Impaired myocardial reserve underlies reduced exercise capacity and heart rate recovery in preterm-born young adults

Smaller Left Ventricular Size But Preserved Function in Adolescents and Adults Born Preterm

BACKGROUND

Prematurely born adults have increased risk for cardiovascular disease. There are limited cardiac data on US-born preterm individuals. We aimed to determine whether adolescents and adults born prematurely have altered left ventricular (LV) structure and function, and to interrogate diastolic function using isometric handgrip exercise.

METHODS AND RESULTS

Adolescents and adults born moderately to extremely preterm (≤32 weeks gestation or <1500 g birth weight) were recruited from the Parkland Health Neonatal Intensive Care Unit Registry. Full-term participants were recruited from the local area. Study procedures included anthropometrics and vitals, handgrip testing, and echocardiography performed at rest and during isometric handgrip exercise. Data were reported as mean±SD. The study enrolled 107 preterm and 48 term participants. Preterm participants (gestational age: 29.5±2.5 weeks) were shorter with higher body mass index (P<0.001) compared with term participants. Preterm participants exhibited smaller LV end-diastolic volume index (50.8±10.1 versus 56.9±10.0 mL/m2, P<0.001), LV stroke volume index (29.6±6.0 versus 34.1±6.5 mL/m2, P<0.001), and LV mass index (67.2±13.1 versus 73.3±14.2 g/m2, P=0.002) compared with term individuals. Preterm participants also had subclinical reductions in LV peak systolic tissue velocity and peak early diastolic tissue velocity lateral at rest. Isometric handgrip exercise promoted a reduction in diastolic function and an increase in hemodynamic measures, but changes during isometric handgrip exercise were similar between groups.

CONCLUSIONS

Adolescents and adults born preterm exhibit overall normal cardiac function despite smaller cardiac volumes and mass compared with individuals born full term. Effects are most pronounced at the lowest gestational ages.

Effects of preterm birth on the pattern of altitude acclimatization at rest and during moderate-intensity exercise across three days at 3,375 m

Preterm birth elicits long-lasting physiological effects in various organ systems, potentially modulating exercise and environmental stress responses. To establish whether prematurely-born adults respond uniquely during early high-altitude acclimatization at rest and during exercise, 17 healthy adults born preterm (gestational age < 32 wk) and 17 term-born, age- and aerobic-capacity-matched, control participants completed a three-day high-altitude sojourn (3,375 m). Oxygen uptake, pulmonary ventilation, and hemodynamic responses, as well as pulse oxygen saturation, brain tissue saturation index (TSI), and skeletal muscle TSI, were measured daily at rest and during moderate-intensity steady-state exercise bouts. In general, the prematurely-born group displayed comparable acclimatization responses at rest, with similar ventilation and cardiac output observed between groups throughout. Resting brain TSI was, however, higher in the preterm group upon arrival at high altitude (72 ± 7% vs. 68 ± 3%; d = 1.20). Absolute exercising oxygen uptake was lower in the preterm participants (P = 0.047), with this group displaying lower exercising cardiac output underpinned by reduced stroke volume (both P = 0.035). Nevertheless, exercising minute ventilation (V̇e) did not differ between groups (P = 0.237) while brain TSI (70 ± 6% vs. 66 ± 3%; d = 1.35) and pulse oxygen saturation (85 ± 3% vs. 82 ± 5%; d = 1.52) were higher with prematurity upon arrival to high altitude. These findings suggest that healthy prematurely-born adults exhibit comparable early acclimatization patterns to their term-born counterparts and better maintain cerebral oxygenation at rest. Together, these data suggest that prematurely-born adults should not be discouraged from high-altitude sojourns involving physical activity.NEW & NOTEWORTHY The acclimatization pattern across three days at 3,375 m, at rest and during moderate-intensity exercise, was similar between healthy adults born prematurely and their term-born counterparts. Preterm adults free from respiratory complications were found to better maintain brain tissue and capillary oxygen saturation at high altitudes, whereas the term-born group experienced larger altitude-induced reductions. Despite apparent cardiac limitations, preterm individuals tolerated exercise similarly to their term-born peers. These findings underscore the notion that preterm birth per se does not predispose healthy adults to decreased altitude tolerance during exercise.

Influence of Preterm Birth and Low Birthweight on Physical Fitness: A Systematic Review, Meta-Analysis, and Meta-Regression

BACKGROUND

Preterm birth and low birthweight (LBW) might be associated with reduced physical fitness, although evidence remains inconclusive.

OBJECTIVE

To examine the influence of preterm birth and LBW on physical fitness, as well as to assess whether variables such as gestational age, birthweight, or age at assessment moderate these effects.

METHODS

PubMed, Scopus, and PsycINFO were systematically searched from inception to 7 December 2023 for case-control and cohort studies analyzing the association between preterm birth or LBW (or gestational age or birthweight as continuous variables) with at least one physical fitness-related outcome (i.e., cardiorespiratory fitness (CRF), muscle strength, flexibility, speed, agility). Random-effects meta-analysis and meta-regression models were used to estimate the pooled effect size, as well as to examine potential associations between the magnitude of the effect and gestational age, birthweight, or age at assessment.

RESULTS

Fifty-two studies (n = 920,603 participants, average age ranging from 4.7 to 34.4 years) were included. Preterm birth was associated with reduced CRF (standardized mean difference (SMD) = -0.38, 95% confidence interval (CI) = -0.51 to -0.25) and muscle strength (SMD = -0.44, 95% CI = -0.79 to -0.08). LBW was associated with reduced CRF (SMD = -0.40, 95% CI = -0.64 to -0.17), muscle strength (SMD = -0.18, 95% CI = -0.24 to -0.13), flexibility (SMD = -0.11, 95% CI = -0.22 to -0.01), and agility (SMD = -0.99, 95% CI = -1.91 to -0.07). Meta-regression analyses showed that a lower gestational age or birthweight were associated with larger reductions in physical fitness, whereas no consistent association was found for the age at assessment.

CONCLUSION

Both preterm birth and LBW seem associated with reduced physical fitness regardless of age, with larger reductions overall observed in individuals with lower gestational age or birthweight. These findings might support the implementation of preventive strategies (e.g., fitness monitoring and physical exercise interventions) in these populations through the life course. PROSPERO registration: CRD42021231845.

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

HAPI Fit: An Exercise Intervention to Improve Peak Aerobic Capacity in Young Adults Born Very Preterm

INTRODUCTION

Individuals born preterm have reduced aerobic capacity, which could be related to impaired organ development. Their capacity to improve aerobic capacity with exercise training could therefore be limited, but this remains unknown. We aimed to test an exercise intervention to improve cardiorespiratory fitness in adults born preterm.

METHODS

Twenty-one very preterm and 37 full-term individuals aged 18-33 yr took part in a 14-wk supervised exercise intervention of cardiovascular, resistance, and flexibility training (two group and one individual sessions per week). Adherence and compliance to intervention were recorded. Primary outcome was change in peak oxygen consumption (peak V̇O 2 ) measured before and after the intervention. Within- and between-group differences were estimated using nonparametric tests.

RESULTS

Of 219 eligible individuals, 58 were enrolled and 14 participants dropped out over the course of the intervention. Among the 44 who completed the intervention, mean adherence was 82% and 66% for group and individual sessions, respectively. Compliance with training requirement varied between 71% and 100%. There was no difference in adherence between the preterm and full-term groups. Because only one preterm male met the adherence criteria, subsequent analyses were done exclusively on females. Both the term and preterm groups achieved higher peak V̇O 2 after the intervention [term = +4.2 (SD 4.3) mL·min -1 ·kg -1 , P < 0.01; preterm = +4.7 (2.9) mL·min -1 ·kg -1 , P < 0.01]. There was no between-group difference in the response to the intervention ( P = 0.729).

CONCLUSIONS

Recruitment and adherence to an exercise intervention are challenging. Results could indicate improvements in cardiorespiratory fitness in young women born preterm after current exercise program. Adaptation of this intervention is needed for wider uptake.

Heart Rate and Heart Rate Variability in Healthy Preterm-Born Young Adults and Association with Vitamin D: A Wearable Device Assessment

Prematurity has been associated with impaired parasympathetic cardiac regulation later in life. Changes in heart rate (HR) and heart rate variability (HRV) may indicate a risk for future cardiac dysfunction. The putative role of Vitamin D on cardiac autonomic function in individuals born preterm (PT) remains unknown. This study involves monitoring autonomic cardiac regulation and Vitamin D concentrations in 30 PT and 16 full-term (FT) young adults in a free-living context. The PT subjects were born between 1994 and 1997 at Oulu University Hospital. The inclusion criteria were (1) being born ≤ 32 gestation weeks or (2) being born < 34 gestation weeks with a birth weight under 1500 g. Participants wore an Oura ring sleep tracer, a smart ring device, for 2 weeks to monitor cardiac autonomic function. Parameters related to autonomic cardiac regulation, lowest nighttime resting HR, and the root mean square of successive differences (RMSSD) to describe HRV were collected. PT males exhibited a tendency toward lower RMSSD (71.8 ± 22.6) compared to FT males (95.63 ± 29.0; p = 0.10). Female participants had a similar mean RMSSD in the FT and PT groups at 72.04 ± 33.2 and 74.0 ± 35.0, respectively. Serum 25-hydroxyvitamin D concentration did not correlate with cardiac autonomic function parameters. When assessing the lowest resting nighttime HRs and HRVs in a long-term, real-world context, healthy female PT young adults performed similarly to their FT peers. In contrast, the present study's results suggest that male PT young adults exhibit impaired autonomic cardiac function, potentially putting them at risk for cardiovascular disease later in adulthood.

Preterm birth and exercise capacity: what do we currently know?

Objectives

The long-term cardiopulmonary outcomes following preterm birth during the surfactant era remain unclear. Respiratory symptoms, particularly exertional symptoms, are common in preterm children. Therefore, cardiopulmonary exercise testing may provide insights into the pathophysiology driving exertional respiratory symptoms in those born preterm. This review aims to outline the current knowledge of cardiopulmonary exercise testing in the assessment of children born preterm in the surfactant era.

Design

This study is a narrative literature review.

Methods

Published manuscripts concerning the assessment of pulmonary outcomes using cardiopulmonary exercise testing in preterm children (aged <18 years) were reviewed. Search terms related to preterm birth, bronchopulmonary dysplasia, and exercise were entered into electronic databases, including Medline, PubMed, and Google Scholar. Reference lists from included studies were scanned for additional manuscripts.

Results

Preterm children have disrupted lung development with significant structural and functional lung disease and increased respiratory symptoms. The association between these (resting) assessments of respiratory health and exercise capacity is unclear; however, expiratory flow limitation and an altered ventilatory response (rapid, shallow breathing) are seen during exercise. Due to the heterogeneity of participants, treatments, and exercise protocols, the effect of the aforementioned limitations on exercise capacity in children born preterm is conflicting and poorly understood.

Conclusion

Risk factors for reduced exercise capacity in those born preterm remain poorly understood; however, utilizing cardiopulmonary exercise testing to its full potential, the pathophysiology of exercise limitation in survivors of preterm birth will enhance our understanding of the role exercise may play. The role of exercise interventions in mitigating the risk of chronic disease and premature death following preterm birth has yet to be fully realized and should be a focus of future robust randomized controlled trials.

Consequences of Preterm Birth: Knowns, Unknowns, and Barriers to Advancing Cardiopulmonary Health

Preterm birth occurs in 10% of all live births and creates challenges to neonatal life, which persist into adulthood. Significant previous work has been undertaken to characterize and understand the respiratory and cardiovascular sequelae of preterm birth, which are present in adulthood, i.e., "late" outcomes. However, many gaps in knowledge are still present and there are several challenges that will make filling these gaps difficult. In this perspective we discuss the obstacles of studying adults born preterm, including (1) the need for invasive (direct) measures of physiologic function; (2) the need for multistate, multinational, and diverse cohorts; (3) lack of socialized medicine in the United States; (4) need for detailed and better-organized birth records; and (5) transfer of neonatal and pediatric knowledge to adult care physicians. We conclude with a discussion on the "future" of studying preterm birth in regards to what may happen to these individuals as they approach middle and older age and how the improvements in perinatal and postnatal care may be changing the phenotypes observed in adults born preterm on or after the year 2000.

Exercise Capacity in Very Low Birth Weight Adults: A Systematic Review and Meta-Analysis

There is an association between very low birth weight (VLBW) and cardiovascular morbidity and mortality in adulthood. Aerobic fitness, measured as the maximal oxygen consumption (VO2 max), is a good indicator of cardiopulmonary health and predictor of cardiovascular mortality. Our aim was to determine the effect of birth weight on aerobic exercise capacity and physical activity. We systematically identified studies reporting exercise capacity (VO2 max and VO2 peak) and physical activity levels in participants born at VLBW aged eighteen years or older compared to term-born controls from six databases (MEDLINE, OVID, EMBASE, CI NAHL, CENTRAL, and Google Scholar). Meta-analysis of eligible studies was conducted using a random effect model. We screened 6202 articles and identified 15 relevant studies, 10 of which were eligible for meta-analysis. VLBW participants had a lower VO2 max compared to their term counterparts (-3.35, 95% CI: -5.23 to -1.47, p = 0.0005), as did VLBW adults who had developed bronchopulmonary dysplasia (-6.08, 95% CI -11.26 to -0.90, p = 0.02). Five of nine studies reported significantly reduced self-reported physical activity levels. Our systematic review and meta-analysis demonstrated reduced maximal aerobic exercise capacity in adults born at VLBW compared to term-born controls.

Impact of premature birth on cardiopulmonary function in later life

Pulmonary function is reduced in children after preterm birth. The variety of subgroups ranges from early to late preterm births. Limitations in pulmonary function can be observed even after late preterm birth without signs of bronchopulmonary dysplasia and/or history of mechanical ventilation. Whether this reduction in lung function is reflected in the cardiopulmonary capacity of these children is unclear. This study aims to investigate the impact of moderate to late premature birth on cardiopulmonary function. Cardiopulmonary exercise testing on a treadmill was performed by 33 former preterm infants between 8 and 10 years of age who were born between 32 + 0 and 36 + 6 weeks of gestation and compared with a control group of 19 children born in term of comparable age and sex. The former preterm children achieved comparable results to the term-born controls with respect to most of the cardiopulmonary exercise parameters [Formula: see text]. The only differences were in a slightly higher oxygen uptake efficiency slope [Formula: see text] and higher peak minute ventilation [Formula: see text] in the group of children born preterm. With respect to heart rate recovery [Formula: see text] and breathing efficiency [Formula: see text], there were no significant differences.

CONCLUSION

 Children born preterm did not show limitations in cardiopulmonary function in comparison with matched controls.

WHAT IS KNOWN

• Preterm birth is associated with reduced pulmonary function in later life, this is also true for former late preterms. • As a consequence of being born premature, the lungs have not finished their important embryological development. Cardiopulmonary fitness is an important parameter for overall mortality and morbidity in children and adults and a good pulmonary function is therefore paramount.

WHAT IS NEW

• Children born prematurely were comparable to an age- and sex-matched control group with regards to almost all cardiopulmonary exercise variables. • A significantly higher OUES, a surrogate parameter for VO₂peak was found for the group of former preterm children, most likely reflecting on more physical exercise in this group. Importantly, there were no signs of impaired cardiopulmonary function in the group of former preterm children.

Aerobic Exercise Training Response in Preterm-Born Young Adults with Elevated Blood Pressure and Stage 1 Hypertension: A Randomized Clinical Trial

Rationale: Premature birth is an independent predictor of long-term cardiovascular risk. Individuals affected are reported to have a lower rate of [Formula: see text]o2 at peak exercise intensity ([Formula: see text]o2PEAK) and at the ventilatory anaerobic threshold ([Formula: see text]o2VAT), but little is known about their response to exercise training. Objectives: The primary objective was to determine whether the [Formula: see text]o2PEAK response to exercise training differed between preterm-born and term-born individuals; the secondary objective was to quantify group differences in [Formula: see text]o2VAT response. Methods: Fifty-two preterm-born and 151 term-born participants were randomly assigned (1:1) to 16 weeks of aerobic exercise training (n = 102) or a control group (n = 101). Cardiopulmonary exercise tests were conducted before and after the intervention to measure [Formula: see text]o2PEAK and the [Formula: see text]o2VAT. A prespecified subgroup analysis was conducted by fitting an interaction term for preterm and term birth histories and exercise group allocation. Measurements and Main Results: For term-born participants, [Formula: see text]o2PEAK increased by 3.1 ml/kg/min (95% confidence interval [CI], 1.7 to 4.4), and the [Formula: see text]o2VAT increased by 2.3 ml/kg/min (95% CI, 0.7 to 3.8) in the intervention group versus controls. For preterm-born participants, [Formula: see text]o2PEAK increased by 1.8 ml/kg/min (95% CI, -0.4 to 3.9), and the [Formula: see text]o2VAT increased by 4.6 ml/kg/min (95% CI, 2.1 to 7.0) in the intervention group versus controls. No significant interaction was observed with birth history for [Formula: see text]o2PEAK (P = 0.32) or the [Formula: see text]o2VAT (P = 0.12). Conclusions: The training intervention led to significant improvements in [Formula: see text]o2PEAK and [Formula: see text]o2VAT, with no evidence of a statistically different response based on birth history. Clinical trial registered with www.clinicaltrials.gov (NCT02723552).

Dose-related cardiac outcomes in response to postnatal dexamethasone treatment in premature lambs

BACKGROUND

Postnatal corticosteroids are used in the critical care of preterm infants for the prevention and treatment of bronchopulmonary dysplasia. We aimed to investigate the effects of early postnatal dexamethasone therapy and dose on cardiac maturation and morphology in preterm lambs.

METHODS

Lambs were delivered prematurely at ~128 days of gestational age and managed postnatally according to best clinical practice. Preterm lambs were administered dexamethasone daily at either a low-dose (n = 9) or a high-dose (n = 7), or were naïve to steroid treatment and administered saline (n = 9), over a 7-day time-course. Hearts were studied at postnatal Day 7 for gene expression and assessment of myocardial structure.

RESULTS

High-dose dexamethasone treatment in the early postnatal period led to marked differences in cardiac gene expression, altered cardiomyocyte maturation and reduced cardiomyocyte endowment in the right ventricle, as well as increased inflammatory infiltrates into the left ventricle. Low-dose exposure had minimal effects on the preterm heart.

CONCLUSION

Neonatal dexamethasone treatment led to adverse effects in the preterm heart in a dose-dependent manner within the first week of life. The observed cardiac changes associated with high-dose postnatal dexamethasone treatment may influence postnatal growth and remodeling of the preterm heart and subsequent long-term cardiac function.

Effect of preterm birth in rats on proliferation and hyperplasia of cardiomyocytes

Aim. To identify the effect of preterm birth on proliferation and hyperplasia of cardiomyocytes in the early postnatal period of ontogenesis in rats.

Materials and methods. Preterm birth (on day 21 and 21.5 of gestation) in Wistar rats was induced by subcutaneous administration of mifepristone. Immunohistochemistry was used to identify and calculate the number of Ki67-positive and Mklp2-positive cardiomyocytes in the left ventricle of preterm and full-term rats on days 1, 2, 3, 4, 5, and 6 of postnatal ontogenesis. Statistical analysis of morphometric parameters was performed using the Shapiro – Wilk test and Mann – Whitney test with the Bonferroni correction.

Results. We revealed an increase in the number of Ki67-positive cardiomyocytes in the left ventricle of the rats: on day 1 of postnatal ontogenesis (in the rats born on day 21 of gestation) and on days 3–5 of postnatal ontogenesis (in the rats born on day 21.5 of gestation). Preterm birth in rats did not result in a change in the number of Mklp2-positive cardiomyocytes in the left ventricular wall.

Conclusion. A change in the pattern of Ki67 expression by cardiomyocytes in the rats born 12 or 24 hours before full term was demonstrated in the early postnatal period of ontogenesis. An isolated increase in Ki67 expression without a change in Mklp2 expression by cardiomyocytes in the left ventricular wall of preterm rats indicates acceleration of cardiomyocyte hypertrophy. Shorter duration of prenatal development is associated with more pronounced morphological and functional rearrangements in the rat myocardium.

Preterm Birth Is Associated With Adverse Cardiac Remodeling and Worse Outcomes in Patients With a Functional Single Right Ventricle

OBJECTIVE

To assess the effects of preterm birth on cardiac structure and function and transplant-free survival in patients with hypoplastic left heart syndrome and associated anomalies throughout the staged palliation process.

STUDY DESIGN

Data from the Single Ventricle Reconstruction trial were used to assess the impact of prematurity on echocardiographic measures at birth, Norwood, Stage II, and 14 months in 549 patients with a single functional right ventricle. Medical history was recorded once a year using medical records or telephone interviews. Cox regression models were applied to analyze transplant-free survival to age 6 years. Causal mediation analysis was performed to estimate the mediating effect of birth weight within this relationship.

RESULTS

Of the 549 participants, 64 (11.7%) were born preterm. Preterm-born participants had lower indexed right ventricle end-diastolic volumes at birth but higher volumes than term-born participants by age 14 months. Preterm-born participants had an increased risk of death or heart transplantation from birth to age 6 years, with an almost linear increase in the observed risk as gestational age decreased below 37 weeks. Of the total effect of preterm birth on transplant-free survival, 27.3% (95% CI 2.5-59.0%) was mediated through birth weight.

CONCLUSIONS

Preterm birth is associated with adverse right ventricle remodeling and worse transplant-free survival throughout the palliation process, in part independently of low birth weight. Further investigation into this vulnerable group may allow development of strategies that mitigate the impact of prematurity on outcomes in patients with hypoplastic left heart syndrome.

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.

Exercise and hypoxia unmask pulmonary vascular disease and right ventricular dysfunction in a 10- to 12-week-old swine model of neonatal oxidative injury

Prematurely born young adults who experienced neonatal oxidative injury (NOI) of the lungs have increased incidence of cardiovascular disease. Here, we investigated the long-term effects of NOI on cardiopulmonary function in piglets at the age of 10-12 weeks. To induce NOI, term-born piglets (1.81 ± 0.06 kg) were exposed to hypoxia (10-12%F iO 2 ${F}_{{\rm{iO}}_{\rm{2}}}$ ), within 2 days after birth, and maintained for 4 weeks or until symptoms of heart failure developed (range 16-28 days), while SHAM piglets were normoxia raised. Following recovery (>5 weeks), NOI piglets were surgically instrumented to measure haemodynamics during hypoxic challenge testing (HCT) and exercise with modulation of the nitric-oxide system. During exercise, NOI piglets showed a normal increase in cardiac index, but an exaggerated increase in pulmonary artery pressure and a blunted increase in left atrial pressure - suggesting left atrial under-filling - consistent with an elevated pulmonary vascular resistance (PVR), which correlated with the duration of hypoxia exposure. Moreover, hypoxia duration correlated inversely with stroke volume (SV) during exercise. Nitric oxide synthase inhibition and HCT resulted in an exaggerated increase in PVR, while the PVR reduction by phosphodiesterase-5 inhibition was enhanced in NOI compared to SHAM piglets. Finally, within the NOI piglet group, prolonged duration of hypoxia was associated with a better maintenance of SV during HCT, likely due to the increase in RV mass. In conclusion, duration of neonatal hypoxia appears an important determinant of alterations in cardiopulmonary function that persist further into life. These changes encompass both pulmonary vascular and cardiac responses to hypoxia and exercise. KEY POINTS: Children who suffered from neonatal oxidative injury, such as very preterm born infants, have increased risk of cardiopulmonary disease later in life. Risk stratification requires knowledge of the mechanistic underpinning and the time course of progression into cardiopulmonary disease. Exercise and hypoxic challenge testing showed that 10- to 12-week-old swine that previously experienced neonatal oxidative injury had increased pulmonary vascular resistance and nitric oxide dependency. Duration of neonatal oxidative injury was a determinant of structural and functional cardiopulmonary remodelling later in life. Remodelling of the right ventricle, as a result of prolonged neonatal oxidative injury, resulted in worse performance during exercise, but enabled better performance during the hypoxic challenge test. Increased nitric oxide dependency together with age- or comorbidity-related endothelial dysfunction may contribute to predisposition to pulmonary hypertension later in life.

Acute and chronic cardiac adaptations in adults born preterm

New Findings

What is the topic of this review?

Studies using cardiovascular magnetic resonance imaging and echocardiography to investigate cardiac alterations at rest and during exercise‐induced physiological stress in adults born preterm.

What advances does it highlight?

People born preterm have a greater long‐term cardiovascular risk, which may be explained in part by their cardiac structural and functional alterations. They have potentially adverse alterations in left and right ventricular structure and function that worsens with blood pressure elevation; an impaired myocardial functional reserve; and an increase in diffuse myocardial fibrosis that may drive their lower diastolic function.

Abstract

Preterm birth accounts for more than 10% of births worldwide and associates with a long‐term increase in cardiovascular disease risk. The period around preterm birth is a rapid and critical phase of cardiovascular development, which might explain why changes in multiple components of the cardiovascular system have been observed in individuals born preterm. These alterations include reduced microvascular density, increased macrovascular stiffness, and higher systolic and diastolic blood pressure. Cardiac alterations have been observed in people born preterm as early as neonatal life and infancy, with potentially adverse changes in both left and right ventricular structure and function extending into adulthood. Indeed, studies using cardiovascular magnetic resonance imaging and echocardiography have demonstrated that preterm‐born individuals have structural cardiac changes and functional impairments. Furthermore, myocardial tissue characterization by cardiovascular magnetic resonance imaging has demonstrated an increase in left ventricular diffuse myocardial fibrosis in young adults born preterm, and under acute physiological stress, their myocardial functional reserve assessed by echocardiography is reduced. The preterm heart is also more susceptible to chronic systolic blood pressure elevation, with a significantly greater increase in left ventricular mass as systolic blood pressure rises observed in preterm‐born compared to term‐born young adults. Given these known, potentially adverse acute and chronic cardiac adaptations in the preterm‐born population, primary prevention strategies are needed to reduce long‐term cardiovascular disease risk in this subgroup of the population.

Physiological aspects of cardiopulmonary dysanapsis on exercise in adults born preterm

Progressive improvements in perinatal care and respiratory management of preterm infants have resulted in increased survival of newborns of extremely low gestational age over the past few decades. However, the incidence of bronchopulmonary dysplasia, the chronic lung disease after preterm birth, has not changed. Studies of the long-term follow-up of adults born preterm have shown persistent abnormalities of respiratory, cardiovascular and cardiopulmonary function, possibly leading to a lower exercise capacity. The underlying causes of these abnormalities are incompletely known, but we hypothesize that dysanapsis, i.e. discordant growth and development, in the respiratory and cardiovascular systems is a central structural feature that leads to a lower exercise capacity in young adults born preterm than those born at term. We discuss how the hypothesized system dysanapsis underscores the observed respiratory, cardiovascular and cardiopulmonary limitations. Specifically, adults born preterm have: (1) normal lung volumes but smaller airways, which causes expiratory airflow limitation and abnormal respiratory mechanics but without impacts on pulmonary gas exchange efficiency; (2) normal total cardiac size but smaller cardiac chambers; and (3) in some cases, evidence of pulmonary hypertension, particularly during exercise, suggesting a reduced pulmonary vascular capacity despite reduced cardiac output. We speculate that these underlying developmental abnormalities may accelerate the normal age-associated decline in exercise capacity, via an accelerated decline in respiratory, cardiovascular and cardiopulmonary function. Finally, we suggest areas of future research, especially the need for longitudinal and interventional studies from infancy into adulthood to better understand how preterm birth alters exercise capacity across the lifespan.

Understanding the Preterm Human Heart: What do We Know So Far?

Globally, preterm birth affects more than one in every 10 live births. Although the short‐term cardiopulmonary complications of prematurity are well known, long‐term health effects are only now becoming apparent. Indeed, preterm birth has been associated with elevated cardiovascular morbidity and mortality in adulthood. Experimental animal models and observational human studies point toward changes in heart morphology and function from birth to adulthood in people born preterm that may contribute to known long‐term risks. Moreover, recent data support the notion of a heterogeneous cardiac phenotype of prematurity, which is likely driven by various maternal, early, and late life factors. This review aims to describe the early fetal‐to‐neonatal transition in preterm birth, the different structural and functional changes of the preterm human heart across developmental stages, as well as potential factors contributing to the cardiac phenotype of prematurity.

Intrauterine inflammation exacerbates maladaptive remodeling of the immature myocardium after preterm birth in lambs

BACKGROUND

Antenatal conditions that are linked with preterm birth, such as intrauterine inflammation, can influence fetal cardiac development thereby rendering the heart more vulnerable to the effects of prematurity. We aimed to investigate the effect of intrauterine inflammation, consequent to lipopolysaccharide exposure, on postnatal cardiac growth and maturation in preterm lambs.

METHODS

Preterm lambs (~129 days gestational age) exposed antenatally to lipopolysaccharide or saline were managed according to contemporary neonatal care and studied at postnatal day 7. Age-matched fetal controls were studied at ~136 days gestational age. Cardiac tissue was sampled for molecular analyses and assessment of cardiac structure and cardiomyocyte maturation.

RESULTS

Lambs delivered preterm showed distinct ventricular differences in cardiomyocyte growth and maturation trajectories as well as remodeling of the left ventricular myocardium compared to fetal controls. Antenatal exposure to lipopolysaccharide resulted in further collagen deposition in the left ventricle and a greater presence of immune cells in the preterm heart.

CONCLUSIONS

Adverse impacts of preterm birth on cardiac structure and cardiomyocyte growth kinetics within the first week of postnatal life are exacerbated by intrauterine inflammation. The maladaptive remodeling of the cardiac structure and perturbed cardiomyocyte growth likely contribute to the increased vulnerability to cardiac dysfunction following preterm birth.

IMPACT

Preterm birth induces maladaptive cardiac remodeling and adversely impacts cardiomyocyte growth kinetics within the first week of life in sheep. These effects of prematurity on the heart are exacerbated when preterm birth is preceded by exposure to intrauterine inflammation, a common antecedent of preterm birth. Inflammatory injury to the fetal heart coupled with preterm birth consequently alters neonatal cardiac growth and maturation and thus, may potentially influence long-term cardiac function and health.

Cardiac structure and function in very preterm-born adolescents compared to term-born controls: A longitudinal cohort study

BACKGROUND

There is emerging evidence of differences in cardiac structure and function in preterm-born adults and increased risk of heart failure. However, there is a paucity of data in populations who have been exposed to modern intensive care and the impact of perinatal factors is unclear.

AIMS

To compare echocardiographic measures of cardiac structure and function in a regional cohort of 17-year-olds born very preterm compared to term-born peers and the influence of perinatal factors.

STUDY DESIGN

Observational longitudinal cohort study.

SUBJECTS

A regional cohort of ninety-one 17-year-olds born at <32 weeks gestation compared to sixty-two term-born controls.

OUTCOME MEASURES

Echocardiographic measures of cardiac structure and function.

RESULTS

Left ventricular and right atrial volume and left ventricular mass, indexed to body surface area, were significantly smaller in preterm-born adolescents compared to term-born controls even when adjusted for sex. There were no between group differences in cardiac function. Within those born preterm we found a significant association between gestational age and birthweight z-score and measures of cardiac function at 17 years. Within the preterm group, those with a diagnosis of bronchopulmonary dysplasia had higher left ventricular posterior wall thickness, higher mitral deceleration time and lower left atrial area and tricuspid annular plane of systolic excursion.

CONCLUSIONS

Adolescents born very prematurely, who have received modern intensive care, have measurable differences in heart structure compared to their term-born peers but heart function is preserved. For those born preterm, gestational age, birthweight and bronchopulmonary dysplasia are associated with differences in cardiac function.

Reduced Exercise Capacity in Adults Born Very Low Birth Weight: A Population-Based Cohort Study

RATIONALE

Population-based data regarding the consequences of very low birth weight (VLBW) and bronchopulmonary dysplasia (BPD) on adult exercise capacity is limited.

OBJECTIVES

To compare exercise capacity in a national VLBW cohort with term-born controls and explore factors contributing to the differences.

METHODS

At 26-30 years of age, 228 VLBW survivors and 100 controls underwent lung function tests, cardiopulmonary exercise testing and assessment of resting cardiac structure/function using echocardiography. Data on self-reported physical activity were collected.

MEASUREMENTS AND MAIN RESULTS

Compared with controls, VLBW adults demonstrated reduced oxygen uptake, work rate and oxygen pulse at peak exercise (9.3%, 10.7%, 10.8% lower, respectively) and earlier anaerobic threshold (all p<0.0001), with all mean values within normal range. VLBW survivors showed reduced physical activity, impaired lung function (reduced FEV1, FEV1/FVC, DLCO), altered left ventricular structure/function (reduced mass, size, stroke volume, cardiac output) and reduced right atrial/ventricular size. Adjustment for the combination of three sets of covariates (physical activity with BMI, lung function, cardiac structure/function) explained most of the exercise group-differences. Beyond the effects of physical activity and BMI, lung function and cardiac structure/function contributed approximately equally. BPD with other prematurity-related perinatal factors (ventilation, antenatal steroids, extremely low birth weight, extreme preterm) were not associated with a reduced exercise capacity.

CONCLUSIONS

Exercise capacity was significantly reduced in VLBW adults, which we speculate is from combined effects of impaired lung function, altered heart structure/function and reduced physical activity. Perinatal factors including BPD were not associated with a reduced exercise capacity.

Decreased ventricular size and mass mediate the reduced exercise capacity in adolescents and adults born premature

BACKGROUND

Premature birth is associated with lower levels of cardiorespiratory fitness (CRF) but the underlying mechanisms responsible remain unclear. This study assessed whether differences in cardiac morphology or function mediate differences in CRF among adolescents and young adults born preterm.

METHODS

Adolescents and young adults born moderately to extremely premature (gestational age ≤ 32 weeks or birth weight < 1500 g) and age-matched term born participants underwent resting cardiac MRI and maximal exercise testing. Mediation analysis assessed whether individual cardiovascular variables accounted for a significant proportion of the difference in maximal aerobic capacity between groups.

RESULTS

Individuals born preterm had lower VO2max than those born term (41.7 ± 8.6 v 47.5 ± 8.7, p < 0.01). Several variables differed between term and preterm born subjects, including systolic and diastolic blood pressure, mean pulmonary artery pressure, indexed left ventricular end-diastolic volume (LVEDVi), right ventricular end-diastolic volume (RVEDVi), LV mass (LVMi), LV stroke volume index (LVSVi), and LV strain (p < 0.05 for all). Of these variables, LVEDVi, RVEDVi, LVSVi, LVMi, and LV longitudinal strain were significantly related to VO2max (p < 0.05 for all). Significant portions of the difference in VO2max between term and preterm born subjects were mediated by LVEDVi (74.3%, p = 0.010), RVEDVi (50.6%, p = 0.016), and LVMi (43.0%, p = 0.036).

CONCLUSIONS

Lower levels of CRF in adolescents and young adults born preterm are mediated by differences in LVEDVi, RVEDVi, and LVMi. This may represent greater risk for long-term cardiac morbidity and mortality in preterm born individuals.

Effect of Preterm Birth on Cardiac and Cardiomyocyte Growth and the Consequences of Antenatal and Postnatal Glucocorticoid Treatment

Preterm birth coincides with a key developmental window of cardiac growth and maturation, and thus has the potential to influence long-term cardiac function. Individuals born preterm have structural cardiac remodelling and altered cardiac growth and function by early adulthood. The evidence linking preterm birth and cardiovascular disease in later life is mounting. Advances in the perinatal care of preterm infants, such as glucocorticoid therapy, have improved survival rates, but at what cost? This review highlights the short-term and long-term impact of preterm birth on the structure and function of the heart and focuses on the impact of antenatal and postnatal glucocorticoid treatment on the immature preterm heart.

Association of Preterm Birth With Myocardial Fibrosis and Diastolic Dysfunction in Young Adulthood

Background

Preterm birth affects about 10% of live births worldwide and is associated with cardiac alterations. Animal models of preterm birth suggest that left ventricular functional impairment may be due to an up-regulation of myocardial fibrosis.

Objectives

The aim of this study was to determine whether diffuse left ventricular fibrosis is evident in young adults born preterm.

Methods

One hundred one normotensive young adults born preterm (n = 47, mean gestational age 32.8 ± 3.2 weeks) and term (n = 54) were included from YACHT (Young Adult Cardiovascular Health sTudy). Left ventricular structure and function were quantified by cardiovascular magnetic resonance and echocardiography. Intravenous administration of a gadolinium-based contrast agent during cardiovascular magnetic resonance was used to quantify focal myocardial fibrosis on the basis of late gadolinium enhancement and, in combination with T1 mapping, to quantify diffuse myocardial fibrosis on the basis of assessment of myocardial extracellular volume fraction.

Results

Adults born preterm had smaller left ventricular end-diastolic and stroke volumes, with greater left ventricular mass and wall thickness (P < 0.001). In addition, longitudinal peak systolic strain and diastolic strain rate by both cardiovascular magnetic resonance and echocardiography, and E/A ratio measured by echocardiography, were lower in preterm-born compared to term-born adults (P < 0.05). Extracellular volume fraction was greater in preterm-born compared with term-born adults (27.81% ± 1.69% vs 25.48% ± 1.41%; P < 0.001) and was a significant mediator in the relationship between gestational age and both longitudinal peak diastolic strain rate and E/A ratio.

Conclusions

Preterm-born young adults have greater extracellular volume fraction in the left ventricle that is inversely related with gestational age and may underlie their diastolic functional impairments.

The Immediate and Long-Term Impact of Preeclampsia on Offspring Vascular and Cardiac Physiology in the Preterm Infant

Hypertensive disorders of pregnancy, including preeclampsia, affect nearly 10% of all pregnancies and are associated with significant long-term detrimental effects on both maternal and offspring cardiovascular health. Current management of preeclampsia involves timely delivery with the more severe form of disease requiring iatrogenic preterm birth. The effects on the maternal cardiovascular system have been studied extensively; however, less is known about the short- and long-term impacts on offspring cardiovascular health. There is a growing body of evidence suggesting that the offspring of pre-eclamptic pregnancies have an altered cardiac structure and function, along with a unique vascular physiology driven by lower endothelial function. Many of these changes can also be seen in those born preterm even in the absence of pregnancy hypertension. It is difficult to determine the relative contribution of pre-maturity and preeclampsia to the cardiovascular phenotype of those exposed to these pregnancy complications as they are, in many cases, inextricably linked. This review, therefore, focuses specifically on the evidence from clinical studies showing a negative cardiovascular impact of preeclampsia in preterm-born offspring, investigating phenotypic similarities and differences between offspring born preterm to normotensive vs. pre-eclamptic pregnancies. We explore the unique cardiac and vascular alterations in pre-eclamptic offspring born preterm, highlighting knowledge gaps, and potential areas of further research in the field.

Preterm Birth With Neonatal Interventions Accelerates Collagen Deposition in the Left Ventricle of Lambs Without Affecting Cardiomyocyte Development

Background

Adults born preterm (< 37 weeks’ gestation) exhibit altered cardiac growth and are susceptible to cardiac dysfunction. Sheep studies have shown that moderate preterm birth results in maladaptive structural remodelling of the cardiac ventricles. The aim of this study was to examine ventricular structure in lambs born at a greater severity of preterm birth and ventilated postnatally.

Methods

Former-preterm lambs delivered at 128 days’ gestation, and mechanically ventilated for a week after birth, were compared with unventilated lambs born at term (150 days’ gestation), at 2 months (term: n = 10, former-preterm: n = 8), and 5 months (term: n = 9, former-preterm: n = 8) term-equivalent age. The right ventricle and left ventricle plus septum were analysed using immunohistochemistry, histology, and stereology.

Results

Cardiomyocyte number, cross-sectional area, proliferation, and apoptosis were not affected by preterm birth or age. Left ventricle plus septum interstitial collagen levels increased with age (P = 0.0015) and were exacerbated by preterm birth (P = 0.0006; 2 months term: 0.57% ± 0.07%, former-preterm: 1.44% ± 0.18%; 5 months term: 1.37% ± 0.25%, former-preterm: 2.15% ± 0.31%). Right ventricle interstitial collagen levels increased with age (P = 0.012) but were not affected by preterm birth.

Conclusion

This study is the first to explore the effect of preterm birth combined with modern neonatal interventions on the ventricular myocardium in lambs. There was no adverse impact on cardiomyocyte growth in early postnatal life. Of concern, however, there was increased collagen deposition in the preterm hearts, which has the potential to induce cardiac dysfunction, especially if it becomes exaggerated with ageing.

Preterm birth and cardiac function in adulthood

Preterm birth affects 1 in 10 pregnancies worldwide, with increasing survival rates over the last 30 years. However, as this new generation of long-term survivors approaches middle age, recent studies have revealed increased cardiovascular risk factors and higher rates of ischaemic heart disease and heart failure. Cardiovascular imaging has identified smaller cardiac chamber size, changes in myocardial mass and impaired ventricular function, particularly under physiological stress. Accordingly, this population should be recognised as having a higher risk of heart failure as they age. In this review, we present current evidence for increased rates of heart failure and evidence of alterations in cardiac structure and function in those born preterm. We discuss potential mechanisms to explain this risk including greater frequency of co-morbidities known to be associated with heart failure. We also explore potential mechanistic links specific to the preterm-born population, including the impact of premature birth on myocardial and vascular development and the effects of perinatal haemodynamic changes and chronic lung disease on the developing heart. We highlight gaps in our knowledge and consider implications for patient management relevant to the adult physician.

The Preterm Heart-Brain Axis in Young Adulthood: The Impact of Birth History and Modifiable Risk Factors

People born preterm are at risk of developing both cardiac and brain abnormalities. We aimed to investigate whether cardiovascular physiology may directly affect brain structure in young adulthood and whether cardiac changes are associated with modifiable biomarkers. Forty-eight people born preterm, followed since birth, underwent cardiac MRI at age 25.1 ± 1.4 years and brain MRI at age 33.4 ± 1.0 years. Term born controls were recruited at both time points for comparison. Cardiac left and right ventricular stroke volume, left and right ventricular end diastolic volume and right ventricular ejection fraction were significantly different between preterm and term born controls and associated with subcortical brain volumes and fractional anisotropy in the corpus callosum in the preterm group. This suggests that cardiovascular abnormalities in young adults born preterm are associated with potentially adverse future brain health. Associations between left ventricular stroke volume indexed to body surface area and right putamen volumes, as well as left ventricular end diastolic length and left thalamus volumes, remained significant when adjusting for early life factors related to prematurity. Although no significant associations were found between modifiable biomarkers and cardiac physiology, this highlights that cardiovascular health interventions may also be important for brain health in preterm born adults.

Impact of the Vulnerable Preterm Heart and Circulation on Adult Cardiovascular Disease Risk

Preterm birth accounts for over 15 million global births per year. Perinatal interventions introduced since the early 1980s, such as antenatal glucocorticoids, surfactant, and invasive ventilation strategies, have dramatically improved survival of even the smallest, most vulnerable neonates. As a result, a new generation of preterm-born individuals has now reached early adulthood, and they are at increased risk of cardiovascular diseases. To better understand the sequelae of preterm birth, cardiovascular follow-up studies in adolescents and young adults born preterm have focused on characterizing changes in cardiac, vascular, and pulmonary structure and function. Being born preterm associates with a reduced cardiac reserve and smaller left and right ventricular volumes, as well as decreased vascularity, increased vascular stiffness, and higher pressure of both the pulmonary and systemic vasculature. The purpose of this review is to present major epidemiological evidence linking preterm birth with cardiovascular disease; to discuss findings from clinical studies showing a long-term impact of preterm birth on cardiac remodeling, as well as the systemic and pulmonary vascular systems; to discuss differences across gestational ages; and to consider possible driving mechanisms and therapeutic approaches for reducing cardiovascular burden in individuals born preterm.