD was originally described 50 years ago, in 1967 by Northway et al. This article possesses two fundamental objectives to provide: a brief historical perspective on BPD; and an update relative to current notions of epidemiology, pathophysiology, evaluation, and clinical management of BPD complicated by vascular disease. The review highlights areas of consensus and ongoing uncertainty.

RECENT FINDINGS

The clinical cause and presentation of infants with BPD has evolved over the past several decades. Considerable improvements in neonatal care, including surfactant replacement therapies, antenatal steroids, nutritional support, ventilator management, and attention to the potential of oxygen toxicity, underlie the evolution of BPD. Most children with BPD improve over time. However, in the presence of vascular disease, the morbidity and mortality associated with BPD increases considerably. Though recent recommendations include procuring an echocardiogram to screen for pulmonary hypertension in infants with established BPD, there is less agreement surrounding the additional diagnostic and putative treatment modalities for infants with BPD and pulmonary hypertension. The indications, rationale, potential benefits, and risks of vasodilator therapy in BPD are discussed.

SUMMARY

The pediatric community has 50 years of experience with BPD. Past experience should be used to inform present and future diagnostic and treatment strategies. This review seeks to arm the clinician with evidence that motivates a physiology-based approach to the management of infants with BPD and pulmonary hypertension.